MUSCULAR
SYSTEM
by
Patty.Pearl.Pop.Ko
rn 11-7
Muscular System
There are three types of muscles in the human body: skeletal muscle,
smooth muscle and cardiac muscle. Skeletal muscles are attached to the
skeleton bones, and provide movement of the body. Smooth muscle is found in
our internal organs such as the digestive system, respiratory system, blood
vessels, and bladder. Cardiac muscle is found only in the heart, and is
responsible for the heart beating or pumping action.
There are about 650 skeletal muscles in the human body. They provide
strength, balance, posture, and movement for the body. They also provide heat
to keep the body warm. Skeletal muscles are attached to bone by tendons.
When muscles contract, they pull on tendons, that in turn pull on the bone.
Without muscles and joints we wouldn't be able to do much, if anything.
Face muscles help us eat, smile and laugh. Hand muscles, arm muscles and
shoulder muscles, along with the elbow joint, help use throw a ball. Hip
muscles, leg muscles and foot muscles, along with the knee joint and ankle
joint, help us to walk. Our thoracic muscles help us breathe. Our back
muscles,abdominal muscles and vertebral muscles help us maintain good
posture and stand upright.
Skeletal muscle
Skeletal muscle is what most people think of as muscle. Skeletal muscle is
responsible for controlling body movement, maintaining body posture, and
generating heat in the body. Skeletal muscle gets its name from the fact that it
is attached to bone.
Skeletal muscle is a striated, or striped, muscle. These striations are the result
of long, parallel muscle fibers making up the muscle. Skeletal muscle is
connected to bones via tendons. Skeletal muscles are responsible for all body
movements from sitting, standing and walking, to smiling and laughing. Skeletal
muscles are voluntary muscles, meaning they are under our conscious control
through the somatic nervous system.
Smooth Muscle
Smooth muscle is found in the walls of hollow internal structures such as blood
vessels, the esophagus,stomach, small intestine, large intestine, and urinary
bladder. Smooth muscles, as the name implies, is smooth not striated. Smooth
muscles are involuntary muscles, meaning they are not under our conscious
control. They are controlled by the autonomic nervous system. It is customary
to classify smooth muscle as single-unit and multi-unit smooth muscle. The
muscle fibers making up the single-unit muscle are gathered into dense sheets
or bands. Though the fibers run roughly parallel, they are densely and
irregularly packed together, most often so that the narrower portion of one fiber
lies against the wider portion of its neighbor. These fibers have connections,
the plasma membranes of two neighboring fibers form gap junctions that act as
low resistance pathway for the rapid spread of electrical signals throughout the
tissue. The multi-unit smooth muscle fibers have no interconnecting bridges.
They are mingled with connective tissue fibers.
Cardiac Muscle
Cardiac muscle makes up most of the wall structure of the heart. It is found
only in the heart. Cardiac muscle is striated or striped with light and dark bands
similar to skeletal muscle. Unlike skeletal muscle, cardiac muscle is involuntary
muscle, not under our conscious control. It is controlled by an internal
pacemaker and the autonomic nervous system. Cardiac muscle cells have a
branched shape so that each cell is in contact with three of four other cardiac
muscle cells. Together all of the cardiac muscle cells in the heart form a giant
network connected end to end. At the ends of each cell is a region of
overlapping, finger-like extensions of the cell membrane known as intercalated
disks.
The mechanism of muscle contractions
Muscle is composed of a large number of muscle fibres. The muscle fibres are
arranged in groups. Each group is under the control of a single motor neuron,
the axon of which sends a terminal branch to each fibre of the group. All the
muscle fibres of a group contract when a nerve impulse travels down their
motor neruon. A motor neuron and the group of muscle fibres innervated by its
axon constitute a functional unit, called the motor unit. The number of muscle
fibre and motor unit is variable and depends on th efineness of the control, a
motor unit has to exercise.
The mechanism of muscle contractions
When a muscle is stimulated, a short latent period follows, during which it is
taking up the stimulus. It then contracts, where it becomes short and thick, and
finally it relaxes and elongates.
In case of a striped muscle fibre the contraction lasts for only a fraction of a
second and each contraction occurs in response to a single nerve impulse. The
force with which a whole muscle contracts is adjusted by varying the number of
fibres contracting and the frequency with which each fibre contracts.
During muscle contraction, the laterally projecting heads
(cross bridges) of the thick myosin myofilaments come in
contact with the thin actin myofilaments and rotate on
them. This pulls the thin myofilaments towards the middle
of the sarcomere past the thick myofilaments. The Z lines
come closer together and the sarcomere becomes shorter.
Length of the A band remains constant. Myofilaments stay
the same length. Free end of actin myofilaments move
closer to the centre of the sarcomere, bringing Z lines
closer together. I bands shorten and H zone narrows. A
similar action in all the sarcomeres results in shortening of
the entire myofibril, and thereby of the whole fibre and the
whole muscle. A contracted muscle becomes shorter and
thicker and its volume remains the same.
The Functions of Muscle Flexors &
Extensors
The human body is made up of hundreds of muscles, each classified as
either skeletal, visceral or cardiac muscle tissue. Both flexors and extensors
are skeletal muscles, and both have a unique function in the body relating to
joint movement.
They bend and straighten the body's joints to create motion and activate
other muscle groups, generating muscle activity -- which is another way to say
working out.
How Flexors Work
Flexors work to bend a joint. You may recognize a common exercise term
right in the word "flex." When you flex your muscles, your flexors contract and
pull on the bone, creating a bending movement of the joint. Try imagining a
bicep curl. As you pull your fist upward to your shoulder, the angle between
your forearm and bicep decreases as the flexor muscle tightens and contracts.
How Extensors Work
Extensors serve the opposite purpose -- extending and straightening joints. In a
bicep curl, the extensor muscles contract as the fist is let down from the
shoulder. The same occurs with walking or running, as hip extensors contract
and pull the thigh back to the anatomical position.
Muscle Fatigue
Muscle Fatigue occurs when the muscle experiences a reduction in its
ability to produce force and accomplish the desired movement. The factors that
explain fatigue are complex and after more than 100 years of investigation are
still a topic of active research. For example, short term fatigue (failure to lift a
heavy weight, do more push-ups, etc.) is different than long term fatigue such
as as a marathon run, a 100 mile bicycle ride, or a full-day hike through the
Rocky Mountains of Colorado.
We do understand though some of the basic reasons that muscles become
fatigued during high intensity exercise, most notably that the demand for
oxygen can be greater than the supply. The blood flow to the muscle can be
reduced because of 1) muscles intensely contracting can reduce blood flow
and thus oxygen availability, or 2) the muscle is simply working so intensely
that there literally is not enough oxygen to meet demand (a sprint at top speed).
If such O2 isn't available as an electron acceptor , the Krebs cycle and
electron transport chain cannot operate, and the muscle must gain ATP from
other sources. For example, for rapid, intense activity, phosphocreatine
(synthesized from amino acids) can serve as a phosphate donor to allow ATP
formation. This is called anaerobic contraction, meaning "not using oxygen."
However, anaerobic contraction can lead to build-up of metabolites and
waste products, and a significant increase in the acidity (decreased pH) inside
the muscle cell, which can interfere with the many biochemical reactions
necessary for the actin and myosin to produce force and slide against each
other. This chemical change is thought to be the cause of the "stinging" or
burning sensation you feel in your muscles as you become fatigued (such as in
arm wrestling or in the last few reps of a difficult weight lifting set).
How Are Muscles, Bones & Tendons
Related?
Protection
● Bones protect fragile organs of the body such as the brain, spinal cord,
heart, lungs and some reproductive organs. Some muscles provide
additional protection where there are no bones. For example, the external,
internal and transverse oblique abdominal muscles protect and support the
intestines.
Movement
● Bones are the levers that muscles and tendons act on. If an arm is a lever
machine, the bone is the lever, the joint is the fulcrum and the muscle
provides the force.
Tendons
● Tendons are fibrous connective tissue that connect muscles to bones.
They are avascular--meaning they have no blood vessels--and therefore
heal slowly if they are torn, stretched or injured.
Strains
● Strains happen when tendons or muscles get stretched or torn. Some of
the most common places for strains are the back or the hamstring tendon.
Achilles Tendon
● One of the most well-known tendons is the Achilles tendon, or calcaneal
tendon. It attaches the bone of the heel--the calcaneus--to the calf
muscles.
What Is the All-or-None Law?
The all-or-none law is a principle that states that the strength of a response
of a nerve cell or muscle fiber is not dependent upon the strength of the
stimulus. If a stimulus is above a certain threshold, a nerve or muscle fiber will
fire. Essentially, there will either be a full response or there will be no response
at all.
Sources
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http://www.livescience.com/26854-muscular-system-facts-functionsdiseases.html
http://www.teachpe.com/anatomy/types_of_muscle.php
https://backyardbrains.com/experiments/fatigue
http://www.kidport.com/reflib/science/humanbody/muscularsystem/Muscle
Types.htm
http://www.ehow.com/facts_5163426_muscles-bones-tendons-related.html
http://psychology.about.com/od/aindex/f/all-or-none-law.htm
http://www.tutorvista.com/content/biology/biology-iv/locomotionanimals/muscular-contraction.php
http://www.uic.edu/classes/phyb/phyb516/smoothmuscleu3.htm