Sarcomerus shortening During relaxation, the sarcomerus’ length is of 2 to 4 mm. In order to reach muscular contraction thin filaments slide over the thick ones towards the sarcomerus center. Facts usually associated to contraction are the following: Formation of Transversal Bridges (reversible chemical union) between the actinia and myosin filaments Association between actinia and myosin heads: This is possible since the myosin head hydrolyzes the TPA, which obstructs it during relaxation. Freed energy is in part utilized to make a swinging movement destined to produce the actinia movement towards the sarcomerus center. During relaxation the myosin head disassociates itself from the actinia and a TPA molecule covers it again. Excito-Contractile mating A nervous signal is necessary in order to unlock the facts, which produce muscular contraction, and it comes from the central nervous system. This signal produces a depolarization of the cell membrane. This depolarization generates a signal, which reaches the Sarcoplasmic reticule through the T tubule. Inside the intracellular deposits, Calcium is thus freed. This fact produces the union of Calcium and C Troponine. I Troponine and actinia union is weakened and actinia-myosin union gets oldstronger. During relaxation calcium is recaptured by a TPA dependent pump, which is found within the sarcoplasmic reticule membrane. Two enzymes participate in this process: calsecuesrine and parbalbumine.
Both are present in the sarcoplasmuc reticule. Muscular contraction and relaxation are two active processes, which require TPA: CONTRACTION IS AN INTEGRATED SEQUENCE OF EVENTS We will now explain the events that are involved during muscular contraction. We will divide into three moments. Moment Zero At this point, the plasmatic membrane is polarized, Calcium is found in the sarcoplasmic reticule, I Troponine is united to actinia and the myosin head is obstructed by a TPA. Sarcomerus is relaxed. Under these circumstances a depolarizing nervous impulse is launched from the central nervous system. Moment One Calcium deposits liberation is a consequence of the depolarizing impulse, which comes from the T tubule to the sarcolplasmic reticule. This ion is transported because of a gradient concentration (passive transportation). Calcium will unite C Troponine provoking I Troponine liberation of actinia. Also, Calcium provokes the TPA hydrolysis found in the myosin head thus freeing the necessary energy, which will allow contraction. Consequently the myosin-free head joins the actinia displacing it towards the sarcomerus center. Muscle is contracted. Moment Two Calcium returns to the sarcoplasmic reticule through a TPA usage since it does so in a counter gradient manner. C Troponine abandons its union to Calcium, and allowing the I Troponine to join the actinia. This TPA molecule returns to cover the myosin head. The muscle is relaxed once again. Chemical energy conversion into heat and mechanical energy Chemical energy transformation into a mechanical one and heat is directly proportional to Contraction’s duration and tension and follows this equation: Chemical energy = mechanical energy plus heat Global mechanical efficiency of muscular contraction reaches 20%. This means that out of the TPA hydrolysis produced energy only a 20% is used in contraction and some 80% turns into heat or it is used in the energy’s recovery (re-captivation of Calcium, re-synthesis of TPA). Maximum Contraction Strength per Muscular Section This parameter is equal in men and women and it reaches a value of 2 or 3 kg/cm2 of each muscular section. However, and due to hormonal differences, men has more muscular mass than women whereas women tend to possess more adipose tissue. This is the reason why men can develop more strength that women. Skeletal Muscle excitation Skeletal muscle fibers are innervated by nervous fibers, which are originated in the moto-neurons within the anterior segment f the Spine Medulla. Each nervous end establishes a neuromuscular union. Nervous fiber branches encapsulate within the muscular fiber interior. This structure is called terminal motor plaque. Contraction is provoked by the following events. A nervous impulse should reach the neuromuscular union in order to produce the liberation of acetilcoline. Acetilcoline unchains the opening of the ionic channels, which are in the cell membrane. The opening of these channels provokes the entering of large quantities of sodium ions (Na+) to the cell interior and they will produce the membrane depolarization. An enzyme known as acetilcolinesterase will later take care of the acetilcoline hydrolyzing thus closing the Na+ channels. The knowledge of these processes is very important to analyze the actions of nicotine or nervous gas, for example. Nicotine shows an acetilcoline analogous action. Fluor-phosphate Disopropile (nervous gas) inactivates the acetilcolinesterase during weeks. Both actions might produce muscular spasms. Nervous gas case is very worrying since it produces asphyxia through larynges spasms. Nicotine overdose might also produce that phenomenon.
Anatomic and Physiological Integration of the Nervous System
According to its topographic distribution we can divide our nervous system into the CNS (central nervous system) formed by the spine medulla and the encephalon (encephalic trunk, cerebellum and brain) and the PNS (peripheral nervous system) integrated by peripheral nerves and glands. According to its function we might distinguish a SNS (somatic nervous system), which is characterized by being conscious and voluntary, and an ANS (autonomic nervous system) which s unconscious, involuntary and automatic. Within the ANS we find two subdivisions: the Sympathetic and the Para-sympathetic. The sympathetic characterizes itself by the utilization of neurotransmitters such as nor adrenalin and adrenaline. This system is activated in stress situations such as fasting, exercising, struggle or fleeing. This response shows through vessel constriction, rise of the five cardiac properties (automatism, excitability, conductibility, contractility and relaxation), bronco dilation, midriasis, glucemia rise, blood flow rise towards the skeletal muscle, and gastrointestinal blood flow diminution. On the other hand, the Para-sympathetic ANS uses acetilcoline (Ach) as neurotransmitter. This system is activated during resting and satiation (postprandium). Para-sympathetic response characterizes itself through vessel dilation, five cardiac properties diminution, vessel constriction, meiosis, glucemia diminution, blood flow diminution towards the skeletal muscle, gastrointestinal blood flow diminution, acid secretion rise, motility, stomach emptying, and motility rise and transit in the thin intestine.
Motor System
The somatic motor system is organized in three hierarchical levels: Movement Diagramming Decision of the type of program to be executed: It requires the will, ability to develop some movement with some defined goal. Motor cortex performs that task. Its damage provokes paralysis. Program selection: It selects the muscles, which have to intervene, and its sequence of activation. The motor of this activity is the pre-motor area. Its damage provokes motor apraxia (without movement). Execution and control of the motor program: base ganglion and cerebellum intervene in the voluntary motor act. Direction, speed and size of the movement are regulated. Movement execution: It is carried by the encephalic trunk (mesenphalus, protuberance and bulb). Muscular contraction direct responsible: This activity is carried on by the spine medulla moto-neurons.
Filament
concentration (passive transportation). Calcium will unite C Troponine provoking I Troponine liberation of actinia. Also, Calcium provokes the TPA hydrolysis found in the myosin head thus freeing the necessary energy, which will allow contraction. Consequently the myosin-free head joins the actinia displacing it towards the sarcomerus center. Muscle is contracted. Moment Two Calcium returns to the sarcoplasmic reticule through a TPA usage since it does so in a counter gradient manner. C Troponine abandons its union to Calcium, and allowing the I Troponine to join the actinia. This TPA molecule returns to cover the myosin head. The muscle is relaxed once again. Chemical energy conversion into heat and mechanical energy Chemical energy transformation into a mechanical one and heat is directly proportional to Contraction’s duration and tension and follows this equation: Chemical energy = mechanical energy plus heat Global mechanical efficiency of muscular contraction reaches 20%. This means that out of the TPA hydrolysis produced energy only a 20% is used in contraction and some 80% turns into heat or it is used in the energy’s recovery (re-captivation of Calcium, re-synthesis of TPA). Maximum Contraction Strength per Muscular Section This parameter is equal in men and women and it reaches a value of 2 or 3 kg/cm2 of each muscular section. However, and due to hormonal differences, men has more muscular mass than women whereas women tend to possess more adipose tissue. This is the reason why men can develop more strength that women. Skeletal Muscle excitation Skeletal muscle fibers are innervated by nervous fibers, which are originated in the moto-neurons within the anterior segment f the Spine Medulla. Each nervous end establishes a neuromuscular union. Nervous fiber branches encapsulate within the muscular fiber interior. This structure is called terminal motor plaque. Contraction is provoked by the following events. A nervous impulse should reach the neuromuscular union in order to produce the liberation of acetilcoline. Acetilcoline unchains the opening of the ionic channels, which are in the cell membrane. The opening of these channels provokes the entering of large quantities of sodium ions (Na+) to the cell interior and they will produce the membrane depolarization. An enzyme known as acetilcolinesterase will later take care of the acetilcoline hydrolyzing thus closing the Na+ channels. The knowledge of these processes is very important to analyze the actions of nicotine or nervous gas, for example. Nicotine shows an acetilcoline analogous action. Fluor-phosphate Disopropile (nervous gas) inactivates the acetilcolinesterase during weeks. Both actions might produce muscular spasms. Nervous gas case is very worrying since it produces asphyxia through larynges spasms. Nicotine overdose might also produce that phenomenon.
