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Neurobiology > Descending Motor System > Flashcards

Descending Motor System Flashcards

1
Q

Paresis

A

partial weakness

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2
Q

Plegia

A

no voluntary movement

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3
Q

Paralysis

A

no voluntary movement

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4
Q

Palsy

A

weakness or no movement

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5
Q

Hemi

A

one side of the body

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6
Q

Para

A

both legs

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7
Q

Mono

A

one limb

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8
Q

Di

A

both sides of the body are equally affected

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9
Q

Quadri/Tetra

A

all four limbs affected

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10
Q

What is an upper motor neuron (UMN)?

A

Neurons with cell bodies in the motor cortex or brainstem whose axons descend in white motor tracts in the CNS to govern activity of lower motor neuron cell bodies

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11
Q

What is a lower motor neuron (LMN)?

A

Neurons with cell bodies in the spinal cord or brainstem with axons that project to muscles in the periphery

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12
Q

True or False
LMN are entirely contained in the PNS

A

False
Cell bodies of LMN are found in the CNS (spinal cord and brainstem)

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13
Q

What is an alpha motor neuron?

A

LMN with a large cell body and target in the skeletal muscle

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14
Q

Gamma motor neuron

A

LMN with a smaller axon diameter and target in muscles spindles to help control stretch reflex

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15
Q

Beta motor neurons

A

LMN that are fewer in number and innervate both muscles within and outside of the muscle spindle

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16
Q

Motor output is influenced by…

A

Basal ganglia
Cerebellum

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17
Q

True or False
Motor output pathways are organized based on their location in the spinal cord

A

True
UMNs are divided in medial motor systems or lateral motor systems

18
Q

Describe the lateral motor system

A
  • Descends in the lateral column of the spinal cord
  • Synapse on lateral ventral horn with LMN or interneuron
  • Controls distal limb muscles
  • Consists of lateral corticospinal tract and rubrospinal tract
19
Q

Describe the medial motor system

A
  • Descends in the anteromedial columns of the spinal cord
  • Synapse on medial ventral horn with LMN or interneurons
  • Control proximal axial muscles
  • Consists of anterior corticospinal tract, vestibulospinal tracts, reticulospinal tract, and tectospinal tract
20
Q

What tracts are in the lateral motor system?

A

Lateral Corticospinal tract
Rubrospinal tract

21
Q

What tracts are in the medial motor system?

A

Anterior Corticospinal tract
Vestibulospinal tract (medial, lateral)
Reticulospinal tract
Tectospinal tract

22
Q

Describe pyramidal tracts

A
  • Originate in cortex
  • Terminate in brainstem or spinal cord
  • Control volitional movement
  • Corticobulbar and Corticospinal tracts
23
Q

Describe extrapyramidal tracts

A
  • Originate in brainstem
  • Modulated by other inputs (cerebellum and basal ganglia)
  • Terminate in spinal cord
  • Involuntary and automatic control of muscle tone, balance, posture, and modulation of other motor plans
  • Rubrospinal, Vestibulospinal, Reticulospinal, Tectospinal tracts
24
Q

True or False
Only damage to pyramidal tracts will present with UMN signs

A

True
They are volitional pathways

25
Q

Describe the Lateral Corticospinal Tract

A

Origin: primary motor cortex
Decussation: pyramidal decussation/cervicomedullary junction
Level of Termination: lateral ventral horn, cervical and lumbar enlargements of cord
Function: volitional movement of contralateral distal extremities

26
Q

What structures does the lateral corticospinal tract travel through?

A

Corona radiata > internal capsule > cerebral peduncle > pyramids > decussation of pyramids > lateral column

27
Q

What is the somatotopic organization of the cortex?

A

Legs are medial and arms are lateral

28
Q

What is the somatotopic organization of all levels aside from the cortex?

A

Legs are lateral and arms are medial

29
Q

What are key aspects of the Corticobulbar tract?

A
  • Fibers project from cortex to brainstem
  • Travel with corticospinal tract
  • Some fibers terminate bilaterally on local circuit neurons, others provide direct input to contralateral LMN at CNN level (CN 5, CN 7, CN 12)
30
Q

Describe the Rubrospinal Tract

A

Origin: red nucleus
Decussation: ventral tegmental decussation
Level of Termination: lateral ventral horn and intermediate zone, cervical cord
Function: movement of contralateral upper limb

31
Q

What tract is suggested to innervate flexor muscles?

A

Rubrospinal tract

32
Q

Flexor (decorticate) posturing will occur in upper extremities with a lesion to….

A

Corticospinal tract above the red nucleus

33
Q

Extensor (decerebrate) posturing will occur in upper extremities with a lesion to…

A

Rubrospinal tract below the red nucleus

34
Q

Describe the Anterior Corticospinal Tract

A

Origin: primary motor cortex
Decussation: some remain ipsilateral , some cross in ventral white commissure of cord
Level of Termination: cervical and upper thoracic
Function: bilateral axial and girdle muscles

35
Q

Describe Medial Vestibulospinal Tract

A

Origin: medial and inferior vestibular nuclei
Decussation: descends bilaterally
Level of Termination: cervical and thoracic cord
Function: positioning of head and neck

36
Q

Describe the Lateral Vestibulospinal Tract

A

Origin: lateral vestibular nucleus
Decussation: does not cross
Level of Termination: entire cord
Function: balance

37
Q

Which Vestibulospinal tract is being described?
- input from semicircular canals
- bilateral
- neck and proximal shoulder muscles
- activates extensors
- align head with body

A

Medial Vestibulospinal Tract

38
Q

Which Vestibulospinal tract is being described?
- input from otoliths
- ipsilateral
- proximal limbs and trunk muscles
- activates extensors and inhibits flexors
- postural alignment and balance

A

Lateral Vestibulospinal Tract

39
Q

What do both the medial and lateral Vestibulospinal tracts do?

A
  • Involuntarily activate extensors
  • Use compensatory feedback to respond to postural instability detected by vestibular system
40
Q

Describe the Reticulospinal Tract

A

Origin: pontine and medullary reticular formation
Decussation: does not cross
Level of Termination: entire cord
Function: automatic posture and gait-related movements

41
Q

Describe the Tectospinal Tract

A

Origin: superior colliculus
Decussation: dorsal tegmental decussation
Level of Termination: cervical cord
Function: coordination of head and eye movement

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