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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

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principles of biology

Principles of Biology


Frank H. Osborne, Ph. D.

Muscular System

non muscular movement

Non-Muscular Movement

It is possible to have motion without muscles.

Turgor pressure

Cytoplasmic streaming

Somersaulting in Hydra

types of 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 muscles1

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.

types of muscles2

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 muscles3

Types of Muscles

Striated muscle

Striated muscle has striations. These cross-bands 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.

types of muscles4

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.

muscle structure

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 structure1

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.

muscle contraction

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 Z-lines 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

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 muscles1

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.

the end

The End

Principles of Biology

Muscular System