Physiology Chapter 6

sensory receptor function

respond to internal or external stimulus and transmit to CNS

sensory transduction (sensory receptors)

graded receptor potential converted to action potential

how do sensory receptors work

tuned for specific (adequate) stimulus but may have bleed over from other stimuli

visceral afferents

subconcious, internal environment (blood pressure, blood CO2 levels, body temp, etc)

sensory afferents

conscious awareness - somesthetic and proprioception (vision, hearing, touch, taste, smell)

6 types of receptors

photoreceptors, mechanoreceptors, thermoreceptors, osmoreceptors, chemoreceptors, nociceptors

stimulation with afferent fiber

alters receptor membrane permiability (inc stimulus = inc permiability of Na+ = inc receptor potential); graded potential

signal intensity

stimulus strength determines graded receptor potential (induces threshold at faster rate with greater signal intensity)

separate receptor cell

1. regional summation of graded potential at receptor cell (Na channel open)

2. potential activates voltage gated Ca2+ channels

3. Ca2+ stimulates exocytosis of neurotransmitter

4. if stimulus great enough, then activates action potential in associated afferent neuron

receptor adaptation: tonic receptors

adapts slowly or not at all - sensitivity remains constant (ex. proprioceptors or baroreceptors)

receptor adaptation: phasic receptors

adapts quickly, on/off response, signals change in intensity (ex. touch or hair receptors)

tacticle receptors: touch mechanoreceptors

light: hair, meissner’s corpuscle, merkel’s disc; deep: pacinians corpuscle and ruffini endings

hair receptors

hair movement and gentle touch (rapid adaptation)

meissner’s corpuscle

light touch and vibrations (rapid adaptation)

merkel’s disc

light sustained touch (slow adaptation)

pacinian’s corpuscle

deep pressure and vibration (rapid adaptation)

ruffini endings

deep pressure and stretch (slow adaptation)

receptive field

region supplying sensory information to sensory neuron (feeling 1 vs 2 points)

pain receptor categories

mechanical nociceptors (cutting, crushing, pinching), thermal nociceptors (temperature extremes), polymodal nociceptors (varied damaging stimuli)

fast pain

mechanical and thermal; A-delta (myelinated); sharp pain; precise location; rapid onset of pain

slow pain

polymodal; C (small, unmylenated); dull, aching, burning pain; poor localization; slow and persistant pain

pain signaling: neurotransmitters

glutamate and substance P (triggers neurogenic inflammation and hypersensitivity)

what pathway to pain signals take

ascending pathways; synapse ascending second-order neurons in dorsal horn of spinal cord; ascend to reticular formation, thalamus, cortex, etc

constriction of the pupil - contracts circular pupil muscles

parasympathetic stimulation

dilation of the pupil - contract radial muscles

sympathetic stimulation

shape of refracive components

convex

shaping of lens

lens supported with suspensory ligaments and attached to ciliary muscle (constatly stretched - makes lens less powerful)

what lens movement makes the lens more powerful

constrict

rods vs cones

gray scale; color

where are photoreceptors concentrated

macula and fovea (highest concentration)

blind spot

where optic nerve and blood vessels pass through retina

photopigments components

opsin + retinol (vitamin A)

retinol sensitivity to light

changes conformation in light and activates opsin (GPCR)

opsin function

break down cGMP (dec cGMP = dec Na+ leak, hyperpolarization = dec neurotransmitter release - glutamate)

rods opsin

rhodopsin

cones opsin

photopsin

s-cones; m-cones; l-cones

blue; green; red

what direction do rods and cones face

away from incoming light

what happens at the blind spot (brain)

brain fills in missing details

left and right field of vision

contralateral

visual processing route

signal routed through thalamus to occipital lobes and mapped on primary visual cortex

sound wave pathway to cochlea

waves channeled by pinna to ear canal, vibrate tympanic membrane (ear ossicles amplify vibration to oval window and fluid within cochlea by 20x)

why do the ossicles need to amplify the vibrations

sound going from air to liquid

what do the bending of hair cells cause (inner hair cells)

opens mechanically gates ion channels (depolarization) → receptor potential

inner vs outer hair cells

afferent vs efferent (gets signal to cause movement and amplifies signals)

high frequency in cochlea

narrow, stiff portion near oval window

low frequency in cochlea

wider, thinner portion near helicotrema

what do excited hair cells release

neurotransmitter (glutamate) on primary afferent neurons of cochlear nerve

gustation vs olfaction

taste vs smell

taste bud

50 spindle taste receptor cell; activated receptor opens Ca 2+ channels and releases neurotransmitter to activate associated afferent neuron

path of taste bud afferent neuron

to brain stem/thymus to primary gustatory cortex (along lateral sulcus)

5 primary taste receptors

salty (direct), sour direct), sweet (G-coupled), bitter (G-coupled), umami (G-coupled)

what neurotransmitter do the taste receptors release through exocytosis

glutamate and ATP