The absolute and relative refractory periods of an action potential determine other parameters of action potentials such as causing unidirectional conduction and limiting their frequency. Describe what is happening during each of the refractory periods
Then use this information to describe how the different periods affect conduction and frequency.
What will be an ideal response?
Answer: Action potentials have both absolute and relative refractory periods. During the absolute refractory period, the inactivation gate is closed and will not be reset until the membrane has repolarized sufficiently. During the relative refractory period, many, but not all, Na+ channels have been reset. Additionally, the membrane is typically hyperpolarized below the resting membrane potential. This means it would take a stronger than normal stimulus to bring the potential to threshold and recruit enough Na+ channels to generate a new action potential. When action potentials are traveling along, the depolarization spreads in both directions (electrotonically), but can only activate channels that are not in the absolute refractory period (i.e., in front of the AP.) Channels in the relative refractory period can be opened, but by the time the current spreads to them, it has decayed enough that it is no longer able to be the stronger than normal stimulus required to generate a new AP. Thus, the AP can move only in the forward direction. The frequency of action potentials is also limited by the absolute refractory period. It is impossible for another action potential to be started until the channels have reset from the first one; thus, there is a limit to the frequency (number of action potentials per unit time).
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A myosin molecule in the thick filaments can be considered a protein having a quaternary structural level. Which of the following best describes this structural level?
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Heart and venous valves serve a similar function. They prevent a ____ flow of blood
a. forward b. backward c. turbulent d. pulsatile e. laminar
The myocardial cells receive their blood supply from the coronary arteries that branch off from the aorta
Indicate whether the statement is true or false.
After a protein is synthesized, it undergoes structural modification. which of the following statements about this process are true? select all that apply.
a) carbohydrates may be added to the protein b) all the introns and exons are removed c) it may involve removal of some amino acid segments d) the protein may be folded and stabilized by disulfide bridges e) this process is known as posttranslational modification