Cardiac Muscle Basic anatomy-chambers and valves, the electrical pathway from th
ID: 3515602 • Letter: C
Question
Cardiac Muscle Basic anatomy-chambers and valves, the electrical pathway from the SA node pacemaker to the AV node to the Bundle of His and Bundle branches to the Purkinje fibers. Why is it important to take the electrical signal to the apex of the heart? How does the contraction mechanism work? Where does Ca+2 come from? How is the pacemaker potential different form the cardiac muscle cell action potential? How is the cardiac muscle cell action potential different from all other types of muscle cells? How does contraction-relaxation cycle with valves and sounds work? (Cardiac cycle graph) How does autonomic regulation parasympathetic vs. sympathetic work? What is the Frank-Starling law? Know what the basic parts of an EKG represent. Why it is better to increase Cardiac output by increasing stroke volume instead of just heart rate. Be able to solve a basic Cardiac Output problem.Explanation / Answer
The mammalian heart consists of 4 chambers.Right and left atrium and right and left ventricle.The sinutrial (SA)node is present in the wall of right atrium lose to the point of entry of the vanea cavae.The atrio-venticular(AV) node is situated at the lower right border of the interatrial septum.In a myogenic heart,contraction is intiated by a Sa node located in the atrium.This node has an inherent power of generating a wave of contraction and is therefore called pacemaker.
The rhythmic excitatory signals flashed by the pacemaker travel aaway through the whole heart muscle over a special conducting system bundle of HIs and Purkine fibres in mammals.A myogenic heart thus exhibits an intrinsic beat which does not require any external trigger for a start.
The SA nodes acts as a pace maker or pace setter of the heart because it is capable of intiating impulses which stimulate the heart muscles to contract..It establishes the basic rhythm at which the heart beats.The fibres of the heart muscles like all cells,are charged positively on the outside and negatively on the inside.In the pacemaker this charge break down simultaneously about 72 times each minute.
The Sinu-atrial node emits an impulse of contraction which spreads as a wave of contraction over the right and left atrial wall,pushing the blood through the atrio-ventricular valves into the ventricles.When this wave of contraction reaches the atrio-ventricular (AV)node,it is stimulated to emit an impulse of contraction which spreads to the ventricular muscle via the atrio-venticuar bundle and Purkinje fibres.
The heart is under the influence of two pairs of nerves which arise in the cardiac center in the medulla oblongata of brain and which reach it through the autonomicnervous system.These nerves accelerator(sympathetic)and inhibitor(parasympathetic)are antagonistic to each other.
The heart acts a pump and its action consists of a regular sequence of events called the cardiac cycle.In a human being when the heart is beating normally the cardiac cycle occurs about 72 times per minute.Thus,each cycle takes about 0.8 of a second to occur.
A cardiac cycle consists of