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Unit 1: The Skeletal and Muscular Systems Task 2
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- PEARSON (PEARSON)
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MusclesCardiac Muscles
Cardiac muscles are highly organized and contain many types of cells. Cardiac muscles only
exist in the heart which perform highly coordinated actions that keep the heart pumping
blood around the body. The movements are involuntary, meaning that they do it
automatically which a human can not control. These muscles never tire because otherwise
the heart would stop circulating blood around the body. The cardiac muscles have
specialized cells called pacemakers. These contract and expand in response to electrical
impulses from the nervous system. Pacemaker cells generate electrical impulses that tell
cardiac muscle cells to contract and relax. The pacemaker cells control heart rate and
determine how fast the heart pumps blood.
Unlike skeletal muscle fibers, cardiomyocytes are single cells typically with a single centrally
located nucleus. A principal characteristic of cardiomyocytes is that they contract on their
own intrinsic rhythms without any external stimulation.
Skeletal muscles
There are three main types of skeletal muscles cells. Skeletal muscles are a form of striated
muscle tissue, which is under the voluntary control of the somatic nervous system. Most
skeletal muscles are attached to bones by bundles of collagen fibers known as tendons.
Unlike smooth muscle and cardiac muscle, skeletal muscle is under voluntary control.
Similar to cardiac muscle, however, skeletal muscle is striated; its long, thin, multinucleated
fibres are crossed with a regular pattern of fine red and white lines, giving the muscle a
distinctive appearance. Skeletal muscle fibres are bound together by connective tissue and
communicate with nerves and blood vessels.
Muscle cells are also known to be the same as muscle fibres. There are three types of
skeletal muscles:
Type 1 - Contract slowly with less force. They are slow to fatigue and suited to longer
duration aerobic activities. They have a rich blood supply and contain many mitochondria to
sustain aerobic metabolism. Type 1 fibres have high capacity for aerobic respiration. They
are recruited for lower intensity, longer duration activities such as long distance running and
swimming.
Type 2 - Fast contracting and able to produce a great force, but are also resistant to fatigue.
These fibres are suited to middle distance events.
Type 2a - Contract rapidly and have the capacity to produce large amounts of force, but they
fatigue more rapidly, making them better suited to anaerobic activity. They depend almost
entirely on anaerobic metabolism and are recruited for higher intensity, shorter duration
activities. They are important in sports that many stop and go or change of pace activities.
Characteristics of muscle fibre Type 1 Type 2 Type 2a
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