Review Sheet Exercise 6 Cardiovascular Physiology Essay

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Cardiovascular Physiology


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-
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This allows your cardiovascular centres in your brain a little bit more latitude as far as controlling your heart rate. If you were to remove a beating heart from someone's body you would find that the heart is no longer being suppressed by the parasympathetic nervous system and it will accelerate to the same pace as the sinoatrial node. The SA node generates action potentials approximately 100 times per minute due to the physiology of the heart, its own permeability to sodium and calcium via its channels, and a host of other things. Anywhere between 80 to 100 beats per minute is normal for the SA node.

7. What are two key differences between cardiac muscle and skeletal muscle?

cardiac is involuntary, skeletal is voluntary cardiac is unstriated, skeletal is striated

8. What is the difference between the effective refractory period and the relative refractory period?
The effective refractory period is the time in which the cell is incapable of responding to a second stimulus between the phases of 0-3.5, while the relative refractory period is the time in which the cell is making preparations to receive stimulus between phase 3.5-4.

9. When the heart is externally stimulated just after the start of the contraction cycle, why does this have no affect on heart rate?

This is because once a contraction has started, the action potential has already fired, stimularing the muscle fibers. Once they
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