Spinal Cord and Spinal Nerves (Glendinning)

Question 1

Describe the relationship between the spinal cord and the vertebral column.

At what level does the spinal cord end?

What makes up the cauda equina?
Where do cauda equina lesions occur?

Answer 1

31 pairs of spinal nerves

C1-C7 spinal nerves exit ABOVE vertebra
C8 exits below C7
Remaining spinal nerves exit BELOW vertebra

Spinal cord ends at about L1 at conus medullaris (tip of SC)

Cauda equina comprises SPINAL NERVES below conus medullaris

• contained within lumbar cistern (aka dural sac)
• cauda equina lesions occur with injuries below L1

Question 2

Describe the arteries that supply the spinal cord, and the regions supplied by each.

Answer 2

Anterior spinal artery

• 1 located in ventral median fissure
• supplies anterior 2/3 of spinal cord

Posterior spinal artery

• 2 located in posterolateral sulci
• supplies posterior 1/3 of spinal cord

Vasocorona
- series of branches from the anterior and posterior spinal arteries that form a crown (“corona”) around the cord

Anterior and posterior radicular arteries arise from segmental arteries at EACH SPINAL LEVEL to serve their respective ROOTS AND GANGLIA

Artery of Adamkiewicz = unusually large anterior radicular artery arising on the left from T9-L1
- supplies majority of the lumbar and sacral SC

Question 3

Explain the basic functions of each of the grey matter areas of the spinal cord.

Answer 3

Dorsal horn (sensory)
Lateral horn/intermediate horn (cell bodies of sympathetic pre-ganglionic)
Ventral horn (motor)

Question 4

Explain the basic functions of each of the grey matter areas of the spinal cord.

Answer 4

Lamina I-VI: Dorsal horn (sensory)

Lamina VII: Lateral horn/intermediate horn (cell bodies of sympathetic pre-ganglionic, parasympathetic neurons in intermediomedial cell column S2-S4)

Lamina VIII-IX: Ventral horn (motor)

Lamina X: Gray matter surrounding central canal

Question 5

Describe the innervation of clinical important dermatomes.

Answer 5

C2 - back of head
C5 - shoulder, lateral arm
C6 - digits 1-2, lateral forearm
C7 - digit 3

T10 - umbilicus
L4 - knee, medial lower leg
L5 - dorsal foot, big toe
S1 - lateral foot, small toe, sole

Question 6

Explain the scoring for tendon reflexes and motor nerves. For each reflex test, name the spinal nerves that are tested.

Answer 6

0+ = absent
1+ = trace
2+ = normal
3+ = brisk
4+ = non-sustained clonus
5+ = sustained clonus

1+, 2+, 3+ generally considered normal UNLESS there is asymmetry or major difference between upper and lower limbs

ABSENT or DECREASED stretch reflex indicates pathology to afferents, efferents, or their spinal cord connection.

INCREASED (abnormally brisk) reflex may indicate pathology above the spinal cord segment (supra spinal)

L3-4 - patella
C5-6 - biceps
C5-6 - brachioradialis
C7-8 - triceps
S1 - achilles

Question 7

In order to test specific myotomes (muscles innervated by spinal nerves), strength test conducted.

What do the scores mean?

Answer 7

0/5 - no contraction
1/5 - muscle flicker, no movement
2/5 - movement, but not against gravity
3/5 - movement against gravity, but not against resistance
4/5 - movement against some resistance
5/5 - normal

Question 8

Describe the receptor, circuit and functions of the stretch reflex, golgi-tendon reflex, and flexor withdrawal reflexes.

Answer 8

Stretch reflex

• Stimulus: stretch
• Response: contraction

Example 1:
1- load increases
2- stretches biceps-brachioradialis
3- reflex contraction of biceps-brachioradialis
4- simultaneously, triceps inhibited

Example 2:
1- quadricep muscle stretch receptor excited (connected to Ia afferent)
2- Ia afferent makes excitatory synapse onto quadriceps motor neurons, causing muscle contraction
3- Ia afferent also makes excitatory synapse onto inhibitory interneuron which inhibits hamstring (flexor) motor neurons

Golgi-tendon reflex = 1b inhibitory reflex:
Stimulus: Muscle tension
Circuit: GTO -> 1b -> 1b inhibitory interneuron -> motor neuron to homonymous muscle (also excites antagonist muscles)

Flexor withdrawal reflex:

• Feedback control to remove a limb from a painful stimulus (i.e. lifting your foot after stepping on a thumbtack)
• Cutaneous afferent fiber from nociceptor (A gamma)
• flexors and extensors activated in both legs

Question 9

Describe the function of a central pattern generator.

Answer 9

Circuits for walking: locomotion (swing -> stance)

Question 10

Describe, generally, the role of descending influences on spinal cord functions.

Answer 10

Will control the state of “readiness” of a reflex

All within each spinal cord segment

Simple reflexes (superior)
Dispersed reflexes
Circuits for patterned movements
Local processing of sensory inputs
Local processing of motor outputs (inferior)

Question 11

Predict the most likely site of a herniated disk based on symptoms.

Answer 11

Usually affect nerve corresponding to the lower vertebral body (cervical) C2-C3 -> C3 nerve affected

L4-L5 disc - L5 nerve affected in lateral recess

Question 12

Describe the features of spinal shock.

Answer 12

Following a spinal cord injury, there is a loss of all motor and autonomic function below the lesion

• Flaccid paralysis
• Bowel and bladder paralysis
• Loss of vasomotor tone (hypotension)

Period of time = 1-6 weeks

Mechanism is thought to be a loss of descending facilitation that keeps spinal cord circuits in a continue state of activation/readiness

Question 13

In order to test specific myotomes (muscles innervated by spinal nerves), strength test conducted.

What do the scores mean?

Answer 13

0/5 - no contraction
1/5 - muscle flicker, no movement
2/5 - movement, but not against gravity
3/5 - movement against gravity, but not against resistance
4/5 - movement against some resistance
5/5 - normal

Question 14

What is muscle tone?

Hypotonia vs hypertonia?

Answer 14

Resting tension in a muscle produced by muscle elasticity

Hypotonia - occurs when spinal nerves are damaged
Hypertonia - occurs with supra spinal lesions b/c stretch reflexes are increased