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
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
- - does not move
- - Actin slides over it.
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 __
- Na+; K+;
- slow accumulation of positive charge (slow depolarization)
HCN channels are activated by __ binding to beta 1 receptor through a 2nd messenger
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
The rapid depolarization phase (of cardiac action potential) is due to activation of __ voltage channels
- 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
- 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
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?
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?
________ is composed of multiple globular molecules polymerized to form long chains or filaments
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 __
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++
- 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
The opening and closure of the atrioventricular and semilunar valves is driven by ________.
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?
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