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1

What are upper motor neurons?

projection neurons from the primary motor cortex to the ventral horn

2

Function of UMNs?

modulate LMN activity 

3

What are lower motor neurons?

final effectors/ motor neurons 

4

Where are the cell bodies of somatic LMNs found?

ventral horn of spinal cord

5

Where are the cell bodies of autonomic LMNs found?

  •  ParaNS = motor nucleus
  •  SymNS = lateral horn of spinal cord) 

6

What two neuronal populations influence LMNs?

UMNs and segmental afferents of PCML tract 

7

Describe how a spinal reflex occurs?

sensory afferents send a branch to interneurons in spinal laminae which activate efferents in the ventral horn of the segment 

8

What type of LMN fibers active extrafusal fibers (skeletal muscle)?

Alpha fibers 

9

What type of LMN fibers active intrafusal fibers (muscle spindles)?

Gamma fibers 

10

What happens to muscle spindles when UMN modulation is lost?

Muscle spindles become more sensitive = muscle weakness & spastic movements

11

How is the Ventral horn topographically arranged?

12

What spinal levels innervated the upper extremities?

C4-T1

13

What spinal levels innervated the lower extremities?

L1-S2

14

What is flaccid paralysis?

LMN lesion resulting in complete loss of motor innervation to a muscle 

15

What are the 5 types of LMN lesion findings?

  1. flaccid paralysis 
  2. areflexia 
  3. atonia 
  4. atrophy 
  5. fasciculations 

16

What is atonia?

Loss of Gamma motor neuron activity = loss of muscle tone 

17

What is atrophy?

loss of muscle mass due to lack of innervation

18

What are fasciculations?

twitching d/t increased sensitivity of motor end plates b/c of lesion to LMN

19

Damage to the ventral horn impairs what?

LMNs only 

20

Damage to nerve roots (radiculopathy) causes what type of nerve impairment?

weakened motor and decrease sensory in a region

 

DTRs may +/-

21

Damage to peripheral nerves (neuropathy) causes what?

weakness & paraesthesia in specific muscle groups

22

What is Poliomyolitis?

Destruction of LMNs in the ventral horn by the poliovirus 

23

What are the signs of poliomyolitis?

  • fever
  • myalgia 
  • Loss of muscle tone & reflexes with normal dermatome testing
    • Negative Hx for polio vaccine

24

Where does the corticospinal tract start?

Primary motor cortex 

25

What is the course of the corticospinal tract?

  1. primary motor cortex
  2. internal capsule of cerebrum 
  3. cerebral peduncles (midbrain)
  4. anterior/rostral pons
  5. medullary pyramids --> decussates
  6.  lateral CST (contralateral) 

*anterior CST is different

26

Does the lateral or anterior corticospinal tract crossover in the pyramidal decussation 

Lateral corticospinal tract 

27

When do the "uncrossed" fibers of the anterior corticospinal tract crossover?

at the targeted spinal level

28

The lateral corticospinal tract accounts for how much of the total fibers of the corticospinal UMNs?

85%; important for thinking about injuries 

29

Where is the lateral corticospinal tract located in the spinal column?

Posterior lateral funiculus, posterior to the ventral horn 

30

Where in the spinal column is the anterior corticospinal tract located?

Anterior funiculus along the anterior median fissure