Facial Muscles
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The facial muscles are associated with facial expressions. These muscles include:
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Frontalis
The frontalis muscle lies over the forehead (Latin – frons). Posteriorly, it attaches to an aponeurosis
and anteriorly it attaches to the skin of the eyebrows. Contraction of the frontalis wrinkles the forehead and raises the eyebrows. |
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Orbicularis oculi
The fibers of the orbicularis oculi encircle the eye. This muscle enables you to close your eyes, squint, blink and wink. |
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Orbicularis oris
This is another circular muscle that is found within the lips. It closes the mouth and protrudes the lips. |
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Buccinator
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This muscle has a name that associates it with a “horn blower”. Its fibers run horizontal in the cheeks and attach to the orbicularis oris. The contraction of this muscle flattens the cheeks as during sucking and whistling or when blowing on a trumpet. The compression of the cheeks also helps to hold food between
the teeth during chewing. |
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Zygomaticus
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This muscle’s fibers extend from the cheek bones to the corners of the mouth. Contraction of the
zygomaticus raises the corners of the mouth as when smiling. |
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Chewing Muscles
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The chewing muscles enable you to chew your food by moving the upper and lower teeth against one another. These muscles
include:
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Masseter
The masseter attaches to the zygomatic process of the temporal bone and inserts on the mandible. This
muscle elevates the mandible during chewing. |
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Temporalis
This muscle, as its name implies, attaches to the flat part of the temporal bone. Its fibers converge to
attach to a process on the mandible. This muscle also works with the masseter to elevate the mandible during chewing. |
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Neck Muscles
The neck muscles move the head and the shoulder girdle. These muscles include:
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Anterior Trunk Muscles
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Pectoralis major
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This muscle is a large fan-shaped muscle that covers the upper part of the chest. The muscle inserts on the proximal part of the humerus and acts to adduct and flex the arm. |
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Intercostal muscles
The intercostal muscles are found between the ribs (costa). These muscles aid in ventilating the lungs
by raising and lowering the ribs during forceful breathing. |
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Muscles of the Abdominal Girdle
These muscles support the wall of the abdominal cavity. They also are involved with flexion of the vertebral column. These muscles are:
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Rectus abdominis
The rectus abdominis muscles are a pair of strap-like muscle on either side of the midline that goes through
the “belly button”. Lean and well-toned muscles give rise to the ever popular “six pack”. The fibers attach to the rib cage and the pubis of the hip bones. Contraction causes flexion of the vertebral column and, when the vertebral column is held in position, compression of the abdominal cavity. |
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External oblique
The fibers of this muscle attach to the lower eight ribs and spiral downward and medially to attach to the hip bone. This muscle also flexes the spine and compresses the abdomen but in addition it also rotates and laterally flexes the spine. |
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Internal oblique
The internal oblique is a muscle that is deep to the external oblique and has fibers that crisscross those of the external oblique. Its actions are similar to those of the external oblique. |
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Transversus abdominis
This is the deepest muscle of the abdominal wall and it has fibers that run transversely. Its main action is to compress the abdominal cavity. |
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Posterior Trunk Muscles
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Trapezius
The trapezius muscles are superficial muscles of the neck and upper trunk. Taken together they form a diamond shape. Because of their broad attachments they have a number of actions that include extending
the head and elevating, depressing, adducting and stabilizing the scapula. |
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Latissimus dorsi
This is another flat, superficial muscle that covers the lower back. It inserts on the proximal end of the humerus and its primary actions are to extend and adduct the humerus. Because of these actions this muscle is sometimes called the “swimmer’s muscle”. |
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Erector Spinae
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These muscles are the deep muscles of the back.
As the name implies, they are extensors of the back. Spasms of these muscles is a common source of back pain. |
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Upper Limb Muscles |
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Deltoid
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The deltoid muscles are fleshy, triangular muscles that give the shoulder its round contour. The muscle has origins on the pectoral girdle and inserts on the lateral side of the humerus. The primary action of this muscle is abduction of the humerus but it also contributes to flexion and extension of the humerus and lateral
and medial rotation of the humerus at the shoulder joint. |
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Biceps brachii
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This muscle, as its name implies, has two heads. Both heads have an origin on the scapula and insert on the radius. This muscle acts to flex the forearm at the elbow joint and also supinates the forearm. It forms a noticeable bulge on the anterior side of the arm when it contracts. |
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Brachialis
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This muscle lies deep to the biceps and flexes the forearm with the biceps brachii. |
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Brachioradialis
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This muscle has its origin on the distal part of the humerus and its insertion on the distal part of the radius.
Hence its name derives from the origin and insertion. It is a weak flexor of the forearm and the muscle lies mainly in the forearm. |
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Triceps brachii
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This muscle is responsible for most of the flesh on the posterior side of the arm. It has three heads as the name implies and inserts on the point of the elbow. It is the main extensor of the forearm at the elbow joint. |
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Hip Joint Muscles
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Gluteus maximus
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This muscle contributes to most of the flesh of the buttocks. It is a powerful extensor of the thigh. It is used primarily when the hip is already flexed as when rising from a sitting position or climbing up stairs. |
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Gluteus medius
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The gluteus medius lies underneath the gluteus maximus. This muscle is an abductor of the thigh at the hip joint and steadies the pelvis during walking. The gluteus medius is the preferred muscle for intramuscular
injections. |
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Iliopsoas
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This muscle is totally hidden from view as its has its origin on the anterior side of the ilium and the lower vertebrae and inserts on the proximal part of the femur. It is the main flexor of the thigh at the hip joint. |
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Adductor Muscles
The adductor muscles form the fleshy mass on the medial side of the thigh. As the name implies they adduct
the thigh at the hip joint. |
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Knee Joint Muscles
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Hamstring Muscles
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The hamstring muscles are a group of three muscles, the biceps femoris, semitendinosus and semimembranosus. These muscle form the fleshy posterior part of the thigh. These muscle are flexors
of the leg at the knee joint but also contribute to extension of the thigh at the hip joint. |
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Sartorius
This is a thin, strap-like muscle that attaches to the hip bone and crosses the anterior side of the thigh to attach to the medial side of the tibia. It is a weak flexor of the leg at the knee joint but also flexes and laterally rotates the thigh as when crossing the knee. Its name means “tailor” because a tailor would cross his legs while
sewing. |
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Quadriceps femoris
This muscle has four heads each with their own name. The rectus femoris attaches to the hip bone and the vastus lateralis, vastus intermedius and vastus medialis attach to the femur. All four heads fuse
and insert on the proximal tibial. The patella or knee cap forms in the tendon of this muscle. The quadriceps femoris is a powerful extensor of the leg at the knee joint. The rectus femoris also contributes to flexion
of the thigh at the hip joint. |
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Ankle and Foot Muscles
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Tibialis anterior
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This muscle is a superficial muscle on the anterior leg. It attaches to the tarsal bones on the medial side of the
foot and dorsiflexes and inverts the foot. |
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Extensor digitorum longus
The name of this muscle says its action. It is an extensor of the toes (2-5) but also dorsiflexes
the foot. |
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Gastrocnemius
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This muscle has two heads and forms the curved calf of the posterior leg. The gastrocnemius attaches to the distal end of the femur and inserts onto the heel bone by way of the calcaneal (Achilles) tendon. It is a plantar flexor of the foot but because it crosses the knee joint, also contributes to flexion of the leg at the knee joint. |
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Soleus
This muscle lies deep to the gastrocnemius muscle. It attaches to the tibia and joins the gastrocnemius at the calcaneal tendon. It is also a plantar flexor of the foot at the ankle joint. |
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