Tag: structure of skeletal muscle

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Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

Contractile fibrils of muscles are called

  1. Neurofibrils

  2. Callogen fibres

  3. Myofibrils

  4. Yellow fibres
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

  • Each muscle fibre(muscle cell) is lined by the plasma membrane called sarcolemma enclosing the sarcoplasm(cytoplasm of muscle fibre). 
  • The characteristic feature of the muscle fibre(muscle cell) is the presence of a large number of parallelly arranged filaments in the sarcoplasm called myofilaments or myofibrils.
  • Each myofibril is made up of two kinds of proteins. They are actin and myosin.
  • The function of the myofibril is to perform muscle contraction via the sliding-filament model. Hence Contractile fibrils of muscles are called myofibrils.
  • So, the correct answer is 'Myofibrils'.

Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

End plate junction is present between

  1. Neuron and striated muscle

  2. Neuron and neuron

  3. Muscle and muscle

  4. Both B and C
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The area of contact between the ends of a large myelinated nerve fibre and a fibre of the skeletal muscle is called the motor end plate junction. It is also called as a neuromuscular junction or myoneural junction.
Thus, the correct answer is the option (A), 'Neuron and striated muscle'.

Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

Sarcomere is the functional unit of contraction in a muscle fibre. Identify the portion of myofibril that constitutes a sarcomere

  1. Portion of myofibril between two successive Z-lines

  2. Portion of myofibril between two successive I-bands

  3. Portion of myofibril between two successive A-bands

  4. Portion of myofibril between two successive M-lines
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  • 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'.
Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

An animal cell with numerous nuclei is called

  1. Coenocyte

  2. Syncytial

  3. <p>Plasmodium</p>

  4. Both A and B
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
  • 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'.
Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

Anisotropic band is made of

  1. Myosin filaments

  2. Actin filaments

  3. Elastin filaments

  4. Both A and B
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • 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'.
Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

Skeletal muscles are controlled by

  1. Somatic nerves

  2. Autonomic nerves

  3. Parasympathetic nerves

  4. Sympathetic nerves
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Somatic nerves are part of the peripheral nervous system and are responsible for the voluntary control of skeletal muscles. Autonomic, sympathetic, and parasympathetic nerves control involuntary functions like heart rate and digestion.

Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

H-zone in skeletal muscle fibre is due to

  1. Extension of myosin filaments in central portion of A-band.

  2. Absence of myofibrils in the central portion of A-band.

  3. Central gap between filaments in A-band.

  4. Central gap between actin filaments extending through myosin filaments in A-band.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • 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'.
Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

Identify the correct statements.

1. A-bands are dark and contain myosin.
2. I-bands are light and contain actin.
3. During the action, A band contracts.
4. The part between two Z-lines is sarcomere.
5. The central part of thin filament, not overlapped by thick filament is the H-zone.

  1. 1, 2 and 3 are correct

  2. 1, 3 and 5 are correct

  3. 1, 2 and 4 are correct

  4. 1 and 2 are correct

  5. 1, 2, 3 and 5 are correct
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
  • 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
Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

Myofibrils show dark and light bands in

  1. Cardiac muscles

  2. Unstriped muscles

  3. Striped muscles

  4. Both A and C
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • The striated appearance of skeletal and cardiac muscle tissue is a result of repeating bands of the proteins actin and myosin that are present along the length of the myofibril.
  • The light bands contain actin and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin. Hence called striped muscles due to the presence of striations.
  • Hence Myofibrils show dark and light bands in Cardiac muscles and striped muscles.
  • So, the correct answer is 'Both A and C'.
Multiple choice zoology movement and locomotion in man structure of skeletal muscle muscles and their structure skeletal muscles

Cross bridges of sarcomere in skeletal muscle are made up of 

  1. Actin

  2. Myosin

  3. Troponin

  4. Tropomyosin
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
  • 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'.