Motor Control Flashcards
Outline the broad principles of motor control
Hierarchical organisation
- higher order areas - involved in more complex tasks, e.g. planning movement
- lower order areas - involved in lower level tasks, e.g. execution of movement
Functional segregation
- Different areas control different aspects of movement
What are the pyramidal tracts?
Corticospinal
Corticobulbar
- Pass through pyramids of the medulla
What are the extrapyramidal tracts?
Vestibulospinal
Tectospinal
Reticulospinal
Rubrospinal
- Do not pass through pyramids of the medulla
Outline the route of the pyramidal tracts and their function
Motor cortex to spinal cord or cranial nerve nuclei in brainstem
Voluntary movements of body and face
Outline the route of the extrapyramidal tracts and their function
Brainstem nuclei to spinal cord
Involuntary (automatic) movements for balance, posture and locomotion
Where is the primary motor cortex and what is its function?
Precentral gyrus
Controls fine, discrete, precise voluntary movements
Provides descending signals to execute movements
Where is the premotor area and what is its function?
Anterior to primary motor cortex
Involved in planning movements
Regulates externally cued movements, e.g. seeing an apple and reaching for it
Where is the supplementary motor area and what is its function?
Located anterior and medial to primary motor cortex
Involved in planning complex movements (e.g. internally cued, speech)
Becomes active prior to voluntary movement
Describe the route of the corticospinal tract
Outline the somatotopic representation of the motor and sensory cortices
What is the function of the corticobulbar tract?
Principal motor pathway for voluntary movements of the face (and neck)
What is the function of the vestibulospinal tract?
Stabilise head during body movements, or as head moves
Coordinate head movements with eye movements
Mediate postural adjustments
What is the function of the reticulospinal tract?
Most primitive descending tract - from medulla and pons
Changes in muscles tone associated with voluntary movement
Postural stability
What is the function of the tectospinal tract?
From superior colliculus of midbrain
Orientation of the head and neck during eye movements
What is the function of the rubrospinal tract?
From red nucleus of midbrain
In humans mainly taken over by corticospinal tract
Innervate lower motor neurons of flexors of the upper limb
What are the negative sign(s) of upper motor neuron lesion?
Loss of voluntary motor function
What is the different between ‘paresis’ and ‘plegia’?
Paresis: graded weakness of movements
Paralysis (plegia): complete loss of voluntary muscle activity
What are the positive signs of upper motor neuron lesion?
Increased abnormal motor function due to loss of inhibitory descending inputs
Spasticity: increased muscle tone
Hyper-reflexia: exaggerated reflexes
Clonus (twitching/jerking): abnormal oscillatory muscle contraction
Babinski’s sign
What is apraxia?
A disorder of skilled movement. Patients are not paretic (don’t have paresis) but have lost information about how to perform skilled movements
What can cause apraxia?
Lesion of inferior parietal lobe
Lesion of the frontal lobe (premotor cortex, supplementary motor area - SMA)
Most common - stroke and dementia
What are the characteristics of a lower motor neuron lesion?
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 motor neuron disease?
Progressive neurodegenerative disorder of the motor system
Spectrum of disorders - upper and lower motor neuron symptoms
Also known as Amyotrophic Lateral Sclerosis (ALS)
What are the upper motor neuron signs of motor neuron disease?
Spasticity (increased tone of limbs and tongue)
Brisk limbs and jaw reflexes
Babinski’s sign
Loss of dexterity
Dysarthria (difficulty speaking)
Dysphagia (difficulty swallowing)
What are the lower motor neuron signs of motor neuron disease?
Weakness
Muscle wasting
Tongue fasciculations and wasting
Nasal speech
Dysphagia
What structures make up the basal ganglia?
Caudate nucleus
Lentiform nucleus (putamen + external globus pallidus) – together caudate and putamen are known as the striatum
Nucleus accumbens
Subthalamic nuclei
Substantia nigra (midbrain)
Ventral pallidum, claustrum, nucleus basalis (of Meynert)
What are the functions of the basal ganglia?
- Decision to move
- Elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions
- Moderating and coordinating movement (suppressing unwanted movements)
- Performing movements in order
Helps us perform fluid movements
What is Parkinson’s Disease?
A condition caused by the degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
What are the symptoms of Parkinson’s Disease?
Bradykinesia - slowness of (small) movements (doing up buttons, handling a knife)
Hypomimic face - expressionless, mask-like (absence of movements that normally animate the face)
Akinesia - difficulty in the initiation of movements because cannot initiate movements internally
Rigidity - muscle tone increase, causing resistance to externally imposed joint movements
Tremor at rest - 4-7 Hz, starts in one hand (“pill-rolling tremor”); with time spreads to other parts of the body
What is Huntington’s Disease?
Condition caused by degeneration of GABAergic neurons in the striatum, caudate and then putamen
What are the symptoms of Huntington’s Disease?
Choreic movements (chorea - dance) - rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
Speech impairment
Difficulty swallowing
Unsteady gait
Later stages, cognitive decline and dementia
What causes Huntington’s Disease?
Genetic neurodegenerative disorder
Chromosome 4
Autosomal dominant
CAG repeat
What is ballism and what is it usually caused by?
Sudden uncontrolled flinging of the extremities
Usually from stroke affecting the subthalamic nucleus
Symptoms occur contralaterally
Where is the cerebellum and what is its function?
Located in posterior cranial fossa
Separated from cerebrum above by tentorium cerebelli
Coordinator and predictor of movement - compares what is happening with what should be happening and makes fine adjustments
What is the function of the vestibulocerebellum?
Regulation of gait, posture and equilibrium
Coordination of head movements with eye movements
What happens when the vestibulocerebellum is damaged?
Damage usually due to a tumour
Causes a syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient is sitting and eyes open)
What is the function of the spinocerebellum?
Coordination of speech
Adjustment of muscle tone
Coordination of limb movements
What happens when the spinocerebellum is damaged?
Damage usually due to degeneration and atrophy associated with chronic alcoholism
Affects mainly legs - causes abnormal gait and stance (wide-based)
What is the function of the cerebrocerebellum?
Coordination of skilled movements
Cognitive function, attention, processing of language
Emotional control
What are the main signs of cerebellar dysfunction?
Ataxia: General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
Dysmetria: Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Intention tremor: Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Dysdiadochokinesia: Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
Scanning speech: Staccato, due to impaired coordination of speech muscles
