heRING 5,6

Question 1

Define hearing ?

Answer 1

our perception of the energy carried by sound waves,
/variations: have alternating peaks of compressed air (zones of compression) and valleys (zones of rarefaction), in which the medium’s molecules are farther apart:
Many animals use sound to detect danger, claim territory, attract a mate, to communicate, etc.

Question 2

What atre sound waves ?

Answer 2

alternating peaks of compressed air (zones of compression) and valleys (zones of rarefaction; medium’s molecules are farther apart).

Question 3

What are Vibration ?

Answer 3

Volume or loudness: function of wave amplitude.
Pitch: function of wave frequency.
Timbre: resonance quality or overtones of sound.
measured in decibals

Question 4

What are soundwaves distinguished by ?

Answer 4

frequency:no of cycles
and amplitude :size or intensity

Question 5

What is auditory threshold ?

Answer 5

of human hearing varies with the frequency: the greatest sensitivity is found between 1000-3000 Hz.
As we age, become less sensitive to higher frequencies: presbycusis

Question 6

What is part of the structure and function of outer ear ?

Answer 6

Auricle/Pinna: mostly consists of elastic cartlidge covered with skin
gathers sound waves from the environment then funnel;s and amplifies them to tympanic membranes /eardrum
external audotry canal :lined with hair &ceruminous gland-earwax
Tympanic membrane :is streched across the end of canal

Question 7

Strcuture and function of middle ear ?

Answer 7

Middle ear/tympanic cavity: bounded laterally by the tympanic membrane and medially by the oval and the round windows.
1 passage for air is through the auditory/Eustachian tube: opens into pharynx; equalizes pressure (to atmospheric):
When pressures are not equalized–> discomfort, pain: can swallow, yawn (like when on an airplane

Question 8

WHat are the 3 bones the middle ear contains ?

Answer 8

Malleus :
incus
stapes
transmit vibrations from eardrum to inner ear
amplifying and trnasmitting ounds
‘Handle’ of malleus is attached to the tympanic membrane.
Incus connects malleus & stapes.
Stapes sits on the oval window.

The oval and round windows separate the air-filled middle ear from the fluid-filled inner ear

Question 9

How can the amount of energy be lessened ?

Answer 9

by 2 small skeletal muscle in the middle air
Stapedius muscle:attahed to staoes ;inverted by facial nerve ->contraction retracts stapes from oval w.
Tensor tympani muscle :attached to malleus ;inverted by the trigeminal nerve (V) ->contraction pulls malleus inward,increasing the tension of they tympanic membrane

These muscles reflexively dampen continuous, loud sounds (sound attenuation reflex)  protects ear structures from such damage.

Question 10

What are structure and function of the inner ear ?

Answer 10

Vestibular apparatus :sensory transducer for our sense of balance
Cochlea:contains sensory receptors for hearing
inner ear consists of Bony labryrinth contains fluid filled sacs and tubes of membranous labyrinth

Question 11

What are the 3 regions of the bony labyrinth ?

Answer 11

the vestibule (utricle &saccule)
semicircircular canals (these 2 regions make up vestibular apparatus ) and cochlea
within bony labyrinth are suspended fluid filled sacs of membraneous labyrinth

Question 12

What is the fluid in membranous labyrinth ?

Answer 12

fluid here is called endolymph similar to intracellular fluid,ICF(high potassium and low potasssium)
Bony labyrinth :fluid filled perilymph similar to plasma and cerebrospinal fluid (lowK + and high Na+)little protein

Question 13

What is a part of the cochlea ?

Answer 13

Scala vestubuli:above cochlear duct from oval window to helicotrema
Scal tympani :below cochlear duct from helicotrema to round window

Question 14

What is the organ of corti ?

Answer 14

cochlear hair cells are the hearing receptor cells
1 row of inner hair cells and 3 rows of outer hair cells are found between the tectorial and basilar membranes

Question 15

What is sound transmission ?

Answer 15

travelling wave of basilar membrane
helicotrema path ; very low frequency sounds
basilar membrane :sounds with frequency high enough to hear create pressure waves that are transmitted thrugh cochlear duct

Question 16

Basilar membrane

Answer 16

is not rigid
width & stiffness varies along its length
short and stiff at base
Base: basilar membrane reponds to high frequency vibrations
Apex:basilar membrane responds to low-frequency vibrations

Question 17

The hair cells in organ of corti ?

Answer 17

apical surface of hair cell is modified into ~ 50-100 stereocillia arranged in ascendign order
-outer hair-embedded in tectorial membrane
-inner hair cells-extend into endolymph
bound together by tip links
connected to mechanically-gated ion channels
Basl regions of hair covered by synaptic terminals os sensiry & efferent neurons

Question 18

How does signal transduction work in hair cells ?

Answer 18

1. Sterocillia displaced and bend toward the tall edge of bundle
2. tension in tip links open channels :K+ influx depolarises the cell
3. Voltage -gated calcium (Ca2+) channels
4. influx of Ca triggers glutmate release at synapse-exocytosis
5. Post synaptic potentuial in afferent nerve fibre triggers an action potential (AP)–>brain via cochlear branch of vestibular nerve

Cell hyperpolarises when stereocilia bend away from tallest one

Question 19

What do outer hair cells do ?

Answer 19

only recieve 5% of cochlear nerve afferent fibres
act as active filters enhancing frequqency selectivity and sensitivity of cochlea
K+ influx depolarises these cells nut once activated they undergo a rapid contraction
results in localised amplification of movement of basilar membrane –>sharpens the tuning of basilar membrane and increases sensitivity of inner hair cells -cochlear implants

Question 20

How do you get deaf ?

Answer 20

3 forms
Central :damage to neural pathway between ear and cerebral cortex ir damge to cortex
Conductive :sound cant be transmitted through external or middle ear-fluid build up in middle-otitis media
Sensorineural :damage to structures of inner ear or auditory nerves and or death of hair cells

Question 21

Causes of hearing loss ?

Answer 21

conductive:fluid,allergens blah
Sensorineural :aging,genetic disease,infections

Question 22

Hoe many semicircular canals are in the inner ear ?

Answer 22

3 arranged at right angles to each other
Detect angular acceleration during rotation of head along 3 axis /planes :roll,yaw,pitch
located in ampulla region of each canal

Question 23

What is crista ampullaris ?

Answer 23

senses rotational acceleration
each membraneous semi-circulr duct has an enlarged swelling at one end called ampulla
cotnains eqm receptor region :crista ampullaris or crista
each crist=surrounded by cupula
hairs are embedded in latter
cuula displaced fluid movments within semicircular canals

Head turns right ->endolymph lags; pushes cupula to left ->displaces/bends stereocilia (toward kinocilium) -> APs fired.

Question 24

What are hair cells stimulated by ?

Answer 24

changes in the rate of head rotation continuos;y rotates endolymph moves at same rate ad head so stereocillia returns to resting position

Question 25

What is the utricle and saccule ?

Answer 25

provide info about linear acceleration of the heas and changes in head positive relative to he forces of gravity
sensory portion=mascula location
hair cells sensitive to stereoci;lia displacement
maculae are orientated in horizontal and vertical

Cilium (kinocilium & stereocilia) of vestibular hair cells in macula are embedded in overlying gelatinous otolith membrane.
Otoliths (calcium carbonate crystals) lie on top

Question 26

What does the utricel and sacculed do ?

Answer 26

Sensing linear acceleration and changes in head position relative to gravity
hair cells in utricle=point straight up when stand respond when tilt their head away from horiizontal plane
-Hair cells in saccule are at right angles (to those in utricle); respond to gravitational effects, e.g. when one moves from lying to standing, or to vertical accelerations

Question 27

What is the Vestibular pathway used for ?

Answer 27

1. To control eye muscles, so that eyes/gaze can remain fixed on same point (despite changes in head position); nystagmus.
2. In reflex mechanisms, maintaining upright posture and balance.
3. In providing conscious awareness of position and acceleration of the body, perception of the space surrounding the body, and memory of spatial information.

Vestibular and sensory information is integrated, leading to a sense of posture (proprioception) and movement: e.g. maintaining your position whilst standing on a moving train

Question 28

Disorders of the vestibular system ?

Answer 28

Vertigo:sensation of environmental movement when lying, sitting or standing still
Menieres disease :abnormal build-up of pressure in the inner ear; disrupts function of cochlea and semicircular canals:
Symptoms: bouts of vertigo, loss of balance, nausea, vomiting…