Anatomy of the vestibular system:

Question 1

What are the three scemi-circular canals and purpose?

Answer 1

Lateral/Horizontal = detects angular acceleration of the head when the head is turned.
Anterior/ superior = detects forward and back head movement, like nodding.
Posterior = detects rotation of the head around the antero-posterior (sagittal) axis, or in other words, rotation in the coronal plane. This occurs, for example, when one moves the head to touch the shoulders, or when doing a cartwheel (roll axis).

Question 2

What are the two otolith organs and purpose?

Answer 2

Utricle = lies horizontally in the ear and detects motion in the horizontal plane. LEFT TO RIGHT
saccule - (smaller than utricle) = oriented vertically, so it detects motion in the sagittal plane (up and down, forwards and back). Tilted vertical by about 30 degrees.

The utricle and saccule are part of the balancing system (membranous labyrinth) in the vestibule of the bony labyrinth (small oval chamber). They use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation.

purpose: Detect changes in linear acceleration and gravitational titles. they are different planes to respond maxiamally to motion in all directions.

Question 3

Semi-circular canal purpose?

Answer 3

• Provide information about angular changes in head velocity
• Lie orthogonal to each other, meaning they respond differently to different
  directions of movement
• Act as coplanar pairs (Push and pull effect, one side excited whilst the other is inhibited).

Question 4

Vestibular hair cells:

Answer 4

1) Type 1 - irregular nerve affarent = used for acceleration movement.
2) Type 2 - Regular nerve affarent = used for constant movement of the head.

Primary affrerents have resting firing rate RFR of 70-100 spikes per second.

Question 5

What happens inside the SSC:

Answer 5

1. You move head side to side. Fluid in SSC moves opposite to the direction of the head movement.
2. This bends the cupola to the side, stimulating hair cells.
3. This bends the cupula to the side, stimulating hair cells.
4. Depending on direction of movement, they make an inhibitory and excitatory response.
5. If excited, this causes them to increase fire rate on nerve fibres. Its either reacting more or reacting less, as one happens to one the other happens to the other.
6. Eventually sent back to the brain, to tell them what direction we are moving.
   Allows you to keep looking and have clear vision, even when head is moved.

Question 6

IMAGE 2 DETAIL:

Answer 6

• Cupula: This moves head side to side.
• Hair cells: Made up of blood, nerve fibres and connected tissue. they rest on:
• SSC
• Ampulla: Inside the flexible plug (cupula). It is widened at the end of the canal.
  Crsitae Ampullaris: at the bottom
  Primary affray fibres: nerve fibres

Question 7

Orientation of SCC

Answer 7

Lateral Anterior matches with lateral Posterior
Right posterior matches with right anterior.

Question 8

Otoconia

Answer 8

CaC03 Crystals.
3x of surrounding fluid.
Provides mass that helps keep head weighted down.
This is to ensure to move the hair cells when they move.

Question 9

What are the two blood supply (arteries) and VN and which parts of the rogan do they go to.

Answer 9

1. Superior VN and anterior vestibular artery
   * Lateral SCC
   * Anterior SCC
   * Utricle
2. Inferior VN and vestibulocochlear artery
   * Posterior SCC
   * Saccule