Tag: skeletal muscles

• The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils. The light bands contain actin(thin filament) and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin(thick filament).
•  In the centre of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line. The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere Sarcomere is considered as the functional unit of contraction in a muscle fibre.
  
• So, the correct answer is 'Portion of a myofibril between two successive Z-lines'.
  

• Syncytial refers to a multinucleate condition where a single cell has more than one nucleus per cell i.e., multiple nuclei with a common cytoplasm.
• It is caused primarily due to multiple cell fusions of uninuclear cells.
• This condition usually arises when cells are infected with certain types of viruses (HIV, pneumoviruses etc.).
• In animals, this condition is seen in skeletal muscles (large skeletal muscle fibres are formed by the fusion of individual muscle cells).
• So, the correct answer is 'Syncytial'.

• Skeletal muscle fiber is made up of two types of filaments. They are thick filament (myosin) and thin filament (actin). The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils.
  
• The A band in skeletal muscle is also called as anisotropic band.
• The anisotropic band is made of both actin filaments and myosin filaments.
  
• So, the correct answer is 'Both A and B'.

• Myofibril is made up of two types of filaments. They are thin filament(actin) and thick filament(myosin).
• The light bands contain actin and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin. The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils.
  
•  In a resting state, the edges of thin filaments on either side of the thick filaments partially overlap the free ends of the thick filaments leaving the central part of the thick filaments. This central part of thick filament, not overlapped by thin filaments is called the ‘H’ zone.
  
• Hence H-zone in skeletal muscle fibre is due to Central gap between actin filaments extending through myosin filaments in A-band.
• So, the correct answer is 'Central gap between actin filaments extending through myosin filaments in A-band'.

• The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils. The light bands contain actin(thin filament) and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin(thick filament). In the centre of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line. The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere 
  
• Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge. 
• This pulls the attached actin filaments towards the centre of ‘A’ band.
  
• The ‘Z’ line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction. Hence the ‘I’ bands get reduced, whereas the ‘A’ bands retain the length.
•  The central part of thick filament, not overlapped by thick filament is the H-zone.
  
• So, the correct answer is '1,2 and 4

• Active sites for myosin (Thick filament) are present on actin which are masked by troponin in resting state. when  Ca++ level increases it leads to the binding of calcium with a subunit of troponin on actin(thin) filaments and thereby remove the masking of active sites for myosin.
  
• Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge. thus myosin forms cross bridges.
• This pulls the attached actin filaments towards the centre of ‘A’ band.
  
•  The ‘Z’ line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction.
• Hence cross bridges of sarcomere in skeletal muscle are made up of myosin.
• So, the correct answer is 'Myosin'.

Bicep muscles are present at front of our upper arm. It contains two tendons that help it to attach it from the bones of the shoulder and other one is attached to the radius bone of the elbow.

Intercalated discs support synchronized contraction of cardiac tissues. They occur at the Z line of the sarcomere and can be visualized easily when observing a longitudinal section of the tissue. Three types of cell junction make up an intercalated disc.