Lec 2 Muscle Contraction

Question 1

True or false: all muscle contraction requires calcium [as opposed to just smooth or skeletal or cardiac]

Answer 1

True

Question 2

Which types of muscle contraction or slow vs fast?

Answer 2

smooth muscle: slow
cardiac muscle: fast
skeletal muscle: fast

Question 3

frequency and strength of contractions in cardiac vs skeletal muscle?

Answer 3

cardiac: periodic contractions
skeletal: sustained contraction of varied strength

Question 4

What is the A band?

Answer 4

extent of length of thick filament

Question 5

What is the I band?

Answer 5

area that contains only thin and not thick filament

Question 6

What is the z line?

Answer 6

scaffold protein that anchors thin filament [a-actinin]

Question 7

What is contained in thick filaments?

Answer 7

myosin heavy and light chains

Question 8

What is contained in thin filaments?

Answer 8

• actin
• tropomyosin
• troponin

Question 9

What is role of Ca in muscle contraction?

Answer 9

• Ca binds troponin-C and moves tropomyosin from actin binding sites allowing actin-myosin binding

Question 10

How does electrical excitation differ in skeletal and cardiac muscle?

Answer 10

cardiac: heart electrically excites itself [not activated by neurons]
skeletal: neurons at neuromuscular junction activate skeletal muscle

Question 11

How is electrical excitation occur in skeletal muscle?

Answer 11

• motor neurons release acetylcholine [Ach] at neuromuscular junction
• Ach binds nicotinic cholinergic receptors in motor end plate
• Na flux through Ach receptor initiates skeletal muscle action potential

Question 12

How does EC coupling differ in skeletal and cardiac muscle?

Answer 12

• heart requires Ca influx and SR releases Ca

- skeletal muscle contraction does NOT require Ca influx

Question 13

How many contractions per action potential in cardiac vs skeletal muscle?

Answer 13

heart: one contraction per action potential
skeletal: contraction can represent sum of many action potentials

Question 14

Does smooth muscle have sarcomeres?

Answer 14

No - thus appears smooth

Question 15

Does smooth muscle have troponin?

Answer 15

No

Question 16

What is function of troponin?

Answer 16

prevents actin-myosin interactions in cardiac and skeletal muscle

Question 17

What requirement of myosin for actin and myosin to interact?

Answer 17

myosin light chain must be phosphorylated

Question 18

What is function of myosin light chain kinase?

Answer 18

• myosin light chain kinase phosphorylates myosin light chain
• causes increase in myosin ATPase
• thus allows myosin to interact with actin

Question 19

What are 3 sources of Ca in smooth muscle

Answer 19

1. voltage-gated membrane Ca channels
2. membrane Ca channels opened by hormones or neurotransmitters
3. Ca release from sarcoplasmic reticulum via IP3 binding IP3 receptors

Question 20

Does smooth muscle contraction require action potential?

Answer 20

No

Question 21

Contraction mechanism in smooth muscle

Answer 21

1. Ca comes in from outside cell and from SR
2. Ca binds calmodulin
3. Ca-calmodulin complex binds and activates myosin light chain kinase [MLCK]
4. MLCK phopsphorylates myosin light chain kinase and allows myosin to bind actin

Question 22

What activates and what deactivates MLCK?

Answer 22

• Ca+Calmodulin complex activates MLCK

- cAMP inhibits MLCK

Question 23

What is effect of B-adrenergic stimulation on smooth muscle contraction?

Answer 23

• relaxes

- activates adenylyl cyclase, cAMP then inhibits MLCK

Question 24

What is effect of a-adrenergic stimulation on smooth muscle contraction?

Answer 24

• contraction

- produces IP3 –> causes Ca release from SR

Question 25

What is effect of nitric oxide on smooth muscle contraction?

Answer 25

• relaxation

- activates guanylyl cyclase, cGMP then inhibits MLCK