Cardiac Muscle

Question 1

1. What is the purpose of cardiac muscle force?
2. What is the difference between conduction and force?
3. Do all cells conduct?
4. do all cells generate force?

Answer 1

1. to generate pressure to pump blood
2. conduction = transfer of AP; force = contraction
3. all cardiac cells function in conduction
4. only some function to produce force

Question 2

1. Define contraction
2. Define conduction
3. Define automaticity

Answer 2

1. contraction - to generate force
2. conduction - conduction pathways in working cells, transfers APs
3. atomaticity - pacemaker function; ability to generate AP

Question 3

Contrast cardiac and skeletal muscle regarding:

1. size
2. connective tissue function
3. rhythm/activation
4. electrical function
5. continuity

Answer 3

1. size: cardiac muscle cells are shorter, and have a smaller diameter
2. cardiac connective tissue matrix functions to limit overstretching
3. cardiac muscle has autorhythmicity and intrinsic activation, as in it does not require motor unit recruitment
4. cardiac muscle has an electrical and functional syncytium (conduction system) so the heart will function as a unit
5. cardiac muscle has continuous function, as we depend on this to live

Question 4

1. Given cardiac myocytes have intercalated discs with gap junctions and low electrical resistance, how does this affect a generated action potential in the atria and ventricle?
2. In a healthy heart, the direction of conduction through the AV node is ______

Answer 4

1. This allows an action potential generated anywhere in the atria or ventricle to spread throughout the whole atria or ventricle.
2. Unidirectional

Question 5

1. What does “heart block” specifically impair?
2. How do different cases of heart block vary?

Answer 5

1. Heart block impairs the conduction through the AV bundle , which causes functional dissociation of the atrial and ventricular syncytia.
2. there can be varying degrees of AV conduction impairment leading to varying degrees of functional dissociation

Question 6

VENTRICLE

1. What does the LS represent?
2. What does the T represent?
3. What structures are in the black box?
   What is their function?
4. What structures are in the black circles?
5. what does the S represent?
6. what does the M represent?

Answer 6

1. LS = lateral sacs of SR
2. T = t-tubule
3. Black box = intercalated disc
   predominantly end-end connections of myocytes that integrate electromechanical function b/t cells
4. black circle = Z line
5. S =
6. M = mitochondria

Question 7

1. What are the major components of the intercalated disks?

Answer 7

1. Fascia adherens
   Desmosomes
   Gap junction

Question 8

1. What is the function of the fascia adherens?
   What structure does it cooperate with to achieve a common goal?
2. What is the function of desmosomes?
3. What is the function of gap junctions?
   What proteins do these consist of?
   Number of gap junctions correlate with ______

Answer 8

1. fascia adherens - transmits force; presence of fascia adherens + intercalated disks correlates with force generating capacity of cardiac myocytes
2. these are pressure studs; they are an attachment site for the cytoskeleton
3. forms electrical connections; they consist of connexion proteins
   number of gap junctions correlate with conduction velocity

Question 9

1. How do atrial and ventricular branching patterns differ?
2. How do atrial and ventricular intercalated disk arrangements differ
3. compare and contrast amount of t-tubules in atrial and ventricular muscle

Answer 9

1. Ventricles are heavily branched while atria generally do not branch
2. ventricular intracalated disks facilitate end-end
   atrial intracalated disks facilitate horizontal, with occasional end-end
3. atria have little to no t-tubules
   ventricles have a well developed t-tubule system

Question 10

1. What are the main components of the myocardial connective tissue?
2. What are the main purposes of the connective matrix?

Answer 10

1. myocardial connective tissue complex
   made of collagen and elastin
2. interconnects myocytes and blood vessels
   provides structural support
   prevents damage, limiting stretch during diastole (overfilling) or during contraction
   force transmission
   determines resting tension (ventricular diastolic pressure)
   collagen may help hold vessels open during diastole

Question 11

1. How is the duration of a cardiac action potential different from a nerve or muscle action potential? what advantages does this have?
2. how is the refractory period of a cardiac AP different from a nerve or muscle AP? What are the advantages of this?

Answer 11

1. cardiac AP is longer duration. ensures total activation of all cardiac cells. ensures sustained contraction to empty cardiac chambers. accounts for long refractory period
2. long refractory period. this disables tetany from happening, and ensures relaxation and filling between beats

Question 12

1. in cardiac muscle, the height and duration of the action potential determins what about the contraction?

Answer 12

1. height and duration determine magnitude and duration of contraction; force generation

Question 13

1. What is the I_Na current responsible for?
2. what is the I_C​_a responsible for?
   What are the important subchannels?

Answer 13

1. rapid depolarization of atrial and ventricular muscle and purkinje fibers
2. contributes to atrial and ventricular depolarization adn contraction
   subchannels - L-type and T-type Ca²⁺ channels