Cortical motor function, basal ganglia and cerebellum Flashcards
What is the location of the primary motor cortex
Precentral gyrus
Anterior to the central sulcus
What is the function of the primary motor cortex
Controls fine, discrete, precise, voluntary movement (input from cerebellum)
Provides descending signals to execute movement
Penfield’s motor homunculus
Describe the corticobulbar pathway (hypoglossal example)
- Originates from head region of motor cortex
- Passes through the internal capsule of basal ganglia
- Synapse in the medulla at the hypoglossal nucleus
- Hypoglossal nerve fibres pass out
Where is the premotor cortex found
Frontal lobe, anterior to primary motor cortex
What is the function of the premotor cortex
Planning of movements
Regulates externally cued movements
Where is the supplementary motor area
Frontal lobe, anterior to primary motor cortex, medially
What is the function of the supplementary motor area
Planning complex movements
Programming sequencing of movements
Regulates internally driven movements e.g. speech
Becomes active when thinking about a movement before executing it
What are the association cortexes
Brain areas whose activity does not correlate with motor output/act
Posterior parietal cortex - ensures movements are targeted accurately to objects in external space
Prefrontal cortex - involved in selection of appropriate movements for a particular course of action
Define lower motor neurone and upper motor neuron
Spinal cord, Brainstem
Corticospinal, corticobulbar
Define pyramidal and extrapyramidal
Lateral corticospinal tract
Basal ganglia, cerebellum
What is the consequence of an upper motor neuron lesion
Loss of function
- Paresis: graded weakness of movements
- Paralysis (plegia): complete loss of muscle activity
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
Stroke and dementia most common causes
Which areas of the brain does apraxia involve
Lesion of the inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area)
What are the clinical features of a lower motor neurone lesion
Weakness Hypotonia Hyporeflexia 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 motor neurone disease
Progressive neurodegenerative disorder of the motor system
Spectrum of disorders
Amyotrophic laurel sclerosis (ALS)
What are the upper motor neuron signs of MND
Increased muscle tone (spasticity of limbs and tongue) Brisk limbs and jaw reflexes Babinski’s sign Loss of dexterity Dysarthria Dysphagia
What are the lower motor neurone signs of MND
Weakness Muscle wasting Tongue fasciculations and wasting Nasal speech Dysphagia
What makes up the basal ganglia
Caudate nucleus
Lentiform nucleus (putamen + external globus pallidus)
Subthalamic nucleus
Substantia nigra
Ventral pallidum, claustrum, nucleus accumbens, nucleus basalis of Meynert
What are the functions of the basal ganglia
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
Describe the circuitry of the basal ganglia
cortex -> globus pallidus, striatum, substantia nigra
Globus pallidus -> subthalamic nucleus -> globus pallidus -> thalamus -> SMA -> substantia nigra (C) -> substantia nigra (r)
What is the neuropathology of parkinson’s
neurodegeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
What are some clinical features of Parkinson’s
Shaking palsy (paralysis agitans) Involuntary motion, with lessened muscular power Propensity to bend the trunk forward and to pass from a walking to a running pace
What are the main motor signs of Parkinson’s
Bradykinesia (slowness of small movements)
Hypomimic face (expressionless)
Akinesia (difficulty in initiation of movements)
Rigidity (increased muscle tone)
Tremor at rest (4-7Hz, in one hand then other body parts)
Describe the nigro-striatal pathway
-
Describe Huntington’s disease
Genetic neurodegenerative disorder
Chromosome 4, autosomal dominant
CAG repeat (>35)
Degeneration of GABAergic neurons in the striatum, caudate and then putamen
What are the motor signs of Hungtington’s disease
Choreic movements (chorea) Speech impairment Difficulty swallowing Unsteady gait Later - cognitive decline and dementia
What are choleric movements
Rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
How are purkinje cells connected to other cells in the cerebllum
Inferior olive projects to purkinje cells via climbing fibres
All other inputs to fragile cells are via mossy fibres and then parallel fibres onwards
All output from purkinje cells are via deep nuclei
What are the divisions of the cerebellum
Vestibulocerebellum
Spinocerebellum
Cerebrocerebellum
Describe the vestibulocerebellum
Regulation of gait, posture and equilibrium
Coordination of head movements with eye movements
Describe the spinocerebellum
Coordination of speech
Adjustment of muscle tone
Coordination of limb movements
Describe the cerebrocerebellum
Coordination of skilled movements
Cognitive function, attention,
processing of language
Emotional control
Describe Vestibulocerebellar Syndrome
Damage (tumour) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open)
Describe Spinocerebellar syndrome
Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)
Describe Cerebrocerebellar or Lateral Cerebellar Syndrome
Damage affects mainly arms/skilled coordinated movements (tremor) and speech
What are the main signs of cerebellar dysfunction
Ataxia - general impairments in coordination and accuray
Dysmetria - inappropriate force and distance
Intention tremor - increasingly oscillatory trajectory of a limb
Dysdiadochokinesia - inability to perform rapidly alternating movements
Scanning speech - staccato, due to impaired coordination of speech muscles
Describe the motor system hierarchy
-
Describe the motor homunculus
From centre in - Leg, arm, face, tongue
Describe the lateral corticospinal pathway
- Primary motor cortex
- Fibres pass down pass through the internal capsule of the basal ganglia
- Descent down through the midbrain and pons
- In the Medullary pyramids the fibres cross over (decussation, no synapse)
- Descent through the spinal cord in the lateral corticospinal tract
- Projection to the ventral root in the relevant spinal level
Describe the anterior corticospinal pathway
- Primary motor cortex
- Fibres pass down pass through the internal capsule of the basal ganglia
- Descent down through the midbrain and pons
- Through the medulla
- Descent through the spinal cord in the anterior corticospinal tract
- Decussation at the level of the spinal cord
