Sensory Transduction: Vestibular System Flashcards
What is the function of the vestibular system ?
- Provides information concerning gravity, rotation and acceleration
- Serves as a reference for the somatosensory & visual systems
- Contributes to integration of arousal, conscious awareness of the body via connections with vestibular cortex, thalamus and reticular formation
Allows for:
- gaze & postural stability
- sense of orientation
- detection of linear & angular acceleration
Basically answers Where am I going? and Which way is up?
Describe the anatomy of the bony labyrinth indicated and state what the vestibular organ is
Vestibular organ = utricle, saccule, and the three semicircular ducts
What are the specific functions of the following:
- Otolith organs - saccule and utricle
- Semicircular canals
- Otolith organs - saccule and utricle sense linear motion and gravity (the straight lines or X, Y axis etc in pic); saccule senses movements in the vertical/ sagittal plane and utricle senses movement in the horiztonal plane
- Semicircular canals - sense rotational movements (around the X, y and Z axis in the pic)
Give a brief overview of the vestibular system
- Initially the peripheral sensory apparatus (vestibular organ) detects & relays information about head angular & linear velocity to central processing system.
- Then the central processing system processes information in conjunction with other sensory inputs for position and movement of head in space
- Then the motor output system - Generates compensatory eye movements and compensatory body movements during head & postural adjustments
Describe the pathway for detection of movements in the semicircular canals
- Each canal is filled with endolymph and contains motion sensors within the fluids.
- At the base of each canal, the bony region of the canal is enlarged which opens into the utricle and has a dilated sac at one end called the osseous ampullae.
- Within the ampulla is a mound of hair cells and supporting cells called crista ampullaris. These hair cells have many cytoplasmic projections on the apical surface called stereocilia which are embedded in a gelatinous structure called the cupula.
- As the head rotates the duct moves but the endolymph lags behind. This deflects the cupula and bends the stereocilia within. The bending of these stereocilia alters an electric signal that is transmitted to the brain.
- Hence detecting the movement
Describe how the otolith organs sense movement
- Hair cells lie in the macula (called stereocilia), stereocilia are oriented in all directions
- Crystals of calcium carbonate called otoconia (otoliths = ear dust) are on the otolithic membrane
- With linear movements and gravity the otoconia will move on the otolithic membrane causing the hair to move ==> movements sensed
Describe the pathway of sensations detected by the vestibular organ
Signals sent to the vestibular nerve and then pathway followed in pic
What are the 3 main vestibular reflexes and describe them?
- Vestibulo-occular reflex - keeps the eyes still in space when the head moves. Designed to maintain clear and stable vision in the presence of head movements. Causes eyes to move in the opposite direction to head movement (stare at something and move head)
- Vestibulo-colic reflex – keeps the head still in space, or on a level plane when you walk.
- Vestibulo-spinal reflex – adjusts posture for rapid changes in position.
Appreciate that the vestibular system is co-orindated with multiple other inputs
Describe vestibular dysfunction and give the classic example of it
Vision was disturbed by head movements as small as those induced by the beat of his heart while at rest. (referring to pic)
Numerous agents, including aminoglycoside antibiotics e.g. gentamicin and some chemotherapy agents, can cause ototoxicity. Also alcohol can cause vestibular dysfunction as it enters into the capula and causes stimulation of hair cells
