Test 3 Study Guide Autonomic Nervous System The ANS consists of motor neurons that o Innervate smooth and cardiac muscle and glands o Make adjustments to ensure optimal support for body control o Operate via subconscious control o Have viscera as most of their effectors The ANS differs from the SNS in 3 different ways 1 Effectors cardiac muscle smooth muscle glands 2 Efferent pathways axons of the ANS are a two neuron chain a Preganglionic first neuron has a lightly myelinated axon b Postganglionic second neuron extends to an effector organ 3 Target organ responses There are two divisions of the Autonomic Nervous System 1 Parasympathetic innervates visceral organs and decreases heart and respiratory rate allowing for digestion and discarding of wastes 2 Sympathetic innervates visceral organs increases heart respiratory rate inhibits digestion and elimination These two divisions counterbalance the other s activity o Most body organs receive impulses from both the sympathetic and parasympathetic NS One stimulates an organ while the other decreases activity Neurotransmitters and Receptors Acetylcholine ACh and Norepinephrine NE are the two major NTs of the ANS o ACh is released by all pre ganglionic axons and all parasympathetic post ganglionic axons Cholinergic fibers ACh releasing fibers o the effect of ACh binding can be inhibitory or excitatory depending on the receptor type of the target organ NE can also be excitatory and inhibitory it also depends on the receptor type of the target organ o Adrenergic fibers NE releasing fibers Generally two types of adrenergic fibers and with each type having two or three subclasses o 1 2 1 2 3 Binding of NE to alpha receptors is stimulatory while binding to beta receptors is inhibitory Sympathetic Outflow From spinal cord segments T1 L2 Preganglionic fibers synapse in the paravertebral ganglia Fibers from T5 L2 form splanchnic nerves abdomen and synapse with collateral ganglia Postganglionic fibers innervate the numerous organs of the body The paravertebral ganglia form part of the sympathetic trunk or chain o Typically there are 23 ganglia 3 cervical 11 thoracic 4 lumbar 4 sacral and 1 coccygeal REMEMBER A GANGLION IS A MASS OF NERVE CELL BODIES Adrenal Medulla Fibers of the thoracic splanchnic nerve pass directly to the adrenal medulla the innermost part of the adrenal gland o Upon stimulation the adrenal medulla releases NE and EPI into the blood Role of the Sympathetic Division The sympathetic nervous system plays a role in the fight or flight system o Involves E activities exercise excitement emergency and embarrassment It also regulates functions that are NOT subject to parasympathetic influence o These include activity of adrenal medulla sweat glands kidneys and most blood THINK STRESS vessels The sympathetic division also promotes metabolic effects that are not reversed by the parasympathetic division o Increase metabolic rate of cells o Raises blood glucose levels o Mobilizes fat as an energy source Role of the Parasympathetic Division Involves D activities digestion defecation and diuresis o Its activity is illustrated in a person who relaxes after a meal Low BP HR and respiratory rate High gastrointestinal activity Skin is warm and pupils are constricted THINK AFTER LUNCH NAP Activation of parasympathetic division creates a few physiological effects o Increase in salivation urination digestion and defecation The balance of autonomic sympathetic parasympathetic tone is regulated by feedback loops between the spinal cord and brainstem with input from the limbic system and oversight by the hypothalamus The Endocrine System A collection of glands that release hormones throughout the body o Hormones metabolic function of other cells chemical substances secreted by cells into the blood that regulate the Chemistry of Hormones There are two main classes of hormones 1 Amino Acid based hormones a Amines thyroxine peptides and proteins 2 Steroids a Synthesized from cholesterol b Gonadal and adrenocortical hormones Mechanism of Hormone Action Hormone actions on target cell 1 Alter plasma membrane permeability of membrane potential by opening or closing ion channels 2 Stimulate synthesis of proteins or regulatory molecules 3 Activate or deactivate enzyme systems 4 5 Stimulate mitosis Induce secretory activity Two mechanisms depending on their chemical nature 1 Water soluble hormones all amino acid based except thyroid hormone a Cannot enter the target cell b Act on plasma membrane receptors c Coupled by G proteins to intracellular second messengers that mediate the target cell s response 2 Lipid soluble hormones steroids and thyroid hormone a Act on intracellular receptors that directly activate genes Hormone Receptor Is a protein to which a particular hormone binds to strongly Responds to several different hormones o Hormones circulate regularly but only activate cells referred to as target cells o Target cells must have specific receptors to which the hormone binds Target cell activation depends on three factors o Blood levels of the hormone Hormones can circulate either free or bound Steroid and thyroid hormones circulate attached to plasma membranes the others circulate freely o Relative number of receptors on the target cell o The affinity of those receptors for the hormone Interaction of Hormones at Target Cells Two types of hormone interaction o Synergism more than one hormone produces the same effects on a target cell Ex Epinephrine and glucagon both raise blood glucose o Antagonism one or more hormones opposes the action of another hormone Ex Insulin lowers blood glucose while glucagon raises it Control of Hormone Release Blood levels of hormones are controlled by negative feedback systems o Levels only vary slightly within a desirable range o The output of the hormone shuts off the original stimulus Ex Release of insulin tells cells to take in more glucose causing blood glucose levels to decline returning body back to normal Ex The same is true for the release of glucagon Different Stimuli for Hormone Release o Humoral Stimuli hormones o Ex Ca2 in the blood Changing blood levels of ions and nutrients directly stimulates secretion of Declining levels of calcium stimulates parathyroid gland to release PTH parathyroid hormone which in turn raises blood calcium levels o Neural Stimuli a neurotransmitter stimulates the gland to release its hormone o NTs stimulate the adrenal medulla to secrete epinephrine and norepinephrine o Hormonal
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