The geniohyoid muscle is a narrow muscle situated superior to the medial border of the mylohyoid muscle. It is named for its passage from the chin to the hyoid bone, it arises from the inferior mental spine, on the back of the mandibular symphysis, runs backward and downward, to be inserted into the anterior surface of the body of the hyoid bone. It lies in contact with its fellow of the opposite side, it thus belongs to the suprahyoid muscles. The muscle is supplied by branches of the lingual artery; the geniohyoid muscle is innervated by fibres from the first cervical nerve travelling alongside the hypoglossal nerve. These fibers are called ansa cervicalis, it may double. The geniohyoid muscle upwards; this dilates the upper airway. During the first act of deglutition, when the mass of food is being driven from the mouth into the pharynx, the hyoid bone, with it the tongue, is carried upward and forward by the anterior bellies of the Digastrici, the Mylohyoidei, Geniohyoidei, it assists in depressing the mandible The inclined position of the geniohyoid muscle has been contrasted to the horizontal position in neanderthals.
This article incorporates text in the public domain from page 393 of the 20th edition of Gray's Anatomy Anatomy figure: 34:02-06 at Human Anatomy Online, SUNY Downstate Medical Center "Anatomy diagram: 25420.000-1". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01. Frontal section
The mylohyoid muscle is a paired muscle running from the mandible to the hyoid bone, forming the floor of the oral cavity of the mouth. It is named after its two attachments near the molar teeth; these muscles are mesodermal in embryologic origin. The mylohyoid muscle is derived from the first pharyngeal arch; the mylohyoid muscle is flat and triangular, is situated superior to the anterior belly of the digastric muscle. It is classified as one of the suprahyoid muscles. Together, the paired mylohyoid muscles form a muscular floor for the oral cavity of the mouth; the two mylohyoid muscles arise from the mandible at the mylohyoid line, which extends from the mandibular symphysis in front to the last molar tooth behind. The posterior fibers pass insert at anterior surface of the hyoid bone; the medial fibres of the two mylohyoid muscles unite in a midline raphe. The mylohyoid muscle separates the sublingual space from the submandibular space, which communicate via a lateral gap between the mylohyoid and hyoglossus muscles at the posterior free margin of mylohyoid muscle.
The submandibular gland wraps around the edges of the mylohyoid, is divided into superficial and deep lobes above and below the muscle. The mylohyoid muscle is innervated by a branch of the inferior alveolar nerve; the mylohyoid nerve is a branch of the inferior alveolar nerve. The mylohyoid nerve emerges to give motor supply to the mylohyoid muscle; the mylohyoid may be replaced by the anterior belly of the digastric muscle. This median raphé is sometimes absent. An area of herniation of the sublingual gland, blood vessels, or fat, may be present, with studies reporting this in 10-50% of people; the mylohyoid elevates the tongue. This is important during swallowing and speaking. Alternatively, if other muscles are used to keep the position of the hyoid fixed the mylohyoid depresses the mandible, it functions as reinforcing the floor of mouth. The mylohyoid may be imaged by CT or MRI; the mylohyoid separates the submandibular space below from the sublingual space above. Around the posterior border of mylohoid, these spaces communicate.
Infections odontogenic infections can spread from one space to the other via this communication, or alternatively penetrate the mylohyoid, a poor barrier to the spread of infection. Because the attachment of mylohyoid becomes more superior towards the posterior of the mandible, posterior infected teeth are more to drain into the mandibular space, infected anterior teeth are more to drain into the sublingual space, since the apices of the teeth are more to be below and above the mylohoid line respectively. Drake, Richard L.. M. Mitchell. Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. ISBN 978-0-443-06612-2. Herring, Margaret J.. Illustrated anatomy of the head and neck. St. Louis, MO: Elsevier/Saunders. ISBN 978-1-4377-2419-6; this article incorporates text in the public domain from page 393 of the 20th edition of Gray's Anatomy "Anatomy diagram: 25420.000-1". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01
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
A nerve is an enclosed, cable-like bundle of nerve fibres called axons, in the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system; each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as Schwann cells that coat the axons in myelin. Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium; the axons are bundled together into groups called fascicles, each fascicle is wrapped in a layer of connective tissue called the perineurium. The entire nerve is wrapped in a layer of connective tissue called the epineurium. In the central nervous system, the analogous structures are known as tracts; each nerve is covered on the outside by a dense sheath of the epineurium. Beneath this is a layer of flat cells, the perineurium, which forms a complete sleeve around a bundle of axons.
Perineurial septae subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium; this forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, meshwork of collagen fibres. Nerves are bundled and travel along with blood vessels, since the neurons of a nerve have high energy requirements. Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid; this acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood-brain barrier. Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation, the amount of endoneurial fluid may increase at the site of irritation; this increase in fluid can be visualized using magnetic resonance neurography, thus MR neurography can identify nerve irritation and/or injury.
Nerves are categorized into three groups based on the direction that signals are conducted: Afferent nerves conduct signals from sensory neurons to the central nervous system, for example from the mechanoreceptors in skin. Efferent nerves conduct signals from the central nervous system along motor neurons to their target muscles and glands. Mixed nerves contain both afferent and efferent axons, thus conduct both incoming sensory information and outgoing muscle commands in the same bundle. Nerves can be categorized into two groups based on where they connect to the central nervous system: Spinal nerves innervate much of the body, connect through the vertebral column to the spinal cord and thus to the central nervous system, they are given letter-number designations according to the vertebra through which they connect to the spinal column. Cranial nerves innervate parts of the head, connect directly to the brain, they are assigned Roman numerals from 1 to 12, although cranial nerve zero is sometimes included.
In addition, cranial nerves have descriptive names. Specific terms are used to describe their actions. A nerve that supplies information to the brain from an area of the body, or controls an action of the body is said to "innervate" that section of the body or organ. Other terms relate to whether the nerve affects the same side or opposite side of the body, to the part of the brain that supplies it. Nerve growth ends in adolescence, but can be re-stimulated with a molecular mechanism known as "Notch signaling". If the axons of a neuron are damaged, as long as the cell body of the neuron is not damaged, the axons would regenerate and remake the synaptic connections with neurons with the help of guidepost cells; this is referred to as neuroregeneration. The nerve begins the process by destroying the nerve distal to the site of injury allowing Schwann cells, basal lamina, the neurilemma near the injury to begin producing a regeneration tube. Nerve growth factors are produced causing many nerve sprouts to bud.
When one of the growth processes finds the regeneration tube, it begins to grow towards its original destination guided the entire time by the regeneration tube. Nerve regeneration is slow and can take up to several months to complete. While this process does repair some nerves, there will still be some functional deficit as the repairs are not perfect. A nerve conveys information in the form of electrochemical impulses carried by the individual neurons that make up the nerve; these impulses are fast, with some myelinated neurons conducting at speeds up to 120 m/s. The impulses travel from one neuron to another by crossing a synapse, the message is converted from electrical to chemical and back to electrical. Nerves can be categorized into two groups based on function: An afferent nerve fiber conducts sensory information from a sensory neuron to the central nervous system, where the information is processed. Bundles of fibres or axons, in the peripheral nervous system are called nerves, bundles of afferent fibers are known as sensory nerves.
An efferent nerve fiber conducts signals from a motor neuron in the central nervous system to muscles. Bundles of these fibres are known as efferent nerves; the nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body. In vertebrates it consists of two main par
Obliquus capitis superior muscle
The obliquus capitis superior muscle is a small muscle in the upper back part of the neck and is one of the suboccipital muscles and part of the suboccipital triangle. It arises from the lateral mass of the atlas bone, it passes superiorly and posteriorly to insert into the lateral half of the inferior nuchal line on the external surface of the occipital bone. The muscle is innervated by the dorsal ramus of the first spinal nerve, it acts at the atlanto-occipital joint to flex the head to the ipsilateral side. This article incorporates text in the public domain from page 402 of the 20th edition of Gray's Anatomy Anatomy figure: 01:07-06 at Human Anatomy Online, SUNY Downstate Medical Center
The foramen magnum is a large oval opening in the occipital bone of the skull in humans and various other animals. It is circular openings in the base of the skull; the spinal cord, an extension of the medulla, passes through the foramen magnum as it exits the cranial cavity. Apart from the transmission of the medulla oblongata and its membranes, the foramen magnum transmits the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membranes and alar ligaments, it transmits the spinal component of the accessory nerve into the skull. The opisthion is the midpoint on the posterior margin of the foramen magnum and is a cephalometric landmark. Another landmark is the basion located at the midpoint on the anterior margin of the foramen magnum; the foramen magnum is a important feature in bipedal mammals. One of the attributes of a bipedal animal’s foramen magnum is a forward shift of the anterior border. Studies on the foramen magnum position have shown a connection to the functional influences of both posture and locomotion.
The forward shift of the foramen magnum is apparent in bipedal hominins, including modern humans, Australopithecus africanus, Paranthropus boisei. This common feature of bipedal hominins is the driving argument used by Michel Brunet that Sahelanthropus tchadensis was bipedal, may be the earliest known bipedal ape; the discovery of this feature has given scientists another form of identifying bipedal mammals. The alar ligament, attached on each side to the tubercle of occipital condyle on each side of Foramen magnum divides it into anterior smaller compartment and posterior larger compartment. Thus, in humans, the neck muscles do not need to be as robust. Comparisons of the position of the foramen magnum in early hominid species are useful to determine how comfortable a particular species was when walking on two limbs rather than four. Posterior cranial fossa This article incorporates text in the public domain from page 129 of the 20th edition of Gray's Anatomy "Anatomy diagram: 34257.000-1".
Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01. Diagram 1 Diagram 2 3D animation showing position of basion on YouTube
The neck is the part of the body, on many vertebrates, that separates the head from the torso. It contains blood nerves that supply structures in the head to the body; these in humans include part of the esophagus, the larynx and thyroid gland, major blood vessels including the carotid arteries and jugular veins, the top part of the spinal cord. In anatomy, the neck is called by its Latin names, cervix or collum, although when used alone, in context, the word cervix more refers to the uterine cervix, the neck of the uterus, thus the adjective cervical may refer either to the uterine cervix. The neck contains vessels. In humans these structures include part of the esophagus, trachea and parathyroid glands, lymph nodes, the first part of the spinal cord. Major blood vessels include the jugular veins. Cervical lymph nodes surround the blood vessels; the thyroid gland and parathyroid glands are endocrine glands involved in the regulation of cellular metabolism and growth, blood calcium levels. The shape of the neck in humans is formed from the upper part of the vertebral column at the back, a series of cartilage that surrounds the upper part of the respiratory tract.
Around these sit soft tissues, including muscles, between and around these sit the other structures mentioned above. Muscles of the neck attach to the base of the skull, the hyoid bone, the clavicles, the sternum; the large platysma, sternocleidomastoid muscles contribute to the shape at the front, the trapezius and lattissimus dorsi at the back. A number of other muscles attach to and stem from the hyoid bone, facilitating speech and playing a role in swallowing. Sensation to the front areas of the neck comes from the roots of nerves C2-4, at the back of the neck from the roots of C4-5; the cervical region of the human spine is made up of seven cervical vertebrae referred to as C-1 to C-7, with cartilaginous discs between each vertebral body. The spinal cord sits within the cervical part of the vertebral column; the spinal column carries nerves that carry sensory and motor information from the brain down to the rest of the body. From top to bottom the cervical spine is curved in convex-forward fashion.
In addition to nerves coming from and within the human spine, the accessory nerve and vagus nerve both cranial nerves, travel down the neck. In the middle line below the chin can be felt the body of the hyoid bone, just below, the prominence of the thyroid cartilage called "Adam's apple", better marked in men than in women. Neck lines appear at a age as a development of skin wrinkles. Still, lower the cricoid cartilage is felt, while between this and the suprasternal notch, the trachea and the isthmus of the thyroid gland may be made out. At the side, the outline of the sternomastoid muscle is the most striking mark; the upper part of the former contains the submaxillary gland known as the submandibular glands, which lies just below the posterior half of the body of the jaw. The line of the common and the external carotid arteries may be marked by joining the sterno-clavicular articulation to the angle of the jaw; the eleventh or spinal accessory nerve corresponds to a line drawn from a point midway between the angle of the jaw and the mastoid process to the middle of the posterior border of the sterno-mastoid muscle and thence across the posterior triangle to the deep surface of the trapezius.
The external jugular vein can be seen through the skin. The anterior jugular vein is smaller, runs down about half an inch from the middle line of the neck; the clavicle or collar-bone forms the lower limit of the neck, laterally the outward slope of the neck to the shoulder is caused by the trapezius muscle. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In addition, the neck is flexible and allows the head to turn and flex in all directions. Disorders of the neck are a common source of pain; the neck has a great deal of functionality but is subject to a lot of stress. Common sources of neck pain include: Whiplash, strained a muscle or another soft tissue injury Cervical herniated disc Cervical spinal stenosis Osteoarthritis Vascular sources of pain, like arterial dissections or internal jugular vein thrombosis Cervical adenitis The neck appears in some of the earliest of tetrapod fossils, the functionality provided has led to its being retained in all land vertebrates as well as marine-adapted tetrapods such as turtles and penguins.
Some degree of flexibility is retained where the outside physical manifestation has been secondarily lost, as in whales and porpoises. A morphologically functioning neck appears among insects, its absence in fish and aquatic arthropods is notable, as many have life stations similar to a terrestrial or tetrapod counterpart, or could otherwise make use of the added flexibility. The word "neck" is sometimes used as a convenience to refer to the region behind the head in some snails, gastropod mollusks though there is no clear distinction between this area, the head area, the rest of the body. Throat Adam's apple Hickey Nape American Head and Neck Society The Anatomy Wiz. An Interactive Cross-Sectional Anatomy Atlas