-
function of troponin
work with tropomyosin as a switch for muscle contraction & relaxation
-
Troponin must work with __ to move tropomyosin in order for cross bridges to attach to actin
calcium
-
In skeletal muscle, calcium release receptors (ryanodine receptors) are
- released from sarcoplasmic reticulum by passive diffusion through calcium release channels
- stimulated by action potentials that open voltage-gated Ca++ channels, which is mechanically coupled to Ca++ release channels to stimulate contraction
-
Myosin
thick filament
- - does not move
- - Actin slides over it.
-
HCN channels
main channel involved in making depolarization occur
- - voltage & chemical gate
- - Na enters same time K leaves
- - When Na enters faster than K leaves, excitatory effect occurs
- - have a hyperpolarizing threshold
-
HCN (funny) channels are activated during __ to allow influx of __ and efflux of __ resulting in __
- Repolarization;
- Na+; K+;
- slow accumulation of positive charge (slow depolarization)
-
HCN channels are activated by __ binding to beta 1 receptor through a 2nd messenger
norepinephrine/epinephrine
-
The HCN channel stays open briefly as the membrane __ to a threshold value for __ channels.
depolarizes; T-type Ca2+
-
As the pacemaker potentials spread away from the SA node, they become __
cardiac action potentials
-
Phases of cardiac action potential
- phase 0: rapid depolarization
- phase 1: early rapid repolarization
- phase 2: plateau
- phase 3: final rapid repolarization
- phase 4: diastolic depolarization
(figure 13.19)
-
The rapid depolarization phase (of cardiac action potential) is due to activation of __ voltage channels
Na+
- phase 0: Na+ channels open
-
The early rapid repolarization phase (of cardiac action potential) is due to inactivation of __ & activation of __ voltage channels.
Na+; K+to (transient-outward K+)
- phase 1: Na+ channel closes, K+to channel opens & closes rapidly
-
The plateau phase (of cardiac action potential) is due to influx of __ through __ channels
Ca2+; L-type
- phase 2: L-type Ca2+ channels fully open; K+ channels open
-
The final rapid repolarization phase is due to closure of __ channels and activation of __ channels.
L-type Ca2+; K+
- phase 3: L-type CA2+ channels close; K+ channels stay open for efflux of K+
-
Diastolic depolarization (of cardiac action potential) is due to spontaneous depolarization of __
SA node (due to pacemaker cells generating a new potential)
- phase 4: heart chamber fills
-
The P-R segment represents the length of time __
the depolarizing wave takes to pass through the AV node & the bundle of His
-
The P-R segment represents conduction through __
AV node & AV bundle
-
What converts the myosin head into the high-energy state?
hydrolysis of ATP
-
The release of an inorganic phosphate from the myosin molecule directly results in
power stroke
-
FEV1
Forced expiratory volume in 1 second, measured during spirometry lab to test lung volume and performance
(decreased during obstruction)
-
In order for crossbridge cycling to occur, the actin-myosin complex must be broken by which of the following?
ATP binding to myosin head
-
The sequence of events that links the action potential to changes in skeletal muscle force development is called what?
Excitation-contraction coupling
-
Increases in the amount of cytoplasmic calcium required to initiate a muscle contraction are mediated by the coupling between a ________ on the T tubule and a ________ on the membrane of the sarcoplasmic reticulum.
Dihydropyridine receptor; ryanodine receptor
-
As skeletal muscle is further stretched beyond the length where optimum force is developed, ________.
- Thin filaments are pulled away from the thick filaments, thereby reducing actin's ability to interact with myosin.
- strength of contraction is decreased because of fewer actin and myosin cross bridge interactions
- As a result, we cannot generate any muscle tension.
-
As the sarcomere length of skeletal muscle is reduced beyond the length where optimum force is developed, ________.
- There is interference between the thin filaments. (They are overlapping because they have nowhere else to go). There is no ability to generate any muscle tension.
- The muscle contraction force is decreased because the sarcomere is short and cross bridge cycling is ineffective and actin may overlap
-
What is an increase in the number of active motor units that would increase the force developed by a skeletal muscle called?
recruitment
-
________ is composed of multiple globular molecules polymerized to form long chains or filaments
actin
-
Each myosin head has a binding site for __
actin & ATP
-
The molecular event that occurs immediately after the power stroke is the __
release of ADP from myosin
-
The relaxation of skeletal muscle relies on the activity of the ________, which decreases cytoplasmic calcium concentration.
-
The brief period of time between the beginning of the action potential in the muscle and the beginning of contraction is referred to as the __
latent period
-
Slow depolarization in the SA node
- from HCN channels activated during repolarization
- allow influx of Na+ and efflux of K+ simultaneously
- resulting in slow accumulation of positive charge in the cell
- T-type Ca++ voltage channels open and allow for brief influx of Ca++
-
gap junctions
- how action potentials travel from one cell to the next cardiac cells
- Tube-like proteins
- Can change diameter to minimize damage to other cells; larger diameter has less resistance
- Cardiac cells that are NOT pacemaker cells.
-
The property of cardiac tissue that results in greater current flow along the length of a fiber than along its width
anisotropy
-
The opening and closure of the atrioventricular and semilunar valves is driven by ________.
pressure
-
Closure of the atrioventricular valve occurs when ________.
- Atrial pressure is low and ventricular pressure is high
- (beginning of systole)
-
What are the two major regions of the heart containing pacemaker cells?
SA and AV nodes
-
Which of the following is the correct conduction pathway through the heart?
SA node → AV node→ bundle of His→ bundle branches→ Purkinje fibers
-
The rapid depolarization phase of a pacemaker cell action potential is caused by which of the following types of ion movement?
Na+ and small amount of L-type CA2+
-
Which of the following ion channels must open for a cardiac pacemaker cell to depolarize to threshold for an action potential?
- HCN (funny) channels
- T-type Ca++ channels
-
What is the role of ryanodine receptors in cardiac muscle?
- release calcium from the sarcoplasmic reticulum
- Opens to release Ca++ for muscle contraction
-
Which of the following components of an ECG represents ventricular depolarization?
QRS complex
-
Which of the following components of an ECG represents ventricular repolarization?
-
If damage to the AV node slowed down conduction through this tissue, what would be observed on an ECG?
longer PR interval, heart block
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