12) Vestibular System Flashcards
What are the 2 otolith organs?
What is their orientation and function?
What is their structure, same for both?
Utricle: Orientation = horizontal
Function = Detects head tilt and linear acceleration in horizontal plane
Saccule: Orientation = vertical
Function = Detects head tilt and linear accel. in vertical plane
Structure: From bottom to top: hair cells extend into a gelationous layer below the otolithic membrane. On top are heavy calcium carbonate crystals.
Vestibular hair cell Characteristics?
How are they different from auditory hair cells?
- Generate graded potentials, NOT APs
- Potassium responsible for both depolarization and hyperpolarization
Differences:
- Release neurotransmitter at rest
- Have a kinocilium
- Movement of sterocilia bundle towards kinocilium = depolarization
- Movement of stereocilia bundle away from kinocilium = hyperpolarization
What is the hair cell organization for each otolith organ?
Organization
Striola = division of hair cells into 2 populations of opposing polarity
Utricle - kinocilium toward striola
Saccule = kinocilium away from striola
Because of the kinocilia orientation and the striola being curved, every direction of tilt depolarizes some cells, hyperpolarizes others, and some don’t change.
What are the 3 semicircular canals and what axis does each one account for?
How are they oriented to one another?
What is at each of their bases?
- Superior = Pitch - rotation around x-axis
- Horizontal = Yaw - rotation around y-axis
- Posterior = Roll - rotation around z-axis
They are oriented 90 degrees relative to one another
At the base of each is an ampullae - bulbous chambers
What is inside an ampulla?
What is it’s function?
Inside is a dense, gelatinous structure called the cupula
- The cupula is flexible, but forms a barrier through which endolymph cannot pass
- The endolymph flow distorts the cupula, which bends the hair bundle
- This leads to an increase/decrease in NT release
- The endolymph flow distorts the cupula, which bends the hair bundle
What happens to the ampulla during acceleration?
What happens to the ampulla during deceleration?
What happens to the ampulla during constant velocity?
Where are the cell bodies of vestibular afferent neurons located?
What do these afferents project to?
Hair cells depolarize or hyperpolarize vestibular afferent neurons.
Vestibular afferents generate APs
The cell bodies are located in the vestibular ganglion called Scarpa’s ganglion
They project to the vestibular nuclei in the medulla and pons
What is the ascending cortical pathway that carries vestibular information?
What are the senses involved?
There is no single primary vestibular cortex, there is a distributed set of cortical areas dedicated to the vestibular info arriving
- B/c of this, many senses are integrated to help our propioception - sense of orientation of body in space
Senses involved:
- sense of self-generated active movements vs passive movements from external forces
- sense of self-motion - vection
Dysregulation - vertigo
What is the Vestibulo-ocular reflex?
What happens without it?
The VOR produces eye movements that counter head movements.
It allows us to focus our gaze on a point even while head/body is moving.
Loss of VOR = oscillopsia or bouncing vision
Function of the Vestibulo-cervical reflex and its nucleus?
Function of the Vestibulo-spinal reflex and its nucleus?
Loss of these leads to what?
VCR: Postural adjustments of the head and body reflexes. Medial vestibular nucleus
VSR: Postural adjustments of the body - maintenance of posture and balance. Lateral vestibular nucleus
Loss of these = dimished head and postural stability = gait deviations and difficulty balancing
