Motor Pathways: Cortical Motor Function Flashcards
What is volition?
Motor systems produce movements that are adaptive and accomplish a certain goal
Describe the hierarchical organisation of motor control.
Association Cortex
Motor Cortex
Brainstem
Spinal Cord
What are postural adjustments and unconscious processing?
Postural Adjustments – the motor system has to compensate for changes in the body’s centre of mass during movements
Unconscious Processing – many of the postural adjustments occur without our awareness
What are the three parts of the motor cortex?
Primary Motor Cortex
Premotor Cortex
Supplementary Motor Area
What makes up the association cortex?
Frontal Cortex
Parietal Cortex
NOTE: this is not exactly part of the motor pathway but it influences the planning and execution of movements
What are the two parts of the pyramidal (descending) system?
Corticospinal Tract – starts in the cortex and exits and innervates the muscles in the arms and legs
Corticobulbar Tract – starts in the cortex then exits and innervates the muscles in the face
Describe the side loops of this descending pathway and their role.
The descending pathway also has two side loops that go to the cerebellum and basal ganglia
The cerebellum and basal ganglia check the motor information before ittravels to the muscles and has its effect
Which lobe are the three parts of the motor cortex found in? Describe their arrangement.
Frontal (anterior to the central sulcus)
The primary motor cortex is on the precentral gyrus
The premotor cortex and the supplementary motor area are anterior to the primary motor area
What is another name given to the three parts of the motor cortex?
Primary Motor Cortex = Broadmann’s Area 4
Premotor + Supplementary Motor Area = Broadmann’s Area 6
What are the most important cells in the primary motor cortex?
Betz Cells (pyramidal cells)
Where are these cells located within the grey matter and which tracts originate from here?
They are found in the 5th layer of grey matter
The corticospinal tracts originate from here
Describe what happens to the upper motor neurones that come from the primary motor cortex.
They travel through the brainstem to the pyramidal decussation in themedulla where 90% of the axons cross the midline.
These axons continue down the spinal cord and synapse with a lower motor neurone and exit into a peripheral nerve to the reach the skeletal muscle.
The pathway of the corticobulbar tract is somewhat similar – upper motor neurones go down into the brainstem and synapse with a lower motor neurone and they exit to the muscles of the face
What are the two types of descending pathway?
Lateral and Medial
Which tracts fall into each of these types?
Lateral Lateral corticospinal tract Rubrospinal tract Medial Anterior corticospinal tract Reticulospinal tract Vestibulospinal tract Tectospinal tract
What is the function of each of these types of pathway?
Lateral Control of proximal and distal musculature Voluntary movements or arms and legs Medial Control of axial muscles Balance and posture
Describe the structure and function of the lateral corticospinal tract.
The lateral corticospinal tract originates in the primary motor cortex from the Betz cells.
Their axons pass down through the brainstem and decussate at the pyramidal decussation in the medulla.
It then passes down the spinal cord and synapses with a lower motor neurone.
It goes onto control mainly the distal musculature.
NOTE: 90% of axons from the primary motor cortex decussate at the medulla (these are the lateral corticospinal tract axons). The 10% that don’t decussate form the anterior corticospinal tract.