3) Pain and Temperature Pathways

Question 1

How is rapid sharp, pricking, precise pain and temperature conveyed?

Answer 1

Direct spinothalamic (“fast” pain) pathway

Question 2

What are the two types of fibers in the direct spinothalamic pathway?

Answer 2

A-delta fibers - myelinated with conduction rate (5-30 m/s) C Fibers - unmyelinated with conduction rate (0.5-2 m/s)

Question 3

How is burning, throbbing, dull, aching, diffuse pain AND crude touch/ pressure conveyed? Via what type of fibers?

Answer 3

Indirect spinthalamic system

Unmyelinated C fibers (.5-2 m/s)

Question 4

Describe the path of both the direct and indirect pathways.

Answer 4

Direct Pathway: receptor → spinal cord → lateral thalamus → somatosensory cortices

Indirect Pathway: receptor → spinal cord → reticular formation → medial thalamus → cingulate, frontal, limbic cortices

Question 5

In the direct spinothalamic pathway… it starts with primary neurons, where are these located?

Answer 5

In the dorsal root ganglion

Question 6

After entering the dorsal root, the fibers ascend or descend in what?

And then the fibers synapse on secondary neurons where?

Answer 6

The posterolateral fasciculus (Lissauer’s tract)

Substantia gelatinosa and nucleus proprius

Question 7

Secondary neurons (coming from the substantia gelatinosa /nucleus proprius) cross where? Then ascend in what, known as what tract?

Answer 7

They cross in the anterior white commissure, ascend in the contralateral anterolateral funiculus, as the lateral spinothalamic tract.

Question 8

In the lateral spinothalamic trat which levels of the body enter first and go where?

Answer 8

Sacral levels enter the tract first and are located in the posterolateral aspect of the tract. Cervical levels enter the tract last and are located in the anteromedial aspect of the tract.

Question 9

In the medulla the lateral spinothalamic tract and spinotectal tract form _______? Which ultimately terminates in the ____________________________ of the dorsal thalamus

Answer 9

Spinal lemniscus (SL)

Ventral posterior lateral (VPL from sensory lecture) nucleus

Question 10

Neurons located in the VPL of the thalamus are known as ______?

The VPL receives ______ information from the _______ body via spinal lemniscus.

Answer 10

Tertiary neurons

Receives sensory information, from the contralateral body

Question 11

The tertiary neurons terminate where?

Answer 11

The primary somesthetic cortex (postcentral gyrus)

Question 12

In the indirect pathway, what is special about the way the fibers course in the fasciculus proprius?

How does this present clinically?

Answer 12

They course bilaterally!

Unilateral lesions of the spinoreticular fibers do not result in significant sensory deficits because they are bilateral and diffuse to be affected by unilateral lesions. Incomplete transections may allow spinoreticular fibers to get around lesion via intact portion of the fasciculus proprius. This is the basis of persistent pain.

Question 13

A lateral spinothothalamic tract lesion would lead to???

Answer 13

Contralateral loss of pain and temperature sense

Question 14

Your patient has a spinal cord lesion, what syndrome does he have?

Pain and temp from contralateral side of body. Complete loss of pain and temperature sensation 1-2 levels below level of lesion (Lissauer’s tract). Discriminative touch and conscious proprioception on ipsilateral side below. Ipsilateral loss of ALL sensation at level.

Answer 14

Brown-Sequard syndrome

Question 15

What is syringomyelia?

Everything about it…

Answer 15

It is a fluid filled cyst within the spinal cord (most common at C8-T1)

Anterior white commissure is affected, then pain and temp is gone (bilaterally, in cape-like/dermatomal distribution)

Motor can be lost if goes into anterior horn

Classic case: Patient presents after burning themselves on stove, iron, etc. They state they weren’t aware that they were burning themselves because of the loss of pain/temperature sensation in upper limbs.

Question 16

Bladder reflex… describe it

It’s lengthy… but basically all types of nerves are involved

Answer 16

Mechanoreceptors in bladder wall (detrusor muscle) are stretched when bladder fills. Impulses are sent to S2-S4 via visceral afferent innervation (pelvic nerve) and enter the dorsal root to synapse on visceral afferent nucleus. Interneurons convey stimulus to sacral autonomic nucleus. Visceral efferent neurons from SAN will cause the detrusor to contract and internal sphincter to relax.
Signals also sent from visceral afferents to pontine micturition center (PMC) which can override the micturition reflex OR increase the reflex depending on current situation (is it okay to urinate?)
When micturition is desired, PMC increases impulses via pelvic nerve (efferent) causing contraction of detrusor muscle. Also, somatic innervation via pudendal nerve to external sphincter is inhibited causing relaxation and micturition.

Question 17

What is atonic bladder and what causes it?

Answer 17

Instead of emptying periodically, the bladder fills to capacity and overflows a few drops at a time through the urethra. This is called overflow incontinence.

Caused by lesions of the dorsal roots S2-S4

Basically, bladder keeps filling because no signals are coming from stretch fibers.

Question 18

What is Reflex/automatic bladder and what causes it?

Answer 18

Typical micturition reflexes can still occur, but they are no longer controlled by brain

Spinal cord damage above the sacral region

During first few days to several weeks after damage to cord has occurred, micturition reflexes are suppresseddue to “spinal shock” from sudden loss impulses from the brainstem and cerebrum (patients require catheterization)
Micturition reflex returns and unannounced emptying occurs