neurons and resting potential

• Sensory neurons - receptors --> CNS 
• Motor neurons - CNS -->motor neurone --> effector 
• Cell body - contains cytoplasm and nucleus, mitochondria and ribosomes.
• Dendrites - branched extensions of the cell body 
• Axon - single ling fibre, can be as long as a metre and less than a micrometre wide. 
• Nerves transmit impulses. 
• Schwann cells - wrap around the axon many times, providing electrical insulation. 
• Myelin sheath - made of Schwann cells, rich in myelin. Not all neurons are myelinated, but myelinated neurons transmit nerve impulses faster. 
• Nodes Ranvier - gaps between adjacent Schwann cells where there is no myelin sheath. Gaps are 2-3 micrometers and occur every 1-3 mm. 
• Two state linked to nerve cells - resting and action potential. 
• Resting potential is when the axon is not transmitting electrical impulses. The inside of the axon is negatively charged with respect to the outside. The axon is polarised, the charge is -70 mV.
• At resting potential sodium-potassium pumps actively transport 3 sodium ions out of the cell and 2 potassium ions into the cell. 
• At resting potential, sodium ion channels are closed (sodium ions are unable to diffuse through). 
• Gated channel proteins allow for facilitated diffusion because they can open and close. 
• During resting state, the sodium-gated channels are closed and the potassium-gated channels are mostly open. This means sodium ions remain outside and have roughly equal concentration on both sides of the membrane. 
• The axon membrane is 100 times more permeable to potassium ions, increasing the potential difference. 
• There is an uneven electrochemical gradient due to differences in charges either side of the membrane. 
• Eventually an electrical equilibrium is established and there is no net movement of ions.