Muscle Anatomy
Muscle Anatomy
Types of Movement
     All muscles exert their             force by pulling between             at least two points of attachment. The movement that results from             contraction is called the action of the muscle. Typically, one attachment remains stationary and             is called the origin and the other attachment moves and is called the insertion.
     Almost all muscles cross at             least one joint (moveable connection between two bones) and cause an             action across that joint. The type of movement that results depends             upon the nature of the joint.
     Common             types of movement that result from muscle contraction include:
Flexion                   � A movement that decreases the angle between two bones                   at the joint.
Extension                   � A movement that increases the angle between two bones                   at the joint. However, if the angle goes past 180o (a straight line) in the direction opposite flexion                   the movement is called hyperextension.
Rotation                   � Rotation is a movement that results in movement of one                   bone around its longitudinal axis.
Abduction                   � A movement that results in the part moving away from                   the midline.
Adduction                   � A movement that results in the part moving toward the                   midline.
     Special             types of movement occur at particular joints and include:
Dorsiflexion and plantar flexion                   � These movements only apply to movements of the foot at                   the ankle joint. Dorsiflexion is when the foot is raised as when you dig in your heels. Plantar                   flexion is when you lower your foot as when you lift                   yourself onto the balls of your feet.
Inversion and eversion � These                   movements also apply only to the feet. Inversion is when you turn your feet inward so that your soles are                   facing one another. Eversion is when you turn your feet outward so that your soles are                   facing laterally.
Supination and pronation � These                   movements apply to the forearm. Pronation is rotation of the radius across the ulna that results is                   your palms facing backwards. Supination is movement in the opposite direction that uncrosses the                   radius from the ulna to cause the palms to face forward.
Opposition                   � This movement enables us to be skillful tool users.                   Opposition is the movement of the tip of the thumb that                   enables it to touch the tips of the other fingers.
Naming Skeletal Muscles
     Memorization of specific             muscles is easier if you have some understanding of how the muscle             was named. Conversely, deciphering the significance of a muscle�s             name will give you information about the muscle. Muscles are named             according to a number of criteria:
Direction                   of muscle fibers
     A muscle may be                         given a name based on the direction of muscle fibers, or                         the muscle as a whole, relative to the longitudinal axis                         of the muscle, or body part with which the muscle is                         associated. The term rectus implies that the fibers or muscle is oriented                         straight with respect to the longitudinal axis. The term oblique means                         that the orientation is at an angle to the longitudinal                         axis.
Relative                   size
     When more than                         one muscle are in the same location they may be                         distinguished by their relative size. These terms                         include:
major for bigger and minor for smaller;
maximus for biggest, intermedius for middle and minimus for smallest;
longus for longest and brevis for shortest.
Location
     Some muscles are                         given a name based on the bone they are associated with                         or the region of the body where they are found. For                         example, the pectoralis                         major is found in the chest region and the rectus femoris is found near the femur.
Number of                   origins
     A                         muscle that has more than one attachment at locations                         that do not move, called origins, and only one attachment at the location that does move, called the insertion, is                         said to have more than one head. The term biceps means two heads; the term triceps means three heads; and the term quadriceps means four heads.
Location                   of the origin and insertion
      A                         muscle may be named for their attachment sites. For                         example, the brachioradialis attaches to the humerus (origin) and the radius (insertion).
 Shape
      Many                         muscles are named according to their shape. For example, deltoid means triangular in shape.
Action
     Muscles are                         often named for their primary action. For example, flexor,                         extensor, adductor and abductor are names associated with the action of the muscle.
Gross Anatomy
     The facial muscles are                   associated with facial expressions. These muscles include:
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.
Orbicularis oculi
     The                               fibers of the orbicularis oculi encircle the eye.                               This muscle enables you to close your eyes,                               squint, blink and wink.
Orbicularis oris
     This is                               another circular muscle that is found within the                               lips. It closes                               the mouth and protrudes                               the lips.
Buccinator
     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.
Zygomaticus
     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.
  Chewing             Muscles
     The                   chewing muscles enable you to chew your food by moving the                   upper and lower teeth against one another. These muscles                   include:
Masseter
     The                               masseter attaches to the zygomatic process of the                               temporal bone and inserts on the mandible. This                               muscle elevates                               the mandible during chewing.
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.
  Neck             Muscles
     The neck muscles move                   the head and the shoulder girdle. These muscles include:
Platysma
     The                               platysma is a broad sheet-like muscle that                               attaches to the connective tissue of the skin of                               the upper chest and inserts on the mandible and                               the skin at the corners of the mouth. Contraction                               of the muscle depresses                               the mandible, depresses the corners of the mouth and tightens                               the skin of the neck.
Sternocleidomasdoid
     The name                               of this muscle describes its attachments. This is                               a two headed muscle in which one head attaches to                               the sternum and the other head attaches the clavicle (cleido). The two heads fuse and attach to the mastoid                               process of the temporal bone. When both                               muscles contract together the head                               flexes as when bowing the head in prayer. If                               only one muscle contracts the head turns                               to the opposite side.
  Anterior Trunk Muscles
Pectoralis                   major
     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.
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.
  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:
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.
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.
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.
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.
  Posterior             Trunk Muscles
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.
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�.
Erector                   Spinae
     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.
  Upper             Limb Muscles
Deltoid
     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.
Biceps                   brachii
     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.
Brachialis
     This muscle lies                         deep to the biceps  and flexes the                         forearm with the biceps brachii.
Brachioradialis
     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.
Triceps                   brachii
     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.
  Hip             Joint Muscles
Gluteus                   maximus
     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.
Gluteus                   medius
     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.
Iliopsoas
     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.
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.
  Knee             Joint Muscles
Hamstring                   Muscles
     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.
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.
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.
  Ankle             and Foot Muscles
Tibialis                   anterior
     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.
 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.
Gastrocnemius
      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.
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.