exam 2 Flashcards
-PNS contain highly specialized nerve cells called ____ or (sensory receptors) : convert energy associated with sensory stimuli into electrical signals (receptor potentials or afferent sensory signals)
receptors
the process of converting the inert of a sensory stimulus into electrical signal
sensory transduction
-stimulus alters the permeability of cation channels in the afferent nerve endings, generating a depolarizing current known as RECEPTOR POTENTIAL or GENERATOR POTENTIAL
-if sufficient in magnitude, the receptor potential allows the afferent neuron to reach threshold –> action potentials occur in the afferent fiber
sensory receptor potentials are ___: their AMPLITUDE REFLECTS INTENSITY OF STIMULUS
***
graded
if stimulus is strong enough in sensory receptor potentials, the intensity of stimulus is converted to ___ of action potentials
frequency
sensory info from the _______ ______ in the skin
-mediates sensations of the touch, vibration, and pressure
*terminate in skin
tactile subsystem
cutaneous mechanoreceptors
sensory info from specialized mechanoreceptors (_____) in muscles, tendons, and joints
-mediates info about the position of body parts
*also mechanoreceptors but are located in muscles, tendons, and joints
*terminate in muscle or tendon
proprioceptive system
proprioceptors
sensory info from the ____
-mediates sensations of pain, temp, and coarse touch
*terminate in skin but free nerve ending
nociceptive subsystem
nociceptors
somatic sensation is conveyed by ____ ____ ____ from afferent sensory neurons (DRG or CNG neurons)
afferent nerve fibers
cell bodies in the afferent sensory system are in the ___ ___ ___ (for body) and in the ___ ___ ___ (for head) of PNS
dorsal root ganglia ; cranial nerve ganglia
afferent sensory neurons are ___: peripheral and central components of afferent fibers are continuous, attached to the cell body in the ganglia by a SINGLE PROCESS
pseudounipolar
largest diameter, myelinated, supply sensory receptors in the muscles for proprioception
A
slightly smaller diameter, myelinated, mostly covert touch sensation
A beta
even smaller diameter, lightly or non-myelinated, mostly convert pain and temp sensation
A delta and C
rank diameter for somatic sensory afferent
A > Abeta> A delta > C
rank conduction velocity for somatic sensory afferent
A > Abeta> A delta > C
the area of the skin surface over which stimulation results in a significant change in the rate of action potentials
receptive field
what are receptive fields determined by
2 point discrimination
the min inter stimulus distance required to perceive 2 simultaneously applied stimuli as distinct
2 point discrimination
-fire in the presence of continued stimulation
-provide information about the SPATIAL ATTRIBUTES OF THE STIMULUS, SUCH AS SIZE AND SHAPE
slowly adapting (SA) afferents
-fire rapidly when a stimulus is first present, then fall silent int eh presence of continued stimulation
-converys info about CHNAGES IN ONGOING STIMULATION SUCH AS STIMULUS MOVEMENT
rapidly adapting (RA) afferents
low thresholds for action potential generation and fire in response to midl to moderate innocuous mechanical stimuli
low threshold mechanoreceptors (LTMRs)
high thresholds for action potential generation and only fire in response to intense noxious mechanical stimuli
high threshold mechanoreceptors
somatic subsist afferents constitute pathways with different physiological types, conduction velocities, receptive field size, dynamics, and effective stimulus features
parallel pathways
afferent fibers are often encapsulated by specialized receptor cells called ___
-____ help tune the afferent fiber to particular features of somatic stimulation
mechanoreceptors
afferent fibers of NOCIRECPTORS lack specialized receptor cells
free nerve endings
sense points, edges, and curvature
Merkel cells
sense objects moved across skin (skin motion)
(messier corpuscles)
sense skin vibration
pacinian corpuscles
sense skin stretch
Ruffini corpuscles
sense skin indentation in hairy skin
touch domes
sense skin stroke
circumferential endings
sense direction selective air deflection and gentle caress
longitudinal lanceolate endings
sensory transduction in mechanosensory afferents is mediated by ___ & ___ mechanosensitive ion channels
Piezo 1 &2
detect MECHANICAL FORCES arising within the body itself to provide continuous info about steps of the limbs and other body part in space
proprioceptors
detect muscle length
muscle spindles
detect muscle tension (muscle force)
Golgi tendon organs
the point for point correspondence of an area of the body to a specific point on the CNS
somatotopy
shows a orderly somatotropin representation
Ventral posterior complex of the tamales
receives projections carrying somatosensory info from the body and posterior head
ventral posterior LATERAL nucleus
receives axons from the trigeminal system converting somatosensory info form the FACE
ventral posterior MEDIAL nucleus
relays neurons for proprioception for the lower body
Clarke’s nucleus
what is the pathway for converting proprioceptive info from the body
dorsal root ganglia –> dorsal column nuclei in medulla –> cross midline –> VPL –> contralateral primary somatosensory cortex
somatic sensory afferents constitute pathways with different physiological types, conduction velocities, receptive field size, dynamics, and effective stimulus features
parallel pathways
the primary somatic sensory cortex in humans comprises what 4 distinct regions
brodmann’s areas 1,2,3a,3b
____ ____ fail to represent the human body in its actual proportions and how a disproportion of the representation of the human body
somatotopic maps
neurons in area 3b and 1 respond to primary ____ stimuli
cutaneous
3a respond mail to the simulation of
proprioceptors
neurons in area 2 process what 2 stimuli
tactile and proprioceptive stimuli
area ___ receives the most input from VP complex and provides a dense projection areas to 1 & 2
**serves as ab obligatory first step in cortical processing of somatosensory info
area 3b
profound deficiencies in ALL textile sensation
area 3b deficit
partial deficits where the us an inability to discriminate the texture of objects
area 1 deficit
partial deficits – inability to discriminate the size and shape of objects
area 2 deficit
primary somatosensory cortex neurons with similar response properties are clustered together into ___ ___ ____
functionally distinct column
3rd degree neurons in ____ VPL or VPM face in thalamus
– somatotopy
contralateral
3rd degree neurons in ____ primary somatosensory cortex
contralateral
**3b –> 1 or 2
-somatotopy
-functional column
-plasticity
nociceptors arise form neurons in ____ root ganglia for face
dorsal
what axons are associated with nociceptors for pain sensation
A delta myelinated and C fibers unmyleinated
convey a sharp pain first
a delta fibers
conniver delayed, diffuse, and longer lasting second pain
C fibers
noxious heat (above 43 degrees celsius) is conferred by what family
transient receptor potential (TRP) channels, TRPV1, found in both c and a delta fibers
-in open TRP channels allow can influx of sodium and calcium the initiates the generation of action potentials in the nociceptive fibers
in the anterolateral system (column) , axons of 2nd order neurons form the ____ ____
anterolateral column
dorsal column deal with what 3 things
deep touch, proprioception, vibration
anterolateral column deals with what 2 things
pain and temp
in dorsal column, the column arises from what
mostly axons from the FIRST order DRG neurons
in anterolateral column, the column arises from what
mostly axons from the SECOND order dorsal horn neurons
location of crossing midline in dorsal column
brainstem or cervical spinal cord
location of crossing midline in anterolateral column
spinal cord
column ascending location in spinal cord in dorsal column
ipsilateral side of spinal cord
column ascending location in spinal cord anterolateral column
contralateral side of spinal cord
stimuli in the inputs and surrounding area s that would ordinarily be perceived as slight painfully are perceived as significantly more so resulting from both peripheral and central sensitization
hyperalgesia
induction of pain by a normally innocuous stimuli
allodynia
chronic, intensely painful experience because the afferent fibers or central pathways themselves are damaged
neuropathic pain
peripheral sensitization results in potential of ___ channel
trp
what is involved in placebo affect
ENDOGENOUS OPIOIDs
activation of mechanoreceptors modulates the transmission of nociceptive info to higher center
gate control theory of pain
most sensory receptor cells derives from the epithelium and form columnar epithelium like structure for the reception of external stimuli
sensory epithelium (neuroepithelium)
all sensory receptors cells are ___ and compartmentalized
polarized
contains neurons sensitive to light and capable of converting light to electrical signals (phototransduction) and transmitting the signals to central targets
retina
circular area where the blood vessels enter the eye and also the site where retinal axons leave the eye and travel through the optic nerve
*contains no photoreceptors and is the blind spot
optic disk
an oval spot near rite center of the retina and is the region of the retina that supports high visual acuity
macula lutea
acuity is the greatest at the center of the macula, a small pit in the retina
fovea
cell layer just outside the neruosensory retina that reduces the backscattering go the light and plugs critical role in maintaining the phototranscurion machinery of retinal photoreceptors
retinal pigment epithelium
retina contains what 5 basic classes of neurons
- photoreceptors (rods and cones)
- bipolar cells
- ganglion cells
- horizontal cells
- amacrine cells
cell bodies of photoreceptors (rods and cones)
outer nuclear layer
the processes and synaptic contacts btw photoreceptor terminals and bipolar cells (and horizontal cells)
outer plexiform layer
cell bodies of bipolar cells, horizontal cells, and amacrine cells
inner nuclear layer
the process and synaptic contacts btw bipolar cells and amacrine cells and dendritic processes of ganglion cells
inner plexiform layer
cell bodies of ganglion cells
ganglion layer
the most direct pathway of info flow from photoreceptors to the optic nerve
3 neuron chain –> photoreceptor –> to bipolar cell –> ganglion cell
what cells mediate lateral interactions in the outer na dinner plexiform layers
horizontal and amacrine
- maintain phototransduction machinery of retinal photoreceptors
- reduced backscattering
pigment epithelium
what is the visual info flow by 3 neuron chain
photoreceptor –> to bipolar cell –> ganglion cell
composed of membranous disks containing light sensitive photopigments
outer segment
contains the cell nucleus and give rise to synaptic terminals that contact bipolar or horizontal cells
inner segment
shining light on either a rod or cone leads to a mem ___ rather than ____
-saturates around -65 mV
hyperpolarization ; depolarization
light activation causes a ___ change in mem potential
graded
______ and light induced changes in the electrical active of photoreceptors
cGMP
absorption of light by the photoreceptor (increases or reduces? ) the cGMP conc
reduces
prices that photoreceptors convert light energy to electrical signals
phototransduction
-GPCRs
proteins with photopigment containing light absorbing chromophore retinal
opsins
-a GCPR
-opsin in rods, contains 7 transmit domains forming a pocket to enclose retinal molecule
rhodopsin
phototransduction process
- photoreceptors absorb photon of light
- double bonds breaks and retinal changes form 11 cis to all trans isomers
- conformation change of rhodopsin leads to activation of transducin
- transducin activates phosphodiesterase that hydrolyze cGMP
- lowering of cGMP conc in the outer segment leads to channel closure and hyperolarization of the cell
mag of the phototransduction amplification varies with the prevailing level of illumination
-photorecpetors are most sensitive to light at low illumination levels
*when illumination levels increase, sensitivity decreases, preventing the receptors from saturating to end the operating range of light intensities
-ca2+ conc in the outer segment play a key role in light adaptation
light adaptation
very low postal resolution acuity but very sensitive to light
rod system
very high spatial resolution (specialized for acuity) but relatively insensitive to light; allows use to see color
cone system
only rod mediated perception at the lowest levels of illumination
scotopic vision
both rods and cones contribute to perception
mesopic vision
illumination increases to level of all mem channels are closed in rods and rod response to light saturates
**only cone mediated color perception
photopic vision
-slow adaption
-high convergence
-high sensitivity
-reduced resolution
rod
-fast adaption
-low convergence
-low sensitivity
-increased acuity
cone
___ don’t saturate at high levels of illumination
cones
___ have high degree of convergence
rods
in fovea ___ density increases 200 fold and in the center of the fovea (foveola) – rod free and avascular (no blood vessel)
cones
superiority of acuity of the cone system is due to
- 1-1 relationship btw cone and ganglion cell
- greater cone density in the fovea
- displacement of the inner layer s of the retina minimize photon scattering
- no retinal blood vessels in central region of fovea
rods contain what single photopigment protein
rhodopsin
cones have what 3 photopigment proteins
3 different wavelengths
short, medium, and long wavelength cones most sensitive to blue green and red lights
normal color vision
trichromatic
impairment in perception of long wavelengths
-difficulty in discrimination of red and green
protanopia
impairment in the perception of medium wavelengths
-difficulty in discrimination of red and green
deuteranopia
produces a burst of action potentials when a spot of light in the receptive field center and reduces the rate of discharge when a dark spot in the receptive center (increase discharge rate in luminance increment)
-ionotropic glutamate receptor
on center ganglion cell
produces a burst of action potentials when a spot of dark in the receptive field center and reduces the rate of discharge when a light spot in the receptive center (increase discharge rate in luminance decrement)
-ionotropic glutamate receptor
off center ganglion cell
use metabotropic glutamate receptor
glutamate is inhibitory and causes hyperpolarization
on center bipolar cells
use ionotropic glutamate receptor and glutamate is excitatory and cause depolarization
off center bipolar cells
when the concentric surrounding region off the receptive field is stimulated, it antagonizes the response to stimulation of the receptive field center
center surround antagonism
___ cell mediated depolarization antagonize phototransduction induced hyperpolarizatino of the center photoreceptor
horizontal
Photoreceptor synapses with off‐center bipolar cells are____‐ ____: the direction of membrane potential (Vm) change of the bipolar cell (de‐ or hyper‐polarization) is the same as that in the photoreceptor
**mem potential change in bipolar cell same as photoreceptor
sign-conserving
Photoreceptor synapses with on‐center bipolar cells are ___‐ _____: the change in the Vm of the bipolar cell is the opposite of that in the photoreceptor
**mem potential change in bipolar cell opp of photoreceptor
sign inverting
response during light stimulation in the center: light increment hyperpolarizes photoreceptor and decreases glutamate release → glutamate is inhibitory, so on‐center bipolar cells are free from the hyperpolarization and they depolarize → On‐center ganglion cells increase discharge rate
on center ganglion cell
response during light stimulation in the center: light increment hyperpolarizes photoreceptor and decreases glutamate release → glutamate is excitatory, so off‐center bipolar cells withdraw from depolarization and they hyperpolarize → Off‐center ganglion cells decrease discharge rate
off center ganglion cell
Circuitry responsible for generating ____ ____ center responses of retinal ganglion cells
receptive field
- light stimulation hyper polarizes the surround cone
- surround horizontal cell becomes hyper polarized and decreased GABA release to center cone
- center cone frees from inhibition and depolarizes to offset light induced hyperpolarization in the center receptive field
- center cone increases glutamate release to inhibit and hyper polarize on center bipolar cell
- on center ganglion cell also hyperpolarize and firing rate decrease
Lateral interaction from horizontal cells in the retina
rod convergence
high 15:30 - 1 to ganglion cell
rod is activated in
scotopic and mesopic vision
cone is activated in
photopic and mesopic vision
Center‐surround antagonism allows ganglion cells to detect _____ _____ in the border
luminance contrast ***
Ganglion cells are relative insensitive to different levels of _____ ____
diffuse illumination
Ganglion cells are sensitive to differences between the level of illumination that falls on the receptive field center and the level of illumination that falls on the surround the ____ ____
luminance contrast
center surround antagonism also contributes to ___ ___
light adaptation
Two functions of center‐surround antagonism
- Detect luminance contrast in the border (make ganglion
cells sensitive to light‐dark borders in the visual scene) - Light adaptation to increase dynamic range of encoding in ganglion cells
what 2 mechanism in the retina help achieve light adaptation
- Photoreceptor light adaptation mediated by decreasing intracellular calcium concentration
- Retinal circuitry light adaptation mediated by surround antagonism from horizontal cells to the center cone cel
what is the function of external ear
boost sound pressure 100 fold
middle ear consists of
-tympanic mem
-malleus, incus, stapes (middle ear)
a membrane‐covered opening at the base of the cochlea between middle and inner ear, the site where the bones of the middle ear contact the inner ear
oval window
function of middle ear
boost the pressure 200 fold
small coiled structure of the peripheral auditory system
cochlea
the other opening of the two openings (oval and round windows) from the middle ear into the inner ear
round window
flexible structures in the middle of cochlea and bisect cochlea into the cochlear partition
basilar and tectorial mem
two fluid‐filled chambers on each side of the cochlear partition; connected through each other by an opening
*fluid is perilymph
Scala vestibuli and Scala tympani
distinct channel rums within the cochlea partition
*fluid is endolymph
scala media
primary auditory neurons transmit sound information from
hair cells to the CNS
spiral ganglion neurons
the receptor organ (or sensory epithelium) for hearing in the cochlea, composed of mechanosensory hair cells (inner hair cells and outer hair cells) and supporting cells
organ of corti
-bears the organ of Corti and hair cells are situated on top of it
-spectral decomposer to decompose a sound stimulus to it’s frequency component
basilar mem
covers the mechanically‐sensitive hair bundles of the hair cells
tectorial mem
cause maximum displacement of basilar membrane at the basal
end
high frequency sound
cause maximum displacement of basilar membrane at
the apical end, giving rise to a topographical mapping of frequency called tonotopy
low frequency sound
spatial arrangement of where different sound frequencies are processed in
different regions of the auditory system
tonotopy
vertical component of the traveling wave is translated into a shearing motion between the two membranes to bend the tiny processes, called _____ (or hair bundles), that protrude from the apical ends of the hair cells, leading to opening of ____ ___ ____
- stereocilia
- mechanoelectrical transducer (MET) channels
T/F sterocilia are NOT graded in height
FALSE. THEY ARE
Fine filamentous structures, known as ___ ___ , run in parallel to the plane of bilateral symmetry, connecting tips of adjacent stereocilia
tip links
the process that hair cells convert mechanical energy from sound waves to electrical signals
mechanoelectrical transduction
- Displacement of the hair bundle parallel to the plane of symmetry in the direction of the tallest stereocilia stretches the tip links, opening the cation‐selective mechanoelectrical transducer (MET) channels located at
the end of the link and generating a graded receptor potential to depolarize the hair cell (hair cells do not fire action potentials) - Depolarizing graded receptor potentials cause opening of voltage‐gated Ca2+ channels and transmitter (glutamate) release accordingly, eliciting action potentials in afferent nerve terminal of spiral ganglion neurons
mechanoelectrical transduction
Endolymph in scala media is K+‐rich, Na+‐poor due to ion‐pumping cells in the stria vascularis pumping K+ into endolymph
Endolymph is about 80 mV more positive than perilymph or 125 mV more positive than the inside of hair cell
The steep electrical gradient drives K+ through open transduction channels into the hair cell and depolarize the hair cell, causing the opening of voltage‐ gated Ca2+ and K+ channels located in the membrane of the cell soma
Because the perilymph at basal end of hair cell is K+‐poor, Na+‐rich and because EKbasal (‐85 mV) is more negative than hair cell’s resting potential, K+ efflux through somatic K+ channels to repolarize the hair cell
ionic basis of mechanotransduction in hair cell
____ influx and efflux through two different K+ channels serves both to depolarize and repolarize the hair cell
K+
a plot of auditory threshold intensity at various frequencies for a single auditory nerve fiber
tuning curve
(frequency at which a given spiral ganglion neuron responds to the smallest sound intensity
characteristic frequency
cochlear amplifier to amplify the sound
outer hair cells
self‐generated sounds from outer hair cells due to their electromobility
Otoacoustic Emissions (DPOAE)
can measures outer hair cell function in the inner ear
otoacoustic emission test (OAE)
The ____ ______ (or frequency map) of the cochlea is retained at all levels of the central auditory system
tonotopic organization
electromobility helps to ____ sound
amplify
peripheral component of the vestibular system formed by the interconnected chambers/canals continuous with the cochlea
Vestibular labyrinth
Vestibular labyrinth also uses (mechanosensory) ____ ____ as
the sensory receptor cells to transduce physical motion into neural impulses
hair cells
The vestibular labyrinth is consists of two ____ (Greek for “ear stones”) organs, the ____ and ____, and three _____ canals
otolith; utricle; saccule; semicircular
___ and ____ are specialized to respond to linear accelerations of the head and static head position relative to the gravitational axis
utricle and saccule
______ _____ are specialized to respond to rotational accelerations of the head
semicircular canals
Vestibular hair cells are located in the utricle and saccule and the ______ of three
semicircular canals
ampullae
Movement of the
stereocilia toward the kinocilium opens
mechanically gated
channels, _______ vestibular hair cells and
causing transmitter release
onto (and excitation of) the
vestibular nerve fibers of
vestibular ganglion neurons
depolarizing
Movement of the stereocilia in the direction away from the kinocilium closes the channels, ______ vestibular hair cells and reducing vestibular nerve firing
hyperpolarizing
firing rates of vestibular fibers can _____ or _____ to faithfully mimic the receptor potentials produced by vestibular hair cells (different to auditory hair cells, which mostly use depolarization to encode signals)
increase/decrease
In the utricle and saccule, a specialized area called the _____ divides the hair cells into two populations with opposing hair bundle polarities
striola
sensory epithelium of the utricle and saccule, which consists of hair cells and associated supporting cells
macula
the otolithic membrane, in which are embedded crystals of calcium carbonate called ____ (ear stone)
otoconia
A tilt of the head to one side has ____ effects on corresponding hair cells of the two utricular maculae or saccular maculae
opp
linear movements in the vertical plane
saccule
linear movements in the horizontal plane
utricle
The kinocilia are directed ____ the striola in the utricular macula but point ____ from the striola in the saccular macula
toward; away
response to head tilt
tonic (sustained) hair displacement
response to linear acceleration
transient hair bundle displacement
sensory epithelium of semicircular canals inside the ampulla, containing the hair cells
crista
a dome‐shaped gelatinous mass over hair bundles, where hair bundles extend into
capula
The semicircular canals sense head ____
rotations
When rotating or turning the head to right, vestibular hair cells in the right horizontal canal are
_____ and vestibular hair cells in the left horizontal canal are _____
depolarized; hyperpolarized
*whatever side u turn, that side depolarizes
The maximum firing rates corresponds to the period of ____
acceleration
maximum inhibition corresponds to the period of _____
deceleration
During the constant‐velocity phase, firing rates return to a _____ level
baseline
vestibulo‐ocular reflex (VOR) for ______ _____
stabilizing gaze
Central vestibular processing is ______ _____ and vestibular inputs are integrated with inputs from visual and somatic sensory system
multisensory nature
Many neurons in vestibular nuclei function as _____ _____ (a.k.a upper motor neurons)
premotor neurons
Processesinformationabouttheidentity,
concentration, and quality of a wide range of airborne, volatile chemical stimuli
odorant
Axons (olfactory nerve, cranial nerve I) arising from receptor cells project directly to neurons in the _____ _____(in the CNS)
olfactory bulb
sensory epithelium of olfaction
olfactory epithelium
sensory receptor cells of olfaction
olfactory receptor neurons
Neurons in the olfactory bulb send projections to the _____ cortex in the temporal lobe and to other forebrain structures via an axon pathway known as the ______ _____
pyriform; olfactory tract
t/f Olfactory system does include a thalamic relay from primary receptors to a cortical region (different than other sensory systems, which all have the thalamic relay)
f it does NOT
a three‐layered archicortex dedicated for processing olfactory sensory information and is phylogenetically older than the six‐layered neocortex
pyriform cortex
relays information directly to hypothalamus and amygdala for feeding, reproduction, and aggressive behaviors
olfactory bulb
bipolar sensory receptor cells give rise to unmyelinated axons at their basal surface to transmit information centrally
-polarized and compartmentalized
*EXPRESSES ONLY ! OF THE ODORANT RECEPTOR GENES
Olfactory receptor neurons (ORNs)
several microvilli protrude from a single knoblike dendritic process (olfactory knob) at the apical surface of an ORN
– olfactory cilia extend into a thick layer of mucus
Olfactory cilia
secret mucus
Bowman’s glands
a population of neural stem cells that divide to give rise to new receptor neurons
Basal cells
structural support and detoxify potentially dangerous chemicals
sustentacular (supporting) cells
mucus layer and epithelium with neural and supporting cells
nasal mucosa
In rodents, most ORNs are renewed every 6 to 8 weeks by new ORNs from what cells
basal cells
glial cells derived from olfactory epithelium to surround axons in the olfactory nerve and bulb and to support the growth of new axons through a mature nervous system
Olfactory ensheathing cells
Odor transduction in the olfactory epithelium begins with odorant binding to specific _____ _____ _____ concentrated on the external surface of olfactory cilia
-encoded by the odorant receptor gene family
-GPCRs
odorant receptor proteins
- ORNs express an olfactory‐specific heterotrimeric G‐protein, Golf
- Alpha subunit of Golf dissociates upon odorant binding to receptors and then activates adenyl cyclase
III (ACIII), an olfactory‐specific adenylate cyclase - An increase in cyclic AMP (cAMP) opens cyclic nucleotide‐gated channels that permit entry of Na+
and Ca2+ (mostly Ca2+), depolarizing the neurons - Depolarization is further amplified by Ca2+‐activated Cl‐ current and is conducted passively from cilia to the axon hillock of the ORN, where action potential are generated via voltage‐gated Na+ channels and transmitted to the olfactory bulb
- In response to elevated Ca2+, and Na+/Ca2+ exchanger extrudes Ca2+ and transports Na+ to re‐ polarize the membrane
- Increases in Ca2+ and activation of calcium/calmodulin‐dependent kinase II (CaMKII) restore the Golf and diminish cAMP levels via activation of phosphodiesterases
odor transduction
Most randomly selected single ORNs have _____ _____ ____ to a variety of odorants
broadly tuned responses
spherical accumulations of neuropil lie just beneath the surface of the bulb and are the synaptic target of the primary olfactory axons
glomeruli
Within each glomerulus, ORN axons contact apical dendrites of _____ cells, the _____ _____ neurons of the olfactory bulb,
principal projection
Axons from ORNs that express a particular odorant receptor gene ____ on a small subset of bilaterally symmetrical glomeruli
converge
_________ increases the sensitivity of mitral cells to ensure maximal fidelity of odor detection and also average out uncorrelated “background” noise
convergence
Olfactory bulbs employs a _____ ______ _____ that cues in on a small number of dominant chemicals within a mixture
sparse coding mechanism
_____ cell axons provide the only relay for olfactory information to the rest of the brain
mitral
The mitral cell axons from each olfactory bulb form the ____ ____ ____ that project ipsilaterally to the pyriform cortex and other forebrain regions
lateral olfactory tract
Individual pyriform cortical cells are _____ ____ to different odors than is the case in the olfactory bulb
broadly tuned
the chemical constituents of food interact with receptor proteins on _____ _____ (sensory receptor), which are located in epithelial specializations called _____ _____ (sensory epithelium of the taste system)
taste cells; taste buds
Taste cells are innervated by sensory afferent axons from neurons in the _____ _____ _____
cranial nerve ganglia
The central axons of these sensory afferent neurons in the cranial nerve ganglia project to the nucleus of the solitary tract (a.k.a. _______ nucleus
gustatory nucleus
Axons from the gustatory nucleus project to ventral posterior medial nucleus of thalamus, which in turn projects to _____ and _____ taste cortex
insular and frontal
pathway of taste system
taste cells in taste buds –> relay neurons in cranial nerve ganglia –> gestatory nucleus in brainstem –> VPM in thalamus –> insular and frontal cortex
multicellular protuberances surrounded by local invaginations (trench) in the tongue
epithelium
taste orillas
(sensory epithelium) are distributed along the lateral surfaces of the papillar
protuberances and in the trench walls
-have lifetime of ~2 weeks and are regenerated by BASAL CELLS
taste buds
found only on the anterior of the tongue and contain 25% of total taste bud
fungiform papillae
form a chevron at the rear of the tongue and contain 50% of total taste buds
9 circumvallate papillae
on the posterolateral tongue and contain remaining 25% of the total taste buds
foliate papillae
the taste system detects five perceptually distinct categories of tastants
salt, sour, sweet, bitter, and umami
The tip of the tongue is most responsive to
sweet, umami, and salty compounds
Sour and bitter taste sensitivity is lowest toward the tip and greatest on
the sides and back of the tongue
Type II cell:
sweet, bitter, umami, or salty
Type III cell
sour
______ _____ is initiated in the apical domain of the taste cells to open ion channels to generate electrical signals by graded receptor potentials (and later the action potentials) for neurotransmitter release at the basal domain
Type I cell: glial‐like supporting cell
Type II cell: sweet, bitter, umami, or salty
chemosensory transduction
Neurotransmitters for taste cells
serotonin, ATP
Ion channels for ____ and _____ tastes
salty and sour
G‐protein‐coupled receptors (GPCRs) for ____, _____, _____ tastes
sweet, bitter, and umami
Salty and sour tastes are elicited directly by ____ ____ such as positively charged ions in
salts (Na+) or the H+ in acids
ionic stimuli
The salty taste is initiated by the amiloride‐sensitive Na+ channels (called _______)
ENaCs
Sour stimuli permeate into cells through ______ channels or via passive diffusion, and cytoplasmic protons block an inward‐rectifier K+ channel, resulting in depolarization
OTOP1
Sweet and umami receptors are heterodimeric GPCRs that share the common TAS1R3 subunits, paired with the TAS1R2 for _____, or with the TAS1R1 for _____
sweet; umami
