The Muscular System

Ilja Fjodorovs

Different types of muscle

There is 3 different types of muscles in our bodies and they are: Smooth muscle, Cardiac muscle, and Skeletal muscle. Muscles themselves are made up of 75% water, 20% protein, and 5% of mineral salts, glycogen and fat.

Smooth muscle are found in many places such as: the lymphatic vessels, the urinary bladder, uterus, both male and female reproductive tracts, also the gastrointestinal and respiratory tracts, erector pill of skin, the ciliary muscle, and the iris of the eye.

The smooth muscle shortens and generates tension to hallow organs such as blood vessels, gastrointestinal tract, the bladder, or the uterus. This type of muscle has many jobs to do within our body and does the actions without you knowing it such as when it digests food and pushes it through the body after you ate. When you need to pee the muscles contract the walls of your bladder to make the urine come out. Smooth muscle also help push the baby out of the womb In a womans body during childbirth. And finally change the size of the pupil when in a dangerous situation or when too much light is exposed. The smooth muscle is not striated, smooth muscle fibers are small and tapered with the ends reducing in size, in contrast to the cylindrical shape of skeletal muscle. Each smooth muscle fiber has a single centrally located nucleus because they are in layers so each one needs to be controlled by a single nucleus.

Cardiac muscle is the muscle that only the heart is made up of, it is a type of involuntary striated muscle found in the walls and histological foundation of the heart, specifically the myocardium, and plays the most important role in the contraction of the atria and vertices of the heart. The fibres in the Cardiac muscle are striated, branched which look like a Y shape, which have a single central nucleus. The fibers are attached at each end by a thick plasma membranes called intercalated discs. The main purpose of the cardiac muscle is to pump the blood through the heart by making alternate contractions and relaxations of the cardiac muscle pumps de oxygenated blood through the right atrium and right ventricle to the lungs, and also pumps the oxygenated blood through the left atrium and left ventricle to the aorta, and then to the rest of the body as all of it needs blood for oxygen. It contracts rhythmically around 72 times per minute but can be altered depending on what situation you are in, nervous system, hormones, and medications because of stress or excitement.

The Skeletal muscle is also known as the 'striated' muscle because of its dark and light stripey appearance of bands of actin and myosin which form the sarcomere which is where the muscle contraction occurs in the presence ATP, calcium and protein within the myofibrils. Each skeletal muscle cell is long and cylindrical shape with many nuclei located towards the edges of the cell. The skeletal muscle covers the skeletal system and is under voluntary conscious control, and are responsible for the stability and all movement of the skeleton. Even though the muscle fatigues easily, it is capable of maintaining powerful, rapid and longer sustained contractions. It includes different types of fibers and all muscles have a blend of them all, anaerobic fibers are used for speed and power at 70% of our maximum intensity, while aerobic is for cardio endurance.

Different tpes of muscle fibers

Muscles are composed of thousands of individual muscles fibers, not all of them are identical in structure and function. The different muscle fibers are divided accorf=ding to the speed and by the methods used to produce energy. There are 3 main types of muscle fibers and they are: Type 1, Type 2a, and Type 2b.

Type 1 fibers are known as slow twitch fibers, which use oxygen efficiently to produce their energy which ATP for continuous, extended muscle contractions over a period of time, an sporting example where this would be used is during the marathon as your legs contract for about an hour without a rest. They are red in colour and have large amounts of mitochondria which act as a powerhouse and break down the food in the digestive system, takes out the useful nutrients and creates energy for the cell. It also has a lot of Capillary network and also a high amount of Myoglobin which is a protein which provides extra reserve of oxygen so that the muscle can maintain a high level of activity for an even longer period of time.

Type 2a are a type of fast twitch muscle fibers which use both aerobic and anaerobic metabolism to create energy for the muscle to move. This type of fiber is similar to type 1, they are also red in colour and have large amounts of myoglobin, mitochondria and capillaries, and also can work aerobically or anaerobically and finally also are resistant to fatigue. But they are mainly used for fast contraction sports, whilst maintaining high intensity, they can only be used for a shirt distance in activities such as 200 meter run or 800 meter swim.

Finally type there's Type 2b fiber muscle,they are also fast twitch fibers, which use only aerobic metabolism to create their energy. They are best at producing quick, powerful bursts of speed, these fibers have the highest rate of contractions but also fatigue much faster than the others. These fibers are actually white unlike the rest, they also have a low amount of myoglobin, few mitochondria and a few capillaries. They can maintain much stronger force of muscle contraction and used for activities with high intensity anaerobically such as power lifting or the 100 meter sprint.

Process of muscular contraction

Muscle contraction is explained by using the sliding filaments theory. Firstly a nervous impulse arrives at the neuromuscular junction, which then causes a release of a chemical called Acetylcholine , and as this is present then the depolarisation of the motor end plate travels through out the muscle by the transverse tubules, causing calcium to be released from the sarcoplasmic reticulum which then turns on the whole process.

The calcium binds to troponin under high concentrations of calcium, changing its shape and therefore moving tropomyosin from the active site of the actin, allowing the myosin filaments to attach to the actin, forming a cross bridge.

As the ATP is broken down, it releases energy which enables the myosin to pull the actin filaments inwards and resulting in the muscle being shortened. This happens along the whole length of every myofibril in the muscle cell.

The myosin then detaches from the actin and the cross bridge is broken when an ATP molecule binds to he myosin head. When the ATP is broken then the myosin head can attach again to an actin binding site further along the actin filament and then repeat this which is called a powerstroke, if this pulling action gets repeated then it would be called a ratchet mechanism.

This action of contraction within the muscle can be repeated as long as there is enough ATP and calcium in it to keep on making energy. As soon as the impulse is stopped, the calcium is pumped back to the sarcoplasmic reticulum and the actin returns to the relaxed position which causes the muscle to get longer and relaxed

Roles of muscles during contraction

There are different ways in which a muscle can be active during exercise, for example when we consider the bicep curl to be the exercise, then the bicep would be the target muscle that we are trying to strengthen, this muscle is therefore known as the agonist muscle which is doing all the prime puling and main action. But all muscles work in pairs which means that the tricep would then be the antagonist which is the opposite of the bicep.

But there is 2 other muscle roles in the muscle contraction, but to make sure the actions are done with the correct form, there are muscles that will contract in an isometric way to fix the body position in case there's a chance of an injury and stabilize nearby joints.

For the bicep curls to be effective, the shoulder joint must remain stationary. That is why the deltoid is know as the fixator muscle in the curl as it only needs to be stable and not contract much at all as any fixator just stabilizes any unnecessary movement rather than contacting the muscle. Finally, after a while of the muscle working it begins to fatigue during a set of exercise, other muscles will need to join in to help assist the joint action. These muscles are known as synergists, while bicep curling, the forearm will be playing that part. This is seen as if heavy weight is done during a curl, the forearm will increase its tension.

Different types of muscle contractions

There is 2 main types of muscular contractions, and they are isometric which are dynamic contractions and isometric which are static contractions. Cross- bridges will happen between actin and myosin will always take place in both of the contractions.

Isotonic contractions are divided into 2 phases of movement, but the muscular contraction involved in both these phases is different.

Isotonic contractions are dynamic and always involve movement and are divided into 2,

Firstly there is the upward phase of the bicep curl, the concentric phase is when the hand is brought closer to your upper arm, this is when the muscle shortens and therefore contracts against the resistance it overcomes. The angle of the joint reduces and the origin and the insertion of the muscle mover towards each other, this is called positive phase of a movement. Concentric contraction is necessary if joint movement is to be in the direction opposite of the gravity.

The opposite of this is the downward phase of this bicep curl exercise and is called the eccentric phase, this is when the muscle lengthens following a contraction against a resistance as external forces over come the muscle. The angle of the joint increases which causes the origin and insertion to move apart from each other which is called negative phase. The muscle tension in eccentric work is enough to cause the movement, but acts as a break control of the speed of movement caused by a different force and works in the same direction as gravity.

Isometric contraction is the one that does not involve movement, it stays the same length following a contraction against a resistance which relates to bicep curling a weight you cannot lift, while trying to lift the weight, the muscle generates tension, as the cross-bridge form, but the muscle strength is not enough to over come the heavy weight. The muscle is exerting the force and is trying to counteract an opposing force. As the joint position is maintained, the contractile part of the muscle shortens, but the elastic connective tissue is the one that lengthens so there's no change in length overall.

Isometric training is a good way of training your muscles, but must be done carefully and with care with people with hyperextension, and pregnant women. If this is the case then the contractions should not be held for more than 10 seconds, as it will cause blood pressure to rise because as the muscles contract, the blood flow within the muscles is reduced.