Spinal Cord and Tracts

Question 1

What are the functions of the spinal cord?

Answer 1

Relay center for incoming sensory information through dorsal roots and horn. Conduit for ascending (afferent) and descending (efferent) pathways.
Origin of lower motor neurons “Final Common Pathway of Sherrington”, and thus “commands” to the skeletal muscles of the body, through ventral horns and roots.

Question 2

What is the Bell-Magendie law?

Answer 2

Sensory information goes into the spinal cord via dorsal roots of spinal nerves.
Motor “commands” leave the spinal cord via ventral roots of spinal nerves.

Question 3

What is an upper motor neuron?
What does a lesion lead to?

Answer 3

They start in higher centers (cortex); send “commands” to Lower Motor Neurons (LMNs).
Lesion leads to spastic (hyperreflexia and hypertonia) paresis or paralysis.

Question 4

What is a lower motor neuron?
What does a lesion lead to?

Answer 4

They start in the spinal cord (ventral horn cells) and brainstem (cranial nerve nuclei); directly “command” muscles to contract via spinal and cranial nerves.
Lesion leads to flaccid (hypo(a)reflexia, hypo(a)tonia) paresis/paralysis.

Question 5

In the grey matter, pericornual cells:

Answer 5

…are the relay center for pain and temperature.

Question 6

In the grey matter, substantia gelatinosa:

Answer 6

… is involved in editing pain.

Question 7

In the grey matter, the nucleus proprius:

Answer 7

…contains cell bodies of neurons in several tracts, e.g., lateral spinothalamic tract (for pain and temperature).

Question 8

In the grey matter, the nucleus dorsalis:

Answer 8

…(Clarke’s column) is in C8-L2,3 only, involved in proprioception of the lower body.

Question 9

In the grey matter, the intermediolateral cell column:

Answer 9

…contains T1-L2 : preganglionic sympathetic neuron cell bodies,
S2-S4: preganglionic parasympathetic cell bodies.

Question 10

In the grey matter, the motor nuclei (ventral horn cells):

Answer 10

…contain cell bodies of lower motor neurons, both alpha (a) and (g) gamma, which innervate skeletal muscle.

Question 11

What are ascending pathways in the white matter?

Answer 11

Structures that carry a specific type of information from lower centers (or the peripheral body) to higher centers. They usually consist of a chain of tracts.

Question 12

Dorsal Columns (Dorsal Funiculus) carry what neurons? What do those neurons communicate?

Answer 12

Primary afferent neurons
Communicate vibration sense, conscious proprioception, discriminatory touch (fine touch), and stereognosis.

Question 13

What are the dorsal columns?

Answer 13

Fasciculus gracilis (medial) and fasciculus cuneatus (lateral).

Question 14

Describe fasciculus gracilis.

Answer 14

Dorsal column carrying primary afferent neuron from ipsilateral lower body to nucleus gracilis in medulla. Exists at all spinal cord levels.

Question 15

Describe fasciculus cuneatus.

Answer 15

Dorsal column carrying primary afferent neuron from ipsilateral upper body to nucleus cuneatus of the medulla. Exists from T6 and above.

Question 16

What information do spinocerebellar tracts carry?

Answer 16

Proprioception info from lower body to ipsilateral cerebellum

Question 17

What does a lesion of a spinocerebellar tract lead to?

Answer 17

Ataxia (unsteady, wide gait)

Question 18

What are the pain and temperature pathways in the spinal cord?

Answer 18

Dorsolateral fasciculus, lateral spinothalamic tract

Question 19

Describe dorsolateral fasciculus.

Answer 19

Contains primary pain and temperature afferent neurons with cell bodies in the dorsal root ganglion. Pathway is ipsilateral to stimulus. Ends in ipsilateral nucleus proprius, 2 levels above where it entered the spinal cord.

Question 20

What information is carried by the dorsal columns - medial lemniscus?

Answer 20

Proprioception, vibration, discriminatory touch, stereognosis (3D knowledge)

Question 21

What information is carried by the spinothalamic tracts?

Answer 21

Pain and temperature

Question 22

What information is carried by the ventrospinothalamic tract?

Answer 22

Light/crude touch

Question 23

What information is carried by the spinocerebellar tract?

Answer 23

Proprioception from the lower body

Question 24

What information is carried by the corticospinal tracts?

Answer 24

Motor commands

Question 25

What information is carried by the lateral corticospinal tract?

Answer 25

Motor to distal flexor muscles

Question 26

What information is carried by the ventral corticospinal tract?

Answer 26

Motor to core muscles

Question 27

Name the primary afferent neurons of the dorsal columns - medial lemniscus.

Answer 27

T6 up is fasciculus cuneatus
T6 down is fasciculus gracilis

Question 28

Name the secondary afferent neurons of the dorsal columns - medial lemniscus. Where do they join?

Answer 28

T6 up is nucleus cuneatus
T6 down is nucleus gracilis
They join in medial lemniscus

Question 29

Where do nerves cross in the dorsal columns - medial lemniscus?

Answer 29

Great sensory decussation

Question 30

A lesion in the dorsal columns - medial lemniscus before the great sensory decussation leads to __________

Answer 30

Ipsilateral loss of sensation

Question 31

A lesion in the dorsal columns - medial lemniscus after (above) the great sensory decussation leads to __________

Answer 31

Contralateral loss of sensation C1 down

Question 32

A lesion in the dorsal columns - medial lemniscus fasciculus cuneatus leads to __________

Answer 32

Loss of sensation from lesion level to T6

Question 33

A lesion in the dorsal columns - medial lemniscus fasciculus gracilis leads to __________

Answer 33

Loss of sensation from lesion level down

Question 34

A lesion in the dorsal columns - medial lemniscus nucleus cuneatus leads to __________

Answer 34

Loss of sensation C1-T6

Question 35

A lesion in the dorsal columns - medial lemniscus nucleus gracilis leads to __________

Answer 35

Loss of sensation T6 down