5: Auditory System

Question 1

1

Hair Cell

Answer 1

If stereocilia moves towards the kinocilium:

1. increment of firing rate
2. depolarization
3. excitatory effect

If stereocilia moves away from the kinocilium

1. decrement of firing rate
2. hyperpolarization
3. inhibitory effect

Question 2

2.

Depolorisation of hair cells

Answer 2

Stereocilia move towards the kinocilium

1. mechanical opening of ion channel
2. Positive ions (K+) enter into the cell
3. Voltage –depended ion channels open and other positive ions enter into the cell
4. DEPOLARISATION
5. Ion channels close
6. Positive ions are pumped outside the cell.

Question 3

3.

Primary auditory area comprises:

Also give the flow of information between the auditory cortex and medial geniculate nuclei and inferior colliculi

Answer 3

Primary auditory area comprises BA 41 and 42

• From medial geniculate nuclei -> IV layer primary auditory cortex
• From auditory cortex (V layer ) -> medial geniculate nuclei
• From auditory cortex (VI layer) -> Inferior colliculi

Question 4

4

Lesions to the _________________________ and to the ______________________ do not give rise to monoaural deficits or compromise _______________ dramatically.

Answer 4

Lesions to the central auditory pathway and to the auditory cortex do not give rise to monoaural deficits or compromise auditory perception dramatically.

Question 5

5

Primary auditory cortex is organised in perpendicular columns:

Answer 5

• Summation columns and Suppression columns
• Neurons in SUMMATION columns respond strongly to the stimulation of either ear.
• Neurons in SUPPRESSION columns are exited by stimulation of one ear but inhibited by stimulation of the other ear (dominance)
• Summation and suppression columns are alternated and are the basis of ear dominance

Question 6

6.

In humans stimuli related to speech are overrepresented and lateralised

Answer 6

Question 7

7.

Musical stimuli are overrepresented in the..?

Answer 7

The right belt area

The belt is the area immediately surrounding the core of the primary auditory cortex.

Note that emotional aspects of speech, as well as prosody, are more linked to right hemisphere activity.

Question 8

8.

Descending pathway

from cortex to hair cells

Answer 8

Auditory cortex -> (V layer) medial geniculate nucleus -> (VI layer) inferior colliculus -> cochlear nuclei (olivary-cochlear path) -> outer hair cells

• Function of the descending pathway is not clear.
• However, it seems that it may modulate (reducing) sensitivity of the basilar membrane to low sound and sensitivity to frequency selectivity -> In turn, modulating attention

Question 9

9.

SOUND LOCALIZATION

Answer 9

• Interaural time differences: a sound coming from the right will reach the right ear first.
• Interaural level difference: a sound coming from the right is more intense in the right ear

Question 10

10

Interaural time differences:

What is the olivary complex?

Answer 10

Interaural time differences: a sound coming from the right will reach the right ear first.

Olivary complex (medial-superior) contains cells sensitive to differences in the time of arrival of auditory stimuli to the two ears.

Question 11

11.

Interaural level difference:

What regions are sensitive to sound intensity differences?

Answer 11

Lateral Superior Olive (LSO) and Medial Nuclei of Trapezoid Body (MNTB) contain cells sensitive to differences in sound intensity.

Question 12

12.

Describe the VESTIBULAR SYSTEM.

Answer 12

The vestibular system detects the position and the motion of the body in space by integrating information from peripheral receptors located in the inner ear on either side of the head.

Question 13

13.

Vestibular System - what are the vestibular sacs?

Answer 13

Vestibular sacs (saccule and utricle) and the Semicircular canals

• respond to acceleration of the head, or acceleration due to gravity
• The three semicircular canals detect head angular acceleration in the three direction - ROTATION-

Question 14

14.

Describe function of the semicircular canals

Answer 14

The three semicanals work in pairs (left and right)

When one canal is stimulated, the other side is inhibited.

Question 15

15.

What is the Vestibulo-ocular reflex

Answer 15

Vestibulo-ocular reflex: a reflex eye movement that elicits eye movement by stimulating the vestibular system.

Signals from the semicircular canals are sent as directly as possible (~10ms) to the eye muscles.

Question 16

16.

Describe the three neuron arc:

How do we turn our eyes left?

Answer 16

Information from the right semicircular canal travels :

1. through the Vestibulocochlear nerve (VIII)
2. Vestibular nucleus (ipsilateral)
3. Abducens nucleus (contralateral - VI)
4. Oculomotor nucleus (III)
5. innervate the left lateral rectus
6. Finally to the right medial rectus muscles of the eyes

Information from the left semicircular canal travels through the same path. BUT it triggers inhibitory process. All this results in a contraction of eyes muscles responsible for turning the eyes to the left.

Question 17

17.

What is the otolith?

Answer 17

The saccule and utricle, in turn, together make the otolith organs. They are sensitive to gravity and linear acceleration.

Because of their orientation in the head, the utricle is sensitive to a change in horizontal movement, and the saccule gives information about vertical acceleration (such as when in an elevator).

Question 18

18.

describe the vestibulocochlear nerve

Answer 18

Information from receptors travels through the vestibulocochlear nerve, which is a part of the auditory nerve then information reaches vestibular nuclei in the medulla

Question 19

19.

Vestibular Nuclei

Answer 19

The vestibular nuclei are the cranial nuclei for the vestibular nerve.

The fibers of the vestibular nerve enter the medulla oblongata on the medial side of those of the cochlear, and pass between the inferior peduncle and the spinal tract of the trigeminal.