the direct motor pathway

lower motor neurons (LMN)

motor neurons located in the ventral horn of the spinal cord that innervates skeletal muscles

neurons in the cranial nerve motor nuclei that innervate all the muscles and glands in the neck and head

post-ganglion neurons in the autonomic ganglia that innervate the organs, glands, and other smooth muscles

upper motor neurons (UMN)

supraspinal motor neurons located above (or rostral to) the spinal cord, either in the brainstem or in the cerebral cortex

send axons descending to the spinal cord and cranial nerve motor nuclei

descending pathways

“-bulbar”, “-nuclear”, “-spinal”

corticospinal tract

descending pathway that projects directly to the spinal motor neurons

how the cerebral cortex influences the spinal cord directly

lateral descending pathways

corticospinal and rubrospinal tracts

terminate at the lateral part of the ventral horn

influence motor neurons for distal muscles

ventromedial descending pathways

medullary reticulospinal, pontine reticulospinal, vestibulospinal, and tectospinal tracts

terminate in more medial parts of the ventral horn

influence motor neurons for axial muscles in postural adjustment

basal ganglia and cerebellum

involved in planning and monitoring movements

do not have direct output to the spinal cord, act primarily by affecting the motor and premotor cortex

pyramidal tracts

corticospinal tracts

voluntary movement

rubrospinal tracts

the principal alternate routes for the mediation of voluntary movement

bigger in animals than humans

red nucleus

→ cross over to contralateral side → traveling lateral part of the brainstem → lateral funiculus of the spinal cord in company with the lateral corticospinal tracts

vestibulospinal tracts

control postural adjustments and head and eye movements, head turning

tectospinal tracts

orienting response, turning of the head in response to visual stimuli

superior colliculus

→ contralateral anterior (ventral) funiculus → cervical cord level of spinal cord

pontine reticulospinal fibers

uncrossed, are located in the anteromedial (ventral medial) white matter of the spinal cord

enhances antigravity reflexes

medullary reticulospinal fibers

some cross near their cells of origin, while others continue uncrossed to the spinal cord

located in the anterolateral (ventral lateral) white matter of the spinal cord

liberates antigravity muscles from reflex control

reticulospinal nuclei

within the reticular formation

receive direct input from motor cortex, so tracts may act in parallel with other anterior corticospinal tract

motor cortex

area 4 (pre-central gyrus, primary motor cortex) and area 6 (premotor cortex) of the frontal lobe

somatotopic organization of precentral gyrus

premotor area (PMA)

lateral region of area 6

supplementary motor area (SMA)

medial region of area 6

area 5

somatosensory, receiving inputs from areas 3, 1, and 2 (primary somatosensory)

area 7

receiving inputs from higher-order visual cortical areas such as MT (visual middle temporal area; V5)

anterior frontal lobes

abstract thought, decision making and anticipating consequences of action

area 6

actions converted into signals specifying how actions will be performed

betz cells

pyramidal cells in cortical layer 5

receive input from cortical areas and thalamus

flaccid paralysis

muscle is limp and uncontracted, no more reflex contractions, muscle slowly atrophies

babinski’s sign

dorsiflexion of the big toe and fanning of the others in response to firmly stroking the sole of the foot

internal capsule

located between the thalamus and caudate nucleus (on its medial side) and lentiform nucleus (on its lateral side)

later becomes the cerebral peduncle → pyramid

with anterior limb, genu, and posterior limb

anterior limb

containing corticopontine, corticothalamic, and thalamocortical fibers, which are not part of the pyramidal system