hearing

Question 1

Properties of sound

Answer 1

1. Pressure disturbance (alternating areas of high/low pressure) produced by vibrating object
2. Sound wave –> moves outward in all directions in sine wave

Question 2

Properties of sound waves

Answer 2

Frequeny = # of waves/time –> pure tones have repeating crests and troughs

wavelength = distance bt waves –> shorter wavelength = higher frequency

pitch = percieved frequency–> normal range = 20-20000 Hz –> higher frequency=higher pitch

quality = rechness and complexity of sounds (music)

amplitude = height of crests –> percieved as loudness –> normal range is 0-120 dB –> hearing loss with prolonged exposure above 90 dB –> rock concerts over 120 dB

Question 3

Transmission of sound to internal ear

Answer 3

• sound wave vibrates tympanic membrane
• ossicles vibrate and amplify pressure at oval window
• cochlear fluid set into wave motion
• pressure waves move thru perilymph of scala vestibuli
• waves go thru cochlear duct, vibrating basilar membrane at specific location according to frequency

(waves with frequencies below threshold travel thru helicotrema and scali tympani to round window)

Question 4

Resonance of basilar membrane

Answer 4

• fibers near oval window are short and stiff –> resonate with high frequency pressure waves
• fibers near cochlear apex are longer and floppier –> resonate with lower frequency pressure waves
• mechanically processes sound before signals reach receptors

Question 5

cells of spiral organ

Answer 5

cells of spiral organ

• supporting cells
• cochlear hair cells (one row of inner hair cells; three rows of outer hair cells –> have many stereocilia and one kinocilum)
• afferent fibers of cochlear nerce coil around bases of hair cells

Function of hair cells is to convert mechanical stimulus (bending) into electrical signal (transduction)

Question 6

Excitation of hair cells in spiral organ

Answer 6

When basilar membrane vibrates
-hair cells move

• bending of tereocilia against tectorial membrane –> towards longest stereocilia –> opens cation K channels –> influx (from endolymph)–> depolarization (elec gradient, not chem) –> voltage gated Ca channels open –> more depolarization –> increased release of glutamate
• bending of stereocilia away from longest stereocilia –> closes K channels –> hyperpolarization

Question 7

Auditory Pathway

Answer 7

• NT release excites sensory neurons at base of hair cells
• axons of sensory neurons form cochlear branch of vestibulocochlear nerve

Nerve VIII goes to

• cochlear nuclei of medulla
• midbrain (inferior colliculi) –> auditory reflex
• cerebellum = motor response to sound
• back to cochlea to inhibit weaker signaling area
• back to mid ear muscles (sound attenuation reflex)
• medial geniculate nucleus of thalamus

Auditory cortex in each hemisphere recieves input from both ears, but not all sensory signals cross over to other side –> partial decussation

Question 8

auditory processing

• pitch
• loudness
• location

Answer 8

• pitch percieved by impulses from special hair cess in dif positions along basilar membrane
• loudness detected by increased number of APs that result when hair cells experience larger deflections
• localization of sound depends on relative intensity and relative timing of sound waves reaching both ears

Question 9

Homeostatic imbalances of hearing

Answer 9

Conduction deafness

• blocked sound conduction to fluids of internal ear
• impacted earwax, perforated eardrum, otis media, ostosclerosis of ossicles

Sensorineural deafness

• damage to neural structures at any point from cochlear hair cells to auditory cortical cells
• usually from gradual hair cell loss –> lose high frequency ones first