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."

In the context of muscular contraction, a cross-bridge refers to the attachment of myosin with actin within the muscle cell.
All muscle types contract by cross-bridge cycling i.e. repeated attachment of actin and myosin within the cell.

Hence, a cross-bridge is formed during muscle contraction. 

Sliding Filament Theory of Contraction:
During muscle contraction, the thin actin filaments slide over the thick myosin filament. The actin filament slides over myosin filament thus reduces the length of the sarcomere and contracts the muscle fibre.
When Calcium is present the blocked active site of the actin clears.

A sarcomere is the basic contractile unit of muscle fiber.

Each sarcomere is composed of two main protein filaments, actin and myosin, which are the active structures responsible for muscular contraction.

• The Assertion (A) is false because myasthenia gravis does not primarily involve the degeneration of muscle fibers; rather, it is an autoimmune disorder affecting the communication at the neuromuscular junction.
• The Reason (R) is true as it correctly describes the mechanism of myasthenia gravis, which indeed leads to fatigue and weakness in skeletal muscles due to the disruption at the neuromuscular junction.
• Therefore, since the Assertion is false and the Reason is true, the correct answer is Option 4: If both Assertion and Reason are false.

Skeletal muscles are also known as voluntary muscles. They have striations and are also known as striated muscles. They are involved in changing of body posture but not in the movement of food through the oesophagus.

• Cardiac muscles are the muscles of the heart.
• Cardiac muscles are involuntary muscles that work continuously to pump blood throughout the body.
• They are branched and are striated in appearance.

Fascia is a layer of connective tissue that surrounds the fascicles or muscle bundles in a muscle. It is made out of collagen. Each muscle bundle contains a number of muscle fibres or muscle cells.

In all myosins, the head domain is a specialized ATP-ase that is able to couple the hydrolysis of ATP with motion. A critical feature of the myosin ATP-ase activity is that it is actin-activated. In the absence of actin, solutions of myosin slowly convert ATP into ADP and phosphate.

Each muscle cell or muscle fibre contains filaments in its sarcoplasm which are arranged in a parallel manner. These filaments are known as myofibrils and they have alternate dark and light bands.

Cardiac muscle is found only in the walls of the heart. When cardiac muscle contracts, the heartbeats and pumps blood.

• Cardiac muscle contains many contains a great many mitochondria, which produce ATP for energy. This helps the heart resist fatigue.
• Contractions of cardiac muscle are involuntary, like those of smooth muscle.
• Cardiac muscle, like skeletal muscle, is arranged in bundles, so it appears striated, or striped.

Hence, option D is correct.

- Statement i is correct because muscle contraction is initiated by a neural signal from the CNS through a motor neuron.

- Statement ii is correct as the neuromuscular junction is indeed where the motor neuron connects to the muscle fibre.

- Statement iii is incorrect because calcium ions do not bind to myosin; they bind to troponin, which then allows myosin to attach to actin.

- Statement iv is correct as troponin binds calcium, causing a conformational change that exposes the active sites on actin.

Thus, the correct statements are i, ii, and iv.

- Statement i is correct because the I-band is indeed composed of actin filaments, which are thinner than myosin filaments.

- Statement ii is incorrect; cardiac muscles are involuntary and are not directly controlled by the nervous system.

- Statement iii is correct as the sarcomere is defined as the segment between two Z-lines and is the functional unit of contraction.

- Statement iv is incorrect; myosin filaments are actually thicker than actin filaments.

Thus, the correct statements are i and iii, making Option A the correct answer.

- Statement i is correct: Each actin filament is indeed composed of two helically wound 'F' actins.

- Statement ii is also correct: 'G' (Globular) actins serve as monomers that polymerize to form filamentous 'F' actins.

- Statement iii is incorrect: Tropomyosin runs parallel to 'F' actins and interacts with them, playing a crucial role in muscle contraction by regulating access to the binding sites on actin for myosin.

- Statement iv is correct: Troponin is distributed at regular intervals along the tropomyosin and is essential for regulating the binding sites for myosin on actin filaments during muscle contraction.

Thus, the correct statements are i, ii and iv, making Option c the right answer.

- Statement i is correct. Myosin filaments are indeed composed of multiple monomeric proteins called Meromyosins.

- Statement ii is incorrect. The heavy meromyosin (HMM) refers specifically to the globular head and short arm, while the light meromyosin (LMM) refers to the tail.

- Statement iii is correct. The cross arm of the myosin filament does project outwards at a regular distance and angle.

- Statement iv is incorrect. The globular head of myosin is an active ATPase enzyme with binding sites for ATP and active sites for actin.

Thus, the correct statements are i and iii, making the correct answer Option A.

- Assertion (A) is true: Muscle fibers are indeed classified into red and white fibers based on myoglobin content.

- Reason (R) is also true: Red fibers do contain more myoglobin, which allows for better oxygen storage and supports aerobic metabolism.

- Since the reason provided accurately explains why muscle fibers are classified this way, the correct option is Option A.

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) and axial skeleton comprises 80 bones.

Topic in NCERT: Skeletal system

Line in NCERT: Axial skeleton comprises 80 bones distributed along the main axis of the body. The skull, vertebral column, sternum and ribs constitute axial skeleton. 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."