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Y2 CONTROL & MOVEMENT > The Auditory Pathway > Flashcards

The Auditory Pathway Flashcards

1
Q

Label the following structures surrounding the ear location

A
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2
Q

What are the 3 divisions of the ear?

Label the diagram

A
  • External ear
  • middle ear
  • inner ear
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3
Q

What bone forms the bony part of the external ear?

A

Temporal bone

the mastoid process and styloid process are visible

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4
Q

What is the role of the external ear?

what is its composition like?

A

The external ear receives sound waves

the lateral 1/3 is cartilaginous and the medial 2/3s are bony

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5
Q

What is the role of the middle ear?

What is its composition like?

A

It is an air-filled space where sound waves are converted to mechanical energy

it contains ossicles

these are bones that mechanically vibrate

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6
Q

What is the role of the inner ear?

What is its composition like?

A

It converts mechanical energy to electrical energy

it contains the cochlea

there is a hollow cavity within the temporal bone through which CN III exits

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7
Q

What is the role of the tympanic membrane?

A

It separates the external ear and middle ear

The external auditory canal transmits sound waves towards the tympanic membrane (eardrum)

it physically moves when sound waves hit it, and transfers these waves to the middle ear

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8
Q

What is the composition of the middle ear like?

Which body part does it communicate with?

A

It is an air-filled space in the petrous part of the temporal bone

it communicates with the nasopharynx via the Eustachian tube (auditory tube)

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9
Q

What bones are found within the middle ear?

What is their function?

A

The ossicles:

  1. Malleus
  2. Incus
  3. Stapes

they vibrate to transmit / amplify sound waves into the cochlea

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10
Q

What happens to the ossicles with age?

A

The ossicles become calcified with age

this means that they are less flexible and able to move and vibrate

this leads to conductive hearing loss

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11
Q

What is the role of the Eustachian tube?

what are its 3 functions?

A

It connects the nasopharynx to the middle ear

  1. it drains the middle ear to prevent accumulation of fluid
  2. it ventilates the middle ear
  3. it equalises pressure between atmospheric pressure and pressure within the ear
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12
Q

How is the Eustachian tube different in adults and children?

A

In an infant, the tube is more horizontal

this means there is a more direct route for infection, so more ear infections are seen in young children

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13
Q

Label the middle ear

What are the main connections shown?

A
  • The facial nerve supplies the facial muscles
  • the chorda tympani (branch of facial nerve) supplies the anterior 2/3 of the tongue
  • the lesser petrosal nerve (branch of facial nerve) supplies the parotid gland
  • the Eustachian tube leads to the nasopharynx
  • the mastoid air cells of the mastoid process are connected to the middle cranial fossa
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14
Q

For which 5 reasons is the middle ear known as a high risk space?

A
  • It is connected to the nasopharynx, making it prone to infection
  • it is connected to the mastoid air cells - infection may spread to the middle cranial fossa
  • the internal jugular vein lies inferior - infection leads to thrombosis risk
  • the internal carotid artery lies anterior - link to pulsatile tinnutis
  • traversed by chorda tympani & facial canal - risk of infection spreading to regions supplied by the facial nerve
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15
Q

What is meant by pulsatile tinnutis?

A

Tinnutis is the perception of sound when no external sound is present

it is “pulsatile” when the sound has the same rate as the heart rhythm

this occurs due to a change in blood pressure within the internal carotid artery

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16
Q

Where is the inner ear located?

What is its composition like?

A

Located within petrous part of temporal bone

it is composed of 2 special sense organs

  1. Vestibular system - balance & equilibrium (posture)
  2. Cochlear system (hearing)
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17
Q

What is meant by the cochlea being tonotopically organised?

A

Different parts of the cochlea detect different frequencies of sound

the apex detects lower frequency sounds

the base detects higher frequency sounds

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18
Q
A
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19
Q

What nerve emerges from the cochlea?

How is it formed?

A

It is a snail-shaped cavity containing sensory receptors for sound

they synapse with spiral ganglia, whose axons fuse to form the cochlear division of the vestibulocochlear nerve (CN VIII)

this transfers sound information to the rest of the CNS

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20
Q

Label the inner ear

A
21
Q

What are the 2 fluid-filled cavities within the inner ear?

What do they contain?

A

Bony (outer) labyrinth:

  • this contains perilymph
  • this is similar to extracellular fluid

Membranous (inner) labyrinth:

  • this contains endolymph
  • this is similar to intracellular fluid
22
Q

what are the components of the bony (outer) labyrinth?

A

Vestibular system:

  • vestibule
  • semicircular canals (SCC)

cochlear system:

  • cochlea

these contain perilymph

23
Q

What is the composition of the membranous (inner) labyrinth like?

A

Vestibular system:

  • vestibule structures
  • semicircular ducts

cochlear system:

  • cochlear duct

these contain endolymph

24
Q

How does the cochlear duct separate the cochlea?

A

It separates the cochlea into two chambers:

  1. Scala vestibuli
  2. Scala tympani

these two chambers are continuous at the apex of the cochlea through a narrow slit (helicotrema)

25
Q

Label the components of the cochlea

A
26
Q

What are the roles of the oval window and round window?

A
  • Stapes transfers vibrations into the inner ear via the oval window
  • fluid vibrations travel through the scala vestibuli and scala tympani
  • fluid vibrations are then reabsorbed at the round window, allowing new sound waves to enter the system
27
Q

Why is it important for the ossicles to amplify sound waves?

A

There is a change in medium from air to fluid when sound waves enter the inner ear

ossicles need to vibrate and amplify the sound to facilitate transfer into a fluid-filled medium

28
Q

What is contained within the cochlear duct?

A

The spiral organ of Corti

29
Q

What membranes are located either side of the spiral organ?

A

The spiral organ sits above the basilar membrane

this contains hair cells which have their projections embedded into the tectorial membrane

the tectorial membrane is above the spiral organ

30
Q

What is significant about the hair cells embedded within the tectorial membrane?

A

Axons that are in contact with the hair cells fuse to form the cochlear nerve

this is a division of the vestibulocochlear nerve

31
Q

What happens when vibrations in the inner ear deform the basilar membrane?

A
  • Deformation of the basilar membrane leads to movement of the tectorial membrane
  • hair cells detect the movement and open their ion channels
  • this causes an action potential in the fibres that go on to form the cochlear nerve
32
Q

What stimulates the spiral organ?

What does this lead to?

A

It is stimulated by the deformation of the cochlear duct by the perilymph in the surrounding SV and ST

it converts fluid pressure into electrical signals via cochlear nerve

33
Q

What are the characteristics of the auditory pathway?

A
  • Polysynaptic as it contains many synapses
  • tonotopically organised
  • bilateral (so sound can be localised) - right & left sides project to both hemispheres
  • it compares 2 inputs - timing and loudness
34
Q

Label the components of the auditory pathway

A
35
Q

What is the pathway taken by the 1o auditory fibres?

A
  • Axons of bipolar neurones in the spiral ganglion form the cochlear division of the vestibulocochlear nerve (CN VIII)
  • CN VIII enters the brainstem at the cerebellopontine angle
  • synapse with 2o neurones in the dorsal & ventral cochlear nuclei (ICP / CS)
36
Q

What are the roles of the cochlear nuclei?

What do they receive and project?

A
  • Receive afferent from cochlear nerve
  • they project BILATERALLY to the superior olivary nuclei
  • fibres travelling to the contralateral olivary nucleus enter the trapezoid body (thick band of white matter)
37
Q

Label the pathway from the cochlear nuclei

A
38
Q

What information does the superior olivary nucleus receive and transmit?

A
  • SON receives BILATERAL auditory information from the cochlear nuclei
  • sends ascending fibres to inferior colliculus via the lateral lemniscus BILATERALLY
39
Q

Where are the inferior colliculus and MGN located?

How are they connected?

A
  • Inferior colliculus located in tectum of midbrain
  • Medial geniculate nucleus (MGN) located in thalamus
  • IC connects to MGN via the brachium of the inferior colliculus
40
Q

What components of the auditory pathway involve the inferior colliculus and medial geniculate nucleus?

A

Inferior colliculus:

  • receives information from lateral lemniscus
  • inferior colliculi may exchange auditory information via the inferior colliculus commisure
  • sends auditory information to MGN via the brachium of the inferior colliculus

Medial geniculate nucleus:

  • fibres pass to the primary auditory cortex via the acoustic radiation
41
Q

What is another name for the primary auditory cortex?

A

Heschl’s gyrus

(superior temporal gyrus)

42
Q

What is meant by tonotopic organisation of the cochlea & auditory cortex?

A

Different regions of the basilar membrane respond to sounds of different pitch

apex responds to low pitch and base responds to high pitch

the pitch of sound is distributed to the auditory cortex

Low frequency - anteroLateral part

high frequency - posteromedial part

43
Q

What are the 2o auditory areas and where are they found?

A

The left hemisphere houses the 2o auditory areas

Broca’s area:

  • involved with motor functions like production of words

Wernicke’s area:

  • involved with sensory functions like understanding
44
Q

what type of stroke leads to non-fluent (Broca’s aphasia)?

A

This is where the person knows what they want to say but they cant find the words

this is caused by a stroke in the anterior distribution of the left middle cerebral artery

this affects Broca’s area

45
Q

What type of stroke leads to fluent (Wernicke’s) aphasia?

A

This is when someone speaks fluently but what they are saying makes no sense

stroke in the posterior distribution of the middle cerebral artery

this affects Wernicke’s area

46
Q

What is the purpose of the descending auditory pathways?

A

They are involved in responding to auditory information that we receive

47
Q

What is the reflex that prevents damage during loud noise?

A
  • Superior olivary nucleus sends fibres to:
    • stapedius via CN III
    • tensor tympani via CN V3
  • these muscles contract to lock the ossicles in place and stop them from vibrating
  • this protects the inner ear from damage due to loud noise
48
Q

What is the purpose of reflex head and eye movements?

Which nerves are involved?

A

Involves CN III, IV and VI

this is movement in response to sound

e.g. Looking at someone who calls your name

Y2 CONTROL & MOVEMENT (69 decks)

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