ANS 100 Study Guide for Midterm #2 final

In insects, organs called sensilla are adapted to receive & transduce which forms of stimuli?

Mechanical and chemical

Parietal lobe

Processing sensory information from the body, including spatial orientation

A specialized site of contact of one neuron with another neuron (or effector) is known as a

Synapse

In insects, the most common form of auditory organ is the

Tympanal organ

Spatial summation

graded potentials from different sites can influence the net charge

Temporal summation

graded potentials that occur at slightly different times and can influence net charge

When a stimulus is continually applied but the action potential frequency declines, this is called

receptor adaptation

Compare and contrast electrical vs. chemical synapses.

(Lecture 19 slide 17) Electrical: rare in complex animals, common in simple animals, fast, bidirectional, postsynaptic signal similar to presynaptic, excitatory Chemical: rare in simple animals, common in complex animals, slow, unidirectional postsynaptic signal different then preseynaptic signal, excitatory or inhibitory.

Luigi Galvani

- first scientist to appreciate link between electricity and life - did famous frog leg experiment

Myelin

- insulating layer of lipid-rich schwann cells are wrapped around an axon - reduce the leakage of charge across membrane

Axon terminal

- where the neurotransmitter is released - the electrical signal (AP) is converted to a chemical signal (NT)

What is the difference between a nerve and a neuron? What is the difference between a ganglion and a brain? (lecture 25)

-A neuron is composed of a cell body (with dendrites), axon hillock, axon, and axon terminals. -The nerve is a bundle of many axons within the CNS. (nerves=many neurons) Ganglion: group of neuronal cell bodies (Ganglia = plural) Brain: groups of neuronal cell bodies (nuclei) within the brain (an integrating center made up of clusters of nuclei)

How does brain size vary with body mass? Be able to draw a diagram of this relationship with well-‐‐labeled axes. Why does brain size related to brain function? (lecture 26, slide 16)

-Brain size (mostly) correlates with body weight, so the bigger the animal, the bigger the brain! However, birds and mammals have a 6-10x larger brain for a given size than reptiles and bony fishes -Diagram axes: vertical = brain weight (g), horizontal = body weight (kg) -Brain size relates to brain function due to the fact that the number of neurons and neuronal connections can increase in larger brains, thus supporting a more complex collection of cognition, communication, and complex behaviors.

How are rods and cones arranged in the retina? How does the arrangement differ at the fovea and why is this important? (lecture 23)

-Rods and cones are in the back of the retina and their tips face backwards. -Fovea contains only cones, it is a small depression in the center of the retina where overlying bipolar and ganglion cells are pushed to the side (since cells are pushed to the side, a depression is formed) . -Provides sharpest images because it is only made up of cones which have very high resolution

In chemical synapses, neurotransmitters are released by

Calcium-dependent exocytosis

Once acetylcholine is released into the synapse it

A broken down by acetylcholinesterase

Absolute refractory period

A cell is incapable of generating new AP

Mixed nerves

A nerve that contains both afferent and efferent neurons

Graded potentials are important in sensory cells. Explain the differences between generator and receptor potentials. Provide an example of each for a specific modality of sensory stimuli.

A receptor potential has the sensory receptor separate from the afferent neuron, and then it is transferred to the neuron. The stimulus acts on the receptor (epithelial sensory cell) which then is able to cause a change in the membrane potential that will release neurotransmitters. The neurotransmitters will then act on the receptors on the afferent neuron which cause a graded potential, initiating it. A generator potential is generated directly on the neuron and it receives a stimulus on the receptor of the neuron itself. It generates action potentials in a sensory neuron. The sensory receptor is also the primary afferent neuron. The AP will be caused by the change in membrane potential that is spread across the membrane.

Phasic receptor

A receptor that produces AP at the beginning or at the end - change in stimulus, not duration - ex: arm hair

Tonic receptor

A receptor that produces AP through stimulus - can have receptor adaptation - ex: a hot bath

Whole animal integration

A selective combination and processing of sensory, endocrine, and Central Nervous System information.

Which of the following is the most common evolved feature of eyes?

A. A lens B. A retina C. Similar genes regulating eye development CorrectD. A rhodopsin-based photoreceptor cell

Which of the following is a shared characteristic between a spiking neuron and a nonspiking neuron?

A. An action potential down the entire length of the axon B. A graded potential down the entire length of the axon C. The Hodgkin cycle CorrectD. Neurotransmitter secretion based on a change in membrane potential E. High concentration of voltage-gated Na+ channels at the axon hillock

Which of the following statements regarding the vertebrate hair cell is false?

A. Hair cells are found in the lateral line system of fish. B. The vertebrate hair cell is an epithelial cell. CorrectC. Tip links reduce shearing forces and prevent cation channels from opening when pressed towards longest sterocilia. D. Displacement toward the longest stereocilia produces a depolarization. E. Displacement away from the longest stereocilia produces a hyperpolarization.

Which of the following is the best explanation for the absolute refractory period of the action potential?

A. Inactivated voltage-gated potassium channels CorrectB. Inactivated voltage-gated sodium channels C. The passive properties of the axon membrane D. Closed voltage-gated sodium channels E. Open slow calcium channels

Which of the following statements about the mammalian vomeronasal organ is true?

A. It interacts with the olfactory system to amplify the signal. B. It integrates the olfactory information before sending it to the brain. CorrectC. It mostly detects pheromones and other chemical signals. D. It increases the sensitivity of the olfactory system. E. It detects chemicals from greater distances than olfaction does.

Which of the following is most responsible for the all-or-none property of the action potential?

A. Leakage of K+ channels CorrectB. Voltage-gated Na+ channels C. Acetylcholine D. Voltage-gated K+ channels E. Myelination

Which of the following statements about a local circuit in an axon is false?

A. Na+ ions move into the cell through open Na+ channels. CorrectB. Anions migrate into the membrane interior. C. An ionic current completes the local circuit as cations move toward the locus of the action potential and anions move away. D. Ions flow in intracellular fluid, carrying current to more distant parts of the membrane. E. At the membrane, the ion movements change the distribution of charges on the membrane capacitance.

Which of the following statements about an animal's nervous system is false?

A. Neurons form highly discrete lines of communication. B. Action potential signals do not degrade over distance. CorrectC. Neurotransmitter is released throughout the body via the blood. D. A neuron must normally make synaptic contact with another cell in order to exert control. E. Signal transmission rate is relatively fast.

Which of the following glial cells are found in the peripheral nervous system?

A. Oligodendrocytes CorrectB. Schwann cells C. Astrocytes D. Both a and b E. Both a and c

Which of the following is not found in the structure of the chemical synapse?

A. Postsynaptic densities B. Mitochondria CorrectC. Gap junctions (known as connexons in vertebrates) D. Scaffolding proteins E. Synaptic vesicles

Which of the following statements about glial cells is false?

A. They help supply metabolic substrates to neurons. B. They increase the velocity of nerve-impulse propagation. C. They mediate immune responses in neurons. D. They act as metabolic intermediaries between capillaries and neurons. CorrectE. They integrate cell membrane potentials to enhance or inhibit action potentials.

How do nonspiking neurons function even though their depolarization signal significantly degrades with distance?

A. Voltage-gated K+ channels compensate for the lack of voltage-gated Na+ channels. CorrectB. These neurons are very short, so there is no major signal decrement. C. These neurons do not release neurotransmitters, so signal degradation is not a problem. D. Voltage-gated Na+ channels are replaced by ligand-gated Na+ channels. E. There are sufficient numbers of voltage-gated Na+ channels to convey the signal without major decrement.

Which of the following is most uniquely associated with a metabotropic receptor?

A. Voltage-gated receptor B. Synaptic vesicle C. Ligand-gated receptor CorrectD. Second messenger E. Neurotransmitter

Which of the following stimuli is not detected by the vertebrate hair cell?

A. flow of water B. acceleration C. sound CorrectD. touch E. balance

Current (l)

Amount of charge moving past a point at a given time

Information transfer along neurons: For a neuron to function properly it must convey stimulus intensity of the chemical messenger to the electrical signal in the soma (cell body) and axon. How is this achieved in both locations? How is the intensity of this electrical signal then converted back to a chemical signal of the appropriate intensity?

AP frequency carries information and it increases with stronger stimuli. Magnitude of each AP does not change (constant). Maximum frequency is limited by the absolute refractory period (part of the sodium ion channel). Mammalian nerves can conduct 500-1000 action potentials per second. Can read intensity of action potentials per second. (Lecture 19: slide 16) Intensity is communicated in the soma via the amount ions/change in Vm from the intensity of stimulus/ligands(chemical messenger) received. The change in Vm(intensity) is proportional to the amount stimulus/chemical messenger received. Intensity is communicated in the axon via the frequency of APs. The greater the intensity the more frequent APs fire(generally speaking). The intensity is communicated back into a proportion chemical messenger intensity since the higher frequency of Paps results in more chemical messengers being released into the synapse within a given time period. Signal Reception occurs in the dendrite and cell body. The goal is to create neurotransmitters. There are membrane bound receptors that bind to the neurotransmitters which traduces the chemical signal to electrical signal. This changes the permeability and ultimately causes a change in membrane potential (aka graded potential). If there are more neurotransmitters there are more ion channels open -> a larger magnitude. To convert the chemical signal back this occurs at Signal Transmission where at the signal transmission zone has Ca2+ channels and the calcium regulates the neurotransmitters. The action potential arrives at axon terminal (pre-synaptic cleft) Voltage gated Ca2+ channels open (depolarization) Ca2+ enters the cell Ca2+ signals vesicles and moves to the membrane Vesicles release through exocytosis Neurotransmitters diffuse across synaptic cleft and bind to receptor (postsynaptic cleft) Binding activities signal transduction pathway

Differentiate between and discuss the characteristics underlying absolute and relative refractory period.

Absolute refractory period: The period from the initiation of the action potential to immediately after the peak. This is the time during which another stimulus given to the neuron (no matter how strong) will not lead to a second action potential. Thus, because Na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials. Inactivation gate is time dependent and once closed, no APs EVER Relative refractory period: The period during which a stronger than normal stimulus is needed in order to elicit an action potential. Continued K+ flow out of the cell would tend to oppose any depolarization caused by opening of Na+ channels that have recovered from inactivation.

In a cell, the difference in ion concentration between the intracellular and extracellular fluids results from

Active ion transport and passive diffusion of ions

Capacitance

An amount of electrical charge stored per unit of voltage

Resistance

Any barrier or bottleneck that prevents an electrical current from moving with ease

Nodes of ranvier

Areas of exposed axonal membrane between Schwann cells

Compare and contrast the autonomic and somatic nervous systems. Within the autonomic nervous system, compare and contrast the sympathetic and parasympathetic nervous system.

Autonomic: -Involuntary -Many effector targets (tissues, glands etc) -2 neurons (ganglia->pre and postganglionic neurons) --Parasympathetic: *Resting and Digesting *Preganglionic cell bodies--> sacral and hindbrain *Ganglia location: far from spinal cord *Neurotransmitter: ACh for both pre and post *Receptor for each NT: Post: nicotinic Target: muscarinic *Effect on Target: excites or inhibits --Sympathetic *Fight or Flight *Preganglionic cell bodies-->Lumbar and Thoracic *Ganglia location: close to spinal cord *Neurotransmitter: Pre: ACh Post: Norepinephrine *Receptor for each NT: Post: Nicotinic Target: Adrenergic *Effect on Target: excites or inhibits Somatic: -Voluntary -Only 1 effector target (skeletal muscle) -1 neuron (no ganglia)

Where on a motor neuron are new action potentials generated?

Axon Hillock

The family of GPCRs that sense bitter compounds is much larger and more disparate in amino acid sequence than those that sense sweet or umami. Why might this be adaptive?

Bitter compounds are usually toxic, and so the ability to sense a wide variety of them is protective.

Nerve

Bundle of many axons outside the CNS

Fascicles

Bundles of axond

Tracts

Bundles of many axons within the CNS

How are mechanical stimuli transformed into electrical signals?

By mechanoreception. All organisms and cells can sense and respond to mechanical stimuli. There are two main types of mechanosensory protein receptors. ENaC - epithelial sodium channels. TRP - transient receptor potential channels. Important for cell volume, blood pressure, touch, hearing and balance.

Explain the cable properties of a neuron. Using Ohm's law, how do you increase current? How does electrical charge move down the axon using saltatory conduction? Define and explain the time constant? Define and explain the length constant. Where is the time constant important in understanding electrical conduction? Where is the length constant important in understanding electrical conduction?

Cable properties: Similar physical principles govern current flow through axons and transatlantic telephone cable (wires) (compared to a river). Ohm's law stated V = IR, (V = voltage, R = resistance, I = current) to increase the current there must be a decrease in the amount of voltage and resistance. Saltatory conduction is when the APs leap from node (of Ranvier) to node down the axon while the electrical current spreads through the internodes. The time and length constants determine the nature of the current in neurons. We want to minimize the time it takes to generate an AP so we increase the length constant and decrease the time constant. The length constant is the distance over which change in membrane potential will change to 37% (1/e) of original value. To increase the length constant decrease the intracellular resistance and increase the membrane resistance. The time constant is time over which membrane potential will decay 37% of its original value; how well the membrane holds its charge. To decrease the time constant; decrease the membrane resistance and the membrane capacitance

Briefly describe the two main types of photoreceptors. How do rods and cones differ in their class of photoreceptor, structure/shape, sensitivity to light, response times and types of photopigments?

Ciliary photoreceptors: (vertebrates) • Have a single, highly folded cilium • Folds form disks that contain photopigments Rhabdomeric photoreceptors: • Apical surface covered with multiple outfoldings called microvillar projections • Microvillar projections contain photopigments Rods: -high sensitivity, -scotopic(dark light), -monochromatic (1 color), -peripheral Cones: -lower sensitivity, -phototopic (bright light), -color (2,3,4,5 colors), -foveal

Which of the following is not a characteristic of the stretch-activated cation channel?

CorrectA. Greater bristle displacement leads to more open channels and larger action potentials. B. It is structurally specialized to respond to mechanical stimuli. C. It belongs to the transient receptor potential family. D. Ankyrin repeats extend into the cytoplasm of the receptor cell and attach to the cytoskeleton. E. The channel opens when the distal tip of an insect bristle mechanoreceptor cell membrane deforms.

Provide me with a diagram that illustrates depolarization, hyperpolarization and repolarization. How do these three differ (or define these three)?

Depolarization: membrane potential becomes less negative and closer to each other Hyperpolarization: Membrane potential become further apart and more negative Repolarization: After Hyper or depolarization going back to resting membrane potential (-70 mV of neuron)

The autonomic nervous system has three main mechanisms for regulating function: Dual Innervation, Antagonistic Action and Basal Tone. Explain all three. Are there certain parts of the autonomic nervous system that don't follow these general rules? Explain.

Dual innervation: most organs receive input from both systems. Antagonistic action: one system stimulates while the other system inhibits. Basal tone: even under resting conditions, autonomic neurons carry APs Parts of the autonomic nervous system that don't follow these rules are: adrenal medulla, sweat glands, arrector pili muscles in skin, kidneys, most blood vessels are only sympathetic innervation.

What is equilibrium potential? How does equilibrium potential affect the degree to which membrane potential can change?

Equilibrium potential: the membrane potential where the flow of ions in and out of the membrane is the same therefor there's no change in membrane potential or a net flow of 0.

Basal tone

Even under resting conditions autonomic neurons carry APs

Using acetylcholine as an example, explain the sequence of events that happens at the synapse.

First acetylcholine is synthesized in the mitochondria, chlorine acetyl transferase catalyzes the conversion of chlorine and acetyl CoA to acteylchlorine (ACh). Next ACh is packaged into vesicles and transported to the synapse where it is released. ACh binds to the receptor protein on the postsynaptic cells. AChE then breaks down ACh into chlorine and acetate terminating the signal in the postsynaptic cell. The presynaptic cell takes the chlorine and acetate and diffuses it out of the cell.

Sketch and label a typical motor neuron. Label and explain briefly the four functional zones of a neuron (like what we did in Friday's Discussion).

Four functional zones 1. Signal reception - Dendrites and the cell body (soma) - Incoming signal received and converted to change in membrane potential 2. Signal integration - Axon hillock - Strong signal is converted to an action potential (AP) 3. Signal conduction - Axon (some wrapped in myelin sheath) - AP travels down axon 4. Signal transmission - Axon terminals - Release of neurotransmitter *Image on lecture 19, slide 15*

Distinguish between a graded and an action potential with respect to how they are initiated, the type of change in membrane potential and where they are initiated.

Graded potential: initiated by opening or closing ion channels in the cell body or dendrites and the change in membrane potential is proportional to the current applied (how many channels are open; more open=larger graded potential)(GP travels short distances) can be hyperpolarized (K+ and Cl- channels open) or depolarized (Na+ or Ca2+ channels open) for changes in membrane potential Action Potential: initiated when the net graded potential at the axon hillock reaches the threshold potential (occurs in the axon), all-or-none response elicited when the threshold is reached; massive depolarization of membrane potential occurs. Always same size, shape, duration, does not decay with distance

The brain and spinal cord contain two types of tissue: gray and white matter. What makes gray vs. white matter? How do the brain and spinal cord differ in location of gray and white matter?

Gray matter - neuronal cell bodies White matter - tracts of axons and their myelin sheaths. Spinal cord is dark (gray) on the inside and light (white) on the outside. The brain is the opposite, light on the inside and dark on the outside.

Ganglia

Groups of neuronal cell bodies

Nuclei

Groups of neuronal cell bodies within the brain

Temporal lobe

Hearing, short/long term memory, emotion, and language

The brain is divided into the forebrain, midbrain and hindbrain. What main functions occur in these different locations? Birds and fish have enlarged midbrains - why? Mammals have very small midbrains. Does that mean they have lost the functions of the midbrain?

Hind brain = reflex response and involuntary behaviors Mid brain = Coordinating visual, auditory and sensory information (although not in mammals) Fore brain = olfactory info, regulating body temperature, eating, sleeping, emotion, learning and memory Birds and fish have enlarged midbrains because they live in a 3D environment (predators attack from all angles), they need a larger midbrain to have better reflexes to touch, smell and auditory. Mammals have smaller midbrains not because they have lost the function in them but because we live in 2D environments.

Cell membrane modifications on sensory receptor cells ...

Increase points of contact between stimuli and receptor molecules

Brain

Integrating center made from clusters of nuclei

Occipital lobe

Integration of movements in focusing the eye, correlation of visual images with previous visual experiences and other sensory stimuli

Sensory receptor cells differ in their mechanisms of transduction. Explain the differences between ionotropic and metabotropic mechanisms of transduction.

Ionotropic - Ligand-gated ion channels - When a neurotransmitter binds an ion channel directly and the channel open/closes - Fast - e.g., nicotinic ACh Metabotropic - Channel changes shape - Signal transmitted via secondary messenger -Receptor and ion channel are separate - Ultimately sends signal to an ion channel (elicits a whole other pathway in addition to letting ions in) - Slow - Long-term changes - e.g., muscarinic ACh (G protein linked to ion channel)

What are a few reasons why we need a nervous system?

It conveys information rapidly over short or long distances to help the body cellular integrate (work together). The nervous system controls predominantly the fine rapid movements of discrete muscles.

What does the motor and sensory homunculus tell us about the nervous system?

It demonstrates the proportion of cortex devoted to particular body parts, with more being devoted to parts of importance to that particular animal. Not proportionally based on size of the body part. Example: hands and lips in humans, front paws and nose in the star-nosed mole

Relative refractory period

It is more difficult to generate AP because you need a larger graded potential since the membrane potential is below the resting membrane potential

Neurons are excitable. What do I mean by this statement? How is this achieved?

It means that neurons can rapidly change their membrane potential. The changes in membrane potential act as electrical signals. Where neurons are promoted to favor action potentials.

How is light transformed into electrical signals in vision? How is the intensity of light transmitted? Explain whether photoreception relies on receptor or generator potential or both? Does photoreception rely on ionotropic or metabotropic mechanisms of transduction or both?

Light to electrical signals = Phototransduction: Chromophore absorbs energy from photon (e.g. retinal) then the Chromophore changes shape and Double bonds isomerizes from cis to trans which Activates chromophore which dissociates from opsin (also known as "Bleaching"). Then Opsin activates the G-protein. G1 protein activates PDE to convert cGMP to GMP which causes Ion channels to close. Change in membrane potential intensity transmitted: through the light and dark photoreceptors. Receptor cells are depolarized in the dark and hyperpolarized in the light. ex. candle in an already lit room vs. a candle in a dark room Photoreception relies on metabotropic mechanisms of transduction and both receptor and generator potential.

What are the differences between maculae and cristae?

Maculae: detect linear acceleration and tilting Cristae: detect angular acceleration

Ultimately, it is the _______ that determines whether the postsynaptic membrane produces an inhibitory postsynaptic potential (IPSP) or an excitatory postsynaptic potential (EPSP).

Movement of ions

Vertebrate neurons can be myelinated. What is myelin and what is its function?

Myelination is like plastic wrapping the neuron Myelin is an insulating layer of lipid-rich Schwann cells wrapped around the axon. They reduce leakage of charge across membranes. The Schwann cells are a type of Glial cell - cells other than neurons that support neuronal function. They are also used to speed up conduction. Also provides support.

How does myelination increase the speed of conduction? How and why does neuron diameter affect the speed of conduction?

Myelination prevents leaking and helps keep the current intact. (more insulation keeps ions from flowing in or out so increases the speed of conduction? As a neuron's diameter increases, the volume increases causing a decrease in intracellular resistance (resistance becomes more spread out in the neuron) thus increasing the speed of conduction (lecture 19 slide 14?)

What equation (just the name) calculates an ion's equilibrium potential? What equation (just the name) calculates the equilibrium potential of all ions?

Nerst equation calculates an ion's equilibrium potential (individually) Goldman Equation calculates the equilibrium potential of all ions (K+, Na+, Cl-)

Postsynaptic cell

Neurons, muscles and endocrine glands

For an axon at resting membrane potential, the K+ leak channel is _______, the voltage-gated Na+ channel is _______, and the voltage-gated K+ channel is _______.

Open; Closed; Closed

During the falling phase of an action potential, the K+ leak channel on the axon is _______, the voltage-gated Na+ channel is _______, and the voltage-gated K+ channel is _______.

Open; Inactivated; open

How does the design of the outer, middle and inner ear allow for the detection of sound of different intensities, frequencies and locations?

Outer: not in all vertebrates, pinna, auditory canal. Pinna acts as a funnel to collect more sound (auditory canal). Middle: not in all vertebrates, interconnected bones in air-filled cavity. It increases the amplitude of vibrations from the tympanic membrane to the oval window. Then the oval window vibrates, and pressure waves in perilymph of vestibular duct, basilar membrane vibrates, stereocilia on the inner hair cells bend, hair cells depolarize, hair cells release neurotransmitter, glutamate excites sensory neuron, and the round window serves as pressure valve. Inner: present in all vertebrates, series of fluid-filled membranous sacs and canals, contains mechanoreceptors (hair cells). Sound waves vibrate tympanic membrane. Basilar membrane is stiff and narrow at proximal end and flexible and wide at distal end. High frequency sound vibrates on the stiff end, low frequency sounds vibrates on the flexible end.

For which of the following senses is the signal transduced by metabotropic mechanisms?

Photoreception

The response of postsynaptic cell is influenced by amount of neurotransmitter in synapse and number of receptors. How is this regulated?

Postsynaptic cells have specific receptors for neurotransmitters. Binding of neurotransmitter to receptor alters ion permeability of postsynaptic cell. Change in membrane potential of postsynaptic cell. Transmission of signal strength at synapse: Response of postsynaptic cell influenced by amount of neurotransmitter in synapse and number of receptors. Amount of neurotransmitter Rate of release - rate of removal Release determined by frequency of APs Removal determined by: Passive diffusion out of synapse Degradation by synaptic enzymes Uptake by surrounding cells Number of receptors Density of receptors on postsynaptic cell

Explain the following concepts: labeled line theory, polymodal receptors, dynamic range, range fractionation, logarithmic coding, population coding and receptor adaptation. (lecture 21)

Principle of Labeled line theory: -The sensory modality or quality of sensation associated with a stimulus depends solely on which receptor cells are stimulated, rather than how they are stimulated. -Discrete pathway from sensory cell to integrating center. -Sensory systems organized into sensory units with multiple sensory receptors synapsing with a single afferent neuron Polymodal receptors: Sensitive to more than one stimulus modality - Ex: nociceptors = polymodal receptors for multiple types of pain (e.g. temperature, pressure & chemicals) Dynamic Range: The range of stimulus intensities over which a receptor exhibits an increased response Range Fractionation: -Groups of receptors work together to increase dynamic range without decreasing sensory discrimination -Stimulus intensity is coded through behavior of populations of sensory receptors Logarithmic Coding: -encode large range of stimulus intensities using single receptor cell (increase dynamic range), -good discrimination at certain intensities and poor discrimination at other intensities Population Coding: ??? Receptor Adaptation: AP frequency decreases if stimulus intensity is maintained at the same level (we don't pay as much attention to stimulus as when it first started; ex: hot bath --> we get used to the hot water)

"The sensory modality or quality of sensation associated with a stimulus depends solely on which receptor cells are stimulated, rather than on how they are stimulated." This generalization is known as the

Principle of labeled lines

Explain the statements that action potentials are "self-‐‐propagating" and "unidirectional".

Problem set Q: They are self-propagating because the spread of the current opens channels down the line so there is a constant shift of voltage happening and once the voltage reaches the threshold potential, AP continues to fire. Action potentials are unidirectional because they start at the axon hillock, traveling down the axon towards the axon terminal and there are activation/inactivation gates that prevent flow in the opposite direction. Absolute refractory period prevents backflow because its inactivation gate is controlled by time, not by voltage. The relatively refractory period requires a strong stimulus in order to fire another AP, thus keeping it moving in one direction.

All sensory stimuli are ultimately converted into APs in a primary afferent neuron. Since all APs are essentially the same, how can an organism differentiate among stimuli or detect the strength of a signal? How specifically do sensory cells/neurons encode stimulus modality, location, intensity and duration?

Problem set Q: The receptor location encodes for both stimulates modality and location. Stimulus modality and location is determined through the use of the Theory of Labeled lines, which states that sensory systems are organized into different sensory units that each have multiple receptors synapsing to one afferent neuron. To further discriminate the location of a stimuli, neurons have smaller receptive fields and overlap them. With lateral inhibition, neurons block the pathways of receptive fields receiving weak stimuli to enhance the contrast of the AP frequency in the strong stimuli. Stimulus intensity is determined by the AP frequency. For example, when there is a strong stimuli the stimulus intensity is high and when the stimuli is weak the frequency of APs is low relaying in a low intensity stimuli. In order for a low intensity stimuli to produce APs it must reach the threshold intensity, while a strong stimuli must remain below the receptor saturation level to generate a response. Stimulus duration is determined using two methods; tonic and phasic. Tonic duration produces APs the length of the stimulus and is the most accurate of the two. Phasic produces APs at the beginning and end of a stimulus which better encodes changes in stimulus compared to duration.

Receptor potential (graded potentials)

Receptor is on another cell

Explain the role of refraction and accommodation in image formation. Explain differences in how we see distant vs. close objects.

Refraction - bending of light rays - Cornea and lens focus light on the retina - In terrestrial vertebrates, most of the refraction occurs between air and cornea (due to density differences) - Lens changes shape to focus on near or far objects (Lens does fine focusing) Accommodation - Light rays must converge on the retina to produce a clear image Distant objects - Light rays are parallel when entering the lens - Ciliary muscles relax - Lens is pulled and becomes thinner • Little refraction of light by lens Close objects - Light rays are not parallel when entering the lens - Ciliary muscles contract - Lens becomes thicker • More refraction of light by lens

Neurons have resting membrane potential like other cells. What sets up this resting membrane potential? How is this resting membrane maintained?

Resting membrane potential is maintained by Na/K ATPase; they regulate the movement of Na/K. It's maintained by opening or closing ion channels

Rods and cones have different receptive fields. How is this apparent based on their arrangement and synapses in the eye?

Rods have large receptive fields- this is because of convergence Many rods synapse with a single bipolar cell which synapse with a single ganglion cell Similar to poor discrimination = fuzzy image because cannot determine where specifically coming from Cones have small receptive fields because each cone synapses with a single bipolar cell which connects to a single ganglion Similar to really good discrimination in a small receptive field because cane determine specifically where coming from

_____________________ is the alternating of electrotonic conduction with action potentials along the length of an axon.

Saltatory conduction

Briefly explain the different parts of an eye and their function in vision.

Sclera: white of the eye Cornea: transparent layer Choroid: pigmented layer Tapetum: reflective layer in the choroid of nocturnal animals Iris: two layers of pigmented smooth muscle Pupil: opening in iris Lens: focuses image Ciliary body: muscles to change lens shape Aqueous humor: fluid in the anterior chamber Vitreous humor: gelatinous mass in the posterior chamber

Synaptic cleft

Space inbetween pre and post cells

Differentiate between temporal and spatial summation. Where are these features important and why?

Temporal summation: graded potentials that occur at slightly different times can influence the net change. Spatial summation: graded potentials from different sites can influence the net change. Important because signals will be sent at different times (temporal) and different places (spatial). Summing up everything that is happening is essential. It influences the net change, and action potential can only occur when membrane potential at axon hillock reaches threshold. I think that it's also important because you can sum up these signals to create a larger graded potential which increases the AP frequency, → higher Ca concentration in the axon terminal (presynaptic cell?) → more neurotransmitters released → greater signal (???)

saltatory conduction

The AP's leap from node to node and cause a very rapid conjugation

Frontal lobe

The decision-making, problem solving, planning, cognition and memory portion of the brain

Length constant (lambda)

The distance which the change in membrane potential will change to 37% of its original value

In an electrical synapse, the main structure responsible for transmission of an impulse from one cell to the next is

The gap junction (known as connexions in vertebrates)

_______ prevents bidirectional propagation of action potentials.

The inactivation of Na+ channels

Repolarization

The membrane potential returns to its resting value

Depolarization

The membrane potential becomes less negative than the resting value/potential

Hyperpolarization

The membrane potential becomes more negative than the resting value

Internodes

The myelinated region

Two sets of axons carry stimuli near the axonal hillock. One set produces an IPSP and the other set produces an EPSP. If both sets produce action potentials at the same time, what is the likely effect at the axonal hillock?

The potentials created will cancel each other out

Cephalization

The sense organs are concentrated at the anterior end

Generator potential (graded potentials)

The sensory receptor is on a different neuron

Neuromuscular junction

The synapse between a motor neuron and a muscle

Time constant (tau)

The time it takes for the membrane to decay 37%

Hair cells are important for equilibrium and hearing. How do hair cells detect mechanical signals of different intensities and direction? Does mechanoreception using hair cells rely on receptor or generator potential or both? Does mechanoreception using hair cells rely on ionotropic or metabotropic mechanisms of transduction or both? Where in the inner ear do vertebrates sense balance and equilibrium? Where in the inner ear do vertebrates detect sound?

The utricle and saccule located in the vestibular apparatus of the ear contain macula which are vessels that contain hair cells surrounded by a fluid or gel like substance. The Macula is able to detect head tilting and acceleration while the hair cells are able to detect the movement and direction of the body. When the body moves or the head is tilted, the fluid/gel surrounding the hair cells move the stereocillia forward or backwards while the tip links help to pull the K+ channels open. With more K+ entering the membrane, the membrane potential is depolarized and the Ca2+ ion channels are opened causing the vesicles to transport the neurotransmitters to the receptor protein located on the neuron which then produces APs. The more stimuli the more ion channels will open and the more depolarized the membrane potential will become leading to more APs being produced. The number of increases in membrane potential over a specific amount of time notifies the brain which activity is taking place. Mechanoreceptors rely on both receptor and generator potential. But they only use ionotropic mechanisms of transduction. The basilar membrane detects sound frequency. The utricle and saccule detect balance and equilibrium.

The conversion of stimulus energy into an electrical signal is known as

Transduction

Population coding

Using a population of neurons to encode a location (overlapping has better accuracy)

The separation of positive and negative charges constitutes

Voltage

How do vertebrates detect color? Why do red-‐‐green color blind people see the same color for shades of red and green?

We detect color by detecting different wavelengths of visible light which requires photopigments with different light sensitivities. Vertebrates are sensitive to 3 cone types (red, blue and green) and a monochrome rod. The brain can tell the AP frequency of each color to distinguish between the different colors. Red-green color people see the same shades of red and green because they are missing red cones.

Electrical potential

a voltage difference across the plasma membrane due to concentration gradients of ions or difference in charge between electrodes

Initiation of the action potential usually occurs _______of the neuron.

at the axon initial segment

The membranes of sensory receptor cells contain specific receptor proteins that are specialized to detect incoming sensory signals. What specific incoming stimuli can they detect?

chemical stimuli (chemoreceptors), pressure stimuli (mechanoreceptors) , and light stimuli (photoreceptors)

When a sensory receptor is an afferent neuron, the membrane potential that is initiated by a stimulus is called a

generator potential

Advantages of populations of receptors, as opposed to individual receptors, include

improved sensory discrimination

With the help of a diagram, demonstrate how a threshold potential needs to be reached before an action potential is generated. What specific ion channels are important in defining the shape of the action potential and how exactly is this achieved? What is the role of Na/K-‐‐ATPase?

lecture 17 slide 13,17; Na+ channels have two gates--> activation which will open at a certain voltage and inactivation gate which is time dependent and allows for an absolute refractory period in which another AP cannot be fired. Inflow of Na+ causes depolarization and when the inactivation gate closes shutting out Na+, membrane potential becomes hyperpolarized (lecture 17 slide 18) Na+ channels open first = depolarization (peak in AP diagram), K+ channels open more slowly = repolarization (downslope of diagram), membrane potential becomes more negative again; moves towards its resting potential), Na+ channels close due to inactivation gate, K+ channels close slowly (relative refractory period caused by open K+ channels) Need Na+/K+ ATPase to pump sodium out of the cell (against the gradient) and to pump potassium in (against gradient) in order to put ions back where they were pre-action potential ) bring cell's membrane potential back to normal essentially

Select the pair below that does not match A. chemoreceptors -‐‐ detect chemicals B. photoreceptors -‐‐ detect light C. mechanoreceptors -‐‐ detect magnetic fields D. thermoreceptors -‐‐ detect temperature

mechanoreceptors -‐‐ detect magnetic fields

Dendrites

part of the cell body (soma) where incoming signals are received and converted to a change in membrane potential

The minimum level of depolarization required to generate an action potential is known as the ________________.

threshold potential

Opening of _____________________ initiates the depolarization phase of the action potential.

voltage-gated Na+ channels

Axon hillock

where action potential is generated