Spinal Cord — Function, Location & Quiz

The spinal cord is not a passive cable from brain to muscle. It contains reflex circuits, lower motor neurons and central pattern generators capable of organizing rhythmic movement while descending systems set goals and adapt behaviour to the environment.

Its clinical map depends on keeping pathway level clear. Corticospinal injury produces upper-motor-neuron signs below the lesion, while damage to the final motor neurons or roots produces flaccidity, atrophy, fasciculations and lost reflexes in the affected segment.

Test this anatomy in the Lesion Localization Quiz or open the interactive 3D brain model.

Location and anatomical map

Contains lower motor neurons, central pattern generators, and reflex arcs.

Atlas category: brainstem.

Functions

  • Lower motor neuron circuits — final common pathway to muscles
  • Central pattern generators (CPGs) — produce rhythmic movement without brain input
  • Reflex arcs — monosynaptic (stretch reflex) and polysynaptic (withdrawal)

Pathways and connections

  • Lateral corticospinal tract → distal muscles (fine motor, crossed)
  • Medial corticospinal tract → proximal muscles (posture, uncrossed)
  • CPGs for locomotion — generate walking rhythm autonomously

Clinical relevance

  • Transection = paralysis below the level of injury, but CPGs still function
  • Cat treadmill experiment: spinalized cats can walk on treadmill (CPGs intact without brain)
  • Lower motor neuron signs: flaccid paralysis, areflexia, atrophy, fasciculations

Key facts

  • CPGs = cruise control for walking — cortex needed only for obstacle avoidance and initiation
  • Headless chicken runs because spinal CPGs generate locomotion without brain input
  • Alpha motor neurons = lower motor neurons = final common pathway

Exam tip

CPGs generate rhythmic movement WITHOUT brain input (headless chicken, spinalized cat). Cortex = start/stop and obstacles only.

Common questions

What motor functions can the spinal cord perform?

It contains reflex arcs, lower-motor-neuron output and central pattern generators that can organize rhythmic locomotor activity without moment-to-moment cortical commands.

What is a central pattern generator?

It is a spinal neural circuit that produces a repeating motor rhythm, such as the alternating pattern of locomotion, even without a separate command for every muscle contraction.

How do upper and lower motor neuron signs differ?

Upper-motor-neuron injury causes spasticity, hyperreflexia and Babinski responses; lower-motor-neuron injury causes flaccidity, areflexia, atrophy and fasciculations.