T2 L13 Physiology of balance, taste & stimuli

Question 1

What is the endolymph in the scala media continuous with?

Answer 1

Apical surface of vestibular hair cells

Question 2

Describe the 6 semi-circular canals

Answer 2

At right angles to one another to detect head rotation in all directions
Left & right lateral semi-circular canals are functionally pairs

Question 3

Describe the 4 otolith organs

Answer 3

Aren’t at right angles to resolve head tilt & linear acceleration in all directions

Question 4

What are the sensory cels in the ampullae of the semi-circular canals embedded in?

Answer 4

Cupula

Question 5

What are the sensory cells in the otolith organs embedded in?

Answer 5

Gelatinous sheet covered with heavy crystals of calcium carbonate

Question 6

What does Newton’s second law show?

Answer 6

Gravity & linear acceleration provide same stimulus to otolith organs

Question 7

What is Newton’s second law?

Answer 7

F = m x a

Question 8

Describe type II vestibular hair cells

Answer 8

Most common

Receive afferent & efferent innervation

Question 9

Describe type I vestibular hair cells

Answer 9

Surrounded by afferent nerve calyx

Not direct contact with efferent nerve fibres

Question 10

Which type of vestibular hair cell appears to be more sensitive?

Answer 10

Type II

Question 11

What is nystagmus?

Answer 11

Slow eye movements followed by fast ones during a continuous head rotation

Question 12

When does physiological nystagmus occur?

Answer 12

When rotating the head

Question 13

What is spontaneous nystagmus?

Answer 13

Eyes move rhythmically side to side in absence of head movements

Question 14

When does spontaneous nystagmus occur?

Answer 14

When one of the canals is damage
There is difference in the vestibular nerve firing rates when the head is stationary as the vestibular nerve innervating the intact canal is still firing

Question 15

What is caloric testing used for?

Answer 15

Test brainstem function in unconscious patient

Question 16

What happens during caloric testing if the brainstem is intact?

Answer 16

Both eyes move toward the side of the cold water

Question 17

What happens during caloric testing if there is a lesion of the medial longitudinal fasciculus?

Answer 17

Movement of eye only on the irritated side

Question 18

What is the diagnosis if neither eyes move during caloric testing?

Answer 18

Low brainstem lesion

Question 19

Why does cold water irrigation cause eye movements?

Answer 19

Increases density of water in semi-circular canals –> convection currents in canal that mimic endolymph movement induced by turning head

Question 20

What is the result of warm water irrigation?

Answer 20

Endolymph rises

Increased firing

Question 21

What is the result of cold water irrigation?

Answer 21

Endolymph falls

Decreased firing

Question 22

What are some causes of vestibular disorders?

Answer 22

Ear infection
Head injury
Whiplash
Ageing
Certain drugs

Question 23

What are some causes if the patient complains of dizziness?

Answer 23

Light headed - check cardiovascular

Vertigo - check vestibular

Question 24

What is benign paroxysmal positional vertigo?

Answer 24

Vertigo caused by changes in head position

Question 25

What is Meniere's disease?

Answer 25

Progressive disease | Episodes of vertigo, tinnitus & progressive hearing loss

Question 26

Why is smell important?

Answer 26

Social interactions - perfumes, deodorants Avoidance of poisons / noxious gases Enjoyment of food

Question 27

How many odourant receptor proteins are there?

Answer 27

More than 1000 | Each receptor cells expresses just 1 of these proteins

Question 28

What is olfactory information coded by?

Answer 28

Pattern of stimulation that the brain learns to interpret | Not coded by individual receptor types

Question 29

What does olfactory transduction depend on?

Answer 29

Second messenger process with cAMP being activated in response to an odourant molecule

Question 30

What happens after the opening of cAMP-dependent ligand gated ion channels?

Answer 30

Non-selective cation channels permeable to Na+ & Ca2+ Influx of Na+ & Ca2+ --> depolarisation of olfactory receptor cells which signals binding of odourant molecule --> action potentials Ca2+ influx indirectly opens Cl- channels --> high intracellular Cl- concentration of olfactory receptors --> contributes to depolarisation

Question 31

What can cause issues with olfaction?

Answer 31

``` Upper respiratory tract infection High age Nasal polyps Diabetes mellitus Head trauma High dose radiation at nasal epithelium Some drugs ```

Question 32

What is the function of taste?

Answer 32

Evaluate nutritious content of food & prevent ingestion of toxic substances

Question 33

What are the 5 different modalities of taste that can be distinguished?

Answer 33

``` Salty Sour Sweet Bitter Umami ```

Question 34

What is the function of a sweet taste receptor?

Answer 34

Identify energy-rich nutrients

Question 35

What is the function of a umami receptor?

Answer 35

Recognition of amino acids

Question 36

What is the function of a salty receptor?

Answer 36

Ensures proper electrolyte balance

Question 37

What is the function of the sour & bitter receptors?

Answer 37

Warn against intake of potentially noxious and/or poisonous chemicals

Question 38

What is the mechanism for salt taste transduction?

Answer 38

Depends on equilibrium potential for Na+ across taste receptors

Question 39

What is the mechanism for sour taste transduction?

Answer 39

Depends on pH with H+ closing K+ channels either directly or indirectly via cAMP as a second messenger

Question 40

What is the mechanism for sweet taste transduction?

Answer 40

Via second messenger system which closes K+ channels --> depolarisation of taste receptors

Question 41

What is the mechanism for bitter & umami taste transduction?

Answer 41

Second-messenger induced increase in intracellular Ca2+ receptors --> neurotransmitter release

Question 42

What cranial nerves signal taste to the nucleus of solitary tract in the brainstem?

Answer 42

VII IX X

Question 43

Where do the fibres from 2nd order taste neurons project to in primates?

Answer 43

Ipsilaterally to ventral posterior nucleus of thalamus

Question 44

Where do thalamic efferents project to?

Answer 44

Insula, defining primary gustatory cortex which projects to orbitofrontal cortex

Question 45

Describe the parabrachial nuclei in pons in rodents

Answer 45

Dorsal thalamic projection & ventral projection that terminates in amygdala & hypothalamic nuclei

Question 46

What are the main causes of issues with olfaction?

Answer 46

Prior upper respiratory tract infection Head injury Poor oral hygiene