Axons

The axon, conductor of nervous impulses, arises from the axon hillock of the perikaryon, an area lacking Nissl bodies. Mitochondria and cytoskeletal organelles are the major axonal components. Two types of axons are Golgi type 1, which are long myelinated axons carrying

TABLE 2.1.

Major Neurotransmitters

Acetylcholine

Amino acids

Catecholamines

Y -Aminobutyric

Dopamine

acid (GAB A)

Norepinephrine

Glutamate

Epinephrine

Aspartate

Serotonin

Glycine

Neuropeptides

Opioids

Neurohypophyseal peptides

Substance P

Enkephalin

nervous impulses to distant neurons, and Golgi type 2, which are short unmyelinated axons connecting local neurons.

Synapses

The neurons communicate with each other at the synapses through chemical substances collectively referred to as neurotransmitters (Table 2.1). The contact between two neurons occurs at the axon of one neuron and the axon, dendrites, or soma of the other neuron. A neu-rotransmitter, released at the axonal terminal of a pre-synaptic neuron, exerts an excitatory or an inhibitory effect on a postsynaptic neuron or on an end organ (muscle, gland).

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