Motor Control Flashcards
hierarchical organisation
- high order areas of hierarchy are involved in more complex tasks (programming and deciding on movements, coordinating muscle activity)
- lower level areas of hierarchy perform lower level tasks (execution of movement)
functional segregation
motor system organised in a number of different areas that control different aspects of movement
motor system hierarchy
motor cortex receives info from other cortical areas and sends commands to brainstem and thalamus
cerebellum and basal ganglia adjust the commands received from other parts of the motor control system
brainstem passes commands from cortex to spinal cord
major descending tracts
pyramidal tracts (pass through pyramids of the medulla) - voluntary movements of body and face extrapyramidal tracts (do not pass through pyramids of medulla)- involuntary movements for balance, posture and locomotion
pyramidal tracts
UMN in motor cortex directly innervate LMN in anterior horn of spinal cord:
- corticospinal
- corticobulbar
extrapyramidal tracts
UMN in brainstem do not directly innervate LMN, interneurones innervate muscle groups:
- vestibulospinal
- tectospinal
- reticulospinal
- rubrospinal
corticospinal tract
UMN cell bodies in primary motor cortex
axon fibres go through internal capsule to form medullary pyramid on ventral surface of brainstem
at the level of the medulla:
- 90% of fibres decussate to form lateral corticospinal tract
- these fibres synapse with LMN in the anterior horn of the spinal cord to innervate limb muscles
- 10% of fibres do not cross and from the anterior corticospinal tract
- these fibres cross over and then synapse with LMN in the anterior horn of the spinal cord to innervate the trunk muscles
corticobulbar tract
UMN cell bodies in primary motor cortex
axon fibres go alongside corticospinal tract to brainstem
These axons will depart the tract and synapse directly with the contralateral lower motor neurons for Cranial Nerves V, VII, XI, and XII at their corresponding levels of the Pons and medulla
Some of the upper motor neurons branch into two fibers which synapse with both the ipsilateral and contralateral motor nuclei
These include cranial nerves V, which controls the muscles for chewing, XI, which controls the muscles of the neck, and the part of VII that innervates the muscles in the upper half of the face
This means the muscles innervated by these nerves receive motor signals from the motor cortex from both hemispheres of the brain
The upper motor neurons of cranial nerve VII that control the lower half of the face, and cranial nerve XII, which control tongue movement, crossover in the brainstem without branching and only synapse with the contralateral nuclei
So the muscles innervated by these cranial nerves only receive motor information from the contralateral cerebral cortex
vestibulospinal tract
From the vestibular nuclei
Stabilise head during body movements, or as head moves
Coordinate head movements with eye movements to keep vision fixed
Mediate postural adjustments
reticulospinal tract
Most primitive descending tract
Large proportion from medulla and pons
Changes in muscles tone associated with voluntary movement
Postural stability
tectospinal tract
From superior colliculus of midbrain(visual system)
Orientation of the head and neck during eye movements
rubrospinal tract
From red nucleus of midbrain
In humans mainly taken over by corticospinal tract , active in primitive species.
Innervate lower motor neurons of flexors of the upper limb
upper motor neuron lesion
Negative signs:
Loss of voluntary motor function
Paresis: graded weakness of movements
Paralysis (-plegia): complete loss of voluntary muscle activity
Positive signs:
Increased abnormal motor function due to loss of inhibitory descending inputs
Spasticity: increased muscle tone
Hyper-reflexia: exaggerated reflexes
Clonus: abnormal oscillatory muscle contraction
Babinski’s sign
apraxia
consequence of UMN lesion
- a disorder of skilled movement
- patients not paralyzed but have lost information about how to perform skilled movements
- lesion of inferior parietal lobe/ frontal lobe (premotor cortex, supplementary motor area)
- any disease of these areas can cause apraxia, most commonly stroke and dementia
lower motor neuron lesion
Weakness
Hypotonia (reduced muscle tone)
hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch at the NMJ
Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination Smaller AP fasciculations not visible to naked eye
signs found in cranial nerve nuclei if LMN of CORTICOBULBAR
signs found in spinal cord if LMN of CORTICOSPINAL
motor neuron disease (MND)
(also known as amyotrophic lateral sclerosis (ALS))
progressive neurodegenerative spectrum of disorders of the motor system that can affect both UMN and LMN
MND UMN signs
Spasticity (increased tone of limbs and tongue) Brisk limbs and jaw reflexes Babinski’s sign Loss of dexterity Dysarthria (difficulty speaking) Dysphagia (difficulty swallowing)
