Intro to Motor Systems Flashcards
(24 cards)
Motor Systems Concepts
Somatic Motor System (GSE)
- movements intitiated (or modulated by) voluntary intent
- targets = striated mm
- reflex component
Visceral Motor System (GVE)
- part of autonomic nervous system
- targets = smooth/cardiac m, glands
Motor Systems Concepts
Motivation (frontal lobe)
- ideation of motor plan
- input from
- sensory stimuli (parietal motor area)
- emotions/memory (limbic syste)
Motor Plan (premotor cx)
- blueprint or module for movement
- premotor cx (lateral BA6 & 8)
Motor Systems Concepts
Action (primary motor cx)
- UMN systems
- locations:
- primary motor cx
- brainstem nuclei
- UMN fibers influence motor neurons in spinal cord (& cranial n motor nuclei) = LMN
- All systems converge on LMNs to provide movement
Alpha LMNs
Synapse on skeletal muscle
Final common pathway
Always excitatory - release NT=contraction
Target ipsilateral to soma
Large
Alpha LMNs continued
Found in
- sp cord ventral horn & cranial nerve motor nuclei
Have baseline activity, changed by excitatory & inhibitory inputs
Motor Units
Motor Unit = 1 LMN + all m fibers it innervates
Size related to function (fine control vs power)
- small number for fine control
1 LMN innervates many fibers
Each m fiber has motor units of various sizes (although certain sizes may predominate)
Motor Units Continued
AP in motor axon is “all or nothing”
Regulate strength of muscle contraction via
- AP frequency
- Recruitment (#motor units firing proportional to strength)
- ordered by size (smaller motor units recruited first, then larger)
- “Size Principle”
Upper Motor Neurons
Axons from brain, influence LMN
- Directly (few) or indirectly (most)
- Excitatory or inhibitory
Never synapse on muscle
Cerebral cx & brainstem
UMN
8 different UMN pathways drive LMNs in spinal cord
- 2 from primary motor cx
- rest from brainstem nuclei
Lateral Motor System
- Distal limb mm
- precise, fractionated movements
Medial Motor Systems
- Axial/Proximal limb mm
- Postural movements
Intro to Cortical UMN Systems
Two Cortical UMN Pathways:
- Corticospinal Tract (Lateral
- Corticobulbular Tract
Important features of LCST:
- large motor tract of humans
- contralateral projections
- some UMNs synapse directly on LMNs
- critical for complex, fractionated movements
Anatomy of the LCST
Premotor Cx - lateral BA6 &8
Motor planning
- most active at start of voluntary movement
Supplementary Motor Cx - medial BA6 & 8
Motor planning
- interconnected w/contralateral side = bimanual movements
Corticobulbar Tract
Corticobulbar similar to corticspinal, except:
- Terminate in brainstem
- Influences
- cranial nerve motor nuclei (LMNs)
- AND UMN nuclei
Corticobulbar fibers ALSO:
Influence activity in brainstem UMN nuclei
- vestibular nuclei
- reticular nuclei
- red nucleus
These nuclei give rise to medial motor systems (control of axial/proximal limb mm) - gain voluntary control of these by sending info from cx to these nuclei via corticobulbar tract
LMN Damage
- LMN damage produce LMN signs
- Hypo- to Areflexia (continuum)
- hypo- to Atonia - decrease stretch reflex
- Paralysis/paresis
- loss of trophic relationships w/motor neuron
- neurogenic atrophy
- EMG changes: spontaneous activity in mm
- fasciculations and fibrilations
UMN Damage
Produces UMN Signs
- Normal to Hyperreflexia
- Increase stretch reflex - hypertonia
- Appearance of pathological reflexes
- Paresis/paralysis
- spastic (especially in antigravity mm)
- Disuse atrophy
- Few EMG changes
Why are reflexes sometimes increased w/UMN damage?
Loss of normal inhibitory background
Sprouting of local afferents (increased output)
Denervation hypersensitivity
- increased expression of receptors on surface of LMNs & interneurons
Damage to Corticospinal system:
Where will deficit manifest?
- All levels at and below lesion
- LMN signs at lesion level
- UMN signs inferior to lesion:
- Lesions above decussation = contralateral signs
- Lesions below decussation = ipsilateral signs
Non-Cortical UMN Systems
Take origin in sites other than cx - aka extrapyramidal systems
Affect primarily axial/proximal limb mm
Important in reflex postural movement
Also under voluntary control (from cx via corticobulbar tract)
Axons of most are ventromedial in cord (i.e., part of “medial motor system”)
Rubrospinal Tract
- Cells bodies: red nucleus
- Axons decussate in midbrain, descend in contralateral lateral funiculus
- Primarily effect: (+)(-) to distal mm of arms (cervical cord only)
- Primarily arm/forearm flexors
- Very small in humans
Vestibulospinal Tract
Medial & Lateral VST
- M/L described in cord & nucleus of origin
Cells bodies:
- MVST - medial/inferior vestibule nucleus
- LVST - lateral vestibule nucleus
In cord:
- MVST = bilateral, through cervical and upper thoracic
- LVST = ipsilateral, thru-out cord
Vestibulospinal Tracts continued
- MVST (aka descending MLF)
- Acts on neck mm (+/-)
- Changes in head/neck posture (bothe reflex & voluntary activity
- LVST
- to axial, antigravity mm
- changes in trunk posture (both reflex & voluntary activity)
Medial Longitudinal Fasciculus (Ascending Portion)
- Commonly: MLF
- Cell bodies: medial/inferior vestibule nucleus
- Ascends to innervate motor nuclei of III, IV, VI (LMNs innervating extraocular mm)
- Bilateral, +/- effects
Reticulospinal Tract
- Medial & Lateral RST
- M/L refers to location in cord
- MRST aka pontine RST
- LRST aka medullary RST
- Cells bodies: reticular formation
- LRST bilateral
- MRST ipsilateral
- Reticulospinal tracts may be “back up” pathways for voluntary movements w/injury to corticospinal tracts (+/- effects)
Tectospinal
- Cell bodies: Superior colliculus
- Decussates in midbrain (contralateral)
- Synaptic effect: (+)(-) to neck mm (tract terminates in cervical cord)
- visual grasp reflex
