1. Define each of the following terms:
• autorhymicity- The heart is autorhythmic. This means it generates its own rhythmic action potential independent of the nervous system. • sinoatrial node- is the impulse-generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. • pacemaker cells- are specialized cells that cause involuntary muscles and tissues to contract or dilate. • vagus nerves- carry a wide assortment of signals to and from the brain, and they are responsible for a number of instinctive responses in the body. 2. The sympathetic nervous system releases the neurotransmitter- Noradrenaline 3. The parasympathetic nervous system releases the neurotransmitter- endorphins and acetylcholine 4. Circle the correct boldfaced term.
The sympathetic nervous system increases heart rate.
The parasympathetic nervous system decreases heart rate.
5. What happens in each of the five phases of cardiac muscle depolarization? PHASE0(RAPID DEPOLARIZATION)
due to opening of fast voltage gated sodium channels
due to closure of sodium channels while loss of potassium is goingon ,making the cell polarized. PHASE2(PLATEAU)
due to opening of calcium channels. influx of calcium neutralizes the effect of out going potassium so prolonged plateau is achieved. PHASE3(FINAL RE POLARIZATION)
due to closure of calcium channels and continue loss of potassium makes the inside of cell more negative resulting in polarization. PHASE4(RMP)
eventually cell returns to resting membrane potential due to K efflux and cell is ready for next cycle
6. Explain why the SA node generates action potentials at a frequency of approximately 100 beats per minute even though the average resting heart rate is 70 beats per minute.
The average heart rate is lower than the sinoatrial node's ability to generate action...