BCS 240 Exam #3

Intrinsic Space Hypothesis

• Electrical "microstimulation" of motor cortex can elicit twitch in individual muscles, as long as stimulation is weak (i.e., current spread is minimal). *as long as stimulus small, spread small & can move single muscle • M1 modulates discharge activity related to movement dynamics: - Muscle force - Movement velocity - Joint position.

Secondary Motor Cortex 2

• Nearly all premotor area (PMA) cells (94%) show extrinsic (i.e. movement-related) activity: - Electrical stimulation of PMA generates complex movement patterns, such as hand-shaping or reaching. *before exp started, firing randomly; then monkey realizes can't move hand yet but knows where it will go in a moment (start firing APs); job not to do motion, but to set up pre-instructions (movement strats prior to action) *secondary motor convey specific instructions to primary motor • For cued movements - Proportion of cells active during the "instruction" period prior to movement is higher in PMA than in primary motor cortex (M1). - M1 > PMA during movement. • Suggests PMA devising specific movement strategies prior to execution.

The Chemical Senses (start 11/1)

-Most ancestral and common of the senses. *Present even in the simplest single-cell organisms (e.g., bacteria). -Functions: *Finding food sources *Judging nutritional value and safety of foods. *Avoiding predators and hazardous environments. *Social communication, mating ("pheromones"). *Monitoring internal physiological state.

Cortical Lateralization of Language

-Numerous fMRI and PET studies of healthy volunteers engaging in various language-related tasks suggest that the brain mechanisms of language predominate in the left hemisphere. 2 auditory cortical areas: -left hem does what for speech processing -music on right side

The Sense of Smell (start 11/4)

**know inputs, where structure going, etc for exam (know brain views) -Olfaction plays a critical role in the survival of most animal species (much like taste, oldest of chem senses; have to know what's out in env) -Primary functions of olfaction: a. Finding and evaluating food *prior to* ingestion (important for flavor perception) b. Avoiding noxious/toxic aerosols c. Predator-prey interactions (some species scent-mark) d. Social behavior and communication -Territoriality -Social aggregation -Mating (pheromones) -Maternal behavior (can smell & recognize own babies)

The Basal Ganglia

-A collection of inter-connected, midline, nuclei located lateral to the thalamus -Includes the striatum (caudate and putamen), globus pallidus (external and internal), subthalamic nucleus and substantia nigra -secondary motor to basal ganglia loop -basal ganglia lateral to thalamus (which is adj to third ventricle)

Stretch Reflex

-A reflex is an involuntary and nearly instantaneous movement in response to an external stimulus. -The patellar tendon reflex is an example of a monosynaptic, stretch reflex (to maintain posture). -Mediated by the muscle-spindle feedback circuit, stretch reflexes serve to produce immediate compensatory contraction to prevent external forces from altering the intended position of the body -muscle spindle activated bc commanded to just be there; seems to have gotten longer which can't happen; muscle spindle sends signal; contract muscle to get back to where it was (activates alpha motor neuron to go back out) -this is a proprioceptor (activating muscle spindle) -would activate free nerve ending w pain

Taste and Survival

-A sensitive and versatile taste system has great survival value for organisms exploiting wide variety of food sources. -Gustation divides the world into a. Nutrients: generally attractive, e.g., sweet and salty. b. "Anti-nutrients": repulsive, e.g., sour and bitter. -Sensitivity to bitter tastants (which number in the thousands) can be extreme (nanomolar thresholds), because such tastants in the natural world are often poisonous. -the most sensitive taste is to bitter

Neuromuscular Junctions

-Acetylcholine released by motor neurons at the neuromuscular junction activates the motor-end plate on each muscle fiber and causes contraction (the only method muscles have of generating force). -motor neurons rel acetylcholine (all somatic muscles covered by rel of acetylcholine) -dominant way to create epsps in target (influx on Na>depolarization>vg Na channels in cell) -muscle cells excitably active tissue - propagate APs down their length, which activates muscle cell -muscles on either side of bone *can only generate force by pushing - NO pulling

Sensation & Perception

-All that we know about the world around us is obtained through our senses ("Esse est percipi") 1. Sensation: • Related to the physical interaction of a stimulus with a sensory receptor. 2. Perception: • Conscious awareness & interpretation of sensation • Related to the particular sensory pathway in the nervous system that processes information from a receptor. • Influenced by "top down" processes: cognition, attention, experience -sensation=get info from senses, receptor to cortex *physical interaction of stimulus w receptor -perception=interpretation of that; influenced by attn, cognition, experience -Sensation ≠ Perception - how things are sensed are not necessarily how they're perceived

Non-Image-Forming Functions

-Approximately 90% of retinal ganglion cells project to the LGN. The remainder (not M or P cells) project to the hypothalamus, pre-tectum and superior colliculus. -M & P cells>thal(LGN)>cortex -but wb ones that don't go to cortex? -can go to hypothalamus (how can tell that it's day vs night) - circadian rhythm -some fibers go to pretectum area (for controlling pupil diameter) -superior colliculus (make you look at st flashing in field of view - cells in periphery that aren't M cells, alert you to danger & reflexively look) -still input from retina but not going to LGN

Sensorimotor Association Cortex

-Association cortex is at the top of the sensorimotor hierarchy. -ppac behind primary somato -what input receive? dorsal streams ("where" info) - There are two major areas of sensorimotor association cortex: • posterior parietal • dorsolateral prefrontal (sits in front of primary motor areas; get lots of sensory inputs, get input from ventral stream indirectly) -Each is composed of several different areas with different functions.

Cerebellar Disorders

-Ataxia: intention tremor disturbances in rate and regularity of alternating movements. -Asynergia (dysynergia): prolonged reaction times "decomposition" of multi-joint movements. -Dysmetria: Undershoot or overshoot of movements toward objects. -probs in motor coordination w cerebellum probs; primary motor has to correct, messages take longer

Posterior Parietal Association Cortex 1

-Before a movement can be initiated, need to know: • current position of body parts; and • location of external objects of interest -The PPAC receives input from the dorsal streams of the somatosensory, auditory and visual systems and thus plays an important role in integrating these two types of information. -which part of stream tells you where your body is located? somatosensory - proprioceptive parts -also have exteroceptive + auditory & visual "where" info

Ocular Dominance Columns 2

-Beyond layer IV-C, the signals from the two eyes are combined at the cellular level; that is, neurons in most layers of visual cortex are binocular. -However, the input from one eye is usually dominant; the bands of cells extending through the thickness of the striate cortex are called ocular dominance columns.

The Blind Spot

-Blind spot: region of retina with no receptors where retinal ganglion cell axons exit the eye (optic nerve) -The visual system "fills in" the blind spot based on information from the other eye or surrounding detail (called "completion") *brain fills in what's needed bc brain assumes objects are continuous *this filling of the blind spot is perception (so are color, brightness, upside down on retina but see right side up, think have great field of view but only have tiny clear spot) -blind spot towards nose -fibers gather & puncture through back of eye to skull -cranial nerve 2/the optic nerve: ganglion cell axons -no receptors here, would be blind if light hit here (on either side of nose) -blind spot for 1 eye not blind spot for other; so as long as have 2 eyes, can fill in missing info from 1 eye w the other eye

Ocular Dominance Columns 1

-By and large, retinal inputs from the left and right eye (with receptive fields in the same spot in space) remain segregated in the LGN and the input layer of visual cortex (layer IVC) (first visualized by Hubel and Wiesel 1974) -how vis cortex organized? 3 org principles a. ocular dominance columns -Hubel & Wiesel: injected radioactive proline in retina, sucked it up, send towards target (anterograde), release from target & picked up from target - can track which eye goes to where -inject into 1 eye, light up only 3/half of layers in thalamus -top 4 processing input from P cells (color acuity), bottom 2 M cells -left & right eyes don't overlap!! every layer in LGN monocular, can only see out 1 eye (sep eyes & sep P/M) -go in layer 4, don't get all of layer 4 -when get past input, then neurons sensitive to both eyes -oc dom columns: each place in cortex has spot for l&r eye each from 1 point in space; go in side by side; then comes into cortex side by side (no neurons sensitive to both eyes until get to layer 4C) - still only see 1 eye in layer 4C; when get past 4C, see both eyes but 1 dominant -in layer 4C you're either 1 eye or the other; above & below 4C, you're a mix of both but 1 will dominate

Emergent Receptive Fields

-Cells in layer IV-C are monocular and have receptive fields with opponent center-surround organization. -Many neurons beyond layer IV-C are "simple" cells • Rectangular receptive field • "On" and "off" regions, like cells in layer IV-C • Neurons are orientation-selective and location sensitive • Many are binocular. -emergene of new RF properties give orientation selectivity - ret gang cell & layer 4C cells (alpha & beta) & 1 other cell have circular RFs -beyond 4C, get rectangular RFs; combining pixels (circular center surround cells); they're now bars of light instead of dots of light -orientation selective bc bar can be in many orientations; most/all are binocular, can compare inputs from 2 eyes & can do depth perception

The Eye 2

-Cornea: primary refractive element -Iris: donut-shaped band of contractile tissue that gives the eye its color and regulates the amount of light entering eye via the size of the pupil (hole in the iris) -Lens: secondary refractive element (for near-vision: "accommodation") -Retina: epithelial tissue upon which image is projected, containing photoreceptors and associated neuronal circuitry -Extra-ocular muscles (horizontal, vertical, and oblique pairs) control eye movements: • Voluntary: Saccadic and smooth pursuit • Reflexive: image stabilization re head movements -cornea + lens = biological lens -iris: gives color to eye -pupil=absence of iris *iris can make pupil big or small (it's a muscle)

Cortical Modules in Visual Cortex

-Cortical modules (or hyper-columns) consist of: • pairs of ocular dominance columns • many orientation columns • blobs and inter-blob regions -Higher-order neurons that prefer the same orientation as simple cells may also be sensitive to the line over larger areas of visual space (complex cells), to the line's length (hyper-complex), and/or to binocular disparity. -hypercolumn: Module is "necessary and sufficient" for analysis of each point in visual space to process vis input from 1 pt in space -flow to thal > v1 >inputs layer 4C (see 1 eye, sets up oc dom columns) > orientation selectivity past 4C > most interesting in bars, can see from both eyes (have as many hypercolumns in 1 cortex as you have pixels in world, more pixels = clearer) > blobs & interblobs also happen here (third part of any hypercolumn) a. 1 eye, oc dom columns b. orientation selectivity c. blobs/interblobs

Dorsolateral Tracts

-Corticospinal tract: descends from primary motor cortex (e.g., Betz cells) through the medullary pyramids, then crosses the midline (decussates) and synapses directly in the cord. Wrist, hands, fingers, toes -Corticorubrospinal tract: synapses at red nucleus, and crosses before medulla. Face, arms and legs. -Dorsolateral tracts tend to synapse on small interneurons in the cord that, in turn, synapse on motor neurons of distal targets -dorsal lateral tracts coming from top to side -corticospinal comes down pyramidal tract, cross in medulla, come down opp side of spinal cord (1 side of cortex control opp side of body) *on way down, hits pontine nuclei to tell cerebellum we're about to move *goes down contralateral; when reach target, synapses in 1 dermatome *red nucleus makes corrections -dorsolateral tracts go upper motor neuron to interneuron to lower motor neuron

Ventromedial Tracts

-Corticospinal tract: descends ipsilaterally and directly to the spinal cord, then branches and innervates interneuron circuits bilaterally in multiple spinal segments -Cortico-brainstem-spinal tract: synapses on various brainstem structures and descends bilaterally, carrying information from both hemispheres -Ventromedial tracts synapse on small interneurons in the cord that, in turn, synapse on motor neurons of the trunk and proximal limb muscles -if want to control extremities, it's 1 side or the other; if want to control middle, control as 1 thing -corticospinal ipsilateral, controls opp & same side of body, both sides, go to multiple dermatomes -control of core all many dermatomes, left & right; signif control contralateral control of 1 dermatome (dorsolat - control extremities)

Sensorimotor Spinal Circuits

-Descending inputs from cortex tend to contact interneurons in the grey matter of the spinal cord -Interneurons may excite or inhibit lower motor neurons -Motor circuits of the spinal cord show considerable complexity and can respond independently of signals from the brain -dorsolateral control limbs, go to 1 dermatome -always excitatory, upper motor neurons exciting -stop at interneuron>then go to lower motor neuron -control of fingers special case: straight from upper to lower motor neuron (direct cortical control) -interneurons can be excite/inhib toward lower motor neuron -which NT dominant for inhib of lower motor neurons?: glycine (dom in spinal cord, GABA cortex)

Taste Transduction

-Direct transduction: Some tastants are ions that carry currents through ion channels. -Indirect transduction: Other (non-ionic) tastants bind selectively to specific G proteincoupled membrane receptors. -Individual taste cells may employ both types of transduction. -vis indirect (G protein, stop inflow of Na); aud direct (stereocilia bent, K flows); somatosensory mainly direct (push things down, bend dendrites, in flow Na) -taste does BOTH ways (only system that does direct & indirect) a. channel open, ions flow: Na, just comes directly in b. others hit metabotropic receptor, hit G protein-coupled rec (creates 2nd messenger > leads to depolarization) *when depolarize cell from receptor, this is NOT enough to activate this cell in particular; they have vg Na channels at base so when depolar a little, activate vg Na channels & Na comes pouring in > creates huge PSP (AP) - vg K channels allow to repolarize *normally vg Na and K channels only on axons, but not true in this system, they have it on receptors; use this as a way to amplify the PSP bc food rarely on tongue for long (has to ooze around papillae, activate taste cell, need to amplify bc not there long) *indiv taste cells have both types of receptors on surface (leakage Na channels (sensitive to salt) + G protein coupled receptors (sensitive to other stuff))

Two Streams from SI (end 10/30)

-Dorsal stream from SI to posterior parietal cortex: direct attention -Ventral stream through SII (bilateral) to prefrontal: perception of object shape -2 streams leave: dorsal & ventral -dorsal tells where info -what info down ventral stream

Olfactory Receptor Distribution

-Each OSN expresses only one OR subtype. -Olfactory epithelium contains four distinct zones along A-P axis. -OR subtype distribution is largely confined to a single zone. -Most OR subtypes are broadly tuned, i.e. activated by many monomolecular odorants with different structures. *Corollary: Each odorant can activate many OR subtypes. -rec proteins widespread on epithelia, but within 4 distinct zones -particular odor likely to hit many recs sensitive to it -project in organized way into next structure; recs somewhat distributed in nasal epithelia; all cells w those receptors converge in bulb (glomerulus)

Olfactory Bulbs: Chemotopic Organization

-Each glomerulus is an anatomical & functional unit, processing input from OSNs expressing a single OR. -Glomerulus contains: a. Synaptic terminals from ~25,000 OSNs (then these 25k axons project to only 1 glomerulus) b. Dendrites of ~100 2nd-order olfactory neurons (mitral, tufted, periglomerular cells). -Zones in the olfactory epithelium expressing same OR genes are topographically mapped in the OB. -output of olfactory sensory neurons gather, this is cranial nerve 1 (axons feed into olfactory bulb) -diff types of rec (based on what protein expressing) project into diff glomeruli -50 mitral & 50 tufted, get all their input from particular glomerulus -have roughly 100 diff second-order neurons, tangling dendrites into glomerulus & get info

Muscle Contraction

-Each α-mn AP elicits a muscle fiber AP in all muscle fibers in the motor unit. -Twitch: A contraction elicited by single spike in a single α-MN. *use single AP to contract muscle first; if that's not enough, have more APs (get temp summ) -Temporal summation: Twitches sum as α-MN firing rate increases, increasing force and smoothness of contraction. *EPSPs build on each other (if fast enough, can reach tetanus) -Tetanus: max. force developed by saturating summation at high MN firing rate. -Rate and temporal pattern of α-MN activity controls the strength of contraction.

Posterior Parietal Association Cortex 2

-Electrical stimulation of the PPAC causes patients to experience the intent to perform a particular action -Damage to PPAC: • apraxia (left): inability to make a requested movement (i.e., cannot form intent) • contralateral neglect (right): inability to respond to stimuli contralateral to the lesion (never form intent/consider anything on opp side of world) *contralateral bc cortex organized to know opposite side of things -Outputs to dorsolateral prefrontal association cortex, secondary motor cortex, and frontal eye field -PPAC forms intent > output to DLPFC

Distribution of Exteroceptors

-Exteroceptors are not uniformly distributed across the body -Finger tips are enriched in mechanoreceptors with small receptive fields. -There is a high density of nociceptors in palms and soles. -There are more cold than warm thermoreceptors in the body, with the highest density of receptors on the face and ears. -use 2 point test (2 fingers or protractor or whatever) - poke in 2 places -if poke on back about 6in apart, will only sense 1 touch; much less receptors on back, many more on fingers & face -much more of small ones on face & fingers (M & M); big ones on other parts (ruffini & pacinian) -high density of pain recs in palms & soles; imp to have on feet bc need feet to get around to foot&avoid danger -more warm & cold recs on face & ears

Dermatomes

-Fibers from cutaneous receptors gather together in nerves & enter spinal cord via the dorsal roots. -Dermatome: area of the body that is innervated by the left and right dorsal roots of a given segment of the spinal cord. -everything coming in from skin (pain, temp, touch), all somatosens info rises, gather, comes into spinal cord in 31 diff pairs -each subserved by single spinal nerve pair -info comes into dorsal part of spinal cord -if lose 1 pair of spinal nerves, would you lose all feeling in dermatome? no, bc they overlap *would lose feeling in part of skin if lose 2 consecutive dermatomes

Tastes

-Five basic tastes: *Sweet (non-ionic) *Sour (ionic) *Salty (ionic) *Bitter (non-ionic) *Umami (MSG, glutamate; non-ionic). -Basic tastes are innate (there are receptors for them!) -Other complex tastes are acquired and modified by experience.

Descending Motor Pathways

-Four major descending pathways: two in the dorsolateral region of the spinal cord; two in the ventromedial region. In each region, one is direct and one is indirect. -come from primary motor, layer 5 of neocortex responsible for sending down (upper motor neurons in cortex) *neurons that go out to muscles called lower motor neurons -usually btwn upper & lower are interneurons, in ventral horn of spinal cord -sensory info rising -pain & temp rises outside the legs - anterolateral -dorsolateral & ventromedial both down 1. Dorsolateral tracts (coming down & to sides) • corticospinal (direct) - right from cortex to spine • corticorubrospinal (cortex to spinal, goes to red nucleus) *cerebellum makes its corrections, goes to red nucleus 2. Ventromedial (down & to center) • corticospinal (direct) - right from cortex to spine • cortico-brainstem-spinal

The Fovea

-Fovea: high-acuity area at center of retina -Processes visual information from central 1° of visual space. -Highest density of receptors, bipolar, and ganglion cells in retina; however, bipolar and ganglion cell bodies displaced, creating a "pit" that minimizes light scattering between the lens and the photoreceptors -peel away excess layers so light can hit receptors more directly; so fovea is the best spot for vision -how big is this field of view? only tiny spot is clear & colorful; rest is blurry & black and white, the brain lies

Ganglion Cell Receptive Fields

-Ganglion cell receptive fields are circular, with antagonistic (opponent) responses between center and surround, i.e., they show centersurround organization. -Receptive fields are either "on-center" or "off-center" -output of retina=ganglion cells (last part of retina, closest to incoming light) -antagonistic!: center & surround show opp responses -on-center: respond to light in center, don't respond to light in periphery (want light in center, don't want it in surround) -off-center: want light in periphery, not in center -RFs circular

Achromatic Vision

-Ganglion cells are sensitive to spectral contrasts by virtue of their opponent, center-surround organization. The onand off-center responses create a push-pull system that provides sensory redundancy and decreases sensitivity to common rate changes (e.g., due to body temperature). • Ganglion cells with inputs mainly from rods (in peripheral retina) are sensitive to light and dark. • Ganglion cells with inputs primarily from cones (in the fovea) are sensitive to color contrasts. -gang cells sensitive to contrast; black on white or white on black (don't like all black or white) -why 2 types (on vs off center)? creates push pull *push pull: way to double amount of sensitivity to stimulus, provides substantial amount of redundancy in response; 1 goes up, everyone else goes down -respond to common rate changes -cones in center, rods in periphery -no color conveyed by periphery of retina all circular, center surround; only convey b&w/light & dark

Formation of Opponent RFs 2

-Ganglion cells inherit the on- and off-center aspect of their receptive field responses from bipolar cells • On-center bipolar cells have metabotropic glutamate receptors (activation of which leads to K+ efflux). Thus, on-center bipolar cells respond best when their receptor input releases less glutamate. • Off-center bipolar cells have ionotropic glutamate receptors (activation leads to Na+ influx). Thus, off center cells respond best when their photoreceptor input releases more glutamate. Ganglion cells (and their bipolar inputs) respond weakly if a stimulus activates their entire receptive field. -light on in center, off in surround: hyperpolarized by that light, 2 around you all in dark -already weakened by light then pummeled by neighbors - produce MINIMUM Glu *under bipolar cells waiting, winner gets a lot of Glu & loser produces v little -off bipolar: normal ionotropic Glu receptor, loves Glu (when sees it, open standard Na channel & depolarize) -ganglion cell doesn't receive Glu, doesn't respond -neuron happy when light is off -off center cells detest bc receiving no Glu -on bipolar cell has Glu receptors but the metabotropic ones (not standard); when see Glu, open K channels; Glu inhibits these channels (bc when K leaves, hyperpolarize) *Glu inhibits these cells (typical excite NT, but rec decides response) -excited by on bipolar cell excited, only excited when no Glu (how create on center, off surround) -off center, on surround: ones around in light & they're weak; one in center strong & pummels it; one in center dominates, strongly (max) excited *when light off and surround on: rel Glu -other shut down & not rel Glu on its cell *which is which lol he was just pointing -lateral inhib create fight btwn rods & cones; on bipolar cells weird , inhib by Glu; off excited by Glu -ganglion cells inherit RF propoerites from bipolar cells, respond to amount of Glu *max excites off, min excites on -if light on everywhere, everywhere weak & no on can knock out (no losers); if light off everywhere, all strong & no winner *there MUST be a winner & loser; ganglion cells sensitive to contrast *bipolar cells only responsive to maximum winners & min

Odorant Processing in the Glomerulus

-Glomerular circuitry is similar to retina: a. Parallel input-output "vertical" pathways via mitral/tufted cells. b. Each mitral/tufted cell gets excitation from a glomerulus processing same OR. c. Granule cell interneurons make lateral inhibitory connections between mitral/tufted cells. -Lateral inhibition sharpens mitral cell selectivity to improve odorant discrimination ("contrast enhancement"). -processing done for contrast, can detect diff odors -when leave, have diff odor rec neurons -350 total glomeruli, each receive inputs from 25k sensory neurons; each rec type responds to many odorants -many axons in, rel NT, get excited by same thing that their inputs are, then have lateral inhibition -tufted/mitral cells do lateral inhib through granule cells *lateral inhib: winner-takes-all (sim in vis, all rods & cones fight - creates center-surround; bipolar cells creates on-off) -best responsive if odor has only 1 type of odorants & not others (allow 3 things to like what they like, output likes fewer things than inputs; 3 things fight against each other & cancel out mutual likes); like fewer odorants, become more selective than your inputs did

Cerebellum

-Gross Anatomy: The visible part of the cerebellum is actually a single thin sheet of folded cortex. It is characterized by a series of shallow ridges call folia. Altogether, the cerebellum constitutes about 10% of brain mass, but more than 50% of its neurons • Cerebellar Cortex: Subdivided into lobes, lobules, vermis (midline region) and lateral hemispheres. • Cerebellar nuclei: Embedded deep in the white matter of the cerebellum; communicate cerebellar cortical output to other brain centers including motor cortex, descending motor pathways, and vestibular nuclei (balance) -50% neurons in brain in cerebellum, but v compact -role in cortical helping primary motor -cerebellum div into L & R, one side controls same side of body (opp of cortex)

Central Pathways for Taste

-Gustatory afferent neurons leave the mouth as part of the 7th, 9th , and 10th cranial nerves to the solitary nucleus of the medulla. -Medulla -> ventral posterior nucleus of the thalamus -> primary and secondary gustatory cortex (ipsilateral). **know sensory pathways -afferents to tongue come from 7th, 9th, 10th cranial nerves; all bring info into solitary nucleus in medulla (vomiting nucleus) > project to thalamus > cortex -taste is processed in & near to touch in thalamus (VPN for touch) -where VPN project to for touch? somatosensory cortex in parietal lobe (postcentral gyrus) -gustatory down & to the side from primary somatosens in parietal -share thalamic nucleus -know lateral & medial view of brain -only 1 pathway out of gustatory (2 out of other systems, dorsal (PPC) & ventral (VLPFC) streams) - don't need to know where taste being done so there's no where component; what component heads up to secondary gustatory cortex (where all senses come together) -taste processed in taste cortex (primary sensory cortex, sense); forebrain doing flavor (perception, senses come together)

Principles of Sensorimotor Function (start 11/6)

-Hierarchical Organization • association cortex at the highest level, muscles at the lowest • signals flow between levels over multiple paths -Motor output is guided by sensory input (sensory feedback to change mvmt) -Learning changes the nature and locus of sensorimotor control (e.g., conscious to automatic) -subroutines: set of commands to make things happen, these sets of commands can be placed in diff parts of motor system (many diff levels); unlike sensory system where if get good at st, that's your job for life (doesn't drop down lower in hierarchy when get good at st)

Principles of Sensorimotor Function (start 11/11)

-Hierarchical Organization • association cortex at the highest level, muscles at the lowest • signals flow between levels over multiple paths -Motor output is guided by sensory input -Learning changes the nature and locus of sensorimotor control (e.g., conscious to automatic) -anterolateral: pain & temp rising -dorsal other ascending -ventromedial: desc, control trunk -dorsolateral: descending, control extremities -primary motor get most sensory feedback, cerebellum also does (get info from ascending somatosens system) - learning changes locus of control

"Image" in V1

-Illustration of image as 'seen' by the retina, LGN and layer IVC of cortex. Note the fall off of color vision and acuity away from fovea. -image upside down, only good acuity&color in center (fovea) in periphery, black&white and blurry

Color Vision

-In the human retina, most cones are red and green type (but the relative ratio can vary widely) and few are blue because the lens focuses longer wavelengths of light onto the retina. -Component (trichromatic) theory: color is encoded (initially) by the ratio of activity in the three kinds of receptors -have least blue bc blue already blurry in back of retina; can't have all 3 in focus at once, focus longer 2 that are the color of the sun

Wernicke-Geschwind Model

-In this model, spoken language is processed by the auditory cortex, and then conducted to Wernicke's area, where its meaning is understood. A similar process occurs for written words, where information flows from the visual cortex to the angular gyrus(which translates the visual code into an auditory code) before passing to Wernicke's area. Then, if a response is necessary, Wernicke's area further translates thought processes into verbal responses, which are transmitted to Broca's areavia the arcuate fasciculus. In Broca's area, this signal activates the appropriate programs that drive the neurons of the primary motor cortex and ultimately the muscles of articulation or of the hands 1) hear sound, primary aud cortex gives info rising -> pitch center determines pitch (male vs female, but don't know what's being said) -> Wernicke's understands words (speech comprehension) -> Wernicke's forms answer & tells Broca's answer via arcuate fasciculus -> Broca's knows what happen in vocal tract (makes vocal tract right shape) to make right sound 2) read -> primary vis cortex see lines, don't know it's words -> pass info to angular gyrus (convert vis impressions to sounds, but doesn't understand) -> send to Wernicke's (understand these sounds have meaning, speech comp) *know these 7 areas

Face Processing in IT Cortex (IT & V4 ventral stream)

-Inferotemporal cortex cells have very large RFs (often bilateral) that include fovea. -Large RF may be important for recognizing objects regardless of orientation in space ("position invariance"). -Specific deficits occur with lesions to ventral stream. Examples: • Achromatopsia: loss of color vision (V4 lesion) • Prosopagnosia: Failure to recognize familiar faces (IT lesion). (May play a role in autism) -how do proc in ventral stream? -IT = lower chunk below primary aud cortex -have v large RFs (they get bigger & bigger, stuff gets more elaborate) -start to process v complicated things; only interested in color & form (don't know where obj is - dorsal stream) -color vision: get continually processed; blobs; v4 damage = loss of color vision -as further along = can't recognize familiar faces -IT - process ever more elaborate forms *starting to be face sensitive, "grandmother cells", recog entire face -V4 color vision, IT face recognition (diff in autism)

Secondary Motor Cortex 1

-Inputs from association cortex (mainly DLPFAC) -Three major areas (each subdivided): premotor, supplementary and cingulate (cumulatively form secondary motor cortex) *DLPFC: get me to the food (big picture decision) *next: how will I do that? (specific set of instructions) *output to primary motor (whose job it is to get me there) -The secondary motor cortex converts general plans of action into a specific set of instructions • active during imagining or planning of movements -Outputs to primary motor cortex -situated right behind prefrontal, right in front of primary motor

Motor System (start 11/8)

-Intent: posterior parietal association cortex *major inputs = dorsal streams, where info (vis, aud, somatosens (exteroceptive & proprio) -Plan of action: dorsolateral prefrontal association cortex *PPAC informs DLPFAC (its first question then is what is going on? asks ventrolateral PFC, which knows what's going on) *DLPFAC now knows where & what - forms big picture plan of action -Specific set of instructions: secondary motor cortex -Execution: primary motor cortex (make muscles move in right order)

LGN Physiology

-Laminae (layers of LGN) are retinotopic: orderly "space map" of contralateral visual hemi-field in each layer of LGN. -Cells are monocular: Segregation of RGC input from each eye in overlapping laminae of LGN. -Receptive fields are circular/opponent, similar to the RGC inputs -only get inputs from gang cells in 1 eye, all monocular (not convergence), all circular & opponent -upper 4 layers show center surround red vs green, blue vs yellow - inherited responses from gang cells, which inherited response from bipolar cells -thalamus=relay nucleus to cortex

The Visual System

-The visual system is the part of the NS which enables organisms to process visual details, as well as to perform several non-image-related response functions. It detects (sensation) and interprets (perception) information from visible light to build a representation of the surrounding environment. a. Eye and Retina • Structures • Transduction b. Retina-geniculate-striate cortex • Pathway • Receptive field properties c. Striate and Association cortex • Higher-order processing

Motor Loop through Cerebellum

-Layer V sensorimotor cortical cells (secondary and primary motor cortex, somatosensory cortex, and posterior parietal cortex) project to the pontine nuclei (in the pons). -Pontine nuclei send massive input to cerebellar cortex. -Lateral cerebellum projects to cortex via lateral nucleus of thalamus (VLc). -Function: • To modulate and sequence muscle contractions for voluntary movements. • To evaluate disparities between intention and action. • To correct output of cortical and subcortical motor systems while movement is in progress. -1,2,3 connect cortex to other areas; layer 4 thal input, layer 6 talks back -layer 5 project down - pyramidal tract - feeds down to thalamus, knows what plan is -thal knows how the plan is going -proprio info rising through dorsal column, decussates at dorsal column nuclei, hit inferior olive (gets proprio info - feeds to cerebellum, corrects issue) on way to VPN -cerebellum gets input from pontine nuclei & inferior olive -outputs to red nucleus to make corrections & reports back to VL to tell primary motor you're doing it -cerebellum compares what plan is to how plan going (sensory feedback) -primary motor also gets substantial sensory feedback (gets input directly from primary somatosens cortex) -cerebellum first know there's a problem w the plan bc info rising to cortex -to find out if cerebellum helped, cortex use layer 4 (VL reports to layer 4); see if correction made or not

The Lens

-Lens: focuses light on the retina -Ciliary muscles alter the shape of the lens as needed. -Accommodation: process of adjusting the lens -The lens adjusts so that longer wavelengths of light (red and green) are in focus on the retina -bend of cornea should be enough to make image focus; but if too close, need to bend them down too, strongly - cornea will bend it, lens bends it more strongly -everything designed to bring red & green into focus, can't get all wavelengths in focus at once so blue blurry -cilliary muscles move lens - flat for far object or more round for near objects & need to bend more

Principles of Optics

-Light is changed by objects it encounters in its path: reflected; refracted (bent); diffracted and absorbed. -Refraction is wavelength-dependent: for a given lens, short wavelengths (blue) are bent more than long (red) wavelengths -light altered by env as go through it, can bounce back (reflective) or bend around obj (refractive), or can be absorbed -all things wavelength can bend -the ones on the side can go faster -light that hits top of lens gets bend down, hit bottom gets bend up; things coming in top of eye goes down & vice versa; things get rotated 180 degrees (right-left & vice versa) -we perceive color, intensity, world right side up even though it's upside down on retina -lens designed to bend red & green into focus on back of eye/retina (longer wavelengths); blue light doesn't focus on retina (always more blurry)

Tonotopic Organization

-Like the cochlea, most structures of the auditory system are arrayed according to frequency (i.e., in a tonotopic manner). - apex vs base -every place in aud system knows what frequencies are in a sound - but this tells you nothing -how what what the sound is? need to know frequency spacing (pitch center) -where sound? need 2 ears

Cortical Localization of Language

-Localization refers to the locations within a (the left) hemisphere that participate in language-related activities. -There are seven main areas of cortex thought to contribute to our ability to comprehend and to produce spoken and written language: •primary auditory cortex; •primary visual cortex (read) •angular gyrus (behind Wernicke's in parietal/temporal junction?) •Wernicke's area (right behind primary aud cortex in temporal lobe) •arcuate fasciculus (connect Wernicke's & Broca's; long bc fasciculus) •Broca's area (project toward front of primary aud?) •primary motor cortex (speech/write) -Wernicke-Geschwind model!

Primary Motor Cortex

-Located in the precentral gyrus of the frontal lobe (in front of the central fissure) -Major point of convergence of cortical sensorimotor signals. Major, but not only, point of departure of signals from cortex. -Controls the execution of movement -secondary motor cortex decides motor plan > but now what specific muscles will we activate? primary motor comm w muscles & tells them which order to activate to move in particular way -primary motor executes, it's not a thinker it's a doer

Coding of Movement in M1

-M1 controls the execution of voluntary movements. -how precisely is motor encoded? -Intrinsic Space Hypothesis: M1 controls muscles, i.e. lowlevel movement dynamics, by controlling parameters such as movement force. *M1 controls at level of muscles, can move indiv muscles if choose to do so -Extrinsic Space Hypothesis: M1 controls movements, i.e. higher-level, more abstract kinematic aspects of movement, such as direction, range, and speed of movement. *M1 controls movements, don't control indiv muscles but rather full body movements

Radial Motion Sensitivity in Area MST

-MST responds best to global motion patterns (aka optic flow) *as you move through space, the world is moving around you - helps you navigate through space -Different cells are selective for apparent movement heading. -May be important for navigation in space, distinguishing self-motion from object-motion. -MT is the input to this area (regional flow); MST interested in global flow, total vis scene (for navigation in space)

Central Representation of Taste

-Many central gustatory neurons exhibit a strong response to a specific tastant but are also able to respond to other tastants. -Imaging studies of the gustatory cortex show that different tastes (salty, sour, sweet and bitter) are represented by specific spatial patterns containing both distinct and overlapping regions. These data support both a labeled line and a population (distributed) code of taste. -when hit target, go everywhere - population code -look at gustatory cortex, sweet activates roughly 1/2 cortex & salty activates 1/2 - BUT activate diff parts -population code: if any one of neurons dies, the code remains

Mirror Neurons (end 11/6)

-Many neurons in motor cortex (up to 50% in some areas) are active not only when performing a specific action, but are also active when a person imagines or watches the same action. -The body does not move when mirror neurons fire because the overall level of activity is lower than needed. -A possible neural basis of learning by imitation, mental rehearsal: special set of neurons in primary sensory motor cortical system called mirror neurons -many neurons in motor cortex & incl secondary motor cortex exhibit mirror neuron bx - when making motion or see someone else make motion, same neurons are activate (whether you do it, think about doing it, or watch someone else doing it, these neurons respond)

Transduction & Transmission

-Mechanotransduction: conversion of mechanical stimulus to an electrical receptor potential is direct -Outer hair cells change length and augment basilar membrane motion (direct transduction) -Inner hair cells release transmitter onto axons of the auditory nerve (indirect transmission) -vis system: photon of light -> hits rod/cone -> in photorec, activates G protein coupled rec (indirect transduction!!) -hairs connected tip to tip, when bend 1 way tips get farther & ion channel phys opens; when bend other way, tips get closer & channels go slack - this is direct transduction!! -can open/close 20k times/sec -normal depolarization we've learned: Na+ floods in *but NOT like this in aud system -high K+ in fluid outside so when channels open it depolarizes; when channels slack, K+ can't flow in & hyperpolarizes -What do w depolarization?? a. outer hair cells change length (make basilar mem jump more) -> AMPLIFIES (second way to increase pressure waves in cochlea, need to amplify to hear bc under water) - direct transduction b. inner hair cell: sense motion; don't have axon, only axon terminal; release NT & aud nerve brings in -> indirect transmission!! (release NT on something else w axon) -know how transduce/transmit, compare diff systems

Olfactory Receptor Sensitivity to Odors

-Most OSNs are odor "generalists", i.e., they show a spectrum of responses to a variety of odors. -Therefore, odor objects activate more than one type of OSN, but to a different extent. -Odorant concentration is also important, but dynamic range of response in single OSNs is limited to about ten-fold change in concentration. -Conclusion: each OSN cannot uniquely code for either the identity or the strength of odorants. -Central olfactory system must "disambiguate" identity and strength to discriminate odors (population coding). *can't say whether weak or strong or what spec odorant is **it's a population code!: (like gustatory) many respond, when 1 dies, message continues *label-blind code (visual, ex; opposite): 1 point on space activates 1 receptor; when call name, 1 stand up, when dead, conversation over -any particular rec responds to many diff odors (taste cells have many diff receptors on them, diff receptors each for 1 taste; here have only 1 receptor protein, but each protein responsive to many diff odors) *both generalists but do it differently -each odor receptor responds to many diff, but not to same extent; more concentrated, more activity *some might be more sensitive at low, med, or high levels; few sensory neurons responsive to diff levels

Motor Units

-Motor units are the smallest unit of motor activity. A motor unit consists of a motor neuron (a-MN) plus all the muscle fibers it contacts. -When a motor neuron fires, all of its fibers contract together. -Number of fibers per unit varies ("innervation ratio") • distal muscles; fine control, low innervation ratio • proximal muscles; forceful movement; high ratio -Recruitment (Henneman Size Principle): *motor units are activated in order from small to large.* -when go out to muscle, have lower motor neuron to muscle -muscle stretch from 1 tendon to the other, 1000s of cells -alpha motor neuron & all muscle cells it contacts -always have 1 motor neuron, but how many muscle cells will you have? -1 alpha motor neuron may only activate single muscle fiber or activate many (innervation ratio) *innervate 1: ratio is 1:1 (can have much finer control) *if ratio high: go out to 10 muscle fibers w 1 motor neuron -much finer control of distal vs proximal muscles -recruit small THEN the large (recruitment principle) - use least amt muscle fibers you can

Recurrent Collateral Inhibition

-Muscle fibers and motor neurons need rest after activity. -Each motor neuron branches before it leaves the spinal cord, and the branch synapses on a small inhibitory interneuron, which inhibits the very motor neuron from which it receives its input. -The inhibitory interneurons responsible for recurrent collateral inhibition are called Renshaw cells. -distribute the load, 1 single muscle fiber shouldn't have to do everything

Proprioception from Muscles

-Muscle have two types of proprioceptors. -Muscle spindles are in parallel with muscle fibers; they signal muscle length. -Golgi tendon organs are in series with muscle fibers; they signal muscle tension. -how long is muscle? tells us where it's located -Golgi tendon organ tells us to let go when about to rip off, meas tension & force in muscles (how much work they're doing)

Natural Sounds are Complex

-Natural sounds are complex patterns of vibrations, but most consist of a harmonic sequence of tones (integer multiples of the fundamental). -Fourier analysis breaks a natural sound down into its component sine waves->the auditory system will do the same -male voice (pitch = 100Hz): lowest freq=100; next freq is 200; goes by 100 so 100, 200, 300, 400, etc **all integer multiple of lowest freq -female voice (pitch = 200Hz bc spacing is 200): 200Hz, next is 400 (then 600, 800, etc) -if hear sounds, determine pitch & compare w memory to figure out what it is (ex. pitch 1000 bird) -auditory system does fourier analysis (math) for you

Visual Cortex (actual end of 10/23)

-Neocortex has 6 layers labeled I to VI from top (pia surface) to bottom • layer IV receives inputs from thalamus • layers interconnected vertically, forming cortical columns, the fundamental processing unit of the cortex. -LGN cells project to lowest part of layer IV (layer IV-C) of striate cortex • P and M cells project to different subdivisions of \ layer IV-C • Inputs from the two eyes terminate side-by-side -V1 is retinotopic; the central (~4°) visual space (esp. fovea) is heavily over-represented -LGN=input -V1=start of cortical processing -know where everything is in lateral view of brain & what it does/its inputs

Primary Visual Cortex

-Neocortex has 6 layers labeled I to VI from top (pia surface) to bottom • layer IV receives inputs from thalamus • layers interconnected vertically, forming cortical columns, the fundamental processing unit of the cortex. -LGN cells project to lowest part of layer IV (layer IV-C) of striate cortex • P and M cells project to different subdivisions of layer IV-C • Inputs from the two eyes terminate side-by-side -V1 is retinotopic; the central (~4°) visual space (esp. fovea) is heavily over-represented

Properties of Light

-No light (no photons), no vision -Light can be thought of in two different ways: • Particles of energy (photons) • Waves -Visible light (for humans) is waves of electromagnetic energy between 380-760 nm -Wavelength (fast vs slow): color -Intensity (big vs small): brightness -light will hit objects then they respond like being physically hit (particles of energy) -shorter wavelengths blue, longer more green -there are many shorter (gamma and x-rays) and higher (infrared) that we can't see

Olfactory Receptor Proteins

-OR's are 7 transmembrane-domain Gprotein coupled receptors, similar to sweet-bitter-umami taste receptors. *7 parts of protein span membrane -Rodents express over 1000 different OR genes (largest family known). *1000s of genes create these receptors, but only ~350 in humans (can sense upwards of 10k diff odorants but only have 350 distinct receptors, 1 rec responds to many diff odors) - this is similar to gustatory (sensitive to more than 1 taste) *In humans only 350 genes actually express ORP's. *Many are "pseudogenes" that do not normally express ORP's. -Each OSN typically expresses only one OR gene. -Therefore, only ~350 different types of human OSNs relay information for tens of thousands of perceptible odors. -only 1 protein, but can respond to many odors

Olfactory Bulbs

-OSN axons form the olfactory nerve (CN I), which projects into the olfactory bulb (OB). -All OSNs expressing a particular OR converge onto one "glomerulus" in the ipsilateral OB. -The organizational principle of the layout of glomeruli is unclear; however, there is mirror symmetry of like-receptor glomeruli in each OB. *Humans express ~350 OR genes, so each OB has ~350 glomeruli (for 700 in total). -project into olfactory bulb (nasal epithelia>skull>olfactory bulb) -350 diff receptors, spread in nasal epithelia in zones; 350 glomeruli *on each side of nasal passage, have 350 glomeruli organized in bulbs -glomeruli don't lines up fruity, floral, etc; just have a pattern, not clear why mixed and matched

Olfactory Sensory Neurons

-OSNs number in the tens of millions: *Rat ~15 million *Human ~20 M. *Rabbit ~50 M. *Bloodhound ~220 M -OSNs turn over every ~28 days by differentiation of basal cells (similar to taste cells, but one of the few places in the brain where new neurons with axons are created in adulthood). *completely refreshed population ~ every 28 days *taste transduce then transmit; release NT, indirect transmission *these guys have axons that extend through roof of nasal passage & then go find targets; they are complete neurons (have axons) - direct transmission *must generate new cell body & dendritic processes & have axon that grows & heads to target - have to do a lot of things

Olfactory Epithelium

-Olfactory sensory neurons (OSNs) are found in the olfactory epithelium of the nasal cavity. -Olfactory epithelium: *Bilaterally located in the "olfactory cleft" at the back of the nose. (2 nostrils, 2 olf epithelia) *Secretes aqueous mucus within which odorants dissolve. *Mucus contains proteins, antibodies, enzymes, salts, and odorant binding proteins that enhance concentration of odorants. -Composed of OSNs, basal (stem) cells, and supporting cells. *processing chemicals toxic; basal cells divide to generate new cells & more basal cells (just like taste, replaced bc doing toxic work) -Area of olfactory epithelium varies by species: Human: 10cm2, Dog: 170cm2 (they have many more receptors, can smell better)

Pitch Perception

-One small area just anterior to the primary auditory cortex has neurons that respond to pitch rather than frequency (responds to a stimulus even if the fundamental is missing) -pitch center next to primary aud cortex -figures out spacing, which determines pitch *frequency spacing (not lowest freq in sound) determines a sound's pitch -ex. 400, 600, 800, 1000: pitch = 200, so it's a female voice *even though no energy at 200Hz -20Hz spacing=elephant stomp; 1000=bird; 100=male voice -once have separation, then knows what sound is bc memory lookup

Central Sensorimotor Programs

-One view of sensorimotor function is that the system comprises a hierarchy of central sensorimotor programs. In this view, levels of the system have patterns of activity programmed into them, and complex movements are produced by activating these programs in proper order. A given movement can be accomplished in various ways, using different programs/muscles (motor equivalence). -who runs program? PPAC & DLPFAC at first; as time goes by, drop to primary motor or spinal cord (locus of learning changes) -as get better, don't need higher level control anymore so drop lower

Retina to Primary Visual Cortex

-Optics of eye project reversed and upside-down image of monocular visual field onto each retina. -Optic nerves exit each eye and project bilaterally to the lateral geniculate nucleus (LGN) of the (visual) thalamus. • Fibers from temporal hemi-retina, which views the contralateral half of a monocular visual field, project to ipsilateral LGN. • Fibers from the nasal hemi-retina, which views the ipsilateral half of a monocular visual field, cross the midline ("decussate") in the optic chiasm, and project to contralateral LGN. -LGN on each side projects ipsilaterally to the primary visual cortex. -Result: Information from each visual hemi-field processed in contralateral hemisphere of visual cortex -output of retina>LGN of thalamus (on either side of third ventricle)>primary vis cortex (but to get there, crossing occurs) -there's a part of middle of field of view that overlaps, can't have that in cortex -nasal part of retinas that cross; light on 1 side of world hits nasal part of 1 side & temporal part of other eye - these must combine -crossing happens underneath brain, optic chiasm **know where thalamus is & what its parts are for exam -when hit optic chiasm, switches PNS to CNS -cranial nerve 2 coming in, cross at chiasm, now at tract (tract is CNS)

Basal Ganglia: Parkinson's Disease

-Parkinson's disease is characterized by slowness or absence of movement (bradykinesia or akinesia), rigidity, and a resting tremor (hands, fingers) -Cause: the loss of the dopaminergic neurons in the substantia nigra *neurons in substantia nigra die, no dopamine flow into striatum *D1=yes voters, D2=no votes - metabotropic dopamine receptors, do whatever G protein tells them to do (tells D1 to open Na channels, depolarize&excite; dopamine suppresses no voters, open K channels&hyperpolarize) *if dopamine can't excite D1 & suppress D2, yes voters weak & no voters strong -Direct pathway striatal neurons have D1 dopamine receptors, which cause depolarization, whereas indirect pathway striatal neurons have D2 dopamine receptors, which cause hyperpolarization. The nigrostriatal pathway thus produces net excitation of cortex in two ways. In Parkinson's disease, balance is tipped in favor of the indirect inhibitory pathway

Transduction (start 10/23)

-Photoreceptors (rods and cones) in the retina are depolarized in the dark, and hyperpolarized in the light -In the dark (i.e. unstimulated): • cGMP-gated Na+ channels are open, leading to inward (depolarizing) Na+ current (the so-called "dark current") • Vrest ~ -40mV • glutamate released -In response to light (stimulated): • retinal changes shape • opsin dissociates and activates a unique G-protein (transducin) • transducin activates the enzyme phosphodiesterase (PDE) which breaks down cGMP. • cGMP-Na+ channels close • membrane hyperpolarizes (~ -70mV) • reduced release of glutamate -close Na channels in response to light -if stimulus directly alters channel, direct transduction; but here phys stimulus (photon of light) goes through G protein before channels affected (indirect) -indirect transmission: these cells don't have axons; these receptors dump NT, then has effect on other cells -light essentially inhibits rods & cones

Motion of the Basilar Membrane

-Pressure changes in the cochlea set up a traveling wave on the basilar membrane which peaks at one place for each frequency in the input. -The basilar membrane "performs" a Fourier analysis of the incoming sound waves by virtue of its biomechanical properties -basilar membrane has 2 ends: base & apex -organ of corti sit on basilar membrane -at apex: big trampoline, held loosely - goes up & down slowly -at base: stiff & low mass (tightly held) -sound waves in & activate right spot on bas mem -high freq activate base, low freq activates apex -male voice (pitch 100) activates many spots (bc actually 100, 200, 300, etc) - basilar membrane does Fourier analysis for you, travels more towards apex -female voice/pitch 200 has 200, 400, 600, etc - travels momre towards base -tototopic organization: any place in basilar mem maximally activated by 1 pitch (retinotopic org in vis: any spot on retina corresponds to 1 spot in world) -receptors sit on bas mem; rec on apex/base go up/down a little/lot (dep bc tight vs loose trampoline) & like diff freqs

Primary Somatosensory Cortex

-Primary somatosensory cortex (SI) is located in the postcentral gyrus. -Input is largely contralateral. -It is organized according to a map of the body (i.e., it is somatotopic). -The somatosensory map or homunculus is distorted; body areas with more sensitive tactile/position discrimination have more cortical representation. -somatotopic map, v distorted (mostly face & hands - where most small recs are & most of cortex inv in these parts) *vis dominated by foveal vision (also distorted); in aud cortex, represent all equally well (not distorted)

Columnar Organization of SI

-Primary somatosensory is composed of four strips. -Each strip is most sensitive to a different kind of somatosensory input -cortex org into strips (4 in primary somatosens cortex) -**middle 2 are for exteroceptive sensors, outer for proprioceptive (don't mix feeling of touch and pain&temp, process sep) -**process mainly fast & v little slow in cortex

Odor & Odor Objects

-Primary task of the olfactory system is to identify odor objects of biological significance to the organism. -Odor objects are complex and unique mixtures of two or more "odorants". -odorant=smallest thing you can detect -Odorants include: a. Small, volatile molecules like alcohols, esters, aromatic compounds, fatty acids. b. Large, complex molecules such as musk, steroids (often used as pheromones). -can detect thousands of odorants

Lateral Geniculate Nucleus Anatomy

-Primate LGN is organized into 6 distinct layers ("laminae"). • Layers 1 and 2 (bottom): Magnocellular Large cells, input from M-RGCs. *b&w; extrafoveal; moving targets • Layers 3-6 (top): Parvocellular Small cells, input from P RGCs. *color; fovea; high resolution; stable images on retina -every place in thalamus corresponds to 1 point in space -LGN cells in each layer are monocular because they receive RGC input from hemi-retina of only one eye: • Layers 1, 4, 6: contralateral nasal hemi-retina. • Layers 2, 3, 5: ipsilateral temporal hemi-retina. -Each lamina is retinotopically organized (adjacent points of the visual field are represented in adjacent regions). Each point in contralateral visual space is precisely aligned across layers (with the fovea over represented). -every layer monocular (input from 2 eyes goes there but only get input from 1) -retinotopic organization: keep l & r eyes sep and foveal & extrafoveal sep

Early Processing of Tastes

-Receptor potential magnitude proportional to both type AND concentration of tastant. -Taste cell selectivity for basic tastes varies: 90% respond to two or more tastes. -Primary gustatory afferents branch many times, innervating numerous taste buds and, within each taste bud, several taste cells. Thus, the electrical activity recorded from a single sensory fiber represents the input of many taste cells. Afferents exhibit taste preferences, suggesting they receive input from taste cells with common tastant selectivity. -each taste cell responds to multiple tastes -touch many cells (each of which can have range of responses), but have particular ability *every cell likes salt + something else -any given receptor sensitive to many tastes; afferents that come out seek out something that has st in common; afferents show selectivity for 1 taste or another -receptors themselves sensitive to multiple tastes; afferents hit many cells but hit ones that have common theme (how produce some selectivity for tastes even though taste cells not sensitive to 1 over another)

Withdrawal Reflex

-Reflexes may be monosynaptic or polysynaptic. Many polysynaptic reflexes involve reciprocal innervation; i.e., antagonistic muscles are activated in a way that permits smooth, unimpeded motor responses. For example, when flexors are excited, extensors are inhibited. -The withdrawal reflex is an example of a polysynaptic reflex involving reciprocal innervation -detected by free nerve ending, info rises in anterolat path on opp side (there are 3 pathways going up for pain: alert goes to RF, looking to sup colliculus, VPN to somatosens cortex tell you there's pain) -if hand extended out & burning, activate flexors to bring it to you (flex & stop extending, inhibit extensor)

Direct Transduction: Salty and Sour

-Salty: Na+ ions permeate amiloridesensitive Na+ channels, directly depolarizing membrane. -Sour: H+ ions (protons) permeate amiloride-sensitive Na+ channels... AND block K+ channels, directly depolarizing membrane. -Depolarization opens Nav and Cav channels, leading to AP's (sometimes) and transmitter release, respectively -salty (Na) & sour (hydrogen/protons; hydrogen channels open at rest > cause 1) depolarization; hydrogen also 2) blocks K channels from inside) direct -any juices that go around papillae that are then sensed by taste cell creates PSP > needs to be amplified by vg channels > depolarize & release NT

Simple Cells are Edge Detectors

-Simple cells can be constructed "simply" from the convergence of center surround inputs. -Optimal stimulus for their elongated RF: edge, bar, or grating precisely oriented and placed at the boundary of on- and off region of RF. -Response may also be direction and velocity selective for visual stimuli moving across RF. -inputs coming into 4cbeta; 3 center surrounds excite higher up (anything besides input layer 4C) -only respond when all 3 of its inputs are activated (all 3 excitatory areas) - bar in right orientation -edge detectors - orientation selective, only like bars of light in certain direction -simple cells first change since retina (nothing in thal or layer 4C) - layer 4C combine center surrounds & get simple cells -rgc>lgn>layer 4c of V1>past that have simple cells -they like bars moving into their receptive fields from 1 direction & not the other (simple cells also selective to direction & velocity of bars)

Basic Types of Motor Units

-Skeletal muscle fibers are usually considered to be one of two types: slow and fast. • Slow fibers are capable of sustained contraction due to vascularization. *near to blood vessels; capillaries infiltrate muscles to deliver sugar & oxygen, nourishment *don't need to store anything bc blood keeps coming, so fatigue high *these are fibers for marathons • Fast muscle fibers fatigue quickly. *muscles farther away *(re)store in times of low energy when not doing anything - can use this energy in rapid, powerful burst *do strong activity but only for short period of time - sprinter fibers *pale, don't have blood (vs slow are red meat) -Individual muscles have a mix of slow and fast fibers. Motor units consist of slow or fast fibers; the motor pool to a given muscle contains both types of motor units -single alpha motor neuron goes out & hits fibers either near or far from blood (rarely both - either slow or fast fibers)

Muscle Innervation

-Skeletal muscle has both extrafusal and intrafusal fibers. -Extrafusal fibers cause muscle contraction. -Intrafusal fibers are found within muscle spindles, one of two types of muscle proprioceptors (Golgi tendon organs are the other type) *"the watchers": watch muscles; if muscle moves, detect this change in motion *if center starts to move, signals that st is happening *sends out gamma motor neuron commands (alpha commands to shorten to this length) - should just be right length, st wrong if not *muscle spindle say how long muscle length is, golgi tendon meas muscle tension -Muscle spindles are in parallel with muscle fibers and signal muscle length. Intrafusal muscle receives its own motor neuron input (g-MN) to keep the spindle responsive to changes in the length of extrafusal muscle

Flexor and Extensor Muscles

-Skeletal muscles belong to one of two categories: flexors or extensors. • Flexors bend or flex a joint. • Extensors straighten or extend a joint. -Synergistic muscles: any two muscles whose contraction produces the same movement -Antagonistic muscles (shown): any two muscles that act in opposition -bring joint towards you: flexors (bicep) -extend/straighten joint: extensor (tricep) -antagonistic muscles bc one brings towards, one brings away -can only push, don't pull -usually other small muscles that help (synergistic w one of the muscles) -tell 1 to bend, & must tell other to stop pulling -analogous to push-pull (not actually inhib other, just not exciting it); but most interested in neural push-pull (on vs off bipolar cells in vis; balance; aud system based on where sounds located)

Taste Chemistry

-Some taste perceptions are directly related to tastant chemistry: a. Salts (nutrients) taste "salty". b. Acids (anti-nutrients) taste "sour". -Other common taste perceptions can be elicited by a wide variety of unrelated chemicals, e.g., "sweet": *Sugars *Certain proteins (e.g. thaumatin) *Sugar substitutes: saccharin (benzoic sulfinide), aspartame (aspartic acid/phenylalanine di-peptide), sucralose ("Splenda", a chlorinated sucrose). -can activate sweet receptor/mimic sweet things like glucose, but don't deliver the sugar (agonists of the receptor but don't actually get sugar rush)

Implicit Space Map

-Sounds located off the midline reach the two ears at different times and different intensities, creating interaural(between-the-ears) time (ITD) and level differences (ILDs) -The superior olive receives inputs from the two ears and responds to ITD and ILD cues in the medial (MSO) and lateral superior olive (LSO) nuclei, respectively. Thus, the superior olive computes an implicit map of space. -many sounds in env, brain has to figure out which freqs correspond to which sounds (there's overlap on bas mem); how know difference? -where sounds came from & what is it? -superior olive processing left vs right; based on how loud in 1 ear vs other & which got there faster -near: louder & get there faster -far: quieter & slower -does in push-pull manner (when 1 superior olive happy w stimulus, other one isn't) *vis: on/off bipolar cells also push-pull

Spinal Cord

-Spinal cord has a core of gray matter (neurons/neuropil), surrounded by white matter (axons). a. Dorsal horn: Sensory inputs b. Intermediate horn: interneurons c. Ventral horn: motor neurons -Each segment of the spinal cord gives off a bilateral pair of spinal nerves (mixed sensory and motor). (31 pairs) -top: afferent comes in -sensory unipolar -upper motor neurons in primary motor -dorsolateral goes to 1 dermatome *Axons of sensory afferents enter the cord via the dorsal root. *Dorsal root ganglion: cell bodies of primary sensory afferents. *Axons of motorneurons exit the cord via the ventral root. -Each segment of spinal cord innervates a specific body region (dermatome). -Sensory inputs, interneurons and motor neurons in each spinal segment form local circuits controlling specific muscle populations associated with dermatome.

Blobs and Inter-blob Regions

-Staining for the mitochondrial enzyme cytochrome oxidase (CO) reveals patches of more ("blobs") or less densely labeled cells (interblob regions) in V1. -Blobs most apparent in superficial layers II and III. -Both blobs and inter-blob regions receive their dominant input from P-type cells. M-type cells project to layer IVB and then out of V1 (to extrastriate cortex). -Functional significance: • Neurons in blobs process object color. • Neurons in "inter-blobs" process form. -all inputs/blob areas stain for cytochrome oxidase (high energy use area) - most found in layers 2 & 3 -both blobs & inter get dom input from P cells; M cells come into 4calpha, project to 4b, then exit - don't process in primary vis cortex (moving b&w info sent elsewhere) -both get same input but blobs process color, interblobs process form (both P cell input, foveal vision processing predominantly in V1)

Transduction in Touch Receptors

-Stimuli applied to the skin deform, bend or stretch the membrane of the receptor, and this in turn changes directly its permeability to ions. -accessory structures wrapped around -rapidly adapting have pillow around them: physically open up & deform membrane when press > open Na channels > Na rushes in (this is direct) *audition also direct, vision indirect (G proteins); also know which ions flow *transduction in aud system: K+ flows (direct, rec has axon & sends APs in) *vision: rods & cones rel NTs; ganglion cells send APs -pillow: poofs up around you, releases pressure - fast adapter *if don't have pillow (no pressure releaser), not fast adapting

Taste Buds and Taste Cells

-TB's are morphologically specialized accessory epithelial structures containing taste cells. * 2000 - 5000 TB's on human tongue. -There are roughly 50 - 100 taste cells per taste bud, along with basal stem cells. *Modified epithelial ("short") sensory receptors. *have cell body, but no axon - short receptors (has nothing to do w transduction; does indirect transmission) *Differentiate from basal stem cells in the taste bud. *Turnover about every 10 days - basal stem cell redivides, replaces taste cell & itself - ongoing neurogenesis! -taste cells on sides of papillae; juices come down to microvillae -taste bud has many taste cells (500k-1 mil total)

Functional Morphology of Taste Cells

-Taste cells are "short" receptors -Apical pole: microvilli a. Protrude through taste pore into mucus of oral cavity. b. Provide large surface area to maximize contact with dissolved tastants. -Basolateral pole: a. Contains typical organelles of epithelial cells. b. Synapses onto primary gustatory afferents (first-order taste neurons), which project to brain via the central gustatory pathway. -which other sensory systems have short receptors? vision, audition (somatosensory long, deliver APs itself) -chemicals on top of tongue>move stuff around>fluid go to side & sensed by microvilli *don't have axon but have axon terminal, rel NT as if they have axon *vg Ca channels, allows them to release Glu

The Tongue

-Taste is primarily a function of the tongue. (there are taste cells on roof of mouth & back of throat too) -Taste buds are grouped in three of the four accessory structures called papillae: vallate, foliate and fungiform -There are subtle regional differences in sensitivity to different tastes over the lingual surface, but most of the tongue is sensitive to all tastes. -foliate: slits on side of tongue, has taste cells -fungiform in filliform - have taste cells -filliform - most abundant - no taste cells, move food around -most of tongue not for taste, for moving food around -taste done everywhere on tongue (diff tastes not done on diff parts of tongue, all of tongue sensitive to all tastes)

"Taste" vs. "Flavor"

-Taste refers to the sensations relayed by taste receptor cells in the oral cavity. -Foods activate different, unique combinations of only 5 basic tastes. -Flavor depends on both taste (gustation) and smell (olfaction), i.e. flavor is a multisensory percept. *flavor=multisensory perception (taste + smell + everything else) -Visual, auditory (crunch) and somatosensory (texture, pain and temperature) factors also influence the percept of flavor.

Dorsolateral Prefrontal Association Cortex

-The DLPFAC receives inputs from, and projects to, the PPAC -Given an intent to move, the DLPFAC, with input from other frontal lobe areas (in particular the ventrolateral PFC; the endpoint of the ventral streams), anticipates the consequences of various movements and forms a plan of action -Outputs to secondary motor cortex, primary motor cortex, and frontal eye field -underneath DLPFAC is VLPFC (receives input from all 5 senses); do flavor here (bc multisensory percept) -st happens in world>DL first asks what is going on over there? asks VL, VL says it is food on the table; DL forms big picture plan of action

Auditory Cortex

-The auditory cortex is located in the temporal lobe -The auditory cortex includes: •a core (primary; A1) and •up to 10 belt (secondary) regions -Each area appears to be organized on the basis of frequency (tonotopic) -central fissure points to primary aud cortex -A1: areas around it (belt) + parabelt stuff *A1 (like V1) just beginning of cortical processing -everything organized by frequency (tonotopic)

From Ear to Primary Auditory Cortex

-The axons of each auditory nerve synapse in the cochlear nuclei on the same side (ipsilateral) -From there, projections lead to the superior olives on both sides of the brain stem (binaural) -Cochlear nuclei and superior olives -> inferior colliculi -> ipsilateral medial geniculate nuclei of the thalamus -> ipsilateral primary auditory cortex -IC = tectum -primary aud cortex = right above ears, temporal lobe -decussation (crossing) @ superior olive (input from both ears > cross > then go ipsilaterally up) *cross in vis system = optic chiasm (only nasal part)

The Cochlea

-The cochlea is divided into three chambers (scala) by Reissner's membrane and the basilar membrane. The auditory receptor apparatus, the organ of Corti, sits on the basilar membrane in the middle scala -cochlea=U-shaped tube, input bulge output -has 3 straws -2 big straws are 1 straw - push on 1 straw, fluid bulges (push up/down on mems) -receptors in middle straw! -2 membranes: basilar & Reissner's *basilar: in & out motion (pressure waves) pushes basilar mem up & down -organ of corti (middle chamber): where receptors sit; sensitive to up & down of basilar membrane

Function of the Auditory System (start 10/28)

-The function of the auditory system is to perceive sounds (i.e., to localize and to identify sounds in space). Physical dimensions of sound relate to perceptual dimensions -where and what? -low & high frequency = pitch (perception) -wavelength of input = sensation -amplitude: big wave = loud, small wave = quiet (vision: brightness = amplitude)

Odor Maps in the Glomerulus

-The glomerulus is the basic structural and functional unit for odor mapping and processing in the olfactory bulb. -Homologous chemical series (e.g., alcohols, aldehydes) activate overlapping, but not identical, sets of glomeruli, reflecting similarity of chemical structure. -Different odorants elicit activity in unique, perhaps partially overlapping, populations of glomeruli; patterns may underlie discrimination. -Pattern of glomerular activation for an odor is similar across individuals. -Increasing odor concentration "recruits" activity in additional glomeruli, may be an encoding mechanism for intensity. -in glomerulus, have nice maps; bc lateral inhib, get selectivity -over population of glomeruli, see relatively good distinction btwn diff odorants -map has same look but gets larger & darker; there's a pattern; don't understand this population code, but can see that there is a code (ex. banana lights up a couple spots, other odorants light up others)

Functional Organization of M1

-The motor cortex is organized in a somatotopic manner; that is, according to a body map -Most of primary motor cortex is dedicated to controlling body parts that are capable of intricate movements, such as the hands and face. -Each site receives feedback (from primary somatosensory cortex) from receptors in the muscles and the joints that the site influences. -homunculous similar to somatosens cortex -association fibers connect; they're arcuate (short) type that connect sides *this is the first major place where have sensory feedback into motor pathway (have sens input to ppac, dl, but this is the first place w feedback) -somatosensory receive proprio & extero inputs, proprio is what matters though

Central Projections

-The olfactory tract projects bilaterally to medial temporal lobe structures including the piriform cortex (3-layered "archicortex") and the amygdala -Only system that does NOT first pass through thalamus before cortex -Two pathways from medial lobe: • limbic system: emotional response to odors • thalamus-orbitofrontal cortex: conscious perception -olfactory bulb w epithelia>cranial nerve 1>primary olf cortex (piriform cortex, located in temporal lobe on inside of medial part), sits right on top of amygdala, behind that is hippocampus; located "at base of thumb">sensory input does NOT go through thalamus (only system that goes directly to cortex, but does eventually go to thalamus indirectly bc output of piriform cortex goes to amyg & hippocampus for emotion & mem)>second pathway goes to dorsomedial nucleus of thalamus>heading to frontal cortex, conveys "what" smell info (ventral stream!) - combines w other senses here

The Otolith Organs

-The otolith organs sense changes of head angle (position of head); they are sensitive to gravity and linear acceleration -slow adapting -have rocks on top of hair cells; rocks get pulled down by gravity, continue to detect that head not upright; only respond if move head side to side -tell you about static, slow head tilt

Transduction 2

-The outer segments of photoreceptors contain disk-bound photoreceptor proteins, specifically rhodopsin (rods) and photopsins (cones). Photo-pigments consist of two components: retinal, a small molecule derived from vitamin A that changes shape as it absorbs light; and opsin, a protein which determines the spectrum of photons captured. -have opsins back in outer segment, like stained glass window, determine which light goes through them based on their shape -inside opsins are retinal, this is the pigment; determine which color accept when light hits -if right color (if light gets through), activate retinal -rhodopsin in rods (blue light activates, but don't see color w it), 3 types of photopsins in cones (red, green, blue)

Retinal Receptive Fields (RFs)

-The receptive field of an individual sensory neuron is the particular region of sensory space (e.g., the visual field, or body surface) in which a stimulus affects the firing of that neuron. -Receptive fields in the retina are circular in shape and defined in terms of degrees of visual space (from hundredths of a degree in the fovea to tens of degrees in the periphery). -light from low hit high & vice versa -each place on retina responsive to 1 space in world (receptive field) -rec fields in retina circular; all you can see well is very small spot the size of the moon; everything else blurry & b&w -in fovea, many cones, each one has much smaller rec field; in periphery, rec fields bigger

The Retina

-The retina converts light to neural signals -5 layers (from front to back): • retinal ganglion cells • amacrine cells • bipolar cells • horizontal cells • photoreceptors "Inside-out": -Light passes through many cell layers before reaching its receptors. The pigmented epithelium absorbs any light that passes through the retina, and also provides metabolic support. -light converted to neural signals by retina; convert to PSPs then launch APs -in front of eye are ganglion cells: have axons, bring APs into CNS -behind them are amacrine cells -next are bipolar cells -then horizontal cells -finally receptors in back -pupil looks black in humans bc light goes in & nothing comes out (cats have reflective eyes, see better in dark but not as clear vision - light bounces & hits another part of retina so can see in low light)

The Semicircular Canals

-The semicircular canals detect turning movements of the head, in particular angular accelerations (rapid adaptation). -Semicircular canals are paired with another on the opposite side of the head. Rotation in one axis excites the hair cells of one canal, and inhibits the other canal: push-pull. -have fast & slow (like everything p much besides muscles & joints (spindles & Golgi, p much both slow)) -3 semicirc canals on either side of head, 2 pairs good for yes, 2 pair good for no, 3rd pair for rocking side to side *they look at the fluid mvmt in them -direct transduction; K+ flows in -once get fluid going, looks like stopped bc going same speed as head (can't detect motion); hair cells bent when fluid moving relative to head -fast adapting -2 sets on either side of head; when move head to left, L side excited & R inhibited (push-pull) *aud system uses push-pull in superior olive; vis uses it w on-off center cells

Basal Ganglia: Huntington's Disease

-The symptoms of Huntington's disease are in many respects the opposite of the symptoms of Parkinson's disease. Huntington's disease is characterized by *choreiform movements*: involuntary, jerky movement of the body, especially of the extremities and face. -Huntington's disease results from the selective loss of striatal neurons in the indirect pathway. Thus, the balance between the direct and indirect pathways becomes tipped in favor of the direct pathway. Without their normal inhibitory inputs, thalamic neurons can fire randomly and inappropriately, causing the motor cortex to execute motor programs without proper control. *get more motion than want *D2 neurons susceptible to dying, no voters die in striatum; BG tries to pump yes voters & suppress no voters but no voters are gone so only vote yes *first cortical loop through bg to help secondary motor make set of instructions, prob w this loop

Pain and Temperature Receptors

-The transduction of painful and thermal stimuli occurs at free nerve endings. -Pain receptors (nociceptors) may respond selectively to strong mechanical, thermal or chemical stimuli, or respond to all three kinds (polymodal). -Thermoreceptors are highly sensitive to temperature in the innocuous range. There are distinct warm and cold types. -Transmission is via myelinated Adfibers (rapid adapting/rapid transmission) or unmyelinated C fibers (slow/slow) -not specially covered if doing pain/temp - only have free dendrites, directly connected to axons -where cell bodies? dorsal root ganglion (practically right at spinal cord) -pain receptors have higher threshold of activation; but both have transient receptor potential receptors (directly activated by stimuli) *strong, painful stimuli cause N & Ca flow in -how get fast & slow varieties? dependent on type of receptors AND whether axon myelinated *Adelta fibers - fast transmission, myelinated (rapid adaptation) *C fibers - slow transmission, no myelin (convey dull throb that follows) AND receptors themselves tend to stay open longer (which cells rapidly adapting (only respond to start of stimulus) in vis? M cells, more sensitive to motion) *rapidly adapt if sensitive to onset of painful stimulus

Formation of Opponent RFs 1

-The two types of center-surround receptive fields exhibited by retinal ganglion cells are created in a two-step process: • First, the opponent center-surround aspect is created by mutual inhibition among photoreceptors that is produced by horizontal cells • Second, the on- and off-center aspect is created by bipolar cells which show opposite responses to the glutamate released by their receptor (i.e., bipolar cells express different glutamate receptors) -ganglion cells sensitive to circular region -cones lined up -2 cones in the dark: excited in the dark -also cone in center - cones tightly packed so where there's 1 there's many -all connected by horizontal cells - use GABA as inhibitory NT *if strong, try to wipe out others around so can stand alone *this is what creates center-surround opponency; if surround weak, you are strong & vice versa a. competition btwn center & surround (horiz cells) b. like light on center vs surround (dep on bipolar cell)

Balance: The Vestibular System

-The vestibular system monitors the movement and position of the head, giving us our sense of balance or equilibrium. The system includes two structures: the semicircular canals and the otolith organs (they're next to cochlea - where start of transduction & transmission in aud system) -they're phys connected even though do diff things (1 about balance, 1 about hearing); share fluids & transmit, transduce in identical way -what ion flows in transduction in vestibular system? K+, bc shared by aud system -together form 8th cranial nerve -indirect transmission (hair cells in both aud and vestibular); things in balance system do diff things but share almost everything w aud system

Proprioception from Joints

-There are four types of mechano-sensitive proprioceptors in joints. -They respond to changes in angle, direction and velocity of the joint. -what is angle of joints? -inside each of bones, have recs inside sensitive to fast & slow angles -if arm moving around, have fast adapters; if not moving, slow -ruffini=slow (says arm is still out there) -pacinian=fast (says you're moving your joint)

Rods and Cones 1

-There are two main types of photosensitive cells - rods & cones - which differ in a number of anatomical and physiological ways. Anatomical differences include size, shape, number and location on the retina. -There are no rods in the fovea, only cones. Rods predominate outside of the fovea. -anatomical rods are taller/bigger, shaped like rods/baseball bats; there are 120 million rods (many more than cones); no rods in fovea -cones shaped like road cones; only 6 million cones; only cones in fovea, cones also found everywhere else

Organ of Corti

-There are two types of hair cells (short receptors) in the organ of Corti: •inner hair cells, ~3,500 •outer hair cells, ~14,000 -All hair cells have stereocilia on their upper surfaces which are in or near the tectorial membrane. -Up-down motion of basilar membrane converted to side-to-side motion of stereocilia -2 receptor types: inner hair cells & outer hair cells -not many & once kill them, can't get them back -hair cells in organ of corti sitting on bas mem; at top of hair cells are hairs; activated when hairs bent as hair cells go up & down -hit tectoral membrane which bends hairs (tect mem side to side motion?)

The Eye 1

-There is a one-to-one correspondence between a point in space and a place on the receptor surface (retina) (an explicit map of space) -Accessory structures (e.g., cornea, lens): shape the input to the receptor -cornea: clear, protein structure that gives outer shape to eye; bulges out, part of biological lens *provides 2/3 bending power of eye -aqueous humor: gives eye shape -behind that is lens *lens does last 1/3 bending power, can change shape -vitreous humor, give shape -in back: retina, where receptors located -lots of accessory structures in the way (all these structures listed in order front to back) -things that hit the top of lens bent down & vice versa -st pointing down would be pointing up on retina **it's 1 to 1: wherever retina activated, that's where the light is ***cornea>aqueous humor>lens>vitreous humor>retina

Development of Sensorimotor Programs (end 11/11)

-There is evidence that central sensorimotor programs may be established with or without practice. -Programs for many species-specific behaviors are established without practice. For example, Fentress (1973) found that mice without forelimbs still make coordinated grooming motions. -Practice can also generate and change the locus of programs. • Response Chunking • Shifting Control to Lower Levels

Properties of Touch Receptors

-Touch mechanoreceptors vary in receptive fields sizes, preferred stimulus frequencies, and pressures. The identification of objects by touch is called stereognosis -light touch vs strong pressure = 1 diff btwn superficial & deep -another diff: small rec field (M & M, to activate needs to be right on top) vs large receptor (strong pressure dispersed throughout skin, can feel pressure in wider area around spot) -need more M & M bc have to be right on top of them -why 2 superficial & 2 deep? fast & slow *fast = I've just been touched/grabbed (meissner & pacinian) - rapid adaptation, signal as soon as been touched *slow = merkel & ruffini say it's still touching/grabbing me -sensory system most interested in when just been touched/grabbed, initial effect more important (more of cortex devoted to rapid proc) 1. Meissner a. Field Diameter: 3-4 mm b. Frequency Range: 10-60Hz c. Adaptation (pressure): Rapid d. Quality: Light touch, stroke 2. Merkel a. Field Diameter: 3-4 mm b. Frequency Range: DC-30 Hz c. Adaptation (pressure): Slow d. Quality: Touch, fine spatial details 3. Ruffini a. Field Diameter: > 10 mm b. Frequency Range: DC-15 Hz c. Adaptation (pressure): Slow d. Quality: Stretch, finger position 4. Pacinian a. Field Diameter: > 20 mm b. Frequency Range: 50-1000 Hz c. Adaptation (pressure): Rapid d. Quality: Vibration, strong pressure

Olfactory Transduction 2

-Transduction currents generate graded receptor potentials that may elicit APs in the OSN axon. -Termination of activity: a. Odorants diffuse away. b. Odorants broken down by enzymes. c. cAMP activates processes that terminate transduction -Adaptation and Desensitization: Response to prolonged or repetitive stimulation wanes w time. -this is much longer & bigger than standard PSP (usually last 5ms, 200x shorter); dendrites close to soma here as well so get big PSP, doesn't taper so much -odorants broken down in mucus (cleaved) & also dragged in by mucus -need to be able to smell the next smell; will be cleared out by the next breath even though it's a huge PSP -some smells just persist, seems to get less intense the longer you smell it (adaptation & densitization) - rapid adaptation, respond at beginning of stimulus (similar to somatosensory & M cells in vision; common feature found in many sensory systems) -if repeat stimulus often, won't respond to second as strong as first (won't respond as much until spread apart)

Basal Ganglia Pathways

-Two major functional pathways through basal ganglia, direct and indirect/hyper-direct, with opposite net effects on thalamic targets. Proper function: balance -secondary motor sends thoughts to striatum (send options 1 at a time to be voted on by caudate&putamen) -if votes yes & likes: output wipes out GPi - inhibits - direct/short way thru basal ganglia, get back to 2nd motor -if vote no: knock GPe out of circuit; GPi no longer inhibited by GPe (disinhib), then inhibits yes man (thalamus) -substantia nigra: send dopamine into striatum to encourage yes vote 1. Direct: excitation Facilitates motor (or cognitive) programs in the cerebral cortex that are adaptive for the present task 2. Indirect/hyper-direct: inhibition Inhibits the execution of competing motor programs

Orientation Selectivity Columns

-V1 neurons show a range of optimal stimulus orientations. As an electrode passes parallel to the surface, the preferred orientation shifts progressively forming orientation columns. -how many orientations are there? -like bars in every orientation you can think of

Ventral Stream: Form/Color Processing

-V4 & IT -don't worry about v2&v3

Motion Sensitivity in Area MT

-dorsal stream -MT & MST process M cell input, they're for motion sensitivity -large RFs, neurons that are only sensitive to onset of stimuli (motion) -MT: neurons sens to motion in particular direction -first proc regional motion sensitivity

Touch Mechanoreceptors of the Skin

-exteroceptive: 1) touch 2) pain & temp -like vision; on skin, correspond to 1 spot on world -these are the long receptors - have axons (rods, cones, and hair cells are short - aka no axon) *tells you about how you transmit (direct) -Skin can be vibrated, pressed, pricked and stroked, and its hairs can be bent or pulled. -Accordingly, there are many kinds of cutaneous receptors scattered about the body (providing an explicit map of space). Among these receptors are neuronal ("long") touch receptors with specialized endings including: •Meissner's corpuscles (superficial) •Merkel's disks (superficial) •Ruffini endings (deep) •Pacinian corpuscles (deep) *why 4 receptors and why paired? do diff things

Extrinsic Space Hypothesis

-find that many neurons very active; any motion typically exhibit involves motion of many body parts at once -motor neurons don't code for 1 muscle, but vote for motion they happen to like & take entire population to make specific motion -motion CAN be of single muscle variety, but requires small activation of motor cortex; typically, it's MANY neurons simultaneously trying to vote, go in direction of most votes (it's a population code in order to make us move) *other population codes: olfactory & gustatory -Activation of the homunculus at a given site with natural duration and amplitude stimulation elicits complex, species-typical movements involving that body part. • M1 neurons prefer a particular direction of movement. • However, directional tuning is broad, esp. compared to precision of actual movement.

Transduction 1

-how transduce physical stimulus into PSP? -transmission: what do you do w that PSP? 1. Photoreceptors are modified epithelial cells or so-called short receptors: • no axonal process (dedrites, soma, axon terminal only) - can generate PSP & release NT (axon terminal) but CAN'T generate AP *as membrane potential depolarizes it's as if AP hit it, end up releasing glutamate (it's the receptor not the NT that matters!!) • "synaptic-mimetic": functionally & morphologically similar to presynaptic nerve endings; transduction currents modulate release of neurotransmitter A. Outer segment: transduction • modified cilium, densely folded. • photopigments respond to light, and alter membrane currents. • replaced daily B. Inner segment: transmission • synapses with bipolar and horizontal cells • transduction currents modulate release of glutamate.

Central Proprioceptive Pathways

-joint info climbs w touch info -proprio rises in dorsal column -just know: vestibular system contributes to proprio system, goes to thalamus & joins it (somatosens info joins together)

Olfactory Transduction 1

-odorant molecule dragged into mucus by binding protein -how go from phys stimulus to PSP? -odorant rec protein on each cilia; on cilia are g-protein coupled receptors (indirect transduction) -odorant binds protein & release Ga (called Golf - specialized G protein, acts like Gas) *stimulate cAMP > opens channels from inside (Ca & Na channels) > a little bit of Na and Ca flow in > get small depolarization > Ca wanders to Cl channel, opens Cl channel > Cl flows (these are special bc Cl transporters on membrane to make inside v high in Cl), Cl desperately wants out > massive influx of pos ions > this is the amplification process (scents not in nasal passages for long) *direction of current opp flow of Cl ions *ultimately: Cl ions out, bringing in pos charged current *indirect (G protein), essentially Gas (even tho Golf), activate cAMP, Cl efflux -Apical pole of OSN forms a knob out of which tufted cilia protrude into mucus layer. -Odorants in mucus bind to odorant receptor proteins (OR) in the ciliary membranes. -Binding stimulates unique olfactory G protein (Golf) transduction cascade leading to elevation of cAMP levels. -cAMP directly opens cation channels, creating inward (depolarizing) Na+ and Ca2+ transduction currents. -Ca2+ -activated Cl− channels also open, outward Cl− current substantially enhances inward depolarizing current

Divisions of the Somatosensory System (start 10/30)

-somatosensory system div into 1) Exteroceptive External stimuli (temp, pain, touch) 2) Proprioceptive Body position (where body located in space?; muscles, joints, balance) 3) Interoceptive Body conditions (internal you; bladder, blood pressure, respiratory rate)

Retinal Ganglion Cell Properties

-summary of cell properties 1. M Cells (magnocellular ganglion cells) -Peripheral retina (~100,000) -Large cell bodies and large RFs -Coarse resolution -Inputs from 1000s of rods and cones - convey light vs. dark information -Rapid adaptation and conduction of APs *they only like change, activated by 1000s rods & cones but only when active same time (only onset); ganglion cell only responds strongly at onset, when all cells like at same time -Motion response better than stationary -Optimized for large-scale, low-contrast moving patterns (wants to know if st large approaching you quickly, not what it is/not if it's small) 2. P Cells (parvocellular) - many more ganglion cells -Central retina (esp. fovea) (~1 million) -Small cell bodies and small RFs -Fine resolution -Inputs from ~1 cone - convey color -Slow adaptation and conduction of APs -Stationary targets better than moving. (so can stare at it & figure out what it is) -Optimized for small-scale, high-contrast fine patterns

Transduction 3

-under membrane have G protein waiting for opsin to be activated (retinal will change shape) -Gbg and Ga break apart -Ga called Gat (transducin) > goes to phosphodyesterase, makes second messengers (goes in opp direction of Gaq and Gas, same as Gai) > takes active second messenger & convert to inactive -at rest, rods depolarized relative to rest (-40) -Photoreceptors are depolarized in the dark, and hyperpolarize in response to light 1. In the dark (i.e. unstimulated): • cGMP-gated Na+ channels are open, leading to inward (depolarizing) Na+ current (the so-called "dark current") • Vrest ~ -40mV • glutamate released 2. In response to light (stimulated): • retinal changes shape • opsin dissociates and activates a unique G-protein (transducin) • transducin activates the enzyme phosphodiesterase (PDE) which breaks down cGMP. • cGMP-Na+ channels close • membrane hyperpolarizes (~ -70mV) • reduced release of glutamate

Posterior & Anterior Streams

1. Auditory signals are conducted to two areas of association cortex: •Posterior parietal cortex •Prefrontal cortex 2. Posterior vs Anterior: •"where" (post) vs "what" (ant) •in register with visual pathways -all systems interested in what/where -up stream: where processed in visual system -auditory down towards front: what pathway -up = where

Two Major Exteroceptor Pathways

1. Dorsal-Column Medial Lemniscus -Mainly touch & muscles/joints -First synapse in the dorsal column nuclei of the medulla -rises on same side of body until hits dorsal column nuclei (in medulla > send input through medial lemn fibers > thalamus (VPN) > somatosensory cortex (parietal lobe behind central fissure)) -where touch info rises (NOT pain & temp) *know thalamic nuclei! 2. Anterolateral System -Mainly pain and temperature -First synapse in the spinal cord -Three tracts -pain & temp synapse immed > opp side of spinal cord > from spine head up to reticular formation (locus coeruleus, alert signal) > also spinal cord to tectum (superior colliculi, make you reflexively look) > also rise from spine to VPN > VPN to primary somatosensory cortex -on way up before hits thalamus, talks to periaqueductal gray (pain modulation) > send fibers back down to use neuropeptides to stop pain info (endorphins, enkephalins) *use substance P to activate pain response, use endorphins to cut down that response -touch rises up in dorsal column (other one up not dorsal), other one descending?

Division of Labor - Descending Motor Pathways (end 11/8)

1. Dorsolateral tracts • one direct tract, one that synapses in the brain stem • terminate in one contralateral spinal cord (cross @ medulla) segment (corticorubrospinal - red nucleus) • distal muscles • limb movements 2. Ventromedial tracts • one direct tract, one that synapses in the brain stem (cortico-brainstem-spinal) • terminate in multiple, bilateral spinal cord segments (many dermatomes) • proximal muscles (muscles in stomach & back) • posture and whole body movements

Cortical Loops and Descending Tracts

1. Two major cortical loops: • one through the basal ganglia and secondary motor cortex that selects and initiates action; • one through the cerebellum and primary motor cortex that modulates and sequences muscle contractions while a movement is in progress. 2. Four major descending pathways (mainly from primary motor cortex): • two in the dorsolateral region of the spinal cord; and • two in the ventromedial region. *secondary motor helped by basal ganglia - does through ventral anterior nucleus of thalamus *VA=basal ganglia, feeds up to respond to motor cortex *VL=cerebellum (know 5 parts of thalamus) -coming out of primary motor are 4 pathways that form 2 big bundles going down

Complex Sensorimotor Reflexes: Walking

1. Walking is defined by an 'inverted pendulum' gait in which the body vaults over the stiff limb or limbs with each step. • Swing phase: flexors active, lifting limb off the substrate. • Stance phase: extensors active, placing limb on the substrate; weight-bearing. • Swing-stance transition: flexors and extensors co-activated. -lose reflex as go from automatic to control 2. Central Pattern Generator: • Flexors and extensors controlled by pools of interneurons and motor neurons. • Mutual inhibition (negative feedback) creates alternating activity in flexors and extensors. • Descending excitation activates CPG to initiate and sustain locomotion. *walking seems complicated but it's a reflex; just have to tell spinal cord to do walking & reflex begin; motor cortex not commanding, just tell spine to walk

Indirect Transduction: Bitter/Sweet/Umami

Bitter, sweet, or umami tastants transduced by G protein-coupled pathways. -Binding of tastant to receptor activates G protein/PLC/IP3 cascade. -IP3 elevates internal [Ca2+] *IP3 causes release of Ca2+ from internal stores. *Opens unique Ca2+ -activated Na+ channel, depolarizing membrane, opening voltagedependent Cav channels. -Ca2+ influx further raises [Ca2+]]i , triggers transmitter release, synaptic stimulation of primary gustatory afferents. -all bind to G protein coupled rec & let loose Gaq > wanders to phospholipase C > turns pip2 into IP3 > goes to internal Ca stores & lets loose a little Ca (stores are smooth ER) > causes a little depolarization > lets in Na > Na triggers AP > get big PSP *at end of every taste transduction process results in Na depolarizing cell > activate vg Ca > cause AP -either direct or indirect = AP (amplifies PSP substantially)

Physiology of Input Layer of V1

By and large, the receptive fields of neurons of layer IV-C (the input layer of primary visual cortex; striate cortex; V1) are similar to those of their LGN inputs and, in turn, of retinal ganglion cells. They are: • monocular • circular • center-surround

Physiology of Input Layer of V1

By and large, the receptive fields of neurons of layer IVC (the input layer of primary visual cortex; striate cortex; V1) are similar to those of their LGN inputs and, in turn, of retinal ganglion cells. They are: • monocular • circular • center-surround -neocortex: layer 4 thalamic input, output layer 6, talk to other parts of cortex 2&3, layer 5 subcortical -inputs from thal goes into bottom 2 layers of v1 (div into 4 layers) -4C alpha processing moving, black & white -4cbeta - stationary, color -layer 4c of cortex identical to cortex (left & right eye sep, M & P cells sep) -RFs smaller in 4cbeta, ones in periphery bigger -input to vis cortex lower 2 layers, cortical processing starts to happen in 4 A and B (top two layers of V1)

Genetics of Communication Disorders (end 10/28)

Deficits in language and speech functions can be of numerous types: •aphasias due to brain damage including ... 1. Wernicke-fluent-receptive-comprehension (fluent but can't comprehend) 2. Broca-nonfluent-expressive-production (can't produce speech but do understand) 3. conduction (arcuate fasciculus) -hallmark is inability to repeat unfamiliar words (ex. want to say telencephalon but instead say airplane/blue) •disorders due to genetic factors including ... 1. dyslexia (angular gyrus) -reading difficulty **NOT problem w visual cortex **problem in angular gyrus (KIAA gene) *angular gyrus doesn't make right sound so Wernicke's can't understand (ex. ang gyrus says T as an L) 2. verbal dyspraxia (Broca) -impaired speech *FOXP2 gene - trouble in Broca's, motor cortex & can't produce speech

Rods and Cones 2

Duplex theory of vision: rods and cones mediate different kinds of vision Rods (scotopic vision): in periphery!! • high sensitivity (nighttime): single photon can activate rod • low-acuity (high convergence): many rods feed 1 ganglion cell • no color Cones (photopic vision): in fovea!! • low sensitivity (daytime): during day, cones get a lot of light; only respond to lots of light • high-acuity (low convergence) • color -rod-fed also have cones coming into it bc there are cones in the periphery; in center of the world, it's cone-fed -rods more periphery (scotopic vision), cones do diff types of vision; photopic vision in fovea

Extrastriate Cortical Areas

Evidence suggests that there are two major parallel output pathways (streams) from V1 to extrastriate cortex: • dorsal: M-cells; motion/space • ventral: P-cells; color and form -moving past V1 now -as outputs of V1 move towards front of brain (heading to spec areas), continually enhanced processing as go along (skipped M cells, only start P cell proc) -when have image of cortex, have idea of where things located (v4, it, mt, etc) - know lateral view of brain

Color Vision

Most ganglion cells with cone inputs are color opponent. The two types of color-opponent cells are: • red-green • blue-yellow (where yellow sensitivity is created by the sum of inputs from red and green cones) -these are the ones from fovea -difference?: have red center, green surround or green center, red surround -if center red, only surrounded & fought by green & vice versa -when red & green activated together, blue fights it -RFs tell you what they want; if don't get it, will be inhibited by it

Dorsal Stream: Spatial Orientation

Parietal cortex lesions lead to selective impairments of spatial processing: • Akinetopsia: Selective inability to perceive motion. • Optic ataxia: impairment of visually guided reaching. • Hemi-neglect syndrome: perceptual unawareness of the half of visual space contralateral to the lesion. -MT & MST going up (part of dorsal stream), in parietal heading to central fissure (right behind central fissure is primary somatosensory) -going to PPAC (posterior parietal assoc cortex) - responsible for proc multisensory info - get input from MT & MST -PPAC: place of spatial processing -knows about motion in opp half of world; damage in PPAC: opp hemisphere not ignored, just doesn't exist (hemispatial neglect) *PPAC tells you about existence in opp side of world

Pathways from Primary Gustatory Cortex (end 11/1)

Primary Gustatory Cortex splits into 1) Forebrain: Taste/Flavor Perception 2) Medullary motor nuclei: Feeding Behavior 3) Hypothalamus, Amygdala: Motivational & Hedonic Value of Food 1. Forebrain: Taste/Flavor Perception • Orbitofrontal cortex (location where chemical signals first merge to form percept of flavor). -where do multisensory perception of flavor - ventral stream -on way to final destination, primary taste cortex project to orbitofrontal cortex; on way, swings past amygdala! -as eating food, taste info sent to amygdala - gives emotional response to food -go to prefrontal for flavor; amygdala for emotion; medulla to say keep chewing (bc that's how get food in) 2. Medullary motor nuclei: Feeding Behavior • Swallowing; Chewing; Gagging, vomiting; Salivation; Respiration 3. Hypothalamus, Amygdala: Motivational & Hedonic Value of Food • Hunger • Palatability

Spectral Sensitivity

Scotopic vs Photopic vision • Rods do not supply information concerning color, but they are most sensitive to shorter wavelengths of light. (blue) • Cones are sensitive to longer wavelengths. (red & green) -There are three types of cones in the retina. Within the photopic range of wavelengths: • red: most sensitive to long wavelengths (L) • green: sensitive to the mid-range of wavelengths (M); and • blue: sensitive to short wavelengths (S) **photons on light activate, takes perception to turn into color

The Ear

Sound propagation: •wave enters auditory canal •strikes the eardrum (or tympanic membrane) •ossicles(hammer, anvil and stirrup) vibrate •oval window vibrates •fluid in cochlea set in motion •vibrations of fluid dissipated at round window 1. outer ear: waves enter ear, focus sound on eardrum/tympanic membrane 2. middle ear: bones (small, same as born); receptors/sensors under water, but can hear through it bc middle ear bones amplify -1 more amplifier inside ear (need bc receptors under water and wouldn't hear if not amplified) -cochlea (oval window) -> press on fluid (encased in bone, so causes bulge at round window) **this is 1 way sound is transduced; fluid motion in gets pressure release - fluid moves

Regions of the Retina

The retina exhibits two special regions: • the fovea (in primates including humans, some birds and reptiles); and • the optic disk. -Fovea: region of the macula (thicker area with an absence of blood vessels) where the layers of the retina above the photoreceptors are displaced laterally so that light can impinge more directly on the photoreceptors. -Optic disk: "blind spot", exit point for optic nerve (axons of retinal ganglion cells). -macula: has much less blood vessels; it's thick/mound; in center, there's a pit (fovea) -fovea: peel back some retinal layers so light hits photoreceptors most directly -optic disk=blind spot, all retinal ganglion cells gather, puncture through

The Visual System (start 10/25)

The visual system is the part of the NS which enables organisms to process visual details, as well as to perform several non-image-related response functions. It detects (sensation) and interprets (perception) information from visible light to build a representation of the surrounding environment. 1. Eye and Retina • Structures • Transduction 2. Retina-geniculate-striate cortex • Pathway • Receptive field properties 3. Striate and Association cortex • Higher-order processing -each cortex responds to vis in opp hemifield (take part of each eye that processes opp hemifield bc overlap) -nasal or temporal, some come from fovea & some extra foveal (M & P cells) -in LGN: left & right eye and also have M (movement) & P (fovea, color, high acuity) cell

Movement Direction Coding in M1

• Neural representation of movement direction is best expressed by a population ("ensemble") code: - Each M1 neuron "votes" for movement direction according to its firing rate for that direction. - Directional vector sum of the population (red arrows) closely matches movement direction. *less activity for neurons that want to go in opp direction; in aggregate, move in 1 direction or the other *summed activity; there are neurons that want to move in diff directions; if want to move up, should activate neurons that want to move up more & others less so; move in direction of the population *don't see push-pull in this neural code, but there is opp commands sent to muscles (akin to push-pull) - here it's just a question of voting

Sensorimotor Adaptation

• The cerebellum is important in reprogramming movements to compensate for sensory disturbances. -Example: Adaptation of motor output to altered visuospatial experience (e.g., ocular prisms). • The cerebellum is also important for learning new motor skills; that is, practice improves efficiency, speed, and precision of motor performance. -major job to correct motor output errors/compensate for sens disturbances -not its job to make you do, just make you do things well

Representation of Odors in Piriform Cortex (end 11/4)

• Topographic mapping of odorants seen in olfactory bulb is lost (!) in PC -Odorants activate PC neurons over a wide area (in part because PC neurons receive more inputs from other PC neurons than they do from the OB) • Activation patterns for different odors overlap extensively, but are nonetheless unique for a given odorant and similar across individuals • The olfactory system uses a population code to represent specific odors -every smell lights up entire cortex; what gained in specificity w lateral inhib, throw it all away in cortex; once in cortex, every neuron contacts every other neuron; all piriform cortex lights up w every single odor; can tell the diff btwn 10s of 1000s of odors bc population code -all mapping in olfactory bulb lost; all glomeruli goes everywhere in cortex, then everywhere in cortex relays every other -this is dangerous - when activate all neurons in piriform cortex, this is a place where wild excitation can overcome brain (place where epilepsy often starts, needs to be removed) -v strong population code; pervasive activation so widespread that it's a common place for epileptic seizures to start