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Chapter: The Massage Connection ANATOMY AND PHYSIOLOGY : Nervous System

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Differences in Propagation of action Potential in Myelinatedand Unmyelinated Axons

The action potential in an unmyelinated neuron travels slowly along the axon because every region of the axon has sodium and potassium channels.

DIFFERENCES IN PROPAGATION OFACTION POTENTIAL IN MYELINATEDAND UNMYELINATED AXONS

The action potential in an unmyelinated neuron trav-els slowly along the axon because every region of the axon has sodium and potassium channels. In a myelinated cell, the myelin sheath serves as insulators, preventing movement of ions through the membrane. Ions move only through the numerous channels lo-cated in the nodes and the action potential is propa- gated from one node of Ranvier to another, literally jumping from node to node across the myelin. Hence, propagation is rapid. This is known as saltatory con-duction. It should be noted that jumping is only ametaphor. Actually, the action potential in one node depolarizes the membrane at the next node to thresh-old and a new action potential is produced there. Ac-tion potential is also faster in thicker axons. The rate of conduction ranges from 1.0 m/sec in thin, un-myelinated fibers to 100 m/sec (225 miles per hour) in thick, myelinated fibers.

When the action potential reaches a synapse, it causes the release of neurotransmitters into the synaptic cleft. The neurotransmitters, in turn, pro-duce electrical changes in the postsynaptic neuron.


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