During the following class we will develop all the processes that lead to muscular contraction and relaxation. We will be interested to analyze biochemistry and mechanical processes and also do not forget the catalyzing factor: the nervous signal. Muscle When we make any reference to the muscle we are talking about a tissue, this means a cellular composition that shares a particular function, contraction in this case. These muscular cells known as miocytes are surrounded by intercellular substance and connective tissue.
The connective tissue that surrounds the miocytes is filled with blood vessels that will provide nutrients and collect discarded elements produced by their activity. Muscular tissue has two basic properties that distinguish them from other tissues: It is an excitable tissue that is able to generate an action potential that will be the key to muscular contraction. It is also a tissue that is able to transform the chemical energy provided by TPA’s hydrolysis into mechanical energy (work, contraction) and heat (unutilized energy). Functions As we have mentioned it before the activity developed by the muscular tissue is contraction and relaxation. Because of this fact, the muscle develops several functions in different parts of the body.
Locomotion
Muscular activity allows us to get around. Evacuation of visceral contents: muscular contraction allows us to empty organs such as the stomach and the bladder. Mastication, ingestion: muscles make movements, which lead to alimentary bolus and its arrival to the stomach. Arterial pressure regulation: the blood vessels and heart walls are made of miocytes. Contraction Types We will briefly describe two types of muscular contraction, which might take place. Isotonic contraction is an activity characterized by the muscle’s shortening. In order to consider a muscular activity an isotonic one, the charge must be constant.
Isometric contraction is carried through the muscular fiber fixation, the muscle’s shortening is thus impeded, and its length is constantly kept. During isometric activity, muscular tension raises substantially. Miocyte The miocyte or muscular fiber is a contraction highly specialized cell with an important concentration of myofibrils (hundreds or even thousands). Its extreme specialization has allowed it to lose its splitting ability. Miocytes do not carry on mitosis. When analyzing cellular morphology we find two types of muscles in the body: Striated, which characterizes by possessing transversal striations (formations only visible if Optic Microscope is utilized). These striations have their origin in a structure named sarcomerus, which allows a faster contraction. There are two types of striated muscle, the skeletal and the cardiac one.
The skeletal we find it in all muscles which allow our locomotion and our stand up position. Its innervations are voluntary, which means that we regulate their activity consciously. The cardiac muscle is the one that builds the heart walls, and carries the responsibility the pumping of blood throughout the organism. In this case, its regulation is involuntary. Straight or Plain muscle: This type of muscle possesses myofibrils. However they do not organize themselves forming a sarcomerus. Its contraction is slower than in the striated case, but it is also more resistant and prolonged (that is why we find ´plain muscles forming the walls of the stomach or the vessels which have a constant contractile activity), Its nervous regulation is involuntary (autonomic). TPA Before we continue, it is necessary to include a brief description of the energy exchange coin that is used by our organism and also our muscular tissue: the TPA. The Tri-phosphate Adenosine is a molecule that possesses two high-energy links, which are established between two phosphate groups. These link’ rupture (generally carried through hydrolysis) produces the liberation of a great amount of energy used by cells’ metabolism of our whole body. In order to form TPA it is necessary to obtain nutrients through alimentation (mainly fats, carbon hydrates, to a lesser extent proteins) and also oxygen obtained through lung gaseous exchange. Two processes lead to the TPA’s synthesis: The oxidation-phosphorilation, which is carried in the mitochondria (slow but lasting process) and the Glucolisis which takes place within the cytoplasm (faster but less lasting).
Locomotion
