Explanation:
Muscles act on joints antagonistically. Some muscles will contract while other contract pulling on bones around joint hence enabling movement. An example is the elbow joint is moved by antagonistic action of biceps and triceps. When your biceps contract and triceps relax you are able to bend your arm at your elbow. When your triceps contract and biceps relax, your arms straighten.
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SA Node<span> which is also known as the sinus node, is the natural pacemaker of
the heart. It controls the heart rate by generating electrical impulses
and then sending electrical signals through the heart muscle, causing
the heart to contract and pump blood throughout the body. </span>
The SA Node is located in the outer layer of the right atrium of the heart, near the superior vena cava. It is made up of a group of cells (myocytes) positioned on the
wall of the right atrium, at the center of the heart and near the
entrance of the superior vena cava. These cells contract at a rate of
about 70-80 times per minute, which make up the natural heart beat.
When salt and sugar dissolve in water it is a physical change. The chemical makeup of the salt and sugar are not changed.
Physical change