neurons

• 100 billion nerve cells in the human nervous system, 80% of which are located in the brain. By transmitting signals electrically & chemically, these provide the nervous system with its primary means of communication
• 3 types of neurons: motor, sensory & relay
• motor neuron:

  connect the CNS to effectors such as muscles & glands, they have short dendrites and long axons
• sensory neurons:

  carry messages from the PNS to the CNS. they have long dendrites and short axons
• relay neurons:

  connect sensory neurons to motor or other relay neurons. they have short dendrites and short axons
• structural elements: cell body, dendrites, axon & terminal buttons

  • cell body: includes nucleus which contains genetic material of the cell
  • dendrite: branch-like structures that protrude from the cell body. these carry nerve impulses from neighbouring neurons towards cell body
  • axon: carries the electrical impulses 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 that 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
• Electrical transmission - 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 happen. This creates an electrical impulse that travels down the axon towards the end of the neuron