11 20 14 2 02 PM Chapter 15 The Autonomic Nervous System Autonomic Nervous System Visceral Motor Division Motor commands sent to viscera internal organs Divided into sympathetic and parasympathetic divisions Regulation of breathing blood pressure heart rate etc o Things outside of conscious control Receptors control these functions o Thermoreceptors Body heat o Baroreceptors Pressure Ex Elderly people become dizzy when they stand up quickly because their baroreceptors don t work as quickly Visceral Reflexes ANS is responsible for body s visceral reflexes Visceral reflex arc Receptors Afferent Neurons Interneurons Efferent Neurons Effectors Baroreflex High blood pressure detected by arterial stretch receptors baroreceptors o Example of homeostatic negative feedback loop Advantageous because body senses pressure of blood as soon as it comes off of aorta away from heart If blood pressure it too high could damage other organs Kidney normally first to be damaged liver normally last to be damaged Information sent to brain when blood pressure gets too high two ways to decrease BP once message gets to brain Blood vessels may dilate Decrease heart rate Autonomic Motor Pathways vs Somatic Motor Pathways Somatic Myelinated fiber from somatic efferent nerve to gland Autonomic Two neurons from CNS to effectors o Preganglionic fiber and postganglionic fiber Myelinated preganglionic fiber synapses on ganglion Fiber that leaves ganglion is an unmyelinated postganglionic fiber that will synapse on the target Functional Organization of Somatic vs Autonomic Conscious somatic vs unconscious autonomic control Divisions of the ANS Sympathetic Division Prepares body for physical activity o Fight or flight Prepares you for stressful situations o Heart rate breathing etc all increase o Digestion decreases Parasympathetic Division Calms body functions o Rest and digest o Heart rate breathing etc normal o Body can focus on digestion Sympathetic Division Thoracolumbar Division Short preganglionic and long postganglionic fibers Short branching preganglionic axon coming off of preganglionic neuron Preganglionic Neurosomas Lead to nearby sympathetic chain of ganglia o Paravertebral ganglia right beside vertebrae o Only in thoracic and lumbar regions White communicating ramus Preganglionic myelinated fiber that is responsible for helping with communication from spinal nerve to ganglia o Information coming off of one nerve able to be distributed to other parts of body o Chain of ganglia Gray communicating ramus Postganglionic fiber unmyelinated Nerve communicates with sympathetic chain of ganglia via WCR and leaves ganglia via GCR o Very short preganglionic fiber because fiber coming off of spinal cord immediately to chain of ganglia o Longer postganglionic fiber to reach target When a spinal nerve synapses and sends information to ganglia 3 possibilities o 1 Send information up or down chain and synapse in another ganglia above below o 2 Nerve may end synapse with a postganglionic fiber within ganglia itself o 3 Go through a ganglia but not synapse on ganglia and synapse at a later ganglion that is not prevertebral located more distally Form pelvic splanchnic nerves or splanchnic nerve Splanchnic Nerves to organs Pelvic Splanchnic Nerves to organs in pelvic region Neural Divergence Not 1 1 ratio may have one nerve that synapses on several postganglionic fibers wide dispersal of information Sympathetic Chain Ganglia The Adrenal Glands Each is two glands with different functions o 1 Adrenal Cortex Outer layer that secretes steroid hormones o 2 Adrenal Medulla Inner core that is essentially a sympathetic ganglion Secretes catecholamines Parasympathetic Division Craniosacral Division Nerves from midbrain medulla oblongata and pons and sacral region S2 S4 o Oculomotor facial glossopharyngeal nerves o Vagus nerve thoracic and abdominal pelvic regions o Nerves in S2 S4 region form pelvic splanchnic nerves Originate in sacral region and innervate some of the lower abdominal organs and all organs in pelvic region i e reproductive bladder etc Enteric Nervous System Nervous system of the digestive system Not connected to the CNS Set of nerves only found in digestive system Composed of 100 million neurons found in walls of digestive tract Regulates esophagus stomach and intestinal motility and secretion of digestive enzymes and acid Has own reflex arc that does not involve CNS Clinical Corner Megacolon Massive dilation of bowel Usually evident in newborns who fail to have their first bowel movement May be caused by something getting stuck and causing blockage or inflamed material Hirschsprung s Disease Aganglionic Megacolon Born without enteric nervous system o Absence of a bowel movement indicates obstruction or hirschsprung s disease o Always diagnosed at birth In adults with megacolon take out colon In children born with hirschsprung s put in a bag for a short period of time and perform surgery to correct problem o Generally no problems after that Neurotransmitters and Their Receptors How can different autonomic neurons have different effects on the same organ constricting some vessels but dilating others o 1 Different receptors o 2 Different neurotransmitters Same neurotransmitter may have different effect depending on neurotransmitter Cholinergic Fibers Acetylcholine as neurotransmitter o All preganglionic fibers in the sympathetic and parasympathetic divisions secrete acetylcholine as their neurotransmitter o All postganglionic fibers in the parasympathetic division secrete acetylcholine as neurotransmitter and some postganglionic fibers in sympathetic division secrete acetylcholine as their neurotransmitter o The remaining postganglionic fibers in the sympathetic division secrete norepinephrine as their neurotransmitters Cholinergic Receptor Acetylcholine as receptor two types o 1 Nicotinic Receptors Always accept excitatory acetylcholine Found on ganglion in both parasympathetic and sympathetic Acetylcholine released in both divisions is always excitatory on the ganglion o 2 Muscarinic Receptors Acetylcholine can be excitatory or inhibitory depending on subclass of receptor and location Excitatory Depolarization usually involves Na going into the cell Acetylcholine allows end plate potentials to happen by allowing Na or Ca2 into the cell to depolarize the membrane Inhibitory Hyperpolarization allow negative ion in or positive ion out Acetylcholine allows potassium out by means of a G protein that allows the