General Blurbs An impulse is an electrical signal. An impulse that is not carrying a signal is: “POLARIZED” The inside of a neuron is NEGATIVELY charged. The inside of a neuron is 70 milliVolts more negative than the outside The difference is referred to as the: RESTING MEMBRANE POTENTIAL. The RESTING MEMBRANE POTENTIAL is –70mV. For a nerve impulse to MOVE, the inside must become more positiviely charged than the outside.
How do you get the inside more negatively charged?SODIUM/POTASSIUM PUMPNerve cell protein channels that:Uses a molecule of ATP to: Moves 3 Na+ ions out of the cell and simultaneously moves 2 K+ ions into the cell. Produces an environment where there is more SODIUM outside of the cell and more POTASSIUM in the cell. Occurs when there is no impulse to keep the voltage at -70mV. The difference in charges across the pump produces a negative charge inside the nerve cell.A. This is the RESTING MEMBRANE POTENTIAL = -70mV
Getting the Nerve Impulse to MoveVoltage Gate Channels An impulse is caused by the movement of ions across the cell membrane. At – 70mV the protein channels close. At the leading edge of an impulse, neuron depolarizes slightly(-50mV). This is the THRESHOLD POTENTIAL.This triggers the opening of the Voltage gate andB. SODIUM IONS flow into the cell…causes the inside to have a TEMPORARY positive charge. THIS IS THE ACTION POTENTIAL (DEPOLARIZATION)…+30 to 35 mV.C. Then the Voltage-gated POTASSIUM channels open and potassium exits the cell. This REPOLARIZES the cell to the RESTING POTENTIAL…and the impulse moves on.
Why does the action potential move in only one direction?
Synapse JUNCTION BETWEEN A NEURON AND ANOTHER CELL(MUSCLE OR GLAND) OR NEURON. Axon of neuron and dendrite of another do not actually touch: Small gap between them: Synaptic cleft. Synapses use NEUROTRANSMITTERS to pass the impulse to the next cell. Neurotransmitters are chemical. Most common: Acetylcholine(Ach) (endorphins and enkephalins) When action potential reaches the TERMINAL END of an axon, the neurotransmitter is released into the synaptic cleft and binds to receptors on dendrites. When receptors bind to neurotransmitter, the process begins on the next neuron.
Refractory Period The very short period of time where a portion of a membrane cannot initiate another action potential. Ensures the impulse is one directional. Nerve is “reset.”