Motor pathways: Cortical motor function, basal ganglia and cerebellum Flashcards
What is the difference in function between the higher and lower cortical areas of the brain?
Higher areas program and coordinate tasks, lower order areas execute tasks
What is the pyramidal tract composed of?
Corticospinal tract
Corticobulbar tract
What makes up the extrapyramidal tract?
Cerebellum
Basal ganglia
Where is the M1?
Pre-central gyrus
What is the function of M1?
Fine, discrete, precise voluntary movement
Describe the layers of M1
6 layers
Layer 5 has Betz cells = very large pyramidal cells
Explain the mapping of M1 and the relevance to stroke
Somatotopic - Penfield’s homunculus
Stroke affecting MCA –> upper limb dysfunction
Stroke affecting ACA –> lower limb dysfunction
Recall the pathway taken by 90% of descending motor neurons
M1 internal capsule cerebral capsules pyramids decussation lateral corticospinal tract ventral horn *synapse with alpha neuron* ventral root spinal nerve musculature
Recall the pathway taken by descending motor neurons that do not decussate in the medulla
M1 internal capsule cerebral capsules pyramids anterior corticospinal tract ventral horn *synapse with alpha neuron* *cross side* ventral root spinal nerve AXIAL musculature
What is the main difference between the corticospinal and corticobulbar tracts?
Corticobulbar = CRANIAL nerves Corticospinal = spinal nerves
What is the function of the premotor cortex and where is it located?
Anterior to M1, regulates externally cued movements
What is the role of the supplementary motor cortex? Recall 3
- Planning of complex movements
- Movement sequences
- Speech mechanics
Recall the 2 association motor cortices
- Posterior parietal
2. Prefrontal
What is the function of each of the association motor cortices?
- PP = ensures movements are targeted accurately to objects in external space
- PF = selects appropriate movements for particular course of action
Recall 2 negative signs of an upper motor neuron lesion
Paresis
Plegia
Recall 5 positive signs of an upper motor neuron lesion
- Babinski’s sign
- Clonus
- Increased muscle tone (spasticity)
- Hyper-reflexia
- Apraxia
What is clonus?
Abonormal oscillatory muscle contraction
What are the most common causes of apraxia?
Stroke or dementia
Dysfunction of which lobes are most likely to result in apraxia
Inferior parietal or frontal
What is apraxia?
Disorder of skilled movement
How does the presentation of a lower motor neuron lesion differ from that of an UMN lesion?
- Decreased tone and reflex speed
- Muscle atrophy
- Fasciculations
- Fibrillations
What is a fasciculation?
Visible twitch due to motor unit damage
By what other name is motor neuron disease known?
Amyotrophic lateral sclerosis
Recall 6 upper motor neuron signs of ALS
- Increased muscle tone and spasticity
- Hyper-reflexIia
- Babinski’s sign
- Dysarthria
- Dysphagia
- Loss of dexterity
Recall 5 lower motor neuron signs of ALS
- Myopathy
- Atrophy
- Tongue fasciculations
- Nasal speech
- Dysphagia
Recall the 8 key component structures of the basal ganglia
- Caudate nucleus
- Lentiform nucleus
- Subthalamic nucleus
- Substantia nigra
- Ventral pallidum
- Claustrum
- Nucleus accumbens
- Nucleus basilis of Meynert
What is the striatum of the BG made up of?
Caudate and lentiform nuclei
What is the lentiform nucleus made up of?
Putamen and external globus pallidus
How can neurosurgeons cure tremor in Parkinson’s patients?
Moddification of subthalamic nucleus
What is the function of the nucleus accumbens?
Underlies reward and addiction behaviours
What is the main function of the nucleus basilis of Meynert?
Memory
Where is the caudate nucleus?
Lateral wall of lateral ventricle
Recall 3 functions of the basal ganglia
- Changing facial expression to match emotions
- Suppressing unwanted movements
- Sequencing movements
Recall the progression of neuron breakdown in Huntingdon’s
GABAergic neuron breakdown
First caudate nucleus
Second GP in LN
What sort of neurons are broken down in Parkinson’s?
Dopaminergic
What is the black substance that makes up the substantia nigra?
Neuromelanin- released from dopaminergic cells
Where is the substantia nigra?
Midbrain
Recall 6 presentations of Parkinson’s
- Bradykinesia
- Hypomimic face
- Micrographia
- Akinesia
- Rigidity
- Tremor at rest
At what frequency is a Parkinson’s tremor?
4-7Hz
Describe the inheritance of Huntingdon’s disease
Chromosome 4
Autosomal dominant
CAG repeats - >35 = almost certain
What are chorea?
Rapid, jerky involuntary movements
Describe the progression of chorea in Huntingdons’s disease
First affects hands and face and then legs and rest of body
Recall 5 signs of Huntingdon’s
- Chorea
- Unsteady gait
- Speech impairment
- Dysphagia
- In later stages, cognitive decline and dementia
Recall the 3 divisions of the cerebellum
- Vestibulocerebellum
- Spinocerebellum
- Cerebrocerebellum
What is the main function of the vestibulocerebellum?
Gait and posture regulation
What are the 3 main functions of the spinocerebellum?
Speech coordination
Coordination of limb movements
Adjustment of muscle tone
WHat are the 4 main functions of the cerebrocerebellum
- Language processing
- Coordination of skilled movements
- Motor learning
- Some emotional control
Recall 2 symptoms of vestibular disease
Gait ataxia
Tendency to fall
What is the most common cause of spinocerebellar syndrome?
Chronic alcoholism
Recall 5 signs of cerebellar dysfunction
- Ataxia
- Dysmetria
- Intention tremor
- Dysdiadochokinesia
- Scanning speech
What is ataxia?
Really drunken-looking gait
What is dysmetria?
Inappropriate force and distance for targeted movements
What is an intention tremor?
Tremor when asked to perform a motor command
What is dysdiachokinesia?
Inability to perform rapidly alternating movements
What is scanning speech and what causes it?
Staccato speech
Causes by laryngeal muscle dysfunction in cerebellar syndromes
