L12 Muscles

Question 1

What are cardiac muscles specific to and what are the adaptations of cardio myoctes?

Answer 1

Cardiac muscles are specific to the heart and cardio myocytes are striated like skeletal muscles and they are shorter and branched.

Question 2

How are myocytes held together?

Answer 2

Intercalated Disks

Question 3

Where does electrical coupling happen?

Answer 3

Electrical coupling is in between adjacent myocytes at the intercalated disk (basically at gap junction)

Question 4

How is action potential happening?

Answer 4

Action potential is initiated in the pacemaker cells of the Sino-Atrial node and propagates between cells through the gap junctions.

Question 5

Name the type of muscle which is involved in mechanical control of organ system as well as control of blood vessel and airway diameter?

Answer 5

Smooth Muscles

Question 6

What are the three main factors that can influence the control of smooth muscle contraction?

Answer 6

1. Autonomic Nervous System
2. Circulating Hormones
3. Inflammatory mediators.

Question 7

Name the two classes of smooth muscles?

Answer 7

Multiunit and unitary.

Question 8

What are the structural features of smooth muscles?

Answer 8

1. Non-striated
2. Dense bodies
3. Thick filament arrangement.

Question 9

What are the variations in action potential generation in smooth muscles?

Answer 9

1. Some smooth muscles can generate action potential similar to neurons.
2. Other smooth muscle cells do not generate action potential but respond to changes in membrane potential.

Question 10

What is the initial event that triggers calcium release in skeletal muscles?

Answer 10

Depolarisation of the T tubule membrane.

Question 11

What are the two main effects of depolarization on calcium release in skeletal muscle?

Answer 11

1. Direct calcium influx - Directly opens L type calcium channels in the T tubule membrane allowing the inflow of calcium ions.
2. Calcium induced calcium release - mechanical tethering between the L-type Ca2+ channels in the T-tubule and Ca2+ release channels

Question 12

Apart from skeletal muscles which muscles have T tubules?

Answer 12

Cardiac muscles

Cardiac and skeletal muscles have T tubules, smooth muscles have caveolae

Question 13

Where are T tubules found in cardiac muscles?

Answer 13

Z line region of the sacromeres.

Question 14

What are ryanodine receptors?

Answer 14

Ryanodine receptors are large calcium channels found in the sacroplasmic (SR) membrane.

Question 15

Are there any mechanical interaction between the voltage gated Ca2+ channels in the T-tubule and Ryanodine receptors in cardiac muscles?

Answer 15

No mechanical interaction in cardiac muscles.

Question 16

What activates Ryanodine receptors?

Answer 16

Influx of Ca2+ through the T-Tubule channels - Calcium Induced Calcium Release

Question 17

How does termination of muscle contraction happen?

Answer 17

Removal of calcium from the cytoplasm.

Question 18

What are the two primary mechanisms for removing calcium ions from the cytoplasm of muscle cells after contraction?

Answer 18

1. Plasma membrane calcium ATPase (PMCA)
2. Sodium - Calcium exchanger (NCX)

Question 19

What is the role of the Sarcoplasmic Reticulum Calcium ATPase (SERCA)?

Answer 19

SERCA is protein present in the membrane of SR (Sacroplasmic membrane) and actively pumps Ca ions from cytoplasm back into the SR

Question 20

What is the structural difference of T tubules in skeletal and smooth muscle?

Answer 20

Skeletal muscles have well developed T - tubules which are deep inside muscle fiber which faciliates calcium release whereas smooth muscles lack T tubules.

Question 21

What do smooth muscles have instead of T-tubules?

Answer 21

Instead, they utilize caveolae, which are small pockets on the surface

Question 22

What are the two types sacroplasmic reticulum (SR) is arranged?

Answer 22

1. Peripheral SR – encircles the caveolae
2. Central SR – runs through the cell

Question 23

What can activate L-type Ca2+ channels in smooth muscles?

Answer 23

Change ion Vm or Action potential.

Question 24

What does the activation of L-type Ca2+ channels lead to?

Answer 24

Leads to CICR, (Calcium induced calcium release) through the activation of ryanodine receptors in SR membrane.

Question 25

What does activation of Gq-coupled membrane receptors leads to?

Answer 25

Leads to IP3 production and stimulation of IP3 receptors

Question 26

Why are sacromere contraction similar in skeletal and cardiac muscles?

Answer 26

They share the basic units of contraction - F-ACTIN, TROPOMYOSIN, TROPONIN and MYOSIN molecule.

Question 27

What is the role of Calcium and Troponin in Skeletal
and Cardiac Muscle in cross-bridge formation?

Answer 27

Calcium ions trigger muscle contraction by binding to troponin. Binding causes conformational change in the troponin-tropomyosin complex, exposing the myosin-binding sites on actin. Once exposed, myosin heads can bind to actin and initiate the cross-bridge cycle, resulting in muscle contraction.

Question 28

What is the key difference in the mechanism of muscle contraction between smooth muscle and skeletal/cardiac muscle?

Answer 28

Smooth muscles do not use troponin instead uses calponin and caldesmon which inhibits actin and mysosin interaction.

Question 29

Downstream effects of smooth muscle contraction?

Answer 29

1. Activation of myosin light chain kinase - Phosphorylates MLC.
2. Removes inhibitory effects of calponin and caldesmon faciliating crossbridge formation and contraction.

Question 30

What needs to be done to stop contraction in smooth muscles?

Answer 30

De-phosphorylate MLC which involves myosin light chain phosphatase (MLCP).