Hip and Lower Limb Muscles

These muscles, particularly those of the hips and thigh, tend to be large and heavy because they are used to move the entire weight of the body and to resist the force of gravity. Therefore, they are important for movement and balance.

Muscles That Move the Thigh

The muscles that move the thigh have at least one origin on the pelvic girdle and insert on the femur. Notice that the iliopsoas is an anterior muscle that moves the thigh, while the gluteal muscles (”gluts”) are posterior muscles that move the thigh. The adductor muscles are medial muscles (Fig. 1.19).

Iliopsoas (includes psoas major and iliacus) originates at the ilium and the bodies of the lumbar vertebrae, and inserts on the femur anteriorly. This muscle is the prime mover for flexing the thigh and also the trunk, as when we bow. As the major flexor of the thigh, the iliopsoas is important to the process of walking. It also helps prevent the trunk from falling backward when a person is standing erect. The gluteal muscles form the buttocks

Gluteus maximus is the largest muscle in the body and covers a large part of the buttock (gluteus means buttocks in Greek). It originates at the ilium and sacrum, and inserts on the femur. The gluteus maximus is a prime mover of thigh extension, as when a person is walking, climbing stairs, or jumping from a crouched position. Notice that the iliopsoas and the gluteus maximus are antagonistic muscles.

Gluteus medius lies partly behind the gluteus maximus. It runs between the ilium and the femur, and functions to abduct the thigh. The gluteus maximus assists the gluteus medius in this function. Therefore, they are  synergistic muscles.

Adductor group muscles (pectineus, adductor longus, adductor magnus, gracilis) are located on the medial thigh. All of these muscles originate from the pubis and ischium, and insert on the femur; the deep adductor magnus. Adductor muscles adduct the thigh that is, they lower the thigh side ways from a horizontal position. Because they press the thighs inward, these are the muscles that keep a rider on a horse.

Skeletal Muscle Group IV

Muscles of the Arm

The muscles of the arm move the forearm.

Biceps brachii is a muscle of the proximal anterior arm (Fig.1.16) that is familiar because it bulges when the forearm is flexed. It also supinates the hand when a doorknob is turned or the cap of a jar is unscrewed. The name of the muscle refers to its two heads that attach to the scapula, where it originates. The biceps brachii inserts on the radius.

Brachialis originates on the humerus and inserts on the ulna. It is a muscle of the distal anterior humerus and lies deep to the biceps brachii. It is synergistic to the biceps brachii in flexing the forearm.

Triceps brachii is the only muscle of the posterior arm (Fig.1.17). It has three heads that attach to the scapula and humerus, and it inserts on the ulna. The triceps extends the forearm. It is sometimes called the fiboxers muscle because it extends the elbow when a punch is thrown. The triceps is also used in tennis to do a backhand volley.

Muscles of the Forearm

The muscles of the forearm move the hand and fingers. Note that extensors of the wrists and fingers are on the lateral forearm and flexors are on the medial forearm.

Flexor carpi and extensor carpi muscles originate on the bones of the forearm and insert on the bones of the hand. The flexor carpi flex the wrists and hands, and the extensor carpi extend the wrists and hands.

Flexor digitorum and extensor digitorum muscles also originate on the bones of the forearm and insert on the bones of the hand. The flexor digitorum flexes the wrist and fingers, and the extensor digitorum extends the wrist and fingers (i.e., the digits).

Skeletal Muscle Group III

Muscles of the Shoulder

Muscles of the shoulder are shown in Figs. 1.13 and 1.14. The muscles of the shoulder attach the scapula to the thorax and move the scapula; they also attach the humerus to the scapula and move the arm. 

 

Muscles That Move the Scapula

Serratus anterior is located below the axilla (armpit) on the lateral chest. It runs between the upper ribs and the scapula. It depresses the scapula and pulls it forward, as when we push something. It also helps to elevate the arm above the horizontal level.

Muscles That Move the Arm

Deltoid is a large, fleshy, triangular muscle (deltoid in Greek means triangular) that covers the shoulder and causes a bulge in the arm where it meets the shoulder. It runs from both the clavicle and the scapula of the pectoral girdle to the humerus. This muscle abducts the arm to the horizontal position.

Pectoralis major (Fig. 1.13) is a large anterior muscle of the upper chest. It originates from a clavicle, but also from the sternum and ribs. It inserts on the humerus. The pectoralis major flexes the arm (raises it anteriorly) and adducts the arm, pulling it toward the chest.

Latissimus dorsi (Fig. 1.14) is a large, wide, triangular muscle of the back. This muscle originates from the lower spine and sweeps upward to insert on the humerus. The latissimus dorsi extends and adducts the arm (brings it down from a raised position). This muscle is very important for swimming, rowing, and climbing a rope.

Rotator cuff (Fig. 1.15). This group of muscles is so named because their tendons help form a cuff over the proximal humerus. These muscles lie deep to those already mentioned, and they are synergists to them.

Skeletal Muscle Group II

Muscles of the Trunk

The muscles of the thoracic wall are primarily involved in breathing. The muscles of the abdominal wall protect and support the organs within the abdominal cavity.

Muscles of the Thoracic Wall 

External intercostal muscles occur between the ribs, they originate on a superior rib and insert on an inferior rib. These muscles elevate the rib cage during the inspiration phase of breathing.

The diaphragm is a domehaped muscle that, as you know, separates the thoracic cavity from the abdominal cavity. Contraction of the diaphragm also assists inspiration.

Internal intercostal muscles originate on an inferior rib and insert on a superior rib. These muscles depress the rib cage and contract only during a forced expiration. Normal expiration does not require muscular action.

Muscles of the Abdominal Wall

The abdominal wall has no bony reinforcement (Fig. 1.12). The wall is strengthened by four pairs of muscles that run at angles to one another.The external and internal obliques and the transversus abdominis occur laterally, but the fasciae of these muscle pairs meet at the midline of the body, forming a tendinous area called the linea alba. The rectus abdominis is a superficial medial pair of muscles. All of the muscle pairs of the abdominal wall compress the abdominal cavity and support and protect the organs within the abdominal cavity.

External and internal obliques occur on a slant and are at right angles to one another between the lower ribs and the pelvic girdle. The external obliques are superior to the internal obliques. These muscles also aid trunk rotation and lateral flexion.

Transversus abdominis, deep to the obliques,extends horizontally across the abdomen. The obliques and the transversus abdominis are synergistic muscles.

Rectus abdominis has a straplike appearance but takes its name from the fact that it runs straight (rectus means straight) up from the pubic bones to the ribs and sternum. These muscles also help flex and rotate the lumbar portion of the vertebral column.

Skeletal Muscle Group II

Muscles of the Neck

Deep muscles of the neck are responsible for swallowing. Superficial muscles of the neck move the head.

Swallowing

Swallowing is an important activity that begins after we chew our food. First, the tongue (a muscle) and the buccinators squeeze the food back along the roof of the mouth toward the pharynx. An important bone that functions in swallowing is the hyoid. The hyoid is the only bone in the body that does not articulate with another bone.

Muscles that lie superior to the hyoid, called the suprahyoid muscles, and muscles that lie inferior to the hyoid, called the infrahyoid muscles, move the hyoid. The suprahyoid muscles pull the hyoid forward and upward toward the mandible. Because the hyoid is attached to the larynx, this pulls the larynx upward and forward. The epiglottis now lies over the glottis and closes the respiratory passages. Small palatini muscles pull the soft palate backward, closing off the nasal passages. Pharyngeal constrictor muscles push the bolus of food into the pharynx, which widens when the suprahyoid muscles move the hyoid. The hyoid bone and larynx are returned to their original positions by the infrahyoid muscles. Notice that the suprahyoid and infrahyoid muscles are antagonists.

Muscles That Move the Head

Two muscles in the neck are of particular interest: The sternocleidomastoid and the trapezius illustrated in Fig. 1.10 and 1.11. Recall that flexion is a movement that closes the angle at a joint and extension is a movement that increases the angle at a joint. Recall that abduction is a movement away from the midline of the body, while adduction is a movement toward the midline. Also, rotation is the movement of a part around its own axis.

Sternocleidomastoid

muscles ascend obliquely from their origin on the sternum and clavicle to their insertion on the mastoid process of the temporal bone. Which part of the body do you expect them to move? When both sternocleidomastoid muscles contract, flexion of the head occurs. When only one contracts, the head turns to the opposite side. If you turn your head to the right, you can see how the left sternocleidomastoid shortens, pulling the head to the right.

Each trapezius muscle is triangular, but together, they take on a diamond or trapezoid shape. The origin of a trapezius is at the base of the skull. Its insertion is on a clavicle and scapula. You would expect the trapezius muscles to move the scapulae, and they do. They adduct the scapulae when the shoulders are shrugged or pulled back. The trapezius muscles also help extend the head, however. The prime movers for head extension are actually deep to the trapezius.