a. conversion of physical or chemical stimulus to a change in membrane potential (receptor potential)
b. strengthen of receptor potential varies with the strength of the stimulus)
transduction
a. respond to stimuli in the external environment
b. examples: vision, hearing, smell, taste, & touch
exteroreceptors
a. respond to stimuli in the internal environment of the body
b. example: muscle spindle (stretch receptor) in muscle
interoreceptors
a) Merkel discs (flattened disk-shaped nerve endings near the surface of the skin)
b) Meissner corpuscles (egg-shaped mass of dendrites wrapped in capsule of connective tissue)
c) hair root plexuses (free nerve endings wrapped around hair follicles)
mechanoreceptors: light touch in human skin
nerve endings called Pacinian corpuscles which are composed of individual dendrites each wrapped in multiple layers of connective tissue – encapsulated nerve ending
pressure
a) = stretch receptors in muscles
b) important in reflex arcs
muscle spindles
1) consists of a canal below the epidermis with periodically-situated vibration-sensing organs
2) canal connected to the surface via pores that allow the entry of water
3) vibration-sensing organ (neuromast) structure = collection of hair cells with sensory hairs imbedded in gelatinous cupula
lateral line of fishes
bending of hairs
a) receptor potential depolarized or hyperpolarized – depends on the direction of hair bending
b) depolarization _______ rate of action potential generation above background rate
c) hyperpolarization ______ the rate of action potential generation below the background rate
increases, decreases
1) typically consists of hair cells surrounding a chamber
2) mineralized _______ in chamber deforms sensory hairs of hair cells
statocysts of invertebrates:
statolith
a) involves the saccule and utricle of the inner ear
b) hair cells in a gelatinous matrix (macula) in these structures deformed by the weight of otoliths on the hairs
static equilibrium and linear acceleration
a) response to rotational acceleration or deceleration
b) involves the three semicircular canals arranged at right angles to each other in three dimensions
c) hairs of the hair cells organized into a cupula within the ampullae of each semicircular canal
d) fluid moving through semicircular canal deforms cupula and induces action potential to be generated by the hair cells
dynamic equilibrium
cold receptors respond to temperature range =
warm receptors respond to temperature range =
10º - 40ºC
32º – 48ºC
a. naked dendrites in the skin and other tissues of the body (except the brain)
b. may be sensitized by prostaglandins (aspirin inhibits prostaglandin synthesis)
nociceptors
2) compound eyes
a) observed in arthropods
b) each photoreceptive unit = _________
c) compound eyes useful for detecting motion
ommatidium
Eye:
______ does the coarse focus adjustment, but its focus is fixed by its fixed shape
cornea
Eye:
_____ contributes to accommodation because a small pupil size increases the depth of field
iris
a) eyeball too long
b) nearsightedness
c) correct with concave lens
myopia
a) eyeball too short
b) farsightedness
c) correct with convex lens
hyperopia
a) abnormal curvature of the cornea or lens
b) lens correction is complex