Motor Pathways; Corticol Motor System, Basal Ganglia & Cerebellum Flashcards
Describe the Functional segregation of motor control
Motor systems are organised in a number of different areas that control different aspects of MOVEMENT
Describe the Hierarchical organisation of motor control
HIGHER ORDER AREAS involved in more complex tasks (i.e. programme movements, coordinate muscle activity)
than LOWER LEVEL AREAS (execution of movement)
What are the hierarchical levels of motor control?
Level 4 (highest) - association cortex
Level 3 - motor cortex (precentral gyrus)
Level 2 - brain stem & cerebellum (refines motor cortex inputs)
Level 1 (lowest) - basal ganglia & spinal cord
3 main areas of the motor cortex?
- Primary Motor Cortex (M1)
- Premotor Cortex
- Supplementary Motor Area
Primary Motor Cortex location?
Precentral gyrus
i.e. ANTERIOR to the CENTRAL SULCUS
Primary Motor Cortex function?
o Control FINE, discrete, precises VOLUNTARY MOVEMENT
o provide DESCENDING signals to execute movement
Which cells are found in the primary motor cortex?
Betz cells!
Pyramidal cells located in LAYER V of the grey matter
Explain the somatotopic organisation of the Primary Motor Cortex
Penfields Motor Homunculus (ONENOTE!!)
Different areas of the cortex control different areas of the body
E.G. face & hands have large area as they have more fine control
Which tracts provides innervation to the arms, legs & axial structures (trunk & abdomen)?
Corticospinal tract
from Primary Motor Cortex
Passage of Lateral Corticospinal tract and what does it innervate?
- R-hemisphere of cortex
- Internal capsule
- Midbrain - cerebral peduncle
- Medulla - decussation at the pyramids!
- Ventral horn of SC - synpase w. LMN
- Innervate distal muscles
Distal muscles of limbs
Passage of Anterior Corticospinal tract and what does it innervate?
- R-hemisphere of cortex
- Internal capsule
- Midbrain - cerebral peduncle
- Medulla
- Ventral horn of SC - synpase w. LMN & decussation at spinal level
- Innervate proximal limbs & trunk muscles
Proximal limbs & trunk muscles
Which tracts provides innervation to the facial muscles?
Corticobulbar Tract
from Primary Motor Cortex - head region
Passage of Corticobulbar Tract and what does it innervate?
- Head region on Primary Motor Cortex
- Internal capsule
- Medulla - synpases at a CRANIAL NERVE NUCLEI (within brainstem)
NT associated with UMNs & LMNs?
Upper to LMN = GLUTAMATE
LMN to muscles fibres = ACH
Location of Premotor Cortex?
Frontal Lobe - ANTERIOR to M1
Function of the Premotor Cortex?
PLANNING of movements
o regulates externally cued movements
Location of the Supplementary Motor Area?
Frontal Love - ANTERIOR to M1 MEDIALLY
Function of the Supplementary Motor Area?
o Planning COMPLEX movements
o Programming SEQUENCING of movements
regulates internally driven movements e.g. speech
When does the Supplementary Motor Area become active?
When THINK about a movement BEFORE actually executing it
i.e. all about PRE-movement
Define the Association Cortex
Brain areas NOT strictly motor areas
AS
their activity does NOT correlate with motor output/act
2 cortical areas that make up the association cortex?
o Posterior Parietal Cortex
o Prefrontal Cortex
Posterior Parietal Cortex?
Part of Association Cortex
o ensures MOVEMENTS are TARGETED accurately to objects in EXTERNAL SPACE
i.e. motor learning & planning
Prefrontal Cortex?
Part of Association Cortex
o involved in SELECTION of APPROPRIATE MOVEMENTS for a particular course of action
i.e. personality input into a movement (e.g. if touch hot plate, avoid it again)
Define LMN & UMN
LMN:
o SC - ventral horn
o Brainstem - bulbar
UMN:
o Corticospinal
o Corticobulbar
Define Pryamidal & Extrapyramidal
Pyramidal:
o LATERAL corticospinal tract
Extrapyramidal:
o Basal Ganglia
o Cerebellum
Difference between pyramidal and extrapyramidal?
The pyramidal tracts (corticospinal tract and corticobulbar tracts) may directly innervate motor neurons of the spinal cord or brainstem (anterior (ventral) horn cells or certain cranial nerve nuclei),
WHEREAS
the extrapyramidal system centers on the modulation and regulation (indirect control) of anterior (ventral) horn cells.
What are the NEGATIVE signs associated with UMN Lesions?
LOSS OF FUNCTION
o Paresis - graded weakness of movements
o Paralysis (plegia) - complete loss of muscle activity
What are the POSITIVE signs associated with UMN Lesions?
INCREASED ABNORMAL MOTOR FUNCTION - due to LOSS of INHIBITORY DESCENDING INPUTS
o Spasticity - increased muscle tone
o Hyper-reflexia – exaggerated reflexes
o Clonus - abnormal oscillatory muscle contraction
o Babinski’s Sign - extensor plansar response
Define Apraxia?
Disorder of SKILLED movement - patient is NOT paretic but HAS lost info. about how to preform skilled movements
Why does Apraxia arise?
Due to UMN lesions of either the:
o Inferior parietal lobe
o Frontal lobe
(PMC & SMA)
Stroke & dementia are the most common causes
Signs of LMN lesions?
OPPOSITE of UMN lesions
o Weakness
o Hypotonia (REDUCED muscle tone)
o Hyporeflexia (REDUCED reflexes)
o Muscle atrophy (as muscles loose innervation)
o Fasciculations - produce spontaneous APs = visible twitch
o Fibrillations - spontaneous twitching of INDIVIDUAL muscle fibres
What is MND?
Motor Neurone Disease
Affects BOTH UM & LM neurones (normally die due to respiratory musculature NO longer working)
Examples of MND?
Progressive neurodegenerative disorder
E.g. ALS (amyotrohpic lateral sclerosis)
MND signs - for UMN?
o Increased muscle tone o Brisk limbs & jaw reflex o Babinski's Sign o Loss of dexterity o Dysarthria - difficult/inacrticulate speech o Dysphagia
MND signs - for LMN?
o Weakness o Muscle wasting o Tounge fasciculations & wasting o Nasal speech o Dysphagia
What is required for the 3 main motor cortical areas to work (PMC, PM & SMA, AC)?
Side-loop structures (SLS)
This includes:
o Basal ganglia
o Cerebellum
Structure of the Basal ganglia?
ONENOTE for more images!!!
Extrapyramidal
o Striatum:
- Caudate nucleus
- Lentiform nucleus (putamen + external globus pallidus) [separated from nucleus via. internal capsule]
o Subthalamic nucleus (beneath thalamus)
o Substantia nigra (in midbrain BUT project to B.G)
o Globus pallidus internia o Ventral pallidum o Claustrum o Nucleus Accumbens o Nucleus basalis of Meynert
Functions of the Basal ganglia?
o Elaborates associated movements (e.g. swinging arms when walking)
o Moderates & coordinates movement (whilst suppressing unwanted movements)
o Performs movements in order
Basic Basal Ganglia circuitry?
- PC thinks of a movement
- SPA imagines/generates sequence for movement
- PMC generates impulse
- Send it to basal ganglia
- Which sends it to the thalamus and to the PMC
- Which then sends it to the muscles
2 main circuit pathways into the basal ganglia?
- DIRECT pathway
o NO projection to STN
o Overall EXCITATORY effect on motor cortex - INDIRECT pathway
o PROJECT to STN
o Overall INHIBITORY effect on motor cortex
Normal functioning relies on balance between these 2 pathways
Which side does the basal ganglia mediate its function for?
Ipsilateral cortex!
2 different classes of syndromes caused by damage to the basal ganglia?
- HYPOkinetic disorders
o DECREASED movements
o e.g. Parkinson’s - HYPERkinetic disorders
o INCREASED movements
o e.g. Huntington’s
Pathophysiology of Parkinson’s?
Neurodegeneration of the DOPAMINERGIC neurones that originate in the:
o STN and project to the striatum
What does the pathophysiology of Parkinson’s cause?
LOSS of DA neurones = loss of NIGRA-STRIATAL PATHWAY (Onenote!!!!)
and so DISRUPTS the fine balance of EXCITATION & INHIBITION = reduction of excitation in the motor cortex
Main Motor Signs of Parkinson’s?
o Bradykinesia - slow movements
o Hypomimic face - expressionless
o Akinesia - difficult in initiation of movements
o Rigidity - muscle tone increases
o Tremor at rest - starts in one hand
o Gait & posture 0 walk slow, small shuffling steps, reduces arm swing, head bent forward & down
Pathophysiology of Huntington’s?
Autosomal dominant - Chr4
Denegeration of GABA neurones in straitum (caudate nucleus, followed by putamen)
What does the pathophysiology of Huntington’s cause?
Disrupts fine balance
SO
motor cortex gets EXCESSIVE EXCITATORY INPUT so sends continous, INVOLUNTARY commands to the muscles
Main Motor Signs of Huntington’s?
o Choreic movements (chorea) - rapid, jerky involuntary movements of the body; hand & face affected first, then legs and rest of body
o Speech impairment
o Difficulty swallowing
o Unsteady gait
o Cognitive decline & dementia
Location of Substantia Nigra?
In the MIDBRAIN
BUT
projects to basal ganglia (DA neurones) so considered part of its circuitry
What does the cerebellum sit in?
Posterior Cranial Fossa
Cerebellum structure when cut horizontally?
Divided into 3 lobes!
- Anterior
- Posterior
3 Flocculonodular
(LUDLEY!!!)
Cerebellum structure when cut sagittaly?
Divides into 3 zones!
- Vermis (middle)
- Intermediate hemisphere (either side of 1.)
- Lateral hemisphere (either side of 2.)
Connections with the cerebellum and NTs?
Connections w. the cerebellum at with the:
o SAME side of the body
o OPPOSITE cerebral hemispheres
Glutamate (+)
GABA (-)
3 divisions of the cerebellum?
Vestibulocerebellum
Spinocerebellum
Cerebrocerebellum
Vestibulocerebellum?
Regulates:
o gait
o posture
o equilibrium
o coordinates head movements with eye movements
Spinocerebellum?
Coordination of:
o speech
o limb movements
o adjusts muscle tone
Which parts do the afferents of the spinocerebellum project?
Spinal afferents from:
o axial body, trigeminal, auditory & visual inputs = project VERMIS
o limbs = project to INTERMEDIATE hemisphere
Cerebrocerebellum?
o coordination of skilled movements
o cognitive function, attention, processing of language
o emotional control
Functions of the Cerebellum?
o Maintenance of balance & posture
o Coordination of voluntary movements (coordinates muscle groups to produce smooth body movements)
o Motor learning (adapting & fine-tuning motor programmes)
o Cognitive functions i.e. language
Vestibulocerebellar Sydndrome?
Damage (tumour) causes syndrome leading to:
o gait ataxia
o tendency to fall
Spinocerebellar Syndrome?
Damage (from degeneration & atrophy due to alcoholism) affects LEGS, causing:
o abnormal gait
o wide-based stance
Cerebrocerebellar Syndrome?
Damage affects mainly:
o arms/skilled coordinated movements (tremor)
o speech
Another word for Cerebrocerebellar Syndrome?
Lateral Cerebellar Syndrome
Main signs of cerebellar dysfunction?
Deficits apparent ONLY UPON MOVEMENT
o Ataxia
o Dysmetria - inappropriate force & distance for target-directed movements
o Intention tremor - only upon movement
o Dysdiadochokinesia - inability to perform rapidly alternating movements
o Scanning speech - staccator due to impaired coodination of speech muscles
What are the BG and Cerebellum responsible for?
Monitoring & coodrination of movements
BY
modifying the output from the motor cortex
