Action Potential

Communications between nerve cells (called neurons) involves short-distance chemical signals between neurons across a synapse and long-distance electrical signals within a neuron down the axon of the cell. 1. Short-distance chemical signaling: Neurotransmitters The small space between two neuron cells is called a synaptic cleft (aka synapse). Short-distance signaling between two neurons occurs when neurotransmitters are released from the sending cell (presynaptic neurons) and bind to ligand-gated ion channel proteins on the receiving cell (post-synaptic neuron). -623564492200 12731108162500CIRCLE THE CORRECT ANSWER: Electrical signals in the sending cell cause the release of neurotransmitters via exocytosis/endocytosis. The neurotransmitters bind to receptor proteins on the receiving cell. The neurotransmitters are rapidly reabsorbed by the sending cell via active transport/facilitated diffusion. 2. Long-distance electrical signaling: the action potential The unequal distribution of ions caused by the sodium-potassium pump across the cell membrane allows for a small electrical gradient to exist, called the membrane potential. The resting membrane potential in neurons is about -70 mV (millivolts). The action potential is an extremely rapid charge reversal and restoration of the resting potential. Opening and closing of gated Na+ and K+ channels in a sequence allows the action potential to travel down the cell. Ion concentrations (mM) inside and outside of mammalian neurons. Ion Intracellular concentration (mM) Extracellular concentration (mM) Na+ 15 150 K+ 140 5 Explain how the sodium-potassium pump maintains the different ion concentrations of Na+ and K+ inside and outside the cell. The action potential: Receipt of a neurotransmitter opens an ion channel which generates an action potential. The action potential travels down the neuron until it reaches the end of the cell where it triggers the release of neurotransmitters to activate the next neuron. The action potential is the rapid reversal (depolarization) followed by the reestablishment (repolarization) of the resting membrane potential The action potential: 1. Membrane at resting potential. Na+ and K+ channels are closed. 2. Voltage-gated sodium channels open. Massive flow of Na+ into the cell reverses the membrane potential. Sodium channels close. 3. Voltage-gated potassium channels open. Massive flow of K+ out of the cell restores the resting potential. Potassium channels close. 4. Resting potential is maintained by the sodium-potassium pump.