The Human Nervous System Part One

Today's post from helium.com (see link below) follows on from yesterday's post about the make up of a nerve cell by explaining how the nervous system works. The information is clearly written and easy to understand and will certainly add to your understanding of which parts of your system are going wrong with neuropathic problems. Part Two tomorrow.
 

An overview on the human nervous system
by Belinda Whitaker: Created on: January 24, 2010
 
If the human body were a business corporation, the Nervous System would be its communication department. Every second your body is receiving information from your surroundings (such as temperature) and various parts of your body are sending their own pieces of information to add to that list too. Your stomach may be telling you that you really shouldn't have skipped breakfast, or your back is telling you that you really need to stretch out those muscles. All of this information is gathered, reviewed, and acted upon by your nervous system.

The building blocks of the nervous system are the Neurons, or nerve cells. These neurons use electrical impulses to carry information throughout the body to and from the spinal cord and brain. Each neuron contains an axon which functions as a transmitter, sending data from neuron to neuron throughout the nervous system.

What we call nerves are actually bundles of these axons. Some of these nerves, such as the Sciatic nerve, contain more axons and are therefore bigger than others. Nerves can vary in size from one inch thick to thinner than a human hair. Each nerve travels to or from one specific part of the body.

Neurons come in three varieties: Sensory, Motor, and Connecting.

Sensory neurons are also known as afferent neurons. These neurons have receptors on the skin, in some organs, and in muscles and joints. These receptors gather information about our outside and inside environment and transmit that data to the Central Nervous System. The CNS consists of the brain and the spinal cord.

Connecting neurons, also known as inter-neurons, are found only in the Central Nervous System. Their job is to receive and process the information from the sensory neurons and reach an appropriate reaction to send back.

Motor neurons are also called efferent neurons. These carry the brain's instructions once again through the nerve pathway to the necessary part of the body.

As each nerve is actually a bundle of many axons, it is possible for one nerve to have both sensory and motor neurons. This enables a single nerve to both carry information to the brain and from the brain.

It is worth mentioning that not all sensory information makes it all the way to the brain to be acted upon. A reflex arc refers to an 'incoming message' that the spinal cord can handle directly. The sensory data reaches the spinal cord, which then uses the same nerves to send its instructions back. An example would be when a doctor taps below your knee to check your reflex. This information only travels as far as the spinal cord before being acted upon, hence the almost instantaneous response.

The Peripheral Nervous System, which contains 12 pairs of cranial nerves and 31 pairs of spinal nerves, connects the CNS to the rest of the body. This peripheral nervous system is actually two systems in one.

The Somatic Nervous System has the nerve pathways that take care of the voluntary muscles and all of your senses such as hearing, vision, etc.The Autonomic Nervous System has the nerves that control the internal organs as well as the involuntary muscles. The autonomic system works well below our conscious level.In summary, the nervous system has three basic functions: 1) Gathering of inside and outside information (PNS), 2) Analyzing the information and determining an appropriate response (CNS), and 3) Relaying that response to the required body part (PNS).

http://www.helium.com/items/1720822-human-nervous-system-overview