Question

Please compare and contrast action potentials in cardiac autorhythmic cells and cardiac contractile cells, including drawings to illustrate your discussion. Would increased sympathetic nervous system activity affect either of these cells? If so, please describe how, including the cellular mechanism that produces the effect. What effect(s) would this have on overall cardiac function?

Answer 1

20N 20 -40 -60 Millivolts -20 -40 -60 -80 Millivolt:s On the left is the action potential of an autorhythmic cell; on the right, the action potential of a contractile cell

Contractilecells contract when stimulated, Autorythmic Cells on other hand ae self stimulating and contract without any external stimulation.

Autorythmic Cells Exhibit Pace-maker Potentials. Depolarisation is due to inward diffusion of calcium(not sodium). Depolarisation begins when---

• Slow calcium channels open( see Number 4 in Image)
• then concludes quickly when fast calcium channels open( see 0)
• Repolarisation is due to outward diffusion of K⁺ (see 3)

In contractile cells--

• Depolarisation is rapid and is due to inward diffusion of sodium (see 0 in action potential image of contractile cell)
• Repolarisation begins with slow outward diffusion of pottasium, but is largely off set by slow inward diffusion of Calcium (see 1 and 2 curve). So. repolarisation begins with a plateau .
• then pottasium diffuses out much more rapidly as the calcium channel close(see 3), and the membrane potential quickly reaches to RESTING Potential (see 4).

Answer2 and its description----

YES sympathetic Nervous System Activity affects Contractile cells because aympathetic fibres richly innervate both atrial and ventricular contractile cells. Sympathetic stimulation increases the strength of contraction, which makes heart beating more forcefully and consequently ejecting more blood . This effect Results from an increase in calcium permeability which enhances the slow influx of calcium and thereby increasing the amount of calcium to participate in excitation- contraction coupling process.

Answer 3

Overall affect as follows

• increase heart rate
• decreasing the delay between atrial and ventricular contraction
• decreasing the time it takes for action potentials to spread throughout the heart
• increasing the force of contraction