Neuro- DAP, IAP, LMNs, corticobulbar/corticospinal tracts

Lower Motor Neuron

connects spinal cord (spinal nerves) or brain stem (cranial nerves) → muscles

damage signs: flaccidity, weakness, loss of reflexes, muscle degeneration, atrophy

LMNs = cranial nerves and spinal nerves

Direct Activation Pathway

Originates: motor cortex → muscle

Path: direct descending corticobulbar and corticospinal tracts

Function: voluntary, precise movements

Indirect Activation Pathway

Originates: motor cortex → brainstem → basal ganglia → LMNs → muscle

Path: indirect descending tracts stopping in reticular formation and red nucleus (brainstem) and basal ganglia

Function: muscle tone, reflexes, posture, respiraton (automatic movements)

Corticobulbar tract / cranial nerves

cortex/UMNs→ cranial nerves/LMNs → muscles (face head neck)

upper face: bilateral innervation (R and L are always innervated independently, so 1 deficit will not affect both)

lower face: contralateral innervation (R only sends signals to L side, so 1 deficit will affect the opposite side)

*think the drawing 🙂

Corticospinal tracts / spinal nerves

cortex/UMNs → spinal nerves LMNs → muscles (body/trunk)

90% crosses at medulla (hand/toes muscles)

10% cross below medulla ((cervical level/trunk muscles)