11 - NS Ear and Audition

Question 1

What are the sensory nerves involved in hearing

Answer 1

CN VIII (vestibulocochlear): hearing and balance
CN X (vagus): sensory to auditory canal

Question 2

What are the motor nerves involved in hearing

Answer 2

CN V (trigeminal): tensor tympani muscle of middle ear

CN VII (facial): stapedius muscle of middle ear

Question 3

From where are the components of the ear carved from

Answer 3

the petrous portion of the temporal bone

Question 4

What are the three principle regions of the ear

Answer 4

external, middle, inner

Question 5

External Ear - glands

Answer 5

ceruminous glands secrete wax that traps foreign bodies and repels insects

Question 6

describe how the skin of the external auditory canal is attached

Answer 6

2/3 = cartilage (contains fat)
1/3 = bone
- firmly attached to the periosteum of the bone

Question 7

What are the parts of the middle ear

Answer 7

ossicles (in middle ear interior)
tympanic membrane cone (eardrum)
connective tissue covered by skin externally, mucosa internally

Question 8

What is the function of the ossicles

Answer 8

mechanically relay vibrations from the tympanic membrane to the oval window of the inner ear

Question 9

where are the ossicles found

Answer 9

suspended by ligaments and connected by synovial joints

Question 10

what are the parts of the ossicles

Answer 10

malleus (hammer)
incus (anvil)
stapes (saddle)

Question 11

which muscles help to dampen sounds

Answer 11

tensor tympani (dampens ossicle movement when chewing - CN V)

stapedius (dampens ossicle movement during loud sounds - CN VII)

muscles tense (constrict) so tympanic membrane can’t vibrate as much

Question 12

What ensures that the tympanic membrane vibrates effectively

Answer 12

pressure equilibration

Tympanic membrane should be able to move back and forth

Question 13

What would happen if there was high pressure in the middle ear

Answer 13

tympanic membrane would be bulging out
can’t vibrate as effectively as sounds come in
deaf

Question 14

What tubes in the middle ear connect to the great outdoors

Answer 14

external auditory canal
auditory tube (from pharanx)

Question 15

Auditory tube

Answer 15

runs through pharanx
surrounded by skeletal muscle
changes shape when you swallow
- swallowing allows pressure to be equilibrated

Question 16

What is the mastoid process

Answer 16

bored out bone at the back of the ear
sponge-like covered by mucous membrane

any part of skull that is not needing absolute strength is hollowed out and put air spaces in
air spaces communicate to great outdoors so head doesn’t explode on the plane
makes skull lighter

Question 17

How do middle ear infections occur

Answer 17

respiratory tract infections ascend that auditory tube to the middle ear

Question 18

What could happen as a result of infections in the middle ear

Answer 18

1. rupture of tympanic membrane and drainage of fluid through external ear (collagen build up)
2. infection spread into mastoid air cells leading to mastoiditis (increase pressure in bone)
3. erosion of temporal bone above middle ear leading to meningitis

Question 19

What is the inner ear made of

Answer 19

series of channels carved out of the temporal bone
- cochlea
- semicircular canals

Question 20

How is hearing transmitted to the inner ear

Answer 20

stapes acts on the oval (vestibular) window to transmit vibrations to the organ of hearing (spial organ) contained within the cochlea which resembles a snail shell

Question 21

How are sound waves transmitted

Answer 21

1. sounds waves collected by the auricle and external auditory meatus and directed to the eardrum
2. sound waves vibrate the tympanic membrane
3. transmission of vibrations across middle ear by the ossicles
4. stapes transfers vibrations to the oval (vestibular) window
5. vibrations transferred to perilymph of scala vestibuli
6. vibrations transfer to scala tympani and eventually cochlear (round) window
7. pressure waves in scala vestibuli and tympani set up waves in the endolymph of the cochlear duct
8. pressure waves in the endolymph cause the basilar membrane to vibrate, moving hair cells (receptors) of the spiral organ -> nerve impulses generated in the cochlear nerve (CN VIII)

Question 22

What does the spinal organ do

Answer 22

Converts vibrations into nerve impulses

Question 23

What does the spinal organ consist of

Answer 23

hair cells (stereo cilia)
supporting cells

Question 24

How are the first order neurons stimulated

Answer 24

stimulation of stereo cilia on hair cells causes NT release, stimulating first order neurons of the cochlear nerve (CN VIII)

Question 25

How does frequency detection work

Answer 25

The length of the basilar membrane fibres acts to tune the different parts of the cochlea to different frequencies

Question 26

Describe the auditory pathway to the brain

Answer 26

1. auditory info travels bilaterally after entering the brainstem 2. Cochlear nuclei (CN VIII): info decussates beyond this point - medulla oblongata 3. Superior olivary nuclei: stereo sound (localization) - pons 4. Lateral lemniscus: white matter tract (part of RAS) 5. Inferior colliculus: acoustic startle reflex - dorsal midbrain 6. Thalamus: selective attention, filters out self-generated sounds (voice, heart, chewing) - medial geniculate nucleus 7. Primary auditory cortex: conscious perception of sound - temporal lobe

Question 27

What are the types of hearing loss

Answer 27

conduction deafness sensory deafness

Question 28

Conduction deafness (where, what, causes)

Answer 28

- middle and outer ear - reduction in sound amplitude - hear sound of blood rushing in carotid arteries - Causes: ear wax, rupture of tympanic membrane, damage to ossicles (arthritis)

Question 29

Sensory Deafness (where, what, causes)

Answer 29

- inner ear, CN VIII - high tones affected (rumbling) - tinnitus (continuous hiss) - Causes: infarct, trauma, prolonged noise, drug toxicity, tumours, Meniere's disease - high endolymph pressure)

Question 30

What are the parts of the vestibular apparatus

Answer 30

Consists of receptor organs for equilibrium - utricle (bag) - saccule (small sac) - semicircular ducts (x3)

Question 31

What are the utricle and saccule

Answer 31

otolithic organs that contain an inner region called the macula

Question 32

What is the semi-circular duct

Answer 32

in a linear plane - the anterior and posterior ducts are on the vertical plane - the lateral duct is on the horizontal plane - all three ducts lie at right angles to one another

Question 33

What is the maculae

Answer 33

Contains hair cells and supporting cells and is part of the utricle and saccule - detects linear acceleration/deceleration

Question 34

What is a hair bundle

Answer 34

hair cells/sensory receptors contain a hair bundle

Question 35

What do the supporting cells do

Answer 35

surround the hair cells and produce the otolithic membrane and otoliths (calcium carbonate crystals)

Question 36

How are the utricle and saccule positioned

Answer 36

perpendicular to each other within the inner aspect of the vestibular apparatus

Question 37

What position does the utricle have when head is upright what do the hair cells respond to

Answer 37

horizantal linear acceleration and deceleration and when the head tilts forward or backward

Question 38

What position does the saccule have when the head is upright what do the hair cells respond to

Answer 38

vertical linear acceleration and deceleration in the vertical direction

Question 39

What is an ampulla

Answer 39

dilated region of the ducts that contain a crista (folds), each consisting of hair cells and supporting cells

Question 40

What is the crista

Answer 40

covered in gelatinous substance (the capula) that moves and bends the hair cells when the surrounding endolymph moves as the head rotates

Question 41

What does bending hair bundles do

Answer 41

in one direction, depolarizes hair cells in opposite direction, hyperpolarizes

Question 42

How does vestibular information travel

Answer 42

from the cortex and is integrated in the brainstem hair bundles --> vestibulocochlear nerve (CN VIII) --> vestibular nuclei (medula/pons) --> thalamus --> sensory cortex (verstibular area in the parietal lobe)

Question 43

How is vestibular information integrated into the brainstem

Answer 43

1. cranial nerves for eye movement (CN III, IV, VI) - scanning motions 2. Accessory nerve (XI) for head/neck control - sternocleidomastoid + trapezius 3. Vestibulospinal tract for skeletal muscle control - indirect motor pathway, posture and balance 4. Cerebellum for limb and axial positional control - dedicated pipeline to coordinate movements