17 The Nervous System: Autonomic Nervous System
Introduction The autonomic nervous system: Functions outside of our conscious awareness Makes routine adjustments in our body s systems The autonomic nervous system: Regulates body temperature Coordinates cardiovascular, respiratory, digestive, excretory, and reproductive functions
Subdivisions of the ANS The autonomic nervous system consists of two major subdivisions Sympathetic division Also called the thoracolumbar division Known as the fight or flight system Parasympathetic division Also called the craniosacral division Known as the rest and digest system
A Comparison of the Somatic and Autonomic Nervous Systems The autonomic nervous system differs from the somatic nervous system in the arrangement of the neurons connecting the central nervous system to the effector organs. Visceral motor neurons in the CNS, known as preganglionic neurons, send their axons, called preganglionic fibers, to synapse on ganglionic neurons, whose cell bodies are located outside the CNS, in autonomic ganglia. Axons from the ganglionic neurons are called postganglionic fibers because they carry impulses away from the ganglion. Postganglionic fibers innervate peripheral tissues and organs, such as cardiac and smooth muscle, adipose tissue, and glands.
Subdivisions of the ANS Sympathetic division Thoracic and upper lumbar nerves synapse in ganglia near the spinal cord Sympathetic activation results in: Increased metabolism and alertness Parasympathetic division Synapses are located near the target organ Parasympathetic activation results in: Energy conservation
The Sympathetic Division Sympathetic division consists of: Preganglionic neurons between T 1 and L 2 Two types of ganglionic neurons near the vertebral columns: sympathetic chain ganglia also called paravertebral ganglia collateral ganglia also known as prevertebral ganglia Specialized neurons in the interior of the suprarenal gland
Figure 17.2 Organization of the Sympathetic Division of the ANS Sympathetic Division of ANS Innervation by postganglionic fibers Ganglionic Neurons Target Organs KEY Preganglionic Neurons Lateral gray horns of spinal segments T 1 L 2 Preganglionic fibers Postganglionic fibers Hormones released into circulation Sympathetic chain ganglia (paired) Collateral ganglia (unpaired) Suprarenal medullae (paired) Through release of hormones into the circulation Visceral effectors in thoracic cavity, head, body wall, and limbs Visceral effectors in abdominopelvic cavity Organs and systems throughout body
Sympathetic division of the ANS Sympathetic division All preganglionic fibers release acetylcholine (Ach) Most postganglionic fibers release norepinephrine (adrenergic) stimulatory effects
The Sympathetic Division Effects of Sympathetic Chain Ganglia Reduction of circulation to the skin More circulation to skeletal muscles Stimulates more energy production by skeletal muscles Releases stored adipose Stimulation of arrector pili muscles Dilation of pupils Increased heart rate Dilation of respiratory tubes
The Sympathetic Division Summary of the Sympathetic Division Consists of parallel chains on either side of the spinal cord Preganglionic fibers are short and extend from the spinal cord to the sympathetic chain Postganglionic fibers are long and extend from the spinal cord to the body organs All preganglionic neurons release Ach Most postganglionic neurons release norepinephrine
Figure 17.4 Anatomical Distribution of Sympathetic Postganglionic Fibers Eye PONS Salivary glands Superior Sympathetic nerves Cervical sympathetic ganglia Middle Inferior Gray rami to spinal nerves T 1 T 1 T 2 T 2 T 3 T 3 Greater splanchnic nerve Cardiac and pulmonary plexuses Heart Lung T 4 T 4 Celiac ganglion T 5 T 5 T 6 T 6 T 7 T 7 Superior mesenteric ganglion Liver and gallbladder T 8 T 8 Stomach T 9 T 9 T 10 T 10 T 11 T 11 Lesser splanchnic nerve Spleen Pancreas Postganglionic fibers to spinal nerves (innervating skin, blood vessels, sweat glands, arrector pili muscles, adipose tissue) T 12 T 12 L 1 L 1 L 2 L 2 L 3 L 3 L 4 L 4 Lumbar splanchnic nerves Inferior mesenteric ganglion Large intestine Small intestine Sympathetic chain ganglia L 5 L 5 S 1 S 1 S 2 S 2 S 3 S 3 S 4 S 4 S 5 S 5 Sacral splanchnic nerves Suprarenal medulla Kidney Spinal cord KEY Preganglionic neurons Ganglionic neurons Coccygeal ganglia (Co 1 ) fused together (ganglion impar) Uterus Ovary Penis Scrotum Urinary bladder
The Parasympathetic Division Parasympathetic Division Preganglionic neurons are in the brain stem and sacral segments Parasympathetic division is more localized and specific as compared to the sympathetic division Postganglionic neurons are near (terminal) the target organ or within (intramural) the target organ
Parasympathetic division of the ANS Parasympathetic division All preganglionic fibers release acetylcholine Postganglionic fibers release acetylcholine (cholinergic) inhibitory effects
The Parasympathetic Division Effects of the Parasympathetic Division Pupil constriction Secretion of digestive enzymes from digestive glands Increased smooth muscle activity of the digestive system Stimulation and coordination of defecation Contraction of the urinary bladder Constriction of respiratory passages Reduced heart rate Sexual arousal
Figure 17.8 Autonomic Distribution of the Parasympathetic Output Pterygopalatine ganglion N III Lacrimal gland Eye PONS Ciliary ganglion N VII N IX Submandibular ganglion Salivary glands Otic ganglion N X (Vagus) Heart Lungs Autonomic plexuses (see Figure 17.9) Liver and gallbladder Stomach Spleen Pancreas Large intestine Pelvic nerves Small intestine Rectum Spinal cord S 2 S 3 Kidney S 4 KEY Preganglionic neurons Ganglionic neurons Uterus Ovary Penis Scrotum Urinary bladder
Relationships between the Sympathetic and Parasympathetic Divisions Sympathetic Widespread stimulatory effect on visceral organs Parasympathetic Modifies/inhibits the activity of structures innervated by specific cranial nerves and pelvic nerves Most vital organs are innervated by both the sympathetic and parasympathetic nerves The two often oppose (antagonistic) each other
Figure 17.10 A Comparison of the Sympathetic and Parasympathetic Divisions Sympathetic Parasympathetic CNS Preganglionic neuron PNS Sympathetic ganglion or Preganglionic fiber Ganglionic neurons KEY Neurotransmitters Acetylcholine Norepinephrine Epinephrine Circulatory system Postganglionic fiber Parasympathetic ganglion TARGET
Relationships between the Sympathetic and Parasympathetic Divisions Dual Innervation The parasympathetic fibers accompany the sympathetic fibers to the target organ The parasympathetic and sympathetic fibers mingle together forming peripheral autonomic plexuses
Visceral Reflexes All are polysynaptic Reflexes can be: Long reflexes Short reflexes
Visceral Reflexes Long Reflexes Visceral sensory neurons go to the CNS via the dorsal roots There are interneurons within the CNS Information is interpreted in the spinal cord or brain ANS sends motor commands to the visceral organs
Visceral Reflexes Short Reflexes Sensory nerve impulses go to the ganglionic neurons Motor commands are distributed by the postganglionic fibers Impulses bypass the CNS
Levels of Somatic Motor Control Summary of somatic motor control Thalamus Controls reflexes associated with visual and auditory stimuli Hypothalamus Responds to hunger, thirst, and sexual activity Pons Regulates the rhythmic breathing patterns
Levels of Somatic Motor Control Summary of somatic motor control Medulla oblongata Alters the breathing patterns Brain stem Controls simple reflexes Spinal cord Controls simple reflexes