2.10 : 脊髄

The spinal cord begins at the base of the brain and extends down the middle of the back, serving as a vital communication link between the brain and the body.

The spinal cord is divided into several segments, eight cervical, twelve thoracic, five lumbar, five sacral, and one coccygeal segment. Nerves arising from the spinal cord connect to specific body parts through the peripheral nervous system.

There are three types of nerve cells in the spinal cord: sensory neurons, motor neurons, and interneurons. 

Sensory neurons transmit sensory information to the spinal cord, while motor neurons send information from the spinal cord to glands and muscles. Interneurons connect sensory and motor neurons and constitute most of the spinal cord's structure.

Additionally, the spinal cord can initiate reflex actions without input from the brain.

For instance, when an individual touches a hot pan, a sensory neuron in the skin detects the pain and sends the signal to the spinal cord. The input is immediately processed by an interneuron, which triggers a motor neuron that quickly prompts the muscles to pull the hand away.