in the heart's pacemaker cells, the timing of the heart rate is determined by the diffusion of calcium into the cells through slow calcium channels.  Temperature can alter this timing because it...     can affect the rate of facilitated diffusion of calcium.     can block ACh receptors.     can accentuate sympathetic receptor action.

A 28-year-old athlete is noted to have a baseline heart rate of 55bpm, which his trainer attributes to excellent parasympathetic (vagal) tone. This parasympathetic effect normally increases Ach release at the SA and AV nodes. Ach release into AV node leads to which of the following effects of its fibers? a. increased action potential amplitudeb. increased conduction velocityc. increased K+ equilibrium potentiald. Hyperpolarizatione. increased rate of depolarization of the pacemaker potential

Which of the following statements best describes the differences in the regulation of cardiac and skeletal muscle contraction?     The amount of contractile force actively generated by muscle cells is increased by stretch in skeletal muscle and decreased by stretch in cardiac muscle.     Cardiac muscle is stimulated by motor neurons and skeletal muscle by neurones from the autonomic nervous system.     Skeletal muscle contractile force is augmented by increasing the firing frequency of action potentials whereas cardiac muscle contractile force is enhanced by noradrenaline increasing calcium influx through ion channels.     Ryanodine receptors in skeletal muscle are opened by a mechanism that requires calcium influx whereas in cardiac muscle membrane depolarisation alone without calcium influx is sufficient to open ryanodine receptors.

1)In the regulation of heart rate, which of the following is the proper stimulus? Group of answer choices -Change in mean arterial pressure -mean arterial pressure -change in heart rate -heart rate   2) If a stimulus is a decrease in mean arterial pressure (MAP), what must be the response if using the baroreceptor reflex? Group of answer choices -Increase in heart rate -Decrease in heart rate -Increase in MAP -Decrease in MAP   3)The brainstem acts as the integrating center for the baroreceptor and chemoreceptor reflexes. Group of answer choices True False   4)A change in MAP causes a change in action potential firing along the afferent pathway of the baroreceptor reflex. Group of answer choices True False