Lecture 23 - Vestibular system Flashcards
The vestibular system provides the brain with
information about head movment and location
Vestibular system is concerned with
our sensation of balance
The vestibular system and its stimuli
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
Pure linear acceleration
Pure linear acceleration = horizontal and vertical accelerations of our body where our head is moving with respect to gravity
Angular acceleration
Angular acceleration = head rotation, nodding, shaking head, lean head from side to side
What does the vestibular system do?
(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)
Vestibular apparatus
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)
The two parts of the vestibular apparatus
Semicircular canals and the otolith organs
Semicircular canals
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
Anterior semicircular canal
Anterior = stimulated by acceleration along the sagittal plane e.g. nodding yes
Posterior semicircular canal
Posterior = largest, stimulated by acceleration in the coronal plane e.g. stretch/tilt neck from side to side
Horizontal semicircular canal
Horizontal = smallest, stimulated by acceleration along the transverse plane e.g. when you are checking for traffic before you cross/saying no movement
The ampulla
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
Resting discharge rate in terms of vestibular signal transduction
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
Resting activity in terms of vestibular signal transcution
There is a resting discharge rate
Inhibition (hyperpolarisation) in terms of vestibular signal transduction
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
Stimulation (depolarisation) in terms of vestibular signal transduction
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
Hair cells are embedded in the
cupula
Semicircular canals need to
detect angular acceleration in 3 directions
Otolith organs made up of
Utricle and saccule
Otolith organs detect
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
Utricle and the movement it detects
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
Saccule and the movement it detects
Saccule approximately vertical when standing (hair cells within it are oriented horizontally)
Therefore will detect vertical linear acceleration
Transduction pathway of semicirulcar canals vs otolith organs
Otolith organs have different structure to semicircular canals BUT have same transduction pathways as semicircular canals
Resting acitvity in otolith organs
Resting discharge rate
Stimulation (depolarisation) in otolith organs
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
Inhibition (hyperpolarisation) in otolith organs
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
Macula in otolith organs
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
Central pathways
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
Vestibular disorders list
vertigo
motion sickness
bedspins
tumours
Vertigo
Caused by disease affecting the vestibule or its afferent fibres
Illusion of movement, dizziness
Motion sickness
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
“Bedspins”
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
Tumours
(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
Ototoxic drugs
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
The vestibular system can detect movement in two directions BECAUSE
the vestibular nerve has a resting discharge rate
