Nerve Impulses

• Each motor neuron is made up of a cell body which contains all the normal components of a cell. Extending from each dendron are fine dendrites. These allow the neuron to make connection (synapses) from relay neurons. Dendrons carry impulses towards the cell body.
• Motor Neurons. Axons carry impulses away from the cell body. Vertebrate neurons are surrounded by the myelin sheath which is made up of cells called Schwann cells that contain a lipoprotein in their membrane called myelin. Myelin acts as a insulator abd helps to speed up the tranmission of impuoses. In between the Schwann cells are gaps known as the Nodes of Ranvier.
• If a microelectrode is inserted into a resting neurone, a small electric charge can be measured. This is known as resting potential.
• There is a relative negative charge inside a resting neurone of -70mV - The outside is more positive than the inside.
• An axon has membrane made of a phospholipid bilayer. Containing sodium-potassium pump (active transport), potassium channel, sodium ion and potassium ion voltage gated channels.
• The sodium-potassium pump in a neuron at rest pumps sodium out and potassium in at a 3:2 ratio.
• Axon, potassium channel. Membrane more permeable to potassium ions - so it diffuses out quicker than sodium ions diffuses in. 100:1
• Axon, Neurone at Rest. Net Effect:

  • 3 sodium ions are actively transported out and 2 potassium ions in. So higher concentration of potassium ions inside and higher concentration of sodium ions outside the neurone.
  • Membrane more permeable to potassium ions than sodium. This means the inside becomes negatively charged compared compared to the outside. An equilibrium reached at about -70mV.