Lect 5 Pain and Temperature

Question 1

temperature and pain receptors

Answer 1

thermoreceptors

nociceptors

Question 2

nociceptors

Answer 2

respond to different stimuli

• mechanical (crushing, cutting)
• thermal (noxious cold or heat)
• chemical (bradykinin, prostaglandin, histamine)

Question 3

primaray afferent axons for pain and temp

Answer 3

A-delta and C-fibers

Question 4

A-delta fibers

Answer 4

sharp localized pain
lightly myelinated
1st pain

Question 5

C-fibers

Answer 5

dull and unlocalized pain, aching sensations
unmyelinated
2nd pain

Question 6

Neuronal chain example 1st,2nd,3rd order

Answer 6

be able to draw this
1st order: periphery to dorsal horn of spinal cord; ipsilateral
2nd order: Spinal cord to thalamus; contralateral
3rd order: Thalamus to cerebral cortex

Question 7

Anterolateral system

Answer 7

Pain and temp are carried here
Second order neurons travel within the anterior lateral aspect of the spinal cord and anterior lateral aspect of the brainstem tegmentum

Question 8

Anterolateral system tracts

Answer 8

spino –> anterolateral system, all second order neurons originate in spinal cord
spinothalamic, spinoreticular, spinohypothalamic and spinomesencephalic

Question 9

Spinothalamic tracts

Answer 9

axons of ALS that originate in the spinal cord and terminate in the thalamus
carries noxious & innocuous temp info, crude non-discriminative sensory info (not major touch pathway)
2 tracts
neospinothalamic tract
paleospinothalamic tract

Question 10

Neospinothalamic tract

Answer 10

this neuronal chain carries sharo, localized pain info to primary somatosensory cortex
this cortical area allows for conscious awareness of the location and nature of the painful stimulus
cut from sharp object

Question 11

Paleospinothalamic tract

Answer 11

neuronal chain carries dull, aching and poorly localized pain to secondary somatosensory cortex (S-II) and other cortical areas
-most fibers that carry this type of pain info take a multisynaptic course through the reticular formation before reaching the cerebral cortex

Question 12

Lissauers Tract

Answer 12

ascends or descends 1-3 segments

Question 13

substantia gelatinosa

Answer 13

aka lamina II
major site for pain and temperature
a delta fiber termination

Question 14

1st order neuron of spinothalamic tract

Answer 14

generally A-delta fibers, C-fibers

Question 15

lamina II

Answer 15

A delta fibers may synapse directly on lamina II interneurons or lamina I and V projection neurons, which have dendrites in lamina II

Question 16

Laminae I and V

Answer 16

comprised of projection neurons. axons of these neurons form the neospinothalamic tract
can have dendrites and interneurons in lamina II

Question 17

2nd order neurons of neospinothalamic tract

Answer 17

projection neurons in lamina I and V
have dendrites that extend into the substantia gelatinosa
communicated directly or thru interneurons with primary pain afferents

Question 18

paleospinothalamic tract 2nd order neurons

Answer 18

laminae VI-VIII receive C fiber input via interneurons that project from lamina II
are projection neurons, their axons form the paleospinothalamic tract

Question 19

White commissure of spinothalamic tract

Answer 19

where it crosses midline

Question 20

Neospinothalamic tract 2nd order neuron synapse

Answer 20

synapses on Ventral posterior lateral Thalamic Nerve (VPL)

Question 21

neospinothalamic 3rd order neuron synapse

Answer 21

synapses on primary somatosensory cortex (S-I)

Question 22

Paleospinothalamic tract 2nd order neuron synapse

Answer 22

synapses on intralaminar thalamic nuclei (ILN)

10-40% of paleo fibers have been found to pass to the thalamus

Question 23

Paleospinothalamic tract 2nd order neuron synapse

Answer 23

S-II primary somatosensory cortex

anterior cingulate, insula

Question 24

Course of neo and paleospinothalamic tracts 3rd order

Answer 24

from VPL or ILN of thalamus -> 3rd order neurons project axons through posterior limb of the internal capsule to reach the cerebral cortex

Question 25

S-I location & function

Answer 25

primary somatosensory cortex, post central gyrus | cortical area allows for conscious awareness of location and nature of painful stimulus

Question 26

S-II location and function

Answer 26

paleo somatosensory cortex, anterior cingulate cortex and insula carries dull, aching and less well defined pain and sensation majority of fibers take a multisynaptic course through the reticular formation

Question 27

Anterior cingulate

Answer 27

thought to mediate the suffering and emotional components of pain

Question 28

insula

Answer 28

contributes to emotional aspects of pain(c fibers)

Question 29

Overview of spinothalamic tract

Answer 29

Primary afferent (soma DRG) --> ascend/descend in lissauers tract --> Synapse in substantia gelatinos --> 2nd order neurons cross to contralateral ALS --> medulla --> pons --> midbrain --> Thalamus (VPL or ILN) --> cortext (S I, S II, anterior cingulate, insula)

Question 30

location of spinothalamic tract in medulla

Answer 30

ALS maintains similar position in the anterolateral tegmentum

Question 31

location of spinothalamic tract in pons

Answer 31

ALS maintains position in anterolateral tegmentum

Question 32

locaiton of spinothalamic tract in midbrain

Answer 32

ALS maintains position in anterolateral tegmentum

Question 33

Visceral afferent fibers

Answer 33

respond to excessive pressure, tension and inflammation in visceral organs afferents enter the spinal cord and may by interpreted by the cerebral cortex as pain

Question 34

Why do we have pain in our left arm during a heart attack?

Answer 34

visceral afferents from the heart enter the upper thoracic spinal cord segments. In the spinal cord, these visceral pain afferents converge on the same spinothalamic tract cells reached by somatic pain fibers. Brain interprets the activation of the spinothalamic tract fibers as pain in somatic region (chest and left arm)

Question 35

Where does the diaphragm refer pain?

Answer 35

shoulder

Question 36

Spinoreticular fibers

Answer 36

second order axons of LAS originated in spinal cord and terminate in the reticular formation laminae VI thru VII/VIII receive c fiber input and give rise to spinoreticular fibers **may be described as collateral branches of paleospinothalamic tract

Question 37

Spinoreticular fibers project to...

Answer 37

Thalamus amygdala - involved in emotional response to pain hypothalamus

Question 38

Synapse of spinoreticular fibers on thalamus

Answer 38

Intralaminar thalamic nuclei (ILN)

Question 39

ILN projects to..

Answer 39

widespread cortical areas including anterior cingulate cortex and insula and frontal lobe (mediates heightened attention to painful stimuli) -chronic pain often disrupts concentration

Question 40

spinohypothalamic tract

Answer 40

receives indirect input from reticular formation | receives bilateral pain information directly from the spinal cord

Question 41

hypothalamicspinal fibers

Answer 41

involved in regulation of autonomic outflow in response to painful stimuli

Question 42

hypothalamic spinal fiber projection

Answer 42

to the lateral horn of the spinal cord (location of preganglionic sympathetic neurons)

Question 43

Spinohypothalamic fiber projections

Answer 43

cross caudally and then move vertical ipsilaterally Some cross contralaterally near hypothalamus at the supraoptic decussation carry C pain and A delta pain

Question 44

spinomesencephalic tract

Answer 44

a delta fibers pass to lamina I and V, give rise to spinomesencephalic fibers, may be considered part of the neospinothalamic tract pass through cerebral aqueduct important in descending pain control pathway

Question 45

spinomesencephalic tract synapse

Answer 45

periaqueductal gray (PAG)

Question 46

periacqueductal gray

Answer 46

receives input from spinomesencephalic tract and hypothalamus, amygdala and several cortical areas

Question 47

Descending pain control pathway

Answer 47

believed to be reason why we do not feel pain in serious situation general steps: 1. PAG receives input 2. Excitation of Enk interneurons 3. Inhibition of tonically active GABA interneurons 4. Excitation of serotonergic neurons 5. Release of serotonin in spinal cord

Question 48

PAG excitation

Answer 48

from the spinomesencephalic tract & other areas (amygdala, hypothalamus)

Question 49

Enk containing inhibitory neurons excitation

Answer 49

inhibits release of GABA from the tonically active GABAergic interneurons

Question 50

Inhibition of GABA neurons

Answer 50

disinhibit the PAG neurons that projecet to the raphe nucleus, this activates the descending pain control pathway

Question 51

Excitation of serotonergic neurons

Answer 51

in the raphe nucleus leads to release of serotonin from neurons at level of spinal cord

Question 52

serotonin in spinal cord

Answer 52

leads to inhibition of S-T tract neurons directly and indirectly by exciting inhibitory interneurons which in turn release enkephalin to inhibit S-T tract neurons

Question 53

opiates

Answer 53

opium, morphine control pain by activating opiate receptors in the PAG, initiate descending pathway