Strong depolarizing stimulus +50 Membrane potential (mV) –50 Threshold Resting potential –100 02 3 4 Time (msec) (c ) Action potential = change in membrane voltage 1 5 0 Action potential 6 K+ Channels Close Na+ Channels close K+ Channels open Na+ Channels open Ligand gated channels open, allowing some Ca 2+ to enter
Conduction of an Action Potential Signal Transmission Axon Plasma membrane Cytosol Action potential Na + Action potential Na + K+K+ K+K+ Action potential K+K+ K+K+ Na +
Saltatory conduction: the action potential “jumps” along the membrane, traveling faster than if myelin sheath were absent. Cell body Schwann cell Depolarized region (node of Ranvier) Myelin sheath Axon
Voltage-gated Ca 2+ channel Ca 2 + 1 2 3 4 Synaptic cleft Ligand-gated ion channels Postsynaptic membrane Presynaptic membrane Synaptic vesicles containing neurotransmitter 5 6 K+K+ Na + Transmission of information between neurons occurs across synapses using neurotransmitters.
Summation of postsynaptic potentials All inputs (excitatory and inhibitory) are summed or added together in the cell body. If the combined input is enough to reach threshold at the axon hillock an action potential will occur. Action potentials is all or nothing. Terminal branch of presynaptic neuron E1E1 E2E2 I Postsynaptic neuron Threshold of axon of postsynaptic neuron Resting potential E1E1 E1E1 0 –70 Membrane potential (mV) (a) Subthreshold, no summation (b) Temporal summation E1E1 E1E1 Action potential I Axon hillock E1E1 E2E2