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Flashcards in The Heart Deck (13)
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1
Q

Succession of beats is caused by…

A

…cardiac rhythmicity - transmitting action potentials throughout the cardiac muscle to cause the heart to beat

2
Q

Cardiac Muscle Fibers

A

3 types - atrial muscle, ventricular muscle, (both contract like skeletal muscles) and conductive muscle (contraction not as strong but rhythmic)

Interconnecting - fibers arranged in a lattice network

Striated with myofibrils (actin and myosin) = similar to skeletal muscle

Cells are individual but electrically connected by intercalated disks = gap junctions (rapid diffusion of ions

3
Q

Due to the electrically connected cells of the cardiac muscle, it is known to be…

A

…a syncytium = an action potential spreads quickly from one cell to the rest of the network (latticework)

4
Q

2 Syncytiums of the Heart

A

Atrial Syncytium = walls of the atria

Ventricular Syncytium = walls of the ventricles

Signal from the atria don’t spread to the ventricles = kept separate

This allows for the atria to beat slightly before the ventricles (specialized conductive system is used instead)

5
Q

Cardiac Muscle Action Potentials are caused by the opening of…

A

…2 types of channels:
Voltage-gated sodium channels (similar to those in skeletal muscle) = fast opening
Voltage-gated L type calcium channels (calcium-sodium channels) - slow opening but remains open for longer = Plateau Phase (0.2-0.3 seconds) = both calcium and sodium rushes in

6
Q

What causes the plateau phase in cardiac muscle?

A

Opening of voltage-gated L type calcium channels that are slow to open and slow to close = longer influx of sodium and calcium

Decrease in potassium permeability once these channels is opened = membrane cannot be repolarized = longer action potential

Permeability increases rapidly when calcium channels close

7
Q

Ventricular Muscle Action Potential

A

RMP = -85 to -95 mV

1) Depolarization = Voltage-gated sodium channels open and cause an influx of sodium (some calcium enters as well)
2) Plateau Phase = Voltage-gated L type calcium channels open = large influx of calcium along with sodium flows in

Membrane becomes less tolerable to potassium

3) Repolarization = Channels close and voltage-gated potassium channels open

8
Q

Excitation of Cardiac Muscle Cells is Controlled by…

A

…Calcium

9
Q

Calcium in Muscle Cell Excitation

A

2 Sources:
Extracellular - Voltage-Gated L Type Calcium Channels
Intracellular - Calcium release channels (Ryanodine) on Sarcoplasmic reticulum (induced by the presence of extracellular calcium)

10
Q

Relaxation of Ventricular Muscle

A

Caused by a decrease in cytoplasmic calcium = caused by:

1) L-type calcium channels and ryanodine receptors closes
2) SERCA = Sarcoplasmic Reticulum calcium ATPase pumps calcium back into the sarcoplasmic reticulum
3) Sodium calcium exchanger on cell membrane uses secondary (counter) transport to exchange sodium for calcium

11
Q

What are the durations of muscle contractions within the heart

A
Atrial = 0.2 sec
Ventricular = 0.3 sec
12
Q

Why does the action potential need to plateau in the heart?

A

B/c the heart needs long sustained contractions, not twitches

13
Q

Refractory Period in Cardiac Muscle

A

Sodium channels are inactivated

Cell may or may not be activated again at this time = when the cells is closer to RMP = more normal contraction