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Anatomy & Characteristics of Human Muscles


Muscle Types

Skeletal MuscleSmooth MuscleCardiac Muscle
Skeletal muscles are anchored to the bones by tendons. They make up the largest single organ and are mainly responsible for the body´s movements. Each muscle is made of cells or fibers that can be up to 2cm long.Smooth muscles shape the walls of inner organs such as stomach or blood vessels. Their contractile speed is relatively slow and the muscle fibers are smaller than the ones skeletal muscles are made of. The name comes from their smooth structureCardiac muscles can only be found in the heart and they are controlled by the autonomic nervous system, therefore they work independently. However, they structure is similar to the skeletal muscles.

Skeletal Muscle Anatomy


Muscle Fibers

Muscle fibers are cell consting of a nucleus, sarcoplasmic reticulums, mitochondrions (responsible for muscle growth) and myofibrils (the contractile elements), which contain sarcomeres made of actin and myosin. Muscle fibers are divided into two categories, slow twitch and fast twitch fibers, with significant different characteristics:

Slow Twitch, Type IFast Twitch, Type II
contractile speedslowfast
mitochondriahigh quantitylow quantity
myoglobinhigh quantitylow quantity
capillary densitiyhighlow
oxygen transport capacityhighlow
lactic acid productionlowhigh

Type II fibers are subdivided into three categories with contractile speeds situated between Type I and Type II. In general it is enough to know the main fibers. The red and white color is caused by the amount of capillaries inside the muscle. Red muscles carry more blood than white ones. Therefore certain animals have red and others have white meat. Every muscle owns fibers of each type. The arrangement is based on individual genetics and the muscle´s particular function.

EndomysiumThe endomysium is a tissue that wrapps a single muscle fiber.
FascicleA fascicle is a bundle of several muscle fibers.
PerimysiumThe Perimysium is a tissue that covers the fasciles.
Blood VesselBlood vessels provide the muscle with blood, carrying oxygen, nutrients and other vital substancies.
EpimysiumThe Epimysium groups the fascicles to give the the muscle its shape.
TendonTendons connect muscles to bones or muscles to muscles. They have the shape of bands and are extremely tension-resistant.