SR is the site of storage and release of calcium ions for contraction. Three types of cardiocytes are found in the myocardium. 1) Cells found at the junction of the great veins and the right atrium have the fastest intrinsic rhythm (this is the sinoatrial (SA) node or 'pacemaker' of the heart). These are the AUTORHYTHMIC CELLS and they spontaneously discharge about 100 times per minute.
1 Higher contribution limits are permitted with a Roth Individual 401k than a Roth IRA. 2  For 2015 participants can contribute up to $18,000 to a Roth 401k ($24,000 if age 50 or older), but they can only contribute $5,500 ($6,500 if age 50 or older) into a Roth IRA.
Like adults, minors are subject to the maximum annual contribution limits for Roth IRAs. As of 2012, the maximum contribution limit is $5,000 per tax year for investors under the age of 50. A minor may not contribute more than $5,000 to a Roth IRA. Contributing to a Roth IRA may have significant advantages for minors.