Lec 2 Muscle Contraction Flashcards
True or false: all muscle contraction requires calcium [as opposed to just smooth or skeletal or cardiac]
True
Which types of muscle contraction or slow vs fast?
smooth muscle: slow
cardiac muscle: fast
skeletal muscle: fast
frequency and strength of contractions in cardiac vs skeletal muscle?
cardiac: periodic contractions
skeletal: sustained contraction of varied strength
What is the A band?
extent of length of thick filament
What is the I band?
area that contains only thin and not thick filament
What is the z line?
scaffold protein that anchors thin filament [a-actinin]
What is contained in thick filaments?
myosin heavy and light chains
What is contained in thin filaments?
- actin
- tropomyosin
- troponin
What is role of Ca in muscle contraction?
- Ca binds troponin-C and moves tropomyosin from actin binding sites allowing actin-myosin binding
How does electrical excitation differ in skeletal and cardiac muscle?
cardiac: heart electrically excites itself [not activated by neurons]
skeletal: neurons at neuromuscular junction activate skeletal muscle
How is electrical excitation occur in skeletal muscle?
- 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
How does EC coupling differ in skeletal and cardiac muscle?
- heart requires Ca influx and SR releases Ca
- skeletal muscle contraction does NOT require Ca influx
How many contractions per action potential in cardiac vs skeletal muscle?
heart: one contraction per action potential
skeletal: contraction can represent sum of many action potentials
Does smooth muscle have sarcomeres?
No - thus appears smooth
Does smooth muscle have troponin?
No
What is function of troponin?
prevents actin-myosin interactions in cardiac and skeletal muscle
What requirement of myosin for actin and myosin to interact?
myosin light chain must be phosphorylated
What is function of myosin light chain kinase?
- myosin light chain kinase phosphorylates myosin light chain
- causes increase in myosin ATPase
- thus allows myosin to interact with actin
What are 3 sources of Ca in smooth muscle
- voltage-gated membrane Ca channels
- membrane Ca channels opened by hormones or neurotransmitters
- Ca release from sarcoplasmic reticulum via IP3 binding IP3 receptors
Does smooth muscle contraction require action potential?
No
Contraction mechanism in smooth muscle
- Ca comes in from outside cell and from SR
- Ca binds calmodulin
- Ca-calmodulin complex binds and activates myosin light chain kinase [MLCK]
- MLCK phopsphorylates myosin light chain kinase and allows myosin to bind actin
What activates and what deactivates MLCK?
- Ca+Calmodulin complex activates MLCK
- cAMP inhibits MLCK
What is effect of B-adrenergic stimulation on smooth muscle contraction?
- relaxes
- activates adenylyl cyclase, cAMP then inhibits MLCK
What is effect of a-adrenergic stimulation on smooth muscle contraction?
- contraction
- produces IP3 –> causes Ca release from SR
What is effect of nitric oxide on smooth muscle contraction?
- relaxation
- activates guanylyl cyclase, cGMP then inhibits MLCK
