motor system

Lower motor neurons located:

Brainstem and spinal cord

Upper motor neurons located:

Primary motor cortex and other cortical regions

Motor actions planned and controlled by:

Association cortex, basal ganglia cerebellum

Neurons for flexors are:

Dorsal

Neurons for extensor are:

Ventral

In spinal cord, neurons for axial muscles are:

Medial

In spinal cord, neurons for distal muscles are:

Lateral

Motor units

Slow twitch, fast twitch fatigue resistant, fast twitch fatigable

Motor units

“size principle”

Recruits small to large

Basal ganglia and cerebellum control motor (via thalamus) by influencing output from

Cortex to brainstem and spinal cord

Vestibulospinal tract

Posture adjustment and head movement

corticospinal tract

Voluntary movement

Reticulospinal tract & rubrospinal tract

Alternate path for voluntary movement

End in lateral spinal cord, influence distal muscles

Tectospinal

From superior colliculus to cervical spinal cord for reflexive turning of head and response to visual info

Vestibulospinal, Corticospinal and tectospinal

End in spinal cord and influence axial muscles

Premotor cortex

Devises a plan for movement and passes plan to primary motor cortex

Association cortex

“Decides” that motor movers is going to happen

M1 then issues command (via brainstem nuclei and interneurons) to-

Lower motor neurons to fire

Face motor movement is more-

Lateral motor cortex

Body movement is more-

Medial motor cortex

Betz cells

• Primary motor cortex contains very large neurons

• Pyramidal neurons

• Axons project through pyramids in brainstem to spinal cord (only 3% of CST is from betz cells)

• Only ½ of CST originate in M1

Primary motor cortex (CST)

on precentral gurus and deep within central sulcus

Premotor cortex (CST)

anterior to M1 on lateral surface

has 4 subdivisions and somatotopic map

Supplemental motor cortex

Anterior to M1 on medial surface

5-6 + subregions and somatotopically organized

“Mirror” neurons are in-

Premotor area (ventral rostral)

DTI fiber tracking of CST

Axons leave M1, some cross CC to contralateral hemisphere, but most descend CST

from m1 heads through centrum semiovale

Then through corona radiata

Through “posterior limb internal capsule”, and cerebral penducle and pons

Fibers keep their somatotpic mapping from M1 through-

Thalamus, internal capsule and brainstem

Ex* foot travels medially, hand laterally

Corticobulbar tract

Cranial Nerve motor nuclei on brainstem also upper motor neurons

Collection of fibers that leave the cortex and end in the brainstem (through Internal capsule and reticular formation) are called corticobulbar tract

-esp for fine motor control regions of the face (lips and tongue)