Neurones and Resting Potential

Myelinated motor neurone

• cell body - typical organelles (proteins and neurotransmitters are made)

• dendrites - carry action potentials to surrounding cells

• axon - long conductive fibre throughout cell that carries nerve impulses (site of multiple action potentials)

• myelin sheath (Schwann cells) - wrap around axon, made up of layers of myelin sheath (lipid - acts as an insulator) charged ions cannot pass through

• nodes of Ranvier - gaps in myelin sheath, action potentials can be generated here

Resting potential - difference between electrical charge inside and outside of neurone

• -70mV (more positive ions (Na+ and K+ on outside compared to inside)

• no stimulus

• maintained by carrier proteins within membrane

  • sodium-potassium pump (protein) - cotransport/active transport (requires ATP)

    • actively transports 3 Na+ out of axon and 2 K+ in to the axon

    • creates and electrochemical gradient (build up of Na+ on outside and excess K+ on inside) so K+ diffuses out (membrane more permeable to K+) and Na+ diffuses in - facilitated diffusion

    • membrane is more permeable to K+ as: more K+ channels than Na+ channels, K+ channels are mainly open (Na+ channels only open at high enough voltage)