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
What are lower motor neurons and upper motor neurons?
- Lower motor neuron
- Spinal cord, brainstem
- Upper motor neuron
- Corticospinal, corticobulbar
Where is the M1?
Pre-central gyrus anterior to the central sulcus
What is the function of M1?
Fine, discrete, precise voluntary movement
Provide descending signals to execute 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
Not much representation of the trunk since musculature is minimal .
- Stroke affecting MCA –> upper limb dysfunction
- Stroke affecting ACA –> lower limb dysfunction
Recall the pathway taken by 90% of descending motor neurons
LATERAL CORTICOSPINAL TRACT
- M1
- internal capsule
- cerebral peduncles in midbrain
- not visible in pons because of transverse fibres
- base of medulla in pyramids = decussation
- lateral corticospinal tract
- ventral horn
- *synapse with alpha neuron*
- ventral root
- spinal nerve
- musculature for voluntary movement
Recall the pathway taken by descending motor neurons that do not decussate in the medulla
Anterior corticospinal tract:
- M1
- internal capsule
- cerebral peduncles
- pyramids - 5% don’t cross and keep going iipsilaterally in the anterior corticospinal tract
- anterior corticospinal tract
- ventral horn
- *synapse with alpha neuron*
- *cross side*
- ventral root
- spinal nerve
- AXIAL musculature - trunk and proximal parts of limbs
What is the main difference between the corticospinal and corticobulbar tracts?
Corticobulbar = CRANIAL nerves (nuclei in brainstem)
Corticospinal = spinal nerves
Recall the corticobulbar pathways.
- Fibres descend from the “head” region of the motor cortex
- Fibres pass through the genu of the internal capsule and down through brainstem
- They then reach the hypoglossal nucleus on the contralateral side and its motor neruons send their axons to the tongue.
- Anteriorly the medulla has three cranial nerves coming out of the lateral medulla -9,10 and 11
- Cranial nerve 12 comes out between the pyramids and the olive.
Label:
What is the function of the premotor cortex and where is it located?
Anterior to M1, regulates externally cued movements and plans movements
e.g. seeing an apple and reaching out for it requires moving a body part relative to another body part (intra-personal space) and movement of the body in the environment (extra-personal space)
What is the role of the supplementary motor cortex? Recall 3
- Planning of complex movements
- Programming sequencing of movements
- Regulates internally driven movements e.g. speech mechanics
Becomes active when thinking about a movement before executing it.
Recall the 2 association motor cortices
- Posterior parietal
- 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 - graded weakness of movements
Plegia (paralysis) - complete loss of muscle activity
Recall 5 positive signs of an upper motor neuron lesion
- Babinski’s sign
- Clonus - abn oscillatory muscle contraction
- Increased muscle tone (spasticity)
- Hyper-reflexia
Also 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 (premotor cortex, supplementary motor area)
What is apraxia?
Disorder of skilled movement
How does the presentation of a lower motor neuron lesion differ from that of an UMN lesion?
- Weakness, hypotonia and hyporeflexia
- Muscle atrophy
- Fasciculations
- Fibrillations - spon twitching of individual muscle fibres
What is a fasciculation?
Visible twitch due to motor unit damage (NB: fibrillations are ndivid muscle fibre twitches and are detected by needle EMG)
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 (limbs and tongue)
- Brisk limb and jaw reflexes
- Babinski’s sign
- Dysarthria
- Dysphagia
- Loss of dexterity
Recall 5 lower motor neuron signs of ALS
- Weakness
- Wasting
- Tongue fasciculations and wasting
- Nasal speech
- Dysphagia
Recall the 8 key component structures of the basal ganglia(extrapyramidal).
- Caudate nucleus
- Lentiform nucleus (putamen + ext globus pallidus)
- 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
- Elaborating associated movements e.g. changing facial expression to match emotions, swinging arms when walking
- Suppressing unwanted movements - moderating and coordinating movement
- Sequencing movements
Recall the circuitry of the basal ganglia and state 3 conditions affecting it.
Recall the progression of neuron breakdown in Huntingdon’s
GABAergic neuron breakdown in striatum then
Caudate nucleus
Then Putamen(/globus pallidus) in lentiform nucleus
What sort of neurons are broken down in Parkinson’s?
Dopaminergic neurons in the substantia niagra which sends neurons to the striatum
What is the black substance that makes up the substantia nigra?
Neuromelanin- released from dopaminergic cells
Where is the substantia nigra?
Midbrain
What is a characteristic sign of Parkinson’s on brain sections?
As you age the substantia niagra should get darker - if the dark line is missing then this is a sign of Parkinson’s
Recall 5 presentations of Parkinson’s
- Bradykinesia - slowness of movements
- Hypomimic face - expressionless due to absense of movements that normally animate the face
- Akinesia - difficulty initiating movements
- Rigidity
- Tremor at rest
Describe the characteristic tremor in Parkinson’s Disease.
“pin rolling tremor”
4-7Hz
Starts in one hand then spreads to other parts of body
Describe the inheritance of Huntingdon’s disease
- Chromosome 4
- Autosomal dominant
- CAG repeats - >35 = almost certain
Pathophysiology: degeneration of GABAergic neurons in striatum, caudate, putamen.
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
- Choreic movements
- 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 and equilibrium
- Coordination of head movements with eye movements
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
- Coordination of skilled movements
- Cognitive function and attention
- Processing language
- Emotional control
Recall 2 symptoms of vestibulocerebellar syndrome.
- Gait ataxia
- Tendency to fall
Usually caused by tumour.
What is the most common cause of spinocerebellar syndrome?
Chronic alcoholism
What are the symptoms of spinocerebellar syndrome?
Damage affects mainly legs, causes abnormal gait and stance (wide-based) (from chronic alcoholism)
What are the symptoms of cerebrocelebellar/lateral cerebellar syndrome?
Arms mainly affected, skilled coordinated movements (tremor) and speech
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
