Spinal tracts

Question 1

What is the difference between an UMN lesion and a LMN lesion?

Answer 1

UMN lesion- affect upper motor neurons running from precentral gyrus to the anterior horn cell in spinal cord
- hypertonia (spastic, clonus), hyper-reflexia, upward plantar reflex, weakness (pyramidal pattern)

LMN lesion- affects lower motor neurons running from the anterior horn cell in spinal cord to the muscle that is to be supplied
- weakness (wasting, fasciculations), hypotonia, hypo-reflexia, plantar reflex down-going

Question 2

Describe the myotomes of the shoulder?

Answer 2

o Abduction: C5, C6

o Adduction: C6, C7, C8

Question 3

Describe the myotomes of the elbow?

Answer 3

o Flexion: C5, C6

o Extension: C7, C8

Question 4

Describe the myotomes of the wrist?

Answer 4

o Flexion: C6, C7

o Extension: C7, C8

Question 5

Describe the myotomes of the fingers?

Answer 5

o Flexion: C7, C8

o Extension: C7, C8
o Abduction; C8, T1
o Adduction: C8, T1

Question 6

What is the function of the corticospinal tract?

Answer 6

Function: voluntary movement of contralateral limbs, reflexes

Question 7

Describe the pathway of the corticospinal tract?

Answer 7

A descending tract

Primary motor cortex (precentral gyrus)

• > descends through internal capsule (anterior 2/3 of posterior limb)
• > cerebral peduncles -> anterior medulla -> decussation at pyramids of medulla (90%)
• > lateral corticospinal tract (10% not decussating are the anterior corticospinal tract)
• > ventral horn -> anterior horn cells
• > exit (become 2nd order neurons) -> NMJ -> innervate muscle

Question 8

What is the function of the spinothalamic tract?

Answer 8

Function: pain and temperature (lateral), and crude touch (anterior pathway) from extremities and trunk

Question 9

Describe the pathway of the spinothalamic tract?

Answer 9

Ascending tract

• First order neurons: pain and temp sensory nerve endings -> cell bodies in dorsal root ganglia -> enter spinal cord (via A-delta and C dorsal root fibers) -> synapse in dorsal horn
• Second order neurons: cell body in dorsal horn grey matter -> axons cross ventral white commissure (decussating in spinal cord)-> form spinothalamic tract in ventral part of lateral funiculus -> ascends spinal cord -> brain stem -> thalamus (ventral posterolateral nucleus (VPL))
• Third order neurons: VPL nucleus -> primary somatosensory cortex (post central gyrus)

Question 10

What is the function of the dorsal medial lemniscus tract?

Answer 10

Function: pressure, vibration, touch, proprioception to lower extremities

Question 11

Describe the pathway of the dorsal medial lemniscus tract?

Answer 11

Ascending tract

• First order neuron: sensory nerve ending -> enters via dorsal horn -> ascends ipsilaterally in dorsal column -> medulla (gracile and cuneate nuclei)
• Second order neuron: fibers decussate in medulla -> form medial lemniscus -> thalamus (ventral posteromedial or posterolateral nucleus)
• Third order neuron: ascend posterior limb of internal capsule -> primary sensory cortex (post-central gyrus)

Question 12

Differentiate between thoracic and cervical vertebrae?

Answer 12

Cervical vertebrae

• Small size
• One vertebral foramen, two transverse foramina
• Spinous process is slender, often bifid (C2-6)
• Small transverse process
• Not articular facets for ribs
• Articular facet directions- posterosuperior and anterosuperior
• Thick intervertebral discs relative to size of vertebral bodies

Thoracic vertebrae

• Larger size
• One vertebral foramen
• Spinous process is long, thick (most project inferiorly)
• Large transverse process
• Articular facets for ribs present
• Articular facet directions- posterolateral, anteromedial
• Intervertebral discs thin relative to size of vertebral bodies

Question 13

Describe the myotomes of the hip?

Answer 13

• Hip Flexion: L2 (femoral)

- Hip Extension: L5 (inferior gluteal)

Question 14

Describe the myotomes of the knee?

Answer 14

• Knee Extension: L3-4 (femoral)

- Knee Flexion: S1 (sciatic)

Question 15

Describe the myotomes of the foot?

Answer 15

• Ankle Dorsiflexion: L4 (deep peroneal)
• Ankle Plantarflexion: S1 (tibial)
• Great toe flexor: L5 (deep peroneal)