FUNCTIONAL ASPECTS OF THEAUTONOMIC NERVOUS SYSTEM
AUTONOMIC NERVOUS SYSTEM The autonomic nervous system is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control Autonomic nervous system innervate smooth muscle (eg, blood vessels, gut wall, urinary bladder) cardiac muscle glands (eg, sweat glands, salivary glands) 3
DIVISION OF ANSParasysmpathetic: routine maintenance “rest &digest”Sympathetic: mobilization & increased metabolism“fight, flight or fright” 4
WHERE THEY COME FROMParasympathetic: Sympathetic:craniosacral thoracolumbar 5
SYMPATHETIC OUTFLOW “fight, flight or fright” Also called thoracolumbar system: all its neurons are in lateral horn of gray matter from T1-L2 Lead to every part of the body (unlike parasymp.) Easy to remember that when nervous, you sweat; when afraid, hair stands on end; when excited blood pressure rises (vasoconstriction): these sympathetic only Also causes: dry mouth, pupils to dilate, increased heart & respiratory rates to increase O2 to skeletal muscles, and liver to release glucose 9
PRE AND POST GANGLION NEURON Somatic division: Cell bodies of motor neurons reside in CNS (brain or spinal cord) Their axons (sheathed in spinal nerves) extend all the way to their skeletal muscles Autonomic system: chains of two motor neurons 1st = preganglionic neuron (in brain or cord) 2nd = gangionic neuron (cell body in ganglion outside CNS) 10
PRE AND POSTGANGLION FIBER Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron Axon of 2nd (postganglionic) neuron extends to the organ it serves 11 Note: the autonomic ganglion is motor
SYMPATHETIC AND PARA SYMPATHETIC GANGLIA Sympathetic ganglia Many lie close to spinal cord(paravertebral) Others lie approximately midway between spinal cord and effector organ(prevrtebral or collateral) Parasympathetic ganglia Lie close to or within the walls of Figure 8-2 effector organ
IMPORTANT NEUROTRANSMITTERS Acetylcholine =Cholinergic Fibers that release acetylcholine are known as cholinergic fibers All preganglionic neurons of the autonomic division and all postganglionic neurons of the parasympathetic division are cholinergic
Norepinephrine = Adrenergic Neurotransmitter between the sympathetic postganglionic fiber and the effector cell Fibers that release norepinephrine are adrenergic fibers Most postganglionic neurons of the sympathetic division are adrenergic Few are cholinergic(sweat gland,some blood vessels in skeletal muscle) 17
CHOLINERGIC RECEPTOR Nicotinic receptor Nicotinic receptors are found on the postganglionic cell bodies in all autonomic ganglia. Response to acetylcholine released from both sympathetic and parasympathetic 18
Muscuranic receptor found on cell membranes of effectors organ (smooth muscle, cardiac muscle, and glands) they bind with acetylcholine released from parasympathetic postganglionic nerve fiber 19
ADRENERGIC RECEPTOR Alpha receptors are located at sympathetic neuroeffector junctions of many organs. In general, alpha receptors mediate excitation or increased activity of the effector cells. alpha receptor have greater affinity for norepinephrine 20
TYPES OF α-ADRENERGIC RECEPTOR α-adrenergic receptors are adrenergic receptors that respond to norepinephrine They are subdivided into two types: α1, found in smooth muscle, heart, and liver, with effects including vasoconstriction, intestinal relaxation, uterine contraction and pupillary dilation, α2, found in platelets, vascular smooth muscle, nerve termini, and pancreatic islets, with effects including platelet aggregation, vasoconstriction, and inhibition of norepinephrine release and of insulin secretion.
Beta receptors are also locatedpostsynaptically at sympatheticneuroeffector junctions of many organs. beta receptors mediate relaxation ordecreased activity of the effector cells.Heart muscle is an important exception tothis rule. Activation of beta adrenoceptorsin heart increases the automaticity andcontractility of all parts of the heart.
β-RECEPTOR TYPES β-adrenergic receptors respond particularly to epinephrine and nor epinephrine There are three known types of beta receptor, designated β1, β2 and β3. β1-Adrenergic receptors are located mainly in the heart. Sensitive to both EN and NOR EN β2-Adrenergic receptors are located mainly in the lungs, gastrointestinal tract, liver, uterus, vascular smooth muscle, and skeletal muscle sensitive to EN only. β3-receptors are located in fat cells.
SYMPATHETIC PARASYMPATHETIC TONE DUAL INNERVATION MASS DISCHARGE(ALARM OR STRESS RESPONSE) LOCAL RESPONSE SOME EXCEPTIONS: BLOOD VESSELS SWEAT GLAND, SALIVARY GLAND 33
VISCERAL REFLEXES These are the simplest functions of the ANS. Each visceral reflex arc consists of a receptor, a sensory neuron, an interneuron, and two visceral motor neurons. All visceral reflexes are polysynaptic. PS reflexes include : gastric and intestinal reflexes, defecation, urination, direct light reflexes, swallowing reflex, coughing reflex, baroreceptor reflex and sexual arousal. S reflexes: cardioaccelaratory reflex, vasomotor reflex, pupillary reflex and ejaculation (in males).
VISCERAL REFLEX ARCS 35*e.g. “enteric” nervous system: 3 neuron reflex arcs entirely within the wall of the gut
Central control of the Amygdala: main limbic region for emotions Autonomic NS Hypothalamus: main integration center Reticular formation: most direct influence over autonomic function 36