Consists of motor neurons that innervate smooth and cardiac muscle and glands PET3322 Exam 3 Study Guide AUTONOMIC NERVOUS SYSTEM Operate via subconscious control Have viscera as most of their effectors Differs from SNS in the following 3 areas Effectors SNS effectors are skeletal muscles ANS effectors are cardiac muscle smooth muscle and glands Efferent pathways Axons of the ANS are a two neuron chain The preganglionic first neuron has a lightly myelinated axon The ganglionic second neuron extends to an effector organ Two divisions of ANS sympathetic and parasympathetic Most body parts have dual innervation Target organ response The nerve impulses from one division stimulates an organ impulses from the other division decrease activity Interactions of the Autonomic Divisions Most visceral organs are innervated by fibers from both divisions Results in dynamic antagonisms that precisely control visceral activity Sympathetic fibers Increase heart and respiratory rates Inhibit digestion and elimination Parasympathetic fibers o o Neurotransmitters and Receptors Decrease heart and respiratory rates Allow for digestion and elimination ACh and NE are the two major neurotransmitters of the ANS ACh Released by all preganglionic axons and all parasympathetic postganglionic axons Cholinergic fibers ACh releasing fibers Inhibit heart stimulate abdominal muscle ACh Receptors On all effector cells stimulated by postganglionic cholinergic fibers ACh binding Can be either inhibitory or excitatory Depends on receptor type of the target organ Catecholamines stimulate heart inhibit abdominal muscle SNS Adrenergic fibers sympathetic postgan axons that release NE NT effects can be excit inhib depending upon the receptor type Adrenergic receptors Two types alpha and beta Each type has two or three subclasses Effects of NE binding to Alpha receptors is generally stimulatory 1 blood vessels o o o o o o o o o o o o o o o o o o Beta receptors is generally inhibitory 2 GI tract pancreas 3 adipose tissue Introduction to ANS Sympathetic Outflow o o o o From spinal cord segments T1 to L2 Preganglionic fibers synapse in the chain paravertebral ganglia Fibers from T5 to L2 form splanchnic nerves abdomen and synapse with collateral ganglia Postganglionic fibers innervate the numerous organs of the body Sympathetic Trunks and Pathways The paravertebral ganglia form part of the sympathetic trunk or chain Typically there are 23 ganglia 3 cervical 11 thoracic 4 lumbar 4 sacral and 1 coccygeal Adrenal Medulla below Fibers of the thoracic splanchnic nerve pass directly to the adrenal medulla A misplaced sympathetic ganglion o Upon stimulation medullary cells secrete NE and EPI into the blood Source of catecholamine Role of the Sympathetic Division fight or flight Involves E activities exercise excitement emergency and embarrassment Regulates many functions not subject to parasympathetic influence Activity of adrenal medulla Sweat glands o o o Kidneys o Metabolic effects o Blood vessels vasoconstriction and vasodilation Not reversed by parasympathetic division Increases metabolic rate of body cells Raises blood glucose levels Mobilizes fat as an energy source Role of Parasympathetic Division Most of the parasympathetic ganglia are located very close to the target organs Involves the D activities digestion defecation and diuresis Illustrated by a person relaxing after a meal o o o Blood pressure heart rate respiratory rates decrease Gastrointestinal tract activity increases Skin is warm pupils constricted Physiology of ANS The balance of autonomic sympathetic para tone is regulated by feedback loops between the spinal cord and brainstem with input from the limbic system and oversight by hypothalamus THE ENDOCRINE SYSTEM Endocrine cell Blood capillary Circulating hormone Hormones chemical substances secreted by cells into the blood regulate the metabolic function of other cells Circulating hormones Chemistry of Hormones Two main classes o o Amino acid based hormones Amines thyroxine peptides and proteins Steroids produced by gonads and adrenal cortex Hormone receptor Synthesized from cholesterol Gonadal and adrenocortical hormones Distant target cells Mechanisms of Hormone Action Two mechanisms depending on their chemical nature 1 Water soluble hormones all amino acid based hormones except thyroid hormone Slide 9 Cannot enter the target cells Receptors on cell membrane Coupled by G proteins to intracellular second messengers that mediate the target cell s response o o o o o o o o o o 2 Lipid soluble hormones steroid and thyroid hormones slide 11 Receptor in nucleus Act on intracellular receptors that directly activate genes Hormone receptor Target Cell Specificity Is a protein molecule to which a particular molecule binds strongly Responds to several different hormones Hormones circulate to all tissues but only activate target cells Target cells must have specific receptors to which the hormone binds Examples of hormone activity ACTH receptors are only found on certain cells of the adrenal cortex Thyroxin receptors are found on nearly all cells of the body Target Cell Activation o Depends on three factors Blood levels of the hormone Relative number of receptors on the target cell The affinity of those receptors for the hormone Interaction of Hormones at Target Cells o Two types of hormone interactions Synergism more than one hormone produces the same effects on a target cell Both EPI and glucagon blood glucose Antagonism one or more hormones opposes the action of another hormone Insulin decreases blood glucose VS glucagon increases blood glucose Control of Hormone Release Blood levels of hormone Are controlled by negative feedback systems Vary only within a narrow desirable range The output shuts off the original stimulus Humoral Stimuli Changing blood levels of ions and nutrients directly stimulates secretion of hormones Ex Ca2 in the blood Declining blood Ca2 concentration stimulates the parathyroid glands to secrete PTH parathyroid hormone PTH causes Ca2 concentrations to rise and the stimulus is removed Neural Stimulus Hormonal Stimuli A NT stimulates the gland to secrete it hormone Hormones stimulate other endocrine organs to release their hormones Hypothalamic hormones stimulate the release of most anterior pituitary hormones Anterior pituitary hormones stimulate targets to secrete still more hormones Hypothalamic pituitary target endocrine organ feedback loop hormones from the final target organs inhibit the
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