18.) Vestibular System

Question 1

The vestibular system holds what function?

Answer 1

Provides sense of balance and spatial orientation.

Question 2

Describe the physiology of the otilith organs, and the structures that give them this function.

Answer 2

Sacculues and Utricles contain two types of hairs: 1.) Stereocilia - Shorter hair cells 2.) Kinocillium - common in the apex of hair cells; taller than hair cells The stereocilia project into a gelatinous cap called *otoconia.* Otoliths are calcium carbonate crystals on the tips of otoconia. This makes the ends of the stereocilia heavy, and therefore responsive to movement. When the head tilts, it causes the membrane to shift relative to the sensory epithelium, causing a shearing motion between the otolithic membrane and the macula (aka sensory epithelium). At rest, there is a basal rate of firing (without any stimuli). The movement of the head moves the stereocilia toward the kinocillium. The vestibular end organs will then open channels for depolarization. Movement of the stereocilia away from the kinocillium causes hyperpolarization, and thus no AP will be induced.

Question 3

What structures in the ear are responsible for detecting head movements? Be specific in what type of head movements they read.

Answer 3

1.) Otolith organs (utricle and saccule): membranous sacs. Register horizontal and linear accelerations of the head. 2.) Semicircular canals: membranous “canals.” Register rotational accelerations.

Question 4

What is the difference between the utricle and the saccule anatomy?

Answer 4

Saccule is oriented vertically, the utricle is oriented horizontally.

Question 5

What are the vestibular end organs?

Answer 5

semi circular canals and otolith organs. *Responsible for transduction.*

Question 6

What fluid is present in the otolith organs? What important solutes does it contain?

Answer 6

Endolymph. Low [Na] and high [K].

Question 7

What is vertigo?

Answer 7

perception of motion or spinning. This is due to residual flow of the endolymph through the semicircular canals.

Question 8

The fusion of vestibular and auditory nerves gives rise to…

Answer 8

the vestibulocochlear nerve.

Question 9

What are some of the other occular reflexes?

Answer 9

The following reflexes are second order vestibular nuclei where the spinal cord controls head and body position. *Vestibular spinal reflex*: extensor activity is induced in the side of the head where it is inclined, and flexor to the opposite. Vestibular cerebellar reflex

Question 10

What types of cells are present in the sensory epithelium?

Answer 10

Supporting cells and receptor cells

Question 11

Where is the ampula in the vestibular ear? What is its function?

Answer 11

Bulbous expansion at the base of the sensory epithelium of the semicircular canals. Function (??)

Question 12

What are the three basic head movements? What axis do they lie on?

Answer 12

Roll: y-axis Pitch: z-axis (yes head motion) Yaw: x-axis (no head motion)

Question 13

What is the macula?

Answer 13

Sensory epithelium in the otolith organs (??)

Question 14

Describe the path of stimulation by a physical stimulus in the vestibular ear to the recognition in the brain.

Answer 14

Vestibular end organs —> *medulla* [medial vestibular nucleus (semicircular canals) and lateral vestibular nucleus (otoliths)] —> cerebellum

Question 15

What are the cristae structures in the vestibular ear?

Answer 15

Sensory epithelium in the semicircular canals (??)

Question 16

What is Scarpa’s ganglia?

Answer 16

Ganglionic body that receives input from the vestibular system and synapses with bipolar afferents. (note there is a superior and infereior scarpas ganglia).

Question 17

Where is the cupula in the vestibular ear? What is its function?

Answer 17

Gelatinous area in the semicircular canals to which hair-cells can project into. Completely covers stereocilia. Function (??)

Question 18

What is the physical stimulus that causes transduction of the vestibular system?

Answer 18

Movement of head in combination with gravity. Note: Motion of air molecules will cause disturbance in the sensory epithelium too.

Question 19

What is the vestibular occular reflex (VOR)? Describe the pathway that confers to its function.

Answer 19

This is essentially how your eyes remain fixed on a certain position even while your head is moving/rotating. central projection of the vestibular system participating in various reflex pathways. e.g. Yaw type head movement to the left (x-axis). Left horizontal semicircular canal detect rotational head movement. Sends information to the left vestibular nucleus. Stimulates left oculomotor nucleus, inhibits left abducens nucleus. Stimulates right abducens nucleus, inhibits right oculomotor nucleus. Check out slide 11