Tag: locomotion and movement

The layers of stomach wall include serosa, muscularis, submucosa, and mucosa these are involuntary in nature and show the presence of cell junctions also, the muscularis layer shows branched and multinucleated appearance.

Contractile fibres are those fibres which are capable in contraction of the muscles.

So, the correct  option is 'Myofibrils'

• Actin and myosin are the contractile proteins, and they interact with each other, causing contraction, while troponin and tropomyosin are regulatory proteins that regulate the interaction between actin and myosin. 
• Myofilaments(actin and myosin) are packed in functional units of striated muscle referred to as sarcomeres. 
• Hence, Troponin and tropomyosin are the regulatory protein in muscle contraction.
• So, the correct answer is 'Troponin and tropomyosin'.

In the sarcoplasmic reticulum of resting muscle, Ca2+ are held together by calmodulin. Calmodulin is also called as calcium-modulated protein, is a calcium-binding protein present in the cytoplasm. It is present in all eukaryotic cells.it's the function is to bind calcium ions in resting muscle. when the motor impulse is generated and reached to neuromuscular junctions calcium is released from calmodulin which facilitates muscle contraction.

• Each myosin (thick) filament is also a polymerized protein. Many monomeric proteins called Meromyosins constitute one thick filament.
• Each meromyosin has two important parts, a globular head with a short arm and a tail. The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.
• The globular head of a myosin molecule that projects from a myosin filament in muscle and is held to attach temporarily to an adjacent actin filament and draw it into the A band of a sarcomere between the myosin filaments to form a cross bridge.
  
• Cross bridges between actin and myosin are broken up by Binding of ATP to the myosin head and The myosin, releasing the ADP and P1 and muscle goes back to its relaxed state.
• So, the correct answer is 'Binding of ATP to the myosin head'.

Muscle is a soft tissue found in most animals. Muscle cells contain protein filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and the shape of the cell. Therefore, (d) is the correct answer. 

• Skeletal muscle fiber is made up of two types of filaments. They are thick filament and thin filament.
  
• Thick filament is made up of a protein called Myosin.
  
• Each myosin (thick filament) is made up of Many monomeric proteins called Meromyosins.
  
• Hence Major protein in the thick filaments of skeletal muscle fiber is Myosin.
• So, the correct answer is 'Myosin'.

• Each myofibril (muscle filament)has alternate dark and light bands on it. 
• The light bands contain actin and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains Myosin.
• Myosin filaments are also called as Thick filaments.
• Hence Myosin filaments are localized in A-Band.
  
• So, the correct answer is 'A-Band'.