Major Skeletal Muscles

There are more than 600 muscles in the body, but only a few of the major muscles are considered here.

Muscles of Facial Expression And Mastication

Muscles of the face and scalp produce the facial expressions that help communicate feelings, such as anger, sadness, happiness, fear, disgust, pain, and surprise. Most have origins on skull bones and insertions on the dermis of the skin.

The epicranius is an unusual muscle. It has a large epicranial aponeurosis that covers the top of the skull and two contractile portions: the frontal belly over the frontal bone and the occipital belly over the occipital bone.

Two major pairs of muscles elevate the mandible in the process of mastication (chewing): the masseter and the temporalis.

Muscles That Move The Head

Several pairs of neck muscles are responsible for flexing, extending, and rotating the head. Table below lists two of the major muscles that perform this function: the sternocleidomastoid and the splenius capitis. The trapezius can also extend the head, although this is not its major function.

Muscle of The Abdominal Wall

The abdominal muscles are paired muscles that provide support for the anterior and lateral portions of the abdominal and pelvic regions, including support for the internal organs. The muscles are named for the direction of their muscle fibers: rectus abdominis, external oblique, internal oblique, and transversus abdominis. They are arranged in overlapping layers and are attached by larger aponeuroses that merge at the anterior midline to form the linea alba, or white line.

Muscles of Breathing

Movement of the ribs occurs during breathing and is brought about by the contraction of two sets of muscles that are located between the ribs. The external intercostals elevate and protract the ribs during inspiration, and the internal intercostals depress and retract the ribs during expiration. The primary breathing muscle is the diaphragm, a thin sheet of muscle that separates the thoracic and abdominal cavities.

Muscles That Move The Pectoral Girdle

Pectoral girdle muscles originate on bones of the axial skeleton and insert on the scapula or clavicle. Because the scapula is supported mainly by muscles, it can be moved more freely than the clavicle. The trapezius is a superficial trapezoid-shaped muscle that covers much of the superior back. The rhomboid major and minor and the ievator scapulae lie deep to the trapezius. Each serratus anterior is located on the lateral surface of the superior ribs near the axillary region. The pectoralis minor lies deep to the pectoralis major. It protracts and depresses the scapula.

Muscles That Move The Arm And Forearm

Movement of the humerus is enabled by the muscles that originate on the pectoral girdle, ribs, or vertebrae and insert on the humerus. The arrangement of these muscles and the ball-and-socket joint between the humerus and scapula enable great freedom of movement for the arm. The pectoralis major is the large superficial muscle of the chest. The deltoid is the thick muscle that caps theshoulder joint. The supraspinatus, infraspinatus, and teres minor cover the posterior surface of the scapula.

The anterior surface of each scapula is covered by the subscapularis. These four muscles and their tendons surround the head of the humerus at the shoulder joint, making up the rotator cuff The muscles and tendons of the rotator cuff are the only structures stabilizing the shoulder joint; thus the joint is fairly unstable compared to other joints. However, this relative lack of stability is what allows the shoulder’s mobility. The fatissimus dorsi is a broad, sheetlike muscle that covers the inferior back. The teres major assists the latissimus dorsi and is located just superior to it.

Muscles moving the forearm originate on either the humerus or the scapula and insert on either the radius or the ulna. Three flexors occur on the anterior surface of the arm: the biceps brachii, brachialis, and brachioradialis. One extensor, the triceps brachii, is located on the posterior surface of the arm.

Arms

Forearms

Muscles That Move The Wrist And Fingers

Many muscles that produce the various movements of the wrist and fingers are located in the forearm. Only a few of the larger superficial muscles are considered here. They originate from the distal end of the humerus and insert on carpal bones, metacarpals, or phalanges. Flexors on the anterior surface include the flexor carpi radialis, flexor carpi ulnaris, and palmaris longus. Extensors on the posterior surface include the extensor carpi radialis longus, extensor carpi ulnaris, and extensor digitorum (table 7.11; and figures 7.18 and 7.19). Note that the tendons of these muscles are held in position by a circular ligament at the wrist. Muscles That Move the Wrist and Fingers

Muscles That Move The Thigh And Leg

Muscles moving the thigh span the hip joint. They insert on the femur, and most originate on the pelvic girdle. The iliacus and psoas major are located anteriorly, the gluteus maximus is located posteriorly and forms the buttocks, the gluteus medius is located deep to the gluteus maximus posteriorly and extends laterally, and the tensor fasciae latae is located laterally. The adductor longus and adductor magnus are both located medially.

The leg is moved by muscles located in the thigh. They span the knee joint and originate on the pelvic girdle or femur and insert on the tibia or fibula. The quadriceps femoris is composed of four muscles that have a common tendon that inserts on the patella. However, this tendon continues as the patellar ligament, which attaches to the tibial tuberosity-the functional insertion for these muscles. The biceps femoris, semitendinosus, and semimembranosus on the posterior surface of the thigh are often collectively called the hamstrings. The medially
located gracilis has two insertions that give it dual actions. The long, straplike sartorius extends diagonally across the anterior surface of the thigh and spans both the hip and knee joints. Its contraction enables the legs to cross.

Thigh

Muscles That Move The Foot And Toes

Many muscles are involved in the movement of the foot and toes. They are located in the leg and originate on the femur, tibia, or fibula and insert on the tarsal bones, metatarsals, or phalanges. The posterior leg muscles include the gastrocnemius and soleus, which insert through a common tendon, the calcaneal (Achilles) tendon, which attaches to the calcaneus. The tibialis anterior is anteriorly located, and the extensor digitorum longus lies lateral to it. Note that although the extensor digitorum extends the toes, as its name implies, it also dorsiflexes the foot. The fibularis longus is located on the lateral surface of the leg.