Neuro 8: motor pathways Flashcards
Define functional segregation
Motor system organised in a number of different areas that control different aspects of movement
State the 2 hierarchies
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)
Differntiate pyramidal and extrapyramidal system
Pyramidal= motor cortex receiving info from other cortical areas and sends commands to thalamus and brainstem then spinal cord (i.e. the mechanical pathway)
Extramedullary= cerebellum and basal ganglia adjust commands received from other parts of motor control system (fine tune)
Where is the primary motor cortex (M1)
Precentral gyrus (in front of the central sulcus)
Function of primary motor cortex
control fine, discrete, precise voluntary movement
Provide descending signals to execute movement
6 layers of cortex….. in layer 5 the pyramidal Betz cells which are the largest cells in the CNS. Send their axons down the corticospinal tract
Outline somatotopic organisation of primary motor cortex
Penfied’s motor homunclulus….
Hands and tongue overrepresented (learn where things are)
Differentiate anterior and lateral corticospinal tract
Common at the beginning: originating from the primary motor cortex, passing down the internal capsule, through the cerebral peduncle, through the pons.
The lateral corticospinal tract then decussates at the pyramidal decussation of the medulla and travels on the contralateral side down the spinal cord.
The anterior corticospinal tract does not decussate at the pyramidal decussation, instead passing through the pyramids on the ipsilateral side, all the way down the spinal cord in anterior corticospinal tract until reaching the level at which it needs to exit, at which point it decussates.
Lateral CS tract carries 90% of motor fibres, anterior just 10%
Lateral CS carries motor fibres to ekeltal muscle in the distant part of the limbs, whereas anterior CS carries mtor fibres to skeletal muscles in proximal part of limbs and the trunk.
What are corticobulbar pathways
Pathways leading from the primary motor cortex to supply cranial nerve nuclei in the brainstem. It contains the UPPER MOTOR NEURONS of the cranial nerves. They terminate on motor neurons within brainstem motor nuclei. This is in contrast to the corticospinal tract in which the cerebral cortex connects to spinal motor neurons, and thereby controls movement of the torso, upper and lower limbs.
Where is the premotor cortex
frontal lobe anterior to M1, laterally
Function of premotor cortex
planning of movements
regulates externally cued movements
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)
Location of supplementary motor area
frontal lobe anterior to M1, medially
Function of supplementary motor area
planning complex movements; programming sequencing of movements
Regulates internally driven movements (e.g. speech)
SMA becomes active when thinking about a movement before executing that movement
What is association cortex
Brain areas not strictly motor areas as their activity does not correlate with motor output/act, but kind of relates to movement
Give 2 examples of association cortex
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 neuron
Alpha motor neurons branching out from CNS:
- Spinal cord ending up at neuromuscular junction
- Brainstem… neurons leaving from nuclei of non-oculomotor cranial nerves which have a motor function e.g. hypoglossal
Define upper motor neuron
Fibres leading from the primary motor cortex to the spinal cord (to synapse onto lower motor neurons innervating skeletal muscles) or brainstem (to synapse onto cranial nerve nuclei)
What does pyramidal tract refer to
The term pyramidal tracts refers to upper motor neurons that originate in the cerebral cortex and terminate in the spinal cord (corticospinal) or brainstem (corticobulbar)
Which 2 areas are involved in extrapyramidal system
Basal ganglia, cerebellum
2 examples of negative sings in Upper motor neuron lesion
Negative sign means loss of normal function
Paresis: graded weakness of movements
Paralysis (plegia): complete loss of muscle activity
What are positive signs in Upper motor neuron lesion
Increased abnormal motor function (positive signs) due to loss of inhibitory descending inputs
Spasticity: increased muscle tone
Hyper-reflexia: exaggerated reflexes
Clonus: abnormal oscillatory muscle contraction
Babinski’s sign
What is apraxia
A disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movements
Lesions to which areas cause apraxia, and what are the most common causes of these lesions
Lesion of inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area).
Common cause: stroke and dementia
Presentation of lower motor lesions
Weakness
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations
Fibrillations
Differentiate fasciculations with fibrillation
Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
(in fasciculation you get denervation of a muscle, so another motor unit reinnervates this area, but generates random APs)
Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination
What is motor neuron disease
Progressive neurodegenerative disorder of the motor system. Affects BOTH upper and lower motor neurons (so if you have a mix of signs, could be this!)
SPECTRUM of disorder
Amyotrophic Lateral Sclerosis
NO SENSORY INVOLVEMENT
Which neurons does motor neuron disease affect
Upper and lower
