Neuroanatomy - UMS Pyramidal Division

Motor functions performed by the two systems:

1. Support body against pull of gravity

2. Establish postural tone

3. produce voluntary movement: initiate/coordinate/modify/terminate muscle activity

4. Muscle contraction

5. Neuronal regulation of LMNs

Neurons that make muscles contract are defined as

lower motor neurons (LMN)

What neurons regulate LMNs?

Upper motor neurons (UMN)

Upper motor neuron (MN)

Neurons contained within the CNS that regulate other LMNs in the brain stem and spinal cord

Cortical motor system is also known as the

Pyramidal motor system

What does the pyramidal motor system do?

Regulates the LMN activity that results in highly skilled motor activity usually with a direct synapse on the LMN

What is included within the pyramidal motor system

discretely organized, interconnected white matter structures formed by axons that pass through the pyramids

What is the non-cortical motor system also known as

Extrapyramidal motor system

What does the extrapyramidal motor system do?

Regulates the LMN activity that is responsible for muscle tone, coarse or stereotyped, and subconscious motor activity

What is included in the extrapyramidal motor system?

motor centers scattered in each division of the brain with axons that are not associated with the pyramids, featuring many synapses within the system before the LMN feels its effect

Important anatomical features of the pyramidal motor system

1. Motor cortex

2. White matter structures

3. Tracts of the pyramidal systems

Motor cortex

Cell bodies

Where are motor cortex - cell bodies located?

in the pre- and post cruciate gryi (species-dependent)

What do descending axons from the cells bodies contribute to?

The formation of discretely organized and identifiable bundles of white matter

What matter structures

cell processes (axons)

Different parts of white matter structures/axons

• Corona radiata

• Internal capsule

• Crus cerebri

• Longitudinal fibers of the pons

• Pyramids

• Axons continue to form corticospinal tracts - lateral and ventral divisions

What are the tracts of the pyramidal system?

1. Corticonuclear system

2. Corticospinal system

Corticonuclear system - from where does it span?

From the pyramidal motor cortex (cortico-) to LMN nuclei (-nuclear) in the brain stem of cranial nerves three-seven and nine-twelve

Where does the corticospinal system span to and from?

From the pyramidal motor cortex to LMN in the spinal cord

75% of the pyramidal fibers cross at pyramidal decussation, descend into the spinal cord to regulate appropriate contralateral lower motor neurons in the ventral gray column of this part of the corticospinal system

Lateral corticospinal tract

25% of the pyramidal fibers do not cross in the pyramid but descend ipsilaterally through the rest of the brainstem and then cross at the appropriate level of the spinal cord to regulate lower motor neurons in the ventral gray column in this part of the corticospinal system:

Ventral corticospinal fiber

Wha tis the cord location for corticospinal fibers?

lateral funiculus and ventral funiculus

Cerebellar input of the pyramidal motor system is responsible for

producing smooth, coordinated movement

What is the function of the cerebellum?

producing smooth, coordinated movement

Where do corticopontocerebellar fibers of the cerebellar input span from?

From the pyramidal motor cortex to the pontine nucleus for synapse, then crossing fibers from the contralateral middle cerebellar peduncle and enter the cerebellum

Where is the pontine nucleus for synapse located?

at the longitudinal fibers of the pons