A Brief Look at the Nervous System - Pharmacology

In order to understand the therapeutic effects of medication used to treat the nervous system, you’ll need to have an understanding of the anatomy and physiology of the system. The nervous system is comprised of the brain, spinal cord, nerves, and ganglia. Collectively, they receive stimuli and transmit information.

There are two nervous systems. These are the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system consists of the brain and spinal cord, which are responsible for regulating body function. The central nervous system receives information from the peripheral nervous system, which is interpreted, and then the central nervous system sends an appropriate signal to the peripheral nervous system to stimulate cellular activity. Depending on the signal, the stimulation either increases or blocks nerve cells, which are called neurons.

The peripheral nervous system is organized into two divisions. These are the somatic nervous system (SNS) and the autonomic nervous system (ANS). The somatic nervous system acts on skeletal muscles to produce voluntary movement. The autonomic nervous system, known as the visceral system, is responsible for involuntary movement and controls the heart, respiratory system, gastrointestinal system, and the endocrine system (glands).

The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems (see Autonomic Nervous System).

The sympathetic nervous system is called the adrenergic system and uses the norephinephrine neurotransmitter to send information. The parasympathetic system, called the cholinergic system, uses the acetylcholine neurotransmitter to transmit information.

Both the sympathetic and parasympathetic nervous systems innervate organs within the body. The sympathetic system excites the organ while the parasympathetic system inhibits the organ. For example, the sympathetic system increases the heart rate while the parasympathetic system decreases the heart rate.

NEUROLOGICAL PATHWAYS

Neurological pathways extend from locations in the spinal cord to various areas of the body. These pathways contain two types of nerve fibers. These preganglionic and postganglionic fibers are connected together by a ganglion. The preganglionic nerve fiber carries messages from the central nervous system to the ganglion. The postganglionic nerve fiber transmits that message to specific tissues and organs from the ganglion.

Neurological pathways in the sympathetic nervous system originate from the thoracic (T1 to T12) and the upper lumbar segments (L1 and L2) of the spinal cord. This is why the sympathetic nervous system is also referred to as the thoracolumbar division of the autonomic nervous system.

The preganglionic fibers of the sympathetic nervous system extend from the spinal cord to the ganglionic fiber. These are relatively short. However, sympathetic postganglionic fibers are long from the ganglion to the body cells.

Neurological pathways in the parasympathetic nervous system originate from cranial nerves III, VII, IX, and X from the brain stem and the sacral segments S2, S3, and S4 from the spinal cord. This is why the parasympathetic nervous system is also known as the craniosacral division of the autonomic nervous system.

Preganglionic fibers are long from the spinal cord to the ganglion and the postganglionic fibers are short from the ganglion to the body cells.


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