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Neuro Test 2 > Motor Systems > Flashcards

Motor Systems Flashcards

1
Q

what is general flow of motor systems?

A

frontal lobes (motivation) —> premotor cortex (motor plan) –> primary motor cortex (action)

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2
Q

Frontal lobes

A

provide “motivation” or “ideation of motor plan”

- input comes from sensory stimuli in the parietal motor area as well as emotions/memory from the limbic system

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3
Q

premotor cortex? BA?

A
  • motor plan
  • provides “blueprint” or “module” for movement
  • premotor cortex (lateral BA6)
  • supplementary cortex (medial BA6 & BA8)
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4
Q

what are the two UMN system?

A
  1. primary motor cortex
  2. brainstem nuclei
  • have action of LMN in spinal cord and cranial motor nuclei
  • all systems converge on LMNs to produce movement, its the final common pathway.
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5
Q

alpha-LMNs

A

synapse on and innervate SKELETAL MUSCLE

  • “final common pathway”
  • always excitatory and release NT => contraction
  • target is ipsilateral to soma
  • very large
  • found in spinal cord ventral rami and cranial n. motor nuclei
  • have baseline activity, changed by excitatory and inhibitory synapses, to adjust firing rate
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6
Q

what is a motor unit

A

1 LMN and all of the m. fibers that it innervates

  • 10 fibers/neuron = fine control, extraocular mm.
  • 1000 fibers/neuron = gross postural control mm.
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7
Q

how do we regulate the strength of muscle contraction?

A
  1. recruitment- “size principle” = # motor units firing = more strength
    (smallest motor units are recruited first)
  2. AP frequency- increased AP frequency results in increased strength
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8
Q

general UMN characteristics

A
  • locations: cerebral cx and brainstem nuclei
  • UMN = axon from brain that influences a LMN, mostly indirectly through interneurons
  • interneurons can be excitatory or inhibitory
  • never synapse directly on muscle
  • 8 different UMN pathways (2 from primary motor cx)
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9
Q

Lateral motor systems

A

influence distal limb mm.

- precise, fractionated mvmts

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10
Q

medial motor systems

A

axial/proximal limb mm.

- affects postural mvmts.

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11
Q

flexors/extensors? distal vs. proximal muscles? - orientation in spinal cord?

A

flexors are posterior in gray matter, extensors are more anterior

proximal musculature is more medial, distal limb musculature for fine mvmts are more lateral

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12
Q

important features of lateral corticospinal tract

A

LCST:

  • largest motor tract of humans
  • contralateral projection
  • some UMNs synapse directly on LMNs
  • necessary for critical and complex fractionated mvmts of hands
  • think “volition”, voluntary
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13
Q

anatomy of LCST?

A

comes from more than just BA4

  • 1/3 from primary motor cortex
  • 2/3 from frontal lobes and somatosensory cortex (“posterior parietal motor area” links motor activity, especially of hands to sensory input)
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14
Q

where is premotor cx of LCST located?

A

in lateral BA6 and 8

- active in motor planning at the start of voluntary unit (involved in blueprint and timing)

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15
Q

where is supplmenetary motor cx of LCST?

A

medial BA6

  • involved in motor planning and interconnected with contralteral side = bimanual mvmt
  • active right before movement takes place
  • will instruct proper UMN to carry out movement
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16
Q

Corticobulbar tract

A

similar to corticospinal but it terminates in brainstem
- influences:

  1. cranial nerve motor nuclei (LMNs) of facial expression/chewing
    * influences nuclei bilaterally
  2. UMN nuclei: gives voluntary control of proximal limb voluntary muscles
    - vestibular nuclei
    - reticular nuclei
    - red nucleus
17
Q

LMN damage?

A
  • hypo- to areflexia
  • hypo- to atonia
  • paralysis/paresis (varying)
  • flaccidity (limp)
  • RAPID/SEVERE ATROPHY (due to loss of trophic relationship with motor neuron- “neurogenic atrophy”)
  • EMG changes: see spontaneous activity in mm.
18
Q

paralysis vs paresis

A 
paralysis = complete loss of mvmt
paresis = partial loss of movement
19
Q

UMN damage?

A

hyperreflexia

  • increased stretch reflex –> hypertonia
  • appearance of pathological reflexes
  • paresis/paralysis (spastic, esp. in antigravity mm.)
  • disuse atrophy
  • Few EMG changes
20
Q

how are reflexes increased with UMN damage?

A
  • loss of normal inhibitory background
  • results in sprouting of local affarents (to increase input)
  • also results in increased expression of receptors on surface of LMNs and interneurons (denervation hypersensitivity)
21
Q

-plegia

A

literally means “stroke” = paralysis from stroke

22
Q

paralysis

A

complete loss of voluntary mvmt

23
Q

paresis

A

partial loss of voluntary mvmt

24
Q

hemi, para, quadra

A

hemi = half
para = pair of limbs
quadra (or tetra) = four limbs

25
Q

rubrospinal tract

A

(technically a part of LMS, but is non-cortical tract)

  • functions in posture and projection bilaterally
  • cell bodies are located in red nucleus
  • axons decussate in midbrain and descend in contralateral lateral funiculus to reach LMN of distal mm of arms (cervical cord only), primarily to arm/forearm flexors
26
Q

vestibulospinal tracts

A
  • Medial and Lateral: describes location in cord and nucleus of origin
  • MVST cell bodies are medial/inferior (projects bilaterally in cervical and upper thoracic)
  • LVST cell bodies are lateral (projects ipsilaterally throughout cord)
27
Q

MVST

A

cell bodies are medial and inferior in medial VS nucleus

  • projects bilaterally in cervical and upper thoracic
  • acts on neck mm
  • makes changes in head/neck posture
28
Q

LVST

A

cell bodies are found more laterally in lateral VS nucleus

  • projects ipsilaterally throughout cord
  • makes + changes to axial/antigravity mm.
  • makes changes in trunk posture
29
Q

medial longitudinal fasciculus “ascending portion”

A

commonly called “MLF”

  • cell bodies located in medial/inferior vestibular nucleus
  • ascends to innervate motor nuclei of III, IV, VI (LMNs of extraoccular eye mm.)
  • bilateral with +/- effects

(located dorsally and medially)

30
Q

Medial reticulospinal tract

A
  • located medially in the cord
  • MRST = pontine RST
  • cell bodies: located in PONTINE reticular formation
  • projects ipsilaterally
  • main back up pathway for voluntary mvmt with injury to corticospinal
31
Q

Lateral reticulospinal tract

A
  • found laterally in cord
    LRST = medullary RST
  • cell bodies found in MEDULLARY reticular formation
  • projects BILATERALLY
  • main back up pathway for voluntary mvmt with injury to corticospinal
32
Q

Tectospinal tract

A

cell bodies: located in superior colliculus

  • decussates in midbrain (contralaterally)
  • provides +/- to neck muscles (tract terminates in cervical cord)
  • aids in the visual grasp reflex
33
Q

Look at where these are in cross section.

A

do it NOW!

34
Q

decorticate

A
  • “flexed arms, extended legs” - mummy position
  • loss of LCST- no flexion of legs
  • unopposed rubrospinal (flexed arms)
  • shows that brainstem is working, but there is damage in cerebral hemispheres or internal capsule or thalamus
35
Q

decerebrate

A
  • extension of arms and legs
  • loss of rubrospinal tract (loss of flexors)
  • unopposed RST (backup pathway)
  • indicates brainstem damage, only RST is working which originates in pons and medulla.
36
Q

Lateral corticospinal tract

A
  • UMN’s originate in cortex (1/3 in primary motor cortex, 2/3 in frontal lobe/ SS cx)
  • the fibers descend ipsilaterally down the IC, through cerebral peduncles, through longitudinal fibers, through pyramids of medulla.
  • will decussate at the pyramidal decussation in lower medulla
  • descend contralaterally in the LCST of the spinal cord
  • will synapse on LMN of the arm and leg
  • will control contralateral complex and fractionated mvmt of the distal limb musculature
37
Q

Rubrospinal tract Path

A

cell bodies located in red nucleus in midbrain

  • decussate in midbrain and descend contralaterally in the contralateral lateral funiculus
  • terminates in cervical spinal cord where they innervate LMN responsible for arm/forearm flexors
  • Note: this is technically in the lateral motor system, but it is still a noncortical tract
38
Q

Vestibulospinal tract pathway

A

Cell bodies are located in the Medial/Lateral Vestibulospinal Nucleus

  • the MVST descend bilaterally and have changes in head/neck posture
  • the LVST descend ipsilaterally and have changes in trunk posture
  • The medial longitudinal fasciculus is the ascending portion of motor nuclei of CN III, IV, VI and control extraoccular eye movment, they synapse in MVNu as well

Neuro Test 2 (13 decks)

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