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Head and Neck Anatomy > The Ear 2 > Flashcards

The Ear 2 Flashcards

1
Q

How do vibration of the perilymph reach the apex of the cochlea?

A

The vibrations are created by movement of the footplate of the stapes and they travel along the scala vestibuli to the apex of the cochlea.

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2
Q

What is the path of the vibrations from the apex of the cochlea?

A

They pass through the helicotrema and into the scala tympani and then downwards to the base of the cochlea and the fenestrae cochleae.

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3
Q

What is the fenestrae cochleae closed over by?

A

It is closed over by the secondary tympanic membrane.

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4
Q

What are movements at the secondary tympanic membrane like compared to movements at the footplate of the stapes and what is the significance of this?

A

Movements occur at the secondary tympanic membrane that are opposite in direction to those of the footplate of the stapes.

The significance of this is that pressure in the inner ear perilymph does not become excessive.

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5
Q

Describe the semicircular canals?

A

These lead posteriorly from the vestibule and they are named anterior/ superior, posterior and lateral.

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6
Q

What is present at one end of each of the semicircular canals?

A

At one end, each of them has a dilation or ampulla which contains organs that are sensitive to body movement.

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7
Q

How are the anterior and posterior canals orientated?

A

They are vertically placed.

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8
Q

What axis does the posterior canal lie in?

A

It lies in the long axis of the petrous temporal bone.

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9
Q

What axis does the anterior canal lie in?

A

It lies at right angles to the axis of the posterior canal.

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10
Q

Why is the anterior canal called the superior canal?

A

When the head is in a horizontal position, the anterior canal lies at a higher level than the posterior canal.

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11
Q

What is the arcuate eminence?

A

The anterior or superior semicircular canal raises a bony eminence on the anterior aspect of the petrous temporal bone in the middle cranial fossa and this is called the arcuate eminence.

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12
Q

How is the lateral semicircular canal orientated?

A

This lies horizontally.

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13
Q

What do the cavities and the canals of the bony labyrinth contain?

A

They contain a series of membranous sacs and tubes filled with endolymph.

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14
Q

How does the membranous labyrinth compare to the cavities and canals of the bony labyrinth?

A

It is smaller than these cavities and canals.

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15
Q

What are the 2 sacs of endolymph that lie within the vestibule?

A

Utricle behind.

Saccule in front.

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16
Q

What are the semicircular ducts continuous with posteriorly?

A

They are continuous the utricle.

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17
Q

What do the semicircular ducts lie within?

A

They lie within the bony semicircular canals.

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18
Q

What does the saccule communicate with in front?

A

In front it communicates with the cochlear duct.

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19
Q

What does the cochlear duct lie within?

A

It lies within the bony cochlear canal.

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20
Q

What is the endolympathic duct?

A

This is a blind ending duct that arises from the utricle and the saccule.

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21
Q

What is the path of the endolymphatic duct?

A

It extends through the petrous temporal bone in the bony aqueduct of the vestibule, comes to lie against the dura in the posterior cranial fossa on the posterior aspect of the petrous temporal bone.

In this position, the dura covers a hole in the petrous temporal bone here.

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22
Q

What happens to the endolymph in the endolymphatic duct as this duct lies against the dura in the posterior cranial fossa on the posterior aspect of the petrous temporal bone?

A

At this point, endolymph is resorbed back into the circulating blood stream from the endolymphatic duct via the vascular plexus in the specialised epithelial cells here.

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23
Q

How is the saccule joined to the duct of the cochlea in front?

A

It is joined to the duct of the cochlea in front by the ductus reuniens.

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24
Q

What is the specialised neuroepithelium in the utricle and the saccule sensitive to?

A

It is sensitive to the pull of gravity.

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25
Q

What is part of the wall of the utricle thickened by?

A

It is thickened by a specialised organ called the macula.

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26
Q

What is the thickening in the wall of the saccule called?

A

This is called the macula of the saccule.

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27
Q

How is the position of the macula of the saccule in relation to the macula of the utricle?

A

They are at right angles to each other.

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28
Q

What are the semicircular canals of the bony labyrinth occupied by?

A

They are occupied by 3 semicircular ducts.

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29
Q

What do the 3 semicircular ducts open into?

A

They open into the utricle.

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30
Q

What happens to the ducts near the orifices?

A

The ducts are dilated as ampullae and each contains a projection called the ampullary crest.

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31
Q

What do the maculae of the utricle and the saccule signal?

A

They signal any alterations in the position of the head with reference to the pull of the gravity.

Information from these organs produces appropriate alterations in muscle tone throughout the body. The supporting muscles of the neck and the muscles that are important for eye movement are usually concerned.

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32
Q

What are the maculae referred to as?

A

They are referred to as organs of static balance.

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33
Q

What is the epithelium of the maculae and ampullary crest made up of?

A

It is made up of hair cells and supporting cells.

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34
Q

What are the bases of most hair cells associated with?

A

They are associated with nerve terminals that belong to the afferent fibres of the vestibular nerve.

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35
Q

What overlies each macula?

A

A gelatinous mass or otolithic membrane which contains crystalline bodies called otoconia.

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36
Q

What are alterations in the position of the head relative to the line of gravity reflected in?

A

They are reflected in the drag of the otolithic membrane on the sensitive hair cells.

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37
Q

What do the ampullary crests of the semicircular canals signal?

A

These signal angular acceleration of the head and not static balance.

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38
Q

What are the ampullary crest covered with?

A

They are covered with a gelatinous dome shaped cupula which rests on the surface of each ampullary crest.

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39
Q

What are the minute stereocilia of sensitive hair cells on the ampullary crest embedded into?

A

They are embedded into the substance of the cupula.

40
Q

What does the cupula do to the flow of endolymph around the semicircular canals?

A

It entirely blocks out the flow of endolymph around the semicircular canals.

41
Q

How is the cupula drawn from side to side?

A

Drag and currents in the endolymph which are set up during movement press against the cupula and draw the cupula from side to side.

42
Q

What does drawing the cupula from side to side stimulate?

A

It stimulates the hair cells which discharge nerve impulses accordingly.

43
Q

What do vestibular nerve fibres have continuously?

A

They have a continuous basal discharge.

44
Q

What happens when we bend the cupula?

A

Bending the cupula to one side increases the frequency of discharge and bending it to the other side decreases the frequency of discharge.

45
Q

What is the cochlear duct?

A

This is a spirally arranged tube that is concerned with hearing.

46
Q

Where does the cochlear duct start and end?

A

It starts below at the ductus reuninens and spirals to a closed end near the apex of the cochlea.

47
Q

What is the floor of the cochlear duct made of?

A

This is the basilar membrane that stretches from the bony spiral lamina to the outer wall of the cochlear canal.

48
Q

What does the cross section of the cochlear duct look like?

A

It has a triangular cross section.

49
Q

Above the attachment of the basilar membrane to the outer wall of the cochlear canal, what do we have?

A

There is a spiral prominence on the outer wall of the cochlear canal.

50
Q

What is the epithelium above the spiral prominence of the outer wall of cochlear canal like?

A

It is highly vascular and it is called the stria vascularis.

51
Q

What do we think the function of the stria vascularis is?

A

We think that it is important for the production of endolymph and that it is also useful in maintaining the ionic composition of the endolymph.

52
Q

What is the spiral organ of Corti?

A

This is the specialised receptor organ for hearing that lies within the cochlear duct on the basilar membrane.

It is composed of several parts.

53
Q

Inner and outer …. ….. sit on the basilar membrane.

A

hair cells.

54
Q

What do the inner and outer hair cells on the basilar membrane form?

A

They form pillars that slope towards each other and create a triangular tunnel of corti between them.

55
Q

What is the tectorial membrane?

A

The outer hairs that sit on the basilar membrane (or stereocilia) are embedded in a fibrogelatinous membrane which extends above them and this is called the tectorial membrane.

56
Q

Are the sterocilia of the inner hair cells also embedded into the tectorial membrane?

A

No, they are free in the tectorial membrane.

57
Q

What are the steps that make up the basic mechanism of hearing (1)?

A
  1. pinna collects sound vibrations
  2. vibrations travel through external auditory meatus to the tympanic membrane
  3. ossicles move and transmit vibrations towards the inner ear
    1. force per unit area at the footplate of the stapes is amplified 20 times.
  4. stapedius and tensor tympani muscles dampen excess vibrations
    1. stiffen the chain of ossicles to do this
  5. vibration of stapes creates pressure waves in fluid within the vestibule
  6. pressure waves are conducted via perilymph of scala vestibuli and scala tympani to basilar and vestibular membranes that lie between them
  7. cochlear system cant be closed off completely or the pressure within it would rise too much and be excessive therefore every inward excursion of the oval window produces a pressure wave through scala vestibuli, around apex of cochlea, through scala tympani and it then dissipated as an outwards movement of the secondary tympanic membrane of the round window.
58
Q

What steps make up the basic mechanism of hearing (2)?

A
  1. sound energy enters oval window, travels up scala vestibuli ato helicotrem ana down the scala tympani to the round window
  2. vibrations that are set up in the scala vestibuli set up vibrations in the basilar membrane
  3. organ of corti sits in basilar membrane
  4. organ of corti moves with respect to the tectorial membrane
  5. relative movement between hair cells and tectorial membrane results in shear/ deflection of their stereocilia
  6. this causes a change in the membrane potential of the cell cells
  7. change in membrane potential leads to firing of an action potential in the nerve fibres that are connected to the hair cells.
  8. more intense sounds = larger movement therefore greater amount of neuronal firing.
  9. sensory nerves pass from hair cells towards modiolus
  10. sensory nerves have their cell bodies in the spiral ganglion of the modiolus.
  11. from the spiral ganglion of the modiolus, neurones pass onwards as the cochlear part of the 8th nerve.
59
Q

What is the 8th cranial nerve called?

A

This is called the vestibulocochlear nerve.

60
Q

What sort of information does the vestibulocochler nerve carry?

A

it carries impulses both from organs of hearing and balance to the brain. `

61
Q

How to hair cells in the cochlear duct set up impulses?

A

They set up impulses when they are deformed by vibrations.

62
Q

How are impulses set up by hair cells conducted?

A

They are conducted through cochlear fibres of the vestibulocochlear nerve

63
Q

Where are the sensory cell bodies of the vestibulocochlear nerve found?

A

They are found in the spiral ganglion.

64
Q

What is the 7th cranial nerve?

A

This is the facial nerve.

65
Q

How does the 7th cranial nerve enter the petrous temporal bone?

A

It enters the petrous temporal bone through the internal acoustic meatus.

66
Q

What is the path of the facial nerve from the petrous temporal bone?

A

They bypass the ear cavities within their own tunnel.

For a short distance, the 7th cranial nerve and the 8th cranial nerves travel together.

67
Q

What does the 7th cranial nerve supply?

A

The 7th cranial nerve supplies the muscles of the face.

68
Q

Describe the path of the facial nerve until it reaches the middle ear cavity.

A

The facial nerve passes laterally along the internal acoustic meatus until it reaches the medial wall of the middle ear cavity.

69
Q

Where are the cell bodies of the sensory fibres within the facial nerve?

A

They are in a ganglion called the geniculate ganglion.

70
Q

What is the path of the facial nerve after the geniculate ganglion?

A
  • nerve turns a right angle backwards and runs along the top of the medial wall of the middle ear cavity in its own bony canal.
  • when it reaches the back of the medial wall it turns a right angle downwards in its canal
71
Q

What does the facial nerve run out of the petrous temporal bone and the skull to?

A

It runs out of the petrous temporal bone through the stylomastoid foramen.

72
Q

When does the facial nerve give off branches?

A

It gives off several branches while in its tunnel in the petrous temporal bone.

73
Q

Which 2 branches of the facial nerve run forwards through the petrous temporal bone?

A

The 2 petrosal nerves.

74
Q

Aside from the 2 petrosal branches, what are the other branches of the facial nerve that are given off in the petrous temporal bone?

A
  • nerve to stapedius
  • chorda tympani
75
Q

Why is the nerve to stapedius so named?

A

This is a branch that enters the cavity of the middle ear and supplies the tiny stapedius muscle.

76
Q

What are the 2 muscles in the middle ear that are attached to the bony ossiscles?

A
  • stapedius
  • tensor tympani
77
Q

What is the function of the stapedius and tensor tympani muscles?

A

They stabilise the excursions of the ossicles and prevent dislocation of the ear ossicles.

78
Q

What is the nerve supply to the stapedius muscle?

A

The nerve supply to the stapedius muscle comes from the 7th cranial nerve.

79
Q

What is the tensor tympani muscle supplied by?

A

It is supplied by the 5th cranial nerve = trigeminal nerve.

80
Q

What does paralysis of the stapedius muscle lead to?

A

It leads to hyperacusia which is an excessive acuteness of hearing.

81
Q

When does the facial nerve give off the chorda tympani?

A

This branch is given off in the bony facial canal as the facial nerve approaches the stylomastoid foramen

82
Q

How does the chorda tympani eventually leave the skull?

A

It runs forwards, high up over the tympanic membrane and handle of the malleus and eventually leaves the skull.

83
Q

What nerve fibres does the chorda tympani carry?

A
  • carries taste fibres from the tongue
  • carries secretor motor fibres to the salivary glands in the floor of the mouth
84
Q

What are frequent causes of complaint in terms of the ear?

A
  • minor infections
  • lodged foreign bodies
  • accumulations of wax

these can cause pain and lead to more serious complications.

85
Q

In what age group are infections of the middle ear more common?

A

They are more frequent in children.

86
Q

Where can an infection of the middle ear cavity spread?

A

They can spread to the mastoid air cells.

87
Q

What is the path of infections in the middle ear?

A

They often originate in the pharynx and track up the auditory tube to the middle ear.

88
Q

What group of children are especially susceptible to infection of the middle ear?

A

Children with a cleft palate.

89
Q

What can persistant infections lead to?

A

They can lead to deafness.

90
Q

What can we see when we examine the ear in middle ear infections?

A
  • tympanic membrane appears red and swollen
  • cone of light is not visible
91
Q

What do we have to do occassionaly with middle ear infections?

A

Occassionaly it is important incise the tympanic membrane to drain the middle ear cavity.

92
Q

Describe the superior half of the tympanic membrane.

A
  • very vascular
  • chorda tympani runs over the top of the membrane
  • handle of malleus is attached to the upper half of the tympanic membrane
93
Q

What is the least vascular portion of the tympanic membrane?

A

The posterioinferior quadrant. This is also the part that avoids all of the important structures.

94
Q

Where are incisions of the tympanic membrane made?

A

They are made in the posterioinferior quadrant.

95
Q

What are 2 causes of vertigo?

A
  • laryrinthitis or inflammation of the membranous labyrinth
  • excess production of endolymph that ileads to increased pressure and subsequent degeneration of hair cells in the maculae – Meniere’s disease.
96
Q

What can cause dizziness?

A

Syringing wax with water that is much above or below body temperature will induce a movement of endolymph that results in dizziness.

97
Q

What are some causes of deafness?

A
  • damage to the vestibulocochlear nerve = 8th cranial nerve
  • mechanical disruption to sound transmission through the chain of ossicles somewhere between the tympanic membrane and the oval window
    • congenital fixation of the stapes to the oval window is a case in point here.

Head and Neck Anatomy (36 decks)

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