defined is a tissue capable of changing shape and length
to cause movement.
Although most of us think of muscle as a tissue that allows
us to move, push, pull or lift weight, there are several
other roles for different types of muscle that are critical
in human function. Skeletal
ddmuscles primarily serve the body as contractile tissue
to allow bones to move around joints. Smooth muscle helps
move blood through our blood vessels and food through
our digestive tract. Perhaps one of the most important
muscles is cardiac, which is your heart.
Muscles typically work in pairs to support and balance
the body. The front thigh (quadriceps) muscle is the opposite
to the back thigh (hamstrings) muscle. The chest (protractor)
muscles are the opposite to the back (retractor) muscles.
These are also called antagonistic muscle groups. Each
contracts to move joints in a certain direction or rotation
to the angle of force being created. When one contracts,
the other must relax. For example, your bicep must relax
and lengthen when your triceps contract and shorten. If
this relationship did not exist and if both muscle groups
were to contract at the same time, your arm would lock
and there would be no movement at the joint.
At both ends of every muscle, the fascia covering the
muscle tapers to form a strong, rope-like length of connective
tissue called a tendon, which is connected directly to
one of your bones. One end, which connects to a relatively
unmoving skeletal part, is the origin of the muscle. The
point where it's attached to a moving bone is the insertion
of the muscle.
muscle is actually a wrapped package, containing other
smaller wrapped packages of long, slender cells known
as muscle fibers. The outer wrapping, made of connective
tissue, is called the muscle fascia. The smaller packages
are called muscle fasciculi (fascicle), and each one contains
a bundle of up to 150 muscle fibers. Endomysium envelopes
all the muscle fibers in a fascicle. Perimysium wraps
all of the fasciculi and the epimysium surrounds the entire
muscle. Thus, when a muscle fiber contracts, it pulls
on the endomysium which pulls on the perimysium which
pulls on the epimysium which in turn pulls on connective
tissue fascia which finally pulls on the tendon, and this
causes the bone to move. The bigger the muscle, the more
force it can generate on the bone.
Each muscle fiber shares a nerve ending with other nearby
fibers, making up a group of fibers known as a motor unit.
A motor neuron must fire from the spinal cord to produce
a signal telling the muscle to contract. Every time the
master motor nerve fires (sends an impulse to a muscle),
this motor unit contracts simultaneously. This effect
is called the "all-or-nothing" principle of muscle contraction.
When the fibers in a motor unit contract in unison, the
result is a muscle contraction. Whatever form of exercise
you're doing, from running to swimming to bicycling, your
movements depend on the repeated, coordinated firing of
the appropriate motor units. The more you develop an athletic
skill the more efficient your motor units become at firing
for the desired result.