Neuro - Motor Control Flashcards
What is the hierarchal organisation of motor control?
→ high order areas of hierarchy = more complex tasks (programme + decide on movements, coordinate muscle activity)
→ lower level areas of hierarchy = lower level tasks (execution of movement)
What is functional segregation?
motor system organised in a no. of different areas that control different aspects of movements
How is the hierarchy organised for motor systems?
What are the 2 types of major descending tracts?
→ pyramidal tracts : passes thru the pyramids of the medulla
→ extrapyramidal tracts : do not pass through the pyramids of the medulla
What are pyramidal tracts? What are 2 examples of pyramidal tracts?
→ pass through the pyramids of medulla
→ motor cortex to spinal chord or cranial nerve nuclei in brainstem
→ voluntary movements of body and face
→ corticospinal + corticobulbar
What are extrapyramidal tracts? What are 4 examples of extrapyramidal tracts?
→ doesn’t pass through the pyramids of medulla
→ brainstem nuclei to spinal chord
→ involuntary movements for balance, posture and locomotion
→ vestibulospinal + tectospinal + reticulospinal + rubrospinal
Where is the primary motor cortex and what does it do?
→ located in precentral gyrus, anterior to the central sulcus
→ controls fine, discrete, precise voluntary movements
→ provides descending signals to execute movements
What is the premotor cortex and what does it do?
→ located anterior to primary motor cortex
→ involved in planning movements
→ regulates externally cued movements e.g. reaching for something after seeing it
What is the supplementary motor area and what does it do?
→ located anterior + medial to primary motor cortex
→ involved in planning complex movements e.g. internally cued, speech
→ becomes active prior to voluntary movements
What route does the corticospinal tract take from the brain to the muscles?
What is a part of the lateral corticospinal tract? What does it do?
→ 85 - 90% crossed fibres
→ innervates limb muscles
What is a part of the anterior corticospinal tract? What does it do?
→ 10-15 % uncrossed fibres
→ innervates trunk muscles
What does the corticobulbar tract do?
principal motor pathway for voluntary movements of face and neck
What route does the corticobulbar tract take?
v
What does the reticulospinal tract do?
→ Most primitive descending tract - from medulla and pons
→ Changes in muscles tone associated with voluntary movement
→ Postural stability
What does the tectospinal tract do?
→ From superior colliculus of midbrain
→ Orientation of the head and neck during eye movements
What does the rubrospinal tract do?
→ 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 upper motor neurone lesions?
→ Loss of voluntary motor function
→ Paresis: graded weakness of movements
→ Paralysis (plegia): complete loss of voluntary muscle activity
What are the positive signs of 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?
→ disorder of skilled movement
→ Patients are not paretic but have lost information about how to perform skilled movements
What can cause apraxia?
stroke, dementia or disease of these areas:
→ Lesion of inferior parietal lobe
→ the frontal lobe (premotor cortex
→ supplementary motor area - SMA)
What are the signs of a lower motor neurone 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 neurone disease?
→ Progressive neurodegenerative disorder of the motor system
→ Spectrum of disorders
What is MND also known as?
ASL (Amyotrophic Lateral Sclerosis)
What are upper motor neurone 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 lower motor neurone signs of MND?
→ Weakness → Muscle wasting → Tongue fasciculations and wasting → Nasal speech → Dysphagia
What are some important structures of the basal ganglia?
→ caudate nucleus → lentiform nucleus = putamen + external globus pallidus → striatum = caudate + putamen → nucleus accumbens → subthalamic nuclei → substantia nigra = midbrain → ventral pallidum → claustrum → nucleus basalis
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 cause of Parkinson’s disease?
Degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
What are 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 is Huntington’s disease? What causes Huntington’s disease?
→ Genetic neurodegenerative disorder
→ Chromosome 4, autosomal dominant
→ CAG repeat
What is the pathology of Huntington’s disease?
Degeneration of GABAergic neurones in the striatum, caudate and then putamen
What are 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 is the pathway of descending (supraspinal) control of reflexes?
1) activates alpha motor neurons
2) activates inhibitory interneurons
3) activates propiospinal neurons
4) activates gamma motor neurons
5) activates terminals of afferent fibres
