Exam 3 Cardiac and Smooth muscle Cardiac muscle Cardiac and smooth muscle are innervated by autonomic visceral motor neurons and these muscles are involuntary All muscle types contract by thin filaments sliding past thick sliding muscle theory applies to all muscle types Striated as are skeletal Have typical sarcomeres Differences cardiac are much shorter skeletal muscle fibers are always linear and cardiac have branches Cardiac muscle cells are attached together with intercalated discs many gap junctions electrically connect all cardiac muscle cells together Cardiac muscle cells of heart form myocardium 2 myocardia of the heart atrial myocardium makes up 2 atrias and ventricular myocardium makes up 2 ventricles When one of the cells gen an ap that ap is rapidly propagated to all the gap junctions of all the neighboring cells All the cells of a myocardium contract together in unison Isn t organized into motor units Myocardia of the heart cannot gen graded contractions Myocardium will contract more forcefully if it is stretched and in the presence of epinephrine and norepinephrine How do you stretch the heart Running muscles in legs will squeeze veins in legs and force more blood back in heart and stretch contract more forcefully and sympathetic response fight or flight neurotransmitters hormones Cells short uninucleate one nucleus and branched Difference skeletal muscle cells won t contract w out innervation some cardiac muscle cells can automatically gen their own aps Usually the heart rate is det by modif cardiac muscle cells called the pacemaker Pacemaker cells gen own aps automatically Speed of pacemaker gen aps constanty being modified by autonomic mervous system sympathetic speeds up para slows it down Smooth muscle 2 types of smooth muscle multi unit and single unit Single unit is more common in walls of hollow organs small intes espohagus stomach artieries and veins bronchiol tubes Cells are connected together by gap junctions contract as a unit Single unit is innervated by autonomic neurons which have synapses in sant these varicosities will release neurotransmitter and cause ap in particular cell and spread to neighbors by gap junctions All cells contract in unison Multiunit much less common cillary muscle in eye determines size of pupil is ex multiunit bc all cells act independently many units each indiv cell innervated by axon of autonomic neuron but cells are not conn together by gap junction as they are in single unit Single Individual cells are spindle shaped uninucleate nonstriated and no sarcomeres Cells contract by thin myofilaments don t have z disc so thin myofilaments must attach to sarcolemma of cell or dense bodies sliding past thick myofilaments Single unit peristalsis alimentary canal and segmentation small intestine Anatomy of smooth muscle cells much more actin than skeletal and cardiac muscle cells Thick myofilaments attach along entire length rather than just at the ends Smooth muscle cells can be stretch so much more than skeletal and cardiac muscle cells and they contract much more slowly Stretched up to 2 and 1 2 times Excitation contraction coupling in smooth muscle No troponin tnc in smooth muscle so no tnc for calcium to attach to Instead has calmodulin similar to tnc and binds to calcium All the calcium for contraction for smooth muscle cells comes from extracellular environment Sarcolemma contains calcium voltage gated channels that open in response to depolarization 2 ways for calcium voltage gated channels to open One way is by epsp depolarization weak contraction or sub threshold action potentials more calcium in strongest contraction can create graded contractions based on how much calcium enters the cell Calcium calmodulin complex then turns on enzyme called myosin light chain kinase MLCK enzyme phosphorylates myosin light chains deals with thick myofilament polypeptide in crossbridge with thick myofilament allows attachment of thin myofilament This system takes place of troponin complex of skeletal and cardiac muscle cells Smooth muscle cell relaxes calcium pumps in sarcolemma pump calcium back in cell myosin phosphatase removes phosphate groups in myosin light chains opposite of MLCK 5 10 of a second the entire heart is in diastole and at that time blood is returning in the heart and going into the right atrium superior to inferior vena cava and left atrium by way of pulmonary veins Goes into 2 atria and past the open av valves into the 2 ventricles By the time at the end of diastole of entire heart ventricles are already 80 full Immediately after that atrial sytole occurs atrial sytole is first thing that happens in cardiac cycle and lasts about a tenth of a sec doesn t generate much blood pressure 10ml mercury doesn t need to bc pumping blood short distance from two atria into 2 ventricles and little friction to overcome After atrial systole ventricles are full Atria top it off by pumping the last 20 The volume of the ventricles is about 115 mls at this time end diastolic volume end pt of diastole of the ventricles Left ventricle pumps same amout of blood as the right ventricle Both total is 115 mils Atrial systole occurs first tenth of a second of the cardiac cycle and then the atria are in diastole all the way to the beginning of the next cardiac cycle 75 beats per min 8 tenths of sec long cardiac cycle Atrial diastole is immedi followed by ventricular systole The pressure gen by left ventricle Ventricular systole lasts about 3 tenths of a sec followed by ventricular diastole 4 8 entire heart is in diastole When ventricles contract they pump out about 2 3 of the blood they contain and the blood they pump out is called stroke volume Blood ejected by ventricle during ventricular systole At the end of ventricular systole the ventricles aren t empty they still contain 45 mls of blood end systolic volume The typical blood pressure is about 120 80 this blood pressure is measured in large artery close to the heart ridicule artery upper arm 120 is systolic pressure and 80 is diastolic pressure When left ventricle contracts the blood pressure in brachial artery will increase with surge of blood is pumped out by the left ventricle and the pressure in the bracial artery is about 120 when the left ventricle is in diastole the pressure in the large artery falls to about 80 milimeters mercury bc of elastic recoil of areteries The left ventricle isn t going to eject any blood until the pressure in the left ventricle is greater than 80 bc to open