The human shoulder is a ball-and-socket joint. true or false

Figure 1: The bones of the shoulder The clavicle is the bone closest to the axial skeleton and is commonly referred to as the “collar bone.” The clavicle articulates anteriorly with the sternum and posteriorly with the scapula, the most posterior bone of the shoulder. The scapula is almost triangular in shape. It is a flat bone that lies over the ribs of the upper back, just lateral to the vertebral column (one scapula on each side of the vertebral column). The humerus is the long bone of the upper arm. The articulation of the humerus with the scapula is critical for arm movement, and as such, the scapula must be considered an important part in any analysis of arm movement. Clavicle – When viewed from the front, the clavicle has a somewhat flat appearance, but it forms a very shallow and long S-shape when viewed from above. The clavicle acts like a strut (structural support resisting a load along its length) to support the upper extremities. It also serves to protect the underlying subclavian neurovascular bundle. The complete length of the clavicle is easily palpated. The muscles that attach to it do not obscure its superior and anterior surface in the front of the neck. If you look at the little dip in the line of bones across the front of the shoulders, just below the neck, the bump lateral to the suprasternal notch (the medial dip you see) is the medial end of the clavicle. You can walk your fingers laterally along the length of the superior surface of the clavicle unt...

Ball-and-socket joints are a special class of synovial joints that enjoy the highest freedom of motion in the body thanks to their unique structure. The shoulder and hip joints are the only ball-and-socket joints in the human body due to the need for great motion at the end of the body’s limbs and the vast amount of musculature needed to move and support such flexible joints. Two main components make up a ball-and-socket joint: a bone with a spherical head and a bone with a cup-like socket. In the shoulder joint, the spherical head of the humerus (upper arm bone) fits into the glenoid cavity of the scapula (shoulder blade). The glenoid cavity is a small and shallow cavity that permits the shoulder joint the greatest range of motion in the human body. A hyaline cartilage ring called the labrum surrounds the glenoid cavity to provide a flexible reinforcement to the joint, while muscles of the rotator cuff hold the humerus in place within the cavity. The hip joint is somewhat less mobile than the shoulder, but is an overall stronger and more stable joint. The added stability of the hip joint is necessary to bear the weight of the body resting on the legs while performing actions such as standing, walking, and running. In the hip joint the rounded, almost spherical head of the femur (thigh bone) fits tightly into the acetabulum, a deep socket in the os coxa (hip bone). Many tough ligaments and the powerful hip muscles hold the head of the femur in place and resist some of the ...

Overview What is the rotator cuff? Your shoulder is a ball-and-socket joint. The “ball” is the head of the humerus (upper arm bone). It fits into the “socket” of your shoulder blade. The rotator cuff consists of Parts of the Rotator Cuff What are the parts of the rotator cuff? The rotator cuff contains four muscles: • Supraspinatus controls internal rotation and lifting of the arm. • Infraspinatus allows you to externally rotate your arm in the shoulder socket. • Teres minor is a small muscle that helps rotate your arm. • Subscapularis controls arm abduction (holding your arm out straight, away from your body). The muscles start at the shoulder blade. Tendons (strong bands of tissue) attach the muscles to bones. The tendons wrap around the head of the upper arm bone, forming a cuff that keeps your arm in the shoulder socket. Which muscle is not part of the rotator cuff? The teres major muscle is not part of the rotator cuff, although it is frequently confused with other muscles in the rotator cuff. The teres major performs similar functions to some of the rotator cuff muscles. Its job is to help with internal rotation of your arm inside the shoulder socket. Injuries to the teres major muscle are much less common than injuries to the rotator cuff muscles. Frequently Asked Questions Common Conditions & Disorders What causes problems with the rotator cuff? Age, What are common rotator cuff injuries? Rotator cuff injuries are very common. The two most frequent injuries are: • ...

Shoulder dislocations occur more often than dislocations in any other major joint. The shoulder can dislocate forward, backward, or downward. In a typical case of a dislocated shoulder, a strong force that pulls the shoulder outward (abduction) or extreme rotation of the joint pops the ball of the humerus out of the shoulder socket. Dislocation commonly occurs when there is a backward pull on the arm.

Learning Objectives • Define the different types of body movements • Identify the joints that allow for these motions Synovial joints allow the body a tremendous range of movements. Each movement at a synovial joint results from the contraction or relaxation of the muscles that are attached to the bones on either side of the articulation. The type of movement that can be produced at a synovial joint is determined by its structural type. While the ball-and-socket joint gives the greatest range of movement at an individual joint, in other regions of the body, several joints may work together to produce a particular movement. Overall, each type of synovial joint is necessary to provide the body with its great flexibility and mobility. There are many types of movement that can occur at synovial joints (Table 1). Movement types are generally paired, with one being the opposite of the other. Body movements are always described in relation to the anatomical position of the body: upright stance, with upper limbs to the side of body and palms facing forward. Watch this video to learn about anatomical motions. What motions involve increasing or decreasing the angle of the foot at the ankle? Flexion and Extension Flexion and extension are movements that take place within the sagittal plane and involve anterior or posterior movements of the body or limbs. For the vertebral column, flexion (anterior flexion) is an anterior (forward) bending of the neck or body, while extension involves...

By the end of this section, you will be able to • Describe the bones that articulate together to form selected synovial joints • Discuss the movements available at each joint • Describe the structures that support and prevent excess movements at each joint Each synovial joint of the body is specialised to perform certain movements. The movements that are allowed are determined by the structural classification for each joint. For example, a multiaxial ball-and-socket joint has much more mobility than a uniaxial hinge joint. However, the ligaments and muscles that support a joint may place restrictions on the total range of motion available. Thus, the ball-and-socket joint of the shoulder has little in the way of ligament support, which gives the shoulder an exceptionally large range of motion. In contrast, movements at the hip joint are restricted by strong ligaments, which reduce its range of motion but confer stability during standing and weight bearing. This section will examine the anatomy of selected synovial joints of the body. Anatomical names for most joints are derived from the names of the bones that articulate at that joint, although some joints, such as the elbow, hip, and knee joints are exceptions to this general naming scheme. Articulations of the Vertebral Column In addition to being held together by the intervertebral discs, adjacent vertebrae also articulate with each other at synovial joints formed between the superior and inferior articular processes cal...