The Autonomic Nervous System Chapter 15 The Autonomic Nervous System

Autonomic Nervous System

Somatic and Autonomic Nervous System Smooth and cardiac muscle and glands Unconscious regulation Target tissues stimulated or inhibited Two synapses Acetycholine by preganglionic neurons and ACh or norepinephrine by postganglionic neurons Somatic Skeletal muscle Conscious and unconscious movement Skeletal muscle contracts Only one synapse Acetylcholine the transmiter

Somatic versus Autonomic NS Principles of Human Anatomy and Physiology, 11e

Principles of Human Anatomy and Physiology, 11e Basic Anatomy of ANS Preganglionic neuron cell body in brain or spinal cord axon is myelinated type B fiber that extends to autonomic ganglion Postganglionic neuron cell body lies outside the CNS in an autonomic ganglion axon is unmyelinated type C fiber that terminates in a visceral effector Principles of Human Anatomy and Physiology, 11e

Sympathetic vs. Parasympathetic NS Principles of Human Anatomy and Physiology, 11e

AUTONOMIC NERVOUS SYSTEM The output (efferent) part of the ANS is divided into two principal parts: the sympathetic division the parasympathetic division Organs that receive impulses from both sympathetic and parasympathetic fibers are said to have dual innervation. Table 15.1 summarizes the similarities and differences between the somatic and autonomic nervous systems.

Sympathetic ANS vs. Parasympathetic ANS Principles of Human Anatomy and Physiology, 11e

Divisions of the ANS 2 major divisions parasympathetic sympathetic Dual innervation one speeds up organ one slows down organ Sympathetic NS increases heart rate Parasympathetic NS decreases heart rate Principles of Human Anatomy and Physiology, 11e

Divisions of the ANS 2 major divisions parasympathetic sympathetic Dual innervation one speeds up organ one slows down organ Sympathetic NS increases heart rate Parasympathetic NS decreases heart rate Principles of Human Anatomy and Physiology, 11e

Sympathetic Ganglia These ganglia include the sympathetic trunk or vertebral chain or paravertebral ganglia that lie in a vertical row on either side of the vertebral column Other sympathetic ganglia are the prevertebral or collateral ganglia that lie anterior to the spinal column and close to large abdominal arteries. celiac superior mesenteric inferior mesenteric ganglia

Parasympathetic Ganglia Parasympathetic ganglia are the terminal or intramural ganglia that are located very close to or actually within the wall of a visceral organ. Examples of terminal ganglia include ciliary, pterygopalatine, submandibular, otic ganglia Principles of Human Anatomy and Physiology, 11e

Sympathetic ANS vs. Parasympathetic ANS Principles of Human Anatomy and Physiology, 11e

Dual Innervation, Autonomic Ganglia Parasympathetic (craniosacral) division preganglionic cell bodies in nuclei of 4 cranial nerves and the sacral spinal cord Ganglia terminal ganglia in wall of organ Sympathetic (thoracolumbar) division preganglionic cell bodies in thoracic and first 2 lumbar segments of spinal cord Ganglia trunk (chain) ganglia near vertebral bodies prevertebral ganglia near large blood vessel in gut (celiac, superior mesenteric, inferior mesenteric) Principles of Human Anatomy and Physiology, 11e

Autonomic Plexuses These are tangled networks of sympathetic and parasympathetic neurons (Figure 15.4) which lie along major arteries. Major autonomic plexuses include cardiac, pulmonary, celiac, superior mesenteric, inferior mesenteric, renal and hypogastric Principles of Human Anatomy and Physiology, 11e

Sympathetic Division Preganglionic cell bodies in lateral horns of spinal cord T1-L2 Preganglionic axons pass through ventral roots to white rami communicantes to sympathetic chain ganglia Four routes possible Spinal nerves Sympathetic nerves Splanchnic nerves Innervation to adrenal gland

Routes by Sympathetic Axons

Parasympathetic Division Preganglionic cell bodies in nuclei of brainstem or lateral parts of spinal cord gray matter from S2-S4 Preganglionic axons from brain pass to ganglia through cranial nerves Preganglionic axons from sacral region pass through pelvic nerves to ganglia Preganglionic axons pass to terminal ganglia within wall of or near organ innervated

Enteric Nervous System Consists of nerve plexuses within wall of digestive tract Sources Sensory neurons that connect the digestive tract to CNS ANS motor neurons that connect CNS to digestive tract Enteric neuron which are confined to enteric plexuses

Distribution of ANS Fibers Sympathetic axons reach organs through Spinal nerves Head and neck nerve plexuses Thoracic nerve plexuses Abdominopelvic nerve plexuses Parasympathetic axons reach organs through Cranial nerves Pelvic nerves

Physiology of ANS Neurotransmitters Receptors Acetylcholine released by cholinergic neruons Norepinephrine released by adrenergic neurons Receptors Cholinergic Nicotinic and muscarinic Adrenergic Alpha and beta receptors

Location of ANS Receptors

Regulation of ANS Autonomic reflexes control most of activity of visceral organs, glands, and blood vessels Autonomic reflex activity influenced by hypothalamus and higher brain centers Sympathetic and parasympathetic divisions influence activities of enteric nervous system through autonomic reflexes Enteric nervous system can function independently of CNS through local reflexes

Autonomic Reflexes

Influence of Brain on Autonomic Functions

Functional Generalizations of ANS Stimulatory versus inhibitory effects Both divisions of ANS Dual innervation Most organs innervated by both Either division alone or both working together can coordinate activities of different structures Sympathetic produces more generalized effects Prepares body for physical activity or flight-or-fight response Parasympathetic more important for resting conditions SLUDD: Salivation, lacrimation, urination, digestion, defecation

“Fight-or-Flight” Responses Increased heart rate and force Blood vessel dilation in skeletal and cardiac muscles Dilation of air passageways Energy sources availability increased Glycogen to glucose Fat cells break down triglycerides Muscles generate heat, body temperature increases Sweat gland activity increases Decrease in nonessential organ activities