Motor Systems Flashcards
1
Q
Motor Cortex
Components
A
- Components:
- Primary motor cortex ⟾ precentral gyrus (BA 4)
- Premotor and supplementary motor areas (BA 6)
- Frontal eye field (BA 8)
-
Output from pyramidal cells in layer V
- form corticospinal tracts
- form pathways to other motor structures
2
Q
Motor System
Regulation
A
Control involves motor cortex, premotor cortex, somatosensory cortex, and frontal eye fields.
- Motor cortex and other cortical outputs regulates basal ganglia and cerebellum
- Regulates some sensory inflow
-
Activates spinal motor systems
- Direct pathway
- Indirectly via rubro, pontine, and medullary connections
3
Q
Motor System
Connections
A
-
Motor control areas projections
- Direct ⟾ corticospinal tracts (pyramidal)
-
Indirect ⟾ cortical extrapyramidal tracts
- project to basal ganglia or via pontine n. to cerebellum
- then modify cortical activity via thalamus
- project to nuclei in brainstem
- then project to spinal cord
- project to basal ganglia or via pontine n. to cerebellum
- Also projects to craniofacial and oculomotor systems
- Cells intermixed in the cortex
- Fibers exit via internal capsule and descend
-
Extrapyramidal fibers synapses with:
- striatum
- superior colliculus
- red nucleus
- pontine nuclei
- reticular formation
- Cortibulbar fibers (of pyramidal system) → cranial nerve nuclei
-
Extrapyramidal fibers synapses with:
4
Q
Motor Area
Projections
A
-
Control circuits for coordination
-
Other cortical areas:
- Supplementary motor & frontal eye field ↔ posterior parietal areas 5 & 7
-
Basal ganglia
- All cortical motor regions ↔ Striatum
-
Pons/Cerebellum
- All cortical areas → somatopically matching pontine n. → cerebellum
-
Other cortical areas:
-
Sensory modulation
-
Thalamus
- Cortical areas ↔ associated thalamic input
- Primary motor ↔ VL
- S1 ↔ VPL
- BA 6 ↔ VA
- BA 4 & 6 ↔ CM ↔ basal ganglia
- Cortical areas ↔ associated thalamic input
-
Dorsal column nuclei
- BA 1,2,3 → LCST → dorsal columns
-
Thalamus
-
Spinal Cord Control
-
Direct
- BA 4 & 6 → LCST
- BA 4 & 6 → VCST
-
Indirect
- BA 4 & 6 → red nucleus & LCST
- BA 4 (trunk) & 6 → MRST, PRST, VCST
-
Direct
5
Q
Extrapyramidal Tract
Somatotopy
A
Cortical fibers → internal capsule → cerebral peduncle → targets.
-
Somatotopically organized projections:
- 1° motor cortex → red nucleus
- Premotor → pontine RF → contralateral cerebellum
- Cortex → lateral reticular n. & inferior olive
- 1° motor cortex (face area) → motor n. of V & VII
- mostly contralaterally
-
Not somatotopically organized projections:
- 1° motor and premotor → mesencephalic RF
- Motor & premotor → medial RF (mostly contralateral)
- Cortex → lateral reticular n. and inferior olive
6
Q
Inputs to
Motor Cortex
A
- Cortical input from posterior parietal cortex
- Thalamic
7
Q
Corticospinal Tract
A
Origins:
premotor cortex
primary motor
primary somatosensory cortex.
8
Q
Motor Functions
A
-
Primary motor cortex
- execution of movement
- fine motor control
-
Premotor cortex
- reflex regulation
- motor set within a limb
-
Supplementary motor cortex
- sequencing
- planning
- bilateral integration of limb movements
9
Q
Primary Motor Cortex
A
M1 or Brodmann’s area 4
-
Contains motor maps
- layer V cells have detailed somatotopy
- can be used to localize strokes or seizure origins
- strokes cause local deficits in muscles groups
- muscles are progressively recruited in a seizure as activity sweeps across motor cortex
-
Can encode force
- appears to be code force precisely
- provide precise muscle specification
- uses inhibition to focus excitation
- provides basis for fractionated movement
-
Provides flexible “long loop” reflexes
- controls force and movement
- uses projections of S1-S3 to control pyramidal outflow
10
Q
Motor Lesions
Overview
A
-
Reflexes and other activites mediated by brainstem, cerebellum, and basal ganglia controlled by cortical efferents
- exaggerated responses without cortical input
- requires coarse stimulus
- Useful movement possible without motor and premotor cortex
- Lesions that leave cortex intact can have significant symptoms
- Cooperation between cortex, basal ganglia, cerebellum, VA, and VL crucial for movement
-
Lower brainstem also important
- ex. brainstem RF lesion can result in significant spasticity
11
Q
Primary Motor Cortex
Lesion
A
Lesions of Brodmann’s area 4 that spare M1 trunk:
- weakness or flaccid paresis of voluntary movement in affected parts
- only trunk areas of BA 4 project to MRST/PRST system
- these systems responsible for spasticity seen with UMN lesions
- all of premotor cortex influences MRST/PRST
12
Q
Premotor Cortex
Lesion
A
- Involved in reflex set up or ‘set’ within a limb
- strongly modulates indirect pathways in brainstem
- activity preceeds activity in primary motor
-
Lesion:
- reflex imbalance
- cortical spasticity
- grasp or Babinski sign
- depends on area
13
Q
Supplementary Motor Cortex
Lesion
A
Concerned with planning sequences, multi-limb integration, and bimanual coordination.
Mental rehearsal of motor acts involves SMA.
Lesions:
deficit in bimanual coordination
unadjusted, poorly planned movements
sequence apraxias
14
Q
Motor Coordination
Considerations
A
Reaching to a point in external space involves:
- extraction of location from visual processing stream
- limb and joint coordinates must be planned
- muscle activations must be chosen to generate movement
- movement has to be carried out
15
Q
Order of Activation
Cortex
A
-
Posterior parietal cortex
- Used for representation of extrapersonal space represented in
-
Premotor and supplementary motor areas
- Set up and plan sequence and reflex patterns for motion
- Helps organize primary motor activity
-
Primary motor cortex
- Acts via corticospinal tract to execute and regulate movement
