Vestibular Apparatus and Equilibrium

Hearing and balance are provided by the structures of ?

• The Inner Ear

Ear Structure Diagram

Equilibrium is a sense of ?

• Balance & Orientation 

• In respect to gravity

• provided by the Vestibular Apparatus

Static Equilibrium is sensed when?

• The Head is still.

Dynamic Equilibrium is sensed when ?

• The head is moving.

Vestibular Apparatus Diagram Structure?

Vestibular Apparatus is located within what bones of the Skull?

• Temporal Bones

What does the Vestibular Appartus consist of?

• 3 Semicircular Canals
  - Posterior, Anterior & Lateral

• Otolith Organs
  - Utricle & Saccule

The Semi CC detect?

• Rotational and Angular Forces

The anterior, posterior and lateral canals are set at?

• 90 Degree Angles

• To Detect Rotational Forces

Movement of the head results the disturbance of a fluid called?

• Endolymph

How many Otolith organs are there?

• 2

• Saccule & Utricle

What is the role of the 2 Otolith Organs?

• Saccule
  - Detect Vertical Acceleration

• Utricle
  - Detects Horizontal Acceleration

The sense of equilibrium is transduced by specialised?

• Neuroepithelial Cells called ‘Hair Cells’.

The Hair cells excite the dendrites of Sensory nerves which form what nerve?

• Vestibulocochlear Nerve (VII)

Vestibular Apparatus Cross Section

Labyrinth Diagram

Internal Structure of the Vestibular Apparatus:

Within the temporal bone, there is a hollow structure known as the?

• Bony labyrinth

Internal Structure of the Vestibular Apparatus:

Within this bony labyrinth sits another structure called the?

• Membranous Labyrinth

Internal Structure of the Vestibular Apparatus:

the membranous labyrinth which is suspended in place by a solution called?

• Perilymph

Internal Structure of the Vestibular Apparatus:
The perilymph sits between the bony labyrinth and the?

• Membranous Labyrinth

Internal Structure of the Vestibular Apparatus:
The membranous labyrinth itself is filled with an extracellular solution called?

• Endolymph

• also contains the sensory structures of equilibrium.

Endolymph is the only Extracellular solution that?

• That has a very high K+ concentration (greater than that of the intracellular fluid)

• And much lower concentrations of Na+ and Ca2+ than other extracellular solutions.

depolarisation of hair cells occurs as the result of inflow of ….. ? into the cell as it moves down its concentration and electrical gradient.

• K+

Location of the Sensory Cells:
Within the membranous labyrinth the sensory cells are bundled together at specific locations called?

• The ampullae at the base of each semicircular canal

• The maculae within the utricle and saccule.

Hell Cells are capable of?

• Depolarization & Hyperpolarization

• And Releasing Neurot at Basolateral membrane.

Sensing Motion Diagram

Each hair cell has ? stereocilia on its apical surface

• 20 -50Each hair cell has 20-50 stereocilia on its apical surface

Movement of the Largest Cilla called … causes?

• Kinocilium causes Depolarization or Hyperpolarization of the cell.

Sensing Motion:
At rest cilla?

• Stand up straight.

Sensing Motion:

This tonic activity of firing provides the brain with?

• Static Equilibrium

Sensing Motion:

The frequency of discharge is altered if the?

• The Stereocilia move

Sensing Motion: If the stereocilia move towards the kinocilium the hair cell?

• Depolarizes

• Exciting the Sensory neuron and generates a greater frequency of action potentials.

Otolith Organs:
The macula is the site where hair cells are found within ?

• The utricle and saccule.

Otolith Membrane:

the cilia of these hair cells are embedded in a ?

• Gelatinous otolithic membrane.

Otolith Membrane:
The otolithic membrane contains

• Otoliths

• Which increase the Mass of the Cell.

• Provides more Inertia

Otolith Organs:

What are Otoliths?

• Microscopic calcium carbonate crystals

When the head is tilted up or down, gravitational force pulls on the?

• Otoliths & Otolithic Membrane

• Results in Depolarization or Hyperpolarization

Semi CC Diagram

Rotational Acceleration Diagram

Semi Circular Canals:

The hair cells of each semicircular canal structure are located at the?

• Membranous Ampullae

• At the Base of the Semicircular Canal

Semicircular Canals:

The cilia of these hair cells emanate out and are embedded in a ?

• Gelatinous Membrane

• Called the Cupula

Semicircular Canals: The Cupula is found where?

• Inside the ampulla of each semicircular canal

Semi Circular Canals:

When the head moves the Endolymph?

• Lags Behind

Semi Circular Canals:

What is the result if the Endolymph lagging behind as the head moves?

• The endolymph is pushed up against the cupula which results in bending of the cupulas as well as the embedded cilia of the hair cells

• This results in stimulation/inhibition the hair cells

Neural Pathways Diagram:

VIII nerve is the ?

• Vestibulocochlear Nerve (VII)

From the vestibular nuclei, signals can be sent to many different areas of the?

• CNS

Axons are projected from the Vestiublar Nuclei to the ?

• Oculomotor Centre of the Brainstem

  • Control of Eye Movements

• Spinal Cord
  - Body movements.

Motion sickness occurs due to ?

• Imbalance between Visual & Equilibrium Senses.

Vertigo is caused by anything that effects the firing mode of the ?

• Vestibulocochlear Nerve (VII)

• Most common cause is a Viral Infection

What is Menieres Disease?

• Chronic Inner Ear Disorder

• Leading to Recurrent Vertigo.

What Causes Menieres Disease?

• Excessive endolymph within the membranous labyrinth

• which can produce excessive dilatation, damage or rupture of the membranous labyrinth.