Motor Cortical Control Flashcards
what kind of organisation exists in the motor system?
functional segregation
Motor system organized in a number of different areas that control different aspects of movement
hierarchical organisation depending on complexity of tasks (higher order control programme and decide movement and lower excecute tasks)
where does information from the primary motor cortex pass to?
basal ganglia, cerebellum, thalamus, spinal cord and brainstem
- brainstem → muscles of head, neck, facespinal cord → rest of muscles
what muscles do motor information in the brainstem get passed to? what about the spinal cord?
brainstem → muscles of head, neck, face
spinal cord → rest of muscles
what do the basal ganglia and cerebellum do?
adjust the commands received from other parts of the motor control system
what are the pyramidal tracts?
corticospinal and corticobulbar
Voluntary precise movement
extrapyramidal tracts?
vestibulospinal, tectospinal, reticulospinal, rubrospinal
Involuntary movement
Are extrapyramidal tracts ascending or descending
Descending
what makes something pyramidal/extrapyramidal?
either pass through pyramids of medulla or don’t
functional differences - what do pyramidal do?
voluntary movements of body and face (motor cortex → cranial nerve nuclei or spinal cord)
functional differences - what do extrapyramidal do?
involuntary movements for posture, balance and locomotion
Brainstem nuclei to spinal cord
Corticospinal tract
Passes down lateral corticospinal tract or anterior corticospinal tract
Decussation occurs where most go to lateral
Lateral control limb muscles anterior control trunk
corticobulbar function?
movements of face and neck → cranial nerve nuclei
vestibulospinal function?
stabilise head during body movement , coordinate head movement with eye movement, postural adjustments
reticulospinal function?
Muscle tone changes with voluntary movement
postural stability
Primitive descending tact
From medulla and pons
tectospinal function?
orientation of head and neck during eye movements
From superior colliculus of midbrain
Rubrospinal
Innervate lower motor neurons of flexors of the Upper limb
From red nucleus of the midbrain
Mainly taken over by corticospinal tract
negative signs of upper motor neuron lesion?
loss of voluntary motor function
paresis (graded weakness of movements)
paralysis-complete loss of movement
Positive signs of upper motor lesions
- spasticityincreased muscle tone
- hyperreflexiaexaggerated reflexes
- clonusabnormal oscillatory muscle contraction
- babinski’s signabnormal upward curling of big toe (normal in infants but not adults) on stimulation
increased abnormal motor function due to loss of inhibitory descending inputs
Apraxia
Loss of skilled movement (loss of info is not paretic)
Have lost info about how to perform skilled movement
Common cause of apraxia
Stroke and dementia
Lesions of inferior parietal lobe ,frontal lobe (premotor cortex,supplementary motor area)
signs of lower motor tract lesion
hypotonia, hyporeflexia, muscle atrophy,weakness
- fasciculationsdamaged motor units → spontaneous action potentials → visible twitch
- fibrillationstwitching of individual muscle fibres recorded during needle electromyography
what are dysarthria and dysphagia?
Difficulty speaking or swallowing
what is motor neuron disease?
progressive neurodegenerative disorder of motor system → spectrum
Also known as amyotrophic lateral sclerosis
UMN-spasticity,brisk limb and jaw reflex,babinski sign,loss of dexterity,dysarthria,dysphagia
LMN-weakness,muscle wasting,tongue fasicukation,nasal speech,dysphagia
basal ganglia main structural elements?
caudate nucleus
lentiform nucleus
substantia nigra (midbrain)
nucleus accumbens
subthalmic nuclei
basal ganglia main function?
decision to move
performing associated movements e.g. changing facial expression in reaction, swinging arms while walking
suppressing unwanted movements
performing movements in order
what is the striatum?
Caudate nucleus and putamen
what is parkinson’s disease?
degeneration of dopaminergic neurons from substantia nigra to striatum
Symptoms include bradykinesia, expressionless face → hypomimic, akinesia (difficulty in initiation of movements), rigidity, tremor at rest
Huntingtons disease
degeneration of GABAergic neurons in striatum caudate and then putamen
Symptoms involve jerky involuntary movement,difficulty swallowing,gait disorder and cognitive decline/dementia
Choreic movement
What is ballism
Contralateral flinging of extremities
Caused by stroke affecting the subthalamic nucleus
Symptoms occur contralaterally
What separates the cerebrum and cerebellum
Tentorium cerebelli
broad function of cerebellum?
Coordinates and predictions of movement
Three main parts of cerebellum
vestibulocerebellum (central strip), spinocerebellum (medial vertical stripe), cerebrocerebellum (lateral stripe)
- vestibulocerebellumregulate gait, posture and equilibrium, coordinate head and eye movements. Damage (tumour) causes gait ataxia and tendency to fall even when sitting with eyes open
- spinocerebellumcoordinate speech, coordinate limb movements, adjust muscle tone. Damage (degeneration and atrophy associated with chronic alcoholism) affect leg causing abnormal gait and stance (wide)
- cerebrocerebellumcoordinate skilled movements, cognitive function & attention, process language, emotional control. Damage affects mainly arms/skilled coordinated movements and speech
main signs of cerebellar dysfunction?
- ataxiagait disturbance
- dysmetriainappropriate force and distance for target oriented movement
- intention tremoroscillatory limb trajectory in target directed movement
- dysdiadochokinesiainability to perform rapidly alternating movements
- scanning speechstaccato bc impairment of speech muscle coordination
- lower motor neurons of brainstem and spinal cord
Alpha motor neurons
Lower motor neurons of brainstem and spinal cord
Innervate extrafusal muscle fibres if skeletal muscle
Extrafusal muscle fibres generate force for muscle contraction
Activation of alpha motor neurons
Causes muscle contraction
what is a motor unit?
single motor neuron along with all the muscle fibres it innervates
On average each motor neuron innervates 600 muscle fibres
different types of motor unit?
slow (type I)- small dendritic trees cell bodies and axons
fast & fatigue resistant (type IIA)-large dendritic trees cell bodie and axons
fast & fatiguable (type IIB)-large dendritic trees cell bodies and axons
difference in force produced by IIA and IIB?
IIA is weaker, IIB (fatiguable) is stronger
Order of motor unit recruitment
Small first to allow slow twitch units (fine movement allowed)
Rate coding
Way for brain to regulate force a muscle produces
The higher the firing rate the more force produced
Summation
unit fires at too fast a frequency to allow muscle relaxation between contractions → recruitment of other motor units
-
what are neurotrophic factors?
growth factors that prevent neuron death and promote growth after injury
what does cross innervation of muscle fibres do?
some properties are switched e.g. muscle fibres can become faster or slower dependent on nerve
What change does aging cause
preferential loss of type II fibres → slower contraction times
- what determines the magnitude and timing of reflex functions?
Intensity and onset stimulus
reflexes can’t be controlled but can be influenced e.g. by Jendrassik manoeuvre → what is that?
pulling against locked fingers to increase magnitude of knee jerk reflex
Can also bite down teeth or clench fist
supraspinal control of reflex arcs under normal conditions?
Inhibitory
what reveals the excitatory control?
Decerebration
how can brain damage affect reflexes?
rigidity and spasticity from brain damage can result in over-active stretch reflexes
hyperreflexia is associated with what kind of lesion?
upper motor neuron lesion → loss of descending inhibition
defining features of clonus?
involuntary and rhythmic muscle contractions
hyporeflexia is associated with what kind of disorder?
Lower motor neurone disease
Descending supraspimal control of reflex
- Activating alpha motor neurons
2.activating inhibitory interneurons
3.activating propriospinal neurons
4.activating gamma motor neurons
5.actuvating terminal of afferent fibres
Primary motor cortex
Located in pre central gyrus anterior to central sulcus
Controls fine discrete precise voluntary movement
Provide descending signal to execute movement
Premotor area
Located anterior to primary motor cortex
Involved in planning movement
Regulates externally cued movement
Eg seeing an apple and reaching out for it
Supplementary motor area
Located anterior and medial to primary motor cortex
Plans complex movement eg internally cued speech
Becomes active prior to voluntary movement
Where are alpha motor neurones found
Anterior horn of grey matter of spinal cord and in brainstem
Why does doing the jendrassik movement cause a large reflex
Removes descending inhibition from brain
