Spinal cord II

Question 1

Ventral Spinothalamic Pathway

Answer 1

Ventral Spinothalamic Pathway

The Ventral Spinothalamic Pathway (VST) system conveys light (passive) touch, crude tactile sensations and pressure. The receptors for this system are free nerve endings, peritrichial nerve endings, and Merkel’s tactile disks. The receptors are innervated by the peripheral processes of pseudounipolar neurons whose cell bodies are located in the dorsal root (spinal) ganglia. These are the primary neurons in this sensory pathway

Question 2

Dorsal Spinocerebellar Tract (DSCT)

Answer 2

The DSCT conveys precise coordination, postural adjustments and precise movements of individual muscles of the lower limbs and body.

Question 3

primary spinal processes of C8-L3

Answer 3

clark’s column

the levels at which the primary axons from the lower limb’s proprioceptive/exteroceptive fibers synapse on dorsalis nuclei

Question 4

course of DSCT tract

Answer 4

primary axons–> secondary nuclei (nucleus dorsalis) –> DSCT tract in the lateral funiculus–> inferior cerebellar peduncle –> vermis of cerebellum

Question 5

L4-S5 spinal nerves

Answer 5

enter the spinal cord below the level of the nucleus dorsalis (Clark’s Column), they must ascend in the fasciculus gracilis before terminating in the nucleus dorsalis. Nucleus dorsalis conveys information from these levels to the cerebellar vermis via the ipsilateral dorsal spinocerebellar tract.

Question 6

1. precise coordination, postural adjustments and precise movements
2. gross postural adjustments, and overall proprioception of the lower limb
3. fine coordination, postural adjustments, and movements of individual muscles of the limbs and body.

Answer 6

1. DSCT
2. VSCT
3. CCT (DAF) cuneocerebellar tract (direct arcuate fibers)
   4.

Question 7

Ventral Spinocerebellar Tract pathway

Answer 7

Conveys gross postural adjustment and overall proprioception of the lower limbs

Lumbosacral spinal nerves (primary n.) –> intermediate gray/base of dorsal horn (secondary n) –> DECUSSATION THROUGH ANTERIOR WHITE COMMISSURE–> ascens in VSCT in lateral funinculus –> asencds THROUGH MEDULLA –> loops through superior peduncle –> vermis

Question 8

Cuneocerebellar Tract

Answer 8

Primary axons from the C1-7 levels –> lateral aspect of the posterior column–> terminate in the accessory cuneate nucleus –> Cuneocerebellar fibers (also called direct arcuate fibers) project from
the accessory cuneate nucleus directly to the cerebellar cortex of the vermis.

Direct arcuate fibers convey fine coordination, postural adjustments, and movements of individual muscles of the limbs and body

Question 9

gross postural and limb proprioception from the upper limbs.

Answer 9

Rostral spinocerebellar tract

This presumed tract conveys gross postural and limb proprioception from the upper limbs. Primary axons terminate on scattered cells located in the base of the dorsal horn and intermediate gray areas of the cervical levels of the spinal cord. Secondary axons probably course in the ipsilateral VSCT, and enter the cerebellum via both the inferior and superior cerebellar peduncles. These fibers will terminate in the cerebellar cortex of the vermis.

Question 10

precise proprioception of individual muscles

Answer 10

1. Upper extremities: cuneocerebellar tracts
2. Lower extremiities: dorsal spinocerebellar tracts

Question 11

Gross proprioception of whole limb, upper extremity and lower extremity

Answer 11

1. Upper extremity: Rostral spinocerebellar
2. Lower extremity: Ventral spinocerebellar

Question 12

A delta (δ) fibers

Answer 12

1. neospinalthalamic system (i.e. LSTT): direct pain pathway
2. conveys fast pain/highly localized sensations/thermal censation
3. thin myelin
4. conduction rate of 5-30 m/s.
5. A δ fibers terminate on secondary neurons in the substantia gelatinosa

Question 13

type C fibers

Answer 13

1. indirect spinothalamic system (“slow” pain pathway)
2. burning pain, deep, dull, diffuse pain
3. polyneuronal, polysynaptic divergent pathway
4. poor localization and discrimination
5. unmyelinated
6. slow conduction rate (0.5-2.0 m/s).
7. principally perceived at the thalamic level
8. C type fibers terminate on secondary neurons in the nucleus proprius,

Question 14

balance of incoming nonnociceptive and nociceptive fibers, endogenous endorphins, and various descending and ascending systems.

Answer 14

The substantia gelatinosa (SG) is located at the tip of the dorsal horn of all levels of the spinal cord. Its intrinsic circuitry is influenced by the balance of incoming nonnociceptive and nociceptive fibers, endogenous endorphins, and various descending and ascending systems.

Question 15

Somatotopic lamination of the LSTT.

Answer 15

from pesterolateral to anteromedial: sacral–>lumbar–>thoracic–> cervical

Question 16

spinal lemniscus

Answer 16

In the medulla, the LSTT joins with the VSTT and spinotectal tract to form the spinal lemniscus (SL). Terminates in the ventral posterior lateral (VPL) thalamic nuclei of the dorsal thalamus

Only about 1/3 of the LSTT fibers reach the thalamus. The remainder of the ascending fibers terminates on interneurons for complex, intersegmental reflexes, and other ascending pathways.

Question 17

Tertiary axons leave the VPL nucleus as…

Answer 17

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

Question 18

dorsolateral fasciculus of Lissaur

Answer 18

unmyelinate type C fibers with a very slow conduction rate (0.5-2.0 m/s). Upon entering the spinal cord they bifurcate, and ascend and descend a variable number of segments in the dorsolateral fasciculus of Lissaur. Throughout its course the primary fiber sends thousands of collateral terminals to the nucleus proprius.

Question 19

C type fibers

Answer 19

1. slow, unlocalized pain
2. travel through dorsolateral fasiculus of lissaur
3. MOST terminate on interneurons: forms neuronal patterns for the complex/stereotyped intersegmental reflexes characteristic of pain responses.
4. SOME fibers terminate in the substantia gelatinosa: ascend in the direct spinothalamic system
5. MAY ascend to the thalamus as spinoreticular fibers within the fasciculus proprius (part of reticular formation)
6. ultimately spinoreticular fibers terminate in the midline reticular formation of the brainstem, hypothalamus, and the centromedian nucleus of the dorsal thalamus on both sides of the brain.
7. diffuse nature is the basis of persistent or intractable pain.
8. principally perceived at the thalamic level.

Question 20

referred to as upper motor neurons.

Answer 20

1. corticospinal , corticorubro, corticoreticulospinal
2. all arise from pyramidally-shaped neurons (cells of Betz) in the primary motor and premotor cortices.
3. Corticorubral and corticoreticular descend from these areas as part of the corticorubrospinal and corticoreticulospinal pathways.
4. Since these tracts synapse on other neurons—they are referred to as upper motor neurons.

Question 21

corticospinal tract (CST) descends through

Answer 21

1. corticospinal tract (CST) descends through the
   
   1. corona radiata–>internal capsule–>cerebral peduncles–> pons–>upper medulla–> lower medulla, 85-90% fibers decussate at the pyramidal decussation–>form Lateral Corticospinal Tract (LCST).
   2. remaining uncrossed fibers continue as the anterior corticospinal tract (ACST

Question 22

lateral corticospinal tract terminate in…

Answer 22

neuronal “pools” (intermediate gray) at all levels of the spinal cord. Only a small number of fiber synapse directly upon lower motor neurons (anterior horn).

Most of the fibers distribute to the cervical (55%) and lumbosacral (25%) enlargements. The corticospinal tracts primarily terminate in lower motor neuron pools which, in turn, exert their collective influence upon intrinsic spinal reflex circuits.

Question 23

the principle descending pathway for autonomic functions (bowel/bladder function etc)

Answer 23

Lateral Reticulospinal Tract

Question 24

LRST originates in

Answer 24

a group of medullary reticular nuclei.

The LRST consists of both uncrossed and crossed fibers which bilaterally descend adjacent to the spinal gray in the anterolateral funiculus

terminates in the intermediate gray of all levels of the spinal cord.

Question 25

the probable link between the reticular formation, the parasympathetic and sympathetic systems

Answer 25

LRST

Question 26

Sequence of events allowing bladder to be voided

Answer 26

stretch receptors in bladder muscle transmit through pseudounipolar neuron to ventral anterior nucleus in S2-S4 segments —> interneurons –> Sacral Autonomic Nucleus in S2-S4 segments –> bladder contraction

Question 27

Atonic bladder

Answer 27

lesion in:

1. dorsal root of S2-S4 or dorsal funiculi

results in:

1. increased bladder capacity
2. voluntary but incomplete voiding
3. flaccid bladder

Question 29

1. descending motor fibers terminate in lower motor neuron “pools”
2. where are they and what is their role?

Answer 29

1. this pool is a group of highly interconnected interneurons in the base of the intermediate gray.
2. These pools play an important role in processing and integrating descending motor information with the incoming “current status” sensory information.

Question 30

reflex bladder

Answer 30

1. when lateral reticulospinal tract is disrupted above S2
2. bladder activity no longer under autonomic control
3. not under voluntary control
4. after spinal shock, reflexes return and voiding occurs spontaneously

Question 31

visceral afferents: where they terminate, where signals are conveyed afterward

Answer 31

1. terminate in visceral afferent nuclei such as the nucleus tractus solitarius (NTS) or visceral afferent nucleus (VAN, sacral spinal cord).
2. sensory nuclei may project to visceral motor nuclei such as the
   
   1. dorsal motor nucleus
   2. sacral autonomic nucleus
   3. Barrington’s nucleus (bowel and urinary bladder)

Question 32

nucleus tractus solitarius (NTS) receives organized GVA and SVA (taste) input from all visceral structures from the oral cavity to mid-colon. These viscerotopic fibers enter the brainstem in bundles according to their origin, i.e., cardiovascular, respiratory, and GI and terminate in restricted regions of the NTS or specialized areas in the adjacent reticular formation (RF). These fibers project to specific (restricted) areas in and around the NTS

Answer 32

receives organized GVA and SVA (taste) input from all visceral structures from the oral cavity to mid-colon.

viscerotopic fibers enter brainstem in bundles according to their origin, i.e., cardiovascular, respiratory, and GI and terminate in restricted regions of the NTS or specialized areas in the adjacent reticular formation (RF). These fibers project to specific (restricted) areas in and around the NTS