Autonomic Nervous System

Main input from autonomic sensory neurons (most associated with interoceptors) monitor internal environment- not conscious example- chemoreceptors for CO2 level

Autonomic motor neurons regulate visceral activities (increase or decrease) function somewhat even if nerve supply damaged example- heart beat difficult to consciously control (i.e. lie detector test, yoga)

See figure 15.1 Most autonomic motor pathways consist of two motor neurons in series through autonomic ganglion (second not myelinated) preganglionic (CNS) and postganglionic (PNS) some extend to adrenal medullae- hormones released

The preganglionic motor neurons of the sympathetic system arise in the spinal cord. They pass into sympathetic ganglia which are organized into two chains that run parallel to and on either side of the spinal cord.

The main nerves of the parasympathetic system is the tenth cranial nerve, the vagus nerve. It originates in the medulla oblongata. Other preganglionic parasympathetic neurons also extend from the brain as well as from the lower tip of the spinal cord.

Anatomy of autonomic motor pathways: Three types of autonomic ganglia sympathetic trunk ganglia- vertical row on either side of vertebral canal sympathetic division innervate organs above diaphragm prevertebral ganglia- anterior to vertebral canal innervate organs below diaphragm terminal ganglia- close to or actually in wall of organ (longer) parasympathetic division Postganglionic neurons- one sympathetic ganglia can synapse with 20+ postganglionic neurons (effect much of body simultaneously)

Autonomic plexuses tangled networks of axons from sympathetic and parasympathetic neurons cardiac (heart), pulmonary (lungs), celiac or solar (liver, gallbladder, stomach, pancreas, spleen, kidneys, testes, ovaries), superior mesenteric (small and large intestines), inferior mesenteric (large intestine), renal (kidneys and ureters)

ANS neurotransmitters and Receptors cholinergic- release acetylcholine (Ach) all preganglionic neurons, parasympathetic postganglionic neurons, some sympathetic postganglionic (sweat glands) nicotinic and muscarinic receptors- effects brief adrenergic (release norepinephrine/ NE) most sympathetic postganglionic alpha and beta receptors- longer lasting agonists can activate receptors, antagonists block receptors

Physiological effects of ANS- tables 15.3 and 15.4 autonomic tone- balance between sym. and parasym.- regulated by hypothalamus Sympathetic dominates during physical or emotional stress (rapid ATP production)--- flight or fight response--- “E situations” (exercise, emergency, excitement, embarassment) Parasympathetic dominates “rest and digest” activities- conserve and restore energy --- SLUDD (salivation, lacrimation, urination, digestion, defecation)

Autonomic reflexes- controlled conditions (i.e. blood pressure) reflex arc: receptor- sensory neuron- integrating center- motor neuron- effector hypothalamus major control center