# 86 The human nervous system

The human nervous system is made up of two parts: 

• Central nervous system (CNS) - brain and spinal cord: role of coordination
• Peripheral nervous system - nerves: connect all parts of the body to the CNS. 

Together, they coordinate and regulate body functions.

Sense organs are linked to the peripheral nervous system. They are groups of receptor cells responding to specific  stimuli: light, sound, touch,  temperature and chemicals. When exposed to a stimulus they generate an electrical impulse which passes along peripheral nerves to the CNS, triggering a response. 

Peripheral nerves contain sensory and motor neurones (nerve cells). 

	transmit nerve impules
Sensory neurone	sense organs  à CNS
Motor neurone	CNS  à  effectors (muscles or glands)

Motor and sensory neurones are covered with a myelin sheath, which insulates the neurone to make transmission of the impulse more efficient. 

The cytoplasm (mainly axon and dendron) is elongated to transmit the impulse for long distances.

Structure	Sensory neurone	Motor neurone
Cell body	Near end of neurone, in a ganglion (swelling) just outside the spinal cord	At start of neurone, indise the grey matter of the spinal cord
Dendrites	Present at end of neurone	Attached to cell body
Axon	Very short	Very long
Dendron	Very long	None

Fun fact: The human nervous system runs on electrical impulses that travel close to the speed of light.

Sample question and answer

Question   Figure above shows a type of neurone. Name this type of neurone and state a reason for your choice.  [ 2 marks]

Answer  Name: motor neurone. 

               Reason: It has a cell body, the cell body is at the end of the cell. 

Video: The Human Nervous System

Video: The Spinal Cord 
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Video: Human Body Nervous System