Speed of conduction

• Three factors that affect the speed of conduction of action potentials are myelination, axon diameter, and neurotransmitter type.
• Some neurons are myelinated, meaning they have a myelin sheath.
• The myelin sheath is an electrical insulator.
• In the peripheral nervous system, the myelin sheath is made of a type of cell called a Schwann cell, which is wrapped around the axon (and/or dendron).
• Between the Schwann cells are tiny patches of bare membrane called the nodes of Ranvier.
• Sodium ion channels are concentrated at the nodes of Ranvier.
• In a myelinated neuron, depolarisation only happens at the nodes of Ranvier where sodium ions can get through the membrane.
• Action potentials are conducted quicker along axons with bigger diameters because there's less resistance to the flow of ions than in the cytoplasm of a smaller axon.
• With less resistance, depolarisation reaches other parts of the neurone cell membrane quicker.
• The speed of conduction only increases up to around 40 °C though — after that the proteins begin to denature and the speed decreases.
• The speed of conduction increases as the temperature increases too, because ions diffuse faster.
• Saltatory conduction is faster than the process where the impulse travels along the whole length of the axon membrane in a non-myelinated neurone.
• Saltatory conduction is a method where the impulse travels as a wave along the whole length of the axon membrane in a non-myelinated neurone.
• The neuron's cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse "jumps" from node to node.