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Questions and Answers, Muscles
1. What is muscle?
Muscle is one of four basic tissues of the body (epithelial, connective,
and nervous tissue are the other three). It is made up of cells that can
shorten or contract.
2. What are the three types of muscle and
some of the general characteristics of each type?
The three types of muscle are cardiac muscle, smooth muscle, and the skeletal
muscle (the most familiar kind).
Cardiac muscle is found in the heart. Starts
heart beating long before an animal is born, and
maintains this function until the animal dies. Is striated, involuntary
Smooth muscle is found all over the body in
places such as the eyes, the air passageways in the lungs, the stomach
and intestines, the urinary bladder, the blood vessels, and the reproductive
Tract. It carries out most of the unconscious internal movements that
the body needs to maintain itself in good working order. Is not striated,
involuntary.
Skeletal muscle moves the bones of the skeleton,
which in turn move the animal around. Also called voluntary striated muscle
because it is under the control of the conscious mind.
3. What’s the difference between a
tendon and an aponeurosis?
Most muscles are attached to bones at both ends by rough, fibrous connective
tissue called tendons. Some muscles are attached to bones or to other
muscles by broad sheets of fibrous connective tissue called aponeurosis.
The most prominent aponeurosis is the linea alba, (white line) that runs
lengthwise between the muscles on an animals’ midline. It connects
the abdominal muscles from each side together and is a common site for
surgical entry into the abdomen.
4. What’s the origin of a muscle?
The insertion?
The origin of the muscle is the attachment site that is more stable. It
does not move when the muscle contracts. The site that undergoes most
of the movement when a muscle contracts is called the insertion of the
muscle.
5. Why might it be of clinical importance
to know the origin and insertion of a muscle?
It’s of clinical importance to know the origin and insertion of
a muscle because both areas are related to movement. If you don’t
know where these points are, you can’t picture how the muscle is
working. And if you can’t picture how the muscle is working, you
can’t give a working description to a veterinarian or anyone else.
6. Describe a skeletal muscle cell in terms
of cell size, shape, number of nuclei, and appearance under a microscope.
Skeletal muscles cells are huge. They are not wide, but are long. Most
body cells are a few micrometers in length or diameter. Skeletal muscles
can be several inches long. They are also thin which gives them an overall
thread or fiber-like shape. They are called skeletal muscle fibers rather
than skeletal muscle cells. Instead of having just one nucleus, like most
cells, they have many. Large ones can have 100 or more nuclei per cell,
all located out at the edge of the cell just beneath the out at the edge
of the cell, beneath the scarcolemma or muscle cell membrane.
7. What are the differences among a skeletal
muscle fiber, a skeletal muscle myofibril, and a skeletal muscle protein
filament?
A skeletal muscle fiber is the equivalent of muscle cell. A skeletal muscle
fiber is made up of hundreds or thousands of smaller myofibrils packed
together lengthwise, which themselves are composed of muscle protein filament.
Muscle protein filament takes the form of two bands, the large dark band
(the A band) is made up of thick myosin filaments. The large light band
(the I band) is made up of thin actin filaments. The dark center line
is the Z line; it is a disk that looks like a line when viewed on end.
It is the attachment site for the actin filaments. The H band is a rock
group that takes the A train to the neuromuscular junction, and if you
are reading this that carefully, then you get a free subway token.
8. What’s a sacromere and what are
its components?
The area from one Z line to the next is called a scaromere and is the
basic contracting unit of the skeletal muscle. Each and every myofibril
is made up of many sacromeres lined up end to end. Each sacromere shortens
slightly when the fiber is stimulated to contract, but when all the sacromere
contractions are added together, the muscle fiber shortens considerably.
Muscles