Anatomy Session 9: Muscular System

Study Notes

Muscle tissue is specialized for contraction and makes up about 40% of a person's body weight.
There are over 650 skeletal muscles in the human body.

There are three types of muscular tissue: skeletal muscle, cardiac muscle, and smooth muscle.
Skeletal muscle:
- Found attached to bones of the skeleton
- Voluntary, striated
- Attached to bone and causes movement of the body
- Known as voluntary muscle because it can be contracted at will
- Appears markedly striated when examined with a microscope
Cardiac muscle:
- Found in the heart
- Involuntary, striated, branching
Smooth muscle:
- Found in organs
- Involuntary, non-striated

Skeletal muscle structure consists of bundles of tiny fibers that run the length of the muscle.
Most fibers are about 3 cm long and 0.05 mm wide.
Three connective tissue sheaths: epimysium, perimysium, and endomysium.
- Epimysium: surrounds the entire muscle, dense irregular connective tissue
- Perimysium: surrounds fascicles, dense irregular connective tissue
- Endomysium: surrounds individual muscle fibers, reticular connective tissue
Nerves and blood vessels enter, exit, and branch throughout connective tissue.

A skeletal muscle cell is called a muscle fiber.
A muscle fiber contains organelles called myofibrils.
Myofibrils are groups of contractile proteins, actin and myosin, arranged in a sarcomere.
Sarcomere arrangement creates the “stripes” seen in skeletal muscle.
Muscle fibers are grouped in bundles called fascicles.
Perimysium layer encases the fascicles.
Epimysium layer surrounds the muscle as a whole and binds all the muscle fibers together.
Connective tissue called fascia surrounds the muscle outside the epimysium.