Contraction Mechanisms of Skeletal, Smooth and Cardiac Muscles 2

Question 1

In skeletal muscle, where does the AP travel along

Answer 1

Sarcolemma

Question 2

Describe the mechanism of skeletal muscle contraction

Answer 2

AP travels alongs Sarcolemma
AP reaches triads (area with 1 tubule and 2 terminal cisternae)
AP stimulates release of Ca 2+ from the terminal cisternae of the sarcoplasmic reticulum

Question 3

What events take place after the release of Ca2+ into the sarcoplasm

Answer 3

Actin active-site exposure 
Cross-bridge attachment 
Pivoting of myosin head
Cross-bridge detachment 
Myosin reactivation

Question 4

What occurs in actin active -site exposure after Ca2+ release

Answer 4

Ca2+ binds to tropinin (TN)
Bonds between TB and tropomysin (TM) weaken
Position of TN changes
TN then causes TM to roll away from active sites on actin

Question 5

What occurs in the cross-bridge attachment

Answer 5

Thick Myosin heads bind to the active sites on the thin actin filaments
Cross bridges form
This starts excitation-contraction coupling (link between the generation of AP and start of muscle contraction)

Question 6

What occurs in the pivoting of myosin head

Answer 6

The myosin heads begin to cock or pivot towards the M-line, pulling the actin filaments closer to the M line (contraction)
As the head pivots the energy stores in them is released as ADP+ Pi. This is called power stroke
Each power stroke shortens the length of the sarcomere by 1%

Question 7

What occurs in the cross bridge detachment

Answer 7

After contraction the cross bridges detach
The muscle relaxes :
Ca2+ levels return to normal
Na channels close
K+ channels open and the initial resting state of the membrane is restored as K+ leaves the sarcoplasm
The sarcomere returns to its original length
More ATP can now attach to the free myosin heads

Question 8

What occurs In myosin reactivation

Answer 8

When more ATP is split by free myosin heads, reactivating of myosin occurs
This process can be repeated as long as there is a continued stimulus, and availability of Ca2+ and ATP

Question 9

True or false, muscle contraction is independent on energy supplied by ATP

Answer 9

False it is dependent

Question 10

True or false, most of the energy is used is used in the power stroke

Answer 10

True

Question 11

What are the small amounts of energy used for in pumping

Answer 11

Pumping Ca 2+ from the sarcoplasm into the SR after contraction
Na+ and K + through the sarcolemma of the muscle fibers to maintain appropriate ionic environment for propagation of muscle fibers AP

Question 12

What are the sources of energy for ADP rephosphorylation to ATP

Answer 12

Phosohocreatine (creatine phosphate): a high energy compound)
Glycolysis of glycogen previously stores in muscle cells
Oxidative (aerobic) metabolism

Question 13

What two energy sources occurs during peak activity

Answer 13

Phosphocreatine, Glycolysis

Question 14

What two sources of energy incorporated anaerobic metabolism

Answer 14

Phosphocreatine (creatine phosphate), glycolysis

Question 15

What source of energy involves oxidative metabolism

Answer 15

Aerobic metabolism

Question 16

What is the reaction for phosphocreatine metabolism

Answer 16

Phosphocreatine + ADP ——> ATP + creatine

Question 17

What is the reaction for glycolysis

Answer 17

Glycogen ———> pyruvate + ATP ———> lactic Acid + Pi

Question 18

What is the reaction for oxidative metabolism

Answer 18

O2 + end products of glycolysis/other food stuff ——-> ATP

Question 19

Which energy source has max contractions of 5-8secs

Answer 19

Phosphocreatine

Question 20

Which energy source has max contractions of many secs > 1 min

Answer 20

Glycolysis

Question 21

Which energy source has max contractions of hours

Answer 21

Oxidative metabolism

Question 22

Which energy source accounts for more than 95% of energy used by muscles

Answer 22

Oxidative metabolism

Question 23

What are the differences in the mechanism of muscle contractions in smooth muscles than skeletal muscles

Answer 23

Ca2+ binds to calmodulin (CaM)
Ca2+- calmodulin activates myosin light chain kinase (MLCK)
MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity
Active myosin crossbridges slide along actin and create muscle tension

Question 24

What are the differences in the mechanism of muscle contractions in cardiac muscles than skeletal muscles

Answer 24

Ca2+ induces Ca2+ release through ryanodine receptor channels (RyR)
Local release causes Ca2+ spark
Summed Ca2+ sparks creates a Ca2+ signal