Spinal Cord

The spinal cord is a long, thin, tubular structure made of nervous tissue that extends from the medulla oblongata (in the brain) down through the vertebral column. It is an important part of the central nervous system (CNS).

• The spinal cord is a bundle of nervous tissue arising from the medulla oblongata of the brain down to the centre of your spine. 
• The spinal cord is a delicate part of the body, and is hence protected by the vertebral column. 
• It is part of the Central Nervous System in your body, which is responsible for both voluntary and involuntary actions. 
• The Spinal cord is the relay centre between your body and the brain, and between the brain and the body, for information transfer and relevant responses. 
• That is, for every sensation you feel, like touch, pain, or temperature, there is a relevant response to it, which is done by this communication system of your body. 

1.0Spinal Cord Structure

The spinal cord of humans is a delicate structure, formed by a combination of various internal and external features, which include: 

External Features

• Morphologically, the spinal cord is about 42 to 45 cm long in a human adult. 
• It arises from the medulla oblongata, beginning from the foramen magnum (the opening of the base of the skull) and ends at the L1–L2 vertebrae. 
• Beyond this endpoint, it continues downward as a bundle of nerves with a different name — the cauda equina.

Internal Features

In the cross-section of a spinal cord, the neurons are arranged into two main parts based on the type of neuron and a central cavity, which are: 

• Grey Matter: It is the H or butterfly-shaped central part of the neural cord, made up of neurons with unmyelinated axons. 
• White Matter: It is the outer part of the structure which surrounds the grey matter. It is mainly composed of myelinated axons of neurons. 
• Central Canal: A hollow canal-like structure in the centre of the spinal cord, which is filled with cerebrospinal fluid. 

Spinal Cord Nerves

As mentioned earlier, the spinal cord is a bundle of nerves, 31 pairs in all, divided into five regions based on their location in the body. These include: 

Protective Layer

The spinal cord structure is complex, yet very delicate, so nature provided it with three protective layers, which are: 

• The Vertebral Column (body protection): It is the bony shield, also known as the backbone. It has a hollow centre through which the spinal cord passes, remaining protected. 
• Meninges: Inside the vertebral column, the spinal cord is protected by three membranes or layers — dura mater (tough outer layer), arachnoid mater (middle web-like layer), and pia mater (thin inner layer that closely hugs the cord).
• Cerebrospinal Fluid (CSF): To protect the spinal cord from external shock, it is also surrounded by spinal fluid, which is also a nutrient supplier to the cord. 

2.0Spinal Cord Function

The functions of the spinal cord can be divided into four broad categories based on the type of work. These include: 

1. Communication Highway: Serves as a connection between the brain and body. It also conveys sensory impulses (from the body to the brain) and motor impulses (from the brain to the body).
2. Reflex Control: Regulates rapid, unconscious actions such as the knee-jerk reflex or withdrawing a hand from heat. It conserves time by avoiding the brain.
3. Coordination: Assists in combining various types of information to ensure smooth body movements. For example, walking involves the coordination of leg muscles under the control of the spinal cord.
4. Autonomic Functions: Involved in governing involuntary functions such as blood pressure, digestion, and sweating.

3.0Reflex Action and Reflex Arc 

One of the most important features of the spinal cord is its reflex action, controlled by a well-coordinated arc. 

For revision, reflex action is a rapid, automatic, and involuntary response to an external stimulus, which we give without thinking. 

For example, the jerking of the leg when hit on the knee. The steps of this involuntary action are: 

• Receptor neurons on the sense organ, mostly skin, detect and receive the signal of a stimulus. 
• This signal is carried by the sensory neurons into the spinal cord. 
• The information of this signal is processed by interneurons of the spinal cord. 
• The processed response is passed to the motor neurons, which in turn send the response to the effector organ. 

All these steps happen in the blink of an eye by bypassing the brain, making the response very quick.