Lecture 23 - Vestibular system

Question 1

The vestibular system provides the brain with

Answer 1

information about head movment and location

Question 2

Vestibular system is concerned with

Answer 2

our sensation of balance

Question 3

The vestibular system and its stimuli

Answer 3

Detects angular (rotational) and linear accelerations of the head (these are the stimuli) 
Not velocity, it is acceleration because it is the rate of change of velocity 
Pure linear acceleration = horizontal and vertical accelerations of our body where our head is moving with respect to gravity 
Angular acceleration = head rotation, nodding, shaking head, lean head from side to side

Question 4

Pure linear acceleration

Answer 4

Pure linear acceleration = horizontal and vertical accelerations of our body where our head is moving with respect to gravity

Question 5

Angular acceleration

Answer 5

Angular acceleration = head rotation, nodding, shaking head, lean head from side to side

Question 6

What does the vestibular system do?

Answer 6

(Detect stimuli and then) Generates reflexes to compensate for head movement and the perception of movement in space
Provides information to help with maintenance of right posture
Provides information for conscious awareness of position/movement/acceleration of the head and body (in relation to space)

Question 7

Vestibular apparatus

Answer 7

Series of membranous filled tubes
2-parts:
The semi-circular canals and the otolith organs
3 parts of the semicircular channels = anterior, posterior and horizontal
Otolith - bulbous parts under semicircular canals - utricle and saccule
Part of the inner ear, but concerned with balance and spatial orientation of the head and body, not with sound (nothing to do with hearing)

Question 8

The two parts of the vestibular apparatus

Answer 8

Semicircular canals and the otolith organs

Question 9

Semicircular canals

Answer 9

Sensitive to angular acceleration during head rotation
Work in pairs, one set in each ear
Work together to brain with information about movements
Aligned in three axes
Each most vigorously stimulated by acceleration in its preferred plane
Filled with endolymph which is like intracellular fluid with low sodium and high potassium
Anterior, posterior and horizontal all responsible for responding to a type of movement

Question 10

Anterior semicircular canal

Answer 10

Anterior = stimulated by acceleration along the sagittal plane e.g. nodding yes

Question 11

Posterior semicircular canal

Answer 11

Posterior = largest, stimulated by acceleration in the coronal plane e.g. stretch/tilt neck from side to side

Question 12

Horizontal semicircular canal

Answer 12

Horizontal = smallest, stimulated by acceleration along the transverse plane e.g. when you are checking for traffic before you cross/saying no movement

Question 13

The ampulla

Answer 13

An ampulla is a part of the inner ear that surrounds sensory receptors that are responsible for movement related sensory experiences like spatial awareness and pressure change. Ampullae (the plural of ampulla) are located throughout the semicircular canals of the inner ear.

Within the ampulla there are lots of hair cells, from these hair cells we have a lot of cilia that project out into the duct/lumen of the semicircular canal. Hair cells sit in a gelatinous blob called the cupola. The cupola blocks the lumen of the semicircular canal which means that fluid in the semicircular canals cannot be moved very freely. SO what happens when we have head movements is that the endolymph has inertia meaning that it pushes back in the opposite direction which puts pressure on the side of the cupola and causes it to bend/change direction which also moves the hair cells

Question 14

Resting discharge rate in terms of vestibular signal transduction

Answer 14

Resting discharge rate means vestibular hair cells can detect movement in 2 directions
When standing upright and not moving at all
The resting rate means that the rate can be increased or decreased which serves as a method for how we can detect movement in two different directions for each of our semicircular canals

Question 15

Resting activity in terms of vestibular signal transcution

Answer 15

There is a resting discharge rate

Question 16

Inhibition (hyperpolarisation) in terms of vestibular signal transduction

Answer 16

Inhibition (hyperpolarisation)
My notes =
Cupula and hair cells bend towards the smallest cilia then the mechanically gated ion channels close so no neurotransmitter release so get a reduction in the firing of the vestibular nerve

His notes =
Bending of cilia towards shortest cilia
Closing of mechanically- gated ion channels
Hyperpolarisation
Closing of voltage-gated Ca2+ channels
No neurotransmitter release, decreased firing rate

Question 17

Stimulation (depolarisation) in terms of vestibular signal transduction

Answer 17

My notes =
If hair cells bend towards the longest cilia, get opening of mechanically gated ion channels (endolymph) therefore have potassium that comes in and causes depolarisation of the hair cell, wave of depolarisation of the hair cell, wave of depolarisation and opening of voltage gated calcium channels, the presence of calcium promotes the release of vesicles containing neurotransmitter to be released on the afferent nerve fibres of the vestibular nerve so get an increase in the firing rate of the vestibular nerve

His notes =
Bending of cilia towards longest cilia
Opening of mechanically- gated ion channels
Potassium influx and subsequent depolarisation of hair cell
Opening of voltage-gated Ca2+ channels and Ca2+ influx
Release of neurotransmitter, increased firing rate

Question 18

Hair cells are embedded in the

Answer 18

cupula

Question 19

Semicircular canals need to

Answer 19

detect angular acceleration in 3 directions

Question 20

Otolith organs made up of

Answer 20

Utricle and saccule

Question 21

Otolith organs detect

Answer 21

Utricle and Saccule
Detect linear acceleration (as opposed to angular)
Moving of our head in relation to gravity e.g. going up a lift or moving back and forward when you slam the breaks on a car

Question 22

Utricle and the movement it detects

Answer 22

Utricle approximately horizontal when standing (hair cells within it are oriented vertically)
Therefore it is detecting horizontal linear acceleration as this is what is going to cause the cilia to bend

Question 23

Saccule and the movement it detects

Answer 23

Saccule approximately vertical when standing (hair cells within it are oriented horizontally)
Therefore will detect vertical linear acceleration

Question 24

Transduction pathway of semicirulcar canals vs otolith organs

Answer 24

Otolith organs have different structure to semicircular canals BUT have same transduction pathways as semicircular canals

Question 25

Resting acitvity in otolith organs

Answer 25

Resting discharge rate

Question 26

Stimulation (depolarisation) in otolith organs

Answer 26

Bending of cilia towards longest cilia Opening of mechanically- gated ion channels Potassium influx and subsequent depolarisation of hair cell Opening of voltage-gated Ca2+ channels and Ca2+ influx Release of neurotransmitter, increased firing rate

Question 27

Inhibition (hyperpolarisation) in otolith organs

Answer 27

Bending of cilia towards shortest cilia Closing of mechanically- gated ion channels Hyperpolarisation Closing of voltage-gated Ca2+ channels No neurotransmitter release, decreased firing rate

Question 28

Macula in otolith organs

Answer 28

Macula = Hair cells sit in an epithelial cell layer called the macula, hair cells then project up into the lumen of the otolith organs and sat on top of this is otoconia which are small stones of calcium carbonate (CaCO3) and what these stones do is act as weights, have their own inertia but do not shift as fast so actually put pressure down on hair cells and cause them to deflect

Question 29

Central pathways

Answer 29

When they release neurotransmitters and create the EPSP on the afferent nerve fibres they project to the vestibular nuclei in the brain Axons project to vestibular nuclei in brainstem From here they project into the structure called the medial longitudinal fascicles up to the oculomotor nucleus and information from here is sent to the muscles of our eyes, also motor neurons in head and neck to stabilise body Info used to Stabilise eyes Stabilise the head Maintain balance

Question 30

Vestibular disorders list

Answer 30

vertigo motion sickness bedspins tumours

Question 31

Vertigo

Answer 31

Caused by disease affecting the vestibule or its afferent fibres Illusion of movement, dizziness

Question 32

Motion sickness

Answer 32

Caused by mismatch between visual and vestibular information Sea legs tablets – Meclozine Hydrochloride (don’t need to remember) Stare at horizon to show boat is moving up and down to prevent mis match

Question 33

"Bedspins"

Answer 33

Caused by alcohol Ethanol infiltrates cupula, lowers density and causes it to “float”, bending hairs on hair cells and creating perception of movement Gelatinous structure that surrounds the hair cells Alcohol has a lower density than water does

Question 34

Tumours

Answer 34

(Note - a lot of disorders that affect our hearing system often also effect our vestibular system because they are affecting our inner ear) Acoustic neuroma (vestibular schwannoma) Abnormal growth along vestibulocochlear nerve Glomus Tympanicum Ear Canal cancer

Question 35

Ototoxic drugs

Answer 35

toxic to the ear Over 600 medications are known to be harmful to hair cells Can result in temporary or permanent hearing loss and disorders of balance Hair cells damaged and disordered which is permanent Antibiotics are the worst culprits

Question 36

The vestibular system can detect movement in two directions BECAUSE

Answer 36

the vestibular nerve has a resting discharge rate