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Unit 14 > Neurobiology of the ear > Flashcards

Neurobiology of the ear Flashcards

1
Q

What are the three anatomical sections of the ear?
What are their boundaries?

A

Outer - until tympanic membrane
Middle - until oval window
Inner - all bony labyrinth and nerves

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2
Q

What are the ossicles within the middle ear?

A

The malleus
The incus
The stapes - which has a base on the oval window

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3
Q

What are the external features of the ear?

A

Note external ear is also called auricle or pinna

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4
Q

What nerve innervates the ear?

A

The vestibulocochlear nerve CN8
Splits into cochlear nerve - for the cochlear- hearing
The vestibular nerve - vestibular system - balance

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5
Q

What are the important features of the bony labrynth?

A

Semicircular canals
Vestibule
Oval window
Round window
Cochlear

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6
Q

What is the important of the round window in the bony larynthe of the ear?

A

Release pressure from within the cochlear.

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7
Q

What makes up the cross section of the cochlea?

A

A scala vestibuli
A scale media
A scale tympani
These are hollow fluid filled spaces
The organ of corti seperates the scala media and scale tympania

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8
Q

What makes up the organ of Corti?

A

Found between the scala media and the scala tympani
The basilar membrane, with overlying support cells and hair cells (with sterocillia).
All overlayed by the heavy tectorial membrane
Inner hair cells link to afferent axons to the cochlear nerve
Outer hair cells link to efferent axons to the cochlear nerve.

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9
Q

What fluid is found within the cochlear?

A

Endolymph - within the scala media
Perilymph within the scale vestibui and the scala tympani

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10
Q

Constrat the function of inner and outer hair cells

A

Inner - afferent nerve fibres - project depolarisation patterns to detect sound to brain
Outer - efferent nerve fibres - increase sensitivity or focus on sound, aka frequency specific.

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11
Q

How is sound transmitted from the external environment to the inner ear?

A

Pinna amplifies sound waves and projects down external auditory canal
Vibrates the tympanic membrane
Causes vibration of the ossicles in the middle ear, of these the stapes bounces on the oval window of the bony labrynthe
Sound waves are amplified and pass into the endolymph and perilymph within the cochlear, this fluid moves due to sound waves in the scala vestibuli, scala media and scala tympania

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12
Q

What is the function of the organ of Corti?

A

Compute sound waves into electrical information
Structure in the inner ear.

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13
Q

How does the organ of Corti process sound waves?

A

Sound waves in scala media cause movement of the basilar membrane
Results in movement of overlying hair cells stereocillia relevant to overlying tectorial membrane
This movement opens ion channels which leads to depolarisation

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14
Q

How does movement of the stereocillia on hair cells lead to ion movement?

A

The kinocilium is the tallest stereocillia on the hair cells, height is progressive across the cell.
Deviation towards this pulls top links connecting sterocillia together - results in opening of K+ channels - trigger increased rates of depolarisation
Neutral position - norm rate of depolarisation (resting state)
Deviate away - decreased rate of depolarisation (hyperpolarised state)

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15
Q

What is meant by a topographic mapping of frequency in the ear?

A

The basillar membrane runs the width from the base to the apex of the cochlear
The base - high frequency sounds
The apex - low frequency sounds.

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16
Q

How is K+ influx in hair cells converted into sound perception?
(identical mechanism for stereocilia in the vestibular apparatus)

A

K+ influx from scala media (with very high K+ conc) through open channels causes depolarisation of hair cells.
Opening of voltage gated Ca2+ channels - which causes glutamate containing vesicles to fuse with the cell membrane, diffuse across and bind to receptor causing AP in the the afferent nerve fibres - travel to spiral/cochlear ganglion and up cochlear nerve.

17
Q

What is the central circuity of sound perception?

A

Afferent projects a pattern of action potential to arrive through auditory (Cochlear) branch of CNVIII
Terminate and synapse on the dorsal/ventral cochlear nuclei at the junction between the pons and medulla.
Cochlear neurons project and synapse to the superior olive both ispi and contralateral to locate the sound.
Travel up the lateral leminiscus pathway to synapse in the inferior colliculus
Project and synapse in the Medial geniculate nucleus of the thalamus
Project and synapse in the auditory cortex. A1

18
Q

What is the purpose of the inferior colliculus?

A

The reaction centre for the auditory stimuli.
Co-ordinates motor reflexes in response to sound

19
Q

Where is the tectum located?
What is its function?

A

The roof over the cerebral aqueduct between 3rd and 4th ventricle
Contains the superior and inferior colliculus.
Gives rise to descending tectospinal/tectobulbar tracts (dedicated in pons).

20
Q

What is the relevant anatomical location of the primary and secondary auditory cortex?

A

A1 - superior temporal gyrus of temporal lobe, deep to A2
A2 - temporal lobe, rostral and lateral superior temporal gyrus BA42 - includes wernicks area posteriorly (BA22). Also contributions from BA39 and BA40

21
Q

What is wernicks aphasia?

A

Lesion in wernicks
Difficulty understanding language /language processing - speak words at normal rate, rhythm,pitch but words do not make sense in sentences or identifying objects
Difficulty following verbal or written instruction.

22
Q

What is Brocas aphasia?

A

Difficulty producing speech - may repeat words and phrases, but have difficulty repeating phrases to you, may only face few/one word at a time.
Have very limited language.

23
Q

What is the role of the Arcuate fasiculus?

A

Connects Wernicks and Broccas area - important to engage and understand conversation.

24
Q

What is the topographic map on the auditory cortex?

A

Arranged by sound frequency matching that of the basillar membrane in the cochlear.

25
Q

What is Brocas area?

A

A specialised bit of premotor cortex that controls the laryngeal region of M1 - aids in speech production
Unilateral on dominant side of brain (often left)

Made from pars opercularis (BA 44)and parts triangularis (BA45) - not memorise

26
Q

What is wernicks area?

A

Posterior BA 40/41/22 and parts BA39/40
Heavily lateralised mainly on dominant hemisphere often lifet

Not memorise

27
Q

Where are the cell bodies of the vestibulocochlear nerve located?

A

Primary sensory neurons cell bodies are located in the spiral/cochlear ganglion (for cochlear nerve) and the vestibular/scarpas ganglion (for the vestibular nerve afferents)

28
Q

What makes up the vestibular apparatus?

A

The semi-circular canals and associated ampulla (base swelling) - x3 anterior lateral and posterior
The vestibule - containing the utricle and saccule each with an inner macule.

29
Q

What is meant by the otolith organs?

A

The saccule and utricle contains an inner macule each.
These maccules contain hair cells within a gelatinous mass

30
Q

What is the function of the otolith organ?

A

Detects tilt and linear acceleration of the head.

31
Q

What is the role of the semicircular canals?

A

Detects rotational acceleration of the head and head position.
With the lateral, anterior and posterior semicircular canals each accounting for a dimension in space and containing hair cells in their ampulla.

32
Q

How is linear acceleration detected in the otolith organs?

A

Sensory hair cells sit in a gelatinous cap that is overlayed by the otoconia (a layer of calcium carbonate crystals)
Weight of otoconia shifts the gel during linear acceleration/deceleration causing movement of the kinocillia - then identicle mechanism of depolarisation in stereocilia as in ear

33
Q

How are the stereocilia arranged in the semicircular canals (vestibule)?
How do they move?

A

Found in ampulla (base swelling)
Contained in a gelatinous cupula that attaches to the bottom and top of the tube forming a blockage.
Rotations movement causes endolymph to flow in the opposite direction, displacing the cupula and its contained sterocilia from underlying hair cells.

34
Q

What is the circuitry for conscious vestibular sensation?

A

Vestibular sensory neurons have cell bodies in the vestibular ganglion
Project to and synapse in the vestibular nuclei in the brainstem
Project to the thalamus
Thalamus projects to distributed network of cortical areas such as S1 to create a sense of self in space

35
Q

What are some of the regions of the cortex the thalamus projects to during conscious vestibular activity?

A

S1
Frontal eye field - conscious eye movement
Parietoinsular vestibular cortex (PIVC)
6v - part of pre-motor cortex with vestibular function.

36
Q

What is meant by a vestibular sensation?

A

Sense of head balance/position

37
Q

What are the three vestibular reflexes?
What do they do?

A

Vestibulospinal - stops falling by innervating LMNs
Vestibulocollic - keep head up by innervating LMNs
Vestibulooclular - keeps gaze fixed by innervating cranial nerve nuclei 3,4,6 (extra-ocular eye muscles)

38
Q

What is the circuitry for the vestibulo-ocular reflex?

A

Vestibular information is transmitted down the CN8
Synapse in the medial vestibular nucleus
Communicates with the nuclei of CN3,4,6
This co-ordinate eys movement to counteract head movement
Underpins the vestibulo-ocular reflex.
Is unconscious vestibular circuitry

39
Q

What is the circuitry for the vestibulocollic and vestibulospinal reflex?

A

Is an unconscious vestibular circuitry
Vestibular information is transmitted down CN8 to the medial and lateral vestibular nuclei in the brainstem
Projects to and from the the cerebellum and also down the lateral (to body) and medial (to head and neck) vestibulospinal tract.

Unit 14 (17 decks)

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