T2 L15: Physiology of Balance, Taste and Smell Flashcards
What is the function of semi-circular canals?
They’re fluid-filled tubes in your inner ear that help you keep your balance.
When your head moves around, the liquid inside the canals sloshes around and moves the tiny hairs that line each canal
How many semi-circular canals are there in total?
6 (3 on each side)
Which semi-circular canals are paired?
- Left and right lateral
- Left posterior and right anterior
- Right posterior and left anterior
If the firing goes up in one, the firing will go down in the other because they detect opposite directions
What are otoliths?
Small calcium carbonate crystals which put pressure on the cilia, inclining them, thereby stimulating the sensory hair cells
How many otolith organs are there?
4 (2 on each side)
Why are the otolith organs not exactly at right angles?
To enable them to resolve head tilt and linear acceleration in all directions
Where are the sensory cells of the semicircular canal found?
In the ampullae of the semicircular canal embedded in the Capula on top of the hair cells
When the fluid in the cupula moves, so does the fluid within the semicircular canals
What are the 2 types of vestibular hair cell?
Found both in the otolith organs and the semicircular canals
Type 1: they’re surrounded by a afferent calyx which the efferent fibres make contact with. There is no direct contact of efferent fibres with the hair cell.
Type 2: receive both afferent and efferent innervation. They provide feedback
What is a utricle?
A small membranous sac paired with the saccule lies within the vestibule of the inner ear
How are the semicircular canals orientated?
At right angles from each other so they can coordinate in 3 planes
How are the semicircular canals orientated?
At right angles from each other so they can coordinate in 3 planes
So they can detect head rotation in all directions
What is the difference in function between the semicircular canals and the otolith organs?
The otolith organs allow us to sense the direction and speed of linear acceleration and the position (tilt) of the head
The semicircular canals allow us to sense the direction and speed of angular acceleration
- Otolith organs: linear acceleration and gravity (forces)
- Semicircular canals: rotation
Where are the sensory cells of the otolith organs found?
Embedded in a gelatinous sheet like in the semilunar canals but its covered with otoliths which move depending on the position of the head
What is the functional difference between type 1 and 2 vestibular hair cells?
Type 2 appear to be more sensitive
Which type of vestibular hair cell is greatest in number?
Type 2
What is nystagmus?
Slow eyes movements followed by fast ones during continuous dead rotation
In healthy individuals, rotating your head elicits physiological nystagmus caused by the vestibulo-ocular reflex
What is spontaneous nystagmus?
When there is rhythmic eye movement from side to side in absence of head movements
What is caloric testing used for?
To test the function of the brainstem in an unconscious patient
If the brain stem is intact, the eyes will move in the direction of where water is being irrigated. Both eyes should move unless there is something disrupting the communication between the eyes
How does caloric testing work?
The cold or warm water will create a currant that moves the hair cells and mimics the movement induced by turning your head
Why do some people feel like they’re rotating when they lie down after drinking alcohol?
Because alcohol gets into the semicircular canal and changes the density of the fluid so you feel like you’re rotating
What are the central vestibular pathways?
The vestibular organs (semicircular canals, utricle, saccule) convey info to either the vestibular nuclei or the cerebellum.
The vestibular nuclei and the cerebellum are connected
The vestibular nuclei sends info to all the other areas then: cerebral cortex, reticular formation, oculomotor nuclei, extraocular muscles
What are some causes of vestibular disorders?
Ear infection Head injury Whiplash Ageing Drugs Eg. aminoglycoside antibiotics
What is meniere disease?
Progressive disease causing episodes of vertigo, tinnitus, progressive hearing loss
Caused by excess fluid in the ear
Usually affects 1 ear
What is benign paroxysmal positional vertigo?
Vertigo caused by changes in head position
What is the mechanism of olfactory transduction?
An odorant molecule activates cAMP which leads to the opening of cAMP-dependent ligand-gated ion channels
This depolarises cells and causes an action potential
What is anosmia?
Inability to smell
affects 5-10%
What is gustation?
Ability to taste
What are the 5 qualities we can taste?
Sweet: identification of energy-rich nutrients
Umami (meaty): recognition of amino acids
Salty: ensures proper dietary electrolyte balance
Sour and bitter: warns us against intake of noxious of poisonous chemicals
What is the mechanism of salty taste transduction?
Depends on the equilibrium potential of Na+ across the taste receptors
What is the mechanism of sour taste transduction?
Depends on the pH
H+ close K+ channels via cAMP which leads to depolarisation of the taste receptors
What is the mechanism of sweet taste transduction?
Happens via second messengers that lose K+ channels leading to repolarisation of taste receptors
What is the mechanism of bitter and umami taste transduction?
Caused by a secondary messenger induced increase in intracellular Ca2+ in the receptors
Ca2+ leads to neurotransmitter release
How does signalling of taste occur in the brain?
Cranial nerve 7, 9, 10 signal to the solitary tract in the brainstem where they synapse
The nerve fibres then continue ipsilaterally tot he ventral posterior nucleus of the thalamus
Projections from the thalamus then go into the insula which then projects into the secondary cortical taste area and the amygdala
