Unit 3 - Descending tracts/ UMN/ LMN

Question 1

What is a descending tract?

Answer 1

neural pathway by which motor signals are sent from the brain to LMN (via UMN)

Question 2

what is the difference between UMN and LMN?

Answer 2

upper: axons remain CNS and cell body in cortex/ brainstem
lower: cell body in ventral horn and axon supplies muscle

Question 3

what are the two types of descending tracts? give origin

Answer 3

pyramidal: voluntary control of body and face
- arise from cortex
extrapyramidal: involuntary and autonomic control of all musculature
- arise in brainstem

Question 4

what is the difference between the two types of pyramidal tracts?

Answer 4

• corticospinal: supplies musculature of all body

- corticobulbar: supplies head and neck

Question 5

describe the pathway of the corticospinal tract

Answer 5

neurons from primary cortex, premotor cortex, supplementary motor area and somatosensory area converge

• descend through internal capsule to cris cerebri, pons to medulla
• tract splits in two at medulla into lateral and anterior tract
• lateral decussates and descends spinal cord to ventral horns to supply body
• anterior remains ipsilateral and descends cord and terminates in ventral horn of cervical/ upper thoracic levels

Question 6

describe the pathway of the corticobulbar tract

Answer 6

neurons from the primary motor cortex converge and descend through the internal capsule to brainstem (cris cerebri, pons, medulla)

• terminate in motor nuclei of cranial nerves and synapse with LMN
• innervate bilaterally

Question 7

what are the two exceptions to the corticobulbar tract?

Answer 7

facial/ hypoglossal nerve - contralateral innervation

Question 8

what are the four extrapyramidal tracts?

Answer 8

vestibulospinal
reticulospinal
rubrospinal
tectospinal

Question 9

what is the type of innervation and function of the extrapyramidal tracts?

Answer 9

vestibulospinal - ipsilateral - balance/posture - axial muscles/ extensors
reticulospinal - ipsilateral - balance/ posture - axial muscles /proximal limb
rubrospinal - contralateral - single finger movements
tectospinal - contralateral - head movement

Question 10

what would be the effect of a lesion to extrapyramidal tract?

Answer 10

dyskinesia - abnormality of voluntary movement

Question 11

what would damage to corticospinal tract cause?

Answer 11

damage = UMN Lesion

• hypertonia (increased tone)
• hyperreflexia (increased muscle stretch reflex)
• clonus (involuntary rhythmic contraction of antagonist muscles)
• babinski’s sign (when hard object scraped on bottom of foot toes go into extension - extensor plantar response)
• muscle weakness
• spastic paralysis - continued contractions due to dissipation of UMN signal

Question 12

what would damage to corticobulbar tract cause?

Answer 12

mild muscle weakness

• facial nerve - spastic paralysis of contralateral lower quadrant of face
• hypoglossal nerve - tongue deviation contralaterally

Question 13

what is a motor unit?

Answer 13

1 LMN and skeletal muscle cells it contacts/ controls

Question 14

smaller muscles require what type of motor units?

Answer 14

smaller motor units - rapid, precise control

Question 15

what is tone?

Answer 15

muscle’s resistance to passive stretch during resting state

Question 16

what are signs of LMN lesions?

Answer 16

muscle weakness

• hypotonia
• hyporeflexia
• fasciculations - involuntary twitches of skeletal muscle
• atrophy