1.4: Physiology of Hearing and Balance Flashcards

1
Q

Give an overview of function of the three parts of the ear?

A

External = Sound collection

Middle = Mechanical force amplifier

Inner = Sound transducer and analyser

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2
Q

Describe sound?

What dictates pitch?

What dictates intensity (loudness)?

A

Sound is pressure wave caused by ossicating molecules

The frequency dictates pitch (high or low sound)

Amplitdue dictates intensity (loudness)

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3
Q

What frequency can humas percieve?

A

20-20,000 HZ

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4
Q

Describe briefly how the middle ear works an amplifier?

A

Due to ossicles

Ossicles work as a chain

Tympanic membrane vibrates and these vibrations pass through the ossicles to the oval window

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5
Q

Describe impendance matching?

A

The ratio of pressure in the tympanic membrane:oval window is about 18:1

This ensures the vibrations from air are concentrated enough to travel through fluid

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6
Q

What is the function of the Eustachian tube?

A

A ventilated pathway for middle ear mucosa

Held open by the tensor veli palantini and the levator palatine muscles

It’s function is to equalise the ears and dysfunction leads to middle ear negative pressure

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7
Q

Describe the oval window and the round window?

A

These are two openings of the cochlea to the middle ear

They allow the transmission of the pressure wave in enclosed canal and vibration of the basilar membrane

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8
Q

Describe the inner ear?

A

This is a curved spiral lamina

There is 2 and 1/2 turns around the central modiolus

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9
Q

Describe the cochlear structure?

A

There is a scala tympanic and scala vestibuli both filled with perilymph

Suspended between these two is the scala media which contains endolymph

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10
Q

Describe the organ of corti?

A

Found in the cochlea in the scala media

This contains the sensory cells - innner and outer hair cells

The inner cells are involved in recieving sound

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11
Q

Describe how the hair cells recieve sound?

A

A wave of liquid rushes over the hair cells, causing them to bend - this is called transduction

The bending of the hair cells generates action potentials

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12
Q

How does the brain determine the frequency of sound?

A

The hair cells bend and cause an action potential when a wave of liquid passes over them

The brain detects the frequency of sound depending which areas of the cochlea the action potential came from

Apex = Low

Base = High

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13
Q

Describe what happens once the inner hair cells produce action potentials?

How do you remember the central pathway?

Which specific part of the brain does the impulses go to?

A

These action potentials stimulate the 8th cranial nerve (vestibulocochlear) and then initiates central pathways

Central Pathway = E.COLI (from ear to brain)

Primary Audiotory Cortex (Superotemporal)

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14
Q

Describe the structure of the inner ear?

A

The inner ear is complex structure called the labrinyth - there is the bony labrinyth and the membranous labrinyth

There is 3 semicircular canals and the cochlea

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15
Q

Describe the otolith organs?

A

Utricle and Saccule

They have cilia projecting into a jelly like matrix - when the head moves, these fibres bend and percieve movement

There are sterocilia projecting in all directions so all planes of movement can be detected

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16
Q

What in contained in the gelatinous matrix above the otolith organs (Utricle and Saccule)?

Function?

A

Calcium Carbonate Crystals

These sit on top of the sterocillia to add weight to them. When the head moves, the force of gravity (due to the weight) pulls the cilia downwards and allows movement to be recognised

17
Q

Describe a cupula?

How does this work?

A

These sit in the ampulla of the semi-circular canals

When you move your head, the perilymph pushes against the cupula. This bends the sterocilia.

  • Increased firing on the side you turn to
  • Decreased firing on the side you turn away from

This is recognised as mismatch

18
Q

If you turn your head to the left, which side of the cupular is stimulated? Which is inhibited?

A

Turning head to left

  • Left side stimulated
  • Right side inhibited
19
Q

Describe the vestibulo-ocular reflex?

A

When you turn your head, the brain detects this

An triggering response is sent to the extraocular muscles of one side of the eyes, an inhibitory response is sent to the extraocular muscles of the other side of the eyes

The eyes move in the opposite direction from the head (Eg: Turn head right, eyes go left)

20
Q

Vestibulo-ocular reflex, fill in the blanks?

A turn of the head is detected which triggers an …. signal to the extraocular muscles on one side and an …. signal to the extraocular muscles on the other side?

A

A turn of the head is detected which triggers an inhibitory signal to the extraocular muscles on one side and an excitatory signal to the extraocular muscles on the other side

21
Q

If you turn your head to the right, describe the effect on the muscles of the RIGHT eye

  • There is an inhibitory signal to the …. muscle
  • There is an excitatory signal to the …. muscle

Fill in the blanks?

A

If you turn your head to the right

There is an inhibitory signal to the lateral rectus of the right eye

There is an excitatory signal to the medial rectus of the right eye

22
Q

Fill in the blanks:

If you turn your head to the right, the ocular muscles stimulated are (both eyes)?

The ocular muscles inhibited are?

A

Stimulated = Right medial rectus, left lateral rectus

Inhibited = Left medial rectus, right lateral rectus

23
Q

Describe the result of pathology/surgery which damages the vestibulo-ocular reflex?

A

Patient may feel dizzy all time (feel like they’re constantly turning)

Nystagmus present

24
Q

Describe how a vestibular schwanomma causes loss of balance?

A

This is a tumour of the vestibulocochlear nerve sheath

There is a slowly progressive loss of function - loss of function results in inability to regulate balance therefore loss of balance