MUSCULAR SYSTEM
Types of Muscle Tissue: Skeletal, Smooth, and Cardiac
* Skeletal, aka “striated”, aka “voluntary” – attached to bones and under
conscious, willful control. Has the ability to contract (shorten) and thereby
bring about movement
I. Muscle and Muscle Fiber Structure: A muscle is composed of many muscle fibers (muscle fiber = muscle cell). The
individual muscles are separated from each other and held in place by a covering called the FASCIA. This fascia also
forms TENDONS and APONEUROSES connecting muscles to bones and muscles to muscles.
A muscle also contains 3 different layers of connective tissue:
Epimysium – outermost layer, surrounds entire muscle
Perimysium – separated and surrounds the FASCICLES (bundles) of muscle fibers
Endomysium – surrounds each individual muscle fiber
Skeletal muscle fibers contain numerous nuclei and mitochondria
The muscle fiber membrane is called the SARCOLEMMA and the cytoplasm is called the SARCOPLASM. Within the
sarcoplasm are many parallel fibers known as MYOFIBRILS
Each myofibril is made of many protein filaments called MYOFILAMENTS. There are two types:
MYOSIN – thick filaments
ACTIN – thin filaments
Actin and Myosin filaments are arranged in an overlapping pattern of light (“I” bands) and dark (“A” bands). In the
middle of each “I” band is a line called a “Z” line. The section of a myofibril from one Z-line to the next Z-line is called a
SARCOMERE. The arrangement of these sarcomeres next to each other produces the STRIATIONS of the skeletal
muscle fibers.
Each Myofibirl is surrounded by a network of membranous channels called SARCOPLASMIC RETICULUM. Other
“tubes”
between the actin and myosin filaments  the filaments slide between each other  this shortens the myofibrils which
in turn shorten the muscle fibers, which shortens the muscles
“Calcium Pump” returns CA++ into the S.R. (requires energy- ATP)
Enzyme Cholinesterase stops action of Acetylcholine
II. ENERGY SOURCE: Provided by ATP around myofibrils. ATP is produced by cellular respiration which occurs in
the mitochondria (requires O2 and glucose)
* Creatine Phosphate provides energy for the
regeneration of ATP
* Only 25% of energy produced during cellular
respiration is used in metabolic processes – the rest
is in the form of HEAT. This is what produces our
body heat and maintains body temperature. More
muscle activity = more heat
ATP= adenosine triphosphate
ADP = adenosine diphosphate
Label Practice
Fascicle
Endomysium (2)
Bone
Muscle Fiber
Epimysium
Perimysium
Tendon