Terminal buttons

Figure 7.1. Stmctural and functional features of a nerve cell. Afferent (=incoming) synapses mainly coimect to the soma and dendrites (although some are also found on the axon). The axon may greatly vary in length (from millimeters to a meter and more). The terminal buttons form the efferent synapse by which the nemon will control other nemons in turn, b The afferent synapses may be either excitatory (red cones) or inhibitory (blue circles), and the balance of their respective firing rates will determine the efferent activity of the nemon in firm.

Figure 7.2. Stractures of synapses, a Some anatomical variations. Left An intemeural synapse connects two nerve cells. Middle A neuromuscular synapse (also called motor endplate) connects the terminal button of a motoneuron to a skeletal muscle cell. Right An automic nerve cell may form several secretory varicosities that release the transmitter in the target tissue, without forming a circtrmscribed contact zone with an individtral target cell, b Electron microcoscopy of a nemomnsctrlar synapse. The synaptic cleft is very narrow, so that diffusion of secreted transmitter to the receptors on the postsynaptic membrane is fast. Ntrmerous vesicles line up close to the presynaptic membrane. Note the striated myofilament in the postsynaptic cell, c Light microscopy. A single nemon branches out and sends terminal buttorrs to multiple muscle fibers.

A second mechanism for removing neurotransmitters from the synapse is called rcuptake. Neurotransmitters arc taken back up into the terminal button after they have been released—hence the term reuptake. This is an economical mechanism of deactivating transmitters because the ncurotransmitter molecule is preserved intact and can be used again without the expense of energ) involved in the manufacture of new transmitters. Some drugs (notably cocaine) exert some of their action by blocking the reuptake process. 

Axon terminal (or terminal button) Enlarged buttonlike structures at the ends of axon branches (Chapter 3). 

Communication in the brain takes place between nerve cells or neurons. Psychoactive substances alter many aspects of communication between neurons, as will be discussed below. Neurons are highly speciahzed cells that exist in many shapes, sizes and varieties. However, they share the following basic structural regions cell body or soma, dendrites, axon, and terminal buttons. The cell body, or soma, is the metabolic centre of the neuron, and contains the nucleus and other structures that sustain the neuron. The nucleus plays a role in mature neurons, where it is used to synthesize proteins in response to a wide variety of stimuli (11, 17). 

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