Cardiac Myocyte Flashcards
Know where the Z lines are and where the intercalated disc lies in this picture. Also the intereclated disc is an electron dense region since there are ton of proteins there that mechanically tie up the two cells together for effective contraction and relaxation motion of the heart
What is the structure of intercalated disc
- Note where the zona adherens and desmosomes are and how they repeat themselves.
- The intercalated disc moves from 1 Z line to the next Z line and forms gap junction when it is changing cells.
What filaments are associated with desmosomes and zona adherens
Desmosomes - cadherins (desmoplankin and plankoglobins) whereas for Zona Adherens it is also cadherins along with vinculin, alpha actinins and catenin
What is the significance of gap junctions
This is where the electrical energy flows from one cell to another
How does the structure of junction complex look like
- They have integrins connected to fibronectin and laminins in the extracellular fluid
- From the inside the integrins connect to talin -> Vinculin -> alpha actinin and then actin
What direction does the gap junctions allow the ions to pass
Any direction, a gap junction is literally a hole connecting one cell’s cytoplasm with the other cell
Reasons for atrial fib
There are ectopic pacemakers in the heart which are a few cells at certain areas of the heart which have leaky channels. They can start an action potential against the regular ryhthm of the heart which can cause atrial fib. This is possible as gap juctions allow flow of ions in any direction so the flow of ions can also be in opposite or somewhat different direction depending on the location and rythm of the ectopic pacemakers
What is the structure of the sarcomere
A sarcomere is a structure that extends from one Z line to the next Z line
Explain the mechanism by which the myosin bind to troponin when Ca is released inside the cell
There are 3 kinds of troponin: Troponin C, I and T.
When Ca is released by the ER inside a caridac muscle cells or a skeletal muscle cell, Ca binds to troponin C, troponin I is what inhibits the troponin C and the myosin heads from interacting. When Ca binds to troponin C, troponin I moves out of the way with the help of troponin T which then allows the myosin heads to interact producing a power stroke
Titin
One thing that we know is that muscles have elastic properties. This elastic property is provided by titin. It is like a rubber band found within the M line and Z line. It physically attaches at one end to the M line and at the other end with the Z line
What happens in cardiac hypertrophy
The number if cardiac cells remain the same but each cell gets bigger by adding more myofibrils.
What is a complication involved in cardiac hypertrophy with cardiac function
As the cardiac cells get bigger, they have more myofibrils and hence they have more titin and other structures of the sarcomere. This causes the heart to force out blood with a larger force but during expansion more force is needed for the heart to expand effectively. Hence the heart doesnt expand and fill with blood as well as it used to since there is more resistance to heart filling and there is a decreased stroke volume
EC coupling
Electronic contraction coupling refers to the fact that electrical simualtion is converted into mechanical force by stimulaing the muscles to contract. In cardiac or skeletal mucles Ca enters the voltage gated Ca channels on the sarcolemma (membrane that surrounds the sarcomere) which then stimualtes the ryanodine Ca channels to open up releasing more Ca towards the myofilaments that causes the power stroke
What determines the strength of the power stroke
Ca, increasing the Ca will allows the muscles to contract with a greater force. This only happens to a certain concentration until all the myofilaments are saturated with Ca. Decreasing the Ca reduces the force of contraction of the muscles
Atheroma formation
Sarcomere structure, know where the bands are
