Muscles: Cardiac Muscle Flashcards
Where is cardiac muscle located
the heart
Structural features of cardiac muscle cells
Striated, Branched cells with 1-3 central nuclei
What connects cardiac muscle cells together
intercalated discs
Do muscle cells contract together or separately
together
is cardiac muscle voluntary or involuntary
involuntary
What does the right side of the heart do
it contracts and sends blood to the lungs to become oxygenated
What does the left side of the heart do
it receives blood from lungs, contracts and sends blood to the body through the aorta
What are the parts of the heart
Right and left atrium and ventricle (4 in total)
What part of the heart has the most muscle
The left ventricle
Structural features of ventricular muscle cells
they are branched
they contain ~1-3 nuclei
Have many mitochondria for respiration
Where is the T-Tubule located in cardiac vs skeletal muscle
Cardiac = at Z disc Skeletal = at end of A band/ and I band
Dimensions of ventricular muscle cells
100 µm x 30 µm
The two types of junctions in intercalated discs
Desmosomes and gap junctions
Function of desmosomes in intercalated discs
prevent cells from separating during contraction
Function of gap junctions in intercalated discs
allow the AP to be carried from one cell to the next (things like Na+ ions to move AP across cells). Allows for the coordinated contraction of all the myocytes
What does the figure 8 arrangement of cardiac muscles allow the heart to do?
Efficiently contract (shorten and narrow) at the same time
Length of Ventricular myocyte AP
> 100 ms
What causes the plateau phase in a Ventricular myocyte AP
Calcium Voltage gated L channels (causing a large sustained Ca2+ current so the membrane potential stays positive for a period of time). These channels are long acting, long time to open and close
When is the membrane potential of cardiac muscle depolarised
Throughout most of the ‘twitch’ (heart beat)
Is an AP longer in cardiac or skeletal muscle
Cardiac due to plateau phase
Why does the heart to relax after a contraction before generating a new AP
blood need to come into the heart during the absolute refractory period to generate a new AP
3 major stages of an AP in a cardiac muscle cell
0 – Rapid depolarisation due to fast voltage gated Na+ channel
2 – Plateau phase due to slow voltage gated Ca2+ channel (L-type Ca2+ channel)
3 – Repolarization due to closing of Ca2+ channels (inward) and opening of K+ (outward) channels
Why is a twitch smaller if generated during relative refractory period of a heart contraction
Because the heart hasn’t completely filled with blood due to less relaxation time (there isn’t enough pressure/tension from heart stretching to open aorta)