Cortical motor function, basal ganglia and cerebellum Flashcards
what is functional segregation?
different areas control different aspects of movement
what is hierarchical segregation?
some areas coordinate more complex tasks than others
high order: programme and decide on movements, coordinate muscle activity
low order:execution of movement
what is the descending order of the hierarchical segregation?
association cortex (highest)
motor cortex
brainstem and cerebellum
basal ganglia and spinal cord (lowest)
what are the 3 main areas of the motor cortex?
describe their locations relative to each other
1) primary motor cortex (M1) aka Broadmann’s Area 4
2) premotor cortex aka Broadmann’s Area 6
3) supplementary motor area also Broadmann’s Area 6
- the primary motor cortex is closest to the midline (precentral gyrus)
- the premotor cortex lies anterior to the PMC (lateral and inferior)
- the supplementary motor area also lies anterior to PMC but above the premotor cortex (medial and superior)
where is the primary motor cortex located?
frontal lobe on the precentral gyrus
anterior to the central sulcus
what is the function of the primary motor cortex?
issues descending commands to lower motor neurons in order to execute basic movements
- control of fine, discrete and precise voluntary movement
- provides the descending signals to execute movement
what are the biggest cells of the cerebral cortex?
Betz cells (in layer 5)
what are the targets of the corticospinal tracts?
motor function:
arms
legs
axial structures (trunk and abdomen)
what are the two main pathways of the corticospinal tract from the PMC?
what do they go?
1) lateral corticospinal pathway–> distal muscles of the limbs (MAIN- most fibres)
2) anterior corticospinal tract–> proximal limbs and trunk muscles
what is the pathway of the lateral corticospinal tract?
- right hemisphere cortex
- internal capsule ipsilateral to the
- midbrain (cerebral peduncle)
- medulla oblongata and pyramidal decussation at the base
- anterior horn of spinal cord (motor)
- synapse with lower motor neurone
- innervation to distal muscle
NB lower motor neurone is from spinal cord to muscle
what is the difference in pathways of the LCP and ACP?
decussation:
-occurs at the medulla in the pyramids in LCP
heads to distal muscles
- occurs at the level of the spine in the ACP
heads to axial (trunk) and proximal muscles
which type of neurone is the longest?
primary neurone, from the brain
what is the pathway for muscles of the face, muscles and neck ?
how does this compare to the pathway for muscles of the body?
upper motor synapses in the brainstem and go straight from here to the muscles
the neurones to the body muscles come from spinal cord which receives from the brainstem
what NT is used from upper motor neurone (UMN) to lower motor neurone (LMN)?
glutamate
what NT is used from the LMN to the muscle fibres?
ACh
what is the significance of Penfield’s motor homunculus ?
somatotopic organisation of the PMC
face and hands have a larger area of the brain to control them therefore they have finer movements
where is the premotor cortex located?
frontal lobe
anterior to the PMC
lateral brain
what is the function of the premotor cortex?
- planning movement
- regulating EXTERNALLY cued movements with understanding of intra- and extrapersonal space
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)
NB different to supplementary motor area that does internally generated movement
where is the supplementary motor cortex located?
frontal lobe
anterior to PMC
medial brain
what is the function of the supplementary motor cortex?
- planning complex movements
- programming sequencing of the movements
- regulated INTERNALLY driven movements such as speech
- becomes active before a movement is executed (thought of action)
NB different to premotor cortex that does externally guided movements
what is the significance of the association cortex even though it is not anatomically in the motor region?
what two parts make up the association cortex?
provides perceptual experience input and is not directly involved in motor output. Made of two regions
- posterior parietal cortex
- prefrontal cortex
what is the function of the posterior parietal cortex of the association cortex?
ensures movements are targeted accurately to objects in external space
what is the function of the prefrontal cortex of the association cortex?
selection of appropriate movements for a particular course of action
Give examples of UMNs
what can cause an UMN lesion?
examples: Corticospinal, corticobulbar
lesion cause: stroke
what are the 2 types of consequences of an UMN lesion?
Loss and Gain consequences
what is the 3rd consequence with neither loss or gain?
1) Loss of function: therefore negative symptoms
- Paresis: graded weakness of movements
- Paralysis (plegia): complete loss of muscle activity
2) Increased, abnormal, motor function due to loss of inhibitory descending inputs: therefore positive symptoms
- Spasticity: increased muscle tone
- Hyper-reflexia: exaggerated reflexes
- Clonus: abnormal oscillatory muscle contraction
- Babinski’s
3) Apraxia: disorder of skilled movement (loss of information to do skilled movements)
what features of functional loss (negative symptoms) are seen in UMN lesions?
paresis- graded weakness of movement
paralysis (plegia)- complete loss of motor activity
what features of abnormal motor function (positive symptoms) are seen in UMN lesion?
- spasticity-increased muscle tone
- hyperreflexia- exaggerated reflexes
- clonus- abnormal oscillatory muscle contraction
- Babinski’s sign- extensor plantar response
what is apraxia (3rd consequence of UMN lesion)
what causes apraxia?
- disorder of skilled movement (loss of information to do skilled movements). Patient is not paretic i.e. no complete loss hence why its not a -ve effect
- cause: lesion of the inferior parietal lobe or frontal lobe affecting the premotor cortex and supplementary motor area
most commonly caused by stroke and dementia
what are signs of LMN lesion?
displays opposite signs of UMN lesion
- weakness
- hypotonia
- hyporeflexia
- muscle atrophy
- fasciculations
- fibrillations
Give an example of a Motor Neurone Disease?
what is MND?
Example: amyotrophic lateral sclerosis (ALS)
MND: group of progressive neurodegenerative disorders ,on a spectrum, affecting both UMNs and LMNs therefore show both sets of signs
What are the signs of Upper MND?
Increased muscle tone (spasticity of limbs and tongue).
Brisk limbs and jaw reflexes.
Babinski’s sign.
Loss of dexterity.
Dysarthria – difficult or inarticulate speech.
Dysphagia.