Skip to main content

Renin Angiotensin Mechanism.

Physiology of Muscle Contraction.

 

Skeletal Muscle Fibre.

  • The single cell of a skeletal muscle is called “Skeletal Muscle Fiber”.

  • They are cylindrical in shape and their length varies as per length of the muscle.

  • They are held parallel to each other and show the presence of alternate dark and light bands due to arrangement of the muscle proteins.

  • The plasma membrane is called “Sarcolemma”.

  • The endoplasmic reticulum is called “Sarcoplasmic reticulum”.

  • The cytoplasm is called “Sarcoplasm”.

  • The muscle fiber is multinucleated i.e. it contains many nuclei.

  • The sarcoplasm contains many mitochondria for production of ATPs.

  • The sarcoplasm contains a special protein called “Myoglobin” which stores oxygen.

Myofibrils and  Filaments.

  • The sarcoplasm of the skeletal muscle fiber contains several thread-like structures called “Myofibrils.”

  • The myofibrils are made up of smaller structures called “Filaments”.

  • The filaments are of two types,

    • Thin filaments: Made up of Actin, troponin-tropomyosin.

    • Thick filaments: Made up of  Myosin.

  • Both filaments work in the process of muscle contraction.

Sarcomere.

  • The basic functional unit of the filament is called a “Sarcomere”.

  • They are placed in a rep[eating arrangement.

  • They contain perpendicular protein plates called “Z lines” that form the boundary of a Sarcomere.

  • Within the boundaries lie alternate thick and thin filaments.

  • M line proteins attach the thick filaments with each other.

  • The thin filaments are attached to the Z line proteins.

  • During the process of contraction the Thick filaments pull the Thin filaments towards the center of the sarcomere, causing the contraction of sarcomere and hence contracting the muscle itself.

Sliding filament mechanism of Muscle contraction.

  • The length of the skeletal muscle shortens as thick and thin filaments of the sarcomere slide over one another, causing contraction of the skeletal muscle.

  • The process is known as “Sliding filament mechanism”.

  • The thin filaments are made up of Actin, troponin, tropomyosin.

  • The thick filaments are made up of,

    • Myosin heads: projected towards thin filaments.

    • Myosin tails: forms the shaft of thick filament.

  • As action potential for muscle contraction is generated the sarcoplasmic reticulum releases stored calcium in the sarcoplasm.

  • The release calcium ions binds with the troponin and hence moves away the troponin-tropomyosin complex away opening the Myosin binding site on thin filaments.

  • The myosin heads now bind to the free binding site on the actin filaments and push them to the center of the sarcomere.

  • Once the site becomes free again the cycle continues.

  • The contraction cycle can be summarized in the following four steps.

    • ATP Hydrolysis.

    • Formation of cross bridges.

    • Power stroke.

    • Detachment of Myosin from Actin.

  1. ATP Hydrolysis:

  • The Myosin head contains an ATP binding site an ATPase enzyme.

  • When ATP binds to the Myosin head the enzyme hydrolyses it to ADP giving the Myosin head energy.

  • The ADP and formed Phosphate group remain attached to the myosin head.

  1. Formation of cross bridges:

  • The energized myosin head attaches to the myosin binding site on the actin filament.

  • This binding of myosin head to the actin during contraction is termed as “Cross Bridge Formation”.

  1. Power stroke:

  • Once cross bridges are formed the power stroke occurs.

  • The cross bridges pull the actin filaments towards the center of the sarcomere this pulling is called powerstroke.

  • This results in the contraction of the sarcomere and ultimately the skeletal muscle.

  1. Detachment of Myosin from Actin:

  • At the end of the powerstroke in the center of the sarcomere an ATP molecule attaches to the myosin head.

  • This causes detachment of the myosin from actin filament.

Commonly Asked Questions:

  1. Write a short note on the structure of a skeletal muscle.

  2. Write a short note on “Physiology of Muscle Contraction”.

  3. Write a short note on the “Sliding Filament Mechanism of Muscle Contraction”.
Labels:

Popular posts from this blog

Rate of Drying Curve.

  Definition Drying is defined as the removal of liquid from a product usually with application of heat. Rate of Drying Curve. Drying process can be divided into three periods Initial Adjustment Period. Constant drying rate period. First falling drying rate period. Second falling rate period. Initial Adjustment Period (A-B): Also called the “ Heating up” period . In this period the substance gets heat and increases in temperature. Drying has not yet started. Constant drying rate period (B-C): During this period the temperature of the solid and the rate of drying remain constant. The moisture evaporating from the surface is replaced by water diffusing from the interior of the solid at a rate equal t o the rate of evaporation.  The moisture content at the end of constant rate (point C) is referred to as the critical moisture content (CMC).  At CMC, dry spots start appearing and drying rate starts falling . First falling drying rate period (C-D): This period is also called the period of
Read more

Heat Exchangers and Heat Interchangers.

  In pharmaceutical industries many types of equipments are used for transfer of heat, they can be classified as follows, Heat Exchangers. Heat Interchangers. Heat Exchangers: These devices are used for transferring heat from a fluid (Hot Gas or Steam) to another fluid (Liquid) through a metal wall. Heat Interchangers: These devices are used for transferring heat from a One liquid to another liquid or one gas to another gas through a metal wall. HEAT EXCHANGERS; The equipment used for heat transferring are known as heat exchangers. Some of the processes that involves heat transfer in pharmaceutical industries are: Preparation of starch paste (in steam jacketed kettle). Crystallization. Evaporation. Distillation.  Classification of heat exchangers On the basis of transfer of heat, heat exchangers are classified as: Direct transfer type:  The hot and cold fluids are separated by a metal wall through which the heat is transferred from hot fluid to cold fluid. E.g. shell and tube heater, 
Read more

Flash Distillation.

  Principle: When a hot mixture is allowed to enter from a high-pressure zone into a low pressure zone, the entire liquid mixture is suddenly vaporized. This process is known as flash vaporization .  During this process, the chamber is cooled.  The less volatile fraction is condensed and the more volatile component remains in the vapor phase .  This process requires time, hence liquid and vapor are kept in intimate contact until equilibrium is achieved. Flash distillation is also called equilibrium distillation because separation of two liquids takes place when liquid and vapor phases are at equilibrium. Equipment used for Flash Distillation: Construction: It consists of a pump, which is connected to a feed reservoir.  Pumps help in pumping the feed into the heating chamber.  The heating chamber is heat supplied by steam.  The other end of the pipe is directly introduced into the vapor-liquid separator through a reducing valve.  The vapor outlet is provided at the top of the separato
Read more