Biology 1440 Prelim 4
touch circuits in the CNS
-individual signals are parallel pathways -each differ in conduction velocity -differ in activity ex: 1. direct and post synaptic dorsal column pathways: only hair, dorsal column nuclei (cuneate nucleus, gracile nucleus), 1st order 2. spinocervical tract pathway: all LTMRs, [cortex, 3rd order, thalamus], [2nd order, lateral cervical nucleus]
movement by peristalsis
-longitudinal muscle relaxes (extended), circular muscle contracted -circular muscle relaxed, longitudinal muscle contracted -both earthworm and much of digestive tract have an arrangement of longitudinal and circular muscles; both cases used to drive peristalsis for movement
hydrostatic skeleton
A fluid skeleton in many soft-bodied invertebrates, including annelids, that allows an organism to change shape but not volume. -body cavity is kept under pressure by antagonistic circular and longitudinal muscles (ex: worms, insect larvae, some mulluscs)
sarcomere
Contractile unit of muscle -repeating unit in a myofibril -sarcomeres are about 2 micrometers in length and span from z-line to z-line; during contraction they contract to about 70% of their normal size **myosin (thick filaments) and actin (thin filaments) -defines the region containing actin and myosin -polarity of actin and myosin reverse at the M-line (middle) -sarcomere length shortens during contraction-- distance between z-lines is decreased and length of filaments (actin and myosin) do not change but their degree of overlap does
smooth muscle
Involuntary muscle found inside many internal organs of the body -found in places such as walls of hollow organs like digestive tract -contractions relatively slow and may be initiated by the muscles themselves -smooth since have no striations (no sarcomeres) **INVOLUNTARY MUSCLES -arranged into sheets of opposing fibers, forming a longitudinal layer and a circular layer -contraction of the opposing layers of muscle leads to a rhythmic form of contraction, called peristalsis, which propels substances through the organs
coding logic of taste receptors
PBDG is bitter for humans and mice do not have a receptor and are unable to taste it exp't: PBDG perceived as sweet--drink MORE; normal drinking (no detection of bitter); PBDG perceived as bitter-- drink LESS
Ca+2 release
caused by: -stimulus leading to contraction of a muscle fiber is an action potential in a motor neuron that makes a synapse with the muscle fiber -action potentials travel to the interior of the muscle fiber along the transverse (t) tubules
Mechanosensory Receptors
monitor touch, vibration, pressure and tension of the skin. -transient receptor potential channels (TRP superfamily 2005) -Piezo genes (2010)
cardiac muscle
muscle found only in the heart -consists of striated cells electrically connected by intercalated disks
muscle spindle responses to stretch
primary and secondary have a linear response -1º: sense change of limb position and rate of change -2º: sense change of limb position
tropomyosin
proteins that bind end to end to make a continuous polymer along the actin filament
withdrawal reflex (flexion reflex)
receptor-- sensory a-delta afferent neuron-- -Path #1: efferent alpha motorneuron--muscle contraction (flexor- ipsilateral) -Path #2: inhibitory interneuron-- efferent alpha motorneuron-- muscle relaxation (extensor- ipsilateral) -Path #3: efferent alpha motorneuron-- muscle contraction (extensor- contralateral) -Path #4: inhibitory interneuron-- efferent alpha motorneuron-- muscle relaxation (flexor- contralateral)
primary somatosensory cortex
region of the parietal lobe where messages from the sense receptors are registered
stronger contractions
resulted from recruitment of multiple motor neurons -if CNS sends weak signal to contract a muscle, the smaller motor units, being more excitable than the larger ones, are stimulated first -multiple motor unit: recruitment generated by increasing the strength of the stimulus
kinesthesia
sensations of limb position and movement -muscle spindles-- located within skeletal muscles -major sensor in kinesthesia are the muscle spindles; made up of several different types of fibers; basically when muscle lengthens the fibers are lengthened as well; causes signals to be sent to the spinal cord via the primary and secondary nerve fibers
Passive electrolocation
sense of objects -sharks ampullae of lorenzini
eye spots
shallow pits lined with light-sensitive cells -planarian (Flat worm): can detect light and move to a shaded location -ocellus: cup shaped eye spot with photoreceptors
five primary tastes
sweet, sour, salty, bitter, umami -mediated by different mechanisms -sweet, umami, bitter: GPCR -salty: Na+ channel -sour: TRP channel, etc *Neurotransmitters released: ATP, acetylcholine (ACh), serotonin (5-HT), norepinephrine (NE), and GABA
taste in mammals
taste buds are a group of modified epithelial cells w/ receptor proteins 1. taste receptor cells are epithelial cells 2. each cell has only one receptor type
z-line
(disc); serves as a point of anchorage for the thin filaments (actin); the thin filament is capped at both ends to prevent unwinding -myosin also anchored to z-disc by protein called titin
smooth muscle in stomach
-muscles used to churn food-- involuntary response -has an extra oblique layer of muscle -2-6 hrs after a meal peristaltic contractions empty stomach
contraction of smooth muscle
Slow, synchronized contractions -When the thin filaments slide past the thick filaments, they pull on the dense bodies, which then pull on the intermediate filaments networks throughout the sarcoplasm; Ca++ is used to control contraction but since there is no troponin regulation of the interaction of myosin with actin involves a different system involving calmodulin.
titin
a protein that positions the myosin filament to maintain equal spacing between actin filaments -actin, myosin, and titin are most abundant proteins in the human body-- supposedly 0.5 kg of titin in adult human -titin made up of 27000 to 33000 amino acids -largest known protein
ribbon synapse
between electrosensory cell (SC) and an afferent neuron (AF)
transduction
conversion of a sensory stimulus into electrical energy in the nervous system by a change in the membrane potential
external (exoskeleton)
cuticle is generally hard, but is a flexible membrane at joints; antagonistic muscles span joints and attach to stiff cuticle (ex: arthropods, most molluscs, brachiopods)
gravity
omnipresent force on earth in which posture and locomotion are always carried out against
reception
receipt of a signal by sensory receptors
saturation
the maximum intensity of a stimulus that produces a response from a sensory system
spindle organs
(in muscles) -capsule surrounding spindle -intrafusal muscle fibers--> groups 1 and 2 afferent neurons -alpha morot neurons and gamma motor neurons signals: -change to muscle length (stretch) -rate of change of length (speed of stretch)
primary cilia
(non-motile) critical for signaling -mechano-, osmo-, and chemosensory units **note: 9+0 arrangement-- typical of non-motile cilia
structure of a skeletal muscle
- bone - tendon - Epimysium - Perimysium - Endomysium - Fascicle - Muscle fibre -muscles receive about 20% of cardiac output at rest and this increases with exercise -blood vessels are located between fasciles but are located inside the perimysium -single cells are surrounded by the endomysium -fascicle is a group of muscle cells surrounded by the perimysium; the whole muscle is surrounded by the epimysium (epi (on) + mys (for muscle))
signal transduction (photoreceptors)
-Photoreceptor signaling is executed via cGMP gated ion channel -different spectral sensitivity of photoreceptors is due to different opsins -each cone type is ambiguous for wavelength (S cone, M cone, L cone) -each wavelength may stimulate different cones *"population coding" comparison across receptor types resolves spectral ambiguity
Electrosensory system
-all animals in the water create electrical fields around them -different fish possess electroreceptors in their skin exquisitely sensitive to such fields -electrical currents depolarize receptor cells (voltage-gated calcium channels) and release neurotransmitters -some fish have electric organs for generating current in the form of electric organ discharges (EODs)-- nearby objects with impedances that are different from the surrounding water perturb this self-generated current, enabling navigation, avoid predators or find prey -therefore, fish can sense not only external fields (passive electrolocation) but also impedances of nearby objects (active electrolocation)
movement in earthworms
-constriction of circular muscles elongates the segments, pushing them forward -bristles anchor the segments to prevent backwards sliding -constriction of longitudinal muscles shortens the segments, pulling the trailing segments forward
summary of sensory-motor integration
-core sensory inputs for proprioception arises from statocyst (invertebrates), muscle spindle organs and the vestibular system (mammals), and the lateral line sense organ (fish) -sensory reception by hair cells is by graded potentials that regulate the amount of neurotransmitter release -reflexes are involuntary rapid responses to a stimulus, and demonstrate the need for speed! -predators can take advantage of these reflexes to predict prey behavior -rhythmic behavior is controlled by central pattern generators that may have couple circuits and may be responsive to sensory input -neuronal circuits are critical for complex rhythmic responses
sensory stimulation of skin
-poke: merkel cells -stroke: lanceolate endings -breeze-- lanceolate endings- no touch only hair
Inside skeletal muscle cell
-sarcolemma is the cell membrane but the endomysium is a layer of connective tissue that wraps around the fiber -single cells are packed with myofibrils which are not present in other cells types -many mitochondria distributed throughout the length of the fiber receiving O2 released from hemoglobin in the blood
sensory receptors
-specialized neuron (afferent neuron) -non-neuronal cell (regulates afferent neuron)
summary of skin sensory processes
-stimuli are translated to neuronal action potentials by receptors -sensory receptors have evolved to promote survival and can be highly specialized -neural pathways transmit and modulate sensory input -the somatosensory cortex is VITAL for perception -perception involves decoding of parallel signals from relevant spatial input
fish skin
-touch receptor of the moray eel shows crenulated connective tissue envelope and straight nerve fibers -electroreceptor of elephant nose fish: the section is perpendicular to the skin surface and the external environment is at the upper edge of the figure
skeletal muscle anatomy
-vertebrate skeletal muscle moves bones and the body and are characterized by a hierarchy of smaller and smaller units -a skeletal muscle consists of a bundle of long fibers, each a single cell, running parallel to the length of the muscle -each muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally **skeletal muscle cells are anywhere from 1 to >10 mm long and are multi-nucleate
hearing in invertebrates
-vibration sensitive organ that can detect sounds-- tympanic membrane -cricket ear-- forelimb (leg)
smell in mammals
1. olfactory receptor cells are neurons (not epithelial cells) 2. receptors are GPCRs (G protein-coupled receptors) 3. each cell has only one receptor type *metabotropic receptor
steps of myosin-actin interaction
1. release acetylcholine in synaptic cleft 2. propagation of action potential 3. moves through t-tubules and SR causes release of Ca+2 into cytosol 4. Ca+2 binds to actin and shifts tropomyosin to allow myosin-actin interaction 5. power stroke 6. Ca+2 pump up concentration gradient out of cytosol 7. troponin complex shifts back and tropomyosin blocks myosin binding sites on actin -acetylcholinesterase catalyzes hydrolysis of acetylcholine to acetate ion and choline -recapture of Ca+2 in SR is via active transport -relaxation restores length
mammalian cochlea
1. vibrations are detected by the tympanic membrane 2. transmitted by the ossicles (malleus, incus, and stapes) 3. transferred to the perilymph 4. moves the basilar membrane
types of cilia
3 types: -motile: enable movement with whipping motion -primary: signaling role, materials uptake -nodal: found during embryogenesis (important for normal development)
cilia structure
9 doublets + 2 singlet arrangement of microtubules Basal body (base of cilium below cell membrane) consists of 9 microtubules triplets with no central microtubules
9+2 structure
9 outside microtubules surrounding 2 central microtubules for stability (structure of cilia&flagella) -entire cilia surrounded by cell membrane -dynein-- attaches to A tubule but faces B tubule -spoke links doublets to central pair -complete tubules in the two central singlets -outer doublets made of an incomplete B tubule and a complete A tubule
flagellum
A long, hairlike structure that grows out of a cell and enables the cell to move. -rotations drives cells through liquid -lost of arrangements -some bacteria use flagella under a membrane for movement -pattern of "runs" and "tumbles" -like cilia-- made up of many proteins -no 9+2 arrangement -rings allow flagella to extend through membranes without disrupting membrane -basal body -Mot proteins couple the energy available from a proton gradient to the rotation of the flagellum -some bacteria use Na+ gradient to drive flagella rotation--Pom protein complex is same as Mot but specific for Na+
myotonia congenita
AD disease causes decrease in Cl- channels in muscle Causes slow muscular relaxation, muscle stiffness, and hypertrophy. Contraction prolonged by repetitive firing of muscle fiber -inherited myotonia--characterized by delayed relaxation and prolonged contraction of skeletal muscles -gene affected: CLCN1 which encodes chloride voltage gated channel 1 -chloride conductance in T-tubule needed to control membrane potential; in response to any change in the membrane potential, large chloride current will flow that tends to return the membrane potential to its previously established resting value -so with a mutation of the chloride channel, the muscle fiber membrane is hyperexcitable and is electrically active longer than normal muscle **chloride influx reduced greatly due to Cl- channel mutation (Cl is inhibitory for AP) so AP lasts longer-- therefore contraction is longer
Control of rhythmic behavior
CPG: Central pattern generator-- can use peripheral sensory feedback -removal of tegula: CPG continues rhythm, but there is delayed onset of elevator motorneuron activity -Primary: Cellular Oscillator-- membrane potential of a cell oscillates between rest and excited independent of any synaptic input -secondary: coupling for patterns within networks-- follower or reciprocal inhibitory ex: rhythmic complex in gait-- horse trot vs pace-- DMRT3 (doublesex and Mab-3 related transcription factor 3)
Organ of Corti
Center part of the cochlea, containing hair cells, canals, and membranes -sound waves beating on ear drum vibrate basilar membrane which bends hairs **Endolymph is high in K+
summary (hearing, smell, taste, and vision)
HEARING: -graded potentials resulting from mechanoreceptors responding to acoustic vibrations are interpreted as sounds -echolocation: some animals have developed the use of vocalization/acoustic vibrations to interpret the environment SMELL: -olfactory reception is via signaling through GPCR in a system that allows combinatorial population coding TASTE: -taste receptors are diverse and coded by the taste cell afferent/sensory innervation VISION: -morphological evolution of the eye and photoreceptors show levels of sensitivity, color vision, and unique properties -photon-mediated activation of GPCRs signal to create different graded potentials in dark vs light -spectral sensitivity allows for population coding to resolve spectral ambiguity -lateral inhibition accentuates the edges of the stimulus
peristalsis
Involuntary waves of muscle contraction that keep food moving along in one direction through the digestive system. -coordinated contraction and relaxation that propagates in a wave down a tube -contraction of circular muscle causes tightening behind the food mass -contraction of longitudinal muscle increases concentration of circular muscle fiber meaning less force has to be applied from circular muscle alone -wave of contractions forces mass forward
Mechanotransduction of hair cells
Leftward movement of head causes a rightward force in the left ear which pushes the kinocilleum toward the steocillia causing a opening of K+ channels causing depolarization and an action potential. Also causes hyperpolarization of right ear hair cells, causing the K+ channels to close, no 2ndary action. -endolymph potassium rich: 1. hair cells are epithelial cells 2. receptors are mechanosensory channels 3. neurotransmitter released: glutamate -depending on direction of deflection, links either pull open mechanosensory channels and K+ enters (depolarization), or channels completely close (hyperpolarization)
lateral inhibition
The pattern of interaction among neurons in the visual system in which activity in one neuron inhibits adjacent neurons' responses. -can sharpen spatial decoding -1st order and second order **because of inhibition next to point of stimulation, it enhances the excitation/amplifies the signal at the point of stimulation
vestibular organ
The sensory structures in the inner ear that provide the brain with information about orientation and movement. -SEMICIRCULAR CANALS, arranged in three spatial planes, detect angular movements of the head. The swelling at the base of each canal contains a cluster of hair cells -the UTRICLE and SACCULE tell the brain which way is up and inform it of the body's position or linear acceleration -hairs of the hair cells project into a gelatinous cap called the CUPULA; when the head starts or stops rotating, the fluid (perilymph) in the semi-circular canals presses against the cupula, bending the hairs -bending of the hairs increases the frequency of action potentials in sensory neurons in direct proportion to the amount of rotational acceleration
sliding filament model
The theory explaining how muscle contracts, based on change within a sarcomere, the basic unit of muscle organization, stating that thin (actin) filaments slide across thick (myosin) filaments, shortening the sarcomere; the shortening of all sarcomeres in a myofibril shortens the entire myofibril -for a muscle to contract, myosin-binding sites must be uncovered -exposure to Ca+2 allows myosin to bind to actin
active electrolocation
The use of an electric field, generated by an electric organ, to obtain information about the environment. Observed in Mormyridae, Gymnarchidae, gymnotiform, and other weakly electrogenic fishes. -tuberous receptors: timing, amplitude -amplitude interval latency -wave form-- frequent -pulse form-- lower frequency
escape behavior
a behavior that results in the termination of an aversive stimulus -mediated by MAUTHNER neurons in fish -predatory water snake exploits this fish escape behavior--> by inducing fish escape response, snake predicts direction for bite and capture -just before strike initiated, snake moves body in "feint" that usually triggers fish escape response away from body and toward the head
bacterial flagella
a filament composed of flagellin + a basal body that anchors and rotates the flagellum + a hook that connects the two --> may have 1 or 2 or many (non eukaryotic)
motor unit
a motor neuron and the skeletal muscle fibers innervated by it
Human skin
a. glabrous b. hairy -merkel cells (guard hair) -ruffini ending (stretch) -meissner corpuscle (suface) -pacinian's corpuscle (deep) -longitudinal lanceolate endings (deflections with hair): AB RA-LTMR, Ad-LTMR, C-LTMR, Circumference lanceolate endings -free nerve endings HTMR (pain or injury)
Primary Ciliary Dyskinesia
absent dynein arm in cilia -mutations target dynein -disease characterized by chronic respiratory tract infections and infertility -bronchiectasis occurs when walls of airways (bronchi) thicken as result of chronic inflammation or infection and results in mucus accumulating -functioning cilia determine position of internal organs-- not functioning internal organs flipped
response of a receptor cell
adaptation -merkel disk (tonic receptor--AP throughout stimulus) -Ruffini ending (tonic receptor) -Meissner's corpuscle (phasic receptor--AP at beginning and ends of stimulus) -Pacinian corpuscle (extremely phasic receptor)
reflex (neuronal)
an involuntary rapid response to a stimulus -blink reflex (palpebral reflex) -gag reflex (pharyngeal reflex) -knee jerk (patellar tendon reflex) -withdrawal reflex (flexion reflex)
basal body
anchors membrane wrapped projection -axoneme: the central strand of a cilium or flagellum, basically the skeleton inside the membrane
receptive fields
collections of rods and cones that funnel signals to specific visual cells in the retina or the brain -size of receptive fields and density of receptors vary across the body -different mechanoreceptors vary in size and structure of their receptive field
torque
control by a dynamic stator structure -torque: rotational equivalent of linear force
how cilia move
dynein arms on the A tubule of one doublet "walk" (grip, pull, release, and repeat) along the adjacent doublet's B tubule toward its base; this movement is ATP dependent and must be restricted by cross-linkage proteins in order for sliding to be converted into bending of an axoneme -upon ATP hydrolysis dynein walking leads to bending -patterns (undulation): effective stroke pilius is extended while during recovery stroke it is more collapsed
receptor potential magnitude
encodes stimulus magnitude -action potential magnitude is all-or-none but encodes stimulus magnitude by frequency of spikes
spinal tracts that control walking
ephrin A4 receptor and Ephrin B3 (ligand) in local neuronal circuits that control walking
muscular dystrophy (MD)
group of hereditary diseases characterized by degeneration of muscle and weakness -group of muscle diseases that cause muscle weakening and breakdown; mutations in many genes
internal (endoskeleton)
flexible joints are held together by proteinaceous ligaments; antagonistic muscles span the joint and attach to stiff plates or bones (ex: deuterostomes-- humans)
sequence of a simple response
foraging by a star-nosed mole -food absent--> mole moves on -food present--> mole bites
Hermann-hering grid
german physiologist Ludimar Hermann (1838-1914) discovered this illusion wile he was reading a physics text in which the figures were printed in a matrix-like arrangement
three types of skeleton
hydrostatic, exoskeleton, endoskeleton
spokes and linking proteins
important to bending -if purified, cilia has linking proteins removed filament sliding (not bending) can occur -intact cilia have the linking proteins and so bend instead of slide
photon-mediated activation of GPCRs
inactive rhodopsin (cis)--photon--> active rhodopsin (trans)
perception
individual interpretation of a sensation; a brain function
compound eye
invertebrates 1. convex arrangement is good for light detection 2. very sensitive to movements 3. color vision (has different photoreceptor cells) 4. bees can see into the ultraviolet range of light 5. mantis shrimp has 12 different color photoreceptors *Insects: can detect light and color
Type IV pili
involved in "twitching motility"; continually assemble and disassemble; grow from inner membrane -extension/retraction via assembly/disassembly not rotation -very important for pathogens
troponin complex
made up of three proteins one of which binds Ca+2 (troponin C)
lateral line sense organ
may allow for the close, synchronization of hundreds of fish that make up a shoal -series of pores--> water flows in and out; sensory nerve endings in pores
olfactory receptors
nerve endings that act as the receptors for the sense of smell -respond to several compounds -dogs have 1000 OR genes but only 800 function -rats have 1500; 1200 function -humans have 960 but only 470 function **Humans can discriminate over 1 trillion odors-- ex: spearmint and caraway from carvone (C8H140)
smooth muscle cell anatomy
no myofibrils but have actin and mysoin -Dense bodies are analogous to the Z-discs and are fastened to the sarcolemma. Dense bodies and intermediate filaments form a cytoskeleton to which actin is attached. When myosin pulls actin this changes the shape of the whole cell. -calcium ions are supplied by the SR and through membrane indentations called CALVEOLi (kind of equivalent to t-tubules in skeletal muscle) -Smooth muscle cells do not contain troponin, cross-bridge formation is not regulated by the troponin-tropomyosin complex but instead by the regulatory protein CALMODULIN
movement in millipeded
not via peristalsis but by coordinated movement of many legs -pattern of metachronal waves-- coordinated movement with a constant phase difference that produces a wave-like appearance -2 stages of movement for each leg: posterior propulsive stroke and anterior recovery stroke -certain # of legs in propulsive phase and recovery phase
Mot complex
number can change as load increases -load is indication of amount of force needed to move cell, so if more force needed, more Mot (Pom) complexes recruited -Pom (Mot) complexes not associated with the flagellum cannot be open pores; so they are plugged when not part of the flagellar complex
ampullae of lorenzini
special sensing organs called electroreceptors, forming a network of jelly-filled canals; these organs help sharks sense electric fields in the water -stefano lorenzini 1968 -the room temp proton conductivity of AoL jelly is very high at 2 +- 1 mS/cm, the highest reported for a biological material so far; suggest that KERATAN SULFATE may contribute to the high proton conductivity of the AoL jelly with its sulfate groups-- acid groups and proton donors
sarcoplasmic reticulum (SR)
specialized smooth endoplasmic reticulum in muscle cells, which stores, releases, and retrieves Ca++ -SR surrounds each myofibril and its main function is to store Ca+2 -transverse (t)-tubules span from outside down into muscle and associates with the SR -transverse (t)-tubules are in close contact with a region of the SR known as the terminal cisternae; these regions are the source of much of the Ca+2 stored in the SR; t-tubules are invaginations of the sarcolemma into the muscle cell -source of Ca+2
gravisensors in plant cells
statocyte: a specialized cell in a wheat plant (contains statoliths) statoliths: starch-rich particles sediment at the bottom of the cell to give the direction of gravity
retina
the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information -photoreceptor organization -optic nerve to brain -vertebrate rods and cones are a sensory modification to cilia
threshold
the minimum intensity of a stimulus that is required to produce a response from a sensory system
echolocation
the process of using reflected sound waves to find objects; used by animals such as bats -Donald Redfield Griffin-- Cornell university 1946-53
dynamic range
the range of intensities that will produce a response from a receptor or sensory system (ie the difference between threshold and saturation)-- even within a modality, individual receptors will have different thresholds and dynamic ranges
golgi tendon organ
the receptor organ at the junction of the tendon and muscle that is sensitive to stretch signals: -muscle tension -rate of change of tension -high threshold, vigorous if threshold is exceeded -tonic discharges similar to group 1 (primary) muscle spindle -only responds to active muscle contractions, and not passive stretches 1. neuron from golgi tendon organ fires 2. motor neuron is inhibited 3. muscle relaxes 4. load is dropped
muscle twitch
the response of a muscle to a single brief threshold stimulus -results from a single action potential in a motor neuron -twitches can be summed by increasing the frequency of the stimulus -as frequency of stimulus increases, contractions sum up, ultimately producing TETANUS and generating more force
primary motor cortex
the section of the frontal lobe responsible for voluntary movement
patellar tendon reflex
the stretch reflex that is elicited when the patellar tendon is struck (knee jerk) Path #1: (excitatory-monosynaptic) receptor-- sensory 1a afferent neuron-- efferent alpha motorneuron-- muscle contraction (agonist) Path #2: (inhibitory) sensory 1a afferent neuron-- inhibitory interneuron-- efferent alpha motorneuron-- muscle relaxation (antagonist) 1. reflex initiated artificially by tapping the tendon connected to quadricep muscle 2. sensors detect sudden stretch in quadriceps, and sensory neurons convey the information to the spinal cord 3. in response to signals from sensory neurons, motor neurons convey signals to quadriceps, causing it to contract and jerking the lower leg forward 4. interneurons in the spinal cord also receive signals from sensory neurons 5. motor neurons that lead to the hamstring muscle are inhibited by the interneurons. this inhibition prevents contraction of the hamstring, which would resist the action of the quadriceps
movement of cilia
unicellular protozoan (paramecium) covered with a few thousand cilia-- used both to move and to bring in food particles -metachronal waves-- difference is that recovery stroke is at 90º to the power stroke so cilia avoid hitting each other (have to be phase controlled otherwise non-productive) -example of unity in diversity of life (in paramecium and human windpipe)
single lens eye
vertebrates (humans) light enters the pupil iris changes diameter to let in more or less light the lens focuses light onto the retina photoreceptor cells 1. lens focusses light to photoreceptors in the retina 2. humans have 3 different types of color photoreceptors **RODS-- detect grayscale **CONES-- detect color
Generating voluntary movements
when brain commands muscle shortening, muscle spindles need to become insensitive -spindle length is adjusted to the current set point for the length of the muscle; this retains spindle sensitivity -co-activation of: alpha motorneuron (extrafusal fibers) and gamma motorneuron (intrafusal fibers)
