motor cortical control Flashcards
what does hierarchical organisation mean in terms of motor control in the brain?
higher order areas of hierarchy are involved in more complex tasks (programme and decide movements, coorinate muscle activity)
lower areas of hierarchy perform lower level tasks (execution of movement)
what is functional segregation with respect to motor control
motor system is organised in a number of different areas that control different aspects of movement
eg. primary motor cortex, non primary motor cortex, basal ganglia and cerebellum, thalamus, brainstem, spinal cord. all these interact with each other to bring about involuntary and voluntary movement
what are the major classes of descending tracts?
pyramidal tracts
extrapyramidal tracts
what are pyramidal tracts and give examples?
pass through the pyramids of the medulla
output neurones in motor cortex -> spinal cord or cranial nerve nuclei in the brainstem
voluntary movements of the body and face
eg. corticospinal and corticobulbar
what are extrapyramidal tracts and give examples?
do not pass through the pyramids of the medulla
upper motor neurones in the cortex, lower motor neurones in brainstem nuclei -> spinal cord
involuntary movements for balance, posture and locomotion
eg. vestibulospinal, tectospinal, reticulospinal, rubrospinal
what is the primary motor cortex
located in the precentral gyrus, anterior to the central sulcus
controls fine, discrete, precise voluntary movements.
provides descending signals to execute movements
final common pathway from the brain down to the lower motor neurones
what is the premotor area?
located anterior to the primary motor cortex (and laterally)
involved in planning movements
regulates externally cued movements (seeing an apple and reaching out for it)
what is the supplementary motor area?
located anterior and medially to the primary motor cortex
involved in planning complex movements, internally cues (eg. speech)
becomes active prior to voluntary movement
what is the corticospinal tract?
descending pyramidal tract
upper motor neurones in the cortex pass through the cerebral peduncle in the midbrain. they then enter the pyramids of the medulla. here they become the corticospinal tract
85-90% decussate in the medulla - forms the lateral corticospinal tract which supplies the limb muscles
10-15% do not decussate - forms the anterior corticospinal tract, which supplies the trunk muscles.
(when nerves of the tract leave the spinal cord they form lower motor neurones)
what is the corticobulbar tract?
descending pyramidal tract
upper motor neurones are in the primary motor cortex. these synapse with brainstem cranial nerve nuclei
principal motor pathway for the voluntary movements of the face and neck
what is the vestibulospinal tract?
descending extrapyramidal tract
stabilises head during body movements
or as head moves coordinates head movements with eye movements
mediates postural adjustments
what is the reticulospinal tract?
descending extrapyramidal tract
most primitive descending tract - from medulla and pons
responsible for changes in muscle tone associated with voluntary movement and postural stability.
what is the tectospinal tract?
descending extrapyramidal tract
from superior colliculus of midbrain
orientation of the head and neck during eye movements
what is the rubrospinal tract?
descending extrapyramidal tract
from red nucleus of midbrai
in humans mainly taken over by the corticospinal tract
innervate lower motor neurones of flexors of the upper limb
what are the signs of an upper motor lesion?
negative signs:
loss of voluntary motor function
paresis - graded weakness of movements
paralysis - 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
clonus - abnormal ascillatory muscle contraction
babinskis sign
what is apraxia?
a disorder of skilled movements. patients are not paretic but have lost information about how to perform skilled movements
due to a lesion of the inferior parietal lobe or the frontal lobe (premotor cortex, supplementary motor cortex
any disease of these areas can cause apraxia, although stroke and dementia are the most common causes
lesions where in the brain are likely to cause apraxia?
inferior parietal and frontal lobe
damage to premotor cortex and supplementary motor area
where does the corticospinal tract decussate?
85% in the medulla - forms lateral corticospinal tract, supplies muscles of the limbs
15% dont decussate - form the anterior corticospinal tract, supplies muscles of the trunk
what are signs of a lower motor lesion?
weakness
hypotonia
hyporeflexia
muscle atrophy
fasciculations (damaged motor units produce spontaneous action potentials, resulting in a twitch)
fibrillations (spontaneous twitching of individual muscle fibres, recorded during needle electromyography examination, not visible to the naked eye, unlike above)
what is motor neurone disease?
progressive neurodegenerative disorder of the motor system
spectrum of disordrs
aka amyotrophic lateral sclerosis (ALS)
affects upper motor neurones, lower motor neurones of the brainstem (eg. voluntary tongue movement), intercostal muscles, upper and lower limb muscles
currently no cure, results in death through lack of respiratory muscle function
what are some symptoms of motor neurone disease?
upper motor neurone:
spasticity, brisk limbs and jaw reflexes, babinskis sign, loss of dexterity, dysarthria, dysphagia
lower motor neurone signs:
weakness, muscle wasting, tongue fasciculations and wasting, nasal speech, dysphagia
what is the structure of the basal ganglia?
Caudate nucleus Lentiform nucleus (putamen + external globus pallidus) Putamen + caudate = striatum Nucleus accumbens Subthalamic nucleus Substantia nigra (mid brain, important in parkisons)) Ventral pallidum, claustram, nucleus basalis (Of Meynert)
look at a diagram
what is the function of the basal ganglia?
decision to move (intention, eg in parkinsons)
elaborating associated movements (facial expressions to emotions, arms to walking)
moderating and coordinating movement (suppresses unwanted movements)
performing movements in order
what is the basal ganglia circuitry?
many input and output pathways between everything
look up the diagram
what is Parkinsons disease?
degeneration of dopaminergic neurones that originate in the substantia nigra (midbrain) and project to the striatum
what are the symptoms of parkinsons?
bradykinesia - slowness of small movements
hypomimic face - expressionless, mask like
akinesia - difficulty in the initiation of movements, cant initiate them internally
rigidity - muscle tone increase, resistance to externally imposed joint movements
tremor at rest - slow, starts in one hand, with time spreads to other parts of the body
visibly less substantia nigra
what is huntingtons disease?
degeneration of GABAergic (inhibitory) neurones in the striatum, caudate and then putamen
genetic neurodegenerative disorder
chromasome 4, autosomal dominant
CAG repeat
visible destruction pf brain matter
what are some symptoms of huntingtons disease?
choreic movements rapid, involuntary, jerky movements of the hands and face first. then legs and rest of body speech impairment difficulty swallowing unsteady gait later: cognitive decline and dementia
what is ballism?
usually from stroke affecting subthalamic nucleus
sudden uncontrolled flinging of the extrematies
symptoms occur contralaterally
generally one sided
what is the cerebellum
located in the posterior cranial fossa
covered by the tentorium cerebelli
coordinator and predictor of movement
takes signals on the way down to muscles, and compares with what is returning from sensory receptors. makes movements fluid
pons connects the two cerebellar lobes round the front
what does the vestibulocerebellum do? what does damage to it do?
regulation of gait, posture and equilibrium
coordination of head movements with eye movements.
damage (tumour) causes syndrome similar to vestibular disease, leading to gait ataxia and tendency to fall
what does the spinocerebellum do? what does damage to it do?
coordinates speech
adjusts muscle tone
coordinates limb movements
damage (degeneration and atrophy associated with chronic alcoholism) mainly affects legs, causes abnormal (wide) gait and stance
what does the cerebrocerebellum do? what does damage to it do?
coordination of skilled movements, cognitive function, attention, processing of language, emotional control
damage effects mainly arms and skilled coordinated movements and speech
what are the areas of the cerebellum?
vestibulocerebellum
spinocerebellum
cerebrocerebellum
what are the main signs of cerebellar dysfunction?
APPARENT ONLY ON MOVEMENT
ataxia- impairment of movement coordination and accuracy, staggering gait
dysmetria - inappropriate force for target directed movement
intention tremor
dysdiadochokinesia - inability to perform rapidly alternating movements
scanning speech - staccato, due to impaired coordination of speech muscles
