neurons

Neurons

• neurons are the basic building blocks of the nervous system

• They are the nerve cells that process and transmit messages through electrical and chemical signals

• There are 100 billion nerve cells in the human nervous system, 80% of which are located in the brain

Types of neurons

• sensory neurons carry messages from the PNS to the CNS. The have long dendrites, short axons and a cell body off to the side

• Relay neurons connect sensory neurons to the motor or other relay neurons. They have short dendrites, short axons and are small and compact

• Motor neurons connect the CNS to effectors such as muscles and glands. They have short dendrites, long axons and a cell body at one end

Structure of a neuron

• The cell body includes a nucleus which contains the genetic material

• Branchlike structures called dendrites carry nerve impulses from neurons to the cell body

• The axon carries the impulses away from the cell body down the length of the neuron

• The axon is covering in a fatty layer called the myelin sheath that protects the axon and speeds up electrical transmission of the impulse

• The myelin sheath is segmented by gaps called nodes of Ranvier

• Terminal buttons at the end of the axon communicate with the next neuron

Location of neurons

The cell bodies of motor neurons are in the CNS but their long axons form part of the PNS. Sensory neurons are located in the PNS in clusters called ganglia. Relay neurons are found in the brain and visual system, they make up 97% of all neurons