All questions of Locomotion and Movement for NEET Exam

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

Mechanism of muscle contraction is best explained by the sliding filament theory, which states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments. The actin filament slide over myosin filament thus reduces the length of the sarcomere and contracts the muscle fibre.

So, the correct answer is option C.

Appendicular skeleton includes

The appendicular skeleton includes the bones of the limbs and their associated girdles. It is one of the two main divisions of the human skeleton, with the other being the axial skeleton. The appendicular skeleton provides support and enables movement of the limbs.

1. Girdles
The appendicular skeleton includes two girdles: the pectoral girdle and the pelvic girdle.

- Pectoral Girdle: The pectoral girdle, also known as the shoulder girdle, consists of the clavicle (collarbone) and the scapula (shoulder blade). It connects the upper limbs to the axial skeleton, allowing for the movement of the arms and shoulders.

- Pelvic Girdle: The pelvic girdle, also known as the hip girdle, consists of two hip bones, also called coxal bones or innominate bones. The pelvic girdle connects the lower limbs to the axial skeleton and supports the weight of the body.

2. Limbs
The appendicular skeleton also includes the bones of the limbs, including the upper limbs (arms) and the lower limbs (legs).

- Upper Limbs: The upper limbs consist of the humerus (upper arm bone), radius and ulna (forearm bones), carpals (wrist bones), metacarpals (hand bones), and phalanges (finger bones). These bones provide support and allow for various movements of the arms, hands, and fingers.

- Lower Limbs: The lower limbs consist of the femur (thigh bone), tibia and fibula (leg bones), tarsals (ankle bones), metatarsals (foot bones), and phalanges (toe bones). These bones provide support and enable movements such as walking, running, and jumping.

3. Function
The appendicular skeleton plays a crucial role in maintaining posture, supporting the body's weight, and facilitating movement. The girdles connect the limbs to the axial skeleton and provide a stable base for the movement of the arms and legs. The bones of the limbs allow for various movements and actions, such as reaching, grasping, walking, running, and performing fine motor skills.

4. Conclusion
In conclusion, the appendicular skeleton includes the girdles and the bones of the limbs. It provides support, stability, and enables movement of the limbs, allowing for a wide range of activities and functions.

Understanding Actin Filaments
Actin filaments are crucial components of the cytoskeleton in eukaryotic cells, playing vital roles in muscle contraction, cell shape, and motility. Let's analyze the statements regarding their structure and function.
Statement Analysis
- i. Each actin filament is composed of two helically wound F (filamentous) actins.
This statement is correct. Actin filaments, or F-actin, are formed by the polymerization of G-actin monomers into long, helical structures.
- ii. G (Globular) actins are monomers that polymerize to form F actins.
This statement is also correct. G-actin monomers assemble to create F-actin, highlighting the dynamic nature of actin filaments.
- iii. Tropomyosin runs parallel to the F actins and does not interact with them.
This statement is incorrect. Tropomyosin binds to F-actin and stabilizes it, playing a significant role in muscle contraction and regulation of myosin binding sites.
- iv. Troponin is attached to tropomyosin at regular intervals and regulates the binding sites for myosin on the actin filaments.
This statement is correct. Troponin interacts with tropomyosin and, in the presence of calcium ions, regulates the exposure of binding sites for myosin, which is essential for muscle contraction.
Conclusion
Given the analysis, the correct statements are ii and iv. Therefore, the correct answer is option 'C' (i, ii, and iv). Understanding these components is crucial for comprehending the mechanisms of muscle contraction and cellular movement.

Understanding Muscle Fiber Classification
Muscle fibers are primarily classified based on their biochemical properties, particularly the presence of myoglobin. This classification is crucial in understanding muscle function and performance.
Assertion (A) Explained
- Muscle fibers are indeed classified as red and white fibers.
- The classification is based on the amount of myoglobin present in them.
Reason (R) Explained
- Red fibers, also known as slow-twitch fibers, contain a higher amount of myoglobin.
- This increased myoglobin allows red fibers to store more oxygen, which is essential for aerobic metabolism.
- Aerobic metabolism is important for endurance activities, as it provides energy over extended durations.
Correctness of Assertion and Reason
- Both Assertion (A) and Reason (R) are true.
- However, while Reason (R) provides a valid explanation for the classification, it does not encompass all aspects of muscle fiber classification. Other factors like fiber type, contraction speed, and fatigue resistance also play roles in differentiating red and white fibers.
Conclusion
- Hence, while both statements are true, the reason does not fully explain the assertion since the classification of muscle fibers is based on multiple criteria.
- Therefore, the correct answer is option 'B': both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.

The correct answer for this question is option 'C' - glenoid cavity. Let's understand why the humerus articulates with the glenoid cavity.

Head of the Humerus:
The humerus is the long bone that forms the upper arm. It consists of a rounded upper end called the head, which is located proximally.

Articulation with the Glenoid Cavity:
The glenoid cavity is a shallow, concave socket located on the lateral side of the scapula. It forms the glenohumeral joint, commonly known as the shoulder joint. The head of the humerus articulates with the glenoid cavity to form this joint.

Explanation:
When the rounded head of the humerus articulates with the glenoid cavity, it allows for a wide range of movement in the shoulder joint. The shallow nature of the glenoid cavity provides stability to the joint while allowing for flexibility and mobility.

The articulation between the humerus and the glenoid cavity is a synovial joint, which means it is surrounded by a joint capsule filled with synovial fluid. This fluid lubricates the joint, reducing friction and allowing for smooth movement.

Importance of the Glenohumeral Joint:
The glenohumeral joint is one of the most mobile joints in the human body. It allows for movements such as flexion, extension, abduction, adduction, medial and lateral rotation, and circumduction of the arm. This joint plays a crucial role in activities that involve reaching, lifting, throwing, and other arm movements.

Conclusion:
In summary, the rounded upper end (head) of the humerus articulates with the glenoid cavity of the scapula to form the glenohumeral joint. This joint provides stability and allows for a wide range of movements in the shoulder.

The sequence begins when a motor neuron's signal generates an action potential in the muscle fiber. This event triggers the release of calcium ions from the sarcoplasmic reticulum. These calcium ions then activate actin, allowing it to bind to myosin heads, forming cross bridges. The formation of these cross bridges enables the actin filaments to slide over the myosin filaments, causing the muscle to contract. Once contraction is completed, calcium ions are reabsorbed into the sarcoplasmic reticulum, actin becomes inactivated, cross bridges are broken, and the muscle relaxes.

Lumbar vertebrae are found in the abdominal region.

Explanation:
The lumbar vertebrae are a set of five vertebrae located in the lower back region of the spinal column. They are the largest and strongest vertebrae in the spinal column and are responsible for supporting the weight of the upper body. The lumbar vertebrae are numbered L1 to L5, with L1 being the topmost lumbar vertebra and L5 being the bottommost.

Here is a detailed explanation of why the correct answer is option 'B' - abdominal region:

1. Structure of the lumbar vertebrae:
- The lumbar vertebrae are larger and thicker compared to the other vertebrae in the spinal column.
- They have a robust body and a wide, thick vertebral arch that protects the spinal cord.
- The spinous processes of the lumbar vertebrae are relatively short and project posteriorly.
- The transverse processes are strong and project laterally.

2. Location of the lumbar vertebrae:
- The lumbar vertebrae are situated between the thoracic vertebrae (in the thoracic region) and the sacral vertebrae (in the sacral region).
- They are located in the lower back region, just above the pelvis.
- The lumbar vertebrae are positioned below the thoracic vertebrae, which are in the thorax region.
- This makes option 'D' - thorax, incorrect.

3. Function of the lumbar vertebrae:
- The lumbar vertebrae provide support to the upper body and help maintain an upright posture.
- They play a crucial role in weight-bearing and are subjected to significant forces during activities such as lifting, bending, and twisting.
- The lumbar vertebrae also contribute to the flexibility and mobility of the lower back.

Based on the above points, it is clear that lumbar vertebrae are found in the abdominal region (option 'B'). They are located below the thoracic vertebrae and above the sacral vertebrae, playing a vital role in supporting the upper body and providing flexibility to the lower back.

The human vertebral column is divided into five regions with the following typical vertebrae counts:

Cervical: 7 vertebrae

Thoracic: 12 vertebrae

Lumbar: 5 vertebrae

Sacral: 1 segment formed by the fusion of 5 sacral vertebrae

Coccygeal: 1 segment formed by the fusion of 4 coccygeal vertebrae

Thus the correct sequence is 7, 12, 5, 1 (fused), 1 (fused), matching Option A.