Problem 123 - Objective Biology for NEET

Question

Each of the pectoral girdle consists of (a) Clavicle (b) Scapula (c) Humerus (d) Both (a) and (b)

Step-by-Step Solution

Answer

The correct answer is: (d) Both (a) and (b).

Step 1: Understanding the Pectoral Girdle

The pectoral girdle, or shoulder girdle, consists of the bones that connect the upper limb to the axial skeleton on each side. In humans, it comprises two bones: the clavicle (or collarbone) and the scapula (or shoulder blade).

Step 2: Comparing with the Options

Examining the options given in the exercise, we can see that option (a) Clavicle and (b) Scapula are the two individual bones that comprise the pectoral girdle. Option (c) Humerus, however, is not a part of the pectoral girdle; it's the bone of the upper arm or forelimb.

Step 3: Selecting the Correct Answer

Therefore, considering our discussion of the pectoral girdle's components, the correct answer among the given options would be (d) Both (a) and (b). This option includes both the clavicle and the scapula, the two bones constituting the pectoral girdle, excluding the humerus which isn't a part of it.

Key Concepts

Clavicle

The clavicle, commonly known as the collarbone, is a slender, S-shaped bone found at the top of the chest. It acts as a key structural component of the pectoral girdle, providing attachment points for muscles and ligaments. This bone serves an essential role in connecting the upper limb to the trunk of the body. The clavicle is unique due to its horizontal placement across the top of the thorax, and it stabilizes the shoulder as the only bony connection to the axial skeleton.
Located between the sternum (breastbone) and the scapula, the clavicle helps to transfer physical stress from the upper limb to the central skeleton. It also aids in keeping the scapula in place so that the shoulder joint operates efficiently.

• The clavicle helps protect neurovascular structures that pass from the neck to the arm.
• It assists with the motion and flexibility of the shoulder.
• Fractures are common but usually heal well without surgical intervention.

The importance of the clavicle in terms of both function and protection makes it a vital part of the human skeleton.

Scapula

The scapula, or shoulder blade, is a flat, triangular bone located in the upper back. Situated behind the ribcage, the scapula plays a crucial role in shoulder movement and foundation. It constitutes a major part of the pectoral girdle, connecting with both the clavicle and the humerus.
This bone features several important structural elements that allow for a wide range of shoulder movements, contributing to arm mobility and strength.

• The acromion process, which extends from the scapula, connects with the clavicle.
• The glenoid cavity forms the socket of the shoulder joint, enabling arm rotation.
• The scapular spine, a prominent ridge, serves as an attachment for various shoulder muscles.

Its configuration not only supports shoulder articulation but also stabilizes it during numerous activities. The shoulder blade's adaptability and strength are central to the full function of the upper limb.

Humerus

The humerus is the long bone in the upper arm, spanning from the shoulder to the elbow. While it is not part of the pectoral girdle, it connects closely to its components to facilitate movement and support. Its head fits into the scapula's glenoid cavity to form the shoulder joint, allowing for a broad range of arm motions.
The lower end of the humerus connects to the bones of the forearm, forming the elbow joint. As a vital component of arm mobility, the humerus serves several pivotal roles:

• Facilitates the flexion, extension, and rotation of the arm.
• Supports muscle attachment sites essential for arm movement and propulsion.
• Houses the brachial artery and other crucial nerves responsible for arm sensation and motor control.

Understanding the humerus's anatomy and function is essential for comprehending how the upper limb operates harmoniously with the pectoral girdle.