Lecture 3: Pain and Temperature Pathways Flashcards
Rapid sharp, pricking, precise localized pain and temperature are conveyed via which pathway; utilizing which fibers?
- Direct spinothalamic (“fast” pain) pathway
- A-delta fiber: myelinated with fast conduction rate
- C-fibers: unmyelinated with slower conduction rate
Burning, throbbing, dull, aching, diffuse pain AND crude touch/pressure are conveyed via which pathway; utilizing which fibers?
- Indirect spinothalamic pathway (“slow” pain pathway)
- C-fibers: unmyelinated with slower conduction rate
What is the basic flow chart for the direct spinothalamic pathway?
What is the basic flow chart for the indirect spinothalamic pathway?
Describe the route of the primary neurons of the direct spinothalamic tract until they synapse.
- Cell bodes of pseudounipolar neurons located in doral root ganglion
- Fibers enter the spinal cord through dorsal root, and ascend or descend (1-2 segments) in the posterolateral fasciculu (Lissauer’s Tract)
- Fibers synapse on secondary neurons in the substantia gelatinosa (lamina II) and nucleus proprius (lamina IV)
After primary neurons of the direct spinothalamic tract synapse on substantia gelatinosa or nucleus proprius what is the next move of the secondary neurons all the way up to the medulla?
- Axons from substantia gelatinosa/nucleus proprius cross in the anterior white commissure (AWC) and ascend in the contralateral anterolateral funiculus as the Lateral Spinothalamic Tract (LSTT)
- In the medulla, the LSTT joins with the VSTT and spinotectal tract to form the spinal lemniscus (SL).
- The spinal lemniscus terminates in the Ventral Posterior Lateral (VPL) nucleus of the dorsal thalamus
There is somatotpic lamination of the LSTT, how do secondary neurons from sacral levels enter versus cervical levels and where are they located?
- Sacral levels enter 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
The tertiary neurons located in the VPL of the dorsal thalamus receives what information from the direct spinothalamic pathway and via where?
- Sensory information from the contralateral body
- Via the spinal lemniscus
Tertiary axons leave the VPL after receiving sensory info from the contralateral body via spinal lemniscus as what, what do they course through and where do they terminate?
- Leave the VPL nucleus as thalamic radiations
- Course through the posterior limb of the internal capsule, and the corona radiata
- Terminate in the primary somesthetic cortex (postcentral gyrus)
What are the primary fibers of the indirect spinothalamic pathway and describe their route from entering the spinal cord to where they synapse?
- Unmyelinated, type C fibers w/ a very slow conduction rate
- Enter spinal cord, bifurcate, and ascend/descend 1-2 segments in posterolateral fasciculus (Lissaur’s tract)
- Through its course, the primary fibers have thousands of synapses with the nucleus proprius (lamina IV)
Secondary fibers from the nucleus proprius of the indirect spinothalamic pathway course how and to where; what is the fasciculus proprius a part of? (clinically important!)
- Course BILATERALLY in fasciculus proprius (clinically important)
- Slow pain info from the nucleus proprius may ascend to the thalamus as spinoreticular fibers
- The fasciculus proprius is part of a diffuse neuronal net called reticular formation, which surrounds the gray matter of spinal cord and extends rostratlly through the core of the brainstem to thalamus
Why is the bilateral course of the secondary fibers from the nucleus proprius in the fasciculus clinically important; what kind of pain?
- You get fibers ascending on the same side and also get fibers sent across to ascend the contralateral side
- This is the basis of the diffuse and hard to localize pain related to the indirect spinothalamic pathway
Where do the spinoreticular fibers associated with slow pain information terminate?
- Reticular formation of the brainstem, hypothalamus, and the centromedian nucleus of the dorsal thalamus
- On BOTH sides of the brain!
The projections through the reticular formation function in what response by the organism to nociceptive input?
Arousal of the organism in response to nociceptive input
Projections to the hypothalams and limbic cortex function in what aspects of pain?
- Autonomic
- Reflex
- Emotional aspects of pain
What is the basis of persistent pain in relation to the indirect spinothalamic pathway and incomplete transections?
- Incomplete transections may allow spinoreticular fibers to get around lesion via intact portion of the fasciculus proprius
- This is the basis of persistent pain
If a patient presents with a deficit of loss of pain and temperature senses on the left at the level of L1; where do you suspect the lesion to be?
- Rule is the lesion is 1-2 levels above the level of the deficit on the contralateral side
- If deficit at L1 on the left, then lesion likely at spinothalamic tract of T11 on the contralateral side (right)
What is the pattern of loss seen in Brown-Sequard Syndrome; what causes these deficits?
- Complete loss of pain and temp from contralateral side of body (1-2 levels below lesion)
- Discriminative touch and concious propioception on ipsilateral side below lesion
- Ipsilateral loss of ALL sensation at level of lesion
- Motor loss
*Result from Hemisection of spinal cord
What is Syringomyelia and what level is most common?
- Formation of fluid filled cyst (syrinx) within the spinal cord (central canal)
- Most common C8-T11
What sensations are affected in Syringomyelia and why?
- Anterior white commissue (2nd order fibers)
- Resulting in bilatral loss of pain/temperature sensation in shawl or cape-like distribution
- Motor also lost IF expands into anterior horn
Patient presents after burning themselvs on a stove, iron, etc. They state they weren’t aware that they were burning themselves, what do you suspect?
- Syringomyelia
- Most common at C8-T1
- Causes loss of pain/temperature sensation in a shawl/cape-like distribution in the upper limbs
Mechanoreceptors in the bladder wall (detrusor muscle) are stetched when bladder fills and where are the impulses sent; what occurs?
- Sent to S2-S4 via visceral afferent innervation (pelvic nerve)
- Enter the dorsal root to synapse on visceral afferent nucleus
- Interneurons convery stimuls to sacral autonomic nucleus
- Visceral afferent neurons from SAN cause the detrusor muscle to contract and internal sphincter to relax
Signals from the visceral afferent neurons involved in bladder reflex are also sent to which higher order center; what affect does this have on the micturition reflex?
Sent to pontine micturition center (PMC)
- Can override the micturition reflex OR increase the reflex depending on current situation (is it okay to urinate?)
What does the PMC do when micturition is desired?
- PMC increases impulses via pelvic nerve (efferent) causing contraction of detrusor muscle and relaxation of the internal urethral sphincter.
- Also, somatic innervation via pudendal nerve to external sphincter is inhibited causing relaxation and micturition
