Auditory and Vestibular Systems

Question 1

What is the stria vascularis?

Answer 1

A vascularised epithelium.

It is a unique body.

Question 2

What does the stria vascularis produce?

Answer 2

Endolymph

Question 3

What kind of afferents are balance and hearing?

Answer 3

Special somatic afferents

Question 4

Which nuclei are important in sound localisation and as relays for stapedial and tensor tympani reflexes?

Answer 4

• Superior olivary nucleus
• Nucleus of lateral leminiscus

Question 5

What is the organisation of fibres superior to the cochlear nucleu?

Answer 5

Some fibres are crossed and some are not, therefore input above this is essentially bilateral.

Question 6

Identify the structure indicated by the arrow

Answer 6

Medial geniculate body

Question 7

Identify the structure indicated by the arrow

Answer 7

Inferior quadrigeminal brachium

Question 8

Identify the structure indicated by the arrow

Answer 8

Inferior colliculus

Question 9

Identify the area

Answer 9

Primary auditory cortex

Question 10

Tonotopic organisation is present in the auditory cortex.

Explain what this means

Answer 10

• Fibres carrying information regarding low frequency sound end in the anterolateral part of the auditory cortex.
• Fibres carrying information regarding information regarding high frequency sound end in the posteromedial part of the auditory cortex.

Question 11

What results from damage to Broca’s area?

Answer 11

• Patients have difficulty producing language, often using few words and only saying the most important words in a sentence.
• They do not usually have difficulty comprehending language.
• Termed expressive aphasia.

Question 12

What results from damage to Wernicke’s area?

Answer 12

• Patients have difficulty comprehending language.
• These patients can manifest defects ranging from words out of order to meaningless words.
• Termed receptive aphasia.

Question 13

Which information is used by the vestibular system in maintenance of equilibrium?

Answer 13

• Vision
• Proprioception
• The vestibular apparatus (labyrinth)

Question 14

Describe the detection of motion in the vestibular system

Answer 14

• Depends on receptive hair cells
• Those in the utricle and saccule detect head position.
• Those in the semicircular canals detect movement.

Question 15

Each semicircular duct contains a swelling. Name this swelling and state what it lies within

Answer 15

• Ampulla
• Lies within a sensory organ called the crista ampullaris

Question 16

Describe the crista ampullaris

Answer 16

It consists of a core of connective tissue bulging into the lumen with a covering of epithelium containing hair cells with stereocillia.

Question 17

Describe the stereocilia in the semcircular ducts

Answer 17

Stereocilia is embedded in a dome of gelatinous material called the cupola.

Question 18

What happens in the semicircular ducts when the head turns?

Answer 18

• Movement of the fluid bows the cupola, and this in turn bends the stereocilia.
• This changes the amount of transmitter released by these cells.
• They have a resting output, so bending them one way increases output, while bending the other way decreases the output.

Question 19

The cupola has a similar density to the fluid in the canal. Why?

Answer 19

So that it responds to turning movement (angular acceleration), but not to static changes, as when one holds one’s head still at an angle.

Question 20

Describe the utricle and saccule

Answer 20

• These are 2 swellings in the vestibule.
• These fluid filled spaces are lined by simple cuboidal epithelium everywhere except a small patch of sensory epithelium in each called the macula.

Question 21

Describe the stereocilia of the hair cells

Answer 21

The stereocilia of the hair cells are embedded in a gelatinous layer which in turn has crystals of calcium carbonate and protein, called otoconia embedded in the surface.

Question 22

How does the density of the otoconia help with positional information?

Answer 22

Because the otoconia are denser than the endolymph fluid around them, they are affected by gravity and therefore provide information about the position of the head when it is static.

Question 23

Where are the superior-most vestibular nuclei found?

Answer 23

Just medial to the inferior cerebellar peduncle

Question 24

What is the main function of the lateral vestibulospinal pathway?

Answer 24

Mostly to extensor (anti-gravity) muscles

Question 25

What is the main function of the medial vestibulospinal pathway?

Answer 25

• Principally to the neck, sternocleidomastoid and trapezius.
• Medial vestibulospinal tract also innervates the upper spinal cord and motor neurons to the spinal accessory nerve to promote movement of the head to help maintain balance and fixation of gaze.

Question 26

Describe the projection of vestibular information into the cerebral cortex

Answer 26

• Bilateral
• Less well defined than for other senses
• Areas where vestibular information converges include:
  
  • An area of the parietal cortex just posterior to the area of the postcentral gyrus that represents the hand and mouth.
  • An area just rostral to the primary auditory cortex.