Motor cortical control Flashcards
what are the main principles of motor cortical control?
- Hierarchical organisation
- Higher order areas of hierarchy involved in more complex tasks
- Functional segregation
- Motor system organised in number of different areas that control different aspects of movement
what does the brain stem do?
passes commands from the cortex to the spinal cord
what does the motor cortex do?
receives information from other cortical areas and sends commands to the thalamus and brainstem
what do the cerebelllum and basal ganglia do?
adjust the commands received from other parts of the motos system
what are the major descending motor tracts?
pyramidal tracts
extrapyramidal tracts
what are the pyramidal tracts?
- Corticospinal
- Corticobulbar
- Pass through pyramids of medulla
- Motor cortex to spinal cord or cranial nerve nuclei via brainstem
- Voluntary movements of body and face
what are the extrapyramidal tracts?
- Vestibulospinal
- Tectospinal
- Reticulospinal
- Rubrospinal
- Do not pass through pyramids
- Brainstem nuclei to spinal cord
- Involuntary (automatic) movements for balance, posture and locomotion
where is the primary motor cortex and what is its function?
where is the pre-motor area and what does it do?
where is the supplementary motor area and what does it do?
how do signals travel down the corticospinal tract?
- upper motor neuron signals travel to cerebral peduncle in midbrain
- travel into medullar to pyramids where they decussate (90%)
- decussated fibres travel down lateral corticospinal tract
- non-decussated fibres travel ipsilaterally down anterior corticospinal tract
- to lower motor neuron
what do the fibres from anterior corticospinal tract control?
trunk muscles
what do fibres from lateral corticospinal tract control?
limb muscles
how are the brain areas dedicated to processing anatomical divisions of the body?
motor homunculus
somatotopic representation
what is the function of the corticobulbar tract?
principle motor pathway for voluntary movements of the face (and neck)
what nerves does the corticobulbar tract act on?
The corticobulbar tract directly innervates the nuclei for cranial nerves:
V - Trigeminal- muscles for mastication
VII- Facial- muscles of the face
XI- Accessory- sternocleidomastoid and trapezius
XII- Hypoglossal- muscles of the tongue
what is the function of the vestibulospinal tract?
stabilise head movements, or as head moves coordinate head movements with eye movements
mediate postural adjustment
what is the function of the reticulospinal tract?
most primitive descending tract
from medullar to pons
changes in muscle tone associated with voluntary movements
postural stability
where does the tectospinal tract run and what are its functions?
from superior colliculus of midbrain
orientation of head and neck during eye movements
where does rubrospinal tract run and what are its functions?
from red nucleus of midbrain
in humans mainly taken over by corticospinal tracts
innervate lower motor neurons of flexors of the upper limb
what are the negative signs of upper motor neuron lesions?
- Loss voluntary motor function
- Paresis- graded weakness of movements
- Paralysis (plegia) – complete loss voluntary muscle activity
what are the positive signs of upper motor neuron lesions?
- 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
a defect in what areas cause apraxia?
- Lesions of inferior parietal lobe, frontal lobe (premotor cortex, supplementary motor area-SMA)
- Any disease of these areas can cause apraxia (stroke and dementia most common)
what is apraxia?
disorder of skilled movements
patients not paretic but lost information about how perform skilled movements
what are the symptoms of lower motor neuron lesions?
- Weakness
- Hypotonia
- Hyporeflexia
- Muscle atrophy
- Fasciculations
- Damaged motor units produce spontaneous action potential= twitch visible
- Fibrillations
- Spontaneous twitching individual muscle fibres, recorded during needle electromyography exam
what is motor neurone disease?
progressive neurodegenerative disorder of motor system
spectrum of disorder
also known as amyotrophic lateral sclerosis (ALS)
affects upper and lower motor neurons
what are the upper motor neuron signs?
- Spasticity
- Babinskis sign
- Loss dexterity
- Dysarthria (diff speaking)
- Dysphagia (diff swallowing)
- Brisk limbs and jaw reflexes
what are the lower motor neuron signs?
- Weakness
- Muscle wasting
- Tongue fasciculation + wasting
- Nasal speech
- dysphagia
what is the structure of the basal ganglia?
cluster of subcortical nuclei
- caudate nucleus
- lentiform nucleus (putamen + external globe pallidus)
together the caudate and putamen are known as the striatum
- nucleus acumbens
- subthalamic nuclei
- substantia nigra (Midbrain)
- ventral pallidum, claustrum, nucleus basalis (of Meynert)
what is the function of basal ganglia?
decision to move
elaborating associated movements (e.g swinging arms when walking; changing facial expressions to match emotions)
moderative and coordinating movement (suppressing unwanted movements)
performing movements in order
what is the development structure of the basal ganglia?
what is the circuitry of the basal ganglia?
what is parkinson’s disease?
- degeneration dopaminergic neurons that originate in substantia nigra and project to striatum
what are the effects of Parkinson’s disease?
- bradykinesia (slowness small movements)
- hypomimic face- expressionless, masklike
- akinesia- difficulty in initiation movements as cannot initiale movement internally
- rigidity- increased muscle tone, causing resistance to externally imposed join movements
- tremor at rest- 4-7 Hz, starts in one hand (pill rolling tremor) and spreads to other parts body
what is Huntington’s disease?
- degeneration of GABAergic neurons in striatum, caudate and then putamen
- genetic neurodegenerative disorder
- chromosome 4, autosomal dominant, CAG repeat
what are the effects of Huntington’s disease?
- choreic- movements rapid jerky involuntary
- speech impairment
- dysphagia
- unsteady gait
- later stages= cognitive decline and dementia
what is ballism caused by?
usually from strokes affecting subthalamic nuclei
what are the effects of ballism?
sudden uncontrolled flinging of extremities
occurs contralaterally
where is the cerebellum located?
posterior cranial fossa
separated from cerebellum above and below by tentorium cerebelli
what are the functional divisions of the cerebellum?
vestibulocerebellum
spinocerebellum
cerebrocerebellum
what is the vestibulocerebellum responsible for?
- Regulation gait, posture and equilibrium
- Coordination head movement with eye movements
what are the effects of damage to the vestibulocerebellum?
- Damage (tumour)= syndrome similar to vestibular disease
- Gait ataxia, tendency to fall even when sitting with eyes open
what is the spinocerebellum responsible for?
- Coordination speech, adjustment muscle tone
- Coordination limb movements
what does damage to the spinal cerebellum cause?
- Damage affects mainly legs- abnormal gait and stance (degen + atrophy assoc with chronic alcoholism)
what are the functions of the cerebrocerebellum?
- Coordination skilled movements
- Cognitive function, attention, processing language
- Emotional control
what does damage to the cerebrocerebellum cause?
- Damage affect mainly arms/ skilled coordinated movements (tremor) and speech
what are the main signs of cerebellar dysfunction?
apparent only on movement
- ataxia
- dysmetria
- intention tremor
- dysdiadochokinesia
- scanning speech
what is ataxia?
general impairments in movement coordination and accuracy
disturbances of posture or gait: wide biased, staggering gait
what is dysmetria?
inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
what is intention tremor?
increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
what is dysdiadochokinesia?
inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
what is scanning speech
staccato due to impaired coordination of speech muscles
