SC Pain and Temperature

Question 1

Distinguish basic difference between direct and indirect spinothalamic pathways

Answer 1

Direct = fast pain pathway; rapid, sharp, pricking, precise, localized pain

Indirect = slow pain pathway; burning, throbbing, dull, aching, diffuse pain AND crude touch/pressure (receptors usually in viscera)

Question 2

The direct/fast pain pathway has what types of nerve fibers?

Answer 2

A-delta = myelinated with conduction rate 5-30 m/s

C fibers = unmyelinated with conduction rate 0.5-2 m/s

Question 3

The indirect/slow pain pathway has what type of fibers?

Answer 3

C fibers = unmyelinated with conduction rate 0.5-2 m/s

Question 4

Order of events in direct/fast pain pathway

Answer 4

Receptor stimulation —> spinal cord —> lateral thalamus —> somatosensory cortices

Question 5

Order of events in indirect/slow pain pathway

Answer 5

Receptor stimulation —> spinal cord —> reticular formation —> medial thalamus —> cingulate, frontal, limbic cortices

Question 6

The direct/fast pain pathway and indirect/slow pain pathway make up what major system in somatosensory pathways?

Answer 6

Anterolateral system

Question 7

Location of cell bodies of primary neurons in direct/fast pain pathway

Answer 7

Cell bodies of pseudounipolar neurons located in DRG

Question 8

Cell bodies of primary neurons of direct/fast pain pathway are located in DRG. Describe their entry to the spinal cord

Answer 8

Fibers enter spinal cord through dorsal root, then ascend and descend 1-2 segments in the posterolateral fasciculus (Lissaur’s tract)

Question 9

Where do primary neurons in direct/fast pain pathway synapse?

Answer 9

Synapse on secondary neurons in either substantia gelatinosa (lamina II) or nucleus proprius (lamina IV)

Question 10

Describe course of secondary neurons in direct/fast pain pathway

Answer 10

Axons from the substantia gelatinosa/nucleus proprius cross in the anterior white commissure and ascend in the contralateral anterolateral funiculus as the lateral spinothalamic tract

Question 11

In the lateral spinothalamic tract, ______ levels enter the tract first, located in the posterolateral aspect. _____ levels enter last, located in the anteromedial aspect

Answer 11

Sacral; cervical

Question 12

The lateral spinothalamic tract joins with the _____ and ________ tract in the medulla to form the spinal lemniscus

Answer 12

VSTT; spinotectal

Question 13

The spinal lemniscus terminates in the ______ of the dorsal thalamus

Answer 13

VPL nucleus

Question 14

The tertiary neurons of the direct/fast pain pathway are located in the VPL nucleus of the dorsal thalamus, which receives sensory info from the ________ side of the body via the __________

Answer 14

Contralateral; spinal lemniscus

Question 15

The tertiary neurons of the direct/fast pain pathway are located in the VPL nucleus of the dorsal thalamus, which receives sensory info from the contralateral side of the body via the spinal lemniscus.

They then leave the VPL nucleus as thalamic radiations which course through the posterior limb of the _____ _____ and ______ ______ and terminate in the primary somesthetic cortex (in postcentral gyrus)

Answer 15

Internal capsule; corona radiata

Question 16

A lesion at T11 on the right side of the spinothalamic pathway would have what effect?

Answer 16

Left-sided loss of pain and temperature sense at L1 (1-2 levels below level of lesion on contralateral side)

Question 17

Brown-Sequard syndrome may result after hemisection of the spinal cord, and is characterized by what myriad of findings?

Answer 17

Loss of pain and temp from contralateral side 1-2 levels below level of lesion (lissaur’s tract)

Loss of discriminitive touch and conscious proprioception on ipsilateral side below lesion

Ipsilateral loss of ALL sensation at that level

Motor loss with anterior horn involvement

Question 18

What condition results from formation of fluid filled cyst within spinal cord central canal, most commonly at C8-T11; classic presentation is pt presenting after burning themselves, not realizing d/t loss of sensation?

Answer 18

Syringomyelia

Question 19

What functions are affected by Syringomyelia?

Answer 19

Pain and temperature affected at level of anterior white commissure (2nd order fibers) — bilateral loss of pain/temp in shawl-like distribution

Motor function also affected if cyst expands into anterior horn

Question 20

Describe path of primary neurons in indirect spinothalamic pathway

Answer 20

Enter spinal cord, bifurcate, and ascend/descend 1-2 segments in posterolateral fasciculus (Lissaur’s tract)

Have thousands of synapses with nucleus proprius (lamina IV) throughout course

Question 21

Secondary neurons in the indirect/slow pain pathway are from the nucleus proprius. They course bilaterally in the fasciculus proprius, which is a part of the _____ ______, which surrounds gray matter of spinal cord and extends rostrally through the core of the brainstem to the thalamus

Secondary neurons may then ascend to the thalamus as ______ fibers, which terminate in the reticular formation of the ______, ______, and ________ on BOTH sides of the brain

Answer 21

Reticular formation

Spinoreticular; brainstem; hypothalamus; centromedian nucleus of the dorsal thalamus

Question 22

Differentiate between the functions slow pain pathway in terms of projections through the reticular formation vs. projections to the hypothalamus and limbic cortex

Answer 22

Projections through the reticular formation function in arousal of the organism in response to nociceptive input

Projections to the hypothalamus and limbic cortex function in autonomic, reflex, and emotional aspects of pain

Question 23

T/F: unilateral lesions of spinoreticular fibers result in significant sensory deficit

Answer 23

False; clinically, unilateral lesions of spinoreticular fibers do not result in significant sensory deficites because they are too diffuse and bilateral

Incomplete transections may allow spinoreticular fibers to get around lesion via intact portion of fasciculus proprius — leading to persistent pain

Question 24

The bladder reflex:

Mechanoreceptors in bladder wall (detrusor muscle) are stretched when bladder fills. Impulses are sent to ____-____ via visceral afferent innervation (______ n.) and enter the ______ root of the spinal cord to synapse on the visceral afferent nucleus

Answer 24

S2-S4; pelvic; dorsal

Question 25

The bladder reflex:

Mechanoreceptors in bladder wall (detrusor muscle) are stretched when bladder fills. Impulses are sent to S2-S4 via visceral afferent innervation (pelvic n.) and enter the dorsal root of the spinal cord to synapse on the visceral afferent nucleus.

Interneurons convey stimulus to _____ _____ nucleus. Visceral efferent neurons from there will cause the detrusor m. to _______ and internal sphincter to _______

Answer 25

Sacral autonomic; contract; relax

Question 26

The bladder reflex:

Mechanoreceptors in bladder wall (detrusor muscle) are stretched when bladder fills. Impulses are sent to S2-S4 via visceral afferent innervation (pelvic n.) and enter the dorsal root of the spinal cord to synapse on the visceral afferent nucleus.

Interneurons convey stimulus to sacral autonomic nucleus. Visceral efferent neurons from there will cause the detrusor m. to contract and internal sphincter to relax.

Signals are also sent from visceral afferents to the ___________ which can override the micturition reflex OR increase it, depending on current situation.

When micturition is desired, the above structure increases impulses via the _____ n. (efferent) causing contraction of detrusor muscle. Also somatic innervation via ______ n. to external sphincter is inhibited causing relaxation and micturition

Answer 26

Pontine micturition center (PMC)

Pelvic; pudendal

Question 27

What condition results from lesions of the dorsal roots of S2-S4?

Answer 27

Atonic bladder

Micturition relfex contraction cannot occur if the sensory nerve fibers from the bladder to the spinal cord are destroyed, thereby preventing transmission of stretch signals from the bladder

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

results in large dilated flaccid bladder and increased bladder capacity

Question 28

T/F: voluntary voiding is possible with an atonic bladder

Answer 28

True, but it is incomplete

Question 29

Causes of atonic bladder

Answer 29

Crush injury to sacral region, diseases such as syphilis damaging dorsal horn/dorsal columns

Question 30

What condition is caused by spinal cord damage above the sacral region (S2), causing lack of control by the brain over micturition reflexes?

Answer 30

Reflex/automatic bladder

During first few days to several weeks after damage to cord, micturition reflexes are suppressed due to spinal shock from suddenloss impulses from brainstem and cerebrum (pts require catheterization)

Micturition reflex returns later and unannounced emptying occurs