lecture 16-17

Mechanorecepetors (somatasensory primary afferent)

activated by deformation

thermoreceptors (somatasensory primary afferent)

warming or cooling

Nociceptors (somatasensory primary afferent)

activated by stimuli that are potentially injurious, mechanical, thermal, or chemical

deep tissue receptors (somatasensory primary afferent)

muscle and joint

Pacinian corpuscles

vibration; sensitive to textures

Ruffini corpuscles

detect stretching of the skin when we move fingers or limbs

free nerve endings

respond to pain, heat & cold

Meissner's corpuscles

tactile corpuscles; respond to changes in stimuli; rapidly adapting/phasic

Merkel's disks

respond to isolated points & edges; slowly adapting; fine texture

list 2 pathways that carry sensory info from skin to brain

1. dorsal column system-touch
2. anterolateral system- pain & temp

dermatone

a strip of skin innervated by a particular spinal root

Nociception vs pain

Nociception --> just signal of potential damage

Pain --> brain's reaction to nociception signal

Define nociception

neural mechanisms involved in detecting tissue damage

how is nociception activated?

\-peripheral receptors on free nerve endings that responds to painful stimuli

\-when tissue is injured, affected cells release chemicals that can activate nociceptors

define pain

an unpleasant sensory or emotional experience associated w/, or resembling that associated w/, actual or potential tissue damage

adaptive purpose of pain

\-helps us withdraw from its source

\-engage in recuperative actions

\-signal others

Pain is subjective or objective? explain

hard for someone to measure

McGrill Pain Questionnaire

\-sensory- discriminative dimension (throbbing, gnawing, shooting)

\-motivational-affective (emotional) dimension (tiring, sickening, fearful)

\-overall cognitive evaluative dimension (no pain, mild, excruciating)

Injured cells release substances that

1\. cause local inflammation

2\. stimulate nerve endings

\-start of anterolateral or spinothalamic system that transmits sensations of pain & temp to the brain

trp system

transient receptor potential vanilloid type 1 (TRPV1 or vanilloid receptor 1) exists in the skin to detect thermal nociceptive stimuli; respond to heat & histamine

Capsaicin

\-a compound that is responsible for the hot in chili peppers (evolved to ward off mammalian predators)

\-ligand that binds to & activates TRPV1 receptors

TRP1 receptors are on___ unmyelinated C fibers so…

thin unmyelinated ... so...

\-conduct more slowly, producing lasting pain

\-dull ache

TRP2

transient receptor potential 2

\-detects hotter temperatures than TRPV1

\-does not respond to capsaicin

TRP2 receptors are on___ myelinated A delta fibers so….

large myelinated...so

\-conduct very rapidly (

A delta & C fibers carry info to where?

dorsal horn of the spinal cord

In the spinal cord what do the A delta & C fibers release?

glutamate (NT) & substance P (peptide neuromodulator)

In the anterolateral pathway where do axons decussate?

spinal cord

Where is pain information integrated?

cingulate cortex

cingulate cortex

extent of activation in cingulate correlates to how much discomfort diff ppl report to same mildly painful stimulus

why can controlling pain be difficult?

cuz pain is a biopsychosocial phenomenon

gate-control theory (dominant model of pain transmission)

hypothesizes the spinal cord contains a neurological "gate" that blocks pain signals or allows them to pass on to the brain

\-effective pain relief may depend on finding ways to cut off pain signal by keeping "gates closed"

analgesia

absence or reduction of pain

Opiate drugs and endogenous opioids

\-opiate drugs mimic endogenous opioids (endorphins and enkephalins)

\-bind to specific receptors in brain to reduce pain, including in the periaqueductal gray (brainstem)

\-can inject locally

\-Epidural (next to spinal cord) or intrathecal (under arachnoid membrane)

electrical stimulation (transcutaneous electrical nerve stimulation=TENS)

relieves pain by stimulating nerves around the source of pain or injured area

placebo effect

relief of a symptom, such as pain, even though treatment is an inert substance

electrical stimulation & placebo are mediated…

partially by opioid mechanisms

\-naloxone (narcan) opioid antagonist that can block the analgesic effect of TENS & placebo

Cannabis

stimulates cannabinoid receptors in spinal cord & brain

\-helpful for chronic pain

acupuncture

relieves pain by inducing endorphin release

stress

can activate analgesia symptoms

\-likely acts by opioid & non-opioid analgesia systems

A pure tone is described by two measures:

amplitude or intensity and frequency

amplitude or intensity

\-measured in decibals (dB)

\-perceived as loudness

Frequency

number of cycles per second of vibration

\-measured in Hertz (Hz)

\-perceived as pitch

Amplitude

sine wave representation of the pressure waves above

amplitude doubled =>

frequency same as above

amplitude same as original =>

frequency doubled

major parts of the ear

external ear, middle ear, inner ear

external ear

captures, focuses, and filters sound

Parts of the external ear

pinna and ear canal

middle ear

concentrates sound energies

middle ear parts

tympanic membrane (eardrum; stretched across auditory canal); ossicles (3 small bones that vibrate in response to tympanic membrane; malleus->incus->stapes)

ossicles

malleus, incus, stapes

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Two muscles of the middle ear

tensor tympani and stapedius

tensor tympani

attaches to malleus & eardrum

stapedius

attached to stapes

inner ear

auditory portion; cochlea

spiral-shaped cochlea converts ____ into ____

vibrations into neural activity

3 parallel canals of cochlea

1\. Vestibular canal/Scala vestibuli

2\. Middle Canal/Scala media

3\. Tympanic Canal/Scala tympani

basilar membrane

flexible; separates tympanic canal from middle canal (also base of organ of corti)

Organ of Corti

part of the cochlea that converts sound into neural activity

The hair cells of the ear are

receptor/sensory cells of auditory system

Inner Hair Cells (IHC)

transmit (send) acoustic stimuli; single row near central axis

Outer Hair Cells (OHC)

modulate acoustic stimuli; 3 rows

stereocilia

small stiff hairs that extend from the top of hair cells

tectorial membrane

lies on top of organ of Corti; stereocilia extend into it

vestibocochlear nerve (cranial nerve VIII)

contains auditory fibers that contact base of hair cells

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afferent nerve ending

send info to the brain CNS (leave hair cell)

efferent nerve ending

exit CNS to PNS

4 kinds of neural connections with hair cells

1)IHC afferents

2)IHC efferents

3)OHC afferents

4)OHC efferents

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1) IHC afferents

convey action potentials that provide sound perception to the brain; release glutamate

2) IHC efferents

lead from the brain to the IHCs--control responsiveness; release acetylcholine onto inner hair cell post synaptic terminal of afferent

3)OHC afferents

convey information to the brain about the state of the basilar membrane; release acetylcholine

4) OHC efferents

lead from the brain to OHCs—the brain can command changes in their length, which affects the basilar membrane; release GABA

diff frequencies elicit maximal response at _______ membrane in cochlea

diff parts of the membrane

_____ frequencies elicit max response near _____ of cochlea

high frequencies elicit max response near base of cochlea

_____ frequencies elicit max response near _____

low frequencies elicit max response near apex of cochlea

steps in conduction of sound

1. sound vibrates the eardrum
2. vibrations communicated by ossicles to the oval window
3. this causes basilar membrane to vibrate
4. hair cells in basilar membrane move, causing stereocilia to bend
5. when stereocilia bend, a link between the cilia (tip link) is distorted & this causes ion channels to open
6. K+ & Ca2+ rush in depolarizing cell
7. initial depolarization opens voltage gated Ca 2+ channels at the base of the cell
8. synaptic vesicles fuse & NT is released

auditory pathway to brain

cochlea (brainstem)--> superior olivary nuclei--> inferior collicus (midbrain)--> medial geniculate nucleus of the thalamus (diencephalon) --> primary auditory cortex (superior temporal cortex; telencephalon)

superior olivary nuclei

part of auditory brainstem; receive bilateral input, the first site of binaural (two-ear; info from 2 ears) processing

inferior colliculus

auditory tectum, part of midbrain; a major site of auditory processing

\-auditory startle response

\-sound localization

medial geniculate

auditory portion of the thalamus relays info from inferior colliculus to auditory cortex; Involved in focusing attention and provides some filtering.

auditory cortex

portion of cortex devoted to processing sound info

\-not needed for perception of simple tones; analyze complex tones (speech & language)

binaural detection

Locating position of a sound source using both ears

\-Relies on differences between the stimuli that reach ears (intensity & latency)

Intensity

diff in sound level/ amplitude @ 2 ears

latency

diff in sound arrival time @ 2 ears

experience having an effect on sensitivity of higher functions in auditory processing ex:

portion of auditory cortex that processes music is much larger in musicians

conduction deafness

disorders of the outer or middle ear that prevent sounds from reaching the cochlea

\-ossicles in middle ear fuse->prevent eardrum vibrations from being conveyed to oval window

\-fluid/ear wax build up

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sensorineural deafness

disorder of cochlea; hair cells fail to respond to movement of basilar membrane

\-tinnitus: damage in hair cells cause persistent ringing in ears

central deafness

hearing loss caused by damage to auditory brain areas, such as by stroke, tumors, or traumatic brain injury

word deafness

unable to recognize spoken words (not processed correctly when heard)

cortical deafness

difficulty in recognizing all complex sounds or speech

Deafness treatment

generate new hair cells: success in lab animals; may be possible in humans, cochlear implants

How do cochlear implants work?

\-a microphone detects sound

\-directs the cochlear implants circuitry to electrically stimulate the cochlea at locations corresponding to sound's pitch

\-auditory nerve is excited & signals the brain as usual

vestibular system

detects the position and movement of the head

semicircular canals

3 fluid-filled tubes in diff planes, connected @ the ends to the utricle & saccule

ampulla

enlarged region at base of canals, containing hair cells

utricle and saccule

fluid-filled sacs that make up the otolith organs; also have hair cells that activate (bend) if head is bent

Vestibular system: what happens when head rotates around axes?

\-rotation is translated into flow of gel w/in semicircular canals

\-results in deformation of hair cells in ampullae at the base, exciting the vestibulocochlear nerve

motion sickness

experience of nausea from too much vestibular excitation

sensory conflict theory

sickness occurs when we receive contradictory sensory such as diff between vestibular and visual input

motion sickness hypothesis

nausea evolved to help body get rid of ingested toxins, after experiencing dizziness (led to barf up toxins) due to potential poisons