Lecture 4: Spinothalmic System (Anteriolateral System)

Question 1

Describe the fiber type alpha delta and type of sensation it carries.

Answer 1

small myelinated fiber with moderate conduction speed carrying cooling, 1st pain and crude touch sensations

Question 2

Describe the fiber type C fibers and the type of sensation it carries

Answer 2

very small unmyelinated fibers that convey warming and second pain sensation.

Question 3

Describe the sensory receptors associated with the anteriolateral system.

Answer 3

no specialized receptor organs, just free endings that contain a variety of receptors that are uniquely sensitive to substances, action that damage tissue and temperature.

Question 4

Name 5 different receptors related to free endings of the anteriolateral system.

Answer 4

high threshold mechanoreceptors (pinching, cutting, stretching); thermal nociceptors (responsive to extreme temps); chemical nociceptors (responsive to chemicals given off by damaged tissue); any combination of the above 3 and “silent receptors that become awakened after tissue inflammation or injury (amplify pain response)

Question 5

What causes a receptor to be sensitive to certain stimuli versus others?

Answer 5

there a variety of receptors that are sensitive to various “painful” things; depending on the channels a free nerve ending has, determines what stimulus it will respond to

Question 6

Name the general name for channels located on free fibers that sense pain.

Answer 6

TRP receptor/ channel; temperature sensitive channels have a temperature range

Question 7

True or false, a given free nerve ending has only one type of TRP channel.

Answer 7

False, some fibers may have mixes of TRP channels i.e. cold/cold fibers may also respond to very hot stimuli

Question 8

Pain and temperature are carried by what two types of fibers?

Answer 8

C (70%) and delta fibers (30%)

Question 9

What is the path of pain/temp fibers before they synapse

Answer 9

branches of pain and temp fibers enter and then ascend/descend 2 levels then synapse

Question 10

Where do pain and temp fibers tracts cross the midline.

Answer 10

fibers cross the midline after synapsing ipsilaterally via the anterior white commissure

Question 11

Cutting the Anteriolateral System (spinothalamic system) will produce what deficiencies?

Answer 11

Loss of all CONTRA pain and temp sensation two levels below and down

Question 12

How are ALS fibers organized as they ascend and what type of cell axon is included in these tracts?

Answer 12

the axons are of the second cell in the chain and as the tract ascend, fibers are pushed more laterally (inferior fibers are most lateral

Question 13

How are C and delta fibers arranged as the ALS tract ascends?

Answer 13

delta information runs contra laterally and runs in the lateral portion of the tract, C fibers run contralaterally and run in the anterior part of the ALS (some C fiber information stays ipsilateral)

Question 14

What types of fibers are the exception to the ALS organization?

Answer 14

some visceral pain fibers don’t run in ALS and run instead in the Fasiciulus gracilis (cell bodies lie close the central canal)

Question 15

Describe referred pain

Answer 15

visceral pain fibers may converge on the same dorsal horn cells getting pain info fro skin, because we rarely get pain from organs, the brain perceives that organ pain is coming form the skin

Question 16

How does rubbing an injured spot chain the pain sensation.

Answer 16

by rubbing and activating AB fibers, you activate inteneurons that turn of the pain pathway

Question 17

How do C fibers interact with interneurons normally to increase pain?

Answer 17

C fibers activate spinothalmic cells and indirectly inhibit interneurons (normally active) to increase pain

Question 18

Why do we scratch an itch?

Answer 18

the sensation of itch activates spinothalamic c fiber nerves but not potential; scratching activates C pain fibers on the same interneurons to bring them to threshold. this signaling will inhibit the sponthalamic cells (itching brings interneurons to threshold and turns off itch pathway

Question 19

Define hyperalgesia

Answer 19

increased sensitivity to pain

Question 20

Define allodynia

Answer 20

pain due to stimuli that does usually cause pain

Question 21

What is the root cause that can bring about hyperalgesia and allodynia?

Answer 21

an injury can shift the pain threshold causing allodynia and hyperalgesia

Question 22

Name 5 mechanisms or hyperalgesia and allodynia.

Answer 22

1) substances released by damaged tissue alters the way the receptors respond (threshold, intensity) which may be permanent 2) injury could lead to accumulation of sodium channels leading to ectopic discharge 3) injury can up regulate receptors 4) excitatory neurons can become hyper excitable 5) interneurons that normally inhibit pain can change/die 6) loss of innervation of pain cells can cause non-pain fibers to sprout

Question 23

What are the two pathways that tracts that ascend to the brain carrying pain fibers.

Answer 23

neospinothalamic pathway and the pale/archi spinothalmic pathway

Question 24

Describe the neospinothalamic pathway

Answer 24

mostly delta fibers (first pain and small receptive field) it carries information from the contralateral side to the the VPL nucleus up tot eh somatosensory cortex

Question 25

Describe the palow/archispinothalamic pathway

Answer 25

(emotional/ autonomic) mostly C fibers that carry information bilaterally to the brain to the thalamus and brainstem with output to the anterior cingulate and insular cortex

Question 26

How are the paelo and neo pathways related?

Answer 26

they process the information via different systems and can work independently after receiving information from the spinal cord

Question 27

How does emotion affect pain?

Answer 27

Pain can be modulated by strong emotion or by blocking opioid receptors (stops the placebo affect)

Question 28

Where are descending pain modulated?

Answer 28

in the periaquadutal grey (midbrain) receives input from higher brain centers (amaygdala, hypothalamus, anterior cingulate cortex)

Question 29

Where do descending pain modulation

Answer 29

dorsolateral funciculus

Question 30

How are opioids related to pain relief?

Answer 30

the body has endogenous opiates that are produced by modulating interneurons that have been found to inhibit transmitter release by pain fibers

Question 31

What are other ways of modulating pain via neurotransmitters?

Answer 31

there are a variety of receptors pre and post synaptic that modulate the signal based on the neurotransmitters from descending pathways (can amplify or reduce the descending signal)

Question 32

What is the zone of Lissauer?

Answer 32

???? c and delta fibers that lie in contralateral DRG of the cervical region