Pain - The Role of the Nervous System

Pain can be experienced in most parts of the human body, although some part of the body have more nerve endings than others. The human nervous system sends the sensation of pain from the body part to the brain.

Our nervous system consists of a network of complex fibres that are called nerves that thread throughout our bodies like household wiring. Our nerves transmit electrical signals backwards and forwards between the brain and the various parts of the body.

Of all our organs the skin has the richest supply of nerves. The skin needs to be very sensitive as it is in the most direct contact with our environment. The nervous system sends messages that it receives from the skin to the brain.

Three Systems

The human nervous system is made up of three different systems that connect to different parts of the brain:

• the motor nervous system, that controls the muscles in our bodies
• the sensory nervous system, that transmits information from the five main senses - sight, sound, touch, taste and smell, and the feeling of pain, to the brain
• the autonomic nervous system, which governs automatic functions such as breathing, our heart beat and digestion

The most significant part of the brain for our central nervous system is that thin outer layer known as the cerebral cortex. Within this the area that controls voluntary muscle motion of the limbs is identified as the motor area. The area that receives feelings of pain and touch is known as the sensory area Except the most simple of signals, all are sent to different areas of the brain and may be altered by other messages of inhibition or stimulation.

The Body's Nerve Pathways

Impulses to the brain are transmitted in nerves or neurons that run from the periphery of the human body into our spinal cord where they are protected by the vertebrae. The spinal cord travels up through these vertebrae to the brain. Messages from the brain are sent via nerves down the spinal cord to the various parts of the body and back again.

The brain is protected by the cranium bones. Damage to the cranium or to our vertebrae places the nervous system at risk and very severe pain can be caused by trapping nerves between vertebrae. The common condition of Sciatica is caused by a trapping of the sciatic nerve at the base of the spine but it is felt as a shooting referred pain down the leg.

Carpal Tunnel Syndrome or Repetitive Strain Injury is likewise caused by the median nerve, that runs to the fingertips, becoming trapped by the radial bones of the wrist. The spinal nerve bundles incorporate nerves of the motor, and sensory, systems.

When the sensory nerves in the hand detect or feel heat and pain from touching a hot saucepan, for example, the sensation is sent via the spinal nerves to the sensory area of our brain. The sensory area then sends a message to the motor area which in turn transmits a message back through the spinal cord. This instructs the hand muscles to let go of the saucepan very quickly.

In order to pass from cell to cell the messages must cross gaps known as synapses. This is done through the release of chemicals that pass the impulse across the gap. It is at the synapse level that the messages can be modified or controlled.

Autonomic Nervous System

The autonomic nervous system governs the body's automatic functions i.e. those which are not usually under conscious control such as breathing. It deals with the maintenance of the usual state of the body and is controlled by the cerebral and the hypothalamus areas within the brain.

The autonomic nervous system is made up of the sympathetic nervous system in addition to the parasympathetic nervous system. The sympathetic system is the emergency nervous system and it governs the emergency fight or flight response. Stimulation of the nerves in this system accelerates our heart beat and our breathing rates, it also increases the blood supply to the muscles, dilates our pupils, and reduces the rate of digestion and urine and saliva production.

The parasympathetic system is the rest and recovery system. This is the one that takes control during time of rest or sleep by slowing the heart and breathing rates and increasing the rate of digestion.

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