Sensory: auditory and vestibular systems

Question 1

Describe the general structure of vertebrate ears

Answer 1

The pinna (outer ear) is the directional filter, the tympanic membrane sense the pressure difference by vibrating, the columella/ossicles transmit and amplifies/dampens vibrations, the vibrations are transmitted to fluid filled cochlea through the oval window, and travels through the vestibular canal to the tympanic canal, and finally the basilar membrane vibrates and stimulates the receptor cells (hair cells)

Question 2

What are the properties of the cochlear?

Answer 2

The basilar membrane changes along the length of cochlear. Specific areas vibrates most with specific frequencies (tones), highest frequencies in the first part, vice versa.

Question 3

Describe the receptor cells in vertebrate hearing.

Answer 3

Several stereovili and cilia forming collar. The cilia and villi are connected by tip links. Vibrations cause stereovilli/cilia to move relative to each other. The tip link directly pulls open stretch sensitive ion channels

Question 4

What is sound?

Answer 4

Oscillations in air pressure

Question 5

What happens in the inner ear?

Answer 5

Oscillations in air are transformed to oscillations in liquid

Question 6

What is Corti’s organ?

Answer 6

The tectorial membrane, inner ear hair cells, outer ear hair cells and the basilar membranee

Question 7

What happens in Corti’s organ when a cilia is diplaced?

Answer 7

Depolarization of hair cell

Question 8

Describe the depolarization of a hair cell.

Answer 8

Mechano-electric transduction:
–> influx of K+ and Ca2+ via tip-link ion channels –> influx of K+ –> depol of receptor potential –> spreads to the rest of the cell –> basolateral Ca2+ channels are gated –> Ca2+ influx –> transmitter release –> –>

Question 9

How does the ear actively control the dynamic range?

Answer 9

By attenuation, adaption and amplification

Question 10

Describe the complex nature of K+ in hair cells.

Answer 10

K+ depolarizes the cells from the endolymph (high [K+] liquid) in apical end
K+ hyperpolarizes hair cells by efflux in the basolateral end

Question 11

What are the differnce between inner and outer hair cells in function?

Answer 11

Inner: sends sound impression via afferent fibers
Outer: amplify and filter via electromotility and efferent input

Question 12

How does the K+ influx in the outer hair cells affect the cells?

Answer 12

K+ influx –> depol –> contraction

Question 13

Describe the signal route from the cochlear to the brain.

Answer 13

Cochlear –> spiral ganglion –> auditory nerve –> cochlear nuclei in rostral medulla –> superior olive in mid pons (either crossing or not)

(crossing) –> nucleus of lateral lemniscus –> inferior colliculus –> medial genculate (thalamus) –> primary auditory cortex

(not crossing) –> inferior colliculus –> medial genculate (thalamus) –> primary auditory cortex (only skipping the nucleus of lateral lemniscus)

Question 14

What is the area of speech perception called?

Answer 14

Wernicke’s area

Question 15

What is the speech producing center called?

Answer 15

Broca’s area

Question 16

How is the stimuli encoded in the CNS?

Answer 16

Via frequency: firing rate in n. cochlearis single axon is proportional with the local amplitude of basilar membrane

Question 17

How are the direction of sound source encoded?

Answer 17

By inter-aural time delay (two ears), and by difference in intencity (two ears)

Question 18

What does the otolith organs cover, and what is it?

Answer 18

Utriculus and sacculus
Perceive gravity

Question 19

Describe the overall structure of both the utriculus and sacculus. How do they differ?

Answer 19

Striola in the middle, utricular/saccular macula around, where the hair cells are oriented
Sacculus: vertical move, macula oriented away from the striola
Utriculus: horizontal move, macula oriented towards the striola

Question 20

Where are the otolith organs found?

Answer 20

Overlying the hair cells in the inner ear (in the vestibule)

Question 21

What is otoconia, and what is the purpose of it?

Answer 21

A layer of small crystals overlaying the gelatanous layer of the otolith membrane. Purpose: to make it heavy so movement can be sensed

Question 22

What are the difference between the inner and outer hair cells?

Answer 22

Inner: 95 % afferents but only 25 % of the hair cells, transducing sensory perception of sound
Outer: controlling the amplitude of different frequencies (amlification and filtering)

Question 23

What does a depolarization of the outer hair cells result in?

Answer 23

Contraction –> amplifying the vibrations

Question 24

What can turning curves be used for?

Answer 24

Identifying the different ganglia cells in the cochlear, as these have different turning curves matching the location on the cochlear

Question 25

How are the tonotopy throughout the auditory system?

Answer 25

Conserved: matching the frequence from lowest –> highest

Question 26

What is the semicircular canals, and where are they found?

Answer 26

The organs perceiving rotation
Next to the otolith organs in the inner ear

Question 27

Describe the semicircular organs.

Answer 27

Semicircle, with ampullae closest to the otololith organs –> where the sensory perception is taking place

Question 28

How does the hair cells in the vestibule depolarize?

Answer 28

Tip-link meachnically opening K+ channels when the hair cells are bend –> influx of K+

Question 29

What makes the hair cells in the vestibular system bend?

Answer 29

The hair cells is overlayed by the otolith membrane, which is a gelatinous layer with a crystal layer on top (otoconia). The crystals purpose is to have a heavy layer, that can move the gelatinous layer in response to movement –> hair cells are tipped –> K+ channels are gated –> depol

Question 30

How is a static gravitational force compared to acceleration on the ottolith organs?

Answer 30

Similar, but as wa have other senses too we can discriminate

Question 31

Describe the ampullae of the semicircular canal.

Answer 31

Capula surrounding a bundle of hair cells –> crista (enlargement, sensory perception takes place here) –> nerve fibers

Question 32

What liquid is found in the vestibular system?

Answer 32

Endolymph

Question 33

How does the endolymph function on the capula?

Answer 33

When the head is rotated, the endolymph will induce a pressure on the capula –> cupula displacement –> hair cells are depoled

Question 34

How are the hair cells oriented in the semicircular organs?

Answer 34

In the same direction in one ear, mirrowing the other –> opposite response in the two ears depending on the direcetion of rotation

Question 35

What happens if you keep rotating?

Answer 35

Adaptation: fire rate of ganglion cell will decrease as cupula is coming back to its original position

Question 36

Describe the central projections of vestibular sensation.

Answer 36

Vestibular nuclei –> ventral posterior nucleus of the thalamus–> parietal lobe

Question 37

What are the vestibular system used for?

Answer 37

1) postural control together with proprioception
2) eye position for stabilization/compensation for body/head movements

Question 38

What is nystagmus, and how many different types are there?

Answer 38

Uncontrolable rapid movements of the eye
4: optokinetic, post-rotation, vestibular and caloric

Question 39

Describe the vestibular ocular reflex (VOR).

Answer 39

When the head is rotated –> semicurcular organs react –> eyes rotate in opposite direction

Question 40

What is motion sickness caused by?

Answer 40

A mismatch between the VOR and the visual scene –> brain interprets as poison

Question 41

What are the functions of the vestibular cervicle reflex, and the vestibular spinal reflex?

Answer 41

VCR: stabalizing the head
VSR: stabalizing tthe body