Electrical Properties Of The Heart 1

Question 1

Describe the structure of a sarcomere.

Answer 1

A sarcomere consists of myosin (thick filaments) and actin (thin filaments) anchored at Z-lines.

Question 2

What is the membrane of a muscle cell called?

Answer 2

The membrane of a muscle cell is called the sarcolemma.

Question 3

Define T-tubules in muscle cells.

Answer 3

T-tubules are deep invaginations in the sarcolemma that help propagate action potentials.

Question 4

How does calcium contribute to muscle cell contraction?

Answer 4

Calcium released from the sarcoplasmic reticulum binds to troponin, allowing actin and myosin filaments to interact and form crossbridges for muscle contraction.

Question 5

Describe the difference in syncytium formation between skeletal and cardiac muscle.

Answer 5

Skeletal muscle forms a true syncytium with fused muscle cells, while cardiac muscle has a functional syncytium where cells are independent but connected physically and electrically.

Question 6

What is the role of gap junctions in cardiac muscle cells?

Answer 6

Gap junctions in cardiac muscle cells allow for electrical connection between cells, enabling coordinated contraction.

Question 7

Explain the process of excitation-contraction coupling in muscle cells.

Answer 7

Excitation-contraction coupling involves the propagation of an action potential along the sarcolemma, release of calcium from the sarcoplasmic reticulum, and interaction of actin and myosin filaments leading to muscle cell contraction.

Question 8

Describe the role of desmosomes in connecting cardiac muscle cells together.

Answer 8

Desmosomes are strong connections that physically stitch all cardiac muscle cells together, allowing them to contract as one big muscle.

Question 9

How does the length of action potential differ between skeletal muscle and cardiac muscle?

Answer 9

The action potential in skeletal muscle is very short (1-2 ms), while in cardiac muscle, it is much longer (200-250 ms) due to the presence of a long plateau phase.

Question 10

Define intercalated discs in cardiac muscle cells.

Answer 10

Intercalated discs are structures formed by the arrangement of gap junctions and desmosomes, connecting cardiac muscle cells and allowing for the spread of depolarization.

Question 11

Describe the impact of calcium influx on cardiac muscle contraction.

Answer 11

Calcium influx into cardiac muscle cells during depolarization leads to cell depolarization and increased crossbridge formation between myosin and actin, affecting the strength of contraction.

Question 12

How do refractory periods differ between skeletal muscle and cardiac muscle?

Answer 12

Skeletal muscle has a short refractory period due to its short action potential, allowing for rapid consecutive twitch contractions. In contrast, cardiac muscle has a longer refractory period.

Question 13

Explain the concept of tetanic contraction in skeletal muscle.

Answer 13

Tetanic contraction in skeletal muscle occurs when consecutive twitch contractions summate, leading to a sustained and forceful muscle contraction.

Question 14

Describe the difference in contraction between skeletal muscle and cardiac muscle.

Answer 14

Skeletal muscle can undergo tetanic contractions, while cardiac muscle contracts and relaxes in a rhythmic manner.

Question 15

Define excitation-contraction coupling in cardiac muscle.

Answer 15

It is the process by which an action potential triggers muscle contraction in cardiac muscle cells.

Question 16

How are cardiac muscle cells connected to each other?

Answer 16

Cardiac muscle cells are connected by gap junctions and desmosomes, forming intercalated discs.

Question 17

Do cardiac muscle cells have a long refractory period?

Answer 17

Yes, cardiac muscle cells have a long refractory period, preventing tetanic contractions.

Question 18

Describe the role of calcium in cardiac muscle contraction.

Answer 18

Calcium enters cardiac muscle cells through voltage-gated calcium channels, regulating the strength of contraction.

Question 19

How do skeletal muscle cells differ from most cardiac muscle cells in terms of resting membrane potential?

Answer 19

Skeletal muscle cells have a stable resting membrane potential of -90 mV, while most cardiac muscle cells have an unstable resting membrane potential.

Question 20

Describe the difference between non-pac and pacemaker action potentials in cardiac muscle.

Answer 20

Nonacemaker cells have a stable resting membrane potential and are depolarized by neighbors, while pacemaker cells spontaneously depolar to their threshold.

Question 21

Define resting membrane potential in cardiac muscle cells.

Answer 21

The stable voltage across the cell membrane when the cell is at rest, typically around -90 mV in non-pacemaker cardiac muscle cells.

Question 22

How do leaky potassium channels contribute to the resting membrane potential in cardiac muscle cells?

Answer 22

Leaky potassium channels allow potassium ions to leak out of the cell, making it more negatively charged and contributing to the resting membrane potential.

Question 23

Describe the role of voltage-gated sodium channels in cardiac muscle cells.

Answer 23

Voltage-gated sodium channels open at threshold, allowing sodium ions to flood into the cell and contribute to depolarization.

Question 24

Explain the function of voltage-gated calcium channels in cardiac muscle cells.

Answer 24

Voltage-gated calcium channels play a role in the depolarization phase by allowing calcium ions to enter the cell.

Question 25

What is the significance of the plateau phase in non-pacemaker action potentials?

Answer 25

The plateau phase allows for an extended period of depolarization, contributing to the sustained contraction of cardiac muscle cells.

Question 26

How does the sodium-potassium ATPase contribute to the ionic balance in cardiac muscle cells?

Answer 26

The sodium-potassium ATPase actively pumps potassium ions into the cell and sodium ions out, maintaining the concentration gradients essential for cell function.

Question 27

Describe the process of depolarization in a cell when it reaches threshold.

Answer 27

When the cell reaches threshold, calcium floods into the cell down its electrical and concentration gradients, causing depolarization.

Question 28

Define resting membrane potential.

Answer 28

Resting membrane potential is the electrical charge difference across the cell membrane when the cell is not actively sending signals.

Question 29

How do voltage-gated sodium channels contribute to rapid depolarization in a cell?

Answer 29

Voltage-gated sodium channels open when triggered, allowing sodium ions to flood into the cell and causing rapid depolarization.

Question 30

Do leaky potassium channels play a role in maintaining the resting membrane potential of a cell?

Answer 30

Yes, leaky potassium channels continually allow some potassium ions to leak out of the cell, helping to maintain the resting membrane potential.

Question 31

Describe the plateau phase in the non-pacemaker action potential.

Answer 31

During the plateau phase, there is a decrease in potassium permeability and an increase in calcium permeability, leading to a sustained depolarization.

Question 32

How do voltage-gated calcium channels differ from voltage-gated sodium channels in terms of opening and duration?

Answer 32

Voltage-gated calcium channels open when the cell is depolarized to threshold but take longer to open than sodium channels, staying open for a longer period of time.

Question 33

Define repolarization in the context of cell action potential.

Answer 33

Repolarization is the phase where the cell rapidly returns to its resting membrane potential after depolarization, often involving the opening of leaky potassium channels.

Question 34

Describe the significance of L-type voltage-gated calcium channels in cell depolarization.

Answer 34

L-type calcium channels are large channels that stay open for a long time, allowing a significant influx of calcium ions and contributing to a large depolarization in the cell.

Question 35

What are channels and how do they differ from other voltage-gated sodium channels?

Answer 35

IF channels are early sodium channels that open during repolarization, unlike other sodium channels triggered by depolarization.

Question 36

Explain the function of T-type voltage-gated calcium channels in the cell.

Answer 36

T-type calcium channels open briefly, allowing a small amount of calcium to enter the cell, causing a minor depolarization.

Question 37

How do pacemaker cells contribute to the autorhythmicity property of the heart?

Answer 37

Pacemaker cells spontaneously depolarize, triggering an action potential that spreads through the heart via gap junctions, causing it to contract rhythmically.

Question 38

Define the term ‘pacemaker potential’ or ‘pre-potential’ in the context of the heart’s electrical activity.

Answer 38

The pacemaker potential refers to the gradual depolarization of pacemaker cells due to changes in ion permeability, leading to the initiation of an action potential.

Question 39

What is the inherent heart rate of pacemaker cells, and how can it be modulated?

Answer 39

The inherent heart rate of pacemaker cells is about 100 bpm, but it can be influenced by factors like drugs, potassium ion concentration, and calcium ion concentration.