the ear

Question 1

what is the function of the outer, middle and inner ear

Answer 1

outer: hearing
middle: hearing
inner: Hearing and balance

Question 2

describe mechanically gated transduction of hearing

Answer 2

• movements (sound vibrations) affect the stretch-sensitive ion channels at the tips of the sensory hairs
• the tip links connecting the cilia open the K+ channels leading to depolarization
• voltage gated Ca2+ channels open
• influx of Ca2+ causes release od neurotransmitters by exocytosis

Question 3

describe how the vestibulocochlear organ works for vestibular orientation

Answer 3

semi circular canals and otolith organs detect movement and tell your brain how your head is organized in space (dynamic and static info)
2 otolith organs (gelatinous mass that detects orientation):
- saccule respionds to verticle info
- utricle responds to horizonatal info

semicircular canals:
- enolymph filled tubes
- movement of fluid moves the cupula to one side and transmits dynamic info to brain
- the flow of the endolymph mathes head rotation in the same plane as the canal and indicates whether the head is resting orr rotating. endolymph has inertia

Question 4

describe the anatomy of the outer ear

Answer 4

• pinna (composed of elastic cartilage and skin, mobile, innervated by CN VII)
• external acoustic meatus (L-shaped tube ending in ear drum, contains sebaceous glands that produce earwax and hairs to act as a barrier to dust, insects, etc.)
• tympanic membrane (AKA ear drum, covered by epithelium on outside and mucus membrane on inside, detects and moves in response to sound waves)

Question 5

describe the anatomy of the inner ear

Answer 5

ossicles
- includes malleus, incus, stapes bones
- acts as a series of levers thatg transmit sound waves
- stapes is attached to membrane covering oval window of cochlear
tympanic bulla
- resonant cavity

Question 6

describe the eustachian tube

Answer 6

• AKA auditory tube
• connects middle ear with pharynx
• narrow and normally closed
• purpose is to equalise pressure on the two sides of the tympanic membrane

Question 7

how is sound transmitted across the middle ear

Answer 7

• middle ear transmits sound energy from air in the ear canal to fluid in the inner ear with minimal loss of energy
• to achieve this, it increased pressure and reduces amplitude of vibrations through the ossicles
• stapes pushes on fluid in inner ear

Question 8

describe the anatomy of the cochlear

Answer 8

• 3 fluid filled canals (upper, middle, lower)
• upper and lower canals are filled with perilymph
• middle canal is filled with endolymph
• sensory cells (hair cells) sit on basilar membrane
• sensory hairs bend when basilar membrane moves up and down

Question 9

describe how hearing is linked to the CNS

Answer 9

• cranial nerve VII communicates with hair cells and enters brainstem just under cerebellum. carries afferent info from organ of Corti and efferent info to organ of Cort
• caudal colliculus takes auditory info and co-orinates head/ear/neck muslces to orient animals head toward sound source