BMSC 207 Muscle 3

Question 1

Cardiac Muscle

Answer 1

• Made up of cardiac myocytes
  which are shorter, branched cells and usually contain a single nucleus.
• Striated
• has sarcomeres containing thick and thin filaments
• Interconnected by Intercalated disks

Question 2

Intercalated disks

Answer 2

Desmosomes: Link mechanically
Gap Junctions: Link them electrically

Question 3

Cardiac muscles have ______ T-Tubules compared to skeletal muscles

Answer 3

Larger

Question 4

Cardiac muscles have smaller or larger amounts of Sarcoplasmic reticulum

Answer 4

Smaller

Question 5

Cardiac muscles have alot or little mitochondria

Answer 5

Alot - Oxidative metabolism

Question 6

Autorhythmic cells (Pacemakers)

Answer 6

Generate AP’s spontaneously

Question 7

Autorhythmic Myocardial cells

Answer 7

Have an unstable resting membrane potential of -60mV they never truly rest.

Question 8

AP’s in contractile myocardial cells

Answer 8

Phase 0 - Na+ channels open at -40
Phase 1 - Na+ channels close at +20
Phase 2 - Ca2+ channels open; fast K+ channels close at +10
Phase 3 - Ca2+ Channels close; slow K+ channels open at -40
Phase 4 - Resting potential at -90

Question 9

Do Cardiac muscles want Short or long refractory periods and why?

Answer 9

Long refractory periods - So all blood can fill up and push enough blood throughout the body.

Question 10

Excitation-Contraction coupling

Answer 10

1. Action Potential enters from adjacent cell.
2. Voltage gated Ca2+ channels open. Ca2+ enters cell
3. Ca2+ induced Ca2+ release. Through ryanodine receptor channels (RyR)
4. Local release cause Ca2+ sparks create a Ca2+ signal.
5. Summed Ca2+ sparks create a Ca2+ signal
6. Ca2+ ions bind to troponin to intiate contraction

Question 11

Relaxed state

Answer 11

Myosin head cocked. Tropomyosin partially blocks binding actin. Myosin is weakly bound to actin.

Question 12

Initiation of Contraction

Answer 12

Calcium signal initiates contraction

Question 13

Muscle Relaxation

Answer 13

Removal of Ca2+ in extracellular space, Reuptake into the sarcoplasmic reticulum is still the primary mechanism

Question 14

SERCA pump is regulated by ________

Answer 14

Phospholamban

Question 15

Phospholamban

Answer 15

Crucial regulator of cardiac contractility
When Phosphorylated: Ca2+ pump inhibition is removed, enhancing relaxation rates and contractility.

Question 16

Enhancing contractile force in cardiac muscle

Answer 16

1. An increase in intracellular Ca2+ in the cardiac myocytes enhances contractile force.
2. Length tension relationship: cardiac muscle generates a greater force when slightly stretched.

Question 17

The heart is innervated by the autonomic nervous system: (sympathetic and parasympathetic)

Answer 17

Sympathetic: increases heart rate/conduction and contractility
Parasympathetic: Decreases heart rate/conduction

Question 18

Sympathetic modulation of contraction

Answer 18

1. Phosphorylation of Ca2+ channels increases calcium conductance during AP’s
2. Phosphorylation of RyR receptors enhances sensitivity to Ca2+, increasing release of Ca2+ from the SR
3. Increase rate of myosin ATPase
4. Phosphorylation of SERCA increase the speed of Ca2+ re-uptake which increases Ca2+ storage

Question 19

Cardiac length tension relationship

Answer 19

Skeletal length tension relationship explained by degree of overlap between thick and thin filaments

Question 20

The plateau phase of contractile myocardial muscle cell action potential is due to

Answer 20

Delayed influx of Ca2+

Question 21

In Cardiac Muscle, force of contraction is increased by:

Answer 21

Activating Sympathetic Neurons

Question 22

Cardiac length tension relationship (2 types)

Answer 22

• A slightly stretched Sarcomere increases the Ca2+ sensitivity of the myofilaments, stretched sarcomere has a decreased diameter which may reduce the distance that Ca2+ needs to diffuse.
• A slightly stretched sarcomere puts additional tension on stress-activated Ca2+ channels, increasing Ca2+ entry from extracellular space and increasing Ca2+ induced Ca2+ release.

Question 23

The heart is under ______ Control

Answer 23

Tonic - allows the heart to respond to sustained changes in circulatory dynamics

Question 24

Parasympathetic does what to heart rate?

Answer 24

Decreases Heart rate. Below 90bpm.
Dominant at RHR

Question 25

Sympathetic Does what to your heart rate?

Answer 25

Increases heart rate over 90BPM

Question 26

Modulation Pacemaker activity (parasympathetic)

Answer 26

Parasympathetic neurons containing ACh mainly innervate with SA and AV node influencing autorhythmic myocardial cells, decreaseing frequency of Action Potentials (Decreasing Heart Rate

Question 27

Sympathetic Modulation of pacemaker activity

Answer 27

Beta 1 Adrenergic Receptors can be activated by NE released from sympathetic neurons or epinephrine from the adrenal medulla.
- Cells reach threshold
- A decreased level of repolarization.