Transcript Chapter 14
Chapter 14 Autonomic Nervous System System of motor neurons innervating smooth and cardiac muscle and glands Autonomic nerves make adjustments to many changes identified by the sensory division of the PNS ANS differs from the SNS in: Their effectors SNS innervates skeletal muscle and ANS innervates smooth and cardiac muscle and glands Efferent pathways SNS - cell bodies of the motor neuron are in the CNS, and their axons extend in spinal nerves all the way to skeletal muscles ANS - two neuron chain The cell body of the first neuron (preganglionic neuron) resides in the brain or spinal cord Its axon (preganglionic axon) synapses with the second motor neuron (ganglionic neuron) in an autonomic ganglion outside the CNS The axon of the ganglionic neuron (postganglionic axon) extends to the effector organ. Synapse in a ganglia Parasympathetic: intramural ganglia: close to the effector organ Sympathetic: chain (paraverterbral) ganglia Target organ responses - neurotransmitter effects SNS - acetylcholine released at their synapse ANS - norepinephrine, epinephrine (adrenergic) and acetylcholine (cholinergic) Divisions of the ANS Parasympathetic and sympathetic Action via ANS is by dual innervation (divisions counterbalance each other's activities) Parasympathetic division in general is most active in nonstressful situations - rest and digest Sympathetic (stress) division in general is most active in emergency or threatening situations - "fight-or-flight" Parasympathetic: - pupils constrict - stimulates salivary, lacrimal and pancreas glands - decrease heart rate - causes contraction and emptying of hollow organs: bladder, gallbladder, stomach, intestines (peristalsis) - vasodilation of penis (erection) and clitoris - no effect on blood vessels Sympathetic: - dilates pupils - inhibits secretion of glands - stimulates sweating - stimulates arrector pili - stimulates medulla of adrenal gland to secrete epi/norepinephrine - increases heart rate - decreases digestive processes - decreases urine output - causes ejaculation - stimulates glycogenolysis in liver (glucose release) - blood vessel constriction/dilation and blood coagulation - bronchiole dilation Parasympathetic Craniosacral division Cranial: CN nerves III, VII, IX and X CN III (Oculomotor): Preganglionic fibers: from oculomotor nuclei in the midbrain synapses in the ciliary ganglion (in eye) Postganglionic fiber: innervates smooth muscle of eye Pupil constriction and lens movement to cause focusing Facial nerve (VII) Preganglionic fibers: from lacrimal nuclei in the pons synapses in the pterygopalatine ganglia Postganglionic fiber: innervates lacrimal glands of eye Lubrication of eye and tear formation Preganglionic fibers: from superior salivatory nuclei in the pons synapses in the submandibular ganglia Postganglionic fibers: innervate submandibular and sublingual salivary glands Production of saliva and secretion of salivary enzymes Glossopharyngeal nerve (IX) Preganglionic fibers: from the inferior salivary nuclei in the medulla synapses in the otic ganglia Postganglionic fibers: innervate the parotid salivary gland Vagus nerve (X) “wanderer” Preganglionic fibers from the dorsal motor nuclei (nucleus ambiguus) of the medulla synapses in terminal ganglia located within the walls of the target organ (intramural) Intramural ganglia ....effects: Heart -decreases/steadies heart rate and constricts coronary veins Lung - constricts bronchioles Gall bladder - expel bile Stomach - stimulates secretion of enzymes Intestines - increase motility (peristalsis) and relaxes sphincters Sacral Outflow Preganglionic fibers from lateral gray matter of spinal cord in segments S2-S4 synapse in terminal ganglia within walls of the target organ Intramural ganglia....effects: Distal large intestines - relaxes sphincters Bladder - contraction of smooth muscle of bladder wall; relaxes urethral sphincter promotes voiding Genitalia - causes penile and clitoral erection Sympathetic Nervous System Thoracolumbar division All preganglionic fibers of sympathetic division arise from cell bodies of preganglionic neurons located in lateral horn of the spinal cord segments T1-L2 These fibers exit the ventral roots of spinal nerves and continue through branches called white rami communicantes before entering the paravertebral sympathetic ganglia located in chains along side the spine. These ganglia make up the sympathetic trunk Once in the paravertebral ganglia the preganglionic fiber can: 1- Synapse with a postganglionic neuron within the same ganglion . 2- Ascend/descend within sympathetic trunk to synapse with another paravertebral ganglion. 3- Pass through the ganglion (splanchnic nerve) and emerge from the sympathetic chain without synapsing until they reach a collateral ganglia (prevertebral) Preganglionic fibers innervating the head and neck arise from spinal cord levels T1-T6. These fibers ascend through the sympathetic trunk and synpase with postganglionic fibers in the cervical ganglia - superior - middle - inferior Superior cervical ganglion: - Stimulates dilator muscles of irises - Inhibits nasal and salivary glands - Stimulates copious sweating - Stimulates arrector pili muscle to contract - Causes blood vessel vasodilation Middle cervical ganglia - innervates heart and skin Inferior cervical ganglia (stellate ganglion) innervates heart, aorta, dilates bronchioles, constrict esophageal sphincter. Synapses in Collateral Sympathetic Ganglion: Preganglionic fibers of T5-L2 synapse in prevertebral ganglia. Fibers enter and leave without synapsing and form several nerves collectively called splanchnic nerves (greater, lesser, and lumbar) Splanchnic nerves synapse at abdominal aortic plexus that clings to surface of abdominal aorta Synapses occur at ganglia of plexus: Greater splanchnic nerve Celiac ganglion - innervates stomach (decrease muscle activity/constricts pyloric sphincter), adrenal medulla (secretes epinephrine/norepinephrine), liver (epinephrine stimulates liver to release glucose), kidney (vasoconstriction, decrease urine output), intestine (decrease smooth muscle activity) Lesser splanchnic nerve Lumbar splanchnic nerve Superior mesenteric (via celiac) ganglion innervates small intestine Inferior mesenteric ganglion - innervates large intestine Lumbar splanchnic nerve Hypogastric ganglion - innervates bladder and urethra (causes relaxation of smooth muscle of bladder wall and constricts urethral sphincter/inhibits voiding), genitalia (causes ejaculation in males and vaginal contractions in females)