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Neuroscience > Hearing and Balance > Flashcards

Hearing and Balance Flashcards

1
Q

What is hearing?

A

Perception of sound

Detection of vibrations, changes of pressure through solid, liquid or gas

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2
Q

What is vestibular function?

A

Perception of position and motion
Static gravitational orientation (position with respect to gravity)/ perception of motion in space (rotations, linear translations)

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3
Q

What is static gravitational orientation?

A

Perception of relationship to gravitational field

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4
Q

What is motion sense?

A

Perception of motion relative to environment
Rotations, linear translations
Essentially acceleration

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5
Q

How are the auditory and vestibular systems intimately connected?

A
  • Receptor organs in ear (membranous labyrinth)
  • Processing of information in the inner ear (bony labyrinth)
  • Common nerve to brain (vestibular cochlear nerve)
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6
Q

What are the main components of the human ear?

A
  • Outer
  • Middle
  • Inner
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7
Q

What makes up the outer ear?

A
  • Pinna (the ear we see)
  • Auditory canal (leads into middle ear)
  • Tympanic membrane (sits at apex of auditory canal)
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8
Q

What makes up the middle ear?

A

Small air filled chamber containing 3 small bones (the ossicles)

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9
Q

Where is the inner ear?

A

Innermost part of ear

In the bony labyrinth of temporal bone

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10
Q

What is the membranous labyrinth?

A
  • A continuous membrane within the bony labyrinth

- Contains fluid

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11
Q

What are the fluids in the labyrinth?

A

Bony= perilymph
Membranous= endolymph
Composition is different

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12
Q

What are the receptor organs within the membranous labyrinth?

A
  • The vestibule= large central area
  • The utricle and saccule= adjacent to vestibule (vestibular)
  • The cochlea (duct)= on one side (auditory)
  • The semi-circular canals= on other (vestibular)
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13
Q

What are the major components of the inner ear?

A
  • Nerve
  • Cochlea
  • Utricle
  • Saccule
  • Anterior, posterior and horizontal canal
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14
Q

How does hearing begin?

A

Sound waves enter the auditory canal

Pressure variations in the air around us, enter and towards the tympanic membrane

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15
Q

Describe the process of hearing

A
  • Tympanic membranes receives and vibrates
  • Vibration transmitted to the ossicles
  • Ossicles transmit vibrations to oval window of the vestibule
  • Then transmitted to cochlea (fluid inside membranous labyrinth to cochlea)
  • Cells in cochlea convert vibrations into electrical signals that are transmitted along axons of V111 cranial nerve
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16
Q

What are the bones of the ossicles?

A
  • Malleus
  • Incus
  • Stapes
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17
Q

Where does the cranial nerve enter the CNS?

A

Vestibulocochlear nerve goes to brain stem effectively at medulla/ pons junction to the cochlear nuclei (ventral anteriorly, dorsal posteriorly)
-Auditory information ascends via tract in medial lemniscus to thalamus and cerebral cortex

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18
Q

What makes up the vestibulocochlear nerve?

A 
Vestibular nerve (superior and inferior)
Cochlear nerve
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19
Q

Describe the two pathways from the cochlear nuclei

A
  • Dorsal= Concerned with the quality of sound, picking apart the tiny frequency differences which allow differentiation of similar sounds
  • Ventral= Concerned with minute differences in the timing and loudness of the sound in each ear in order to localize sound
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20
Q

Describe the path of the axons from the ventral cochlear nerve

A

Axons go to superior olive then to inferior colliculus, medial geniculate body, cerebral cortex

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21
Q

Describe the path of the axons from the dorsal cochlear nerve

A

Axons go directly to inferior colliculus, medial geniculate body, cerebral cortex

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22
Q

Where is the primary auditory cortex?

A

Side of brain in temporal region

Bilaterally represented

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23
Q

How many turns are there in the cochlea?

A

2.5 turns around its axis in humans

24
Q

What are the chambers of the cochlear?

A

-Scala vestibuli (abuts the oval window so the stapes transmits vibrations into this)
-Scala tympani (abuts the round window)
-Scala media (duct in middle surrounded by membrane)
Contain perilymph except for media which contains endolymph

25
Q

What are the membranes that define the cochlear duct?

A
  • Reissner’s membrane= separates cochlear duct from Scala vestibuli
  • Basilar membrane= separates the cochlear duct from Scala tympani
26
Q

Describe the role of the Basilar membrane

A
  • Relatively stiff
  • Supports the Organ of Corti (core part of auditory-sensory apparatus)
  • Determines mechanical wave propagation properties of cochlea (as vibrations transmitted around fluid channels)
27
Q

Where is the Organ of Corti?

A

Within cochlea duct in Scala Media

28
Q

What is the Organ of Corti?

A
  • Sensory epithelium
  • A cellular layer on basilar membrane
  • Hair cells
  • Topped with hair-like structures that fit into tectorial membrane above
29
Q

How is the Organ of Corti important in hearing?

A
  • Waves in Scala fluid
  • Cause movement of basilar membrane
  • Hair cells produce electrical responses
  • Axons form part of the V111 nerve
30
Q

How does stiffness of the basilar membrane vary?

A
  • Stiffness and width varies along the cochlea= stiffest near start at oval window
  • Allows different parts of BM to respond to different frequencies
31
Q

What is the purpose of coiling?

A
  • Enhances low frequency waves as they travel along cochlea

- Highest frequency near oval window, lowest frequency near other end

32
Q

Static gravitational orientation and perception of motion arise from which sensory apparatus?

A
  • Visual= moving in relation to environment
  • Somatosensory (proprioception)
  • Vestibular
33
Q

What two components of the vestibular system reflects rotations and linear translations?

A

-Semi-circular canals= rotation
-The Otoliths= linear translations
Vestibular apparatus detects angular and linear acceleration

34
Q

What are the semi-circular canals?

A 
-Three semi-circular canals (for 3D spatial world) in a non-orthogonal relationship (not at 90 degrees to each other)
=Horizontal/ lateral
=Anterior/ superior
=Posterior/ inferior
*Anterior and posterior: vertical
35
Q

Describe the role of each semi-circular canal

A
  • Horizontal= detect rotation of the head around a vertical axis
  • Anterior and posterior= rotations of head in sagittal plane/ rotations of the head in frontal plane
36
Q

Describe the anatomy of the semi-circular canals

A
  • Each canal@: a continuous endolymph-filled hoop
  • Special hair cells sit in a small swelling called the ampulla
  • Hair cells project into gelatinous mass: the cupula
37
Q

What occurs in the semi-circular canals due to movement of the head?

A
  • Motion in the plane of the canal

- Inertia of endolymph= causes movement of fluid= movement of hairs= hair cell activity changes= electrical impulse

38
Q

What is the relationship between the paired semi-circular canals (R and L)?

A

Movement one way
=Inhibition on one side
=Excitation on the other

39
Q

Describe the anatomy of the Utricle and Saccule

A
  • Both have a sheet of hair cells (macula)
  • Macula have cilia embedded in a gelatinous mass
  • Embedded in this gel= small crystals (otoliths)
  • The otoliths provide inertia- movement bends hair cell
40
Q

How is linear translation detected by the utricle and saccule?

A

Motion: the otolith-gel mass drags on the hair cells

=hair cells five information to 8th cranial nerve

41
Q

How are hair cells arranged in the utricle and saccule?

A

-Arrayed in different directions to cover different directions of movement
=Utricle: horizontal
=Saccule: sagittal (up/down, forward/back)

42
Q

Describe the vestibular pathway

A
  • Sensory cells in labyrinth

- V111 nerve to brain stem, vestibular nuclei, cerebellum

43
Q

What are the vestibular nuclei connections?

A
  • Cerebellum (integrate motor action)
  • Spinal cord (Vestibulo-spinal tract, adjust movements of body)
  • Eye movement motor nuclei
  • Cerebral cortex
44
Q

What is the important output of the vestibular system?

A

Neural structures controlling eye movements

-Reflex to move while focussed on an object

45
Q

Describe the Vestibulo-ocular reflex

A
  • A critical role of the semi-circular canal system
  • To keep your eyes still in space while your head moves around them
  • Turning head left= left semi-circular canal excited, directly to 3rd and 6th nerves to medial and lateral rectus muscles
46
Q

Example of Vestibulo-ocular reflex

A
  1. Detection of rotation
  2. Excitation of extraocular muscles on the other side, inhibition of extraocular muscles on one side
  3. Compensating eye movement
47
Q

What is Vertigo?

A

One or more of the following

  • A distortion of static gravitational orientation (feeling leaning to one side)
  • An erroneous perception of movement of the sufferer (bobbing up and down/ spinning in relation to the environment)
  • An erroneous perception of movement of the environment (environment spinning around you/ bobbing up and down)
48
Q

What does Vertigo result from?

A
  • Unusual stimulation of intact systems (motion sickness)

- Pathological dysfunction of those systems (vestibular apparatus disease)

49
Q

What are the outputs/ targets of the vestibular nucleus?

A
  • Cortex= spatial orientation, motion perception
  • Brainstem= eye movements, vegetative effects
  • Spinal cord= posture
50
Q

What are the components of vertigo syndrome?

A
  • Perceptual= vertigo, disorientation
  • Oculomotor= nystagmus (jerky eye movements), ocular deviation
  • Postural= ataxia, falls
  • Autonomic/ vegetative= nausea, vomiting, sweating
  • Secondary= anxiety, avoidance behaviour
51
Q

What is BPPV?

A
  • Benign Paroxysmal Positional Vertigo

- Bits of otoliths break of and get lodged

52
Q

How does BPPV present?

A

-One of the commonest causes of vertigo in general practice
-Attacks of rotational vertigo
-Provoked by
=positional change
=lying down or sitting up
=turning over in bed
=looking up or bending forward

53
Q

What are the causes of BPPV?

A
  • Degenerative debris in cupola or semi-circular canal
  • 40% antecedent event (head injury)
  • 60% no obvious antecedent event (age)
54
Q

How do we test and treat BPPV?

A
  • Positional testing (60 degrees upright, 30 degrees below lying down)
  • Particle repositioning manoeuvres= fluid to wash debris
55
Q

What is the clinical relevance of eye movements?

A
  • Nystagmus in diagnosis of ear/ brainstem disease

- Vestibulo-ocular reflex part of brain stem death criteria

Neuroscience (33 decks)

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