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Home , Autonomic nervous system, Pupil

CHAPTER 3

The Autonomic Mary Ann Stuhan, PharmD, RPh | Raymond A. Lorenz, PharmD, BCPP Alejandro Pino-Figueroa, PhD | Mark Böhlke, PhD Timothy J. Maher, PhD (with contributions from Karen A. Newell, MMSc, PA-C, and Elizabeth P. Rothschild, MMSc, PA-C)

LEARNING OBJECTIVES KEY TERMS AND DEFINITIONS PART After completing this chapter, you should be able to — endocrine 2 gland situated on top of each , 1. Defi ne the (ANS) and its divisions, the parasympathetic which produces and releases and sympathetic autonomic nervous systems (PANS and SANS, respectively) epinephrine (also known as ) 2. Outline the , physiology, and functions of the ANS, PANS, and SANS to stimulate functions of the SANS. Adrenergic— related to the actions 3. Describe the targets/sites of action of endogenous and of of the hormone epinephrine exogenous drugs that act on the ANS (adrenaline); sometimes used to 4. Review the classifi cation and mechanisms of action of drugs acting on the ANS designate actions and responses to the sympathetic autonomic nervous system. 5. List therapeutic applications of the primary drug classes acting on the ANS Afferent — neuron 6. State the brand and generic names of representative therapeutic agents acting on the carrying impulses to the CNS ANS, together with their routes of administration, side effects, and potential drug ( and ) from the periphery (other parts of the body). interactions Autonomic nervous system— system of that controls automatic bodily actions such as he nervous system is the most complex system in the body. It has the functions of glandular tissues, T two main anatomical and functional divisions: the the and , and (CNS), discussed in Chapter 4, and the peripheral nervous system (PNS). The involuntary movements and body functions (including secretions, pulse, PNS is divided into two subsystems: the somatic and autonomic nervous sys- and ). tems. The involves voluntary movement such as walk- — elongated protrusion of the ing or talking. It will be discussed in more detail in Chapter 11. The autonomic neuron that conducts impulses away nervous system (ANS) is the major involuntary, unconscious, automatic por- from the cell. tion of the PNS. For example, the ANS keeps the heart beating. A heart doesn’t Catecholamines— hormones need to be told by the conscious mind to continue beating, it just does. Other produced in the adrenal gland, such examples of the ANS at work include regulating blood pressure, saliva secre- as epinephrine and tion, sweating, gastrointestinal motility, and bronchial air exchange. The ANS that exert their effect in the SANS and agents that are chemically similar relies on neurotransmitters acting on certain receptors to cause its actions. to these hormones. See Figure 3-1 for a graphical representation of the relationships between the Cholinergic— related to the divisions of the nervous system. Knowledge of the anatomy and physiology, actions of the neurotransmitter synthesis and release, signal termination, receptor character- . Cholinergic effects istics, and functional integration of the ANS is important to an understanding include slowed , increased of how many drugs act on many systems and organs of the body. secretion, and increased activity of the .

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Effector — cells or tissues Peripheral Nervous System that perform their functions in response to a stimulus (such as a nerve impulse); sometimes called target organs. Those receiving stimulation Somatic nervous system Skeletal from the nervous system are (voluntary) muscles designated by the term neuroeffector. Efferent neuron— neuron carrying nerve impulses toward an effector SANS SANS Sympathetic Paraympathetic PANS organ. postganglionic ACh preganglionic preganglionic ACh PANS neuron autonomic autonomic neuron neuron nervous nervous postganglionic Endocrine secretion— release system system neuron ACh (SANS) (PANS) of hormones synthesized by glands

directly into the bloodstream to Adrenal gland circulate throughout the body. (Contrasts with paracrine secretion, in which substances are released to act locally on nearby tissues.) Epi ACh Endogenous— refers to an agent synthesized or produced within the organism. Effector organs (, heart, Exocrine secretion— release of blood vessels, , GI tract, glandular products to ducts or tracts glands) that lead directly to the outside of the body. Examples are sweat and . — mass of neuronal bodies. Plural = ganglia. — physiologic Figure 3-1. The peripheral nervous system. equilibrium required for life processes and maintained by several systems and biologic mechanisms. Innervate— supply an organ or tissue Anatomy and Physiology with nerves. (The function of supplying tissue with nerves is innervation.) The ANS has two functional divisions: the sympathetic autonomic nervous system Neuron— a nerve cell. (SANS) and the parasympathetic autonomic nervous system (PANS). These two divi- Neurotransmitters— endogenous sions have opposite effects and serve to keep the body in a balanced state called homeo- chemical compounds that relay, stasis . The PANS is involved in conserving body processes such as and resting amplify, and/or modulate signal secretions transmission between two (causing decreased heart rate and increased ). The SANS contributes to the or between neurons and other cells. provision of energy and stamina in emergency situations such as fi ghting or escape from Parasympathetic— pertaining to danger (sometimes called the fi ght or ightfl reactions ). For example, both the SANS and autonomic functions mainly governing PANS stimulate muscles in the to change size. The SANS increases pupil size to the body at rest, including glandular () resulting in better far range vision for emergency situations or night/low light secretions, tone and contractility of conditions. The PANS decreases pupil size (), which produces better short range smooth muscle, and slowing the vision for reading or viewing fi ne details. heart rate. All body systems are affected by ANS neurons , but not all organs have both PANS Secretion— the process of innervation production and release of chemical and SANS . Innervation is described as the distribution of nerve fi bers to a compounds from a tissue (gland). specifi c body system or organ. The overall response of an organ to ANS stimulation will The secreted product has a function equal the sum of infl uences from both PANS and SANS fi bers. This means that if more as opposed to an excreted waste. SANS nerves are activated in a specifi c organ, then the SANS actions will predominate there. Sensory nerves ( afferent neurons ) communicate the happenings in the periphery (outside the CNS) back to the brain through the spinal cord. This communication allows the appropriate ANS actions to occur in a given situation. These responses are also inte- grated with the somatic nervous system so appropriate voluntary movements can occur. Figure 3-2 is an anatomical representation of the ANS. The variety of effects of the ANS on effector organs in the is summarized in Table 3-1.

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