Quiz 4- Vestibular and Chemical Flashcards
What does the vestibular system do
Processes info underlying responses to and perceptions to motion, position, orientation to stabilize and help with movement and postural reflexes
3 axes of angular acceleration
3 semicircular canals detect rotational motion around the axes
Yaw: z-axis
roll: x-axis
pitch: y-axis
why is vestibular system important
many people have dizziness/imbalance issues
Labyrinth
works similar to cochlea, is continuous with it – converts physical motion from linear and rotational acceleration into neural impulses
2 otolith organs, 3 semicircular canals, vestibular hair cells
utricle and saccule
linear acceleration of head and head position relative to gravitational axis
semicircular canals
respond to head rotation
vestibular hair cells
utricle, saccule, 3 ampullae
vestibular hair cells
work like auditory hair cells, since some channels are open some nerve fibers have spontaneous activity
striola
divide hair cell into two populations
movement towards kinocilum
leads to K influx and depolarization
movement away from kinocilium
less k, hyperpolarization and less ca2+
otolithic membrane, gelatinous layer
contain small crystals otoconia that deflect hair bundles during tilting
utricle
horizontal movements
saccule
vertical movements
distribution of hair cells and orientation of stereocilia in utricle and saccule is
continuous to encode all possible directions
hair bundle movement occurs
tonically in response to head tilting, transiently in response to acceleration
semicircular canals
encode head rotations– hulbous expansion at each canal is the ampulla with the sensory epithelium
crista
contains hair cells
hair cells extend out of the crista into
the cupula
do hair cells/cupula have orientation
yes, opposite on each side of head
what happens when head rotates
fluid in canal distorts the cupula, turning it away from direction of head movement, causing displacement of hair bundles in crista
how are the semicircular canals on both sides of the head organized
each canal works with its partner on the other side that has hair cells oppositely aligned so that tilting head to one side depolarizes direction you turn head in and hyperpolarizes other
pairs of semicircular canals
two horizontal canals
left anterior and right posterior
right anterior and left posterior
this arrangement provides info about rotation of head in any direction
semicircular canals encode
head rotation
vestibular fibers exhibit
high level of spontaneous activity
how do vestibular fibers transmit info
increasing or decreasing fire rate
what happens to firing rate in semicircular canals with acceleration, deceleration, constant velocity?
acceleration: max firing rate, cupula deflected
Deceleration: minimum firing rate (cupula deflected in opposite direction)
constant velocity: firing rate returns to baseline
central vestibular processing is inherently
multisensory
many neurons in vestibular nuclei
act as premotor neurons and give rise to ascending projections
central projections from vestibular nuclei are involved in
maintaining equilibrium and gaze during movement
maintaining posture
vestibulo ocular reflex
eye movements that counter head movements and maintain gaze
pathway of vestibulo ocular reflex
vestibular branch of CN - cell bodies reside in scarpas ganglion, with distal processes innervating semicircular canals and otolith organs and central processes projecting to ipsilateral medial vestibular nuclei
the medial vestibular nucleus goes to the contralateral abducens nucleus and causes the lateral rectus of right eye to contracct; it also crosses midline, ascends the medual longitudinal fasciculus to the original side oculomotor nucleus, causing the medial rectus of left eye to contract
in the same pathway, medial vestibular nucleus goes to the ipsilateral abducens nucleus with inhibitory neurons, causing lateral rectus of left eye to relax and ascending midline/crossing mlf to right oculomotor nucleus, causing medial rectus of right eye to relax
turning head left– right eye movement
pathways for stabilizing gazse, head and posture
descending projections thru vestibular nuclei for vestibulospinal reflex, vestibulocervical reflex to maintain body and head
lateral vestibulospinal to lateral vestibular nucleus and cerebellum
medial vestibulospinal tract to medial vestibular nucleus to cerebellum
patients with lesions to descending projections through vestibular nuclei
problems with balance and gait, more pronounced in low light or uneven surface, integration of
superior and lateral vestibular nuclei project to
the ventral posterior nucleus of the thalamus
and to the vestibular cortical system which is a distributed set of cortical areas in the parietal and posterior insular regions – multisensory neurons responding to multiple stimuli
PIVC
perception of body orientation and sense of self-motion
olfaction
detection of airborne chemical stimuli called odorants
purpose of olfaction
guides search for food or mates, avoid predators, reproductive/endocrine functions, mother-child interactions, warns about danger
oldest/most primitive sense
olfactory
odorants interact with
olfactory receptor neurons in olfactory epithelium– axons go through cribiform plate directly to neurons in olfactory bulb
cribiform plate
thin perforated region of skull separating olfactory epithelium from brain
bulb sends projections to
pyriform cortex and other forebrain structures via the olfactory tract
why is the olfactory system unique?
does not include a thalamic relay from primary receptors to cortical region
pyriform cortex has
3 layered archicortex dedicated to olfaction
does the olfactory system ever touch the thalamus
yes but not immediately
pathway of olfactory info
- olfactory receptors
- olfactory bulb
- pyriform cortex (goes to orbitofrontal cortex), olfactory tubercule, amygdala, entorhinal cortex (goes to hippocampal formation)
- all go to hypothalamus, thalamus, orbitofrontal cortex
- orbitofrontal cortex and thalamus interact
least acute sense in humans
olfaction
how do animals express stronger olfaction
more olfactory receptor neurons, expanded olfactory epithelium, larger portion of forebrain for olfaction
sniffing increases as
scent tracking is learned
can humans sniff out a scent trail
yes
with training how does olfaction change
speed increases, deviation from track decreases
anosmia
inability to detect odors due to genetics, toxins, illness, injuries, aging (normal), alzheimers/parlinsons
olfactory epithelium
where olfactory information begins, lines about half of nasal cavity
respiratory epithelium
lines remaining surface of nasal cavity, maintaining appropriate temp and moisture and providing an immune barrier
mucus layer
secreted by bowman’s glands – contains enzymes and antibodies to prevent passing infection to brain
controls ionic environment for olfactory cilia, thicker means less acuity
olfactory receptor neurons
bipolar, unmyelinated, has apical surface with knob extending olfactory cilia into mucus layer
olfactory cilia
primary site of odorant transduction
basal cells
stem cells of adult olfactory epithelium
sustenacular cells
detoxify dangerous chemicals
olfactory receptor neurons are
continuously regenerated and protected by mucus due to higher exposure (basal cells have stem cells regenerating neurons thru life)
odor transduction begins with
odorant binding to receptor proteins on olfactory cilia- must be presented to cilia and not cell body
odorant receptors are
metabotropic (G protein coupled)
process of odorant binding
g alpha subunit dissociates with odorant binding, activating adenyl cyclase which increases cAMP which opens Na and Ca channels, leading to depolarization, amplified by Ca activated Cl outward current
this depolarization goes to the ORN and to olfactory bulb
do olfactory receptors have specificity
yes but are also broadly tuned
olfactory receptor axons
form a large bundle that make up the olfactory nerve, which projects ipsilaterally to the olfactory bulb
glomeruli in olfactory bulb
synaptic target of primary olfactory axons where ORN axons contact apical dendrites of mitral cells
also 50 tufted cells and periglomerular cells for each glomerulus
mitral cells
glutamatergic, principal projection neurons of olfactory bulb
why do glomeruli receive many inputs but few mitral cells
increases mitral cell sensitivity and evens out background noise
granule cells
synapse on basal dendrites of mitral cells- inhibitory circuits, plasticity
layers of olfactory bulb
glomerular layer– dendritic tufts of mitral cells, orn axon terminals, periglomerular cells in margins
external plexiform layer– lateral mitral dendrites, cell bodies and lateral dendrites of tufted cells, dendrites of granule cells synapsing with other elements
mitral cell layer (cell bodies of mitral cells)
internal plexiform layer with mitral cell axons
granule cell layer with granule cell bodies
glomeruli in olfactory bulb
respond selectively to distinct odorants
increased odorant concentration
more glomeruli activity
olfactory system employs
coding mechanism to look at dominant chemicals and represent these chemicals over subset of glomeruli
projection from mitral cells form
mostly ipsilateral olfactory tract
main target of olfactory tract
pyriform cortex– neurons have broad responses and integrate different odors
pyriform cortex projects to
orbitofrontal cortex, amygdala
t or f: pyriform cortical neurons respond to one stimuli
no- multiple odors cause a reaction
segregation of info in olfactory
seen in bulb, not in cortex, maybe in amygdala
vomeronasal system
carnivored and rodents, organ has receptors and separate region of olfactory bulb called accessory olfactory bulb that detects odors from predators, prey, mates
projections from accessory olfactory bulb
distinct from remainder of olfactory, mainly in hypothalamus/amygdala, mainly encode and process info about odorants for feeding, reproduction
pheromones vs kairomones
kairomones from other animals
taste cells transduce
identity, concentration, quality
pathways working together for taste
olfaction, taste, trigeminal receptors
taste buds in
tongue, pallate, epiglottis, esophagus
axons for taste
cranial nerves 7, 9, 10, project to nucleus of solitary tract (gustatory) and then to thalamus (VPM) and then to insula and orbitofrontal cortex
chemical constituents of food
interact with receptors
taste buds sit in
trenches around 3 types of papilla– circumvallate (cranial nerve 9), foliate, and fungigorm papillae (7)
taste cells
clustered in taste buds, clustered around a taste pore
taste cells regenerated
every 2 weeks
gustatory afferents
go to cns
5 categories of tastants
sour, bitter, salty, sweet/umami (maintained in insular cortex)
taste transduction
begind in apical domain of taste cell, graded receptor potentials cause electrical signals at base
microvilli of apical taste cells contain
taste receptor proteins and related signalling molecules
receptors on taste cells
VG ion channels, second messengers– activation releases intracellular calcium
neurotransmitters released by taste cells
serotonin, atp, gaba
salty and sour
Na+ and H+ sensitive trp channel (ion channels)
sweet and savory
gpcr signals plc IP3 to open trp channels to let calcium in
bitter receptors
gpcr with gustducin, alpha binding to plc Ip3, ca2+ channel open
