1b// 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, progrmamme and deciding movements, coordinate muscle activity
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 cortex
precentral gyrus
anterior to the centrla sulcus
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
located anterior and medial to primary motor cortex
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%)
Label this corticospinal tract.
What is homunculus and somatotopy?
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?
corticobulbar tract
trigeminal motor nucleus
what nucleus controls the muscles of the face?
corticobulbar tract
facial nucleus
what nucleus controls the tongue?
corticobulbar tract
hypoglossal nucleus
what is the role of the vestibulospinal tract? (3)
stabilise head during body/head movements
coordinates head & eye movement
mediates postural adjustments
What are the extrapyramidal tracts?
vestibulospinal
reticulospinal
tectospinal
rubrospinal
what is the reticulospinal tract? And where does it originate?
Most primitive descending tract - from medulla and pons Changes in muscles tone associated with voluntary movement Postural stabilitychanges in muscle tone associated with voluntary movement
The Reticulospinal tract is responsible primarily for locomotion and postural control
what is the role of the tectospinal tract?
from superior colliculus of midbrain
orientation of the head and neck during eye movements
what is the role of the rubrospinal tract?
from red nucleus of midbrain
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 is paresis and paralysis?
Paresis: graded weakness of movements
Paralysis (plegia): complete loss of voluntary muscle activity
what are the positive signs associated with upper motor neuron lesions? (5)
* increased abnormal motor function due to inhibitory descending inputs * spasticity * hyperreflexia: exxagerated reflexes * clonus: abnormal oscillatory muscle contraction * babinskis sign
what are the signs of a lower motor neuron lesion? (6)
Weakness
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination
what is apraxia?
A disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movements
What lesion causes apriaxia?
Lesion of inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area - SMA)
any diease of these areas can cause apraxia, although stroke and dementia are the most common causes
what is motor neuron disease (MND) also known as?
ALS (amyotrophic lateral sclerosis)
what is ALS?
Amyotrophic Lateral Sclerosis
progressive neruodegenerative disorder of the motor system
spectrum of disorders
Why can amyotrophic lateral sclerosis (ALS) cause difficulty breathing?
when intercostal muscles are affects
what are the upper motor neuron signs of ALS? (6)
spasicity brisk limbs and jaw reflexes babinskis sign loss of dexterity dysarthria (difficulty speaking) dysphagia
what are the lower motor neuron signs of ALS? (5)
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
Label the letters.
C - caudate nucleus
P – putamen
G – (external) globus pallidus
T - thalamus
Acc – nucleus accumbens
Am – amygdala
AC – anterior commisure
Describe the basal ganglia circuitry.
and what specific areas are affected in…
- huntington’s
- ballism
- parkinson’s
- huntington’s= Globus Pallidus interior
- ballism= subthalamic nucleus
- parkinson’s= substantia nigra (rostral)
what is parkinsons disease?
degeneration of dopaminergic neurons originating in substantia nigra and project to striatum
what are the symptoms of parkinsons disease? (5)
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 bradykinesia and akinesia?
Bradykinesia - slowness of (small) movements (doing up buttons, handling a knife)
Akinesia - difficulty in the initiation of movements because cannot initiate movements internally
What is meant by rigidity in parkinson’s disease?
Rigidity - muscle tone increase, causing resistance to externally imposed joint movements
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
Choreic movements (chorea - dance)
rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
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? And where is it located?
coordinator and predictor of movement
Located in posterior cranial fossa
Separated from cerebrum above by tentorium cerebelli
what is the function of the vestibulocerebellum?
regulation of gait, posture and equilibrium
coordination of head movements with eye movements
what does damage to the vestibulocerebellum cause
Damage (tumour) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open)
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: wide based, staggering (drunken) gait
what is dysmetria?
inappropriate force and distance for target-directed movements (knocking over a cup rather than picking it up)
what is an intention tremor?
increasingly oscillatory trajectory of limb in target-directed movements (nose finger tracking)
what is dysdiadochokinesia?
inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
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 does activation of alpha motor neurones lead to?
muscle contraction
Where are all the alpha motor neurones?
Motor neuron pool contains all alpha motor neurons innervating a single muscle
what is a motor unit?
a single neuron and all the muscles it innervates
on average each motor meurone supplies about 600 muscle fibres
smallest functional unit with which to produce force
What happens when one motor unit is stimulated?
contraction of all the muscle fibres in that unit
what are the main classifications of muscle fibre and how are they classified
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 II2 motor units?
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
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?
they are a type of growth factor that prevent neuronal death and promtoes growth of neurones after injury (muscles w/out nerves still atrophym these provide trophic factors)
motor unit and fibre characteristics are dependent on the nerve which innervates them
If a fast twitch muscle and a slow muscle are cross innervated, the soleus becomes fast and the FDL becomes slow.
The motor neuron has some effect on the properties of the muscle fibres it innervates.
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?
Ageing associated with loss of type I and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle (evidence from slower contraction times).
Describe/ Explain a reflex function.
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 exert inhibitory and excitatory regulation upon the stretch reflex? And what is dominant?
higher centres of the CNS
Inhibitory control dominates in normal conditions (N).
Decerebration reveals the excitatory control from supraspinal areas (D).
What can rigidity and spasticity of reflexes be caused by?
Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex.
Describe the steps of the descending (supraspinal) control of reflexes.
what is hyperreflexia associated with?
upper motor neuron lesions (loss of descending inhibition)
what is clonus?
involuntary and rhythmic muscle contraction
loss of descending inhibition
associated with upper motor neuron lesions
what is the babinski sign?
sole of foot stimulated by blunt instrument (stroked) the big toe should react
associated with upper motor neuron lesions
what is a positive babinski sign?
big toe curls upwards (but normal in infants)
What is hyporeflexia associated with?
lower motor neuron diseases
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
