Ch7 - Audition

Question 1

Human hearing range

Answer 1

30 - 20,000 oscillations per second

Question 2

Outer & middle ear

Answer 2

via pinna through ear canal to tympanic membrane (eardrum)

ossicles (bones), melleus (hammer) transmit vibrations via incus & stapes to cochlea

Question 3

Inner ear

Answer 3

Bottom of steps presses against membrane behind oval window (opening in bone)

Organ of corti - receptive organ (basilar mem, hair cells, tectorial mem) - in scala media between (hollow) scala vestibuli & scala tympani - in mem surrounding cochlea in bone

Basilar membrane: apex (wide & floppy, high frequencies), base (narrow & stiff, low f)

Question 4

Transduction

Answer 4

Hair cells (inner, 3500 & outer, 12000) - contain cilia which form synapses w dendrites

Transduction apparatus in hair cells - top link attached to insertional plaque (each contains 1 cation channel) - K+ & Ca2+ enter ion channel

Question 5

Cilia

Answer 5

core of actin filaments surrounded by myosin filaments - rigid

Question 6

Cochlear nerve connections

Answer 6

Afferent connections (auditory info to brain via cochlear nerve) vs efferent (fibres make up olivocochlear bundle)

Question 7

Auditory pathways

Answer 7

Cochlear nerve ganglion (cochlear nerve) → Auditory nerve (in medulla) → ventral & dorsal cochlear nucleus → superior olivary complex (medulla) → lateral lemniscus (bundle of fibres) → inferior colliculus (tectum) → medial geniculate nucleus (thalamus) → auditory cortex

Question 8

pathways - contralateral or ipsilateral?

Answer 8

Both ears, but mostly contralateral

Some info also goes to cerebellum & reticular formation

Question 9

olivocochlear bundle

Answer 9

Efferent fibres (makes up olivocochlear bundle) form synapses on outer hair cells - terminal buttons secretes acetylcholine (inhibitory) -

Question 10

Auditory cortex

Answer 10

Tonotopic representation - basilar membrane frequencies

Hierarchal organisation (like visual, but regions vs lairs) - core region (primary, gyrus on dorsal surface of temporal lobe), belt region (1st level of auditory association), parabelt

2 processing streams: anterior (analysis of complex sound), posterior (sound localization)

Question 11

Qualities of sound

Answer 11

Pitch: med-high frequencies detected by place coding (diff locations in basilar membrane) while low detected by rate coding (neurons are in synchrony w movement of basilar membrane)

Loudness: cochlear nerve alters rate of firing action potentials (loudness of low-frequency signalled by number of axons arising from neurons in basilar membrane)

Timbre: fundamental frequency (basic pitch) & overtones - basically breaks down

Question 12

Spatial location - 3 physiological methods

Answer 12

difference in arrival times of sound waves (superior olivary complex)
Phase differences for low Hz - angle of movement of eardrum (superior olivary complex)
Intensity differences for high Hz
Analysis of timber - height, if its front or behind - angle of sound waves striking the folds and ridges of pinna

Question 13

Parallels visual system:

Answer 13

Tonotopy (auditory) or retinotopy (visual) preserved from sensory cells to cortex
Convergence of inputs from lower levels → neurons at bigger levels have more complex responses (binocular or binaural)

Question 14

Music

Answer 14

harmony (inferior frontal cortex), beat (right auditory cortex), rhythm (left auditory cortex), timing (cerebellum & basal ganglia)