Physiology of Balance, Taste & Smell Flashcards
What is the vestibular system responsible for?
Balance & spatial awareness
Important in - motor coordination, response, eye movement & posture
Which is the primary organ of the vestibular system?
The inner ear
What are the two parts of the vestibular system?
Semicircular canals
Otolith organs
What do semicircular canals detect?
Angular acceleration
What do otolith organs detect?
Linear acceleration
What are the names of the two otolith organs?
Utricle and saccule
How are the semicircular canals arranged?
At 90 ° to each other - x,y & z orientation
What is linear acceleration?
Linear motion relative to gravity
What detects linear acceleration?
Utricle and saccule
What are the utricle and saccule in composition?
Membranous sacs containing endolymph
What is the ionic balance of endolymph?
High K+
Low Na+
What is the sensory tissue of the utricle and the saccule?
The macula
What does the macula contain?
Hair cells - supported by epithelial cells.
What types of hair cells are found in the vestibular system?
Type I and Type II
How do the macula of the saccule and utricle lie in relation to each other?
At almost 90 ° to each other
When P is upright - which planes do the macula of the utricle and saccule lie in?
Utricle macula = horizontal plane
Saccule macula = vertical plane
What does the otolithic membrane consist of?
A gelatinous membrane with hair cell cilia embedded in it.
What detects the linear accelerational force?
Stereocilia of the hair cells of the otolithic membrane
What do the semicircular canals open into?
The utricle
Where are the sensory cells of the semicircular canals located?
In the ampulla of each canal (dilated end).
What contains the hair cells inside the ampulla of the semicircular canals?
What are they embedded in?
Crista ampullaris
Orientated at a right angle to the canal’s axis
Hair cells are embedded in gelatinous mass
What is the gelatinous mass containing hair cell cilia in the crista ampullaris called?
The cupula
What types of cilia are found on hair cells in the semicircular canals?
Stereocilia
Kinocilium = longer stereocilia
How do cilia in the semicircular canals generate an AP?
Bending them in one direction = depolarisation
Other direction = hyper-polarisation and inhibition
What does movement do to the vestibular sensory receptors?
Creates a complex series of excitation and inhibition events - which are then interpreted by the brain as direction of movement
Which nerves innervate the vestibular sensory receptors?
Vestibular afferent nerves
Where do vestibular afferent nerves carry stimuli to?
The vestibular nuclei
What is the pathway of the vestibular nerves from receptors to brain?
Receptors via afferent nerves –> vestibular nuclei –> abducens nuclei –> trochlear nucleus –> oculomotor complex
What can the vestibular nuclei innervate?
CNS III, IV & VI (oculomotor, trochlear & abducens)
What do descending pathways from the oculomotor complex regulate?
Posture
Muscle tone
What can vertigo be caused by?
Accumulation of debris –> increase sensitivity to angular movement
Nerve / nuclei lesions
Inner ear infection & inflammation of labyrinth
Head injury
Ototoxicity
Meniere’s disease
What are the symptoms of Ménière’s disease?
Intermittent vertigo
Possible hearing distortion / tinnitus
What is Ménière’s disease caused by?
Accumulation of endolymph from poor drainage - endolymph oedema can cause damage to hair cells.
How do eyes move following head rotation? What is this called?
Head moves one way - eyes slowly rotate in opposite as fixed in one plane of vision. This is followed by rapid eye movement towards the new direction of rotation to align with the new field of vision.
Called = nystagmus
What is slow eye movement of head rotation controlled by?
Vestibular nuclei
What is fast eye movement in the direction of rotation controlled by?
Brainstem (paramedian pontine reticular formation)
What does nystagmus in the absence of head movement indicate?
Damage / lesion to the vestibular system
What is the test for vestibular system damage called?
Caloric test
How does the caloric test work?
Warm water irrigation of left ear = firing of hair cells + activation of vestibular nuclei - stimulates head movement to the left, eyes should deviate to the right.
Cold water = should not cause firing - stimulated movement should be to the right with eye movement to the left.
Absence of these expected eye movements = poss damage to the vestibular system.
What type of receptors detect smell?
Chemical sensory olfactory neuron receptors
Where are the olfactory receptors located?
In the mucosal epithelium of the nose.
What is the life span of the olfactory receptors? Is this long or short?
30-60 days - short life span
Where do the axons of olfactory neuron receptors project to?
The olfactory bulb
What happens in the olfactory bulb?
The olfactory receptors synapse with second order olfactory neurons.
What is the synapse in the olfactory bulb called? Why?
A glomerulus - the neurons are intertwined.
Olfactory sensory neuron dendrites extend into what?
Cilia which are embedded in nasal mucosal epithelium
What are olfactory neurons supported by? What is their function similar to?
Epithelial cells
Similar function to neural glial cells
What does the basal epithelium contain that can replace the olfactory neurons?
Stem cells
Are olfactory neurons myelinated?
No
What do olfactory neurons synapse to form?
The olfactory nerve
How do olfactory sensory neurons detect smell?
They contain G-protein coupled receptors.
Odorous molecules activate G-coupled proteins (inc AC, inc cAMP, cAMP opens CNGC channels - causing influx of Ca and Na, efflux of Cl = depolarisation).
Ion influx depolarises the cilia -> AP.
What NT do olfactory sensory neurons use?
Glutamate
What NT do olfactory bulb neurons release?
GABA & Dopamine
What does the olfactory tract project to?
Olfactory cortex & entorhinal cortex - both in temporal lobe
AND
Amygdala
Where do the olfactory cortex & entorhinal cortex project to?
The frontal cortex, hippocampus and hypothalamus.
What is loss of smell called?
Anosmia
What is reduction in smell called?
Hyposmia
What things can cause anosmia or hyposmia?
Head injury (damage to olfactory bills or olfactory neurons)
Infection (damage to olfactory neurons)
Nasal polyps
Age
Alzheimer’s or Parkinsons
Smoking
Chemical exposure
Drugs
Radiation
What is olfactory hallucination of unpleasant smells called? What can it be caused by?
Cacosmia (or Phantosmia)
Seizures of temporal lobe
Tumour
Parkinson’s
Head injury
What are the five basic senses of tase?
Sweet, Bitter, Salty, Sour, Umami (pleasant savoury)
Do different areas of the tongue detect different tastes?
No - receptors on all areas of the tongue detect each of the five senses
What are the sensory organs of the gustatory system?
Taste buds
What are taste buds interspersed amongst?
Different types of tongue papillae
What are protrusions on the surface of the tongue called?
Papillae
How do fluids from the oral cavity enter the taste bud?
Via a pore
Do taste buds have long or short life cycles?
Short
Which ganglia do the afferent taste nerves project to?
Ganglia of
VII
IX
X
How do taste receptors work?
Chemical substances in saliva enter tase bud via pore - come into contact with microvilli
= Cascade of events (depending on substance)
= Depolarisation of the taste cells
= Release of NTs
= NTs stimulate AP in afferent neurons -> taste sensation to the brain.
Salty substances cause an influx of which ion?
Na
Sour substances cause an influx of which ion? Why do cells depolarise with sour substances?
Influx of H+
Depolarisation occurs due to closure of K+ channels - causing an influx of Ca
How do sweet receptors work?
Sweet substance - detected by G-protein channels - inc AC, inc cAMP, inc PKA - closes K+, causes influx of Ca -> release of NTs.
How to bitter substances work?
Bitter substance - detected by G-protein channel - inc PKC and IP3 -> inc of Ca -> release of NTs
What do all taste cell pathways have in common?
Depolarisation by the substance opens the voltage-dependant Ca channels = influx of Ca = release of NTs
Which NTs are released via taste receptors?
ATP and serotonin
What is the gustatory pathway?
Chorda tympani (VII) + IX & X - project to nucleus of solitary tract and thalamus - then to the gustatory cortex.
What is loss of taste called?
Ageusia
What is partial loss of taste called?
Hypogeusia
What is the sensation of unpleasant taste called?
Dysgeusia
What can disruption to sense of taste be caused by?
Infection
Head injury
Medicine
