Physiology of Balance, Taste & Smell

Question 1

What is the vestibular system responsible for?

Answer 1

Balance & spatial awareness

Important in - motor coordination, response, eye movement & posture

Question 2

Which is the primary organ of the vestibular system?

Answer 2

The inner ear

Question 3

What are the two parts of the vestibular system?

Answer 3

Semicircular canals
Otolith organs

Question 4

What do semicircular canals detect?

Answer 4

Angular acceleration

Question 5

What do otolith organs detect?

Answer 5

Linear acceleration

Question 6

What are the names of the two otolith organs?

Answer 6

Utricle and saccule

Question 7

How are the semicircular canals arranged?

Answer 7

At 90 ° to each other - x,y & z orientation

Question 8

Answer 8

Question 9

What is linear acceleration?

Answer 9

Linear motion relative to gravity

Question 10

What detects linear acceleration?

Answer 10

Utricle and saccule

Question 11

What are the utricle and saccule in composition?

Answer 11

Membranous sacs containing endolymph

Question 12

What is the ionic balance of endolymph?

Answer 12

High K+
Low Na+

Question 13

What is the sensory tissue of the utricle and the saccule?

Answer 13

The macula

Question 14

What does the macula contain?

Answer 14

Hair cells - supported by epithelial cells.

Question 15

What types of hair cells are found in the vestibular system?

Answer 15

Type I and Type II

Question 16

How do the macula of the saccule and utricle lie in relation to each other?

Answer 16

At almost 90 ° to each other

Question 17

When P is upright - which planes do the macula of the utricle and saccule lie in?

Answer 17

Utricle macula = horizontal plane

Saccule macula = vertical plane

Question 18

What does the otolithic membrane consist of?

Answer 18

A gelatinous membrane with hair cell cilia embedded in it.

Question 19

What detects the linear accelerational force?

Answer 19

Stereocilia of the hair cells of the otolithic membrane

Question 20

What do the semicircular canals open into?

Answer 20

The utricle

Question 21

Where are the sensory cells of the semicircular canals located?

Answer 21

In the ampulla of each canal (dilated end).

Question 22

What contains the hair cells inside the ampulla of the semicircular canals?
What are they embedded in?

Answer 22

Crista ampullaris

Orientated at a right angle to the canal’s axis

Hair cells are embedded in gelatinous mass

Question 23

What is the gelatinous mass containing hair cell cilia in the crista ampullaris called?

Answer 23

The cupula

Question 24

Answer 24

Question 25

What types of cilia are found on hair cells in the semicircular canals?

Answer 25

Stereocilia Kinocilium = longer stereocilia

Question 26

How do cilia in the semicircular canals generate an AP?

Answer 26

Bending them in one direction = depolarisation Other direction = hyper-polarisation and inhibition

Question 27

What does movement do to the vestibular sensory receptors?

Answer 27

Creates a complex series of excitation and inhibition events - which are then interpreted by the brain as direction of movement

Question 28

Which nerves innervate the vestibular sensory receptors?

Answer 28

Vestibular afferent nerves

Question 29

Where do vestibular afferent nerves carry stimuli to?

Answer 29

The vestibular nuclei

Question 30

What is the pathway of the vestibular nerves from receptors to brain?

Answer 30

Receptors via afferent nerves --> vestibular nuclei --> abducens nuclei --> trochlear nucleus --> oculomotor complex

Question 31

What can the vestibular nuclei innervate?

Answer 31

CNS III, IV & VI (oculomotor, trochlear & abducens)

Question 32

What do descending pathways from the oculomotor complex regulate?

Answer 32

Posture Muscle tone

Question 33

What can vertigo be caused by?

Answer 33

Accumulation of debris --> increase sensitivity to angular movement Nerve / nuclei lesions Inner ear infection & inflammation of labyrinth Head injury Ototoxicity Meniere's disease

Question 34

What are the symptoms of Ménière's disease?

Answer 34

Intermittent vertigo Possible hearing distortion / tinnitus

Question 35

What is Ménière's disease caused by?

Answer 35

Accumulation of endolymph from poor drainage - endolymph oedema can cause damage to hair cells.

Question 36

How do eyes move following head rotation? What is this called?

Answer 36

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

Question 37

What is slow eye movement of head rotation controlled by?

Answer 37

Vestibular nuclei

Question 38

What is fast eye movement in the direction of rotation controlled by?

Answer 38

Brainstem (paramedian pontine reticular formation)

Question 39

What does nystagmus in the absence of head movement indicate?

Answer 39

Damage / lesion to the vestibular system

Question 40

What is the test for vestibular system damage called?

Answer 40

Caloric test

Question 41

How does the caloric test work?

Answer 41

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.

Question 42

What type of receptors detect smell?

Answer 42

Chemical sensory olfactory neuron receptors

Question 43

Where are the olfactory receptors located?

Answer 43

In the mucosal epithelium of the nose.

Question 44

What is the life span of the olfactory receptors? Is this long or short?

Answer 44

30-60 days - short life span

Question 45

Where do the axons of olfactory neuron receptors project to?

Answer 45

The olfactory bulb

Question 46

What happens in the olfactory bulb?

Answer 46

The olfactory receptors synapse with second order olfactory neurons.

Question 47

What is the synapse in the olfactory bulb called? Why?

Answer 47

A glomerulus - the neurons are intertwined.

Question 48

Olfactory sensory neuron dendrites extend into what?

Answer 48

Cilia which are embedded in nasal mucosal epithelium

Question 49

What are olfactory neurons supported by? What is their function similar to?

Answer 49

Epithelial cells Similar function to neural glial cells

Question 50

What does the basal epithelium contain that can replace the olfactory neurons?

Answer 50

Stem cells

Question 51

Are olfactory neurons myelinated?

Answer 51

No

Question 52

What do olfactory neurons synapse to form?

Answer 52

The olfactory nerve

Question 53

How do olfactory sensory neurons detect smell?

Answer 53

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.

Question 54

What NT do olfactory sensory neurons use?

Answer 54

Glutamate

Question 55

What NT do olfactory bulb neurons release?

Answer 55

GABA & Dopamine

Question 56

What does the olfactory tract project to?

Answer 56

Olfactory cortex & entorhinal cortex - both in temporal lobe AND Amygdala

Question 57

Where do the olfactory cortex & entorhinal cortex project to?

Answer 57

The frontal cortex, hippocampus and hypothalamus.

Question 58

What is loss of smell called?

Answer 58

Anosmia

Question 59

What is reduction in smell called?

Answer 59

Hyposmia

Question 60

What things can cause anosmia or hyposmia?

Answer 60

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

Question 61

What is olfactory hallucination of unpleasant smells called? What can it be caused by?

Answer 61

Cacosmia (or Phantosmia) Seizures of temporal lobe Tumour Parkinson's Head injury

Question 62

What are the five basic senses of tase?

Answer 62

Sweet, Bitter, Salty, Sour, Umami (pleasant savoury)

Question 63

Do different areas of the tongue detect different tastes?

Answer 63

No - receptors on all areas of the tongue detect each of the five senses

Question 64

What are the sensory organs of the gustatory system?

Answer 64

Taste buds

Question 65

What are taste buds interspersed amongst?

Answer 65

Different types of tongue papillae

Question 66

What are protrusions on the surface of the tongue called?

Answer 66

Papillae

Question 67

How do fluids from the oral cavity enter the taste bud?

Answer 67

Via a pore

Question 68

Do taste buds have long or short life cycles?

Answer 68

Short

Question 69

Which ganglia do the afferent taste nerves project to?

Answer 69

Ganglia of VII IX X

Question 70

How do taste receptors work?

Answer 70

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.

Question 71

Salty substances cause an influx of which ion?

Answer 71

Na

Question 72

Sour substances cause an influx of which ion? Why do cells depolarise with sour substances?

Answer 72

Influx of H+ Depolarisation occurs due to closure of K+ channels - causing an influx of Ca

Question 73

How do sweet receptors work?

Answer 73

Sweet substance - detected by G-protein channels - inc AC, inc cAMP, inc PKA - closes K+, causes influx of Ca -> release of NTs.

Question 74

How to bitter substances work?

Answer 74

Bitter substance - detected by G-protein channel - inc PKC and IP3 -> inc of Ca -> release of NTs

Question 75

What do all taste cell pathways have in common?

Answer 75

Depolarisation by the substance opens the voltage-dependant Ca channels = influx of Ca = release of NTs

Question 76

Which NTs are released via taste receptors?

Answer 76

ATP and serotonin

Question 77

What is the gustatory pathway?

Answer 77

Chorda tympani (VII) + IX & X - project to nucleus of solitary tract and thalamus - then to the gustatory cortex.

Question 78

What is loss of taste called?

Answer 78

Ageusia

Question 79

What is partial loss of taste called?

Answer 79

Hypogeusia

Question 80

What is the sensation of unpleasant taste called?

Answer 80

Dysgeusia

Question 81

What can disruption to sense of taste be caused by?

Answer 81

Infection Head injury Medicine