Functions of Specific Neurotransmitter Substances in the Basal Ganglial System

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Figure 56-14 demonstrates the interplay of several specific neurotransmitters that are known to function within the basal ganglia, showing (1) dopamine pathways from the substantia nigra to the caudate nucleus and putamen, (2) gamma-aminobutyric acid (GABA) pathways from the caudate nucleus and putamen to the globus pallidus and substantia nigra, (3) acetyl-choline pathways from the cortex to the caudate nucleus and putamen, and (4) multiple general pathways from the brain stem that secrete norepinephrine, serotonin, enkephalin, and several other neurotrans-mitters in the basal ganglia as well as in other parts of the cerebrum. In addition to all these are multiple glutamate pathways that provide most of the excitatory signals (not shown in the figure) that balance out the large numbers of inhibitory signals transmitted especially by the dopamine, GABA, and serotonin inhibitory transmitters.We will have more to say about some of these neurotransmitter and hormonal systems in subsequent sections when we discuss diseases of the basal ganglia, as well as in subsequent chapters when we discuss behavior, sleep, wakefulness, and functions of the autonomic nervous system.

For the present, it should be remembered that the neurotransmitter GABA always functions as an inhibitory agent. Therefore, GABA neurons in the feedback loops from the cortex through the basal

From cortex

Caudate nucleus

Substantia nigra

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Essentials of Human Physiology

Essentials of Human Physiology

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