GENERAL FEATURES OF NERVE TISSUE & THE NERVOUS SYSTEM 2

ØB. Impulse Conduction: Within a neuron, signals (impulses) are propagated as a wave of depolarization along the plasma membrane of the dendrites, soma, and axon. Depolarization involves channels (ionophores) in the membrane, which allow ions (e.g, Na+, K-) to enter or exit the cell. In unmyelinated axons, depolarization is continuous. In myelinated axons, depolarization occurs only at nodes of Ranvier, jumping from node to node (saltatory conduction). Impulse conduction is thus faster in myelinated axons.


ØC. Synapses: Signals pass from neuron to target cell by specialized connections called synapses. The target may be another neuron or a cell in the end organ leg, gland or muscle) it supplies. At chemical synapses, the signal is transmitted by exocytosis of neurotransmitters, chemicals such as acetylcholine that cross the narrow gap (synaptic cleft) between the cells to initiate depolarization of the target cell. At the less common electrical synapses, the signal is transmitted by ions flowing through a gap junction-like complex.