Autonomic Nervous System PDF

Dr. Mai Adawi Mohamed Lecturer of physiology FOM - SCU  Motor Overview of the structural and functional organization of the nervous system General Organization of efferent divisions  General Organization Of The Autonomic Nervous Sys...

Dr. Mai Adawi Mohamed Lecturer of physiology FOM - SCU  Motor Overview of the structural and functional organization of the nervous system General Organization of efferent divisions  General Organization Of The Autonomic Nervous System Autonomic nervous system is made up of two neurons in series that connect the central nervous system and the effector cells. The first neuron has its cell body in the central nervous system. The synapse between the two neurons is outside the central nervous system in a cell cluster called an autonomic ganglion. The neurons passing between the central nervous system and the ganglia are called preganglionic neurons; those passing between the ganglia and the effector cells are postganglionic neurons. Difference Between Somatic Nervous System & Autonomic Nervous System  Anatomical origin of parasympathetic nervous system (Craniosaccral) Cranial nerves(III, VII, IX, and X) S2–S4 Anatomical origin of Sympathetic nervous system (Thoracolumbar) (T1–L2)  Location of Ganglia in Both Divisions of ANS The two divisions also differ in the location of ganglia. Most of the sympathetic ganglia lie close to the spinal cord and form the two chains of ganglia one on each side of the cord known as the sympathetic ganglion chains. Other sympathetic ganglia, called collateral ganglia—the celiac, superior mesenteric, and inferior mesenteric ganglia are in the abdominal cavity, closer to the innervated organ  In contrast, the parasympathetic ganglia lie within, or very close to, the organs that the postganglionic neurons innervate.  Regulation Of Autonomic Nervous System Activity The efferent nervous activity of the ANS is regulated by several regions in CNS in particular by the hypothalamus and the brainstem. Many important variables in the body are monitored and regulated in the hypothalamus and the brainstem including heart rate, blood pressure, gastrointestinal peristalsis and glandular secretion, body temperature, hunger, thirst, plasma volume, and plasma osmolarity.  Two Important Features Of Both Systems 1. Many tissues are innervated by both systems (dual innervation) Exception: Vascular smooth muscle and sweat glands are regulated by the sympathetic system only 2. Both systems are tonically active. In other words, they provide some degree of nervous input to a given tissue at all times. Each System Is Dominant Under Certain Conditions The sympathetic systempredominates during emergency fight-or-flight reactions and during exercise. The overall effect of the sympathetic system under these conditions is to prepare the body for strenuous physical activity. More specifically, sympathetic nervous activity will increase the flow of blood that is well-oxygenated and rich in nutrients to the tissues that need it, in particular, the working skeletal muscles. The parasympathetic system predominates during quiet, resting conditions. The overall effect of the parasympathetic system under these conditions is to conserve and store energy and to regulate basic body functions such as digestion and urination (rest and digest).  FUNCTIONS OF ANS The sympathetic and parasympathetic nervous systems dually innervate most visceral organs. Most visceral organs are innervated by both sympathetic and parasympathetic nerve fibers. Innervation of a single organ by both branches of the autonomic nervous system is known as dual innervation the sympathetic and parasympathetic nervous systems generally exert opposite effects in a particular organ. Sympathetic stimulation increases the heart rate, whereas parasympathetic stimulation decreases it; sympathetic stimulation slows movement within the digestive tract, whereas parasympathetic stimulation enhances digestive motility. both systems increase the activity of some organs and reduce the activity of others.  FUNCTIONS OF ANS Usually, both systems are partially active. This ongoing activity is called sympathetic or parasympathetic tone. Under given circumstances, activity of one division can dominate the other. Sympathetic dominance to a particular organ exists when the sympathetic fibers’ rate of firing to that organ increases above tone level, coupled with a simultaneous decrease below tone level in the parasympathetic fibers’ The reverse situation is true for parasympathetic dominance. The balance between sympathetic and parasympathetic activity can be shifted separately for individual organs to meet specific demands EXCEPTIONS: Innervated blood vessels receive only sympathetic nerve fibers. Sweat glands are innervated only by sympathetic nerves. Salivary glands are innervated by both autonomic divisions, but unlike elsewhere, sympathetic and parasympathetic activities are not antagonistic. Both stimulate salivary secretion, but the saliva’s volume and composition differ, depending on which autonomic branch is dominant. Sympathetic nervous system Neurotransmitters In ANS  Neurotransmitters At the ganglia, the neurotransmitter for both sympathetic and parasymp. is acetylcholine (Ach) Post ganglionic sympathetic release adrenaline and nor adrenaline Post ganglionic parasympathetic release acetylcholine.  Release of Acetylcholine : 1. All preganglionic neurons of ANS. 2. All parasympathetic postganglionic neurons 3. Some sympathetic postganglionic neurons traveling to sweat glands Receptors For Autonomic Neurotransmitters Cholinergic and Adrenergic receptors I. Acetylcholine binds to two types of cholinergic receptors: nicotinic receptors and muscarinic receptors. a. Nicotinic receptors are found on the cell bodies of all postganglionic neurons in the ganglia of the ANS, both sympathetic and parasympathetic divisions. b. Muscarinic receptors are found on the cell membranes of the effector tissues II. There are two classes of adrenergic receptors for norepinephrine and epinephrine: alpha (α) and beta (β). Furthermore, there are at least two subtypes of receptors in each class: α1, α2, β1, and β2. a1 receptors are present on most sympathetic target tissues. a2 receptors are located mainly on digestive organs. b1 receptors are restricted to the heart. b2 receptors are found on smooth muscles of arterioles and bronchioles (small blood vessels and airways).  Drugs Acting on Sympathetic nervous system: 1. Agonist : Sympathomimetic drugs, Drugs that act on adrenergic effector organs. 2. Antagonist: Sympatholytic drugs 1-Blocking synthesis & storage of norepinephrine : Reserpine 2-Blocking release of norepinephrine : Guanethidine 3-Blocking adrenergic alpha receptors: Phenoxybenzamine Phentolamyne 4-Blocking adrenergic beta receptors: Propranolol & metoprolol (Selective beta1)  Drugs Acting on Parasympathetic system: 1. Parasympathomimetic Drugs (Cholinergic Drugs) 1-Anticholinesterase drugs: neostigmine 2-Nicotinic receptors stimulation: Nicotine 3-Nicotinic & muscarinic stimulation: methacholine 4-Muscarinic action only: pilocarpine 2. Parasympatholytics: 1-Antimuscarinic drugs: atropine homatropine 2-Nicotinic blocker drugs: hexamethonium THANKS FOR YOU ATTENTION