Motor Control Flashcards
What is direct control of muscles via?
Alpha motor neurons in the spinal cord
What control spinal reflexes?
Brainstem nuclei
What four systems control movement?
Descending control pathways
Basal ganglia
Cerebellum and local spinal cord
Brain stem circuits
What innervate muscles to initiate reflex and voluntary movements?
Lower motor neurons at cranial and spinal levels
What happens to lesions at lower motor neurons at cranial and spinal levels?
Flaccid paralysis and muscle atrophy
What regulates alpha motor neuron activity?
Upper motor neurons in brainstem or cortex synapse with multiple lower circuit neurons
What neurons are the proximal shoulder muscles mapped to?
Medial motor neurons
What happens if there is damage to sensory inputs?
Paralysis as if the motorneurons themselves had been damaged
What nerve does the biceps jerk test?
C6
What nerve is the triceps jerk reflex?
C7
What nerve is the patellar tendon reflex?
L4
What nerve is the achilles tendon reflex?
S1
What do flexor or withdraw reflexes use?
Information from pain receptors in skin muscles and joints
What do flexor or withdrawal reflexes do?
Withdraw part of the body war from painful stimuli and in towards the body
What can increased sensory action potentials from pain receptors cause?
Increased activity in the flexor muscles of the affected part via a number of excitatory interneurons
Antagonistic extensors are inhibited
What does excess load cause?
GTO reflex to be activated
How can stretch reflexes be overridden?
Strong descending inhibition hyper polarises alpha motor neurons and the stretch reflex can’t be evoked
What does activity of gamma motor neurons depend on?
Descending pathways - high activity causes muscle to become extremely resistant to stretch and is spastic
What pathways control voluntary movements of distal muscles?
Lateral pathways
What do ventromedial pathways control?
Posture and locomotion
Where does 2/3rds of the cortocospinal tract originate?
Areas 4 and 6 of frontal motor cortex
Where does the corticospinal tract decussate?
Medulla
Where do the CST axons synapse?
Ventral horn motor neurons and interneurons to control muscles
Where does the RST start?
Red nucleus of midbrain
What happens if there are lesions in the CST and RST?
Fine movements of arms and hands lost
Can’t move shoulders, elbows, wrists, fingers independently
What happens if there is a lesion in the CST alone?
Same deficits but after a few months functions reappear as they have been taken over by RST
Where do the ventromedial pathways originate?
Brainstem
What do area 6 neurons drive?
Complex movements on either side of the body
What is the function of the pre motor area of area 6?
Connects reticulospinal neurons innervating proximal motor units
What is the function of the supplementary motor area of area 6?
Innervates distal motor units directly
What does microstimulation in a specific area of the primary motor cortex elicit?
Coordinated movements of hand and mouth or movements that bring hands into central space to inspect/manipulate objects
What ares generate the mental image of body in space?
Areas 5 and 7
What happens when these areas are damaged?
Humans with damage have bizarre body images, may neglect or ignore one side of their body
Where are decisions taken about what actions/movements to take and their likely outcome?
Prefrontal and parietal cortex
What does cortical damage cause?
Immediate flaccidity of contralateral muscles - lift limb and release it drops passively
What is initial hypotonia?
Spinal circuits deprived of cortical input when they regain function, the spare connections strengthen and new connections sprout
What is Babinski’s sign?
When the lateral side of dorsal foot is touched, plantar flexion should occur
However in babies and those with cortical damage you see extension
What is spasticity?
Increased muscle tone, hyperactive stretch reflex, clonus oscillatory contract muscles in response to stretch
What are the features of upper motor neurone syndrome?
Injury site determines symptoms Initital hypotonia Babinski's sign Spasticity Loss of fine finger movements
Where does subcortical input to area 6 come from?
Ventral lateral nucleus in dorsal thalamus
What is the subcortical input called?
VLo, arises from basal ganglia
What are the major components of basal ganglia?
Corpus striatum - caudate and putamen nucleus
What receive excitatory cortical inputs on dendrites?
Medium spiny neurons in putamen and caudate
What does the putamen fire before?
Limb/trunk movements
What does the caudate fire before?
Eye movements
Is the cortex to putamen inhibitory or excitatory?
Excitatory
Is putamen to globus pallidus inhibitory or excitatory?
Inhibitory
Is globus pallidus to Vlo neurons inhibitory or excitatory?
Inhibitory
Is VLo to SMA inhibitory or excitatory?
Excitatory
What is the effect of cortical excitation?
Excites putamen which inhibits the globus pallidus whichh release cells in VLo from inhibition so boosts SMA activity
What do lesions to the cerebellum cause?
Uncoordinated inaccurate movements (Ataxia)
What does the cortico-ponto-cerebellar projection connect?
Cortex, pontine nucleus and cerebellum
