Motor control & movement disorders Flashcards
what are the main principles of motor control?
hierarchical organisation and functional segregation
what is hierarchical organisation?
higher order areas = more complex tasks e.g planning
lower level areas = lower level tasks e.g movement execution
what is functional segregation in terms of motor control?
motor system is organised in a number of different areas that control different aspects of motion ie basal ganglia, brainstem etc
what are the major descending tracts?
pyramidal and extrapyramidal tracts
what is the function of the pyramidal tract?
voluntary movements of body and face
what is contained within the pyramidal tracts
corticospinal and corticobulbar
what is contained within the extrapyramidal tracts?
Vestibulospinal
Reticulospinal
Tectospinal
Rubrospinal
what is the pathway for pyramidal tracts?
pass through pyramids of the medulla
motor cortex to spinal cord or cranial nerve nuclei in brainstem
what is the pathway for extrapyramidal tracts?
brainstem nuclei to spinal cord
do not pass through pyramids of the medulla
where is the area for primary motor control
precentral gyrus
what is the role of the primary motor cortex?
controls fine, discrete precise voluntary movement - descending signals for execution
where is the premotor control area?
anterior to primary motor cortex but not up to top of brain
what is the role of the premotor area?
planning movements, regulating externally cued movements (reactions to environment e.g catching an apple)
where is the supplementary motor area?
above premotor area extending to longitudinal fissure
what is the role of the supplementary motor area?
planning complex movements and regulating internally cued movements (things you think about before doing it e.g speech)
active prior to voluntary movements
what is the corticospinal tract split into?
lateral (limb muscles) and anterior (trunk) corticospinal tract
which corticospinal fibres cross in the pyramids of decussation?
lateral corticospinal tract (85-90%) of corticospinal
which corticospinal fibres don’t decussate in the pyramids?
anterior corticospinal tract (10-15%)
what is the function of the corticobulbar tract?
principle motor pathway for voluntary movements in the face and neck
what nuclei do eye movements originate from?
oculomotor, trochlear and abducens nucleus
what nucleus controls the muscles of the jaw?
trigeminal motor nucleus
what nucleus controls the muscles of the face?
facial nucleus
what nucleus controls the tongue?
hypoglossal nucleus
what is the role of the vestibulospinal tract?
stabilise head during body/head movements
coordinates head & eye movement
mediates postural adjustments
what is the role of the reticulospinal tract?
changes in muscle tone associated with voluntary movement
postural stability
what is the role of the tectospinal tract?
orientation of the head and neck during eye movements
what is the role of the rubrospinal tract?
innervate lower motor neurones of flexors of upper limb (mainly taken over by corticospinal)
what are the negative signs of upper motor neuron lesions?
loss of voluntary motor function
paresis
paralysis (plegia)
what are the positive signs associated with upper motor neuron lesions?
increased abnormal motor function inhibitory descending inputs spasticity hyperreflexia clonus babinskis sign
what are the signs of a lower motor neuron lesion?
weakness hypotonia/reflexia muscle atrophy fasciculations fibrillations
what is apraxia?
disorder of skilled movement caused by lesion of inferior parietal lobe or frontal lobe (premotor and supplementary areas)
what is motor neuron disease also known as?
ALS (amyotrophic lateral sclerosis)
what is ALS?
progressive degenerative disorder spectrum of NS
what are the upper motor neuron signs of ALS?
spasicity brisk limbs and jaw reflexes babinskis sign loss of dexterity dysarthria (difficulty speaking) dysphagia
what are the lower motor neuron signs of ALS?
weakness muscle wasting tongue fasciculations and wasting nasal speech dysphagia
what does the basal ganglia consist of?
caudate nucleus
lentiform nucleus (putamen+external globus pallidus)
nucleus accumbens
subthalamic nucleus
substantia nigra
ventral pallidum, claustrum, nucleus basalis
what is the striatum?
caudate and putamen combined
what is the function of the basal ganglia?
decision to move
elaborating associated movements e.g arm swing when walking
moderating and coordinating movement
performing movements in order
what is parkinsons disease?
degeneration of dopaminergic neurons originating in substantia nigra and project to striatum
what are the symptoms of parkinsons disease?
bradykinesia, akinesia rigidity resting tremor/pin roll tremor shuffling gait hypomimic face
what is a hypomimic face? (parkinsons)
expressionless, mask-like face (absence of facial animation)
what is huntingtons disease?
degeneration of GABAergic neurons in striatum, caudate and putamen
what is the genetic component of huntingtons disease?
neurodegenerative - chromosome 4 abnormal dominant (CAG repeat)
what are the symptoms of huntingtons disease?
hyperkinesia/choreic movements speech impairment difficulty swallowing unsteady gait cognitive decline and dementia eventually
what is ballism?
sudden, uncontrolled flinging of extremities
what is ballism the result of?
usually stroke subthalamic nucleus
symptoms appear contralaterally
what is the function of the cerebellum/
coordinator and predictor of movement
what is the function of the vestibulocerebellum?
gait, posture and equilibrium
coordinates head & eye movement
what does damage to the vestibulocerebellum cause
ataxia, tendency to fall even with eyes open and sat down
what is the function of the spinocerebellum?
speech coordination, adjustment of muscle tone and coordination of limb movement
what is a common cause of damage to the spinocerebellum?
degeneration and atrophy associated with chronic alcoholism
what does damage to the spinocerebellum present as?
abnormal gait and wide based stance
what is the function of the cerebrocerebellum?
coordination of skilled movement, cognitive function, attention, language processing, emotional control
what does damage to the cerebrocerebellum present as?
mainly arms - skilled coordinated movement tremor and speech issues
what is ataxia?
general impairment in movement coordination and accuracy, disturbances of posture/gait
what is dysmetria?
inappropriate force and distance for target-directed movements
what is an intention tremor?
increasingly oscillatory trajectory of limb in target-directed movements
what is dysdiadochokinesia?
inability to perform rapidly alternating movements
what is scanning speech?
staccato, impaired coordination of speech muscles
what are the signs of cerebellar dysfunction?
ataxia dysmetria intention tremor dysdiadochokinesia scanning speech
what are alpha motor neurons
lower motor neurons of the brainstem and spinal cord that innervate extrafusal muscle fibres of skeletal muscle, responsible for reflex actions
what is a motor unit?
a single neuron and all the muscles it innervates
smallest functional unit with which to produce force
what are the main classifications of muscle fibre
slow S type I
fast fatigue resistant FR type IIA
fast fatiguable FF type IIB
what are the features of type I muscle fibres?
smallest diameter cell bodies
small dendritic trees
thinnest axons
slowest conduction velocity
what are the features of type IIA muscle fibres?
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
fast fatigue resistant
what are the features of type I muscle fibre contractions?
least force, slow to contract but maximal force is maintained
what are the features of a type IIA muscle fibre contraction? (fast fatigue resistant)
more force, fairly fast contraction but held for long time
what are the features of a type IIB muscle fibre contraction?
most force, fast contraction but fairly short
what are the mechanisms by which the brain regulates force of a single muscle?
recruitment- number of motor units involved
rate coding- how fast the units contract
what is the principle of recruitment for muscle fibres?
size principle - smaller units recruited first(usually slow twitch fibres), as more force is required, more units recruited
allows fine control when low force levels are required
what is rate coding?
motor unit has a range of frequencies they can fire at
as rate firing increases, force produced by the unit increases
- summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials
muscle fibres are unrecruited in the order they were recruited
what is the significance of neurotrophic factors?
motor unit and fibre characteristics are dependent on the nerve which innervates them
this shows plasticity
when is the most common change of IIB to IIA?
muscular endurance training
what can cause a change of I to II fibres?
spaceflight
spinal cord injury
(deconditioning)
how does ageing affect muscle fibre types?
preferential loss of fast muscles (type II)
describe the course of a monosynaptic reflex?
sensory receptor - sensory neuron - motor neuron = action
what is the jendrassik manoeuvre?
creating larger reflexes by clenching teeth, making a fist, pulling against locked fingers and then testing a reflex
what is hyperreflexia associated with?
upper motor neuron lesions (loss of inhibition)
what is clonus?
rhythmic involuntary muscle contraction after manual stretch
what is the babinski sign?
sole of foot stimulated by blunt instrument (stroked) the big toe should react
what is a positive babinski sign?
big toe curls upwards (but normal in infants)
pathway for corticospinal tract
motor cortex (from motor homunculus)
to cerebral peduncle
in medulla pyramids - anterior stays ipsilateral, lateral goes contralateral (lateral =limbs)
travel through spinal cord as anterior or lateral corticospinal tracts
synapse in ventral horn of spinal level they exit at
continue as lower motor neurons
