All questions of Locomotion and Movement for NEET Exam

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Introduction:
The pivot joint between the atlas and axis is a crucial joint in the vertebral column that allows for rotation of the head. This joint is classified as a synovial joint.

Synovial Joints:
Synovial joints are the most common type of joint in the body and are characterized by the presence of a synovial cavity. These joints are highly mobile and allow for various types of movements, such as flexion, extension, rotation, abduction, and adduction. Examples of synovial joints include the knee, shoulder, hip, and elbow joints.

Pivot Joint:
A pivot joint is a type of synovial joint that allows for rotation around a central axis. It consists of a rounded or pointed surface of one bone that fits into a ring or notch of another bone. The joint between the atlas (C1) and axis (C2) is a specific example of a pivot joint.

Atlas and Axis:
The atlas (C1) and axis (C2) are the first two vertebrae in the vertebral column. The atlas is responsible for supporting the weight of the head and allowing for nodding movements. The axis, on the other hand, has a unique feature called the dens or odontoid process, which acts as a pivot for rotation of the atlas and head.

Anatomical Structure:
In the pivot joint between the atlas and axis, the rounded surface of the dens fits into the ring formed by the anterior arch of the atlas. This arrangement allows for the rotation of the head, as the atlas rotates around the dens. The joint is supported by ligaments and surrounded by a synovial capsule that contains synovial fluid, which lubricates and nourishes the joint.

Function:
The pivot joint between the atlas and axis is responsible for the rotatory movements of the head. This joint allows for the shaking of the head to indicate "no" and the rotation of the head to look over the shoulder.

Conclusion:
In conclusion, the pivot joint between the atlas and axis is a synovial joint that allows for rotation of the head. This joint is crucial for various movements of the head and neck and is supported by ligaments and synovial fluid.

The joint found between the sternum and the ribs in humans is a cartilaginous joint. This type of joint is also known as a synchondrosis. It is formed by the articulation between the costal cartilages of the ribs and the sternum, specifically the first seven pairs of ribs.

Cartilaginous joints are classified into two types: synchondroses and symphyses. Synchondroses are joints where the bones are joined by hyaline cartilage, while symphyses are joints where the bones are joined by fibrocartilage.

In the case of the joint between the sternum and the ribs, it is a synchondrosis because the bones are connected by hyaline cartilage. The costal cartilages of the ribs attach to the sternum through this type of joint, allowing for some flexibility and movement.

The sternum, or breastbone, is a flat bone located in the center of the chest. It consists of three parts: the manubrium, the body, and the xiphoid process. The ribs, on the other hand, are long curved bones that form the ribcage, protecting the organs in the thoracic cavity.

The cartilaginous joint between the sternum and the ribs provides stability to the ribcage while allowing for some movement. This movement is important for activities such as breathing, as the ribcage needs to expand and contract to facilitate the inhalation and exhalation of air.

Cartilaginous joints, including the joint between the sternum and the ribs, have limited mobility compared to other types of joints such as synovial joints. This is because the cartilage connecting the bones restricts their movement to some extent. However, the flexibility provided by these joints is essential for proper functioning of the body.

In conclusion, the joint found between the sternum and the ribs in humans is a cartilaginous joint. Specifically, it is a synchondrosis formed by the articulation between the costal cartilages of the ribs and the sternum. This joint allows for some movement and flexibility, contributing to the overall function and stability of the ribcage.

Understanding Sarcomere
The sarcomere is the fundamental contractile unit of striated muscle tissue, playing a critical role in muscle contraction.
Structure of Sarcomere
- Z-lines: The sarcomere is defined as the segment between two Z-lines. These lines are crucial as they anchor the thin filaments (actin) and delineate the boundaries of each sarcomere.
- A-band: This region contains the thick filaments (myosin) and overlaps with the thin filaments. It appears dark under a microscope due to the density of these proteins.
- I-band: This section contains only thin filaments and is lighter in appearance. The I-band spans across two adjacent sarcomeres and extends from the Z-line to the start of the A-band.
Why Option D is Correct
- Definition: The sarcomere is specifically the area between two Z-lines. This demarcation is essential for understanding how muscle fibers contract and how they are organized.
- Functionality: During muscle contraction, the sarcomeres shorten, pulling the Z-lines closer together, which leads to the overall shortening of the muscle fiber.
- Importance in Physiology: The arrangement of sarcomeres aligns perfectly for coordinated muscle action, enabling efficient movement and strength.
Conclusion
The correct answer is option 'D' because the sarcomere is distinctly defined by the space between two Z-lines, making it the essential unit of muscle contraction. Understanding this structure is vital for students in fields related to biology and medicine, particularly in contexts like the NEET examination.

Understanding Osteoporosis
Osteoporosis is a progressive skeletal disorder characterized by decreased bone density and increased fragility, leading to a higher risk of fractures. It is particularly common in older adults, especially postmenopausal women.
Role of Estrogen
- Estrogen is a key hormone that helps maintain bone density.
- It inhibits the activity of osteoclasts, the cells responsible for bone resorption.
- A decrease in estrogen levels, especially during menopause, leads to increased bone resorption and decreased bone formation.
Why Option C is Correct
- The correct answer is option 'C', which states that osteoporosis may occur due to decreased levels of estrogen.
- This hormonal change accelerates bone loss, making bones weaker and more susceptible to fractures.
Other Options Explained
- Option A: Immune disorder affecting the neuromuscular junction leading to fatigue does not directly relate to bone density issues.
- Option B: High concentrations of Ca++ and Na+ can affect various physiological processes but are not directly responsible for osteoporosis.
- Option D: Accumulation of uric acid leading to joint inflammation is associated with gout, not osteoporosis.
Conclusion
Understanding the hormonal influences on bone health is critical for preventing and managing osteoporosis. The decline in estrogen levels is a primary risk factor, making awareness and timely intervention essential, especially for postmenopausal women.

The correct answer is option 'B' which states that the total number of bones in the hind limb of a man is 30.

The hind limb, also known as the lower limb, is the lower appendage of the human body that extends from the hip to the foot. It consists of several bones that work together to provide support, stability, and movement.

The bones in the hind limb can be divided into three main regions: the pelvic girdle, the thigh, and the leg/foot. Let's discuss each region and the bones present in them:

1. Pelvic Girdle:
- The pelvic girdle consists of two hip bones, also known as the coxal bones or innominate bones.
- Each hip bone is made up of three fused bones: the ilium, ischium, and pubis.
- Therefore, the pelvic girdle has a total of 2 bones.

2. Thigh:
- The thigh bone is called the femur, which is the longest and strongest bone in the human body.
- Therefore, the thigh has a total of 1 bone.

3. Leg/Foot:
- The leg consists of two bones: the tibia and fibula.
- The tibia is the larger and stronger bone, located on the medial side of the leg. It bears most of the body's weight.
- The fibula is the smaller bone, located on the lateral side of the leg. It provides support and muscle attachment.
- Therefore, the leg has a total of 2 bones.

- The foot consists of several bones, including the tarsals, metatarsals, and phalanges.
- There are 7 tarsal bones in the foot: talus, calcaneus, navicular, cuboid, and the three cuneiform bones.
- There are 5 metatarsal bones in the foot, which are located in the midfoot region.
- There are 14 phalanges in the foot, divided into proximal, middle, and distal phalanges.
- Therefore, the foot has a total of 26 bones (7 tarsals + 5 metatarsals + 14 phalanges).

Adding up the bones from each region:
Pelvic Girdle: 2 bones
Thigh: 1 bone
Leg: 2 bones
Foot: 26 bones

Total number of bones in the hind limb = 2 + 1 + 2 + 26 = 31

Therefore, the correct answer is not option 'B' but seems to be option 'D' which states that the total number of bones in the hind limb of a man is 21.