The Autonomic Nervous System

The Autonomic Nervous SystemThe ANS (Autonomic Nervous System) vs. somatic motor system possesses both CNS & PNS componentscontrols involuntary effectors (smooth muscle, cardiac muscle and glandular tissues)divided into sympathetic (throracolumbar) and parasympathetic (craniosacral) divisions; presynaptic vs. postsynaptic neurons

Parasympathetic (craniosacral) division with preganglionic neuronal cell bodies in nuclei of CN's III, VII, IX, and X and spinal cord levels S2, S3, & S4 and postganglionic neuronal cell bodies in parasympathetic terminal or intramural ganglia. Ach is released from both pre- & postganglionic nerve terminals Presynaptic neurons - relatively long - terminate in ganglia (Ach) Postsynaptic neurons - relatively short - terminate in effectors (Ach)

Sympathetic (thoracolumbar) division with preganglionic (or presynaptic) neuronal cell bodies in spinal cord intermedio-lateral cell column (T1 L2) and postganglionic (or postsynaptic) neuronal cell bodies in autonomic ganglia (also known as sympathetic chain or paravertebral ganglia)

Prevertebral ganglia (or collateral ganglia) also exist which contain postganglionic nerve cell bodies which synapse with preganglionic neurons of splanchnic nerves. These preganglionic neurons have cell bodies in the T1 to L2 spinal cord with axons that travel through the sympathetic chain ganglia WITHOUT SYNAPSING to form the greater splanchnic nerve (which synapses with postganglionics primarily found in the celiac ganglion), the lesser splanchnic nerve (which synapses with postganglionics primarily found in the superior mesenteric ganglion) and the least splanchnic nerve (which synapses with postganglionics found in the inferior mesenteric ganglion). The sympathetic (fight or flight) system possesses preganglionic neurons that release acetylcholine (Ach) within the ganglia and most postganglionic neurons that release norepinephrine (NEpi) at involuntary effectors.Presynaptic neurons - relatively short - terminate in ganglia (Ach)Postsynaptic neurons - relatively long - terminate at effectors (most release NE, a few release Ach)

Dual innervation - for most involuntary effectors except sweat glands, vascular smooth muscle, and arrector pili muscles (which receive sympathetic only)

An example of dual innervation is observed with pupillary function.

CNS Control of the ANS

Development of the ANS

Autonomic Reflexes

CNS controls on the ANSMedulla oblongata- most directly controls

ANS. Almost all autonomic responses can be provoked from stimulating this area- including circulatory, respiratory, urinary, reproductive, and digestive systems through vagus nerve.

Hypothalamus- control and integration center for the ANS, including endocrine controls. Centers that regulate aggression, eating behavior and sexual behavior are here, as well as thirst and body heat regulation.

• Limbic system- group of fiber tracts and nuclei that form a ring around the brain stem, includes cingulate gyrus, hypothalamus, fornix, hippocampus, and amygdaloid nucleus. Rhinencephalon= smell brain.• ANS centers involved in fear, anger, sex, hunger, and short-term memory. Circuits are responsible for visceral responses such as blushing, pallor, fainting, and “butterflies in the stomach”.• Activity of the limbic system is modulated by the cerebellum (motion sickness- nausea, sweating, CV changes) and frontal and temporal lobes with emotion and personality.