Info

Figure

{a) The thoracic cage includes the thoracic vertebrae, the sternum, the ribs, and the costal cartilages that attach the ribs to the sternum. {b) Radiograph of the thoracic cage, anterior view. The light region behind the sternum and above the diaphragm is the heart.

is a flat, elongated bone that develops in three parts—an upper manubrium (mah-nu'bre-um), a middle body, and a lower xiphoid (zif'oid) process that projects downward (see fig. 7.40).

The sides of the manubrium and the body are notched where they articulate with costal cartilages. The manubrium also articulates with the clavicles by facets on its superior border. It usually remains as a separate bone until middle age or later, when it fuses to the body of the sternum.

The manubrium and body of the sternum lie in different planes so that the line of union between them projects slightly forward. This projection, which occurs at the level of the second costal cartilage, is called the sternal angle {angle of Louis). It is commonly used as a clinical landmark to locate a particular rib accurately {see fig. 7.40).

Head

Neck

Head

Anterior end

Costal groove (a)

Spinous process Facet

Tubercle

Costal groove (a)

Figure 7.41

Figure 7.41

(a) A typical rib (posterior view). (b) Articulations of a rib with a thoracic vertebra (superior view).

The xiphoid process begins as a piece of cartilage. It slowly ossifies, and by middle age, it usually fuses to the body of the sternum also.

Red marrow within the spongy bone of the sternum produces blood cells into adulthood. Since the sternum has a thin covering of compact bone and is easy to reach, samples of its marrow may be removed to diagnose diseases. This procedure, a sternal puncture, suctions (aspirates) some marrow through a hollow needle. (Marrow may also be removed from the iliac crest of a coxal bone.)

Which bones comprise the thoracic cage? Describe a typical rib.

What are the differences among true, false, and floating ribs?

Pectoral Girdle

The pectoral (pek'to-ral) girdle (shoulder girdle) is composed of four parts—two clavicles (collarbones) and two scapulae (shoulder blades). Although the word girdle suggests a ring-shaped structure, the pectoral girdle is an incomplete ring. It is open in the back between the scapulae, and the sternum separates its bones in front. The pectoral girdle supports the upper limbs and is an attachment for several muscles that move them (fig. 7.42).

Clavicles

The clavicles are slender, rodlike bones with elongated S-shapes (fig. 7.42). Located at the base of the neck, they run horizontally between the sternum and the shoulders. The medial (or sternal) ends of the clavicles articulate with the manubrium, and the lateral (or acromial) ends join processes of the scapulae.

The clavicles brace the freely movable scapulae, helping to hold the shoulders in place. They also provide attachments for muscles of the upper limbs, chest, and back. Because of its elongated double curve, the clavicle is structurally weak. If compressed lengthwise due to abnormal pressure on the shoulder, it is likely to fracture.

Scapulae

The scapulae are broad, somewhat triangular bones located on either side of the upper back. They have flat bodies with concave anterior surfaces. The posterior surface of each scapula is divided into unequal portions by a spine. Above the spine is the supraspinous fossa, and below the spine is the infraspinous fossa. This spine leads to a head, which bears two processes—an acromion (ah-kro'me-on) process that forms the tip of the shoulder and a coracoid (kor'ah-koid) process that curves anteriorly and inferiorly to the clavicle (fig. 7.43). The acromion process articulates with the clavicle and provides attachments for muscles of the upper limb and chest. The coracoid process also provides attachments for upper limb and chest muscles. On the head of the scapula between the processes is a depression called the glenoid cavity (glenoid fossa of the scapula). It articulates with the head of the arm bone (humerus).

The scapula has three borders. The superior border is on the superior edge. The axillary, or lateral border, is directed toward the upper limb. The vertebral, or medial border, is closest to the vertebral column, about 5 cm away.

The Shoulder Complex Worksheet

Upper Limb

The bones of the upper limb form the framework of the arm, forearm, and hand. They also provide attachments for muscles, and they function as levers that move limb parts. These bones include a humerus, a radius, an ulna, carpals, metacarpals, and phalanges (fig. 7.44).

Humerus

The humerus (fig. 7.45) is a long bone that extends from the scapula to the elbow. At its upper end is a smooth, rounded head that fits into the glenoid cavity of the scapula. Just below the head are two processes—a greater tubercle on the lateral side and a lesser tubercle on the anterior side. These tubercles provide attachments for muscles that move the upper limb at the shoulder. Between them is a narrow furrow, the intertubercular groove, through which a tendon passes from a muscle in the arm (biceps brachii) to the shoulder.

The narrow depression along the lower margin of the head that separates it from the tubercles is called the anatomical neck. Just below the head and the tubercles of the humerus is a tapering region called the surgical

U Which bones form the pectoral girdle?

What is the function of the pectoral girdle?

In the epic poem the Iliad, Homer describes a man whose "shoulders were bent and met over his chest." The man probably had a rare inherited condition, called cleidocranial dysplasia, in which certain bones do not grow. The skull consists of small fragments joined by connective tissue, rather than large, interlocking hard bony plates. The scapulae are stunted or missing.

Cleidocranial dysplasia was first reported in a child in the huge Arnold family, founded by a Chinese immigrant to South Africa. The child had been kicked by a horse, and X rays revealed that the fontanels atop the head had never closed. The condition became known as "Arnold head." In 1997, researchers traced the condition to a malfunctioning gene that normally instructs certain cells to specialize as bone. Mice missing both copies of this gene develop a skeleton that is completely cartilage — bone never replaces the original cartilage model.

Superior border

Scapular notch

Supraspinous fossa

Infraspinous fossa

Medial (vertebral) border

Superior border

Scapular notch

Supraspinous fossa

Infraspinous fossa

Medial (vertebral) border

Lateral (axillary) border

Scapula Articulates With

(a) Posterior surface of the right scapula. (b) Lateral view showing the glenoid cavity that articulates with the head of the humerus. (c) Anterior surface.

Lateral (axillary) border ure 7.43

Figure

(a) Posterior surface of the right scapula. (b) Lateral view showing the glenoid cavity that articulates with the head of the humerus. (c) Anterior surface.

neck, so named because fractures commonly occur there. Near the middle of the bony shaft on the lateral side is a rough V-shaped area called the deltoid tuberosity. It provides an attachment for the muscle (deltoid) that raises the upper limb horizontally to the side.

At the lower end of the humerus are two smooth condyles—a knoblike capitulum (kah-pit'u-lum) on the lateral side and a pulley-shaped trochlea (trok'le-ah) on the medial side. The capitulum articulates with the radius at the elbow, whereas the trochlea joins the ulna.

Above the condyles on either side are epicondyles, which provide attachments for muscles and ligaments of the elbow. Between the epicondyles anteriorly is a depression, the coronoid (kor'o-noid) fossa, that receives a process of the ulna (coronoid process) when the elbow bends. An other depression on the posterior surface, the olecranon (o"lek'ra-non) fossa, receives an olecranon process when the upper limb straightens at the elbow.

Many a thirtyish parent of a young little leaguer or softball player becomes tempted to join in. But if he or she has not pitched in many years, sudden activity may break the forearm. Forearm pain while pitching is a signal that a fracture could happen. Medical specialists advise returning to the pitching mound gradually. Start with twenty pitches, five days a week, for two to three months before regular games begin. By the season's start, 120 pitches per daily practice session should be painless.

Humerus

Olecranon process

Ulna

Radius

Ulna

Carpals Metacarpals

Phalanges

Radius

Blood Vessels Breaking Forearms
Humerus

Olecranon process

Ulna

Elbow Anatomy

Head of radius Neck of radius

Head of radius Neck of radius

Blood Vessels Breaking Forearms

Figure

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment