Physiology exam 2- hearing and pain

Amplitude

intensity of sound wave

frequency

related to pitch

Outer Ear

Pinna and cartilage that is responsible for altering the reflection of sound waves into the middle ear from the outer ear and helping locate the source of the sound.

Middle Ear

Tympanic membrane (ear drum), malleus, incus, and stapes (hammer, anvil, and stirrup)

Inner Ear

Oval window, filled with fluid, the cochlea, basilar membrane, organ of corti

cochlea

semicircular canals and utricle and sacule

• Three fluid-filled tunnels with hair cells between the basilar and tectorial membrane that receive audio. Excite the cells of the auditory nerve by opening ion channels.

Place theory (pitch perception)

each area along the bailar membrane hair cells sensitive to only one specific frequency of sound wave

frequency theory (pitch perception)

the basilar membrane vibrates in synchrony with the sound and causes auditory axons to produce action potentials at the same frequency

current pitch theory

low frequency sounds best explained by frequency theory (lf)

high frequency sounds best explained by place theory (hp)

the volley principle

auditory nerve produces volleys of impulses (4000 per second) with auditory cells precisely timing their responses

Auditory cortex

A1, destination for most information from the auditory system in the superior temporal cortex

“what” pathway

A1 important for auditory imagery

“where” pathway

superior temporal cortex

auditory cortex

processes information by providing a tonotopic map where some cells are more responsive to preferred tones

localize low frequency sound

phase difference

localize high frequency sound

loudness differences

sound shadow

high frequency sounds (2000-3000 Hz) produce a …

localizing sounds with sudden onset

difference in time of arrival

phase difference

provides cues to sound localization with frequencies up to 1500 Hz

conductive/middle ear deafess

if bones in middle ear fail to transmit sound waves properly to the cochlea

nerve/inner-ear deafness

damage to the cochlea, the hair cells, or the auditory nerve

tinnitus

frequent or constant ringing in the ears - experienced by ppl with nerve deafness, sometimes after damage to the cochlea, axons representing other part of the body innervate parts of the brain previously responsive to sound.

• similar to phantom limb

vestibular sensation

detects the position and movement of the head

vestibular organ

the cochlea’s duty

2 otolith organs (the saccule and the utricle)

3 semicircular canals

otolith

calcium carbonate particles that push against different hair cells

semicircular canals function

filled with jellylike substance and hair cells that are activated when the head moves

somatosensation

sensation of the body and its movements

touch receptors may be:

• simple bare neuron ending

• a modified dendrite (merkel disks)

• elaborated neuron ending

• a bare ending surrounded by non-neural cells that modify its function

cold-sensitive neurons

adapt quickly, show little response to constant, cold, temperatures

heat-sensitive neurons

respond to absolute temperature

dermatome

body area innervated by a single sensory spinal nerve

sensory information entering the spinal cord is

well-defined and distinct (pain vs. touch pathways)

various aspects of the body’s sensations

remain separate all the way to the cortex

somatosensory cortex

located in the parietal lobe

different sub areas of the somatosensory cortex

respond to different areas of the body

damage to the somatosensory cortex

impairment of body sensations

pain sensation

bare nerve endings - some also respond to acids, heat, or cold

axons carrying pain information

have little or no myelin so the impulses travel slowly

brain processes pain information

rapidly and motor reponses are fast

mild pain

triggers the release of glutamate in the spinal cord

stronger pain

triggers the release of glutamate and several neuropeptides including substance P and CGRP

relieving pain

opiates bind to receptors found mostly in the spinal cord and the periaqueductal gray area in the midbrain

endorphins

group of chemical that attach to the same brain receptors as morphine

• different types for different types of pain

placebo

decreases the brain’s emotional response to pain perception, not the sensation itself.

cannabinoids

chemicals related to marijuana that block certain kinds of pain mainly in the periphery of the body

capsaicin

produces a temporary burning sensation folled by a longer period of decreased pain

sensitization of pain

damages or inflamed tissue releases histamine, nerve growth factor, and other chemicals that increase the responses of nearby pain receptors

intense barrage of painful stimuli

leads to increased sensitivity or chronic pain later

itch

caused by release of histamines on the skin

• activates a distinct pathway in the spinal cord

• impulses travel slowly along this pathway (half a meter per second)

pain and itch

inhibitory relationship

• opiates increase itch while antihistamines decrease itch