2.10 : Spinal Cord

The spinal cord, a critical component of the central nervous system, extends from the base of the brainstem to the lumbar region of the vertebral column. It is essential for maintaining physical stability and facilitating communication between the brain and peripheral parts of the body.

• Encased within the protective bony structure of the spine, the spinal cord is divided into 30 segments that correspond to the vertebrae.
• These segments play a vital role in connecting specific body regions through a vast network of nerves, allowing for a bidirectional flow of information crucial for various bodily functions.
• Each spinal segment connects to a specific part of the body through paired spinal nerves, which are categorized into — cervical, thoracic, lumbar, sacral, and coccygeal regions based on their location along the vertebral column.
• These nerves exit the spinal cord through spaces between the vertebrae, transmitting sensory and motor information.

The spinal cord consists of three primary types of nerve cells: sensory neurons, motor neurons, and interneurons.

• Sensory neurons are pivotal in conveying information about external stimuli from sensory receptors to the spinal cord. This information includes sensations such as touch, temperature, and pain.
• Interneurons, the most numerous within the spinal structure, process and integrate this sensory information. They act as intermediaries, enabling communication between sensory and motor neurons and facilitating the coordination of appropriate motor responses.
• Motor neurons transmit impulses from the spinal cord to the body's muscles and glands, initiating and controlling all voluntary movements and many involuntary actions. This underscores the spinal cord's integral role in motor function.

A notable function of the spinal cord is its ability to coordinate reflex actions independently of the brain. Reflex arcs are neural circuits that activate directly in response to sensory inputs to produce immediate reactions. For instance, upon touching a hot surface, sensory neurons quickly send a signal to the spinal cord. Interneurons immediately process this information and activate motor neurons, resulting in the rapid withdrawal of the hand. This reflex action occurs to protect the body from harm and highlights the spinal cord's complex functionality and its critical role in the human body's operational hierarchy.