11.23 B Flashcards
Why does an intercalated disc appear so dark on a cardiac EM?
because it is very dense due to the need to stand up to a great deal of mechanical force as it conveys that force from one myocyte to another
Sarcomeres in different cardiac myocytes connect at what general structure?
the zonula adherens
The intercalated disk functionally takes the place of what sarcomere structure?
the Z disk
At an intercalated disk, what are some of the conections between the two cells that are present?
zonula adherens, macula adherens, gap junctions
How is mechanical force conveyed across an intercalated disk?
- via a zonula adherens junctional complex
- the actin of the terminal sarcomere in both cells connects to integrin which connects to the ECM
- with both cells doing this, there is a physicla connection between the two terminal sarcomeres
Describe how the flow of ions is regulated at gap junctions?
it isn’t; ions are free to flow in either direction and at a rate limited only by the size of the pore
Describe the structure of a gap junction.
Six connexion proteins linked together in the membrane of one cell connecting with a complex of six connexion proetins in another membrane
What is the A band of a sarcomere?
the width of the sarcomere that includes the myosin tails and where they overlap the actin filaments
What is the M line of a sarcomere?
the width of the sarcomere that includes only the myosin proteins in the space not overlapped by actin
What is the I band of a sarcomere?
the area where there is only actin that is not overlapped with myosin
What is tropomyosin?
a molecule that interferes with the interaction between actin and myosin in a sarcomere
What is troponin C?
binds to calcium and then creates a conformational change in troponin I to free up the myosin-actin interaction in a sarcomere
Generally speaking what is titan?
a spring like molecule that expands under mechanical force or the entrance of a water molecule and which serves as a major contributor to the elastic component of muscle
What molecule mediates the difficulty relaxing cardiac myocytes that accompanies hypertrophy?
the amount of titan, which spans from the end of a myosin filament to the Z line, increases with hypertrophy and thus more force is required for relaxation
What is a Diad?
a structure formed by a T-tubule contacting a single sarcoplasmic reticulum in cardiac muscle
What is a T-tubule?
a structure that conducts electrical potential and triggers the release of calcium from the sarcoplasmic reticulum
Describe the sequence of events that leads to muscle contraction.
- action potential travels down the T-tubule to the SR
- voltage-gated calcium channels open
- the influx of calcium opens Ryanodine channels
- even more calcium enters and binds troponin
- the actin-myosin interaction is disinhibited and the muscle contracts
What are purkinje fibers?
modified cardiac myocytes with less actin and myosin that help conduct the AP from the bundle branches to the ventricular myocytes
Histologically, how do purkinje fibers compare to cardiac myocytes?
purkinje fibers are larger than working cardiac muscle cells and they are separated from these cells by a heavy connective tissue layer as well as they have less actin and myosin
