Motor pathways; cortical motor function Flashcards
Explain the different levels of the motor system heriachy
Level 1: [lowest, no higher order function] Spinal cord for reflex movements
Level 2: Brainstem, integrates info from the vestibular, auditory and visual systems
Level 3: Primary motor cortex, Premotor and supplementary; program movements and voluntary actions
Level 4: Association cortices (Parietal and frontal), makes decisions in planning and executing movement
What are the two side loops?
Basal ganglia and cerebellum
What structures is the basal ganglia composed of?
Caudate nucleus, Putamen, Globus pallidus, Substantia nigra, Subthalamic nucleus
What are the two main parts of the pyramidal (descending system)?
Corticobulbar tract (innervates the face) Corticospinal tract (innervates the body)
What are the three parts to the motor cortex and where are they found?
All found in the frontal lobe, anterior to the central sulcus
Primary motor cortex; Broadmann’s area 4
Premotor cortex; Broadmann’s area 6
Supplementary motor cortex; Broadmann’s area 6
What is the function of the primary motor cortex?
Controls fine, precise, discrete voluntary movements
Betz/pyramidal cells are in the fifth layer of the grey matter
Corticospinal tracts originate from here (descending signals to execute movements)
What is the function of the lateral motor pathways?
Control distal and proximal muscles
Voluntary movements of arms and legs
What is the function of the medial motor pathways?
Control axial muscles
Balance and posture
Which descending motor pathways are classified as lateral and medial?
Lateral: lateral corticospinal, rubrospinal, lateral reticulospinal
Medial: ventral corticospinal, medial reticulospinal, tectospinal, vestibulospinal
Describe the pathway of the lateral corticospinal tract
Axon from first motor neurone originates in the primary motor cortex
Decussation at the medulla oblongata
Reaches anterior horn of the spinal cord and synapses with second motor neurone in the ventral horn
Describe the pathway of the anterior corticospinal tract
Axon from first motor neurone originates in the primary motor cortex
Remains ipsilateral descending into the spinal cord
Decussates and terminates in the cervical and upper thoracic levels
Innervates proximal limbs
Describe the pathway of the corticobulbar tracts
Axon originates from the lateral aspect of the primary motor cortex
Passes through the internal capsule to the brainstem
Terminates on the motor nuclei of the cranial nerves
Synapses with lower motor neurones to send signals to muscles of the tongue and face
Which neurotransmitters are used between
i) upper and lower motor neurones
ii) lower motor neurones and muscles
i) Glutamate
ii) ACh
What is the function and location of the premotor cortex?
Plans movements
Regulates externally cued movements
Anterior to primary motor cortex laterally
What is the function and location of the supplementary motor area?
Involved in planning complex movements and sequential actions
Regulates internally driven movements
Anterior to primary motor cortex medially
What is the function of the posterior parietal cortex?
Ensures movements are directed accurately in space
What is the function of the prefrontal cortex?
Involved in selection of movements for particular course of action
What are the symptoms of an upper motor neurone lesion and where are they seen?
Loss of function (negative signs):
- Paresis; graded weakness
- Paralysis
Increased abnormal motor function due to loss of descending inhibitory signals (positive signs):
- Spasicity
- Hyperreflexia
- Clonus
- Extensor plantar response/Babinski’s sign
Seen on the contralateral side
What are examples of upper motor neurone lesions?
Cerebral infarction
Damage to corticospinal tract
Why is there no muscle atrophy in subjects with an upper motor neurone lesion?
No muscle atrophy as nutrients supplying the muscle is from lower motor neurones which are still intact
What is apraxia and what can cause it?
Upper motor neuron lesion; disorder of skilled movement not from weakness, abnormal tone, posture or movement disorders. Patients have lost ability to perform skilled movements, therefore are uncoordinated.
Lesion to inferior parietal lobe, frontal lobe (premotor, supplementary motor area).
Usually caused by stroke or dementia.
What are the symptoms of a lower motor neurone lesion and where are they seen?
Weakness Hypotonia Hyporeflexia Muscle atrophy Fasciculations Fibrillations
What are examples of lower motor neurone lesions?
Damage to peripheral nerves
Lesion at the nerve root
How are fibrillations tested and what are they?
Spontaneous twitching of individual muscle fibres.
Recorded using needle electromyography
