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In humans, the mandible, or lower jaw, is connected to the temporal bone of the skull via the temporomandibular joint. This is an extremely complex joint which permits movement in all planes. The muscles of mastication originate on the skull and insert into the mandible, thereby allowing for jaw movements during contraction.
This causes a mild rise in stroke volume during the first few seconds of the maneuver. Reduced venous return and compensation Return of systemic blood to the heart is impeded by the pressure inside the chest. The output of the heart is reduced, and stroke volume falls. This occurs from 5 to about 14 seconds in the illustration.
In a healthy heart all activities and rests during each individual cardiac cycle, or heartbeat, are initiated and orchestrated by signals of the heart's electrical conduction system, which is the "wiring" of the heart that carries electrical impulses throughout the body of cardiomyocytes, the specialized muscle cells of the heart.
As with skeletal muscles the heart can increase in size and efficiency with exercise. [1] Thus endurance athletes such as marathon runners may have a heart that has hypertrophied by up to 40%. [ 3 ] : 1063–64 The difference between maximum and minimum cardiac outputs is known as the cardiac reserve and this measures the residual capacity to ...
The conduction system consists of specialized heart muscle cells, situated within the myocardium. [3] There is a skeleton of fibrous tissue that surrounds the conduction system which can be seen on an ECG. Dysfunction of the conduction system can cause irregular heart rhythms including rhythms that are too fast or too slow.
The muscles of mastication (the temporalis muscle, masseter muscle, medial pterygoid muscle and lateral pterygoid muscle) are paired on either side and work together to move the mandible, which hinges and slides around its dual articulation with the skull at the temporomandibular joints. Some of the muscles work to elevate the mandible (close ...
The digastric muscle (also digastricus) (named digastric as it has two 'bellies') is a bilaterally paired suprahyoid muscle located under the jaw.Its posterior belly is attached to the mastoid notch of temporal bone, and its anterior belly is attached to the digastric fossa of mandible; the two bellies are united by an intermediate tendon which is held in a loop that attaches to the hyoid bone.
Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart .