Chapter VI - Human_Anatomy

Shoulder Girdle

The human upper arm, the shoulder joint is composed of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone). Two joints facilitate shoulder movement. The acromioclavicular (AC) joint is located between the acromion (part of the scapula that forms the highest point of the shoulder) and the clavicle. The glenohumeral joint, to which the generic term "shoulder joint" usually refers, is a ball-and-socket joint that allows the arm to rotate in a circular fashion or to hinge out and up away from the body. (The "ball" is the top, rounded portion of the upper arm bone or humerus; the "socket," or glenoid, is a dish-shaped part of the outer edge of the scapula into which the ball fits.) Arm movement is further facilitated by the ability of the scapula to slide both laterally and vertically along the rib cage. The capsule is a soft tissue envelope that encircles the glenohumeral joint. It is lined by a thin, smooth synovial membrane.

The bones of the shoulder are held in place by muscles, tendons, and ligaments. Tendons are tough cords of tissue that attach the shoulder muscles to bone and assist the muscles in moving the shoulder. Ligaments attach shoulder bones to each other, providing stability. For example, the front of the joint capsule is anchored by three glenohumeral ligaments.

The rotator cuff is a structure composed of tendons that, with associated muscles, holds the ball at the top of the humerus in the glenoid socket and provides mobility and strength to the shoulder joint.

Two filmy sac-like structures called bursae permit smooth gliding between bone, muscle, and tendon. They cushion and protect the rotator cuff from the bony arch of the acromion.

RIBCAGE
The human rib cage. In anatomy, ribs (Latin costae) are the long curved bones, which form the rib cage. Ribs surround the chest (Latin thorax) of land vertebrates, and protect the lungs, heart, and other internal organs of the thoracic cavity.

Types of Ribs
The human skeleton has 24 ribs, 12 on each side. (A small proportion may have one pair more or fewer.) They are attached behind the vertebral column. The first seven pairs are connected to the sternum in front and are known as true ribs (costae verae, I-VII). The eighth, ninth, and tenth are attached in front to the cartilaginous portion of the next rib above and are known as false ribs (costae spuriae, VIII-X). The lower two, that is the eleventh and twelfth, are not attached in front and are called floating ribs (costae fluitantes, XI-XII). The spaces between the ribs are known as intercostal spaces; they contain the intercostal muscles, nerves, and arteries. The rib cage allows for breathing due to its elasticity. In some humans, the rib remnant of the 7th neck vertebra on one or both sides is replaced by a free extra rib called a cervical rib, which can cause trouble for the nerves going to the arm.

Rib Anatomy

Typical ribs
The third through ninth ribs are "typical ribs" since they share the same structure. They each have a head that has two facets separated by a crest. One head articulates with the rib's corresponding vertebra and one head articulates with the vertebra superior (above) to it. They have a neck that connects the head with the shaft. The neck meets the shaft at a tubercle. The shaft is thin, flat, and curved. The curve is most prominent at the costal angle. The concave (inside) surface has a groove to protect the intercostal nerve and vessels.

Atypical ribs
The atypical ribs are the 1st, 2nd, and 10th to 12th.

The first rib has a shaft that is wide and nearly horizontal, and has the sharpest curve of the seven true ribs. Its head has a single facet to articulate with the first thoracic vertebra (T1). It also has two grooves for the subclavian vessels, which are separated by the scalene tubercle.

The second rib is thinner, less curved, and longer than the first rib. It has two facets to articulate with T2 and T1, and a tubercle for muscles to attach to.
The 10th to 12th ribs have only one facet on their head, and the 11th and 12th ribs are short with no necks or tubercles.

Rib Fractures and Associated Injuries
The first rib is rarely fractured because of its protected position behind the clavicle (collarbone). However, if it is broken serious damage can occur to the brachial plexus of nerves and the subclavian vessels.

The middle ribs are the ones most commonly fractured. Fractures usually occur from direct blows or from indirect crushing injuries. The weakest part of a rib is just anterior to its angle, but a fracture can occur anywhere.

A lower rib fracture has the complication of potentially injuring the diaphragm, which could result in a diaphragmatic hernia.

Rib fractures are painful because the ribs have to move for inspiration and expiration of air. Rib pain may also be associated with metastasis of cancer, especially from the breast or prostate.

Bifid rib, bifurcated rib
A Bifid rib or bifurcated rib is a congenital abnormality occurring in about 1% of the population. The sternal end of the rib is cleaved into two. It is usually unilateral. Effects of this neuroskeletal anomaly can include respiratory difficulties, neurological difficulties, limitations, and limited energy from the stress of needing to compensate for the neurophysiological difficulties.

Vertebral column

The vertebral column (backbone or spine) is a column of vertebrae situated in the dorsal aspect of the abdomen. It houses the spinal cord in its spinal canal.

Curves
Viewed laterally the vertebral column presents several curves, which correspond to the different regions of the column, and are called cervical, thoracic, lumbar, and pelvic.

Cervical curve: The cervical curve, convex forward, begins at the apex of the odontoid (tooth-like) process, and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves.

Thoracic curve: The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra.

Lumbar curve: The lumbar curve is more marked in the female than in the male; it begins at the middle of the last thoracic vertebra, and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two.

Pelvic curve: The pelvic curve begins at the sacrovertebral articulation, and ends at the point of the coccyx; its concavity is directed downward and forward. The thoracic and pelvic curves are termed primary curves, because they alone are present during fetal life. In the early embryo, the vertebral column is C-shaped, and the cervical and lumbar curvatures are not yet present in a newborn infant.

The cervical and lumbar curves are compensatory or secondary, and are developed after birth, the former when the child is able to hold up its head (at three or four months), and to sit upright (at nine months), the latter at twelve or eighteen months, when the child begins to walk.

The vertebral column also has a slight lateral curvature, the convexity of which is directed toward the right side. This may be produced by muscular action, most persons using the right arm in preference to the left, especially in making long-continued efforts, when the body is curved to the right side. In support of this explanation it has been found that in one or two individuals who were left-handed, the convexity was to the left side. This curvature is regarded by others as being produced by the aortic arch and upper part of the descending thoracic aorta – a view which is supported by the fact that in cases where the viscera are transposed and the aorta is on the right side, the convexity of the curve is directed to the left side.


Surfaces

Anterior surface
When viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebrae; below this there is again a gradual and progressive increase in width as low as the sacrovertebral angle. From this point there is a rapid diminution, to the apex of the coccyx.

Posterior surface
The posterior surface of the vertebral column presents in the median line the spinous processes. In the cervical region (with the exception of the second and seventh vertebrae) these are short and horizontal, with bifid extremities. In the upper part of the thoracic region they are directed obliquely downward; in the middle they are almost vertical, and in the lower part they are nearly horizontal. In the lumbar region they are nearly horizontal. The spinous processes are separated by considerable intervals in the lumbar region, by narrower intervals in the neck, and are closely approximated in the middle of the thoracic region. Occasionally one of these processes deviates a little from the median line — a fact to be remembered in practice, as irregularities of this sort are attendant also on fractures or displacements of the vertebral column. On either side of the spinous processes is the vertebral groove formed by the laminae in the cervical and lumbar regions, where it is shallow, and by the laminae and transverse processes in the thoracic region, where it is deep and broad; these grooves lodge the deep muscles of the back. Lateral to the vertebral grooves are the articular processes, and still more laterally the transverse processes. In the thoracic region, the transverse processes stand backward, on a plane considerably behind that of the same processes in the cervical and lumbar regions. In the cervical region, the transverse processes are placed in front of the articular processes, lateral to the pedicles and between the intervertebral foramina. In the thoracic region they are posterior to the pedicles, intervertebral foramina, and articular processes. In the lumbar region they are in front of the articular processes, but behind the intervertebral foramina.

Lateral surfaces
The lateral surfaces are separated from the posterior surface by the articular processes in the cervical and lumbar regions, and by the transverse processes in the thoracic region. They present, in front, the sides of the bodies of the vertebrae, marked in the thoracic region by the facets for articulation with the heads of the ribs. More posteriorly are the intervertebral foramina, formed by the juxtaposition of the vertebral notches, oval in shape, smallest in the cervical and upper part of the thoracic regions, and gradually increasing in size to the last lumbar. They transmit the spinal nerves and are situated between the transverse processes in the cervical region, and in front of them in the thoracic and lumbar regions.


Vertebral canal
The vertebral canal follows the different curves of the column; it is large and triangular in those parts of the column which enjoy the greatest freedom of movement, such as the cervical and lumbar regions; and is small and rounded in the thoracic region, where motion is more limited.

Abnormalities
Occasionally the coalescence of the laminae is not completed, and consequently a cleft is left in the arches of the vertebrae, through which a protrusion of the spinal membranes (dura mater and arachnoid), and generally of the spinal cord (medulla spinalis) itself, takes place, constituting the malformation known as spina bifida. This condition is most common in the lumbosacral region, but it may occur in the thoracic or cervical region, or the arches throughout the whole length of the canal may remain incomplete.

The following abnormal curvatures may occur in some people:

Kyphosis is an exaggerated posterior curvature in the thoracic region. This produces the so-called "humpback".

Lordosis is an exaggerated anterior curvature of the lumbar region, "swayback". Temporary lordosis is common among pregnant women.

Scoliosis, lateral curvature, is the most common abnormal curvature, occurring in 0.5% of the population. It is more common among females and may result from unequal growth of the two sides of one or more vertebrae.

Arm
In anatomy, the arm is the upper limb of a bipedal mammal, specifically the segment between the shoulder and the elbow. Arm can also refer to any analogous structure, such as one of the paired forelimbs of a quadruped, or any muscular hydrostat similar to a tentacle, as seen on some cephalopods, such as octopuses.

The term arm also refers to the entire upper limb in an organism. Anatomically, the segment between the elbow and wrist is properly called the forearm.

In primates the arms are richly adapted for both climbing and for more skilled, manipulative tasks. The ball and socket shoulder joint allows for movement of the arms in a wide circular plane, while the presence of two forearm bones which can rotate around each other allows for additional range of motion at this level.

Anatomy of the human arm
The human arm contains bones, joints, muscles, nerves and blood vessels. Many of these muscles are used for everyday tasks. There are clinical uses for the arm, including venepuncture and peripheral venous cannulation in the cubital fossa.

Bony structure and joints
The humerus is the (upper) arm bone. It articulates with the scapula above at the glenohumeral joint (shoulder) and with the ulna and radius below as the elbow joint.

Shoulder joint
The shoulder is the ball-and-socket joint between the proximal end of the humerus and the clavicle and scapula.

Elbow joint
The elbow joint is the hinge joint between the distal end of the humerus and the proximal ends of the radius and ulna.

Osteofascial compartments
The arm is divided by a fascial layer (known as lateral and medical intermuscular septa) separating the muscles into an anterior and posterior osteofascial compartments. The fascia merges with the periosteum (outer bone layer) of the humerus. The compartments contain muscles which are innervated by the same nerve and perform the same action.

The anterior compartment is known as the "flexor compartment" as flexion is its main action. The muscles contained therein are:

Biceps brachii
Brachialis
Coracobrachialis
They are all supplied by the musculocutaneous nerve, which has nervous origins of C5, C6, C7 (see brachial plexus).

The deltoid muscle is considered to have part of its body in the anterior compartment. This huge muscle is the main adductor of the upper limb and extends over the shoulder.

The brachioradialis muscle originates in the arm but inserts into the forearm. This muscle is responsible for supination.

The posterior compartment contains muscles, which are all supplied by the radial nerve. This compartment is also known as the "extensor compartment", extension being its main action. Muscles of this compartment are:

Triceps brachii, a huge muscle which contains three heads, the lateral, medial and middle.

Anconeus, a tiny muscle, which some embryologists suggest may be the fourth head of the triceps brachii muscle. This muscle stabilizes the elbow joint during movements. As the upper and lower limbs have similar embryological origins and the lower limb contains the quadriceps femoris muscle (the lower limb equivalent of the triceps), which has four heads, this would seem to make sense.

Cubital fossa
This important area is clinically important for venepuncture and for blood pressure measurement. It is an imaginary triangle with borders being:

Laterally, the medial border of brachioradialis muscle.
Medially, the lateral border of pronator teres muscle.
Superiorly, the intercondylar line, an imaginary line between the two condyles of the humerus
The floor is the brachialis muscle
The roof is the skin and fascia of the arm and forearm

The structures, which pass through the cubital fossa, are vital. The order from which they pass into the forearm are as follows, from medial to lateral:

1. Median nerve, which starts to branch
2. Brachial artery
3. Tendon of the biceps brachii muscle
4. Radial nerve
5. Median cubital vein - this important vein is where venepuncture occurs. It connects the basilic and cephalic veins.
6. Lymph nodes

Nervous supply

Important nerves related to arms:
1. Musculocutaneous nerve
2. Radial nerve
3. Median nerve
4. Ulnar nerve

Blood supply and venous drainage
The main artery in the arm is the brachial artery. This artery is a continuation of the axillary artery. The point at which the axillary becomes the brachial is distal to the lower border of teres major. The brachial artery gives off an important brach, the profunda brachii (deep artery of the arm). This branching occurs just below the lower border of teres major.

The profunda brachii travels through the lower triangular space with the radial nerve. From here onwards it has an intimate relationship with the radial nerve.

The veins of the arm carry blood from the extremities of the limb, as well as drain the arm itself. The two main veins are the basilic and the cephalic veins. There is a connecting vein between the two, the median cubital vein, which passes through the cubital fossa and is clinically important for venepuncture (withdrawing blood). The basilic travels on the medial side of the arm and terminates at the level of the 7th rib. The cephalic travels on the lateral side of the arm and terminates as the axillary vein. It passes through the deltopectoral triangle, a space between the deltoid and the pectoralis major muscles.