Anatomical terms of motion
Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints and specific sections of the body; the terminology used describes this motion according to its direction relative to the anatomical position of the joints. Anatomists use a unified set of terms to describe most of the movements, although other, more specialized terms are necessary for describing the uniqueness of the movements such as those of the hands and eyes. In general, motion is classified according to the anatomical plane. Flexion and extension are examples of angular motions, in which two axes of a joint are brought closer together or moved further apart. Rotational motion may occur at other joints, for example the shoulder, are described as internal or external. Other terms, such as elevation and depression, describe movement above or below the horizontal plane. Many anatomical terms derive from Latin terms with the same meaning. Motions are classified after the anatomical planes they occur in, although movement is more than not a combination of different motions occurring in several planes.
Motions can be split into categories relating to the nature of the joints involved: Gliding motions occur between flat surfaces, such as in the intervertebral discs or between the carpal and metacarpal bones of the hand. Angular motions occur over synovial joints and causes them to either increase or decrease angles between bones. Rotational motions move a structure in a rotational motion along a longitudinal axis, such as turning the head to look to either side. Apart from this motions can be divided into: Linear motions, which move in a line between two points. Rectilinear motion is motion in a straight line between two points, whereas curvilinear motion is motion following a curved path. Angular motions occur when an object is around another object decreasing the angle; the different parts of the object do not move the same distance. Examples include a movement of the knee, where the lower leg changes angle compared to the femur, or movements of the ankle; the study of movement is known as kinesiology.
A categoric list of movements of the human body and the muscles involved can be found at list of movements of the human body. The prefix hyper- is sometimes added to describe movement beyond the normal limits, such as in hypermobility, hyperflexion or hyperextension; the range of motion describes the total range of motion. For example, if a part of the body such as a joint is overstretched or "bent backwards" because of exaggerated extension motion it can be described as hyperextended. Hyperextension increases the stress on the ligaments of a joint, is not always because of a voluntary movement, it may be other causes of trauma. It may be used in surgery, such as in temporarily dislocating joints for surgical procedures; these are general terms. Most terms have a clear opposite, so are treated in pairs. Flexion and extension describe movements; these terms come from the Latin words with the same meaning. Flexion describes a bending movement that decreases the angle between a segment and its proximal segment.
For example, bending the elbow, or clenching a hand into a fist, are examples of flexion. When sitting down, the knees are flexed; when a joint can move forward and backward, such as the neck and trunk, flexion refers to movement in the anterior direction. When the chin is against the chest, the head is flexed, the trunk is flexed when a person leans forward. Flexion of the shoulder or hip refers to movement of the leg forward. Extension is the opposite of flexion, describing a straightening movement that increases the angle between body parts. For example, when standing up, the knees are extended; when a joint can move forward and backward, such as the neck and trunk, extension refers to movement in the posterior direction. Extension of the hip or shoulder moves the leg backward. Abduction is the motion of a structure away from the midline while adduction refer to motion towards the center of the body; the centre of the body is defined as the midsagittal plane. These terms come from Latin words with similar meanings, ab- being the Latin prefix indicating "away," ad- indicating "toward," and ducere meaning "to draw or pull".
Abduction refers to a motion that pulls a part away from the midline of the body. In the case of fingers and toes, it refers to spreading the digits apart, away from the centerline of the hand or foot. Abduction of the wrist is called radial deviation. For example, raising the arms up, such as when tightrope-walking, is an example of abduction at the shoulder; when the legs are splayed at the hip, such as when doing a star jump or doing a split, the legs are abducted at the hip. Adduction refers to a motion that pulls a structure or part toward the midline of the body, or towards the midline of a limb. In the case of fingers and toes, it refers to bringing the digits together, towards the centerline of the hand or foot. Adduction of the wrist is called ulnar deviation. Dropping the arms to the sides, bringing the knees together, are examples of adduction. Ulnar deviation is the hand moving towards the ulnar styloid. Radial deviation is the hand moving towards the radial styloid; the terms elevation and depression refer to movement below the horizontal.
They derive from the Latin terms with similar meaningsElevation refers to movement in a superior direction. For example
Coronoid process of the mandible
The mandible's coronoid process is a thin, triangular eminence, flattened from side to side and varies in shape and size. Its anterior border is continuous below with the anterior border of the ramus, its posterior border forms the anterior boundary of the mandibular notch. Its lateral surface is smooth, affords insertion to the Temporalis and Masseter, its medial surface gives insertion to the Temporalis, presents a ridge which begins near the apex of the process and runs downward and forward to the inner side of the last molar tooth. Between this ridge and the anterior border is a grooved triangular area, the upper part of which gives attachment to the Temporalis, the lower part to some fibers of the Buccinator. Mandible fractures are common injuries. However, coronoid process fractures are rare. Isolated fractures of the coronoid process caused by direct trauma are rare, as is anatomically protected area complex zygomatic arch-temporo-zygomatic bone and associated muscles. Etiology, most fractures are caused by strokes.
Ramus mandibulae This article incorporates text in the public domain from page 174 of the 20th edition of Gray's Anatomy lesson1 at The Anatomy Lesson by Wesley Norman Anatomy photo:22:os-1006 at the SUNY Downstate Medical Center - "Osteology of the Skull: Mandible of Intact Skull" "Anatomy diagram: 34256.000-2". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01
Zygomaticus major muscle
The zygomaticus major is a muscle of the human body. It is a muscle of facial expression which draws the angle of the mouth superiorly and posteriorly to allow one to smile. Like all muscles of facial expression, the zygomatic major is innervated by the facial nerve, more the buccal and zygomatic branches of the facial nerve; the zygomaticus extends from each zygomatic arch to the corners of the mouth. It raises the corners of the mouth. A single unit, Dimples are caused by variations in form, it is thought. Zygomaticus Major Clips of muscle action
The zygomatic arch, or cheek bone, is formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone, the two being united by an oblique suture. The jugal point is the point at the anterior end of the upper border of the zygomatic arch where the masseteric and maxillary edges meet at an angle; the jugal point is the anterior end of upper border of the zygomatic arch where it meets the process of the zygomatic bone. The arch is typical of Synapsida, a clade of amniotes that includes mammals and their extinct relatives, such as Moschops and Dimetrodon; the zygomatic process of the temporal arises by two roots: an anterior, directed inward in front of the mandibular fossa, where it expands to form the articular tubercle. A posterior, which runs backward above the external acoustic meatus and is continuous with the supramastoid crest; the upper border of the arch gives attachment to the temporal fascia. High cheekbones are pronounced zygomatic arches, causing the upper part of the cheeks to jut out and form a line cut into the sides of the face.
High cheekbones, forming a symmetrical face shape, are common in fashion models and may be considered a beauty trait in both males and females, at least in Eurocentric societies. The term zygomatic derives from the Greek ζύγωμα zygōma, meaning "bolt, bar", derived from ζυγο-, "yoke, join"; the Greek word was used with this anatomical sense by Galen in the 2nd century AD. The zygomatic arch is referred to as the zygoma, but this term refers to the zygomatic bone or the zygomatic process; the zygomatic arch is significant in evolutionary biology, as it is part of the structures derived from the ancestral single temporal fenestra of the synapsid ancestor of mammals. Zygoma fracture Zygomasseteric system Zygomaticotemporal suture Zygomatic complex fracture This article incorporates text in the public domain from page 183 of the 20th edition of Gray's Anatomy lesson1 at The Anatomy Lesson by Wesley Norman "Anatomy diagram: 34257.000-1". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01
The platysma is a superficial muscle that overlaps the sternocleidomastoid. It is a broad sheet arising from the fascia covering the upper parts of the pectoralis major and deltoid. Fibres at the front of the muscle from the left and right sides intermingle together below and behind the symphysis menti, it is not a true symphysis. Fibres at the back of the muscle cross the mandible, some being inserted into the bone below the oblique line, others into the skin and subcutaneous tissue of the lower part of the face. Many of these fibers blend with lower part of the mouth. Sometimes fibers can be traced to the margin of the orbicularis oris. Beneath the platysma, the external jugular vein descends from the angle of the mandible to the clavicle. Variations occur over the clavicle and shoulder. A more or less independent fasciculus, the occipitalis minor, may extend from the fascia over the trapezius to fascia over the insertion of the sternocleidomastoideus; the platysma is supplied by cervical branch of the facial nerve.
When the entire platysma is in action it produces a slight wrinkling of the surface of the skin of the neck in an oblique direction. Its anterior portion, the thickest part of the muscle, depresses the lower jaw. However, the platysma plays only a minor role in depressing the lip, performed by the depressor anguli oris and the depressor labii inferioris. In a similar fashion to other muscles, the platysma is vulnerable to tears and muscle atrophy among many other possible conditions; the platysma is vulnerable to neck injuries. A type of medical imagining called CTA, used to visualise arterial and venous vessels, is useful to minimise the number of neck explorations, thus improving the handling of the condition. Another area of importance of the platysma lies in plastic surgery. Neck bands in the area become most noticeable with age, aggravated by facelift. If it doesn't heal with time, there are many options to correct this: Botox/Dysport/Xeomin and platysmaplasty. Platysmaplasty is a surgery in this area, that can be open or closed, in the latter a specialised instrument called plastymotome that allow the surgery to be done without incisions.
It takes 2 weeks for the symptoms to be reduced. This article incorporates text in the public domain from page 387 of the 20th edition of Gray's Anatomy BooksSusan Standring. Gray's anatomy: the anatomical basis of clinical practice. London: Churchill Livingstone. ISBN 978-0-8089-2371-8
Merriam-Webster, Inc. is an American company that publishes reference books and is known for its dictionaries. In 1828, George and Charles Merriam founded the company as G & C Merriam Co. in Springfield, Massachusetts. In 1843, after Noah Webster died, the company bought the rights to An American Dictionary of the English Language from Webster's estate. All Merriam-Webster dictionaries trace their lineage to this source. In 1964, Encyclopædia Britannica, Inc. acquired Inc. as a subsidiary. The company adopted its current name in 1982. In 1806, Webster published A Compendious Dictionary of the English Language. In 1807 Webster started two decades of intensive work to expand his publication into a comprehensive dictionary, An American Dictionary of the English Language. To help him trace the etymology of words, Webster learned 26 languages. Webster hoped to standardize American speech, since Americans in different parts of the country used somewhat different vocabularies and spelled and used words differently.
Webster completed his dictionary during his year abroad in 1825 in Paris, at the University of Cambridge. His 1820s book contained 70,000 words, of which about 12,000 had never appeared in a dictionary before; as a spelling reformer, Webster believed that English spelling rules were unnecessarily complex, so his dictionary introduced American English spellings, replacing colour with color, waggon with wagon, centre with center. He added American words, including skunk and squash, that did not appear in British dictionaries. At the age of 70 in 1828, Webster published his dictionary. However, in 1840, he published the second edition in two volumes with much greater success. In 1843, after Webster's death, George Merriam and Charles Merriam secured publishing and revision rights to the 1840 edition of the dictionary, they published a revision in 1847, which did not change any of the main text but added new sections, a second update with illustrations in 1859. In 1864, Merriam published a expanded edition, the first version to change Webster's text overhauling his work yet retaining many of his definitions and the title "An American Dictionary".
This began a series of revisions. In 1884 it contained 118,000 words, "3000 more than any other English dictionary". With the edition of 1890, the dictionary was retitled Webster's International; the vocabulary was vastly expanded in Webster's New International editions of 1909 and 1934, totaling over half a million words, with the 1934 edition retrospectively called Webster's Second International or "The Second Edition" of the New International. The Collegiate Dictionary was introduced in 1898 and the series is now in its eleventh edition. Following the publication of Webster's International in 1890, two Collegiate editions were issued as abridgments of each of their Unabridged editions. With the ninth edition, the Collegiate adopted changes which distinguish it as a separate entity rather than an abridgment of the Third New International; some proper names were returned including names of Knights of the Round Table. The most notable change was the inclusion of the date of the first known citation of each word, to document its entry into the English language.
The eleventh edition includes more than 225,000 definitions, more than 165,000 entries. A CD-ROM of the text is sometimes included; this dictionary is preferred as a source "for general matters of spelling" by the influential The Chicago Manual of Style, followed by many book publishers and magazines in the United States. The Chicago Manual states. Merriam overhauled the dictionary again with the 1961 Webster's Third New International under the direction of Philip B. Gove, making changes that sparked public controversy. Many of these changes were in formatting, omitting needless punctuation, or avoiding complete sentences when a phrase was sufficient. Others, more controversial, signaled a shift from linguistic prescriptivism and towards describing American English as it was used at that time. Since the 1940s, the company has added many specialized dictionaries, language aides, other references to its repertoire; the G. & C. Merriam Company lost its right to exclusive use of the name "Webster" after a series of lawsuits placed that name in public domain.
Its name was changed to "Merriam-Webster, Incorporated", with the publication of Webster's Ninth New Collegiate Dictionary in 1983. Previous publications had used "A Merriam-Webster Dictionary" as a subtitle for many years and will be found on older editions; the company has been a subsidiary of Encyclopædia Britannica, Inc. since 1964. In 1996, Merriam-Webster launched its first website, which provided free access to an online dictionary and thesaurus. Merriam-Webster has published dictionaries of synonyms, English usage, biography, proper names, medical terms, sports terms, Spanish/English, numerous others. Non-dictionary publications include Collegiate Thesaurus, Secretarial Handbook, Manual for Writers and Editors, Collegiate Encyclopedia, Encyclopedia of Literature, Encyclopedia of World Religions. On February 16, 2007, Merriam-Webster announced the launch of a mobile dictionary and thesaurus service developed with mobile search-and-information provider AskMeNow. Consumers use the service to access definitions and synonyms via text message.
Services include Merr
Skeletal muscle is one of three major muscle types, the others being cardiac muscle and smooth muscle. It is a form of striated muscle tissue, under the voluntary control of the somatic nervous system. Most skeletal muscles are attached to bones by bundles of collagen fibers known as tendons. A skeletal muscle refers to multiple bundles of cells joined together called muscle fibers; the fibers and muscles are surrounded by connective tissue layers called fasciae. Muscle fibers, or muscle cells, are formed from the fusion of developmental myoblasts in a process known as myogenesis. Muscle fibers have more than one nucleus, they have multiple mitochondria to meet energy needs. Muscle fibers are in turn composed of myofibrils; the myofibrils are composed of actin and myosin filaments, repeated in units called sarcomeres, which are the basic functional units of the muscle fiber. The sarcomere is responsible for the striated appearance of skeletal muscle and forms the basic machinery necessary for muscle contraction.
Connective tissue is present in all muscles as fascia. Enclosing each muscle is a layer of connective tissue known as the epimysium. Muscle fibers are the individual contractile units within a muscle. A single muscle such as the biceps brachii contains many muscle fibers. Another group of cells, the myosatellite cells are found between the basement membrane and the sarcolemma of muscle fibers; these cells are quiescent but can be activated by exercise or pathology to provide additional myonuclei for muscle growth or repair. DevelopmentIndividual muscle fibers are formed during development from the fusion of several undifferentiated immature cells known as myoblasts into long, multi-nucleated cells. Differentiation into this state is completed before birth with the cells continuing to grow in size thereafter. MicroanatomySkeletal muscle exhibits a distinctive banding pattern when viewed under the microscope due to the arrangement of cytoskeletal elements in the cytoplasm of the muscle fibers; the principal cytoplasmic proteins are myosin and actin which are arranged in a repeating unit called a sarcomere.
The interaction of myosin and actin is responsible for muscle contraction. Every single organelle and macromolecule of a muscle fiber is arranged to ensure form meets function; the cell membrane is called the sarcolemma with the cytoplasm known as the sarcoplasm. In the sarcoplasm are the myofibrils; the myofibrils are long protein bundles about 1 micrometer in diameter each containing myofilaments. Pressed against the inside of the sarcolemma are the unusual flattened myonuclei. Between the myofibrils are the mitochondria. While the muscle fiber does not have smooth endoplasmic cisternae, it contains a sarcoplasmic reticulum; the sarcoplasmic reticulum surrounds the myofibrils and holds a reserve of the calcium ions needed to cause a muscle contraction. Periodically, it has dilated end sacs known as terminal cisternae; these cross the muscle fiber from one side to the other. In between two terminal cisternae is a tubular infolding called a transverse tubule. T tubules are the pathways for action potentials to signal the sarcoplasmic reticulum to release calcium, causing a muscle contraction.
Together, two terminal cisternae and a transverse tubule form a triad. Muscle architecture refers to the arrangement of muscle fibers relative to the axis of force generation of the muscle; this axis is a hypothetical line from the muscle's origin to insertion. For some longitudinal muscles, such as the biceps brachii, this is a simple concept. For others, such as the rectus femoris or deltoid muscle, it becomes more complicated. While the muscle fibers of a fascicle lie parallel to one another, the fascicles themselves can vary in their relationship to one another and to their tendons; the different fiber arrangements produce broad categories of skeletal muscle architectures including longitudinal, unipennate and multipennate. Because of these different architectures, the tension a muscle can create between its tendons varies by more than its size and fiber-type makeup. Longitudinal architectureThe fascicles of longitudinally arranged, parallel, or fusiform muscles run parallel to the axis of force generation, thus these muscles on a whole function to a single, large muscle fiber.
Variations exist, the different terms are used more specifically. For instance, fusiform refers to a longitudinal architecture with a widened muscle belly, while parallel may refer to a more ribbon-shaped longitudinal architecture. A less common example would be a circular muscle such as the orbicularis oculi, in which the fibers are longitudinally arranged, but create a circle from origin to insertion. Unipennate architectureThe fibers in unipennate muscles are all oriented at the same angle relative to the axis of force generation; this angle reduces the effective force of any individual fiber, as it is pulling off-axis. However, because of this angle, more fibers can be packed into the same muscle volume, increasing the Physiological cross-sectional area; this effect is known as fiber packing, and—in terms of force generation—it more than overcomes the efficiency loss of the off-axis orientation. The trade-off comes in the total excursion. Overall muscle shortening speed is reduced compared to fiber shortening speed, as is the total distance of shortening.
All of these effects scale with pennation angle.