BRS

Chapter 21 Neurotransmitters and Pathways

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1. Nigrostriatal pathway ■ the substantia nigra projects to the striatum. ■ destruction of dopaminergic nigral neurons results in parkinsonism . 2. Mesolimbic pathway ■ the ventral tegmental area projects widely to the structures of the limbic system. ■ linked to behavior and schizophrenia. 3. Mesocortical pathway ■ the ventral tegmental area projects to the prefrontal cortex. ■ linked to motivation and emotional response. 4. Tuberohypophyseal (tuberoinfundibular) pathway ■ the arcuate nucleus of the hypothalamus projects to the portal vessels of the infundibulum. ■ released dopamine inhibits the release of prolactin from the adenohypophysis.

III. ACETYLCHOLINE

A. Characteristics ■ the major neurotransmitter of the peripheral nervous system, neuromuscular junction, para sympathetic nervous system, preganglionic sympathetic fibers, and postganglionic sympa thetic fibers to the sweat glands. ■ found in neurons of the somatic and visceral motor nuclei in the brainstem and spinal cord. ■ receptors are muscarinic (metabotropic; postganglionic parasympathetics and sweat glands) or nicotinic (ionotropic; preganglionic sympathetic and parasympathetic, by all alpha, beta, and gamma motor neurons).

B. Major cholinergic pathways (Figure 21.3) 1. Septal nuclei

■ project via the fornix to the hippocampal formation. 2. Basal nucleus of Meynert ■ located in the substantia innominata of the basal forebrain, between the globus pallidus and the anterior perforated substance. ■ projects to the entire neocortex.

Acetylcholine

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Fornix

Septal nuclei

Medial habenular nucleus

Striatum

Habenulointerpeduncular tract Interpeduncular nucleus

Basal nucleus of Meynert

Hippocampal formation

Cranial motor neurons and preganglionic parasympathetics

Copyright © 2023 Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. Autonomic preganglionic neurons Spinal motor neurons

FIGURE 21.3. Distribution of acetylcholine (ACh)-containing neurons and their axonal projections. The basal nucleus of Meynert projects to the entire cortex; this nucleus degenerates in Alzheimer disease. Striatal Ach-local circuit neurons degenerate in Huntington disease.