Comparison of sns and ans autonomic means without

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1. Comparison of SNS and ANS. Autonomic means without conscious control. The autonomic nervous system (ANS) is involved in the unconscious regulation of visceral functions (function of internal organs) such as heart, intestine etc that are critical for maintaining homeostasis in the body. At end of last chapter you learned about somatic nervous system (SNS). A quick comparison between the two before we look at the ANS in more detail (Please also see Table 15.1on page 579) Somatic Nervous System Autonomic Nervous System Effectors – Skeletal muscles Effectors – Smooth, Cardiac muscles, and glands Mostly Conscious (voluntary) regulation Unconscious (Involuntary) regulation Excitatory action – skeletal muscle contracts Excitatory and Inhibitory action on target tissues Single synapse Two synapses – preganglionic and ganglionic neurons Neurotransmitter- Acetylcholine Neurotransmitter - Acetycholine by preganglionic neurons and ACh or norepinephrine/epinephrine by postganglionic neurons Seldom effects long term survival Critical for homeostasis and survival 2) Autonomic Nervous System (ANS). Motor neurons of ANSregulate smooth muscle, cardiac muscle, and glands. Involve a network of two neurons, preganglionic neuronsand ganglionic neurons.Preganglionic neuronGanglionic neuron First neuron in pathway Second neuron in pathway Cell body in the CNSCell body located outside CNS in peripheral autonomic ganglionAxons of preganglionic neurons (preganglionic fibers) leave CNS as cranial or spinal nerve and synapse on ganglionic neurons Axons of ganglionic neurons (called postganglionic fibers) extends to effectors: smooth muscle, cardiac muscle and glands Axons typically myelinated Axons typically unmyelinated Always releases acetylcholine(Ach)at synapse: Cholinergic neuronReleases Achor norepinephrine(NE)or epinephrine(E)at synapses Note: Neurons that release the acetylcholine (Ach) at synapses are called cholinergic neurons. Neurons that release the norepinephrine (NE) or epinephrine (E) at synapses are called adrenergic neurons. The type of receptorpresent on the target cell will dictate the response of the cell to the neurotransmitter.3) Divisions of the ANS Parasympathetic Division Sympathetic DivisionAlso called the craniosacral division Also called the thoracolumbar division Rest & Digest” response "Fight or Flight" response Innervates only specific visceral structures Widespread impact; Reaches organs and tissues throughout body Preganglionic neurons (craniosacral)Preganglionic neurons (thoracolumbar)
5 Most organs aredually innervated, meaning they are under the control of both the sympathetic and parasympathetic divisions of the ANS. In general,they will have opposing effects; If the sympathetic division causes excitation, the parasympathetic causes inhibition. For example, sympathetic division increases heart rate, parasympathetic division decreases heart rate; sympathetic division dilates pupil, parasympathetic constricts pupil.

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Term
Spring
Professor
Beatrix
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