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Muscular System-Muscular structure

3 Types of Muscles

Skeletal, Smooth, Cardiac

Skeletal Muscle

Attached to bone, voluntary muscle, cells shaped like cylinders or tubes, striated.
Function: movement, posture, support joints, producing heat.

Smooth Muscle

Walls of organs (visceral) involuntary muscle, non-striated, digestive system, respiratory system.

Cardiac Muscle

Heart muscle only, involuntary, striated muscle, cells are long branching and fit tightly together to promote rapid conduction of electronic signals thoughout the heart.
Function: Pump Blood

Belly of the muscle

enlarged fleshy body of the muscle between the slender points of attachment. Composed of thousands of muscle fibers (muscle cells).

muscle fibers

muscle cells


surrounds the skeletal muscles, tough connective tissue.


outer layer of fascia


The fascia that extends toward and attaches to the bone, a strong cord-like structure.


layer of connective tissue that surrounds the fascicles (smaller bundles of muscle fibers).


small bundle of muscle fibers


Individual muscle fibers are found within the fascicles and are surrounded by a third layer of connective tissue.

3 ways of muscle attachment

Tendon attaches to the bone
Muscle attaches to the bone or soft tissue directly (without a tendon)
A flat sheet-like fascia (aponeurosis) connects muscle to muscle or muscle to bone

Muscle cell

an enlongated muscle fiber, has more than one nucleus and is surrounded by a thin cell membrane called the sarcolemma

Transverse Tubules -T Tubules

at several points the cell membrane penetrates deep into the interior of the muscle fiber. Cuts though

Sarcoplasmic Reticulum

within the muscle fiber, specialized endoplasmic reticulum, a layer underneath sarcolemma houses calcium.
Where Calcium is stored, when muscle is relaxed.


Each muscle fiber is composed of long cylindrical structures, consist of sarcomeres.


each myofibril is made up of a series of contractile units that extend from z-line to z-line, formed by a unique arrangements of two contractile proteins called actin and myosin.

actin filaments

thin, extend toward the center of the sarcomere from the z lines inside of sarcomere, contractile protein

Myosin Filaments

thicker, sits between the actin filaments, have myosin heads-contractile protein

Myosin Heads

structures extending from the myosin filaments

Muscle Contraction-sliding filament theory

Muscles can only pull, not push.
To contract the muscle must shorten.
The sarcomeres shorten due to the actin and myosin filaments sliding past each other to form crossbridges.
Need calcium and ATP to contract.


Form when stimulated.
The myosin heads make contact with the actin, forming temporary connections

muscle relaxation

Occurs when the crossbridges are broken, and the actin and myosin return to their original position. Uses ATP to break the crossbridge. Calcium returns to the sarcoplasmic reticulum (SR).

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