Exam 2: Ch 10 Sensory Physiology Flashcards
Sensory receptors transduce (=change) environmental information into
APs – the common language of NS
Each type of sensory receptor responds
a particular modality (=form of info, e.g. sound, light, pressure)
Different modalities are perceived as different because
because of CNS pathways they stimulate
2 classification schemes for sensory receptors
1. Structural
2. Functional
1. Structural
simple dendritic endings of neurons
• Free (pain, temperature)
• Encapsulated within non-neural structures (pressure) or modified epithelia (taste)
2. Functional
Functional classification of sensory receptors groups them according to type of stimulus they transduce
Functional classification of sensory
- chemoreceptors
- photoreceptors
- thermoreceptors
- mechanoreceptors
- nociceptors
- proprioceptors
Chemoreceptors
sense chemical stimuli (taste buds, olfactory receptors)
Photoreceptors
transduce light (rods and cones)
Thermoreceptors
respond to temperature changes (heat and cold)
Mechanoreceptors
respond to deformation of their cell membrane (touch, pressure, hair cells of inner ear)
Nociceptors
respond to intense stimuli by signaling pain
Proprioceptors
signal positional information of body parts (joint receptors, golgi tendons, muscle spindles)
Sensory receptors can also be categorized according to location:
- Cutaneous receptors
- Special sense receptors
Cutaneous receptors
are near an epithelial surface (respond to touch, pressure, temperature or pain)
Special sense receptors
are part of a sensory organ (hearing, sight, equilibrium)
Sensory Receptor Responses
Tonic receptors
Phasic receptors
Tonic receptors
respond at constant rate as long as stimulus is applied (e.g. pain)
Phasic receptors
respond with burst of activity but quickly reduce firing rate to constant stimulation
Which sensory receptor is Responsible for sensory adaptation
Phasic receptors
- • e.g. smell and touch
Generator (receptor) potentials
sensory receptor equivalents of EPSPs
Generator (receptor) potentials is produced why
in response to adequate stimulus
Generator (receptor) potentials are proportional to
stimulus intensity
• NOTE: After threshold is reached, intensity is coded for by AP frequency
In phasic receptors the generator potential
adapts to a constant stimulus & quickly diminishes in amplitude
In tonic receptors, generator potential
does not adapt to a constant stimulus
Cutaneous sensations include the following
- touch
- pressure
- heat
- cold
- pain
- ruffini endings & merkel’s discs
Cutaneous sensations are mediated by
free & encapsulated nerve endings
heat
mediated by free nerve endings; located deeper in dermis
heat elicits pain thru
capsaicin receptors; capsaicin is “hot” chemical in chili peppers
cold
mediated by free nerve endings; located in upper dermis
pain
- mediated by free nerve endings called nociceptors
• Use glutamate & substance P as NTs; substance P called “pain NT”
Ruffini endings & Merkel’s discs
are slow-adapting, expanded free nerve endings that mediate touch
Encapsulated nerve endings
- mediate touch, pressure
- adapt quickly and include Meisner’s & Pacinian corpuscles
Two-point touch threshold
Is minimum distance at which 2 points of touch can be perceived as separate
Two-Point Touch Threshold Measure of
of tactile acuity or distance between receptive fields (area of skin whose stimulation results in changes in the firing rate of a neuron)
Lateral Inhibition
Is CNS process that sharpens sensation
Sensory neurons at center of stimulation area inhibit more lateral neurons
Lateral Inhibition eg.
- when blunt object touches skin sensory neurons in center are stimulated more than outer ones & inhibit them
- Object perceived as single touch with well-defined borders
Taste and smell receptors are
are exteroceptors because respond to chemicals in external environment
Interoceptors
respond to chemicals in internal environment
Taste/Gustation Detects
sweet, sour, salty, bitter, & amino acids (umami)
Taste receptor cells are
modified epithelial cells
How many taste receptors in each taste bud?
50-100 are in each taste bud
Salty & sour
do not have receptors
act by passing through channels
Sweet & bitter
- have receptors
- act thru G-proteins
Smell (olfaction) receptors
located in olfactory epithelium at top of nasal cavity
Olfactory apparatus consists of
receptor cells, supporting cells, & basal cells
Receptor cells of olfactory apparatus are
are bipolar neurons that send axons to olfactory bulb
Basal cells of olfactory apparatus are
are stem cells that produce new receptor cells every 1-2 months
supporting cells of olfactory apparatus
contain detoxifying enzymes
Odor molecules bind to
receptors & act through G-proteins
Ears & Hearing; Vestibular Apparatus
provides sense of equilibrium orientation to gravity
inner ear
Vestibular apparatus & cochlea
Vestibular apparatus consists of
otolith organs (utricle & saccule)
semicircular canals
Sensory structures of the vestibular apparatus are located with in
membranous labyrinth
membranous labyrinth is filled with
endolymph = fluid similar to intracellular fluid
membranous labyrinth is located within
bony labyrinth
Utricle and saccule provide
info about linear acceleration
linear acceleration
changes in velocity (acceleration and deceleration) when moving horizontally or vertically)
Semicircular canals,
- oriented in 3 planes,
- give sense of angular (rotational) acceleration
Vestibular Apparatus
- Hair cells
- modified epithelial cells
are receptors for hearing and equilibrium
each contains 20-50 hair-like extensions called stereocilia
stereocilia
- processes with filaments of protein
* 1 of these extentions (longer one) = kinocilium (cilia)
When stereocilia are bent toward kinocilium,
hair cell depolarizes & releases NT that stimulates CN VIII
When stereocilia are bent in the opposite direction
- hair cell hyperpolarizes
In this way, frequency of APs in hair cells carries information about movements that cause the hair cell processes to move
Otolith organs
Utricle & Saccule
Utricle and saccule
- each have a macula
patch of specialized epithelium containing hair and support cells
Hair cell extensions are embedded in gelatinous otolithic membrane
gelatinous otolithic membrane
contains calcium carbonate crystals (=otoliths) that resist change in movement
Utricle =
sensitive to horizontal acceleration
Hairs pushed backward during forward acceleration
Saccule
sensitive to vertical acceleration
Hairs pushed upward when person descends
Semicircular canals
= provide information about rotational acceleration
project in 3 different planes
each contains a semicircular duct
At base of Semicircular canals
is crista ampullaris where sensory hair cells are located
Hair cell processes are embedded in
gelatenous membrane = cupula of crista ampullaris with higher density than endolymph
when endolymph moves
cupula moves and sensory processes bend in opposite direction of angular acceleration
Vestibular nystagmus
involuntary oscillations of eyes
occurs when spinning person stops
eyes continue to move in direction opposite to spin, then jerk rapidly back to midline
Vertigo
is loss of equilibrium
Vertigo
natural response of vestibular apparatus or pathological may be caused by
anything that alters firing rate of CN VIII
Ex: often caused by viral infection
Outer Ear
Sound waves funneled by
by pinna (auricle) into external auditory meatus
External auditory meatus
channels sound waves to tympanic membrane
Middle ear
between tympanic membrane & cochlea; holds ossicles
Malleus (
hammer) is attached to tympanic membrane; carries vibrations to incus (anvil)
Stapes
(stirrup) receives vibrations from incus, transmits to oval window (cochlear membrane)
Stapedius muscle
attached to stapes
provides protection from loud noises
• can contract to dampen large vibrations to prevent nerve damage in cochlea
ear membrane)
Organ of Corti
where sound is transduced
Sensory hair cells located on
the basilar membrane have projections (steriocilia) projecting into cochlear duct
1 row of inner cells extend length of basilar membrane & multiple rows of outer hair cells are embedded in
tectorial membrane, which overhangs hair cells with cochlear duct
• Pressure waves moving thru cochlear duct create
shearing forces between basilar & tectorial membranes, moving & bending stereocilia
• Causing ion channels to open, depolarizing hair cells
• The greater the displacement, the greater the amount of NT released & APs produced
Conduction deafness
occurs when transmission of sound waves to oval window is impaired
helped by hearing aids
Sensorineural (perceptive) deafness
is impaired transmission of nerve impulses
often impacts some pitches more than others
• helped by cochlear implants, which stimulate fibers of CN VIII in response to sounds
Sclera
(white of eyes) is outermost layer
Transparent cornea
continuous with sclera
light passes thru
cornea into anterior chamber, then thru pupil which is formed by the pigmented muscle = iris (controls size of pupil), then thru lens & vitreous to retina
• Iris
(a pigmented muscle) controls size of pupil
• Pupil constricts by
contraction of circular muscles
• Under parasympathetic control
• Pupil dilation is
via contraction of radial muscles
Structure of Eye
Photoreceptors are in retina
Retina absorbs some light, the rest is absorbed by dark choroid layer
Axons of retinal neurons gather at
optic disc (blind spot) & exit eye in optic nerve
Visual field
part of the external world projected onto retina
Cornea and lens focus the
right part of the visual field to the left half of the retina and the left part of the visual field to the right half of the retina
Visual acuity
sharpness of vision
visual acuity Depends upon
resolving power: ability to distinguish (resolve) 2 closely spaced dots
With myopia (nearsightedness) image
focused behind retina because eyeball too short; object will have to be further away to be seen
With astigmatism
cornea or lens is not symmetrical; light is bent (refracting) unevenly, causing uneven focus
Retina = a multilayered epithelium consisting of
Neurons
pigmented epithelium
photoreceptors (rods & cones)
photoreceptors (rods & cones)
• neural layers are extension of brain; light must pass through several neural layers before striking rods & cones
Rods & cones face away from
from pupil; send sensory info to bipolar cells
Bipolars send electrical activity to
ganglion cells
Ganglion cells project axons
thru optic nerve to brain
Horizontal cells & amacrine cells are
interneurons involved in visual processing in retina
Electrical Activity of Retinal Cells
Ganglion & amacrine cells produce APs
Rods, cones, bipolar, & horizontal cells produce graded potential changes
Visual transduction is
inverse of other sensory systems
In dark, photoreceptors release
inhibitory NT that hyperpolarizes bipolars
• Inhibited bipolars do not release excitatory NT onto ganglion cells
Light inhibits photoreceptors from
releasing inhibitory NT, thus stimulating bipolars, which excite ganglionic cells, which transmit AP to brain
Rods & cones contain
many Na+ channels that are open in dark
This depolarizing Na+ influx is the dark current
Light hyperpolarizes by
by closing Na+ channels
• cGMP keeps Na+ channels open; light converts cGMP to GMP & Na+ channels close
