Deltoid Muscle Origin, Function & Area | Body Maps Your message has been sent. OK We're sorry, an error occurred. We are unable to collect your feedback at this time. However, your feedback is important to us. Please try again later. Close Deltoid The deltoid muscle is located on the outer aspect of the shoulder and is recognized by its triangular shape. The deltoid muscle was named after the Greek letter Delta due to the similar shape they both share. The deltoid muscle is constructed with three main sets of fibers: anterior, middle, and posterior. These fibers are connected by a very thick tendon and are anchored into a V-shaped channel. This channel housed in the shaft of the humerus bone in the arm. The deltoid muscle is responsible for the brunt of all arm rotation and allows a person to keep carried objects at a safer distance from the body. It is also tasked with stopping dislocation and injury to the humerus when carrying heavy loads. One of the most common injuries to the deltoid muscle is a deltoid strain.

Deltoid strain is characterized by sudden and sharp pain where injured, intense soreness and pain when lifting the arm out from the side of the body, and tenderness and swelling caused by (and located at) the deltoid muscle. Deltoid Muscle - Anatomy Pictures and Information Home > Muscular System > Muscles of the Arm and Hand > Muscles of the Shoulder > Deltoid Muscle Deltoid Muscle The deltoid muscle is a rounded, triangular muscle located on the uppermost part of the arm and the top of the shoulder. It is named after the Greek letter delta, which is shaped like an equilateral triangle. The deltoid is attached by tendons to the skeleton at the clavicle (collarbone), scapula (shoulder blade), and humerus (upper arm bone). The deltoid is widest at the top of the shoulder and narrows to its apex as it travels down the arm. Contraction of the deltoid muscle results in a wide range of movement of the arm at the shoulder due to its location and the wide separation of its muscle fibers....

Move up/down/left/right: Click compass arrows Rotate image: Click and drag in any direction, anywhere in the frame Identify objects: Click on them in the image 2D Interactive 3D Rotate & Zoom Change Anatomical System Full Deltoid Muscle Description [Continued from above] . . . The deltoid has three origins: the lateral end of the clavicle, the acromion of the scapula at the top of the shoulder, and the spine of the scapula. Each origin gives rise to its own band of muscle fibers with the anterior band forming at the clavicle, the lateral fibers forming at the acromion, and the posterior fibers forming at the spine of the scapula. The bands merge together as they approach the insertion point on the deltoid tuberosity of the humerus. The deltoid has three distinct functions that correspond to the three bands of muscle fibers. Contraction of the anterior fibers flexes and medially rotates the arm by pulling the humerus towards the clavicle. Flexion and medial rotation of the arm moves the arm anteriorly, as in reaching forward or throwing a ball underhand. The lateral fibers abduct the arm by pulling the humerus toward the acromion.

Abduction of the arm results in the arm moving away from the body, as in reaching out to the side. Contraction of the posterior fibers extends and laterally rotates the arm by pulling the humerus toward the spine of the scapula. Extension and lateral rotation moves the arm posteriorly, as in reaching backwards or winding up to throw a ball underhand. Prepared by Tim Taylor, Anatomy and Physiology Instructor Shoulder Human Anatomy: Image, Function, Parts, and More Next The shoulder is one of the largest and most complex joints in the body. The shoulder joint is formed where the humerus (upper arm bone) fits into the scapula (shoulder blade), like a ball and socket. Other important bones in the shoulder include: The acromion is a bony projection off the scapula. The clavicle (collarbone) meets the acromion in the acromioclavicular joint. The coracoid process is a hook-like bony projection from the scapula. The shoulder has several other important structures: The rotator cuff is a collection of muscles and tendons that surround the shoulder, giving it support and allowing a wide range of motion.

The bursa is a small sac of fluid that cushions and protects the tendons of the rotator cuff. A cuff of cartilage called the labrum forms a cup for the ball-like head of the humerus to fit into. The humerus fits relatively loosely into the shoulder joint. This gives the shoulder a wide range of motion, but also makes it vulnerable to injury. Shoulder Conditions Frozen shoulder : Inflammation develops in the shoulder that causes pain and stiffness. As a frozen shoulder progresses, movement in the shoulder can be severely limited. Osteoarthritis : The common "wear-and-tear" arthritis that occurs with aging. The shoulder is less often affected by osteoarthritis than the knee. Rheumatoid arthritis : A form of arthritis in which the immune system attacks the joints, causing inflammation and pain. Rheumatoid arthritis can affect any joint, including the shoulder. Gout : A form of arthritis in which crystals form in the joints, causing inflammation and pain. The shoulder is an uncommon location for gout. Rotator cuff tear : A tear in one of the muscles or tendons surrounding the top of the humerus. A rotator cuff tear may be a sudden injury, or result from steady overuse.

Shoulder impingement : The acromion (edge of the scapula) presses on the rotator cuff as the arm is lifted. If inflammation or an injury in the rotator cuff is present, this impingement causes pain. Shoulder dislocation : The humerus or one of the other bones in the shoulder slips out of position. Raising the arm causes pain and a "popping" sensation if the shoulder is dislocated. Shoulder tendonitis : Inflammation of one of the tendons in the shoulder's rotator cuff. Shoulder bursitis : Inflammation of the bursa, the small sac of fluid that rests over the rotator cuff tendons. Pain with overhead activities or pressure on the upper, outer arm are symptoms. Labral tear: An accident or overuse can cause a tear in the labrum, the cuff of cartilage that overlies the head of the humerus. Most labral tears heal without requiring surgery. Continued Shoulder Tests Magnetic resonance imaging ( MRI scan ): An MRI scanner uses a high-powered magnet and a computer to create high-resolution images of the shoulder and surrounding structures.

Computed tomography ( CT scan ): A CT scanner takes multiple X-rays, and a computer creates detailed images of the shoulder. Shoulder X-ray : A plain X-ray film of the shoulder may show dislocation, osteoarthritis or a fracture of the humerus. X-ray films cannot diagnose muscle or tendon injuries. Shoulder Treatments Shoulder surgery : Surgery is generally performed to help make the shoulder joint more stable. Shoulder surgery may be arthroscopic (several small incisions) or open (large incision). Arthroscopic surgery: A surgeon makes small incisions in the shoulder and performs surgery through an endoscope (a flexible tube with a camera and tools on its end). Arthroscopic surgery requires less recovery time than open surgery. Physical therapy : An exercise program can strengthen shoulder muscles and improve flexibility in the shoulder. Physical therapy is an effective, nonsurgical treatment for many shoulder conditions. Pain relievers : Over-the-counter relievers like acetaminophen (Tylenol), ibuprofen (Motrin) and naproxen (Aleve) can relieve most shoulder pain. More severe shoulder pain may require prescription medications. RICE therapy : RICE stands for Rest, Ice, Compression (not usually necessary), and Elevation.

RICE can improve pain and swelling of many shoulder injuries. Corticosteroid (cortisone) injection: A doctor injects cortisone into the shoulder, reducing the inflammation and pain caused by bursitis or arthritis. The effects of a cortisone injection can last several weeks. WebMD Image Collection Reviewed by Varnada Karriem-Norwood, MD on November 15, 2014 Sources Muscles of the Chest and Upper Back Home > Muscular System > Muscles of the Chest and Upper Back Muscles of the Chest and Upper Back The muscles of the chest and upper back occupy the thoracic region of the body inferior to the neck and superior to the abdominal region and include the muscles of the shoulders. These important muscles control many motions that involve moving the arms and head – such as throwing a ball, looking up at the sky, and raising your hand. Breathing, a vital body function, is also controlled by the muscles connected to the ribs of the chest and upper back....

Move up/down/left/right: Click compass arrows Rotate image: Click and drag in any direction, anywhere in the frame Identify objects: Click on them in the image Full Muscles of the Chest and Upper Back Description [Continued from above] . . . The bones of the pectoral girdles, consisting of the clavicle (collar bone) and scapula (shoulder blade), greatly increase the range of motion possible in the shoulder region beyond what would be possible with the shoulder joint alone. The muscles of this region both allow for this range of motion and contract to stabilize this region and prevent any extraneous motion. On the anterior side of the thoracic region, the pectoralis minor and serratus anterior muscles originate on the anterior ribs and insert on the scapula. These muscles work together to move the scapula anteriorly and laterally during pushing, throwing, or punching motions. In the upper back region, the trapezius, rhomboid major, and levator scapulae muscles anchor the scapula and clavicle to the spines of several vertebrae and the occipital bone of the skull.

When these muscles contract, they elevate the pectoral girdle (as in shrugging) and move the scapula medially and posteriorly toward the center of the back (as in rowing). The trapezius also contracts along the back of the neck to extend the head at the neck and hold it upright throughout the day. Nine muscles of the chest and upper back are used to move the humerus (upper arm bone). The coracobrachialis and pectoralis major muscles connect the humerus anteriorly to the scapula and ribs, flexing and adducting the arm toward the front of the body when you reach forward to grab an object. On the posterior side of the arm the teres major and latissimus dorsi extend and adduct the arm towards the scapula and vertebra when you pull an object down off of a shelf above your head. The deltoid and supraspinatus muscles run superiorly between the scapula and humerus to abduct as well as flex and extend the arm. These muscles allow us to raise our arm in the air or swing the arm as in throwing a ball underhand.

Rotation of the humerus is achieved by the actions of the subscapularis, infraspinatus, and teres minor muscles that run from the scapula to the humerus. These three rotator muscles, along with the supraspinatus, end in wide tendons that completely surround the head of the humerus and form a structure known as the rotator cuff, which holds the humerus in place and prevents dislocation. Rotation of the humerus by the rotator cuff muscles is necessary for activities such as throwing a ball overhand or swinging a hammer. In addition to moving the arm and pectoral girdle, muscles of the chest and upper back work together as a group to support the vital process of breathing. The diaphragm is a strong, thin, dome-shaped muscle that spans the entire inferior border of the rib cage, separating the thoracic cavity from the abdominal cavity. Contraction of the diaphragm causes it to descend towards the abdomen, increasing the space of the thoracic cavity and expanding the lungs, filling them with air.

Small muscles running between the ribs, known as the external intercostal muscles, lift the ribs during deep breathing to further expand the chest and lungs and provide even more air to the body. During exhalation, the diaphragm relaxes to decrease the volume of the thoracic cavity, forcing air out of the lungs. Additional air can be forced out of the lungs during deep exhalation by contraction of the internal intercostal muscles, which push the ribs together and help compress the thoracic cavity. Prepared by Tim Taylor, Anatomy and Physiology Instructor human muscle system | Britannica.com Human muscle system renal system Human muscle system, the muscles of the human body that work the skeletal system , that are under voluntary control, and that are concerned with movement, posture, and balance. Broadly considered, human muscle—like the muscles of all vertebrates—is often divided into striated muscle (or skeletal muscle), smooth muscle , and cardiac muscle . Smooth muscle is under involuntary control and is found in the walls of blood vessels and of structures such as the urinary bladder , the intestines , and the stomach . Cardiac muscle makes up the mass of the heart and is responsible for the rhythmic contractions of that vital pumping organ; it too is under involuntary control.

With very few exceptions, the arrangement of smooth muscle and cardiac muscle in humans is identical to the arrangement found in other vertebrate animals. Skeletal muscles are attached to the bones by tendons. Created and produced by QA International. © QA International, 2010. All rights reserved. Lateral view of the human muscular system. Encyclopædia Britannica, Inc. This article is concerned with the skeletal muscles of the human body, with emphasis on muscle movements and the changes that have occurred in human skeletal musculature as a result of the long evolutionary process that involved the assumption of upright posture. Smooth muscle and cardiac muscle and the physiology of muscle contraction are treated at great length in the article muscle . For descriptions of disorders that affect the human muscle system, see muscle disease . The muscle groups and their actions The following sections provide a basic framework for the understanding of gross human muscular anatomy, with descriptions of the large muscle groups and their actions. The various muscle groups work in a coordinated fashion to control the movements of the human body. Anterior view of the human muscular system. Encyclopædia Britannica, Inc. Posterior view of human muscular system. Encyclopædia Britannica, Inc.

human aging The motion of the neck is described in terms of rotation, flexion, extension, and side bending (i.e., the motion used to touch the ear to the shoulder). The direction of the action can be ipsilateral, which refers to movement in the direction of the contracting muscle, or contralateral, which refers to movement away from the side of the contracting muscle. Muscles of the neck. Encyclopædia Britannica, Inc. Rotation is one of the most-important actions of the cervical (neck) spine . Rotation is accomplished primarily by the sternocleidomastoid muscle, which bends the neck to the ipsilateral side and rotates the neck contralaterally. Together, the sternocleidomastoid muscles on both sides of the neck act to flex the neck and raise the sternum to assist in forced inhalation. The anterior and middle scalene muscles, which also are located at the sides of the neck, act ipsilaterally to rotate the neck, as well as to elevate the first rib. The splenius capitis and splenius cervicis, which are located in the back of the neck, work to rotate the head. Side bending also is an important action of the cervical spine.

The sternocleidomastoid muscles are involved in cervical side bending. The posterior scalene muscles, located on the lower sides of the neck, ipsilaterally bend the neck to the side and elevate the second rib. The splenius capitis and splenius cervicis also assist in neck side bending. The erector spinae muscles (iliocostalis, longissimus, and spinalis) are large, deep muscles that extend the length of the back. All three act to ipsilaterally side bend the neck. Neck flexion refers to the motion used to touch the chin to the chest. It is accomplished primarily by the sternocleidomastoid muscles, with assistance from the longus colli and the longus capitis, which are found in the front of the neck. Neck extension is the opposite of flexion and is accomplished by many of the same muscles that are used for other neck movements, including the splenius cervicis, splenius capitis, iliocostalis, longissimus, and spinalis muscles. The back Human Body: Fact or Fiction? Multiple muscles in the back function specifically in movements of the back.

The erector spinae muscles, for example, extend the back (bend it backward) and side bend the back. The semispinalis dorsi and semispinalis capitis muscles also extend the back. The small muscles of the vertebrae (the multifidi and rotators) help rotate, extend, and side bend the back. The quadratus lumborum muscle in the lower back side bends the lumbar spine and aids in the inspiration of air through its stabilizing affects at its insertion at the 12th rib (the last of the floating ribs). The scapula (shoulder blade) is elevated by the trapezius muscle, which runs from the back of the neck to the middle of the back, by the rhomboid major and rhomboid minor muscles in the upper back, and by the levator scapulae muscle, which runs along the side and back of the neck. The shoulder The shoulder is a complex ball-and-socket joint comprising the head of the humerus , the clavicle (collarbone), and the scapula. The shoulder’s main motions are flexion, extension, abduction, adduction, internal rotation, and external rotation.

Muscles of the shoulder. Encyclopædia Britannica, Inc. Shoulder flexion is movement of the shoulder in a forward motion. An example of shoulder flexion can be seen when reaching forward to grasp an object. That action is accomplished primarily by the combined actions of the deltoid muscle in the uppermost extent of the arm, the pectoralis major muscle in the chest, the coracobrachialis muscle on the inside of the upper arm, and the biceps brachii muscles on the front of the upper arm. Connect with Britannica Facebook Twitter YouTube Instagram Pinterest Extension of the shoulder is opposite to flexion. Pure shoulder extension is the movement of the arm directly behind the body, as in receiving a baton in a relay race. That movement is accomplished by the actions of the deltoid muscle, the latissimus dorsi muscle in the back, the teres major muscle in the armpit area, and the triceps muscle in the back of the upper arm. The triceps, as the name suggests, consists of three heads that originate from different surfaces but share the same insertion at the olecranon process of the ulna (a bone in the forearm); the three heads together act to extend the elbow .

Shoulder adduction and abduction serve to lower the arm toward and lift the arm away from the body, respectively. They can be visualized by picturing someone doing jumping jacks. Adduction is accomplished primarily by the pectoralis major, latissimus dorsi, teres major, triceps, and coracobrachialis. The deltoid and the supraspinatus, a muscle that runs along the scapula in the back, are the two main abductors of the shoulder. An example of external rotation of the shoulder is seen in a tennis backhand stroke. External rotation is attributed primarily to the deltoid, the teres minor in the armpit area, and the infraspinatus muscle, which covers the scapula. Internal rotation of the shoulder is the opposite of external rotation. An example is the shoulder movement that occurs when reaching into a back pocket. That movement is achieved through the coordinated action of the pectoralis major, latissimus dorsi, deltoid, teres major, and subscapularis muscles.

(The subscapularis is a deep muscle situated on the anterior, or front-facing, surface of the scapula.) The teres minor, subscapularis, supraspinatus, and infraspinatus muscles together form the rotator cuff, which stabilizes the humeral head (the ball portion of the ball-and-socket shoulder joint). The muscles of the rotator cuff are common sites of injury in adults, particularly among people who perform overhead motions repeatedly (e.g., throwing a baseball or painting a ceiling). Several of the rotator cuff muscles have tendons that run under the acromion, a bony prominence at the distal end of the scapula. (The term distal describes a relative position away from the centre of the body; it often is contrasted with the term proximal, which describes a relative position near to the centre of the body.) The position of the tendons and of the subacromial bursae (fluid-filled sacs located beneath the acromion) leaves them vulnerable to compression and pinching, which can result in an injury known as shoulder impingement syndrome.

The arm Editor Picks: Exploring 10 Types of Basketball Movies In addition to aiding the movement of the shoulder, the muscles of the upper arm produce various movements of the forearm. For example, the primary muscles involved in forearm flexion, in which the angle formed at the elbow becomes smaller (i.e., the hand moves closer to the shoulder), are the biceps brachii, the brachialis (situated beneath the biceps brachii in the upper arm), and the brachioradialis (the origin of which is on the humerus). Minor contributions to forearm flexion are provided by the coracobrachialis and by flexor muscles situated in the anterior compartment of the forearm (the palm side of the forearm; also known as the flexor compartment), including the pronator teres, the flexor carpi radialis, the flexor digitorum superficialis, the palmaris longus, and the flexor carpi ulnaris. Muscles of the upper arm. Encyclopædia Britannica, Inc. Muscles of the human forearm (anterior view, superficial layer). Encyclopædia Britannica, Inc.

Extension of the forearm increases the angle at the elbow, moving the hand away from the shoulder. That action is accomplished primarily by the triceps brachii. Other muscles that make minor contributions to forearm extension include the extensor muscles of the posterior compartment of the forearm (the side of the forearm that is contiguous with the back of the hand; also known as the extensor compartment), including the extensor carpi radialis longus, the extensor carpi radialis brevis, the extensor digitorum, the extensor carpi ulnaris, and the anconeus. The wrist Wrist flexion refers to movement of the wrist that draws the palm of the hand downward. That action is carried out by the flexor carpi radialis, the flexor carpi ulnaris, the flexor digitorum superficialis, the flexor digitorum profundus, and the flexor pollicis longus. Muscles of the forearm (posterior view). Encyclopædia Britannica, Inc. Lady Flora Hastings Wrist extension, by contrast, shortens the angle at the back of the wrist.

The muscles responsible for that action are the extensor carpi radialis longus and the extensor carpi radialis brevis, which also abduct the hand at the wrist (move the hand in the direction of the thumb, or first digit); the extensor digitorum, which also extends the index to little finger (the second to fifth digits); the extensor digiti minimi, which also extends the little finger and adducts the hand (moves the hand in the direction of the little finger); and the extensor carpi ulnaris, which also adducts the hand. Other small muscles that cross the wrist joint may add to wrist extension, but they do so to only a small degree. Wrist supination is the rotation of the wrist that brings the palm facing up. The supinator muscle in the posterior compartment acts to supinate the forearm. The biceps brachii also adds to supination. Pronation is the opposing action, in which the wrist is rotated so that the palm is facing down. The pronator quadratus, a deep muscle in the anterior compartment, along with the pronator teres, pronates the forearm.

The hand The hand is a complex structure that is involved in fine motor coordination and complex task performance. Its muscles generally are small and extensively innervated. Even simple actions, such as typing on a keyboard, require a multitude of precise movements to be carried out by the hand muscles. Because of that complexity, the following paragraphs cover only the primary action of each hand muscle. Several muscles that originate at the posterior surface of the ulna or the radius (the other bone in the forearm) have their actions in the hand. Those include the abductor pollicis longus, which abducts and extends the thumb; the extensor pollicis brevis, which extends the metacarpophalangeal (MCP) joint of the thumb; the extensor pollicis, which extends the distal phalanx (finger bone) of the thumb; and the extensor indicis, which extends the index finger at the MCP joint.

(MCP joints are located between the metacarpal bones, which are situated in the hand, and the phalanges, which are the small bones of the fingers.) Although several of the muscles that move the hand have their origins in the forearm, there are many small muscles of the hand that have both their origin and their insertion within the hand. Those are referred to as the intrinsic muscles of the hand. They include the palmaris brevis, which assists with grip; the umbricals, which flex the MCP joints and extend the interphalangeal joints (IPs; the joints between the phalanges) of the fingers; the palmar interossei, which adduct the fingers toward the middle finger (the third digit); and the dorsal interossei, which abduct the fingers away from the middle finger. All the interossei flex the MCP joints and extend the IP joints. The thenar eminence is located on the palm side of the base of the thumb and is composed of three muscles, the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis, all of which are innervated by the median nerve.

The abductor pollicis brevis abducts the thumb; the flexor pollicis brevis flexes the MCP joint of the thumb; and the opponens pollicis acts to oppose the thumb to the other fingers. The adductor pollicis, which is not part of the thenar eminence, acts to adduct the thumb. The hypothenar enimence is located on the palm side of the hand below the little finger. It contains three muscles that are innervated by the deep branch of the ulnar nerve. The abductor digiti minimi abducts the little finger. The flexor digiti minimi flexes the little finger. The opponens digiti minimi opposes the little finger with the thumb. The abdomen There are three muscular layers of the abdominal wall, with a fourth layer in the middle anterior region. The fourth layer in the midregion is the rectus abdominis, which has vertically running muscle fibres that flex the trunk and stabilize the pelvis. To either side of the rectus abdominis are the other three layers of abdominal muscles .

The deepest of those layers is the transversus abdominis, which has fibres that run perpendicular to the rectus abdominus; the transversus abdominis acts to compress and support the abdomen and provides static core stabilization. The internal oblique layers run upward and forward from the sides of the abdomen, and the external oblique layers, which form the outermost muscle layers of the abdomen, run downward and forward. The internal oblique layers act in conjunction with the external oblique on the opposite side of the body to flex and rotate the trunk toward the side of the contracting internal oblique (“same-side rotator”). Muscles of the abdominal wall. Encyclopædia Britannica, Inc. The hip The hip joint is a complex weight-bearing ball-and-socket joint that can sustain considerable load. The socket of the joint is relatively deep, allowing for stability but sacrificing some degree in range of motion. The movements described in this section include flexion, extension, abduction, and adduction. Anterior view of the muscles of the human leg. Encyclopædia Britannica, Inc. Posterior view of the right leg, showing the muscles of the hip, thigh, and lower leg. Encyclopædia Britannica, Inc.

Hip flexion is the hip motion that brings the knee toward the chest. The major muscles of hip flexion include the iliopsoas, which is made up of the psoas major, psoas minor, and iliacus. Together, those muscles act mainly to flex the hip, but they also contribute to abdominal flexion and hip stabilization. Other hip flexors include the sartorius, the rectus femoris, the pectineus, and the gracilis. The sartorius also contributes to external hip rotation and knee extension and abduction, and the rectus femoris also acts in knee extension. The pectineus is also involved in hip adduction and internal rotation. Hip extension is accomplished primarily by the muscles of the posterior thigh and buttocks, which when contracted serve to move the thigh from a flexed position toward the midline of the body or the trunk of the body from a bent position toward a more-erect posture. Hip extension is accomplished mostly by the gluteus maximus, the biceps femoris (which is divided into two heads, the long head and the short head), the semitendinosus, and the semimembranosus.

A minor contribution is also provided by the adductor magnus and other small pelvic muscles. The movement of adduction is used to describe a direction of limb motion that serves to take the limb from a lateral position to its more-axial alignment. During a jumping-jack exercise, for example, abduction of the leg occurs when it is moved away from the midline and adduction when it is moved back toward the midline. The main abductors of the hip are the gluteus medius, gluteus minimus, and tensor fascia lata. Those three muscles also serve to internally rotate the thigh in an extended position and externally rotate the thigh in the flexed position. Another minor contributor is the piriformis. The main hip adductors are the adductor magnus, the adductor brevis, and the adductor longus. A minor contribution to hip adduction is performed by the pectineus and the gracilis. The upper leg and knee Extension of the knee is accomplished by a group of muscles collectively referred to as the quadriceps femoris , which increases the angle of the knee, bringing the lower leg into a straight position.

Knee extension is used in the forward, swing phase of the gait and is integral in movements such as kicking. The quadriceps femoris group includes the vastus medius, vastus lateralis, vastus intermedius, and rectus femoris. A minor contribution to knee extension is provided by the sartorius. Knee flexion refers to bending of the knee from the straight position. The muscles that perform that action oppose those of knee extension and are generally referred to as the hamstring muscles. The hamstring muscles are situated in the back of the thigh and include the biceps femoris, the semitendinosus, and the semimembranosus. Small contributions to knee flexion are made by the gastrocnemius muscle in the back of the calf and by several small muscles that cross the knee joint posteriorly. The lower leg and foot The muscles of the lower leg and foot are complex and work in many planes. Their actions depend on whether the person is bearing weight, as well as on the position of the foot. The following paragraphs provide a brief overview of the actions of the muscles of the lower leg and foot. Dorsal view of the right foot, showing major muscles, tendons, and nerves.

Encyclopædia Britannica, Inc. Dorsiflexion refers to ankle flexion in the direction of the dorsum, or anterior surface of the foot (the surface of the foot viewed from above). Dorsiflexion is accomplished by several muscles, including the tibialis anterior, which in addition to dorsiflexion also inverts the foot (tilts the foot toward the midline), stabilizes the foot when striking the ground, and locks the ankle when kicking. The extensor digitorum longus (EDL) also acts in dorsiflexion and functions to extend the last four toes. In addition to the EDL, some individuals also have a muscle called the peroneus tertius (fibularis tertius), which participates to a limited extent in dorsiflexion and eversion of the foot (tilting of the foot away from the midline). The extensor hallucis longus primarily acts in big toe (hallux) dorsiflexion, but it also acts to dorsiflex, as well as weakly invert, the ankle. Plantarflexion refers to flexion of the ankle in the direction of the sole of the foot.

That is most easily demonstrated by having a person stand on his or her toes. The majority of ankle plantarflexion is performed by the large calf musculature, including the gastrocnemius and the soleus, which lies just behind the gastrocnemius. It is generally accepted that those are two distinct muscles; however, there is some debate as to whether the gastrocnemius and the soleus are two parts of the same muscle. Other muscles of the lower leg and foot include the plantaris, which runs obliquely between the gastrocnemius and the soleus; the flexor hallucis longus, which contributes to ankle flexion but is involved primarily in big toe flexion; the flexor digitorum longus, which also flexes the second to fifth toes; the peroneus longus, which flexes the ankle and everts the foot; and the peroneus brevis, which is involved in plantarflexion and eversion of the foot. Intrinsic muscles of the foot arise in the foot and do not cross the ankle joint. Hence, their action is confined to the foot.

The intrinsic muscles of the foot include the abductor hallucis, which abducts the big toe; the flexor digitorum brevis, which flexes the second to fifth toes; the abductor digiti minimi, which abducts and flexes the fifth toe; the quadratus plantae, which assists in toe flexion; the lumbricals, which flex the metatarsophalangeal (MTP) joints and extend the distal IP and proximal IP joints of the toes; the flexor hallucis brevis, which flexes the big toe; and the adductor hallucis, which flexes and contracts the big toe. The adductor hallucis has two heads, the oblique head and the transverse head, which share an insertion on the lateral (outer) side of the base of the proximal phalanx of the big toe. The oblique head arises from the base of the second to fourth metatarsal bones, and the transverse head arises from the ligaments of the MTP joints of the third to fifth toes. The flexor digiti minimi brevis extends and adducts the fifth toe.

The dorsal interossei abduct the toes, and the plantar interossei adduct the toes. Shoulder Anatomy, Area & Diagram | Body Maps Written and medically reviewed by the Healthline Editorial Team Co-developed by: In Depth: Shoulder The shoulder is a complex combination of bones and joints where many muscles act to provide the widest range of motion of any part of the body. Numerous muscles help stabilize the three joints of the shoulder while giving it motion. At the shoulder, three major bones meet and create a 90-degree angle: Clavicle: Also known as the collarbone, the clavicle extends across the front of the shoulder from the sternum to the scapula. It helps stabilize the shoulder’s movements. Scapula: More commonly known as the shoulder blade, the scapula is a flat triangular bone located in the upper back. It connects with the collarbone at the front of the body. Humerus: The largest bone of the arm, the humerus connects to the scapula and clavicle in the shoulder. The head of the bone has a ball-like knob to create a ball-and-socket joint with the scapula.

The junctions of these three bones and the sternum (chest bone) form three joints: Glenohumeral joint: This shallow ball-and-socket-style joint created by the humerus and scapula allows the arm to rotate circularly and to move up and out from the body. It is surrounded by soft tissue and strengthened by fibrous ligaments. Acromioclavicular (AC) joint: This joint forms the highest point of the shoulder and provides the ability to raise the arm above the head. The meeting of the scapula and clavicle forms it. Sternoclavicular joint: This joint is at the center of the chest where the clavicle meets the sternum. It allows the clavicles to move. Each joint is surrounded by: cartilage, to pad the meetings of the bones; ligaments, to connect the bones; muscles; and tendons, to attach the muscles to the bones. The collection of muscles and tendons in the shoulder is known as the rotator cuff. It stabilizes the shoulder and holds the head of the humerus in the glenoid, a shallow cavity in the scapula.

The muscles of the rotator cuff include the suprasinatus, infraspinatus, teres minor, and subscapularis. Because shoulders have such range of movement and are used often, they are commonly injured. Some injuries include: Dislocation of the glenohumeral joint Arthritis Tear of the rotator cuff Fractured clavicle Deltoid (Muscles) Deltoid muscles of the human torso The deltoid muscles (sometimes called the deltoideus muscles) are thick triangular muscles that cover the shoulder joints. There is one deltoid muscle over each shoulder joint. Each deltoid muscle can be described in terms of three parts that originate from three distinct sets of fibres or 'heads'. They are: Anterior Part: Originating in the anterior or 'clavicular' fibres, also known as the anterior deltoid or the front delts. Lateral Part: Originating in the lateral or 'acromial' fibres, also known as the lateral deltoid. Posterior Part: Originating in posterior or 'spinal' fibres, also known as the called posterior deltoid, or the rear deltoid or rear delts.

Origin, Insertion and Actions of the Deltoid muscles: Points of Origin: Lateral part of the clavicle ('collar') bone Lateral Part: Spine of scapula , on the scapula bone Point of Insertion: Deltoid tuberosity of the humerus (upper-arm) bone Actions: The deltoid muscles have several actions that can be summarized as: abducts the arm at the shoulder joint flexes the arm at the shoulder joint extends the arm at the shoulder joint rotates the arm at the shoulder joint Descriptions of the actions of the parts of the deltoid muscles vary. Which parts of the deltoid muscles perform which functions depends partly on the initial position of the body and on the stage of the movement (if movement is in progress). The different parts of the deltoid muscle work in co-operation with other muscles to perform certain movements. In some cases the relevant fibres of the deltoid muscles make only a small contribution to the force applied to produce the movement. Examples of some actions of the parts of the deltoid muscles include: Anterior Part: Protracts (draws forward) the humerus / upper-arm Medially rotates the humerus / upper-arm.

Lateral Part: Abducts the humerus at the shoulder joint - continuation of movement initiated by the supraspinatus muscle Posterior Part: Human Muscles Human Muscles Human Muscles Use the filters on the left to identify muscles around a particular joint as well as for specific joint actions. Click on the links below for more detailed explanations including origins, insertions and related sports injuries. Ankle Adductor Brevis Adductor Brevis is the smallest and shortest of the three short adductor muscles. It originates on the pelvis and inserts into the thigh bone and adducts inwards and flexes the hip out forwards. It is most commonly injured in a groin strain. Adductor Longus Adductor Longus is the middle of the three short adductor muscles. It adducts the hip inwards and assists in hip flexion or moving the leg forwards. Originating on the ramus of the pelvis and inserts into the femur or thigh bone. Biceps Brachii The Biceps brachii crosses both the elbow and shoulder joints. Its action on the shoulder joint is very weak flexion. It supinates the forearm and is a strong flexor of the elbow.

The bicep curl exercises is a common one to strengthen this muscle. Biceps Femoris Biceps Femoris is one of the three muscles which form the hamstring group forming the back of the thigh. The muscle is described as having a long head (the attachment from the ischium) and a short head (attached to the femur). Your Muscles Your Muscles Tus músculos Did you know you have more than 600 muscles in your body? They do everything from pumping blood throughout your body to helping you lift your heavy backpack. You control some of your muscles, while others — like your heart — do their jobs without you thinking about them at all. Muscles are all made of the same material, a type of elastic tissue (sort of like the material in a rubber band). Thousands, or even tens of thousands, of small fibers make up each muscle. You have three different types of muscles in your body: smooth muscle, cardiac (say: KAR-dee-ak) muscle, and skeletal (say: SKEL-uh-tul) muscle. Smooth Muscles Smooth muscles — sometimes also called involuntary muscles — are usually in sheets, or layers, with one layer of muscle behind the other.

You can't control this type of muscle. Your brain and body tell these muscles what to do without you even thinking about it. You can't use your smooth muscles to make a muscle in your arm or jump into the air. But smooth muscles are at work all over your body. In your stomach and digestive system, they contract (tighten up) and relax to allow food to make its journey through the body. Your smooth muscles come in handy if you're sick and you need to throw up. The muscles push the food back out of the stomach so it comes up through the esophagus (say: ih-SAH-fuh-gus) and out of the mouth. Smooth muscles are also found in your bladder. When they're relaxed, they allow you to hold in urine (pee) until you can get to the bathroom. Then they contract so that you can push the urine out. These muscles are also in a woman's uterus, which is where a baby develops. There they help to push the baby out of the mother's body when it's time to be born. You'll find smooth muscles at work behind the scenes in your eyes, too. These muscles keep the eyes focused.

continue A Hearty Muscle The muscle that makes up the heart is called cardiac muscle. It is also known as the myocardium (say: my-uh-KAR-dee-um). The thick muscles of the heart contract to pump blood out and then relax to let blood back in after it has circulated through the body. Just like smooth muscle, cardiac muscle works all by itself with no help from you. A special group of cells within the heart are known as the pacemaker of the heart because it controls the heartbeat. Skeletal Muscle Now, let's talk about the kind of muscle you think of when we say "muscle" — the ones that show how strong you are and let you boot a soccer ball into the goal. These are your skeletal muscles — sometimes called striated (say: STRY-ay-tud) muscle because the light and dark parts of the muscle fibers make them look striped (striated is a fancy word meaning striped). Skeletal muscles are voluntary muscles, which means you can control what they do. Your leg won't bend to kick the soccer ball unless you want it to.

These muscles help to make up the musculoskeletal (say: mus-kyuh-low-SKEL-uh-tul) system — the combination of your muscles and your skeleton, or bones. Together, the skeletal muscles work with your bones to give your body power and strength. In most cases, a skeletal muscle is attached to one end of a bone. It stretches all the way across a joint (the place where two bones meet) and then attaches again to another bone. Skeletal muscles are held to the bones with the help of tendons (say: TEN-dunz). Tendons are cords made of tough tissue, and they work as special connector pieces between bone and muscle. The tendons are attached so well that when you contract one of your muscles, the tendon and bone move along with it. Skeletal muscles come in many different sizes and shapes to allow them to do many types of jobs. Some of your biggest and most powerful muscles are in your back, near your spine. These muscles help keep you upright and standing tall. They also give your body the power it needs to lift and push things.

Muscles in your neck and the top part of your back aren't as large, but they are capable of some pretty amazing things: Try rotating your head around, back and forth, and up and down to feel the power of the muscles in your neck. These muscles also hold your head high. previous continue Face Muscles You may not think of it as a muscular body part, but your face has plenty of muscles. You can check them out next time you look in the mirror. Facial muscles don't all attach directly to bone like they do in the rest of the body. Instead, many of them attach under the skin. This allows you to contract your facial muscles just a tiny bit and make dozens of different kinds of faces. Even the smallest movement can turn a smile into a frown. You can raise your eyebrow to look surprised or wiggle your nose. And while you're looking at your face, don't pass over your tongue — a muscle that's attached only at one end! Your tongue is actually made of a group of muscles that work together to allow you to talk and help you chew food. Stick out your tongue and wiggle it around to see those muscles at work.

Major Muscles Because there are so many skeletal muscles in your body, we can't list them all here. But here are a few of the major ones: In each of your shoulders is a deltoid (say: DEL-toyd) muscle. Your deltoid muscles help you move your shoulders every which way — from swinging a softball bat to shrugging your shoulders when you're not sure of an answer. The pectoralis (say: pek-tuh-RAH-lus) muscles are found on each side of your upper chest. These are usually called pectorals (say: PEK-tuh-rulz), or pecs, for short. When many boys hit puberty, their pectoral muscles become larger. Many athletes and bodybuilders have large pecs, too. Below these pectorals, down under your ribcage, are your rectus abdominus (say: REK-tus ab-DAHM-uh-nus) muscles, or abdominals (say: ab-DAHM-uh-nulz). They're often called abs for short. When you make a muscle in your arm, you tense your biceps (say: BYE-seps) muscle.

When you contract your biceps muscle, you can actually see it push up under your skin. Your quadriceps (say: KWAD-ruh-seps), or quads, are the muscles on the front of your thighs. Many people who run, bike, or play sports develop large, strong quads. And when it's time for you to take a seat? You'll be sitting on your gluteus maximus (say: GLOOT-ee-us MAK-suh-mus), the muscle that's under the skin and fat in your behind! Muscular System: Facts, Functions & Diseases Muscular System: Facts, Functions & Diseases By Kim Ann Zimmermann, Live Science Contributor | March 11, 2016 07:35pm ET MORE While most people associate muscles with strength, they do more than assist in lifting heavy objects. The 650 muscles in the body not only support movement — controlling walking, talking, sitting, standing, eating and other daily functions that people consciously perform — but also help to maintain posture and circulate blood and other substances throughout the body, among other functions.

Muscles are often associated with activities of the legs, arms and other appendages, but muscles also produce more subtle movements, such as facial expressions, eye movements and respiration, according to the National Institutes of Health (NIH). [ Image Gallery: The BioDigital Human ] Three types of muscles The muscular system can be broken down into three types of muscles: skeletal, smooth and cardiac, according to the NIH. Skeletal muscles are the only voluntary muscle tissue in the human body and control every action that a person consciously performs. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other, according to The Merck Manual . Visceral, or smooth, muscle is found inside organs such as the stomach and intestines, as well as in blood vessels. It is called a smooth muscle because, unlike skeletal muscle, it does not have the banded appearance of skeletal or cardiac muscle. The weakest of all muscle tissues, visceral muscles contract to move substances through the organ, according to The Merck Manual. Because visceral muscle is controlled by the unconscious part of the brain, it is known as involuntary muscle, as it cannot be controlled by the conscious mind.

Found only in the heart, cardiac muscle is an involuntary muscle responsible for pumping blood throughout the body, according to The Merck Manual. The heart's natural pacemaker is made of cardiac muscle that signals other cardiac muscles to contract. Like visceral muscles, cardiac muscle tissue is controlled involuntarily. While hormones and signals from the brain adjust the rate of contraction, cardiac muscle stimulates itself to contract. Muscle shapes Muscles are further classified by their shape, size and direction, according to the NIH. The deltoids, or shoulder muscles, have a triangular shape. The serratus muscle, which originates on the surface of the second to ninth ribs at the side of the chest, and runs along the entire anterior length of the scapula (shoulder blades), has a distinctive sawlike shape. The rhomboid major, which attaches the scapula to the spinal column, is a diamond shape. Size can be used to differentiate similar muscles in the same region. The gluteal region (the buttocks) contains three muscles differentiated by size: the gluteus maximus (large), gluteus medius (medium) and gluteus minimus (smallest), the NIH noted.

The direction in which the muscle fibers run can be used to identify a muscle. In the abdominal region, there are several sets of wide, flat muscles, according to the NIH. The muscles whose fibers run straight up and down are the rectus abdominis, the ones running transversely (left to right) are the transverse abdominis and the ones running at an angle are the obliques. As any exercise enthusiast knows, obliques are among the hardest muscles to develop to achieve "six-pack" abs. Muscles also can be identified by their function. The flexor group of the forearm flexes the wrist and the fingers. The supinator is a muscle that allows you to roll your wrist over to face palm up. Adductor muscles in the legs adduct, or pull together, the limbs, according to the NIH. Diseases of the muscular system There is no single type of doctor that treats muscular diseases and disorders. Rheumatologists, orthopedists and neurologists may all treat conditions that affect the muscles, according to the American Medical Association . There are a number of common neuromuscular disorders, according to Dr. Robert Schabbing, chief of neurology at Kaiser Permanente in Denver.

Common primary muscle disorders include inflammatory myopathies, including polymyositis, which is characterized by inflammation and progressive weakening of the skeletal muscles; dermatomyositis, which is polymyositis accompanied by a skin rash; and inclusion body myositis, which is characterized by progressive muscle weakness and wasting. Other common disorders are muscular dystrophies and metabolic muscle disorders, he said. Muscular dystrophy affects muscle fibers. Metabolic muscle disorders interfere with chemical reactions involved in drawing energy from food.Neuromuscular junction disorders impair the transmission of nerve signals to muscles, Schabbing noted. The most common neuromuscular junction disorder is myasthenia gravis, which is characterized by varying degrees of weakness of the skeletal muscles. Schabbing said. "There are many types of peripheral neuropathies that can be secondary to other medical conditions, such as diabetes, or due to a variety of other causes, including toxins, inflammation and hereditary causes," he said. Motor neuron disorders affect the nerve cells that supply muscles, Schabbing said. The most recognizable motor neuron disease is amyotrophic lateral sclerosis, or ALS, commonly known as Lou Gehrig's disease. Learn about the muscles that move your body and keep you alive.

Credit: by Ross Toro, Infographics Artist Symptoms, diagnosis and treatment The most common symptom or sign of a muscle disorder is weakness, although muscle disorders can cause a number of symptoms, according to Schabbing. In addition to weakness, symptoms include abnormal fatigue with activity, as well as muscle spasms, cramping or twitching. Neuromuscular disorders affecting the eyes or mouth can cause drooping eyelids or double vision, slurred speech, difficulty swallowing or, sometimes, difficulty breathing. Electromyography — commonly referred to as an EMG — is often used to diagnose muscular disorders. An EMG helps characterize causes of nerve and muscle disorders by stimulating nerves and recording responses, Schabbing noted. Rarely, nerve or muscle biopsies are needed. Steroids and other medications can help to reduce spasms and cramping. Milder forms of chemotherapy can help treat many muscular disorders, according to Dr. Ricardo Roda, an assistant professor of neurology, neuroscience and physiology at NYU Langone Medical Center . Editor’s Note: If you’d like more information on this topic, we recommend the following book:

Question: Where in the human body are the deltoid muscles?
Answer: Shoulder