4 Pain and Temperature - A

Question 1

Name 2 main tracts that are motor and descending pathways?

Answer 1

1. Pyramidal tracts
2. Extrapyramidal tracts

Question 2

What are the sub-tracts of Pyramidal tracts? (2)

Answer 2

1. Lateral corticospinal tract
2. Anterior corticospinal tract

Question 3

What are the sub-tracts of Extrapyramidal tracts? (4)

Answer 3

1. Rubrospinal tract
2. Reticulospinal tract
3. Olivospinal tract
4. Vestibulospinal tract

Question 4

Name the 3 main tracts of sensory and ascending (afferent) pathways?

Answer 4

1. Dorsal Column Medial Lemniscus System
2. Spinocerebellar tracts
3. Anterolateral system

Question 5

What are the sub-tracts of Dorsal Column Medial Lemniscus system? (2)

Answer 5

1. Gracile fasciculus
2. Cuneate fasciculus

Question 6

What are the sub-tracts of the Spinocerebellar tracts? (2)

Answer 6

1. Posterior spinocerebellar tract
2. Anterior spinocerebellar tract

Question 7

What are the sub-tracts of the Anterolateral system? (2)

Answer 7

1. Lateral spinothalamic tract
2. Anterior spinothalamic tract

Question 8

What pathway are rapid, sharp, pricking, precise localized pain and temperature conveyed via?

Answer 8

direct spinothalamic (“fast” pain) pathway

Question 9

What are the two types of fibers that are part of the direct spinothalamic (“fast” pain) pathway?

Answer 9

1. A-delta fibers
2. C fibers

Question 10

Describe A-delta fibers.

Answer 10

myelinated with conduction rate (5-30 m/s)

Question 11

Describe C fibers.

Answer 11

unmyelinated with conduction rate (0.5-2 m/s)

Question 12

How are burning, throbbing, dull, aching, diffuse pain AND crude touch/pressure conveyed via?

Answer 12

indirect spinothalamic system (“slow” pain pathway)

Question 13

What fibers make up the indirect spinothalamic system (“slow” pain pathway)?

Answer 13

C fibers

Question 14

Describe the direct spinothalamic (“fast” pain) pathway.

Answer 14

receptor –> spinal cord –> lateral thalamus –> somatosensory cortices

Question 15

Describe the indirect spinothalamic system (“slow” pain pathway).

Answer 15

receptor –> spinal cord –> reticular formation –> medial thalamus –> cingulate, frontal, limbic cortices

Question 16

Primary neurons of the direct spinothalamic (“fast” pain) pathway start where?

Answer 16

1. peripheral pain/temperature receptors.

Question 17

Primary neurons of the direct spinothalamic (“fast” pain) pathway enter the spinal cord where ascend/descend via what tract?

Answer 17

2. Fibers enter the spinal cord through the dorsal root ganglion and ascend/descend (1-2 segments) in the posterolateral fasciculus (Lissauer’s tract)

Question 18

Primary neurons of the direct spinothalamic (“fast” pain) pathway terminate on 2nd order neurons where?

Answer 18

3. Fibers then synapse on the secondary neurons in the substantia gelatinosa and some synapse in the nucleus proprius

Question 19

Secondary neurons of the direct spinothalamic (“fast” pain) pathway start where and cross via ___ to enter which part of the anteriolateral/spinothalamic tract?

Answer 19

1. the substantia gelatinosa/(nucleus proprius) cross in the anterior white commissure (AWC) and ascend in the Lateral spinothalamic Tract (LSTT) of the contralateral anterolateral funiculus

Question 20

Secondary neurons of the direct spinothalamic (“fast” pain) pathway organize themselves how in the LSTT?

Answer 20

2. Somatotopic lamination of the Lateral Spinothalamic Tract (LSTT).
   * 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 21

Secondary neurons of the direct spinothalamic (“fast” pain) ascend through spinal cord via what tract(s) and terminate where?

Answer 21

3. In the medulla, the Lateral Spinothalamic Tract (LSTT) joins with the Ventral Spinothalamic Tract (VSTT) and spinotectal tract to form the spinal lemniscus (SL). The SL terminates in the Ventral Posterior Lateral (VPL) nucleus of the dorsal thalamus

Question 22

Tertiary neurons of the direct spinothalamic (“fast” pain) pathway start where?

Answer 22

1. Neurons located in the ventral posterior lateral nucleus (VPL) of the dorsal thalamus.

The VPL nucleus receives sensory information from the contralateral body via the spinal lemniscus.

Question 23

Tertiary neurons of the direct spinothalamic (“fast” pain) pathway travel through what structure and terminate where?

Answer 23

2. Tertiary axons leave the VPL nucleus as thalamic radiations which course through the posterior limb of the internal capsule, and the corona radiata and terminate in the primary somesthetic cortex (postcentral gyrus).

Question 24

Primary neurons of the indirect spinothalamic (“slow” diffuse pain) pathway start and end where? [Step 1]

Answer 24

Primary fibers are unmyelinated, type C fibers with a very slow conduction rate (0.5-2.0 m/s)

It enters the spinal cord and bifurcates either ascend/descend 1-2 segments in the posterolateral fasciculus (Lissaur’s tract). Throughout its course, the primary fibers synapses with the nucleus proprius (lamina IV). [This is the part that’s different from direct pathway, which would synapse with substantia gelatinosa]

Question 25

Secondary neurons of the indirect spinothalamic ("slow" diffuse pain) pathway start and end where? [Step 2/3]

Answer 25

Secondary fibers from the nucleus proprius course **bilaterally** in **fasciculus proprius**. (CLINICALLY IMPORTANT) Slow pain information from the nucleus proprius may ascend to the thalamus as **spinoreticular fibers**. The fasciculus proprius is part of a diffuse neuronal net called the **reticular formation**, which surrounds the gray matter of the spinal cord and extends rostrally through the core of the brainstem to the thalamus.

Question 26

Spinoreticular fibers (of indirect pathway) terminate in **reticular formation** of the ______ (3 areas) on **both** sides of the brain.

Answer 26

1. brainstem 2. hypothalamus 3. **centromedian nucleus** of the dorsal thalamus

Question 27

The projections through the reticular formation (indirect pathway) function in the ______ of the organism in response to nociceptive input.

Answer 27

**arousal**

Question 28

Projections (indirect pathway) to the **hypothalamus** and the **limbic cortex** function in the _____ (3) aspects of pain.

Answer 28

1. autonomic 2. reflex 3. emotional

Question 29

Why clinically, do **unilateral lesions** of the spinoreticular fibers (indirect pathway) do not result in significant sensory deficits?

Answer 29

Because it is **bilaterally** and **too diffuse** to be affected by unilateral lesions. Incomplete transections may allow spinoreticular fibers to get around lesion via intact portion of the fasciulus proprius. This is the basis of **persistent pain**.

Question 30

Loss of sensation for pain/temperature at L1 and below on the right. Where is the lesion?

Answer 30

Lesion is 1-2 segments above on the contralateral side (T10-11) Just spinothalamic tract lesion only!

Question 31

Describe what you would see with a patient with Brown-Sequard Syndrome.

Answer 31

HEMISECTION OF SPINAL CORD - Loss of 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) - Loss of Discriminative touch and conscious proprioception on ipsilateral side below - ipsilateral loss of ALL sensation at level - motor loss

Question 32

What is Syringomyelia?

Answer 32

Formation of **fluid filled cyst (syrinx)** within the spinal cord (within central canal), most common C8-T1 - **Pain and temperature** affected **Anterior white commissure** (2nd order fibers of spinothalamic tract affected) - Results in **bilateral** loss of pain/temperature sensation in **shawl or cape-like distribution** - **Motor** also lost if the cyst expands into anterior horn

Question 33

Describe the normal bladder reflex.

Answer 33

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 34

What lesions cause Atonic Bladder

Answer 34

**dorsal roots** of **S2-S4**

Question 35

What is seen clinically due to Atonic Bladder.

Answer 35

(Remember lesions at **dorsal roots of S2-S4**) Micturition reflex 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 the urethra. This is known as **overflow incontinence**.

Question 36

What is the disease process called for a large, dilated, flaccid bladder and increased bladder capacity. Voluntary voiding is possible, but incomplete. Causes: crush injury to sacral region, diseases (e.g., Syphilis, damage to dorsal horn/dorsal columns)

Answer 36

ATONIC BLADDER

Question 37

What spinal cord damage is seen with reflex/automatic bladder?

Answer 37

Spinal cord damage **above** the sacral region (S2)

Question 38

Can micturition reflexes still occur with reflex/automatic bladder and are they still controlled by the brain?

Answer 38

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

Question 39

Describe what is seen with patients with Reflex/Automatic Bladder.

Answer 39

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