2. Somatosensory 2

Question 1

fast pain:

receptor, fiber type, tracts

Answer 1

1. mechanical and thermal nocioceptors
2. small myleinated fibers
3. neospinothalamic tract

Question 2

slow pain:

receptor, fiber type, tracts

Answer 2

1. polymodal nocioceptors
2. unmyelinated fiber
3. paleospinothalamic, and spinoreticulothalamic tracts

Question 3

FAST PAIN:

thalamus, cortex, and fxn

Answer 3

• lateral VPL (in thalamus)
• primary somatosensory cortex
• sharp, localized pain

Question 4

SLOW PAIN:

thalamus, cortex, and fxn

Answer 4

1. medial thalamus
2. frontal and limbic lobes of cortex
3. cortical arousal, affect

Question 5

nociception:

define, and biomechanical features

Answer 5

• tissue damage from mechanical trauma
• proteases
  
  • breakdown kininogen to bradykinin (causing slow contraction, involved in inflammation)
  • bradykinin bind to receptors that activate ion channels
• ATP: binds to ATP-gated ion channels
• K+: depolarized neuron membranes

Question 6

stimuli of nociception?

Answer 6

• tissue damage from mechanical trauma
• temperature extremes (heat over 43 degrees –> heat-senstivie ion channels open)
• oxygen deprivation

Question 7

biochem of oxygen deprivation and nociception

Answer 7

• w/ oxygen deprivation (anoxia) –> anaerobic metabolism releases lactic acid
• lactic acid –> high levels of H+ ions
• activation of H+ gated ion channels on nociceptors

Question 8

types of nociceptors

Answer 8

• polymodal (mechanical, thermal, & chemical stimuli)
• mechanical nociceptors - strong pressure
• thermal nociceptors
• chemical nociceptors

Question 9

capsaicin:

function

Answer 9

1. activates TRPV1 receptor –> which channels open at lower temperatures
2. results in inflammation-induced thermal hyperalgesia

Question 10

hyperalgesia:

define

Answer 10

a condition where a person develops an increased sensitivity to pain

Question 11

key characteristics of pain & temperature fibers

Answer 11

• A-delta (type III) fibers
• larger diameter, lightly/thinly myelinatied
• fast conduction
• sharp, prickly pain

Question 12

key characteristics of slow pain and temperaure

Answer 12

• C (type IV) fibers
• smaller diameter, UNMYELINATED; polymodal
• slower conduction
• dull, burning, poorly localized pain

Question 13

which fibers are associated with the first pain after noxious stimulus?

which fibers are with second pain?

Answer 13

1. First pain: A-delta (fast; sharp/prickly pain fibers) - more intense pain
2. Second pain: C fibers (slow, dull burning pain) - less intense pain

Question 14

ascending pathways of pain include:

Answer 14

1. information from receptors –>
2. spinal cord –>
3. ascend thru spinal cord –>
4. ascend thru brainstem –>
5. head somatosensory information –>
6. to thalamus –>
7. to cortex

Question 15

ascending pathway from receptors are important for which 2 key functions

Answer 15

1. position of body in space (w/in the environment)
2. arousal

Question 16

ALS (anterolateral system) aka Spinothalamic pathway:

functions

Answer 16

• pain
• temperature
• itch
• touch (less so)

Question 17

anterolateral system (spinothalamic pathway):

structure (input, relay nuclei, decussation)

Answer 17

1. sensory input: thermo, noci, and itch receptors
2. relay nuclei: spinal cord
3. decussation: occurs in spinal cord –> then ascends to ALS pathway

Question 18

Synapses of the Anterolateral System

(Spinothalamic pathway)

Answer 18

Synapses

1. VPL thalamus to primary somatic sensory cortex
2. Ventromedial posterior to primary somatic sensory cortex & insular cortex
3. Medial dorsal thalamus to cingulate gyrus (assoc. w/ emotions)
4. Intralaminar nuclei

Question 19

what enters the dorsal root entry zone?

Answer 19

pain fibers enter the dorsal root entry zone laterally

Question 20

which neurons enter the DC/ML of dorsal root entry zone?

what about the ALS system?

Answer 20

• DC/ML: has heavily myelinated neurons (think: fast pain)
• ALS: has lightly myelinated neurons (think: slow conduction, slow pain)

Question 21

what is another name for the dorsal root entry zone?

and where is it found?

Answer 21

Zone of Lissauer: a small strand situated in relation to the tip of the posterior column close to the entrance of the posterior nerve roots;

spinal cord gray matter

Question 22

overview of anterolateral spinothalamic tract

Answer 22

• these axons are located in the anterolateral tract, which extends from the lateral into the anterior funiculus of the spinal cord
• axons ascend the brainstem
• axons then cross the midline and ascend the spinal cord

Question 23

where does pain/temp information from LEFT SIDE OF THE BODY ascend?

Answer 23

to the RIGHT side of the spinal cord;

due to decussation between brainstem/spinal cord

(info travels on the opposite side)

Question 24

dorsal root ganglion neurons:

define

Answer 24

primary afferent neurons that transmit info. from peripheral receptors into the spinal cord

Question 25

comparison of PWC-ML and ALS systems

Answer 25

* **PWC-ML system:** neuron #1's axons at Dorsal Root entry zone and in fasiculus gracilis and fasiculus cuneatus * dorsal white column on same side * **ALS system:** neuron #1 at dorsal root entry zone; cell bodies in the dorsal horn; axons in anterior white commissure * then contralateral anterolateral tract (ALS)

Question 26

what are some inputs to the 2nd order neuron?

Answer 26

mechanoreceptors and interneurons

Question 27

gate theory

Answer 27

by stim larger diameter fibers, to synapse on interneuron in dorsal horn --\> to inhibit the second order neuron from firing

Question 28

ascending in the spinal cord: where do second order neurons ascend **contralaterally**? where do these synapse?

Answer 28

* Second order neurons ascend **contralaterally in the:** * **medulla** * **pons** * **midbrain** * synapse in the **thalamus,** but spinothalamics **synapse in the VP nucleus**

Question 29

**spinoreticular tract (spinoreticulothalamic)** define and function

Answer 29

* indirect pathway * info to the **reticular nuclei** which project to the **intralaminar nuclei** of the thalamus * fxn: important in **arousal**

Question 30

**spinomesencephalic tract (paleospinothalamic):** define and function

Answer 30

* indirect pathway * info to **midbrain tectum** --\> fxn: coordinate eye & head mvmts * info to **periaqueductal gray matter (PAG) --\>** fxn: pain regulation

Question 31

w/in the spinal cord, how do the ALS and DC-ML pathways differ?

Answer 31

they are on opposite sides, but meet in caudal medulla; **DC-ML** pathway stays on same side as stimulus until crossing over at medulla **ALS** pathway crosses over at dorsal root axon

Question 32

**CC: brown-sequard syndrome** mechanisms and symptoms

Answer 32

caused by: **hemisection of spinal cord** sxs: * **loses pain from the opposite side of the body**, about 2 levels below the lesion * **loses touch etc. on the same side** of the body as the lesion

Question 33

where does **spinomesencephalic tract** project to?

Answer 33

* **superior colliculus** --\> orienting to pain stimulus * **periaqueductal gray** --\> pain modulation

Question 34

**3 key nuclei of thalamus**, and overall functions

Answer 34

* 3 nuclei * posterior thalamic nuclei * medial dorsal nucleus * intralaminar nuclei * Fxn: plays a role in affective and motivational aspects of pain and in the memory of painful stimuli

Question 35

where in the cortex is the **painful stimuli** recorded?

Answer 35

insular cortex, and the anterior cingulate (insular cortex is found between the temporal and frontal lobes)

Question 36

cortical projections from layers 5 & 6: project to, function

Answer 36

* project to: * thalamus * brainstem * spinal cord * modulate sensory information that is ascending

Question 37

decribe the **pain modulation** of the nucleus raphe magnus

Answer 37

1. from **periaqueductal gray** 2. to **nucleus raphe magnus** 3. neurons of Raphe magnus --\> project to spinal cord; are serotonergic; and excite interneurons (enkephalinergic, and inhibit 1st & 2nd order pain neurons)

Question 38

decribe the pain modulation of the **locus ceruleus**

Answer 38

* neurons in LC are **noradrenergic** * excite interneurons; enkephalinergic (which inhibits 1st and 2nd order pain neurons)