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Compare and Contrast Cardiac and Skeletal Muscle

Keywords: cardiac muscle composition, skeletal muscle structure

Something that differentiates pets or animals from other organisms is their capability to voluntarily carry out actions using their muscles. They do this by muscle cells changing span, which is recognized as contracting. You will find three types of muscle, which can be recognized by their set ups and functions. They are cardiac, skeletal and clean muscle. Here I shall be contrasting the constructions of cardiac and skeletal muscle and looking at how their histological, structural and functional differences allow them to carry out their specific assignments better.

Cardiac muscle is available only in the center and causes contractions, in the heart called systole, which pump the bloodstream from the center and around your body supplying the air and other vital substances to cells. Skeletal muscle is attached to tendons, which put on bones. The contractions of skeletal muscles cause the tendons to move on the bones, which results in movement of, for example, an arm.

There is only one similarity between the buildings of cardiac and skeletal muscles. Both their set ups are striated (striped), made by actin and myosin myofilaments. They may be tightly organised into repeating patterns so that actin can glide above the myosin during contraction.

Figure 1 shows one of those repeating models in cardiac and skeletal muscle, called a sarcomere. For contraction to occur in cardiac and skeletal muscle, the actin filaments slip in the myosin filaments in a process known as the sliding-filament theory. So in figure 1 the thin pink filaments would glide above the dark blue filaments (not true colors). Myosin heads are attached to the actin. Adenosine triphosphate (ATP) induces the dissociation of the myosin head, the myosin brain then connects again to the actin and finally inorganic phosphate (Pi ) is released changing the viewpoint of the myosin head, triggering the actin filaments to slip on the myosin filament. This causes a reduction in length of the I music group but the A band always stays on the same span.

One of the key differences between the two types of muscle is in the way that their contractions are brought about. If one wanted to increase their arm, their brain would produce an action potential via the somatic nervous system (SNS). The action probable will lead to a muscle action potential and the T-tubules will depolarize and open up calcium ion (Ca2+) stations, resulting in cross-bridge cycling, where the actin and myosin glide past each other and cause the skeletal muscle to contract, raising the bone with it. Therefore the muscle will not contract minus the source of the anxious system.

Cardiac muscle is also linked to the nervous system. But as contractions are involuntary, cardiac muscle is linked to the autonomic stressed system (ANS). However, unlike in skeletal muscle, the real action potentials that stimulate muscle contraction are manufactured by myogenic skin cells in the center. Myogenic means that it's the skin cells themselves that induce the electro-mechanical action potentials, without the need for any external input. The cells are found in the Sino Atrial Node (SAN), which itself is situated by the right atrium; the cells in the SAN are known as the pacemaker. They create a pacemaker potential "which models the frequency of action potentials and therefore the intrinsic tempo of the normal center. " The ANS, connected to the SAN, only modulates the heartrate, with the sympathetic nervous system speeding up the heart rate ready for the struggle or flight effect and the parasympathetic stressed system slowing the heartrate down.

It is important that the heart and soul is handled automatically so that we are not aware of the heart beating, since it would be almost impossible and probably exhausting for us to have to consciously think about making each and every heart beat, specially when we live asleep. In addition, because the heart is myogenic, there are benefits for transplants because the heart and soul muscle can continue conquering while the heart and soul is being taken up to the new body.

Skeletal muscle must be under voluntary control so that every action can be executed consciously, such as picking up a cup. If it were computerized there would be no conscious control of when the muscles should written agreement and our limbs would not be under our control. Nevertheless in reflex reactions, the skeletal muscle will come under the control of the ANS. For instance, if one's hands was to touch a hot subject, the ANS would react following a reflex arc of stimulus, receptor, sensory neuron, relay neuron, engine neuron, effector, response; the arm would automatically move away from the heat source. Generally, compared to the beating of the heart and soul, there is absolutely no such pattern in our voluntary skeletal muscle contractions thus an programmed myogenic tempo of action potentials aren't required in skeletal muscles.

Looking at a fasciculus from both a cardiac and skeletal muscle shows that they are structured slightly differently. Body 2. 1 and Body 2. 2 (see below) show simplified variants of the structure of both muscles. Shape 2. 1 shows an example of skeletal muscle. It is made of long slim cylindrical fibres, each being innervated by a single somatic alpha motoneuron. The axon enters the muscle and branches, attaching to sole muscle fibres.

In cardiac muscle the fibres are linked together by a type of intercalated disk called a gap junction. Also the fibres are placed along by adherens junctions. These strengthen the overall composition of the cardiac muscle therefore the forceful contractions in the heart and soul don't rip the fibres. The difference junctions are vital for the performing of the center. They allow the electrical signals created from the SAN to complete between muscle cells so they all agreement in a synchronised way and the atria followed by the ventricles experience systole. The heart has Purkinje fibres that execute the action potential so that they go from the SAN in the right atrium all the way to the left ventricle. Damage to cardiac muscle fibres may cause unsynchronised contractions. This abnormal and fast contraction of the heart and soul is named fibrillation. If this occurs in somebody, with no treatment they are likely to die. It could be treated by a big electric shock provided across the chest by the use of a defibrillator. This aims to avoid and then restart the APs from the SAN and therefore for the heart to defeat regularly again.

Cardiac and skeletal muscle will both respond to an individual action potential by creating a solitary twitch response. Once the frequency of indicators increase, skeletal muscles show summation, where two APs, which occur very close alongside one another, will cause one more powerful response alternatively than two normal replies. Eventually a tetanus can occur and rather than simply undergoing a series of single twitches for each action probable, the muscle remains in a contracted talk about for brief cycles, which is far more reliable. This tetanus occurs because the refractory period is a lot shorter than the time it takes for an individual routine of contraction and rest.

In cardiac muscle cells however, the period of the action potential will be a lot longer, anticipated to slowly activating calcium stations and the T-tubules being relatively much longer. Because another action potential cannot appear before response of the prior action potential has been completed, cardiac muscle cannot undergo a tetanus. That is vitally important for cardiac muscle because time is necessary for the heart and soul to sufficiently fill with blood prior to the next action potential arrives. A tetanus would prevent this going on and the center would undertake systole and relaxation (diastole) at times when there is very little or no bloodstream in the heart and soul. Again, fibrillation is likely to occur. Due to the fact that cardiac muscle relaxes completely between contractions, it generally does not tire like skeletal muscle does. This is an advantage for cardiac muscle because if the guts started to wheel one would get angina and some regions of cardiac muscle may learn to die.

Due to the heart being constantly lively, much more ATP is necessary in cardiac muscle skin cells than in skeletal muscle cells, which only contract when required to. Therefore cardiac muscle has a larger number of mitochondria than skeletal muscle. Cardiac muscle goes through regular oxidative phosphorylation to supply the ATP necessary for the actin to slide over myosin and so for the muscle to written agreement. This means the cardiac muscle also requires its supply of oxygen and respiratory substrates to respire aerobically. They are supplied via coronary arteries, which branch faraway from the ascending aorta. Having this resource and consequently producing far more ATP, is very effective for contractions. Skeletal muscle though, does not have as many mitochondria because it contracts relatively less frequently and doesn't need the constant way to obtain ATP.

Relatively there is a massive difference in the space of a cardiac muscle fibre and a skeletal muscle fibre. Each cardiac fibre is up to 100m whereas each skeletal fibre is between a few mm to a 10cm. A muscle fibre is also known as a muscle cell. Most cells, including cardiac muscle fibres (cells), have one nucleus. Skeletal muscle fibres have many nuclei along the fibre (body 2. 1).

This can be discussed by looking again at the lengths of each type of fibre. Each skeletal muscle fibre is at least ten times the length of the cardiac muscle fibre. It would not be very effective for skeletal muscle to possess just one nucleus to supply the whole amount of the cell. The abrasive endoplasmic reticulum, which is put in the cell nearby the nucleus, has ribosomes on its surface where polypeptides are put together. Therefore even if the nucleus was situated in the middle of the cell, any polypeptides or protein will be synthesised near there and would require ATP to transport it to where it is necessary along the distance of the cell. As a result, it is far more effective to acquire many nuclei scattered along the muscle fibre. Cardiac myocytes (muscle skin cells) are relatively a whole lot shorter, thus one nucleus will do to provide for the whole fibre (see body 2. 2).

Aerobic respiration is essential in cardiac muscle. It really is the main source of ATP in cardiac muscle and is also as a result of oxidative phosphorylation. The primary respiratory substrates in cardiac muscle are essential fatty acids, and also carbohydrates. Around 1 - 2% of the ATP in the center hails from anaerobic respiration in basal metabolic conditions. This may go up to around 9% in hypoxic conditions, however in any longer extreme hypoxic circumstances not enough oxidative phosphorylation occurs so there's not enough ATP produced for cardiac contractions, and the cardiac muscle will start to die.

Skeletal muscles have three resources of phosphate to make ATP as so when it is necessary: creatine phosphate, glycogen and cellular respiration. The creatine phosphate provides its phosphate for an ADP to leave ATP and creatine. There is about 10 times the quantity of creatine phosphate than there is of ATP, which means this is provides a good way to obtain ATP. Skeletal muscle only includes about 1% glycogen. It could though undergo glycogenolysis to convert glycogen to glucose-1-phosphate. This goes on to yield just two molecules of ATP, so evidently this is a restricted source. Cellular respiration is the key source of ATP during prolonged exercise and when changing lactic acid to glycogen.

There are many distinctions between cardiac and skeletal muscle. Both have striations but beyond that, they have got special unique features that produce their functions more effective. The center is myogenic making it self-sufficient whereas skeletal muscle is manipulated by the stressed system. It is also vital that the heart's cardiac muscle works without the problems, as even the slightest of problems in the heart and soul can result in loss of life. Both types of muscle are essential to not only humans but all family pets. Cardiac muscle, as previously mentioned, is vital to your life; without it we could not survive as it is required to circulate oxygen and nutrients around your body. Skeletal muscle we can interact with our environment with ease and for humans this is most important as it allows us to drive a car, use your personal computer or walk to school for example. For other family pets it allows them to chase prey or run from a predator. And when the muscles weren't as effective, there could be less reduce when carrying out such activities.

Literature cited

Gillian Pocock, Christopher D. Richards (2006). Individuals Physiology - THE FOUNDATION of Treatments. Oxford Core texts. Pages 84 & 85, Site 87 body 7. 6

http://www. ucl. ac. uk/~sjjgsca/MuscleCardiac. html

Jos Marn-Garca & Michael J Goldenthal (2002) - 'The Mitochondrial Organelle and the Heart', Rev Esp Cardiol, Level 55, Concern 12, pp. 1293 - 1310, ISSN: 1579-2242

http://users. rcn. com/jkimball. ma. ultranet/BiologyPages/M/Muscles. html

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