Striated and Smooth Muscle

Question 1

What are the physical and functional characteristics of skeletal muscle?

Answer 1

Striated and it uses motor nerves.

Question 2

What are the physical and functional characteristics of smooth muscle?

Answer 2

Unstriated and it can be automatic and made up of single units or multi-units.

Question 3

What are the physical and functional characteristics of cardiac muscle?

Answer 3

It is striated and is automatic without nerve input.

Question 4

What is marks the endings of the sarcomere?

Answer 4

Z lines

Question 5

What is the I Band?

Answer 5

It is a section of the sarcomere with thin actin filaments only.

Question 6

What is the A Band?

Answer 6

It is the dark section of the sarcomere with both thick myosin and thin actin filaments.

Question 7

What is the M Line?

Answer 7

It is the center of the sarcomere and it contains protein that anchors the thick filament (titin)

Question 8

What is the Z Line?

Answer 8

It is where the actin filaments attach.

Question 9

Describe the steps involved in EC coupling.

Answer 9

AP travels down the sarcolemma to the T tubule -> 
depolarization activates the DHPR  -> 
DHPR conformational change activates the RyR ->
Ca2+ is released from the SR -> 
Ca2+ binds troponin C -> 
Contraction is initiated ->
Tropomyosin moves actin to the groove ->
Myosin binds acting ->
POWERSTROKE ->
SERCA pumps Ca2+ back into SR ->
Relaxation

Question 10

Describe the chemical and mechanical steps of the cross bridge cycle.

Answer 10

Myosin-ADP-Pi binds actin (high actin binding affinity) ->
ADP-Pi leaves and Myosin-Actin (stay in rigor mortis) ->
ATP binds into Myosin-Actin-ATP (low actin binding affinity) ->
Hydrolysis of ATP ->
POWER STROKE ->
Contracting and pulling of the Z line together ->
Myosin-Actin-ADP-Pi (high actin binding affinity) ->
Cycle Restarts

Question 11

In the length tension relationship of skeletal muscle, why is the tension very low if the length is really short?

Answer 11

If the sarcomere length is really short, then the actin filaments begin to overlap each other and cause steric hindrance.

Question 12

In the length tension relationship of skeletal muscle, why is the tension very low if the length is really long?

Answer 12

If the sarcomere length is really long, then there are not enough actin-myosin cross bridges and the tension is low as a result.

Question 13

In the length tension relationship of skeletal muscle, what happens to the tension as the length of the sarcomere gradually increases?

Answer 13

The tension will gradually increase with increases in length until it is too long and the cross bridge count is too low as a result.

Question 14

Describe the velocity-force relationship.

Answer 14

When the load is 0 then the velocity is max.

The velocity of shortening decreases as the load increases.

When the load is maximum then the velocity is 0.

Question 15

What is isometric contraction?

Answer 15

Muscle is actively held at fixed length and the force is measured.

Question 16

What is isotonic contraction?

Answer 16

Force of the muscle is held constant and the length of the muscle is measured.

Question 17

What is the difference in skeletal muscle EC coupling and in cardiac muscle EC coupling?

Answer 17

In skeletal muscle, the EC coupling is done with the physical coupling of DHPR to RyR via the conformational change of the DHPR.

In cardiac muscle, the EC coupling is done through Ca2+ induced Ca2+ release based on the depolarization of the T tubules causing an influx of Ca2+ which induces RyR into Ca2+ release from the SR.

Question 18

What is the difference between smooth muscle EC coupling and skeletal muscle EC coupling?

Answer 18

Smooth muscle EC coupling is Ca2+ induced rather than physical like skeletal muscle.

Question 19

Describe the IP3 pathway in smooth muscle activation.

Answer 19

-Does NOT require membrane depolarization

Binding of ligand to IP3 results in a release of Ca2+ from SR leading to MLCK-dependent contraction (myosin light chain kinase) via Ca2+-calmodulin

Question 20

Describe the cAMP pathway in smooth muscle activation.

Answer 20

-Does NOT require membrane depolarization

cAMP activates PKA which phosphorylates MLCK -> decreases its Ca2+ sensitivity and increases SR Ca2+ pumping -> Relaxation

Question 21

Describe the cGMP pathway in smooth muscle activation.

Answer 21

-Does NOT require membrane depolarization

cGMP -> MLC phosphatase -> Decreased myofilament activation -> Relaxation

Question 22

What pathways in smooth muscle activation DO require membrane potential changes?

Answer 22

All require depolarization induced Ca2+ entry into the smooth muscle cell.

• Voltage-Gated Ca2+ Channel -> varies Ca2+ and the contractile state
• Ligand-Bound Ca2+ Channel -> sufficiently activates the voltage-gated Ca2+ channels and varies the Ca2+ and the contractile state as a result

Question 23

What is electromechanical coupling of smooth muscle cells?

Answer 23

It is coupling that requires a change in the membrane potential.

Question 24

What is pharmomechanical coupling of smooth muscle cells?

Answer 24

It is coupling that does not require a change in the membrane potential.

Question 25

How does alpha-adrenergic stimulation cause smooth muscle activation?

Answer 25

α-adrenergic stimulation is activated through the IP3 receptors which act to initiate contraction via calmodulin

Question 26

How does beta-adrenergic stimulation cause smooth muscle relaxation?

Answer 26

β-adrenergic stimulation is activated through cAMP which activates PKA. PKA goes and Pi MLCK. This results in relaxation as MLCK activity is diminished.

Question 27

How does NO cause relaxation in smooth muscle?

Answer 27

NO causes relaxation by responding to ACh release by endothelial cells and it increases the activity of guanylyl cyclase which increases cGMP. cGMP increases the MLC phosphatase which competes with the MLCK and therefore results in relaxation.

Question 28

What does Ca2+ bind to in striated muscle? Smooth muscle?

Answer 28

Troponin.

Myosin Light Chain Kinase