Cortical Motor Control Flashcards
What is hierarchial organisation?
Areas of higher order are involved in more complex tasks (programme and decide movements, coordinate muscle activity e.g. primary motor cortex)
Lower level area of hierarchy perform lower level tasks (execution of movement e.g. spinal cord, brainstem)
What are the 2 types of descending tracts?
Pyramidal
Non-pyramidal
What are the 2 pyramidal tracts?
Corticospinal
Corticobulbar
What are the 4 non pyramidal tracts
Tectospinal
Rubrospinal
Reticulospinal
Vestibulospinal
What are pyramidal tracts for?
Voluntary movement of the body and face
What are non-pyramidal tracts for?
Non voluntary movements for balance, locomotion and posture
Describe how pyramidal tracts decend
Through pyramidal cells pf medulla
From the motor cortex to the spinal chord or cranial nerve nuclei in the brainstem
Describe how non-pyramidal tracts decend
Not through the pyramidal cells of the medulla
From brainstem nuclei to spinal chord
What is the vestibulospinal tract for?
Stabilises head during body movements
Coordinates head movements with eye movements
What is the reticulospinal tract for?
Changes muscle tone associated with voluntary movement and postural stability
What is the rubrospinal tract for?
Innervate lower motor neurons of flexors of the upper limb
What is the tectospinal tract for?
Orientation of the head and neck during eye movements
What is the role of the primary motor cortex?
Controls fine, discrete, precise voluntary movements
Provides descending signals to execute movement
What is the role of the supplementary area?
Involved in planning complex movements (e.g. internally cued, speech), is active prior to voluntary movement
What is the role of the premotor area?
Involved in planning externally cued movements
Where does the corticospinal tract decussate?
Pyramidal cells of the medulla
What symptoms are associated with an upper motor neuron lesion?
Negative signs:
Loss of voluntary motor function
Paresis: graded weakness of movements
Paralysis (plegia): complete loss of voluntary muscle activity
Positive signs:
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 Babinski’s sign?
Big toe curls upwards instead of down when sole of the foot is stroked (note this is normal for babies but in anyone older they should curl down)
What is apraxia?
Causes/ most common causes
Patients have lost information of how to perform skilled movement
Causes: lesion to inferior parietal lobe, frontal lobe
Most common causes: stroe and dementia
What symptoms are associated with a lower motor neuron lesion?
Weakness
Hypotonia
Hyporeflexia
Muscle atrophy
Fasciculations- damaged motor units producing spontaneous APs leading to twitch
Fibrillations- spontaneous twitching of individual muscle fibres- recorded during needle electromyography exam
In MND, what upper motor neuron signs symptoms do patients have?
Spasticity (increased tone of limbs and tongue) Brisk limbs and jaw reflexes Babinski’s sign Loss of dexterity Dysarthria (difficulty speaking) Dysphagia (difficulty swallowing)
In MND, what lower motor neuron signs do patients have?
Weakness Muscle wasting Dysphagia Tongue fasciculations and wasting Nasal speech
What are key components 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, moderating and coordinating movement, performing movements in order
What happens in Parkinsons?
Degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
How does Parkinson’s present?
Bradykinesia- slow movements
Hyponomic (expressionless face)
Akinesia- difficulty initiating movements
Rigidity- increased muscle tone
Tremor at rest (starts in one hand)- starts in one hand and eventually spreads to other parts of the body
What happens in Huntingtons?
Degeneration of GABAergic neurons in the striatum, caudate and then putamen due to chromosome 4 CAG repeat (autonomic dominant)
How does Huntington’s present?
Choreic movements
Unsteady gait
Dysphagia
Speech impairment
Later: cognitive decline and dementia
What is ballism?
Sudden flinging of extremities, happens contralaterally
Why does ballism arise?
Due to stroke in subthalamic nucleus
Where is the cerebellum located?
Posterior cranial fossa
What is the role of the cerebellum?
Coordinator and predictor of movements
What are the 3 subparts of the cerebellum?
Vestibulocerebellum
Spinocerebellum
Cerebrocerebellum
How does damage to the vestibulocerebellum usually occour?
Tumor
How does damage to the spinocerebellum usually occour?
Chronic alcoholism causes degeneration and atrophy
How does damage to the vestibulocerebellum present?
Gait ataxia and tendency to fall
How does damage to the spinocerebellum present?
Affects mainly legs, causes abnormal gait and stance
How does damage to the cerebrocerebellum present?
Affects mainly arms/skilled coordinated movements (tremor) and speech
What are the main signs of cerebellar dysfunction? When do they present?
Only apparent on movement:
Ataxia (impaired movements in coordination and accuracy)
Dysmetria (can’t judge distance)
Intention tremor
Dysdiadochokinesia (can’t perform rapid alternating movement)
Scanning speech (fragmented speech due to incoordination of speech muscles)
What is the location of the primary motor cortex?
In precentral gyrus, anterior to central sulcus
What is the location of the premotor area?
Anterior to primary motor cortex
What are the 2 parts of the corticospinal tract and what do they innervate and what is their proportion of crossed/uncrossed fibres?
Lateral corticospinal tract- 85-90% crossed fibres, go to limb muscles
Anterior corticospinal tract- 10-15% uncrossed fibres, go to trunk muscles
What is the role of the corticobulbar tract?
What are motor nerves from these nuclei are involved in?
Principal motor pathways for voluntary movements of face and neck
Motor nerves from these nuclei are involved in:
- eye movements
- muscles of the jaw
- eye movements
- muscles of the face
- the tongue
What is motor neurone disease also known as?
Amyotrophic lateral sclerosis
What does motor neurone disease affect?
Tongue Upper limb muscles Upper motor neurones Brainstem LMNs Axon bundles Intercostal muscles Spinal cord LMNs
What separates the cerebellum and the cerebrum?
Tentorium cerebelli
Explain denervation and reinnervation?
Denervation: muscle fibres of a motor neurone lose their nerve supply
Reinnervation: axons of remaining motor units will grow and reach out to denervated muscle fibres
What is the result of denervation and reinnervation?
The resulting new motor unit is larger and less stable and prone to ectopic generation of electrical stimuli in the distal axon that cause contraction of the muscle fibres. A fasciculation.
