special senses (hearing)

Question 1

describe the anatomy of the ear

Answer 1

• external: pinna, ear canal and tympanic membrane
• middle: three ossicles / bone (maleus, incus, stapes), oval and round windows and eustachian tube
• internal: cochlear and semi-circular canals

Question 2

what is the relationship between hearing and balance

Answer 2

• hearing: outer, middle and inner ear
• equilibrium: inner ear
• receptors: respond to separate stimuli and are activated independently
• afferent fibres: hearing receptors (cochlear) and equilibrium receptors (vestibule)
• info. from inner ear as AP via vestibulocochlear nerve

Question 3

describe the inner ear in detail

Answer 3

• amplifies sound as it hits water in canals
• bony labyrinth: tortuous channels through temporal bone, filled with perilymph
• contains vestibule, cochlear and semicircular canals
• membraneous labyrinth: membranous sacs within bony labyrinth, filled with K rich fluid

Question 4

how do we perceive sound

Answer 4

1. outer ear / external auditory canal passively capture acoustic energy
2. sound waves vibrate tympanic membrane
3. formation of perilymph wave within cochlea
4. wave travels length of cochlea and displaces basilar membrane
5. stereo cilia bend due to shearing force = change in resting membrane potential of hair cell

Question 5

how do we code sound waves

Answer 5

• pitch: frequency, number of wavelengths

- loudness: intensity, amplitude / height of waves

Question 6

describe the process behind hearing different pitch

Answer 6

• each frequency corresponds to a specific place on the basilar membrane
• low freq. = can’t move short stiff fibres at base but continue to longer floppier apex fibres and vice versa

Question 7

how does sound transduction by hair cells occur (rotation)

Answer 7

1. oscillations of cochlea membrane cause stereo cilia to bend
2. 1 stereo cilia are different lengths and bend either towards tallest (kino cilium)
3. 2 away from tallest
4. 1 bending towards = opens k gated channels
5. 1 bending away = closes k gated channels
6. 1 K enters, depolarisation, Ca enters, release neurotransmitter
7. 2 hyperpolarisation, inhibits nerve fibre
8. 1 action potentials
9. 2 no action potentials
10. 1 signals from hair cells transmitted to brain via cochlear nerve

Question 8

describe the auditory pathway to the brain

Answer 8

• vestibulocochlear nerve (CN8): vestibular nerve joins cochlear nerve at internal acoustic meatus
  1. spiral ganglion transmit to brainstem via CN8
  2. synapses at cochlear nuclei
  3. axons from ventral cochlear nucleus to inferior colliculus
  4. travel to and synapse at medial geniculate body of thalamus
  5. arrives at auditory cortex

Question 9

what is the vestibular apparatus

Answer 9

• 3 semicircular canals (endolymph), 3 ampulla’s at base of canals (contain cupola), 1 utricle and 1 saccule
• linear acceleration (utricle and saccule)
• rotational acceleration (cupola and ampulla)

Question 10

what is the relationship between the utricle and the saccule

Answer 10

• linear acceleration
• receptor cells (cilia) extend into gelatinous layer containing small Ca carbonate crystals (otoliths)
• forwards: hairs bend to kino-cilium, depolarisation, AP
• backwards: hair bend away from kino-cilium, hyper polarisation, no AP

Question 11

describe the relationship between smell and taste chemoreceptors

Answer 11

• chemoreceptors responde to chemicals in aq. solution, depolarisation
• smell and taste are related
• ‘registered’ as a particular smell by the brain before tasting the food

Question 12

what is the relationship between the ampulla and cupola

Answer 12

• rotational acceleration
• ampulla: base of canals, crista extend to cupola (cilia)
• cupola: float, displaced by fluid movements (direction opposite to movement), endolymph movement, bends the hairs, initiates AP