Descending Spinal Cord Systems Flashcards
What is the principal descending system discussed in lectures?
Corticospinal tract, AKA pyramidal tract
What is the function of the corticospinal tract?
Relays motor information. Controls fine motor movements (think piano playing)
Define motor unit
alpha motor neuron + skeletal muscle fibers it innervates
Describe functional differences between small and large motor units
Small motor units result in precise movements.
Large motor units result in coarse or axial movements.
What diseases destroy the anterior horn?
ALS and polio
Describe clinical implications of ALS relevant to the corticospinal tract
Destroys anterior horn cells and wipes out corticospinal tract.
Describe result of MCA stroke on corticospinal tract
Destroys pyramidal cells and their axons.
What is the Babinski sign?
Rubbing bottom of foot -> patient flexes toes (rather than extends). CST damage, upper motor neuron injury. Leads to spasticity.
Describe the corticospinal tract pathway
Fibers originate from area 4, converge in the corona radiata, pass through the internal capsule, through crus cerebri (cerebral peduncles of rostral midbrain), through pons, through pyramids of medulla where ~90% of fibers decussate to lateral funiculus area, and continue down spinal cord through corticospinal tract where they synapse in the anterior horn of grey matter. The lower motor neuron stretches from the anterior horn to the target muscle.
Describe the difference between an upper motor neuron and a lower motor neuron
UMN: from cortex to ventral horn.
LMN: from ventral horn to target muscle.
Describe clinical manifestations of an upper motor neuron injury (corticospinal tract injury)
Loss of fine motor movements. Movements will be coarse/axial. Leads to spasticity.
Describe clinical manifestations of a lower motor neuron injury
Flaccid paralysis below site of injury.
