Human Spinal Cord - What is the function of the spinal cord and What is Reflex?

Human brain receives messages from all over the body and sends messages in return.
This is how coordination of all the different parts of body takes place.
But how do the messages travel to and from the brain?
The messages are carried along by nerve cells.
Throughout the body, there is a network of these cells. Nerve cells use impulses of electricity to carry messages.
Nerve cells are ball-shaped with thin branches extending from them. The shorter branches, called dendrites, take in messages from other nerve cells.
The longer branches carry messages out of the nerve cell. These branches are called axons.
The axons connect with other nerve cells and may pass their messages on to different parts of the body, such as muscle cells, glands, or organs.
The brain is made of billions of nerve cells, each one making a network of connections with other nerve cells. When you think, millions of tiny electric currents are running through these networks.
Even when you are asleep, millions of electric currents pulse through your brain, because the brain is busy keeping you alive.

What is the function of the spinal cord?

The base of the brain, the brain stem, extends into the spinal cord. 

This is a thick bundle of nerve cells. It runs down the back inside the backbone. 

Along the way, nerves branch off from the spinal cord. 

Some go to the arms, others to the lungs, heart, liver, stomach, and other internal organs. 

Lower down, nerves branch off to the legs and feet.

What Is Reflex?

Human leg muscles flex and move to allow them to stand up because their brain has sent them messages on what to do.
But there are some movements, such as drawing our hand away from something hot, which do not involve the brain.

These are called reflexes. Reflexes help to protect us from danger. 

Blinking our eyes as something comes very near to our face is another reflex.
Doctors can test whether our reflexes are working properly by using the knee-jerk test.

The person sits on a chair with one leg crossed over the other.
The doctor taps a spot just below the knee of the top leg, and the persons leg jerks into the air.
We can’t control it.
When our knee is tapped, a message travels up a nerve in our thigh to our spinal cord.
It does not go to the brain.
The spinal cord sends a message straight back to a nerve connected to the thigh muscle.
This muscle contracts suddenly and our leg jerks upwards.