How Pain occurs?

Pain is a complicated process that involves an intricate interaction between a number of important chemicals found naturally in the brain and spinal cord. In general, these chemicals called neurotransmitters transmit nerve impulses from one cell to another.
Receptors on the skin activate a series of events upon receiving a stimulus. It begins with an electrical impulse that travels from the skin to the spinal cord where the stimulus is carried by nerve fibres. The picture below shows the pain receptors found in the skin.

The body's chemicals act in the transmission of pain messages by stimulating neurotransmitter receptors found on the surface of cells. Each receptor has a corresponding neurotransmitter.
Receptors function much like gates that enable pain messages to pass through and on to the neighbouring cells.
The spinal cord acts as a relay centre where pain signals can be blocked, enhanced, or otherwise modified before it is relayed to the brain. One area of the spinal cord in particular, called the dorsal horn is important in the reception of pain signals.
The most common destination in the brain for pain signals is the thalamus and then the cortex, the headquarters for complex thoughts. This is where the signals are interpreted as pain.

There are many different neurotransmitters in the human body acting in various combinations to produce painful sensations in the body. Some chemicals govern mild pain sensations while others control intense or severe pain.
A type of receptor that responds to painful stimuli is called nociceptors. Nociceptors are thin nerve fibres in the skin, muscle, and other body tissues, that when stimulated, carry pain signals to the spinal cord and brain. Normally, nociceptors only respond to strong stimuli such as a pinch. However, when tissues become injured or inflamed, chemicals are released making nociceptors much more sensitive causing them to transmit pain signals in response to even gentle stimuli such as breeze or a caress. This condition is called allodynia; a state in which pain is produced by harmless stimuli.


Pain is sometimes felt not only at the site of stimulation but in other parts of the body supplied by nerves in the same sensory path for example, the pain of angina pectoris or coronary thrombosis may extend to the left arm. This phenomenon is known as referred pain.

This is a simple video showing how pain occurs.