Comparison of somatic and autonomic systems Targets – Somatic = skeletal muscle – Autonomic = smooth/cardiac muscle & glands Efferent pathways – Somatic = no ganglia; myelinated axon from ventral horn of cord all the way to effector – Autonomic = 2 neuron pathway; first is preganglionic and body resides in brain/S.C.; 2 nd is postganglionic and body resides in autonomic ganglion. Pre’s are lightly myelinated; post’s are unmyelinated

Sympathetic and parasympathetic system sympathetic parasympathetic SNS = short pre/long post ganglionic axon PsNS = long pre/short post ganglionic axon

Neurotransmitters Somatic = all motor neurons release ACH which is always stimulatory Visceral = ACH & norepinephrine – All preganglionic fibers release ACH – All postganglionic PsNS fibers release ACH – Most postganglionic SNS fibers release norepinephrine (Except…….) – Stimulation of Post ganglionic nerve fibers can be stimulatory or inhibitory based on receptor types

Cholinergic Receptors The two types of receptors that bind ACh are nicotinic and muscarinic Nicotinic receptors are found on: – Motor end plates (somatic targets) – All ganglionic neurons of both sympathetic and parasympathetic divisions – Epinephrine, norepinephrine-producing cells of the adrenal medulla The effect of ACh binding to nicotinic receptors is always stimulatory

Muscarinic receptors M1 muscarinic receptors: located in the neural system. M2 muscarinic receptors: located in the heart (decreasing rate, contractility) M3 muscarinic receptors: located at many places in the body, such as: *** the lungs causing vasoconstriction & bronchoconstriction. *** They are also found in the smooth muscles of the GIT, which help in increasing intestinal motility and dilating sphincters. ***M3 receptors are also located in many glands that help to stimulate secretion in salivary glands and other glands of the body.

Types of  -adrenergic receptor They are subdivided into two types:  1: pupillary dilatation, coronary constriction, sphincters constriction, constriction of blood vessels  2: found in vascular smooth muscle causing vasoconstriction, in intestine causing a decrease intestinal secretion and in pancreatic islets (decrease secretion of insulin).

 -receptor types There are three known types of beta receptor, designated β1, β2 and β3. β1-Adrenergic receptors are located mainly in the heart (increase in rate, contractility). β2-Adrenergic receptors are located mainly in the lungs (dilatation), heart (increase in rate and contractility and dilatation of coronaries), gastrointestinal tract, liver, uterus and vascular smooth muscle (dilatation). β3-receptors are located in fat cells (lipolysis).

FIGHT OR FLIGHT RESPONSE increase in heart rate, blood pressure and cardiac output Diversion of blood flow from the skin and splanchnic vessels to those supplying skeletal muscle Increased pupil size, bronchiolar dilation, contraction of sphincters and metabolic changes such as the mobilization of fat and glycogen