Motor Cortical Control Flashcards
What is the Hierarchical organization of Motor control?
Higher orders - more complex tasks, e.g. programme & decide on movements, coordinate muscle activity.
Lover level areas - lower level tasks e.g. execution of movement.
How is the Motor system segregated?
Number of different areas that control different aspects of movement.
What are the two types of Major descending tracts?
Pyramidal Extrapyramidal (do not pass through the pyramids of the medulla)
What are some examples of Pyramidal tracts and their functions?
Corticospinal, Corticobulbar
Motor cortex to spinal cord or cranial nerve nuclei in brainstem.
Voluntary movements of body and face.
What are some examples of Extrapyramidal tracts and their function?
Vestibulospinal, Tectospinal, Reticulospinal, Rubrospinal.
Brainstem nuclei to spinal cord.
Involuntary (autonomic) movements for balance, posture & locomotion.
Where is the Primary motor cortex located, and what is its function?
Precentral gyrus, anterior to the central sulcus.
Controls fine, discrete, precise voluntary movements.
Provides descending signals to execute movements
Where is the Premotor area located, and what is its function?
Anterior to primary Motor cortex
Involved in planning movements and regulates externally cued movements. Seeing an apple and reaching out for it.
Where is the Supplementary motor area located, and what is its function?
Anterior and medial to PMC
Involved in planning complex movements, internally cued (speech). Becomes active prior to voluntary movement.
What makes up the Corticospinal tract?
Lateral Corticospinal tract - 85-90% crossed fibres , Limb muscles.
Anterior Corticospinal tract - 10-15% uncrossed fibres, trunk muscles.
What does the corticospinal tract pass through to get to the medulla
Cerebral Peduncle
What does somatotopic mean in regard to the brain?
A particular region in the brain correlates to contol of a particular region in the body
What is the Corticobulbar tract responsible for?
Principal motor pathway for voluntary face movements of the face and neck.
Which nuclei are responsible for the movements of the Extra ochlear muscles?
Oculomotor nucleus
Trochlear nucleus
Abducens nucleus
Which nucleus is responsible for the muscles of mastication?
Trigeminal Motor nucleus
Which nucleus is responsible for muscles of the face?
Facial nucleus
Which nucleus is responsible for muscles of the tongue?
Hypoglossal nucleus
What is the responsibility 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 responsibility 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 responsibility of the Tectospinal tract?
From superior colliculus of midbrain
Orientation of the head and neck during eye moveme
What is the responsibility 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 signs of an upper motor neuron lesion?
Loss of voluntary motor function
Paresis: graded weakness of movements
Paralysis (plegia): complete loss of voluntary muscle activity
What are the positive signs of an upper motor neurone lesion?
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
What is Apraxia?
A disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movements
What causes Apraxia?
Lesion of inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area - SMA)
Stroke & dementia are the most common causes
What are the signs of Lower motor neuron lesions?
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 an example of a disease that effects both upper and motor neurons?
Motor neuron disease MND e.g. ALS
What does ALS effect?
Progressive neurodegenerative disorder of the motor system. Affecting; Upper motor neurons Brainstem lower motor neurons Axon bundles tongue intercostal muscles spinal cord lower motor neurons lower limb muscles upper limb muscles
What are the upper motor neuron signs of MND?
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 MND?
Weakness Muscle wasting Tongue fasciculations and wasting Nasal speech Dysphagia
What makes up the structure of 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
What is the structural order of the basal ganglia?
C - caudate nucleus P – putamen G – (external) globus pallidus T - thalamus Acc – nucleus accumbens Am – amygdala AC – anterior commisure
What happens in Parkinson’s disease?
Degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
What are the signs 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 happens in Huntington’s disease?
Degeneration of GABAergic neurons in the striatum, caudate and then putamen
What are the signs 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 are the genetics of Huntington’s disease?
Genetic neurodegenerative disorder
Chromosome 4, autosomal dominant
CAG repeat
What is Ballism?
Symptoms occur contra laterally, uncontrolled flinging of the extremities.
Usually occurs due to a stroke affecting the subthalamic nucleus.
Where is the Cerebellum located, and what is its function?
Located in posterior cranial fossa
Separated from cerebrum above by tentorium cerebelli
Coordinator & predictor of movement
What is the function of the Vestibulocerebellum?
Regulation of gait, posture and equilibrium
Coordination of head movements with eye movements
What are the signs of dysfunctions of the Vestibulocerebellum?
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?
Coordination of speech
Adjustment of muscle tone
Coordination of limb movements
What does damage to the Spinocerebellum present as?
Damage (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 does damage to the Cerebrocerebellum present as?
Damage affects mainly arms/skilled coordinated movements (tremor) and speech
Define Ataxia
General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
Define Dysmetria
Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Define Intention tremor
Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Define Dysdiadochokinesia
Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
Define scanning speech
Staccato, due to impaired coordination of speech muscles
What is similar in all the main signs of cerebellar dysfunction?
Apparent only on movement
