Cortical Motor Function, Basal Ganglia and Cerebellum Flashcards
Describe the hierarchical segregation of the motor cprtex
higher = more complex tasks
level 4 = association cortex
level 3 = motor cortex
level 2 = brain stem and cerebellum (side loop structure (SLS))
level 1 = basal ganglia (e.g caudate nucleus) and spinal cord
What are the main ares of the motor cortex?
- primary motor cortex or M1 ( broadmann’s are 4)
- premotor cortex - area 6
- supplementary motor cortex - area 6
Where is the primary motor cortex located?
frontal lobe
precentral gyrus, anterior to central sulcus
What is the function of the primary motor cortex?
control fine, discrete, precise voluntary movement
provides the descending signals to execute movement
What are the biggest cells of the cerebral cells?
Betz cells in layer V of cerebral cortex
What are the divisions of the corticospinal tract?
*provides innervation to arms, legs and axial structures (trunk and abdomen)
- lateral corticospinal tract - distal muscles of limbs
- right hemisphere of cortex -> internal capsule -> emerge as cerebral penucles in midbrain -> medulla oblongata and decussion(crossing over to other side) at pyramids -> anterior horn of spinal cord and synapse with lower motor neurone -> innervation of distal muscles - anterior corticospinal tract - proximal limbs and trunk muscle
* similar pathway but crosses at spinal level
**What are the two main sensory pathways?
dorsal column - touch
spinothalamic - temp. and pain
What are the corticobulbar pathways?
Hypoglossal neurone
Head region of motor cortex ->genu of internal capsule (cortico tubular tract) -> synapses near inferior cerebellar penucle (switches side) [hyoglossal nuclei] -> inferior olivary nucleus -> Tongue muscles
Upper motor neurones synapse in brain stem after crossing over into the lower motor neurone
Upper MN NT= glutamate
Lower = ACh
Desecriibe the somatorophic organisation of the primary motor cortex
Known as Penfield’s motor homunulus
Face and hands have a large area of brain to control them because they have more fine control
Describe the location and function of the promotors cortex
Location - frontal lobe, anterior to M1, lateral to suplementary MC
Function - involved in planning movement (involves regulating external cued movement)
Describe the location and function of the supplementary motor cortex
Location - frontal lobe, anterior to M1, medial to premolar cortex
Function - planning complex movements, programming sequencing of movement (internally driven movements such as speech and becomes active before move to is executed)
What is the association cortex?
Brai areas to strictly motor areas as their activity doesn’t correlate with motor output
Posterior parietal cortex - ensures movements are targeted accurately to objects I external space
Prefrontal cortex - involved in selection of appropriate movements from a particular course of action
What are :
Lower motor neurones?
Upper motor neurones?
Pyramidal neurones?
Extrapyramidal neurones?
L = spinal cord, brain stem - sit in spinal cord and project out
U = corticospinal, corticotubular - sit in cortex and projections to spinal cord
P = lateral criticospinal tract
E = basal ganglia, cerebellum - modify output
What are the effects of an upper motor neuron lesion/
Loss of function (negative signs)
- paresis (garden weakness of movement)
- paralysis [plegia] (complete loss of muscle activity
Increased abnormal motor function (positive signs) due to loss of inhibitory descending output
- spasticity ( increased muscle tone)
- hyper -reflexia) ( exaggerated reflexes
- clonus (abnormal oscillatory muscle contraction)
- Babinski’s sign (extensor plantar response)
What is apraxia?
Disorder of skilled movement - patient not paretic but has lots information on how to perform skilled task
due to lesion of inferior partial lobe or frontal lobe (premolar/supplementary MC)
- most commonly caused by stroke / dementia
What are the effects of a lower motor neuron lesion?
Weakness
Hypotonia
Hyporeeflexia
Muscle atrophy
Fsciculations (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 are the effects of motor neurone disease?
Progressive neurodegeneative disorder of the motor system (affects both upper and lower MC)
Also known as amyotrophic lateral sclerosis (ALS)
Upper motor neuron signs:
Increased muscle tone (spasticity f limbs and tongue)
Brisk limbs and jaw reflexes
Babinski’s sign
Loss of dexterity
Dysarthria (motor speech disorder)
Dysphasia (problems with swallowing n eating)
Lower mot neuron signs: Weakness Muscle weakening Tongue fasciculations and wasting Nasal speech Dysphasia
What are the ey ares of the basal ganglia?
*Extrapyramidal
Includes: Caudate nucleus Lentiform nucleus (putamen + external globus pallidus) Subthalamic nucleus Substantial nigra Ventral pallidum Claustrum Nucleus accumbens Nucleus basalis Meynert
**striatum = lentiform + caudate
What is the function of the basal ganglia?
Elaborates associated movements e.g swinging arms when waking
Moderates and coordinates movement (whilst suppressing unwanted movements, changing facial expressions to match emotions)
Performs movements in order
Describe the circuitry of the basal ganglia
Primary motor cortex -> BG -> Thalamus -> motor cortex -> muscles
Cortex -> striatum
Striatum -> globus pallidus subthalamic nucleus -> globus pallidus -> thalamus
[ballism]
Striatum -> globus pallidus -> T
[affected by HD]
Striatum substantia nigra (r)
[affected by PD]
*see diagram
What are the pathophysioogical feactures of Parkinson’s disease?
Neuronal degeneration of substantia nigra pars compacta (SNc) -> 80% loss of DA cells
Degeneration of DA neurones causes loss of nigra-striatal neurones and disrupts fine balance of excitation and inhibition leading to reduction of excitation in motor cortex
What are the main signs of Parkinson’s?
Bradykinesia (slow movement)
Hypomimic face (expressionless)
Akinesia (difficulty in initiation of movements )
Tremor at rest
Gait and posture - walking slow, small shuffling steps, reduced arm swing and head bent forward and downward
Describe the pathophysiology of Huntington’s disease
Abnormality in Chr4
Autosomal dominant
CAG repeats (>35)
Degeneration of GABA neurones in striatum(caudate then putamen)
Disrupts fine balance
Motor cortex gets excessive excitatory input so tends to send continuous involuntary commands to the muscles
What are the main signs of Huntington’s?
Choreic movements (rapid jerky involuntary movements of the body, hands and face affected first -> legs and rest of the body)
Speech affected
Difficulty swallowing
Unsteady gait
Later stages - cognitive decline and dementia
Describe the structure of the cerebellum
Horizontally divide into 3 lobes:
Anterior
Posterior
Flocculonodular
Sagitally divided into 3 zones:
Vermis
Intermediate hemisphere
Lateral hemisphere
Describe the layers of the cerebellum
3 layers
Molecular - very few neurones, some glial cells
Piriform - purkinje cells found here
Granular - very small neurones found, closely packed
Describe the input and output of the cerebellum?
Inferior olive projects to purkinje cells via climbing fibres
All other input to granule cells via mossy fibres and then onwards via parallel fibres
All output from purkinje cells via deep nuclei
What are the functions of each of the divisions of the cerebellum?
Vestibulocerbellum
- regulation of gait, posture and equilibrium
- coordination of head movements with eye movements
Spinocerbellum
- coordinates speech
- adjustment of muscle tone
- coordination of limb movements
Cerebrocerebellum
- coordination of skilled movements
- cognitive function, attention, processing of language
- emotional control
What does dysfunction in each division of the cerebellum cause?
Vestibulocerbellar syndrome - damage (tumour) causes syndrome similar to vestibular disease leading to gait at axis and tendency to fall (even when sitting and eyes open)
Spinocerebellar - damage ( degeneration/ atrophy with chronic alcoholism) affects annoy legs,causes abnormal gait and stance (wide-based)
Cererocellebelalr/ lateral cerebellar - damage affects mainly arms/ skilleeed coordinated movements (tremor) and sech
What are the main signs of cerebellar dysfunction?
Deficits apparent only upon movement
Ataxia
- general imparments in movement coordination and accuracy
- disturbances of posture or gait
- wide- base
- staggering gait
Dysmetria
- inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Intention tremor
- increasing oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Dydiadochokinesia
- inability to perform rapidly alternating movements
(rapidly pronating and supinating hands an forearms)
Scanning speech
- staccato due to impaired coordination of speech muscles
