Cardiac Contraction Flashcards
skeletal muscle contraction and membrane
long striated cells with multiple nuclei. contraction initiated by nervous system. membrane contains receptors that stimulate contraction. acetylcholine is neurotransmitter
smooth muscle contraction and membrane
long spindle shaped cells.contraction initiated by nervous system, hormones, stretch of muscle. membrane has receptors that can either stimulate or inhibit contraction
cardiac muscle contraction
branching striated cells. contraction initiated by specialized cardiac cells (pacemaker)
myofibrils
muscle fibers composed of these. Each one is made up of thick and thin threads called myofilaments
myosin filaments
thick protein. approx. 1500 per myofibril
actin filament
thin protein. 3000 per myofibril
sarcolemma
plasma membrane enclosing muscle fiber. has special cytoplasm called sarcoplasm. within sarcolemma lie numerous mitochondria with large number of myofibrils running parallel
intercalated disc
hold fibers together and aid of conduction from one fiber to another. unique to cardiac cells
sarcoplasmic reticulum
surrounds each myofibril. network of tubes and sacs that hold mad calcium dog.
t tubles
cross sarcoplasmic reticulum at right angles and communicate to outside. easy movement of action potential from exterior to interior of the cell
sarcomere
fundamental unit of muscle contraction. extends from z to z line. does work son!
I band
thin actin strands alone (letter I is skinny)
Z line
anchor actin filaments composed of filamentous protein (z is last letter of alphabet and last part of sarcomere)
A band
composed of overlapping thick myosin and thin actin myofilaments (length of myosin myofilament)
H ZONE
only myosin strands
m line
mid line connects adjacent myosin
titin
framework for sarcomere. large protein (3,000,000 daltons). one end anchored to z disk and other is attached to myosin. (springy and changes length as muscle contracts and relaxes)
anatomy of actin
strands about 1 um long. composed of 2 F- actin molecules wrapped around each other. basic unit F actin is G actin.
g actin
42,000 daltons. each one has a molecule of ADP attached. site of attachment for myosin cross bridges
tropomyosin
70,000 daltons, 40 nanometers long. covers active binding sites during resting phase of action potential
troponin complex
holds tropomyosin in place on the actin. consists of troponin I, T, and C
troponin I
strong affinity for actin
Troponin T
strong affinity for tropomyosin
Troponin C
strong affinity for calcium
anatomy of myosin
each myosin fiber is a bundle of 200 myosin molecules. each molecule is 480,000 daltons . made of six polypeptide chains 2 heavy (200,000 daltons each) and 4 light (20,000 daltons each)
heavy chains of myosin
wrapped in double helix and form the tail. one end of each heavy chain is folded to create 2 heads. (each head acts as ATPase enzyme)
light chains
2 light chains attach to each head to help control action during contraction
contraction of sarcomere
calcium enters cell and reacts with troponin. tropomyosin undergoes conformational shift in tropomyosin
and exposes binding sites. once actin exposed cross bridges are formed. works like oars on a boat
myosin attached to actin at start of cycle
myosin head lacks a bound nucleotide and is attached to actin in a rigor state (rigid) very short lived. terminated by binding of ATP
Myosin releases actin
ATP binding to cleft on back of cause conformational change in actin binding sites. reduces head’s affinity for actin and allows it to move away from actin
hyrolysis of ATP on myosin head
causes cleft to close like a clam shell around ATP. triggers large shape change that causes head to move along actin about 5nm. ADP and inorganic phospahte remain on head
myosin rebinding to actin
weak binding of myosin to new site releases inorganic phosphate produced by hydrolysis. head is now able to tightly bind to actin
phosphate released- power stroke
the release of phosphate triggers the power stroke in which the head regains original conformation. during the course of power stroke the head loses ADP and starts cycle over (rigid again)
muscle relaxation
calcium transported to SR. tropomysoin blocks actin binding sites. Z lines move further apart
tension only
isometric. if muscle ends held in place max tension muscle can develop will be represented
muscle ends free
isotonic (fixed tension) ability to shorten but no tension. shows max velocity of contraction
heart develops tension to..
overcome given afterload then begins to shorten. both tension and velocity of shortening will be less than max
increased contractility results in
developing more tension for a given resting tension (changes final muscle length not resting)
beta 1 interaction
NE and Epi stimulates increased calcium influx during phase 2. increased influx loads calcium channel releases even more calcium on the next depolarizations. calcium removal rate also increases. the duration of the AP is decreased
law of Laplace
T=P(R)
T=total wall tension P= intraventricular pressure R= ventricular radius
easier to produce pressure at end of ejection than at beginning. dilation plays huge role on pressure generation
