Principles of Biology
By
Frank H. Osborne, Ph. D.
Muscular System
Non-Muscular Movement
It is possible to have motion without muscles.
• Turgor pressure
• Cytoplasmic streaming
• Somersaulting in Hydra
Major Human
Muscles
Types of Muscles
Smooth muscle
•Smooth muscle is the type of muscle found in all
of the involuntary organs except the heart.
"Involuntary" means that you cannot control it.
•The tissue is made of individual muscle cells,
each with its own nucleus.
Types of Muscles
Smooth muscle
•The cells of smooth muscle do not have
striations. Striations are parallel lines that are
perpendicular to the long axis of the muscle cell.
They are found in striated muscle and cardiac
muscle but not in smooth muscle.
Smooth muscle
Types of Muscles
Striated muscle
•Striated muscle is also called voluntary muscle.
It is found attached to the bones of the skeleton
by tendons.
•The individual cells of striated muscle are very
long, as long as the muscle itself. Cells this long
must have many nuclei so striated muscle cells
are multinucleate. Each individual nucleus
controls its own area.
Types of Muscles
Striated muscle
•Striated muscle has striations. These crossbands result from the inner molecular structure
of the muscle.
•Striated muscle is under voluntary control.
These are the muscles that you can move when
you want them to do something for you.
Striated muscle
Types of Muscles
Cardiac muscle
•Cardiac muscle is found only in the heart. The
cells are striated. The cells are connected to each
other at their ends at which are located
intercalated discs.
•Each individual cardiac muscle cell has its own
nucleus.
Cardiac muscle
Muscle Structure
Structure of muscle
•Muscle consists of thick fibers called myosin and
thin fibers called actin. These are found in all
types of muscles.
•The actin fibers are attached to vertical
structures called Z-lines. The actin and myosin
fibers overlap and are in close proximity to each
other. This is called the actomyosin complex.
Muscle Structure
Structure of muscle
•The bands cause the striations of skeletal muscle
and cardiac muscle.
•The A band is the complete length of myosin.
•The I band is the space between myosins.
•The H band is the space between actins.
Structure of muscle (relaxed)
Structure of muscle (contracted)
Muscle Contraction
•In relaxed muscle, the Z-lines are far apart and
the H and I bands are wide.
•When the muscle contracts, the actin and
myosin bands slide over each other and the Zlines get closer.
•Also, the H and I bands become much shorter.
•As the units shorten, the entire muscle shortens.
This is how muscles contract.
Attachment of Muscles
•Muscles are attached in a way as to provide pairs
of muscles for each moving part of the body. The
forearm is an example.
•When the biceps muscle contracts, it closes the
angle that the arm makes. This muscle is called a
flexor.
•The triceps is used to extend the arm and open
the angle. It is called an extensor.
Attachment of Muscles
•Normally these muscles do not contract
simultaneously.
•When the flexor contracts, the extensor permits
itself to become extended.
•When the extensor contracts, the flexor permits
itself to become extended.
•Any muscle can only contract. It cannot extend
itself. To extend it must be pulled by a force
from another muscle.
Human Forearm
The End
Principles of Biology
Muscular System