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The Nervous system:

The nervous system is conventionally divided into the Central nervous system (CNS; the brain and spinal cord) and the Peripheral nervous system (PNS; neuronal tissues outside the CNS). The motor (efferent) portion of the nervous system can be divided into two major subdivisions:

1). Autonomic Nervous System

2). Somatic Nervous System

The autonomic nervous system (ANS) is largely independent (autonomous) in that its activities are not under direct conscious control. It is concerned primarily with visceral functions such as cardiac output, blood flow to various organs, and digestion, which are necessary for life.
The somatic subdivision is largely concerned with consciously controlled functions such as movement, respiration, and posture. Both systems have important afferent (sensory) inputs that provide information regarding the internal and external environments and modify motor output through reflex arcs of varying size and complexity.

Nervous system

The ANS is composed of sympathetic and parasympathetic divisions that regulate several involuntary actions of the body, whereas the somatic nervous system innervates the skeletal muscles. Agents acting in the ANS include adrenergic agonists and antagonists, cholinergic agonists and antagonists, and indirectly acting agents that could affect one or the other system. These drugs are useful for treating various ailments, including blood pressure disturbances, bronchial asthma, cardiac dysfunctions, anaphylactic reactions, nasal congestion, and skeletal muscle spasticity. Drugs affecting the CNS produce anesthesia and sedation, relieve pain and anxiety, suppress movement disorders and epileptic seizures, and treat psychotic and affective disorders. Drugs acting on the nervous system achieve their pharmacologic effects by modifying the synaptic concentrations or receptor actions of neurotransmitters. Other drugs modulate the intracellular pathways by which neurotransmitter actions are conveyed to yield the ultimate physiological response.

nervous system graphic

Schematic diagram comparing some anatomic and neurotransmitter features of autonomic and somatic motor nerves. Only the primary transmitter substances are shown. Parasympathetic ganglia are not shown because most are in or near the wall of the organ innervated. Cholinergic nerves are shown in blue; noradrenergic in red; and dopaminergic in green. Note that some sympathetic postganglionic fibers release acetylcholine or dopamine rather than norepinephrine. The adrenal medulla, a modified sympathetic ganglion, receives sympathetic preganglionic fibers and releases epinephrine and norepinephrine into the blood. ACh, acetylcholine; D, dopamine; Epi, epinephrine; M, muscarinic receptors; N, nicotinic receptors; NE, norepinephrine.

The Nervous system introduction Video Part 1:

The Nervous system introduction Video Part 2: