What band gets shorter in the sarcomere during muscle contraction?
The I band
What are thick filaments surrounded by?
What makes up a muscle cell?
Sarcomeres lined up make myofibrils. Muscle fibers (cells) are a bunch of packed myofibrils.
What regulatory proteins are associated with the F actin strand?
G actin molecules, Nebulin, Troponin and Tropomyosin
Where do the myosin heads point?
Towards the Z line
How do actin and myosin work together in muscle contraction?
Adding ATP to the sarcomere binds ATP to the myosin and causes dissociation of myosin from actin. Myosin then hydrolyzes ATP and the myosin head cocks when it is bound to ADP and Pi. Pi is released from myosin and the head can interact again with actin further down the chain. ADP is released, the myosin de-cocks and pulls the actin filament along with it. The cycle will continue as long as ATP is present.
How does the muscle get energy to contract?
What determines how quickly a muscle can contract?
How fast myosin hydrolyzes ATP.
Type I muscle fibers
Oxidative that has slow ATP hydrolysis rate.
Type II muscle fibers.
Glycolytic that has a fast ATP hydrolysis rate.
What regulates the ability of actin and myosin to contract?
What blocks the binding site on actin for myosin? How is this removed?
Tropomyosin covers the myosin binding site on actin. Ca binds to troponin and allows troponin to move tropomyosin so myosin can bind to actin.
How does a neuron tell the muscle to contract?
Action potential is generated in the sarcolemma, it causes an increase in Ca in the cytoplasm and causes myofilament sliding and contraction.
How does the cell keep its Ca levels low?
It stores Ca in the sarcoplasmic reticulum or sends it out of the cell.
What structures allow Ca to pass from the sarcoplasmic reticulum into the cell?
Ryanodine receptors in the sarcoplasmic reticulum and dihydropyridine receptors (DHPR) in the T-tubules. An action potential causes the depolarization of the T-tubule and causes a conformational change of the DHPR which will pull open the ryanodine receptor and allow Ca to flood into the cytoplasm.
What promotes relaxation of the muscle cell?
Removal of Ca from the cytoplasm via the ATP pump SERCA, which pumps Ca back into the sarcoplasmic reticulum.
What happens in a muscle when action potentials are generated before Ca levels return to normal in the muscle cell?
You get a higher level of muscle contraction and force generation as you recruit more muscle fiber contraction
What is maximal muscle contraction in a single cell called?
Where can things go wrong in muscle contraction?
Neurotransmission at neuromuscular junction (myasthenia gravis), DHPR (congenital myotonia and periodic paralysis), ryanodine receptor (malignant hyperthermia), and myofilaments become less sensitive to Ca.
How is cardiac muscle different from skeletal muscle in contraction initiation?
No neuromuscular junction and Ca induced Ca release (Ca outside of cell interacts with the ryanodine receptor, opens receptor, more Ca enters cell and causes contraction)
How is smooth muscle different from skeletal muscle in contraction initiation?
Actin comes from the dense bodies, ATPase is slow so contractions are slow. The thick filaments are activated for muscle contraction: Ca activates Calmodulin which activates myosin light chain kinase. Myosin light chain kinase phosphorylates the myosin light chain and initiates muscle contraction.
Where does smooth muscle get its Ca for muscle contraction?
Outside the cell (voltage dependent channels), transmitter channels (open on neurotransmitter contact), Ca-dependent Ca release at the ryanodine receptor and IP3 generation (opens Ca release channel in sarcoplasmic reticulum)
How does relaxation take place in smooth muscle?
Dephosphorylation of the myosin light chain.
What determines the muscle tone in smooth muscle?
The balance between the kinase (contraction) and phosphatase (relaxation) of the myosin light chains.