Autonomic Nervous System Chapter 12 1

So much of what happens within us, is automatic!! When we are eating – we do not make an effort to increase flow of our digestive enzymes or increase the rate of contraction of intestinal muscle to enhance the digestive process…

Autonomic (visceral) Reflexes Similarly to the knee-jerk (patellar) reflex….there are also visceral reflexes… They are mediated by the Autonomic nervous system Visceral reflexes regulate organ function Such as… heart rate, BP, body temperature, digestion, airflow through respiratory passages, elimination and pupillary responses

Pathways.. Activation of a receptor Transmission of sensory information to the CNS Processing of the information of the CNS Motor response sent to receptor organ Example… A sudden decrease in BP activates pressure receptors (baroreceptors) the info about low BP is carried to the medulla oblongata in the brain stem by sensory nerves - the medulla oblongata determines that the BP is low and sends motor signals to the visceral effector organs (heart and blood vessels) motor responses results in changes in the heart and blood vessels that elevate the blood pressure

Division of the Autonomic Nervous System The ANS is part of the peripheral nervous system that supplies motor activity to the visceral effector organs: glands, smooth muscles w/in organs, and heart. Two divisions: Sympathetic – causes the body to become more active Fight or Flight Parasympathetic – mostly involved w/ relaxation

A single organ often receives fibers from both divisions of the ANS = dual innervation – typically opposing effects on organ when stimulated. One Exception… Example… the cell of the heart that determine rate – receive both sympathetic and parasympathetic fibers. Stimulation of the sympathetic fibers increases heart rate Stimulation of the parasympathetic fibers decreases heart rate

Sympathetic Parasympathetic Heart Increases rate, strength of contraction Decreases rate, no direct effect on strength Bronchial tubes Dilates (incr airflow) Constricts Iris of Eye Dilates (pupils enlarge) Blood vessels No innervation Sweat glands Stimulates Intestines Inhibits motility Stimulates motility/secretion Adrenal medulla Stimulates secretion of epinephrine/norepinephrine No effect Salivary glands Stimulates thick secretion Stimulates watery secretions

Sympathetic Nervous System Fight or Flight Activated during periods of stress/feelings of threat Causes you to prepare to either confront (fight) or remove yourself from the situation (flight) Periods are usually short-lived Prolong periods of high alert/stress…takes it’s toll on the body – stress-induced illnesses! Laughter, play, rest, relaxation diminish sympathetic outflow

Parasympathetic Nervous System Feed and Breed Most active during quiet, no-stressful conditions Plays important role in regulation of digestion and reproductive function “resting and digesting” Paradoxical fear… although sympathetic system is associated w/ fear – the parasympathetic system can be stimulated when the situation seems hopeless – fight or flight seems futile. Massive parasympathetic discharge can result in severe low heart rate – fainting/possible death Uncontrolled urination/defecation

Autonomic Terminology Pharmacology Sympathomimetic – a drug that mimicks the effects of the sympathetic nervous system Increases heart rate, force of cardiac contratcion and blood pressure Sympatholytic – a drug that inhibits the effects of the sympathetic system Prevents an increase in cardiac activity when the sympathetic nerves are fired Parasympathomimetic – mimicks the effects of the parasympathetic nervous system Decreases heart rate, increases digestive activity Parasympatholytic – drug that prevents activation of the parasympathetic nervous system If the heart is suffering the effects of a parasympathetic system…these drugs can reverse the effects - Atropine