Title 9. PHARMACOLOGY OF DRUGS ACTING ON ANS.pdf ✅

PHARMD GURU Page 1 INTRODUCTION TO NERVOUS SYSTEM:  The nervous system is divided into two anatomical divisions: the central nervous system (CNS), which is composed of the brain and spinal cord, and the peripheral nervous system, which includes neurons located outside the brain and spinal cord—that is, any nerves that enter or leave the CNS. PHARMACOLOGY OF DRUGS ACTING ON ANS Hi students, This is just an introduction to ANS, this is not asked in our syllabus, but you must learn these basics for better understanding the Pharmacology of ANS. Learn the overview of ANS and later study the pharmacology of Drugs acting on ANS.
PHARMD GURU Page 2  The peripheral nervous system is subdivided into the efferent division, the neurons of which carry signals away from the brain and spinal cord to the peripheral tissues, and the afferent division, the neurons of which bring information from the periphery to the CNS.  Afferent neurons provide sensory input to modulate the function of the efferent division through reflex arcs, or neural pathways that mediate a reflex action. FUNCTIONAL DIVISIONS WITH IN THE NERVOUS SYSTEM:  The efferent portion of the peripheral nervous system is further divided into two major functional subdivisions, the somatic and the autonomic systems.  The somatic efferent neurons are involved in the voluntary control of functions such as contraction of the skeletal muscles essential for locomotion.  The autonomic system, conversely, regulates the everyday requirements of vital bodily functions without the conscious participation of the mind. Because of the involuntary nature of the autonomic nervous system as well as its functions, it is also known as the visceral, vegetative, or involuntary nervous system.  It is composed of efferent neurons that innervate smooth muscle of the viscera, cardiac muscle, vasculature, and the exocrine glands, thereby controlling digestion, cardiac output, blood flow, and glandular secretions. ANATOMY OF THE ANS: 1. Efferent neurons: The ANS carries nerve impulses from the CNS to the effector organs by way of two types of efferent neurons (Figure 3.2). The first nerve cell is called a preganglionic neuron, and its cell body is located within the CNS. Preganglionic neurons emerge from the brainstem or spinal cord and make a synaptic connection in ganglia (an aggregation of nerve cell bodies located in the peripheral nervous system). These ganglia function as relay stations between a preganglionic neuron and a second nerve cell, the postganglionic neuron. The latter neuron has a cell body originating in the ganglion. It is generally nonmyelinated and terminates on effector organs, such as smooth muscles of the viscera, cardiac muscle, and the exocrine glands.
PHARMD GURU Page 3 innervate and regulate. The sympathetic nervous system is also called the thoracolumbar division because of its origins. In most cases, the preganglionic nerve endings of the sympathetic nervous system are highly branched, enabling one preganglionic neuron to interact with many postganglionic neurons. This arrangement enables this division to activate numerous effector organs at the same time. [Note: The adrenal medulla, like the sympathetic ganglia, receives preganglionic fibers from the sympathetic system. Lacking axons, the adrenal medulla, in response to stimulation by the ganglionic neurotransmitter acetylcholine, influences other organs by secreting the hormone epinephrine, also known as adrenaline, and lesser amounts of norepinephrine, into the blood.] 2. Afferent neurons: The afferent neurons (fibers) of the ANS are important in the reflex regulation of this system (for example, by sensing pressure in the carotid sinus and aortic arch) and in signaling the CNS to influence the efferent branch of the system to respond. 1. Afferent neurons: The afferent neurons (fibers) of the ANS are important in the reflex regulation of this system (for example, by sensing pressure in the carotid sinus and aortic arch) and in signaling the CNS to influence the efferent branch of the system to respond. 2. Sympathetic neurons: The efferent ANS is divided into the sympathetic and the parasympathetic nervous systems as well as the enteric nervous system. Anatomically, the sympathetic and the parasympathetic neurons originate in the CNS and emerge from two different spinal cord regions. The preganglionic neurons of the sympathetic system come from thoracic and lumbar regions (T1 to L2) of the spinal cord, and they synapse in two cordlike chains of ganglia that run close to and in parallel on each side of the spinal cord. The preganglionic neurons are short in comparison to the postganglionic ones. Axons of the postganglionic neuron extend from these ganglia to the tissues that they
PHARMD GURU Page 4 3. Sympathetic neurons: The efferent ANS is divided into the sympathetic and the parasympathetic nervous systems as well as the enteric nervous system. Anatomically, the sympathetic and the parasympathetic neurons originate in the CNS and emerge from two different spinal cord regions. The preganglionic neurons of the sympathetic system come from thoracic and lumbar regions (T1 to L2) of the spinal cord, and they synapse in two cordlike chains of ganglia that run close to and in parallel on each side of the spinal cord. The preganglionic neurons are short in comparison to the postganglionic ones. Axons of the postganglionic neuron extend from these ganglia to the tissues that they innervate and regulate. The sympathetic nervous system is also called the thoracolumbar division because of its origins. In most cases, the preganglionic nerve endings of the sympathetic nervous system are highly branched, enabling one preganglionic neuron to interact with many postganglionic neurons. This arrangement enables this division to activate numerous effector organs at the same time. [Note: The adrenal medulla, like the sympathetic ganglia, receives preganglionic fibers from the sympathetic system. Lacking axons, the adrenal medulla, in response to stimulation by the ganglionic neurotransmitter acetylcholine, influences other organs by secreting the hormone epinephrine, also known as adrenaline, and lesser amounts of norepinephrine, into the blood.] 4. Parasympathetic neurons: The parasympathetic preganglionic fibers arise from cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal), and X (vagus) as well as from the sacral region (S2 to S4) of the spinal cord and synapse in ganglia near or on the effector organs. [The vagus nerve accounts for 90% of preganglionic parasympathetic fibers in the body. Postganglionic neurons from this nerve innervate most of the organs in the thoracic and abdominal cavity.] Due to the origin of the parasympathetic nervous system, it is also called the craniosacral division. Thus, in contrast to the sympathetic system, the preganglionic fi bers are long, and the postganglionic ones are short, with the ganglia close to or within the organ innervated. In most instances there is a one-to-one connection between the preganglionic and postganglionic neurons, enabling the discrete response of this division.