Motor Cortical Control Flashcards
What are the two principles of motor control?
Hierarchical organisation
Functional segregation
What is Hierarchical organisation?
high order areas of hierarchy are involved in more complex tasks
What are considered to be more complex tasks (hint: secondary cortices function)?
programme and decide on movements, coordinate muscle activity
What is considered to be a lower level task?
execution of movement
What is functional segregation?
Motor system organised in a number of different areas that control different aspects of movement
What are the major tracts downwards?
Pyramidal tracts
Extrapyramidal tracts
What is the the pathway of the pyramidal tracts?
Pass through the pyramids in the medulla
Output neurones in the motor cortex
Project down to the spina cord or cranial nerve nuclei
What are the two pyramidal tracts?
Corticospinal
Corticobulbar
What are the 4 extrapyramidal tracts?
Vestibulospinal
Tectospinal
Reticulospinal
Rubrospinal
What is the pathway for the extrapyramidal tracts?
Do not pass down through the pyramids of the medulal
Upper MN in the cortex
Lower MN in the brain stem nuclei
What is the function of the pyramidal tracts?
Voluntary movements of body and face
What is the function of the extrapyramidal tracts?
involuntary (automatic) movements for balance, posture and locomotion
Where is the primary motor cortex located?
Located in precentral gyrus, anterior to the central sulcus
What is the function of the primary motor cortex?
controls fine, discrete, precise voluntary movements.
Provides descending signals to execute movements.
last common pathway from the brain to the lower motor neurons in the brainstem or spinal cord
Where is the premotor cortex located?
Located anterior to primary motor cortex
What is the function of the premotor area?
involved in planning movements
Regulates externally cued movements
e.g. seeing an apple and reaching out for it
Where is the supplementary motor area located?
Located anterior and medial to primary motor cortex
What is the function of the supplementary motor area?
Involved in planning complex movements (e.g. internally cued, speech)
Becomes active prior to voluntary movement
Where is the cerebral peduncle located?
Midbrain
Where does the corticospinal tract decussate?
Medulla
What is the name given to the tract that decussates?
Lateral corticospinal tract
85-90%
What is the name given to the tract that stays on the same side?
Anterior corticospinal tract
10-15%
Whats the function of the lateral corticospinal tract?
Responsible for limb muscle control
Whats the function of the anterior corticospinal tract?
Responsible for innervation of the axial musculature
What is the motor homunculus?
The little man that shows the distribution of innervation
What is the somatotropic representation?
Maps regions of the brain and where they control
What is the function of the corticobulbar tract?
Responsible for voluntary movements of the face
Motor cortex contains the UMN synapse with brainstem cranial nerve nuclei to go to muscles that control movements of the face
What are the nuclei that provide facial movements?
Oculomotor nucleus (Eye) Trochlear nucleus Trigeminal motor nucleus (Jaw muscles) Abducens nucleus (Eye) Facial nucleus (Muscles of the face) Hypoglossal nucleus (tongue)
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?
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 affects of an upper motor neurone lesions?
Loss of voluntary motor function
Paresis: graded weakness of movements
Paralysis (plegia): complete loss of voluntary muscle activity
What is meant by negative?
Loss of function
What is meant by positive?
Unwanted gain of function
What are the positive affects of an upper motor neurone lesions?
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?
Consequence of UMN lesion
disorder of skilled movement
Patients are not paretic but have lost information about how to perform skilled movements
What can cause apraxia?
Lesion of inferior parietal lobe, the frontal lobe
e.g. stroke and dementia
What are the symptoms of a lower motor neurone lesions?
Weakness
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations
Fibrillations
What are fasciculations?
damaged motor units produce spontaneous action potentials, resulting in a visible twitch
What are fibrillations?
spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination
What is MND?
Motor Neuron Disease
What is motor neurone disease?
Progressive neurodegenerative disorder of the motor system
Affects UMN and LMN’s
Also known as Amyotrophic Lateral Sclerosis (ALS)
Which muscles are particularly affected by MND?
Tongue
Upperlimb
Intercostal muscles
Lower limb
What are the signs of upper motor neurone disease? in MND
Spasticity (increased tone of limbs and tongue) Brisk limbs and jaw reflexes Babinski’s sign Loss of dexterity Dysarthria (difficulty speaking) Dysphagia
What are the signs of lower motor neurone disease? in MND
Weakness Muscle wasting Tongue fasciculations and wasting Nasal speech Dysphagia
What makes up the basal ganglia?
Caudate nucleus
Lentiform nucleus
Nucleus accumbens
Subthalamic nuclei
Substantia nigra (midbrain)
Ventral pallidum claustrum, nucleus basalis (of Meynert)
What makes up the lentiform nucleus?
(putamen + external globus pallidus) – together caudate and putamen are known as the striatum
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
Summarise the structures of the basal ganglia
caudate nucleus putamen (external) globus pallidus thalamus nucleus accumbens amygdala anterior commisure
What disorders are associated with basal ganglia dysfunction?
Parkinson’s
Huntington’s
Ballism
What causes Parkinson’s?
Degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
What are the symptoms of Parkinson’s?
Bradykinesia Hypomimic face Akinesia Rigidity Tremor at rest
What is bradykinesia?
slowness of (small) movements (doing up buttons, handling a knife)
What is hypomimic face?
expressionless, mask-like (absence of movements that normally animate the face)
What is akinesia?
difficulty in the initiation of movements because cannot initiate movements internally
What is rigidity?
muscle tone increase, causing resistance to externally imposed joint movements
What are the main feature of the Parkinson’s tremor?
4-7 Hz, starts in one hand (“pill-rolling tremor”); with time spreads to other parts of the body
What causes Huntington’s disease?
Degeneration of GABAergic neurons in the striatum, caudate and then putamen
Genetic neurodegenerative disorder
Chromosome 4, autosomal dominant
CAG repeat
What are the symptoms of Huntington’s?
Choreic movements Speech impairment Difficulty swallowing Unsteady gait Later stages, cognitive decline and dementia
What are 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?
Usually from stroke affecting the subthalamic nucleus.
Sudden uncontrolled flinging of the extremities
Symptoms occur contralaterally.
Where is the cerebellum located?
Located in posterior cranial fossa
What separates the cerebrum and the cerebellum?
Separated from cerebrum above by tentorium cerebelli
What is the function of the cerebellum?
Coordinator and predictor of movement
What is the function of the vestibulocerebellum?
Regulation of gait, posture and equilibrium
Coordination of head movements with eye movements
What does damage of the vestibulocerebellum result in?
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 of the spinocerebellum result in?
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 of the cerebrocerebellum result in?
Damage affects mainly arms/skilled coordinated movements (tremor) and speech
What are the main signs of cerebellar dysfunction?
Ataxia Dysmetira Intention tremor Dysdiadochokinesia Scanning speech
What is ataxia?
General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
What is dysmetria?
Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
What is intention tremor?
Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
What is dysdiadochokinesia?
Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
What is scanning speech?
Staccato, due to impaired coordination of speech muscles
