contraction and contractility

study guide

smooth muscle contraction around vessels causes

vasoconstriction

relaxation of smooth muscle surrounding vessels results in

vasodilation

how does vasoconstriction affect resistance? how does vasodilation affect resistance?

vasoconstriction increases resistance; vasodilation decreases resistance

what does Ca2+ bind to 

calmodulin

what does the combination of Ca and Calmodulin do to MLCK

activates it causing vasoconstriction

what are the general ways that Ca is made available for smooth muscle contraction

IP3-gated Ca2+ channels, ligand-gated Ca2+ channels, voltage gated Ca2+ channels

what are the names for the muscle cell? plasma membrane? sarcoplasmic reticulum?

muscle cell = muscle fiber

plasma membrane = sarcolemma

Endoplasmic reticulum = sarcoplasmic reticulum

what are the t tubules and what are they specializations od

T-Tubules are specialized “dips into the sarcolemma. They allow action potential to run adjacent and have Ca flood into the cell

what is the function of the sarcoplasmic reticulum

Ca++ storage

what defines a sarcomere

Z disc to Z disc

what is the thin filament? what is the thick filament

actin; myosin

what is the function of troponin I, C, and T

I : inhibits actin - myosin interactions when at rest

C: binds calcium ions triggering contraction

T: anchors troponin complex to tropomyosin

what is the clincial relevance of troponin I and T

used as biomarkers for heart damage

what is tropomyosin

thread like protein that winds around actin filaments. blocks myosin - binding sites preventing contraction

what is the receptor/Ca channel on the sarcolemma called

L-type voltage-gated calcium channel or dihydropyridine receptor (DHPR)

what is the receptor on the sarcoplasmic reticulum that binds Ca from the ECF called

RYR (ryanodine receptors)

what is the pump that puts Ca back into the SR for storage

SERCA Pump

what is the function of intercalated discs

connects cardiac cells, rapid spread of APs, and ensures the heart contracts as a unified whole

which part of the intercalated disc allows for passage of ions/AP from cell to cell

gap junctions

explain the optimal length of a sarcomere

overlap of actin and myosin to generate max force

what does optimal length allow for

max force

why is there less force generated when the sarcomere is too short

actin is too close to M line, so it doesn’t have anywhere to go

why is there less force generated when the sarcomere is too long extended

minimal actin and myosin overlap

What is the relationship between preload/EDV and stroke volume

increase preload, increase EDV, increase SV

What is the relationship between stretch and tension/force?

direct; one increases, so does the other

what causes the cardiac muscle cell to become depolarized

autorhythmic cells depolarize the contractile cells

once depolarized, what channels in the T tubules open up

L-type / dihydropyridine

what ion enters to cause release of Ca from SR? what is the name of the receptor on the SR for this ion? what channel opens?

Ca induced Ca release; RYR receptor; L-type Ca channel

what is the meaning of Ca 2+ dependent Ca release in terms of the cardiac muscle cells?

amplified calcium signal needed for contraction.

once the SR releases Ca, where does the calcium bind

troponin C

what happens to allow crossbridge formation once Ca binds to troponin

Calcium binding to troponin removes the tropomyosin blockade, allowing myosin to latch onto actin and initiate contraction.

what is happening to the sarcomere after crossbridge formation

sarcomere shortens (muscle contraction)

Powerstroke is equivalent to ______, which is the contraction phase of the heart

systole

during relaxation, what pumps Ca back into the SR and how does the pump operate

SERCA Pump; Ca2+ ATPase

what pumps Ca to the extracellular fluid and how does this pump operate

Na/Ca exchanger; made possible by the NA/K ATPase

how does preload, contractility and afterload affect stroke volume

increased preload or contractility = increased stroke volume. Increased afterload = decreased SV

what is contractility

the ability of the cardiac muscle cells to develop force for contraction - Ca dependent

what is inotropy

contractility

ultimately the contractility is dependent upon the availability of 

calcium

how does contractility affect the Frank-Starling Relationship?

positive: increased contraction force (increased SV)

negative: decreased contraction force (decreased SV)

Discuss the positive inotropic effects of the sympathetic NS

increase force of contraction, increased SV, increase preload

how do cardiac glucosides increase contractility? what do they inhibit? what does this do to primary active transport? secondary active transport of Ca? which direction are the ions moving?

decrease activity of the Na/K ATPase, increases intracellular Na which leads to a decrease in the Na gradient across the membrane. causes less Ca to be extruded through the Na/Ca exchanger. More Ca = increased contractility (positive inotropy)

Negative inotropic effects of the parasympathetic NS

ACh binds muscarinic cholinergic receptors on myocardial contractile cells inhibiting Adenylyl cyclase which decreases intracellular Ca = less force and decreased SV

Given a graph for the length tension relationship, what is on the x-axis and what is on the y-axis

X axis: EDV

Y axis: CO or SV

How do we translate these units to apply to cardiac “stretch” and “force,” IOW the length-tension relationship in cardiac muscle is represented by _________ on the x-axis and _______ on the y axis

EDV; SV

If EDV increases what happens to stroke volume? If EDV decreases what happens to stroke volume?

increases; decreases