Muscular tissue can be
classified as skeletal, smooth or cardiac that responsive to stimuli and produce
force. The main role of muscle in the human body is the ability to contract.
But there is more, it is also acts as metabolic organ in the case of skeletal
muscle, a functional pump for the pumping of the heart and regulates the blood
flow in terms of smooth muscles. The different types of muscular tissue may
have the same properties but they are different from one another in terms of
their microscopic anatomy, location and how they were controlled by the nervous
and endocrine system.
The skeletal muscle are
mainly used to move the skeletal bones. There is only a few skeletal muscles
that is attach and move the skin or other skeletal muscle. Skeletal muscle are
seen in striations, alternating lights and protein bands can be seen when
observed under the microscope. The skeletal muscles tissue works voluntary
which means it act in its own will but its can be apprehensively controlled by
the nerve cells. Most of the skeletal muscles are controlled subconsciously to
a certain extent. But at the same time, the muscles does not have to be
consciously being controlled for example to maintain the body positions or the
body posture. Skeletal muscles that produces movement perform by the action of
bone pulling. The bones are seen as levers while the joints is serve as
The contraction of muscles
helps the body in a few aspects. First, the muscles helps in producing
movements of the body such as running, swimming, writing and more. All this
movements rely on the contractions of muscle and also the skeletal muscles.
Next, it is helpful in stabilizing the body positions. The skeletal muscle
stabilize the joints and thus helps maintaining the body positions. Other than
that, muscular tissue acts as a storage and transfer substances within the
body. Storing is achieved by sustained contractions of smooth muscle which is
called sphincters. This will prevent the outflow of the contents of a hollow
organ. Contraction and relaxation of the smooth muscle the blood vessels
promotes the rate of the blood flow. Finally, it also generate heat. When the
muscular tissue contracts, it generates heat. This process is called
thermogenesis. The heat generated is used to maintain the body temperature.
Muscular tissue involved in
homeostasis by producing movement of the body. It is the movement of substances
such as body fluids throughout the body and producing heat to maintain normal
body temperature. There is four properties that enable it to contribute for
homeostasis. First is electrical excitability. It is a property of both muscle
and nerve that works together to respond to a stimuli by action potentials
generates by electrical signals. Two types of stimuli that triggers the action
potential, autorythmic and chemical stimuli. Example of autorythmic are the pacemaker
of the heart. It arises from the muscle tissue itself. The example of chemical
stimuli is the neurotransmitters transmitted by the neurons. Then, is the
contractility. Contractility is the ability of muscular tissue to contract
forcefully when stimulated by the action potential. When it contracts, it
creates tension and gets shorten but some generates tension but does not
shorten. The third principle is extensibility. It is the ability of muscle
tissue to stretch to its limits without damaging itself. For example, whenever
a person’s is eating, the smooth muscle of the stomach stretches. A person’s
will know that their stomach is full and will stop eating. Finally, is
elasticity, the ability of the muscle tissue return to its original shape and
length after the muscles has contracts or extends.
Muscle contraction and
relaxation occurs in the body multiple times in the humans daily routine lives,
especially if you are active. Muscles have fibers and are grouped into
fascicles or bundles, which form individual skeletal muscles. There are three
states in which muscles exist, they are contracted, relaxed or stretched. The
beginning of contraction, calcium ions was released by the sarcoplasmic
reticulum into sarcoplasm. Then, they bind to troponin which then troponin
moves tropomyosin away from the myosin binding site on actin. When the binding
site are free, the contraction cycle begins.
Contraction cycle consists of
four steps. The first step is the hydrolyzation of ATP. Myosin head includes an
ATP binding site and ATPase, an enzyme that hydrolyze ATP into ADP and a
phosphate group. This hydrolysis reaction reorients and energies the myosin
head. The product of the hydrolysis are still attached to the myosin head.
Secondly, the attachment of myosin to actin to form cross-bridges. The
energized myosin head attaches to the myosin binding site on actin and releases
the previous hydrolyzed phosphate group. Cross-bridges are referred to the
myosin heads attach to actin during contraction. The third cycle is the power
stroke that occurs after the cross-bridges was formed. The ADP is still bound
opens during the power stroke. This makes the myosin head rotates and releases
ADP. Thus, it then generates force as it rotates towards the center of the sarcomere.
Then sliding the thin filament past the thick filament towards the M line. The
final step is the detachment of myosin from actin. At the final of the power
stroke, the cross-bridges remains firmly attached to the actin until it binds
to another ATP molecule. The myosin head detaches the actin as ATP binds to the
The cycle repeats as the
myosin ATPase hydrolyzed the new ATP molecule and continue as long as ATP and
calcium ions level are high at the thin filament. When contraction occurs, the
amount of calcium ions increased while it decreases during relaxation. The
cross-bridges keeps rotating back and forth with each of the power stroke and
pulling the filaments towards the M line. There is two types of contraction,
isotonic and isometric contraction. For isotonic contraction, the force of
contraction developed in the muscles remains constant while the muscles changes
its length. This contractions are used for the movement of the body and also
moving of objects. The isotonic contraction can be divided into two, they are
concentric and eccentric isotonic contraction. Concentric isotonic contraction
focuses on the force to overcome the resistance of the object to moved. The
muscle shortens and pulls on another structure to produce movement and reduce
angle at the joint. For eccentric, tension exerted by the myosin cross-bridges
resists movement of a load and slows the lengthening process. Further onto
isotonic contraction, the tension generated is not enough to exceed the
resistance of the object moved and the muscle does nor change its length.
Moving on to the mechanism of
weightlifting, the first step begins at the squad position. The bar was raised
until at the knees and the hands was just outside the legs. During this phase,
the muscles at the hands up towards the shoulder is contract. The muscles was
trapezius, deltoid, triceps, biceps, palmaris longus and flexor carpi radialis.
Besides that, the muscles also mainly used at the hips as its need to support
the weight. The muscles are vastus lateralis, vastus medialis, the abductor and
femoris. Basically it is used for counterbalance the weight.
For the second step, the bar
was raised up until just above the chest and shoulders are role out. The body
posture must be at 900 as possible. At this phase, abdominal parts
starts its role. Some of the muscle parts are the serratus, rectus abdomina and
the external oblique. The back muscle are also used to support this action. For
example, infraspinatus, teres major and latissimus dorsi. In addition, the
lower part of the legs supports the person to balance so that the person would
not fall. The muscles used are biceps femoris, gastrocnemius lateral head,
medial head and tendon.
Finally, the bar was raised
on top the head and the hands are fully straight. The legs are also must
straight position. If the leg is bend, it would be more harder for the
weightlifter to lift up the bar. For this phase, the pectoralis muscle, the
chest muscle, contracts. The muscles used during this phase are the same as the
Muscle fibers have three
sources of ATP production. The sources are creatinine, anaerobic glycolysis and
aerobic respiration. Creatinine kinase catalysts the transfer of a high energy
phosphate group from the creatinine phosphate to ADP to form new ATP molecules.
Together, they provide enough energy for muscles to contract maximally for at
least 15 seconds.
In the process of glycolysis,
glucose is converted to pyruvic acid. It yield two ATP’s without using oxygen.
Anaerobic glycolysis can provide enough energy for approximately 2 minutes of
maximal muscle activity. Muscular activity that occurs over a prolonged time
depends on aerobic respiration. While mitochondrial reactions require oxygen to
produce ATP. Muscle fatigue is the inability of a muscle to contract forcefully
after prolonged activity. Furthermore, recovery oxygen uptake is when elevated
oxygen use after an exercise.
There are various types of
exercises that can induce changes in the fibers of a skeletal muscles.
Endurance or aerobic type of exercises can cause a gradual transformation of
some fast glycolytic fibers into a fast oxidative glycolytic fibers. Exercises
that requires great strength for short periods will produces an increase of the
size and strength of fast glycolytic fibers. The increase size is due to the
increased synthesis of thick and thin filaments.