Neurons

• there are 100 billion nerve cells (neurones) in the human nervous system, 80% of which are located in the brain. by transmitting signals electrically and chemically, these provide the nervous system with its primary means of communication.
• what are the three types of neurons?

  motor neurons, sensory neurons and relay neurons.
• what is the role of motor neurons?

  connect the CNS to effectors such as muscles and glands. they have short dendrites and long axons.
• what is the role of sensory neurons?

  carry messages from the PNS to the CNS. they have long dendrites and short axons.
• what is the role of relay neurons?

  connect sensory neurons to motor or other relay neurons. they have short dendrites and short axons.
• what are the basic structural elements of neurons?

  cell body (or soma), dendrites, axon and terminal buttons.
• cell body (or soma)

  includes a nucleus which contains the genetic material of the cell.
• dendrites

  branch-like structures that protrude from the cell body. these carry nerve impulses from neighbouring neurons towards the cell body.
• axon

  carries the electrical impulse away from the cell body down the length of the neuron

  • covered in a fatty layer of myelin sheath that protects the axon.
  • gaps in the axon called nodes of ranvier speed up the transmission of the impulse.
• terminal buttons

  found at the end of the axon. communicate with the next neuron in the chain across the synapse.
• electric transmission- the firing of a neuron

  when a neuron is in a resting state the inside of the cell is negatively charged compared to the outside. when a neuron is activated, the inside of the cell becomes positively charged for a split second causing an action potential to occur. this creates an electrical impulse that travels down the axon towards the end of the neuron.