Cardiac Muscle Structure Flashcards
Relationship between exercise intensity and CO
Positive
Incr exercise and need of skeletal muscle, incr CO
Define Preload
volume in the ventricle before ejection
Define afterload
pressure ventricles pushing against to eject blood (usu aortic pressure or pulm HTN)
Largest cell population in heart
1) endothelial cells
2) cardiac fibroblasts
function of cardiac fibroblast
lay down ECM of heart for myocytes to function
most predominant components of ECM
fibrillar collagen type 1 and 3
Unique features of skeletal muscle
1) striated
2) not under direct neural control (like skeletal)
3) muscle shorter, narrower, richer in mitochondria than skeletal
4) ATPase activity of myosin slower in cardiac
5) Ca2+ binding to troponin C regulates actomyosin
cardiac muscle cells connected with each other through ____
intercalated discs
each cardiac muscle is from __ to __ and contain ___ and ___
z disc to z disc
contain desmosomes and gap junctions
function of desmosomes
adhesion and assure force transferred from cell to cell
function of gap jucntion
low resistance path for electric current
coupling between cardiac muscle cells is both ___ and ___
mechanical and electrical
what is cardiac muscle made primarily of
myocytes in a collagen weave
what does each cardiac myocyte contain?
contains multiple rod strands called myofibrils
what are myofibrils composed of?
end to end array of sarcomere
what is a sarcomere
contractile unit made of actin and myosin from Z to Z
what is a myofiber
1 multinucelate muscle cell with all usual organelles + myofibrils
what is in thin filament?
actin
what is in thick filament
myosin
what is a thin filament also known as
I band extending from Z line
what is a thick filament also known as
A band-
what is myosin made of?
2 heavy chains + 4 light chains (2 regul + 2 essential)
what are the two forms of myosin?
alpha
beta
which myosin isoform has higher ATPase activity? and which form is associated with heart failure?
higher ATPase = alpha
heart failure = beta
what does actin bind on to?
tropomyosin
troponin
what is troponin C structure
1 Ca2+ binding site
skeletal muscle has 2
What is troponin I
has N-terminal extension with 2 PKA phosphorylation site
interacts with Trop C but is released with phsophorylation
what is troponin T
binds tropomyosin
what is tropomyosin
only alpha isoform in heart
Cross bridge cycle
1) Depol open plasma membrane Ca2+ channel
2) Ca2+ binds RyR2 on membrane of SR to induce more Ca2+ release
3) Ca2+ binds Trop C –> conformation change in tropomyosin to expose cross bridge sites on actin
4) ATP on myosin hydrolyzed to ADP + Pi
5) Actin interact with myosin –> crossbridge
6) muscle contract when ADP dissoc
7) Ca2+ released from troponin resets tropomyosin blocking actin
8) ATP rebinds myosin head –> reset
1 Rest state
4 state crossbridge cycle
No Ca2+
weakly bound
no force generate
4 state crossbridge cycle #2 transition state
Ca2+ bound
cross bridge weak bound
no force generate
4 state crossbridge cycle #3 active state
Ca2+ bound
cross bridge strong bound
force generate
4 state crossbridge cycle #4 active state
No Ca2+
cross bridge strong bound
force generate
How is cross bridge cycling regulated?
Via calcium flow (level of calcium determine whether cross bridge forms)
Sliding filament hypothesis
how does thin filament change?
NO CHANGE IN LENGTH BTWN CONTRACT AND RELAX STATE
Sliding Filament hypothesis
how does thick filament change
NO CHANGE IN LENGTH LIKE THIN BUT DOES CHANGE ORIENTATION OF HEAD
Function of Titin
allow interaction btwn myosin and actin to contract and relax without changing intracellular distance btwn actin/myosin
diastolic propertis
what are 2 diff titin isoforms? which is longer and less stiff?
N2b N2ba (longer and less stiff)
which titin isoform is found in diastolic heart failure
incr N2b
what is frank starling law of heart
1) MORE VOLUME OF BLOOD ENTER HEART IN DIASTOLE (EDV)
2) MORE VOLUME BLOOD EJECT DURING SYSTOLE (SV)
what is frank starling law of heart based on?
length tension relationship
incr fiber length, incr force of contraction (tension)
how does length tension relationship apply to heart?
incr preload
incr fiber length
incr force of contraction
is there a limit on length tension relationship?
YES, OVERSTRETCH BEYOND OPTIMUM WILL DECREASE TENSION AND CONTRACTION
what are the mechanisms behind length-tension relationship
1) extent of overlap
2) changes in sensitivity of myofilament to calcium
3) incr calcium release
mechanisms behind length tension relationship
extent of overlap
Change resting length of muscle –> proportional change in individual sarcomere
Peak at 2.2-2.3 uM
mechanisms behind length tension relationship
change in sensitivity of myofilament to calcium
what is main factor in myocardial contraction
1) calcium is main factor in myocardial contraction
mechanisms behind length tension relationship
change in sensitivity of myofilament to calcium
what is aclacium sensitivity
responsiveness of myofilament to calcium
mechanisms behind length tension relationship
change in sensitivity of myofilament to calcium
what are factors that regulate calcium sensitivity of myofilament
Troponin I phosphorylation
Isoform composition
sarcomere length
