Motor pathways Flashcards
Corticospinal tract
- Function
- Origin
- Crossing
- End point
Plans/ execute movement
Origin
- Primary motor cortex (PMC)
- PMC—> UMN
- UMN—> posterior lmb of internal capsule (vulnerable to cerebral ischaemia)
- Pyramidal decussation (crosses at lower medulla)
- Descends the lateral corticospinal tract - UMN synapses with LMN in anterior horn
- LMN synapse with skeletal muscle.
Features of a lesion in the primary motor cortex/ corticospinal tract (6)
- Brisk reflex
- Voluntary-Involuntary dissociation
- Spasticity, hypertonia(gamma motor neurons modulated, sensitivity increased)
- Preserved muscle bulk.
Lesions above medulla
- weakness on contralateral side
Lesions below medulla
- weakness/ defects are ipsilateral.
Innervation of facial muscles
- UMN and LMN lesion presentation
Innervated by CN5 and CN7
- Crosses above medulla
UMN Provides innervation bilaterally
UMN lesion
- Forehead sparing
LMN lesion
- affects entire half of the face
Brain stem nuclei
- Midbrain
- Pons
- Medulla
Midbrain
- 3,4
Rules of 4:
Pons
- 5,6,7,8
Medulla
- 9,10, 11, 12
Premotor area
- Location
- function
Frontal lobe
- Selects motor programme for complex movements
- Plans movement based on non-external cue
Role of somatosensory cortex in movement
Located in parietal lobe
- Uses information from external cues to feed back into planning of movement
Basal ganglia’s role in movement
Initiates movement
- Feedback into areas of the cortex
- Linked with limbic system to stimulate emotional movement
Role of cerebellum in movement
Compares the actual movement with intended movement
- receives real time feedback from proprioceptors and detects if there’s an overshoot/ undershoot
Signs of cerebellar lesion
- Dysmetria (overshoot of movement)
- Intention tremor
- Incoordination
- Ataxia
Length dependency in peripheral neuropathy
Starts at arm and feet before spreading proximally
- Due to the longest axons being more metabolically demanding
If it is a demyelinating disorder, proximal lesion occurs first as short and long nerves are affected the same.
Inputs in maintaining posture and balance
Visual input
Vestibular system
Joint proprioception
Inputs are integrated into the brainstem
Outputs in maintaining posture and balance
Vestibulospinal, reticulospinal tract and rubrospinal located medially
- Calculates centre of gravity and body posture
Activate antigravity muscles
Alpha motor neurones
Synapses with skeletal muscles and receive input from UMN
- regulates contraction of skeletal muscle to produce
movement
Gamma motor neurones
Regulate the sensitivity of the muscle spindles
for modulation of alpha LMN excitability
Presentation of length-dependent neuropathy
- Causes
Glove-stocking distribution
- Starts peripherally, moves more proximally
Causes
- Diabetic neuroopathy
- Alcohol
