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Nervous System

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by

Robert Sweeper

on 14 May 2012

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Transcript of Nervous System

THE NERVOUS SYSTEM The nervous system is an electrical and chemical telecommunication system that sends billions of messages around the body every day.

Most of these occur unconciously and are responsible for keeping the body safe and functioning correctly.

These signals or messages are due to the activity of neurones, or nerve cells. Anatomy of the Nervous System The nervous system can be split into two sub-systems - the Central Nervous System (CNS) and the Peripheral Nervous System (PNS) The CNS consists of the brain and spinal cord.

The PNS consists of the peripheral nerves that branch off from the spinal cord to all parts of the body.

These nerves are split into three divisions:
Autonomic nerves carry instructions to and from the CNS and the body's organs and glands
Sensory nerves relay information gained from the body's five senses
Motor nerves carry messages to and from the CNS and the skeletal muscles Nerve Cells The nervous systems is made up of billions of nerve cells. Cells called neurones create and relay the signals and messages. Cells called neuroglia are support cells for the neurones. Neurons have a cell body with a nucleus and other organelles necessary for normal function.

Extending from the cell body are a number of projections called processes or neutrites.

The large process that carries signals away from the cell body is called the axon. Axons can be up to 1m in length.

The smaller processes that receive signals from other neurons are called dendrites.

Neurons can have varied numbers of axons and dendrites. The axon is covered in a substance called myelin. This insulates the axon and prevents short circuits between nerves. Nerve Impulses
Dendrites receive a chemical message from neighbouring axons.This triggers an electrical impulse which travels in one direction to the cell body and down the axons. At the end of the axon is the synaptic knob. This contains vesicles of chemicals called neurotransmitters. These are released and spread out across the synapse (gap) between the axon and surrounding dendrites, triggering the same process in the next neuron. Effectors Motor and autonomic neurons at the end of nerves attach to cells in muscles or glands. These muscles or glands are called effectors, as they put the message from the nerves into action. Reflex Actions Reflexes are important for escaping, feeding, defence and reproduction. Receptors in the body identify changes in the environment surrounding and within the body, and immediately send impulses along sensory neurones to the spinal cord. Relay neurones in the spinal cord then pass the message to relevant motor neurons which send messages to the muscles to react accordingly. This is called a reflex arc.
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