Test: Types of Movement & Muscle - NEET MCQ

The clavicle is commonly called the collar bone. It articulates with the acromion of the scapula to form part of the shoulder joint.

Line in NCERT: "This bone is commonly called the collar bone."

Following are the correct statements about the mechanism of muscle contraction: 
(i) Acetylcholine is released when the neural signal reaches the motor end plate.
(ii) Repeated activation of the muscles can lead to lactic acid accumulation.
So, the correct answer is (B).

Line in NCERT: "Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron." "Repeated activation of the muscles can lead to the accumulation of lactic acid due to anaerobic breakdown of glycogen in them, causing fatigue." "A neural signal reaching this junction releases a neurotransmitter (Acetyl choline) which generates an action potential in the sarcolemma."

The region between two Z lines is called a sarcomere; sarcomeres can be considered the primary structural and functional unit of muscle tissue. Ultrastructure of a group of myofibrils, showing the sarcoplasmic reticulum and transverse tubules, which constitute the two membrane systems within a muscle fibre.

Line in NCERT: "The portion of the myofibril between two successive 'Z' lines is considered as the functional unit of contraction and is called a sarcomere."

A. A bands of muscle fibre are dark and contain myosin.

• This statement is correct. The A bands are the darker areas of the sarcomere in muscle fibers that contain the thick filaments, primarily composed of the protein myosin.

B. I bands of muscle fibre are light and contain actin.

• This statement is correct. The I bands are the lighter areas that contain the thin filaments, which are primarily composed of the protein actin.

C. During muscle contraction, the A bands contract.

• This statement is incorrect. During muscle contraction, the A bands do not shorten; rather, it is the I bands that shorten while the A bands stay the same length. What actually happens is that the thin filaments slide past the thick filaments, shortening the sarcomere.

D. The part between two Z lines is called sarcomere.

• This statement is correct. A sarcomere is the segment of a myofibril between two Z lines, which is the functional unit of muscle contraction.

E. The central part of the thin filament not overlapped by the thick filament is the H zone.

• This statement is incorrect. The H zone is the central part of the A band where there is no overlap of thin filaments (actin). During muscle contraction, the H zone becomes narrower as the actin slides over the myosin.

Based on the evaluation above, the correct statements are A, B, and D, while C and E are incorrect.

Line in NCERT: "A detailed study of the myofibril has established that the striated appearance is due to the distribution pattern of two important proteins – Actin and Myosin. The light bands contain actin and is called I-band or Isotropic band, whereas the dark band called 'A' or Anisotropic band contains myosin. The portion of the myofibril between two successive 'Z' lines is considered as the functional unit of contraction and is called a sarcomere."

Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscles, with the other two being skeletal and smooth muscles. It is an involuntary, striated muscle that constitutes the main tissue of the walls of the heart.

The human skeletal system has 206 bones. The axial skeleton includes the skull, vertebral column, sternum, and ribs. The skull consists of 22 bones (8 cranial and 14 facial)

Line in NCERT: "The skull is composed of two sets of bones - cranial and facial, that totals to 22 bones."

During muscular contraction myosin cross bridges heads. Myosin is not only an actin binding protein, it is also an ATPase (an enzyme) which is activated by Ca²⁺ and Mg²⁺ ions. Hence, ATPase enzyme is located in myosin.

Line in NCERT: "The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin."

Adenosine Triphosphate (ATP) is the immediate source of (chemical) energy for muscle contraction. Very little ATP is stored in muscle fibres (= 'muscle cells'), only enough to power muscle contractions for a few seconds. The ATP in muscles must be constantly replenished as it is used for various processes.

Line in NCERT: "Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge."

Smooth muscles are plain, non- striated, involuntary or unstriped muscles due to the absence of striations. These occur in the walls of hollow internal organs, in capsules of lymph glands, spleen etc, in iris and ciliary body of eyes, skin dermis, penis and other accessory genitalia etc. 

During shortening of the muscle, i.e., contraction, the ‘I’ bands get reduced, whereas the ‘A’ bands retain the length 

• Calcium Release: Calcium ions are released into the sarcoplasm.
• Troponin Binding: Calcium binds to troponin on actin filaments, exposing the active sites for myosin.
• Cross Bridge Formation: Myosin heads bind to the exposed active sites on actin, forming cross bridges.
• Filament Sliding: Utilizing energy from ATP hydrolysis, myosin heads pull actin filaments towards the center of the 'A' band, leading to the contraction of the sarcomere.
• Sarcomere Shortening: The 'I' bands shorten, while the 'A' bands retain their length, resulting in muscle contraction.
   

Line in NCERT: "It is clear from the above steps, that during shortening of the muscle, i.e., contraction, the 'I' bands get reduced, whereas the ‘A' bands retain the length."