Muscle contraction Flashcards
What are the three types of muscles?
- smooth (sloppy, less organized)
- cardiac (striated, branched)
- skeletal (striated, multi-nucleated fibers)
What are the three types of muscle fibers?
- Slow oxidative (contract slowly, O2 and glucose used to ATP, fatigues slowest, use more mitochondria)
- Fast oxidative (contract fast, O2 used, fatigues fast, use more mitochondria, fast ATPase activity)
- Fast glycolytic (contract fast, glucose used, fatigues fastest, use less mitochondria)
What does a muscle comprise of?
- Muscle have bundles of fascicules which contain muscle fibers, which then contain myofibrils which contain sarcomere with actin and myosin.
- Muscle fiber is packed with protein, mitochondria, and many nuclei
- muscle fibers extend the entire length of muscle
What is the cell membrane of skeletal muscle cells called?
- sarcolemma
What is the resting potential of skeletal muscle cell?
- (-90mV)
What happens at the neuromuscular junction when the action potential arrives?
- AP arrives at the axon terminal –> Voltage gated calcium channels open –> influx of calcium causing exocytosis of acetylcholine in the synaptic cleft –> acetylcholine binds to post synaptic acetylcholine gated channels –> Na flows in, reaching threshold potential –> action potential then propagates down the muscle fiber
what is agonist and antagonist and what is an example of agonist of acetylcholine receptor?
agonist= drugs/molecules that activate certain receptors or a reaction
ex. nicotine (not destroyed by acetylcholinesterase)
antagonist= drugs that block certain receptors or block reaction of other drugs
What is myasthenia gravis and what could be a treatment option?
- autoimmune disorder where antibodies produced block the post synaptic acetylcholine receptors.
- treatment include acetylcholinesterase inhibitors so acetylcholine has more time in the neuromuscular junction to bind to any remaining acetylcholine receptors.
What does sarcomere comprise of?
- actin (thin filament)
- myosin (thick filament)
- tropomyosin (covers myosin binding site on the actin, contains troponin c which is a binding site for calcium)
What does sarcoplasmic reticulum store?
- large amount of Ca2+
How does action potential on muscle fiber result in muscle contraction?
AP propagates to muscle fiber(sarcolemma) and along t- tubule –> causes sarcoplasmic reticulum to release calcium –> calcium binds to troponin C on tropomyosin –> tropomyosin shape changes and uncovers the myosin binding site –> myosin head binds to actin –> myosin moves actin(power stroke) with ADP and inorganic phosphate –> ADP and inorganic phosphate released after “power stroke” –> ATP binds to myosin head,
resulting in unbinding of myosin and actin –> returning to original position and ATP is then hydrolyzed.
What are the two types of smooth muscles?
- Multi-unit (each cell contracts independently, each cell has a neuromuscular junction)
- unitary smooth muscle (mass of fiber/unit contract all at once, gaps junctions for action potential propagation)
What are varicosities on neurons in smooth muscle?
-vesicles/bulges filled with neurotransmitters on an autonomic neuron axon as it wraps around smooth muscle
What is the difference between smooth muscle and skeletal muscle contraction?
- smooth muscle: extracellular calcium binds to calmodulin, can contract through nervous signal, hormonal signal, stretching of nearby organ. It has longer contractions, latch phenomenon, low energy usage, able to contract 80% of the length.
- skeletal muscle: uses intracellular calcium from sarcoplasmic reticulum to bind to troponin C, requires acetylcholine as only mechanism for AP and contraction. Only contract 30% of its length.
How does relaxation occur of the vascular smooth muscle?
- relaxation happens without nervous intervention when decrease oxygen, increased CO2 and increased hydrogen ion concentration are detected in local tissues
