Motor Pathways Flashcards
What are the broad principles of motor control?
Functional segregation - Motor system organised in a number of different areas that control different aspects of movement
Hierarchical - high order areas of hierarchy are involved in more complex tasks (programme and decide on movements, coordinate muscle activity)
Lower level areas of hierarchy perform lower level tasks (execution of movement) See slides
Where and what is the primary motor cortex?
M1 is located in the precentral gyrus. Its function is control of fine, discrete, precise voluntary movement. And it provides descending signals to execute movement. See slide on the somatotopic organisation
Note: anteriolaterally is supplementary motor cortex and inferiolaterally premotor cortex. See diagram
Where is the primary sensory cortex located?
Somatosensory - located in the postcentral gyrus
Describe the two descending motor pathways
See diagram, slides and kenhub
What are the symptoms of upper motor neurone lesion?
Loss of function:
Muscle weakness - Paresis
Paralysis (plegia) - complete loss of muscle activty
No fasiculations
Decreased motor control: increased abnormal motor function due to loss of inhibitory descending inputs
Increased tone - Spasticity
Exaggerated and sometimes repeating deep tendon reflexes = hyperreflexia = clonus
Babinski sign - normal condition when you rub a sharp object on the base of the foot the toes flex and point downwards. However you get extension of the toes in UMN syndrome = +ve babinski reflex
What are the symptoms of lower motor neurone syndrome?
Muscle weakness
Decreased tone - hypotonia
Muscle atrophy (wasting)
Fasiculations - damage motor units produce spontaneous action potentials, resulting in a visible twitch
Reduced deep tendon reflexes = hyporeflexia
Fibrillations - spontaneous twitching of individual muscle fibres; recorded during needle electromyography
Describe the corticobulbar pathway
See notes
What is the premotor cortex?
It is the frontal lobe anterior to M1
Involved in planning of movements and regulates externally cued movements. See slides
What is the supplementary motor cortex?
It is the frontal lobe anterior to M1, medially
Planing complex movements; programming sequencing of movements (one movement after the other to pick up an apple)
Regulates internally driven movements (e.g speech)
SMC becomes active when thinking about movement before executing movement.
What is the association cortex?
These are brain areas are not strictly motor areas as their activity does not correlate with motor output however they do affect movement.
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
Spinal cord, brainstem. (a-motor neurones)
Define upper motor neurone
Corticospinal, corticobulbar
What is apraxia?
A disorder of skilled movement. Not paretic but have lost information about how to perform skilled movements
What can cause apraxia?
Lesion of the premotor cortex and/or supplementary motor cortex. Lesion of the inferior parietal lobe and/or the frontal lobe.
Stroke and dementia
What is motor neurone disease?
Progressive neurodegenerative disorder or the motor system
Spectrum of disorders
Amyotrophic Lateral Sclerosis (ALS)
Usually progresses in a caudal rostral way. People lose control of their respiratory muscles then die.
What are the signs of MND?
Affects both the upper and lower motor neurones
Upper motor neurone signs:
1) Increased muscle tone (spasticity of limbs and tongue)
2) Brisk limbs and jaw
3) Babinski’s sgn
4) Loss of dexterity
5) Dysarthria (problems with speaking)
6) Dysphagia (problems with swallowing)
Lower motor neurone signs:
1) Weakness
2) Muscle wasting
3) Tongue fasciculations and wasting
4) Nasal speech
5) Dysphagia
Describe the basal ganglia
It is extrapyramidal - meaning its not part of the descending tract
It includes:
Caudate nucleus
Lentiform nucleus (putamen + globus pallidus)
Subthalamic nucleus
Substantia nigra
Amygdala
Ventral pallidum, claustrum, nucleus accumbens, nucleus basalis of Meynert
Striatum = lentiform nucleus + caudate
See the cross sections on the brain on the slides
What lies between the two lateral ventricles?
Septum pellucidum.
Note the lateral wall of the lateral ventricle is made up by the caudate nucleus
What are the functions of the basal ganglia?
Elaborating associated movements (e.g swinging arms when walking or changing facial expression to match emotion)
Moderating and coordinating movement (suppressing unwanted movements)
Performing movements in order
Draw the basal ganglia circuitry
See lecture
Describe parkinsons disease?
See lecture slides.
Loss of dopamingeric neurones going to the striatum in the substantia nigra (nigro-striatal projections). This is the classical primary pathology. The black colour of the substantia nigra is caused by neuromelanin
What are the main motor signs of Parkinson’s disease?
Bradykinesia
Hypomimic face - expressionless ace
Akinesia - difficulty in the initiation of movements because cannot initiate movements internally
Rigidity - muscle tone increase, causing resistance to externally imposed joint movements (e.g doctor moving the joints)
Tremor at rest (pill-rolling tremor) - 4-7Hz starts at one hand spreads to other parts of the body
Parkinsons symptoms are almost always unilateral to begin with.
Describe huntingtons disease?
Genetic neurogenerative disorders.
Chromosome 4 autosomal dominant
CAG repeats
Results in degeneration of GABAergic neurones (generally inhibitor neurones - think about the effect of loss of inhibition) in the striatum, caudate and then putamen.
Motor signs of huntingtons disease?
Choreic movements (chorea) - rapid jerky involuntary movements of the body; hands and face affected first; then legs and the rest of the body
Speech impairment
Difficulty swallowing
Unsteady gait
Later stages, cognitive decline and dementia
Describe the structure of the cerebellum
3 layers of grey matter:
Molecular layer - few neurones mainly cell processes
Piriform layer - purkinje cell layer: main processing cell
Granular layer - small neurones, closely pact
The inferior olivary nucleus projects to the purkinje cells by the climbing fibres. They synapse on the dendritic trees of the purkinje cells.
All other input to granule cells via mossy fibres and then onwards via parallel fibres
All output comes from Purkinje cells via deep nuclei
See notes/slides
This is the modulation of fine movement and motor learning of the output of the primary motor system.
What are the divisions of the cerebellum?
Vestibulocerebellum - regulation of gait, posture and equilibrium. Coordination of head movements with eye movements - linked to superior collicolus.
Spinocerebellum - Coordination of speech. Adjustment of muscle tone. Coordination of limb movements.
Cerebrocerebellum - coordination of skilled movements. Cognitive function, attention, processing of language. Emotional control
The cerebellum is connected to the medulla and spinal cord the inferior cerebellar peduncle.
Describe the symptoms associated with the damage of all the divisions of the cerebellum?
Vestibulocerebellar Syndrome
Damage (tumor) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open)
Spinocerebellar syndrome
Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)
Cerebrocerebellar or Lateral Cerebellar Syndrome
Damage affects mainly arms/skilled coordinated movements (tremor) and speech
What are the main signs of cerebellar dysfunctions apparent only upon movement?
Ataxia - General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
Dysmetria - Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Intention tremor - Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Dysdiadochokinesia - Inability to perform rapidly alternating movements, (rapidly pronating and supinating hands and forearms)
Scanning speech - Staccato, due to impaired coordination of speech muscles
