Slide 1Cardiac muscleSmooth muscleExcitation/contraction coupling in smooth muscleSlide 5Into to Electrical activity of the heartPacemaker potentialSlide 8Slide 9Excitation/contraction coupling in cardiac muscleSlide 11Slide 12Exam 3 Cardiac and Smooth muscleCardiac 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