If ACh channels are opened on a muscle fiber that is held at +55 mV, which ion moves predominantly? In which direction does this ion move across the muscle cell membrane?
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If ACh channels are opened on a muscle fiber that is held at +55 mV, which ion moves predominantly? In which direction does this ion move across the muscle cell membrane?
In general, nerves and muscles generate and transfer electrical signals and these excited signals are used to carry out basic functions.
excitable cells have a huge number of voltage gated ion channels, and they use action potentials to initiate the responses. Examples of excitable cells are nerves, skeletal muscles, heart, etc.
The resting potential of a mammalian neuron is around -70mV. At the input of a signal, voltage gated ion channels open of Na+, Cl- or Ca2+. This leads to a graded potential at the dendrites or the body of the cell.
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- If ligand-gated K+ channels were to open in an unstimulated muscle fiber,how would this affect the resting membrane potential?As mentioned in class, one additional major use of ATP in skeletal muscle (besides powering the myosin heads) is the recycling of calcium ions back into the sarcoplasmic reticulum after depolarization. The resting concentration of Ca++ in the muscle cell cytoplasm is about 50-100 nM, and the spike concentration after depolarization is about 10-20 μΜ. a) Consider a single sarcomere. What is the number of free calcium ions within the sarcomere at rest? What is the number of free calcium ions after depolarization? b) The major ion pump responsible for calcium ion recycling is SERCA (sarco/endoplasmic reticulum calcium ATPase). SERCA uses one molecule of ATP to pump two calcium ions, and the resting level can be restored in about 10-20 ms. How many molecules of ATP are used in a single sarcomere for pumping calcium in a single "twitch"? c) Assume that a single "twitch" is sufficient to drive one sarcomere from its fully extended length (about 2.5 µm) to its fully contracted length (about 1…Explain the intracellular mechansim of smooth muscle relaxation of agaonist such as mepyrimine and atropine. Give diagram for each.
- Discuss the following statement: “The basal lam-ina of muscle fibers serves as a molecular bulletin board,in which adjoining cells can post messages that direct thedifferentiation and function of the underlying cells.”Put these events that occur in skeletal muscle in the correct chronological sequence: 1. Activation of voltage-gated dihydropyridine (DHP) receptor in the T-tubule 2. Opening of mechanically-gated ryanodine receptors (RyR) on the sarcoplasmic reticulum 3. Na+ influx through ligand-gated ion channels on the motor end plate 4. Ca2+ binding to troponin 2, 1, 4, 3 4, 3, 2, 1 4, 3, 1, 2 3, 1, 4, 2 3, 1, 2, 4Please fill in the blanks: A(n) ["action potential", "muscle twitch", "contraction"] consists of a wave of depolarization that moves along the plasma membrane of a neuron or a muscle fiber. This wave of depolarization is immediately followed by repolarization. Depolarization is when the cell's membrane potential becomes more ["resting", "negative", "positive"] . Depolarization occurs when calcium channels open in the plasma membrane. Repolarization is when the cell's membrane potential becomes more ["resting", "positive", "negative"] , returning the cell to its resting potential. Repolarization occurs when ["calcium", "sodium", "potassium"] channels close and ["sodium", "calcium", "potassium"] channels open.
- Put these events that occur in skeletal muscle in the correct chronological sequence: 1. Opening of mechanically-gated ryanodine receptors (RyR) on the sarcoplasmic reticulum 2. Ca²+ binding to troponin to initiate contraction 3. Activation of voltage-gated dihydropyridine (DHP) receptor in the T-tubule 4. Na+ influx through ligand-gated ion channels on the motor end plate 4, 3, 2, 1 2, 1, 4, 3 3, 1, 2, 4 4, 3, 1, 2 3, 1, 4, 2Discuss the similarities and differences by which Ca2+ activity is involved in initiating muscle contraction in skeletal versus smooth muscle fibers (hint: include Ca2+ sources, proteins it binds to, and signaling cascade it activates leading to contraction). (please explain in sentences, max 12 sentences)How is resting membrane potential established in a neuron and muscle cell?
- Define what the NMJ is and why it's important for muscle contraction. Explain in short the process of the NMJ signaling the muscle to contract. Note the difference between a motor unit and the NMJ.When a cardica muscle is isolated and placed in a solution of sodium chloride, potassium chloride, and sodium bicarbonate, will muscle contraction occur if:a. muscle is stimulated directly by depolarizing the membrane? (provide a short explanation)b. muscle is stimulated by stimulating the nerve to the muscle? (provide a short explanation)a) What happened to the number of fibers contracting as you increased the voltage? b) In light of the "all or none" law of muscle contraction, how can you explain the graded response?