Absolute And Relative Refractory Period

Action potentials can occur more frequently as long there is a continued source of stimulation, as long as the relative refractory period has been reached, which in experiment 2 the refractory period was complete.

2. With the exception of the R-R interval, which time interval shows the greatest difference between resting and post- exercise? Explain this observation.

At the latter end of the p-q interval, atrial contraction occurs forcing additional blood into the ventricles. At the beginning of the QRS interval on an ECG reading, the mitral valve closes and the ventricles are at EDV (135ml). During the QRS interval, ventricular contraction occurs increasing the pressure in the ventricle and the aorta. When the pressure continues in the ventricle exceeds the pressure in the arteries, the aortic valve opens and blood is ejected. The increased pressure continues through the t peak. The ventricles are now in ESV (65ml) and the aortic valve is closed. Now the ventricles are relaxed causing pressure to fall and the cardiac cycle starts over again. This ECG reading was from a normal tracing. Keep in mind that an ECV is easy to obtain, but there are some subtleties that are very complex.

Arrhythmias are irregular rhythms of the heartbeat which can be fast paced or slow paced.

Smooth muscle contraction occurs when calcium is present in the smooth muscle cell and binds onto calmodulin to activate myosin light chain kinase (Wilson et al., 2002). Phosphorylation of myosin light chains result in myosin ATPase activity thus cross-bridge cycling occurs causing the muscle to contract (Horowitz et al., 1996). There are two known models of excitation and contraction in smooth muscle, electromechanical coupling (EMC) and pharmomechanical coupling

Tachycardia: Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate. When the heart beats rapidly, the heart pumps less efficiently and provides less blood flow to the body and the heart. The rapid heartbeat increases the workload and oxygen demand of the heart. Problems will occur with the heart as tachycardia persists over time. The heart is maintaining less oxygen, which will lead to an MI due to death of the myocardial cells. Patient will start to have angina because of this. Tachycardia is noted in many diseases and disorder like: fever endocarditis, anemia, HTN, pericarditis, abnormal heart impulses, anxiety, older age, sleep apnea, COPD, electrolyte imbalances, and many more.

Table 5. The effects of Atropine measured by the ventricle of the frog’s heart by amplitude, period, and BPMs.

This stage is called repolarisation. The K+ channels then close, the sodium-potassium pump restarts, restoring the normal distribution of ions either side of the cell surface membrane and thus restoring the resting potential. In response to this the Na+ channels in that area would open up, allowing Na+ ions to flood into the cell and thus reducing the resting potential of the cells. If the resting potential of the cell drops to the threshold level, then an action potential has been generated and an impulse will be fired.

When a membrane is excited depolarization begins. When the membrane depolarizes the resting membrane potential of -70 mV becomes less negative. When the membrane potential reaches 0 mV, indicating there is no charge difference across the membrane. the sodium ion channels start to close and potassium ion channels open. By the time the sodium ion channels finally close. The membrane potential has reached +35 mV. The opening of the potassium channels allows K+ to flow out of the cell down its electrochemical gradient ( ion of like charge are repelled from each other). The flow of K+ out of the cell causes the membrane potential to move in a negative direction. This is referred to as repolarization. ( Marieb & Mitchell, 2009). As the transmembrane potential comes back down towards its resting potential level and the potassium channels begins to close, the trasmembrane potential level goes just below -90mV, causing a brief period of hyperpolarization (Martini, Nath & Bartholomew, 2012). Finally, as the potassium channels close, the membrane turns back to its resting potential until it is excited or inhibited again.

The atrial contraction is represented by the P wave. This is an upward, or positive wave of the line on the graph. The ventricular contraction is displayed by the QRS complex. The QRS

The cardiac cycle can be subdivided into two major phases, the systolic phase and the diastolic phase. Systole occurs when the ventricles of the heart contract. Accordingly, systole results in the highest pressures within the systemic and pulmonary circulatory systems. Diastole is the period between ventricular contractions when the right and left ventricles relax and fill.

2. What occurs in the muscle during this apparent lack of activity? Ca++ is being released from the sacroplasmic reticulum and filament movement is taking up slack.

8. What is the difference between the effective refractory period and the relative refractory period?

In addition, scientists have found that genetics also plays a role in cardiac arrhythmias and that in some cases patients have commented that they had no symptoms before they succumbed to some form of episode of cardiac distress, like a sudden heart attack. This has proven to be standard for many different forms of arrhythmias, whether it’s due to genetics or not. One such case is the long QT syndrome (LQTS) which is estimated to affect one in every 5000 people and is recognized as a family disorder, frequent in children during their childhood years (Wilde, and Bezzina 1352–1358.) Patients with this disorder can have symptoms of a fluttering heartbeat, shortness of breath, and chest pain, while other patients might not experience any symptoms at all (Wilde, and Bezzina 1352–1358.) Another known disorder is cardiac conduction disease, which is mostly due to some form of cardiac injury (Wilde, and Bezzina 1352–1358.) Symptoms for this

3. Refractoriness – this prevents heart muscle from responding to a new stimulus while the heart is still in a state of contraction due to an earlier stimulus, and thus, helps to preserve heart rhythm. Irritability is lowest during refractory period. During the absolute refractory period, the heart muscle will not respond to any stimulus however, strong;during the relative refractory period, the heart muscle slowly regains irritability.