The Human Nervous System

• The HNS consists of the CNS (Central Nervous System) :

  • Brain
  • Spinal Cord

  and the PNS (Peripheral Nervous System) :

  • Nerve cells that carry information to or from the CNS
• A nerve is a bunch of neurons (nerve cells)
• Neurones are adapted to carry electrical impulses from one place to another.
• • a cell body that contains the nucleus and all of the other major organelles
  • a long fibre (axon) 
  • which means signals can be transmitted quickly without cell-cell transfers
  • the axon is insulated by a fatty sheath 
  • with small un-insulated sections called nodes
  • means that the electrical impulse does not travel down the whole axon, but jumps from one node to the next
  • cell body has tiny branches (dendrons) 
  • these then branch further as dendrites at each end
  • means they can connect to many other neurones and receive impulses from them
• sense: sight

  sense organ : eyes

  stimulus : light
• sense : hearing

  sense organ : ears

  stimulus : noise
• sense : smell

  sense organ : nose

  stimulus : smells (chemicals in the air)
• sense : taste

  sense organ : tongue / tastebuds

  stimulus : sweet / sour
• sense : touch

  sense organ : skin

  stimulus : contact & heat / cold