Chapter 13 Cardiovascular System Cardiac Func9on The Soma c Nervous System Unlike the autonomic nervous Unlike the autonomic nervous system which controls the func ons of many di erent types of e ector organs the soma c nervous type of es ector ystem ocontrols rgan sokeletal nly one type of e ector organ skeletal muscle muscle In addi on the soma c nervous In addi on the soma c nervous system has only a single type of e erent neuron that innervate skeletal muscle motor neurons Most skeletal muscle is under voluntary control you can consciously decide to contract a Structure of Skeletal Muscle Skeletal muscle contains many bundles called fascicles of individual muscles cells Each fascicle contains hundreds to thousands of muscle cells which are called muscle bers due to their elongated shape 3 Types of Muscle in the Body However there are two other types mHowever of uscle in the there body are stmooth wo other types of muscle in the body smooth muscle and cardiac muscle Like skeletal muscle smooth muscle has thick and thin laments and generate force through cross bridge cycle arranged in sacromeres therefore lacks stria ons and therefore lacks stria ons It is found in internal organs blood vessels and other structures that are not under voluntary control 3 Types of Muscle in the Body muscle cells are extensively connected to each other via gap junc ons Anatomy of the Heart The heart is located centrally in the thoracic cavity just above the diaphragm Generates force from contrac on that propels blood ow throughout the vasculature The Heart The Heart Blood follows an essen ally circular path as it travels through the body Consists of two divisions pulmonary circuits which consists of all the blood vessels connec ng the lungs with the heart systemic circuit which encompasses the rest of the blood vessels in the body Anatomy of the Heart To carry out this func on To the wcalls arry of otut he th his eart func on the walls consist primarily of the hoeart f consist pmrimarily cardiac uscle of cardiac muscle heart wall 3 layers of the Epicardium Epicardium uter ayer w of all 3 layers of othe hleart connec9ve 9ssues outer layer of connec9ve 9ssues Myocardium middle layer of cardiac muscle Myocardium middle layer of muscle inner layer cEardiac ndothelium of cells inner layer eEpithelial ndothelium The hearts pumping ac on is The hearts pumping ac on is This squeezing increases the pressure within the chamber Electrical Ac vity of the Heart The heart has the ability to generate its own signal to trigger its the heartbeat contrac ons on a periodic basis called autorhythmicity This property is due to a small percentage of muscle cells that generate liWle to no force but coordinate and provide rhythm to the heartbeat Pacemaker Cells Contrac ons of the heart are ini ated by pacemaker cells which spontaneously generate ac9on poten9als Contrac ons of the heart are Although located in nearly all ini ated by pacemaker cells which spontaneously generate ac9on poten9als Although located in nearly all parts of the heart they are concentrated in two speci c Ionic Basis of Electrical Ac vity in the Heart A pacemaker cell is able to re ac on poten als spontaneously because it Does not have a steady res9ng membrane poten9al AYer an ac on poten al a pacemaker cell immediately begins to depolarize slowly and con nues to do so un l it reaches threshold which triggers another ac9on poten9al Ionic Basis of Electrical Ac vity in the This triggers the K channels begin to close and Heart opening of a second opening of funny channels K channels begin to close and Membrane poten al becomes Depolariza on triggers the opening of voltage gated calcium Membrane poten al becomes Depolariza on triggers the depolarized opening of voltage gated calcium This triggers the Depolariza on triggers the opening of K Depolariza on channels and the triggers the opening of pKhase repolariza on of channels the ac on and poten al the repolariza on phase of PURPLE Cardiac Muscle Cells Ac on Poten als Cardiac AP s are broad Cardiac AP s are broad and last for hundreds of them quite di erent than AP s of most Electrical Ac vity of the Heart Ac on poten als generated by pacemaker cells in the SA node spread to adjacent muscle cells by means of electrical current passing through conduc9on of bers connected by gap junc9ons The Conduc on System of the Heart 1 AP ini ated at SA node and spreads to the bulk of atrial muscle 2 Impulse is conducted to the cells of the AV node 3 Impulse travels through bundles of His 4 Bundles splits into leY and right branches go to leY and right ventricles 5 Impulses travel through Purkinje bers to the ventricles Electrocardiogram Electrocardiogram ECG or EKG is a noninvasive means for Electrical ac vity ini ated by the heart spreads through the body whose uid func ons as a Electrodes are placed on the skin at corners of an imaginary equilateral triangle that measure the di erence in surface electrical poten al between posi ve and nega ve electrodes Electrocardiogram The waveforms depend on whether the di erence between the two electrodes is posi ve or nega ve i e depolarizing wave traveling toward posi ve electrode causes an upward de ec on The EKG normally shows three characteris c waveforms Electrocardiogram
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