The Autonomic Nervous System and Visceral Sensory Neurons 15 PART 1 The Autonomic Nervous System and Visceral Sensory Neurons

The ANS and Visceral Sensory Neurons The ANS—a system of motor neurons Innervates Smooth muscle Cardiac muscle Glands

The ANS and Visceral Sensory Neurons The ANS—a system of motor neurons Regulates visceral functions Heart rate Blood pressure Digestion Urination The ANS is the General visceral motor division of the PNS

Central nervous system (CNS) Peripheral nervous system (PNS) Figure 15.1 Place of the autonomic nervous system (ANS) and visceral sensory components in the structural organization of the nervous system. Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Motor (efferent) division Somatic sensory Visceral sensory Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division 4

Comparison of Autonomic and Somatic Motor Systems One motor neuron extends from the CNS to skeletal muscle Axons are well myelinated, conduct impulses rapidly

Comparison of Autonomic and Somatic Motor Systems Autonomic nervous system Chain of two motor neurons Preganglionic neuron Postganglionic neuron Conduction is slower than somatic nervous system because Axons are thinly myelinated or nonmyelinated Motor neuron synapses in a ganglion

Figure 15.2 Comparing Somatic Motor and Autonomic Innervation 7

Divisions of the Autonomic Nervous System Sympathetic and parasympathetic divisions Chains of two motor neurons Innervate mostly the same structures Cause opposite effects Sympathetic division mobilizes the body during extreme situations Fear, rage, exercise Parasympathetic division controls routine maintenance functions

Divisions of the Autonomic Nervous System Sympathetic—“fight or flight” Activated during EXTREME situations Exercise Excitement Emergencies

Divisions of the Autonomic Nervous System All sympathetic responses help us respond to dangerous situations Increase heart rate and breathing rate Increase blood and oxygen to skeletal muscles Vasoconstriction of other blood vessels Dilate pupils and bronchioles Inhibit motility of the digestive tract and urinary tracts

Divisions of the Autonomic Nervous System Parasympathetic division- “Digest and rest” Active when the body is at rest Concerned with conserving energy Directs “housekeeping” activities Digestion Elimination of feces and urine Heart rate, blood pressure, respiration at low-normal levels

Figure 15.3 Overview of the subdivisions of the ANS. Parasympathetic Sympathetic Eye (constricts pupil)  Eye (dilates pupil)  Brain stem  Salivary glands Skin*  Cranial Salivary glands  Sympathetic ganglia  Heart Cervical Lungs (dilates airways)  Lungs (constricts airways)  T1 Heart  Stomach  Thoracic  Stomach Pancreas  Liver   Pancreas L1 Gall- bladder  Gall- bladder  Lumbar Adrenal gland   Bladder Bladder  Genitals (erection)  Genitals (ejaculation)  Sacral  stimulatory effect  inhibitory effect 12

Issue from different regions of the CNS Divisions of the ANS Issue from different regions of the CNS Sympathetic Also called the thoracolumbar division Parasympathetic Also called the craniosacral division

Length of postganglionic fibers Divisions of the ANS Length of postganglionic fibers Sympathetic—long postganglionic fibers Parasympathetic—short postganglionic fibers Branching of fibers Sympathetic fibers—highly branched Influence many organs at once Parasympathetic fibers —few branches Localized effect

Neurotransmitter released by postganglionic axons Divisions of the ANS Neurotransmitter released by postganglionic axons Sympathetic Most release norepinephrine (adrenergic) Parasympathetic Release acetylcholine (cholinergic)

Table 15.1 Anatomical and Physiological Differences Between the Parasympathetic and Sympathetic Divisions 16

The Parasympathetic Division Cranial outflow Originates from the brain Innervates Organs of the head, neck, thorax, and abdomen Sacral outflow Innervation supplies Remaining abdominal and pelvic organs

Figure 15.4 Parasympathetic division of the ANS. (1 of 2) CN III Ciliary ganglion Eye Lacrimal gland CN VII Pterygopalatine ganglion Nasal mucosa CN IX CN X Submandibular ganglion Submandibular and sublingual glands Otic ganglion Parotid gland Heart Cardiac and pulmonary plexuses Lung Preganglionic Postganglionic CN Cranial nerve 18

Figure 15.4 Parasympathetic division of the ANS. (2 of 2) Liver and gallbladder Celiac plexus Stomach Pancreas S2 Large intestine S4 Pelvic splanchnic nerves Small intestine Inferior hypogastric plexus Rectum Urinary bladder and ureters Genitalia (penis, clitoris, and vagina) Preganglionic Postganglionic CN Cranial nerve 19

Cranial Outflow (Parasympathetic) Preganglionic fibers run via Oculomotor nerve (III) Facial nerve (VII) Glossopharyngeal nerve (IX) Vagus nerve (X) Cell bodies of preganglionic neurons located in motor cranial nerve nuclei in gray matter of the brain stem

Outflow via the Oculomotor Nerve (III) Parasympathetic fibers innervate smooth muscles in the eye Cause pupil constriction Preganglionic cell bodies Located in the oculomotor nucleus in the midbrain Postganglionic cell bodies Lie in the ciliary ganglion

Outflow via the Facial Nerve (VII) Parasympathetic fibers stimulate secretion of glands in the head Lacrimal nucleus Located in the pons Synapse in the pterygopalatine ganglion Superior salivatory nucleus Synapse in the submandibular ganglion

Outflow via the Glossopharyngeal Nerve (IX) Parasympathetic fibers Stimulate secretion of glands in the head Lacrimal nucleus—located in the pons Synapse in the pterygopalatine ganglion Superior salivatory nucleus—located in the pons Synapse in the submandibular ganglion

Outflow via the Vagus Nerve (X) Fibers innervate visceral organs of the thorax and most of the abdomen Stimulates: Digestion, reduction in heart rate, and reduction in blood pressure Preganglionic cell bodies Located in dorsal motor nucleus in the medulla Postganglionic neurons Confined within the walls of organs being innervated Cell bodies form intramural ganglia

Sends branches through Path of the Vagus Nerve Sends branches through Autonomic nerve plexuses Cardiac plexus Pulmonary plexus Esophageal plexus Celiac plexus Superior mesenteric plexus

Figure 15.5 Autonomic nerves, plexuses, and ganglia. Superior cervical ganglion Left vagus nerve Cardiac branches of the vagus Middle cervical ganglion Trachea Stellate ganglion Thoracic spinal nerves (ventral rami) Sympathetic cardiac nerves Cardiac plexus Aortic arch Pulmonary plexus on the bronchus Sympathetic trunk ganglia Aorta Esophagus Vagus nerve Thoracic splanchnic nerves Esophageal plexus Diaphragm Stomach with vagus nerve Adrenal (suprarenal) gland Celiac ganglion and plexus Superior mesenteric ganglion and plexus Kidney Aortic plexus Inferior mesenteric ganglion and plexus Lumbar and sacral splanchnic nerves Superior hypogastric plexus Inferior hypogastric (pelvic) plexus Pelvic sympathetic trunk 26

Innervates organs of the pelvis and lower abdomen Sacral Outflow Emerges from S2 to S4 Innervates organs of the pelvis and lower abdomen Preganglionic cell bodies Located in visceral motor region of spinal gray matter Axons run in ventral roots to ventral rami Form pelvic splanchnic nerves Run through the inferior hypogastric plexus

The Sympathetic Division Basic organization Issues from T1 to L2 Preganglionic fibers form the lateral gray horn Supplies visceral organs in internal body cavities and structures of superficial body regions Contains more ganglia than the parasympathetic division

Sympathetic Trunk Ganglia Located on both sides of the vertebral column Linked by short nerves into sympathetic trunks Sympathetic trunk ganglia are also called Chain ganglia Paravertebral ganglia

Sympathetic Trunk Ganglia Joined to ventral rami Fusion of ganglia  fewer ganglia than spinal nerves Fusion of ganglia most apparent in the cervical region

Figure 15.6 The sympathetic trunk, thoracic region. Spinal cord Dorsal root Ventral root Rib Phrenic nerve Sympathetic trunk ganglion Body of thoracic vertebra Sympathetic trunk Esophageal plexus Ventral ramus of spinal nerve Azygos vein Thoracic aorta Diaphragm Thoracic splanchnic nerves Location of the sympathetic trunk Dissection of posterior thoracic wall, right side 31

Differ from sympathetic trunk ganglia in three ways Collateral Ganglia Differ from sympathetic trunk ganglia in three ways Unpaired, not segmentally arranged Occur only in abdomen and pelvis Lie anterior to the vertebral column Main ganglia Celiac, superior mesenteric, inferior mesenteric, and inferior hypogastric ganglia

Sympathetic Pathways Preganglionic neurons in the thoracolumbar spinal cord send motor axons through Adjacent ventral root into Spinal nerve, then to The associated sympathetic trunk ganglion

Sympathetic Pathways to the Body Periphery Innervate Sweat glands Arrector pili muscles Peripheral blood vessels

Sympathetic Pathways to the Head Preganglionic fibers originate in spinal cord at T1–T4 Fibers ascend in the sympathetic trunk Synapse in superior cervical ganglion

Postganglionic fibers associate with large arteries Pathways to the Head Postganglionic fibers associate with large arteries Carried by these structures to Glands Smooth muscle Vessels throughout the head

Pathways to Thoracic Organs Preganglionic fibers originate at spinal levels T1–T6 Some fibers synapse in nearest sympathetic trunk ganglion Postganglionic fibers run directly to the organ supplied

Sympathetic Pathways to Thoracic Organs Sympathetic fibers to heart have a less direct route Functions Increase heart rate Dilate bronchioles Dilate blood vessels to the heart wall Inhibit muscles and glands in the esophagus and digestive system

Figure 15.8 Sympathetic division of the ANS. Eye Lacrimal gland Pons Nasal mucosa Sympathetic trunk (chain) ganglia Blood vessels; skin (arrector pili muscles and sweat glands) Superior cervical ganglion Salivary glands Middle cervical ganglion Heart Inferior cervical ganglion Cardiac and pulmonary plexuses Lung T1 Greater splanchnic nerve Lesser splanchnic nerve Liver and gallbladder Celiac ganglion L2 Stomach White rami communicantes Superior mesenteric ganglion Spleen Adrenal medulla Sacral splanchnic nerves Kidney Lumbar splanchnic nerves Inferior mesenteric ganglion Small intestine Large intestine Rectum Preganglionic Postganglionic Genitalia (uterus, vagina, and penis) and urinary bladder 39

Pathways to Abdominal Organs Preganglionic fibers originate in spinal cord (T5–L2) Pass through adjacent sympathetic trunk ganglia Inhibit activity of muscles and glands in visceral organs

Pathways to the Pelvic Organs Preganglionic fibers originate in the spinal cord from T10 to L2 Fibers descend in the sympathetic trunk to lumbar and sacral ganglia

Pathways to the Pelvic Organs Other preganglionic fibers pass directly to autonomic plexuses and synapse in collateral ganglia Postganglionic fibers go from these plexuses to the Bladder, reproductive organs, and distal large intestine

The Role of the Adrenal Medulla in the Sympathetic Division Major organ of the sympathetic nervous system Constitutes largest sympathetic ganglia Secretes great quantities of norepinephrine and epinephrine (adrenaline) Stimulated to secrete by preganglionic sympathetic fibers

Figure 15.9 Sympathetic innervation of the adrenal medulla. Sympathetic trunk Ventral root Spinal cord: T8–L1 Thoracic splanchnic nerves Kidney Adrenal gland Adrenal medulla Epinephrine and norepinephrine Capillary Adrenal medulla cells 44

Table 15.2 Effects of the Parasympathetic and Sympathetic Divisions on Various Organs (1 of 3) 45

Table 15.2 Effects of the Parasympathetic and Sympathetic Divisions on Various Organs (2 of 3) 46

Table 15.2 Effects of the Parasympathetic and Sympathetic Divisions on Various Organs (3 of 3) 47

Visceral Sensory Neurons General visceral sensory neurons monitor these sensations within visceral organs Stretch Temperature Chemical changes Irritation Cell bodies are located in Dorsal root ganglion

Visceral Sensory Neurons Visceral pain No pain results when visceral organs are cut Visceral pain results from chemical irritation or inflammation Visceral pain often perceived to be of somatic origin Phenomenon of referred pain

Visceral sensory and autonomic neurons Visceral Reflexes Visceral sensory and autonomic neurons Participate in visceral reflex arcs Defecation reflex Micturition reflex Some are simple spinal reflexes Others do not involve the CNS Strictly peripheral reflexes

Central Control of the ANS ANS is not under direct voluntary control Activities regulated by CNS Brain stem Spinal cord Hypothalamus Amygdaloid body Cerebral cortex

Figure 15.13 Levels of ANS control. Communication at subconscious level Cerebral cortex (frontal lobe) Limbic system (emotional input) Hypothalamus The “boss”: Overall integration of ANS Brain stem (reticular formation, etc.) Regulates pupil size, heart, blood pressure, airflow, salivation, etc. Spinal cord Reflexes for urination, defecation, erection, and ejaculation 52

Control by the Brain Stem and Spinal Cord Reticular formation exerts most direct influence Medulla oblongata

Control by the Hypothalamus and Amygdala Hypothalamus—the main integration center of the ANS Direct parasympathetic functions and Direct sympathetic functions Amygdaloid body Main limbic region for emotions