The muscles of the head and neck
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The muscles of the head and neck perform many important tasks, including movement of the head and neck, chewing and swallowing, speech, facial expressions, and movement of the eyes. These diverse tasks require both strong, forceful movements and some of the fastest, finest, and most delicate adjustments in the entire human body.
The muscles of the face are unique among groups of muscles in the body. While most muscles connect to and move only bones, facial muscles mostly connect bones to skin. These muscles, including the zygomaticus major and orbicularis oris, pull on the skin to produce a seemingly infinite number of facial expressions and to move the lips and cheeks during speech and eating.
Producing the body’s ability to close the mouth, bite, and chew food, the muscles of mastication move the mandible relative to the rest of the skull. These muscles, including the masseter and temporalis, elevate the jaw forcefully during chewing and gently during speech.
An extensive complement of tightly interlaced muscles allows the tongue a range of complex movements for chewing and swallowing, as well as the important function of producing speech. Of these, four extrinsic muscle sets (connecting the tongue to the surrounding bones) move the tongue in virtually any direction, with fine shape changes (such as for speech) the province of the four intrinsic tongue muscles.
As for the eye, six extrinsic eye muscles provide superior, inferior, lateral, and medial motion, as well as rotation of the eyeball. These muscles produce extremely fine movements almost constantly throughout the day with tremendous speed and accuracy. Located inside the eye, the intrinsic eye muscles work tirelessly to dilate the pupils and focus the lens of the eye to produce clear vision.
Even the middle ear takes part in the muscular system of the head and neck. In fact, the smallest muscle of the skeleton is the stapedius, which measures around 1 millimeter (1/20th of an inch) in length. The muscles of the middle ear contract to dampen the amplitude of vibrations from the eardrum to the inner ear.
The neck muscles, including the sternocleidomastoid and the trapezius, are responsible for the gross motor movement in the muscular system of the head and neck. They move the head in every direction, pulling the skull and jaw towards the shoulders, spine, and scapula. Working in pairs on the left and right sides of the body, these muscles control the flexion and extension of the head and neck. Working individually, these muscles rotate the head or flex the neck laterally to the left or right. Neck muscles contract to adjust the posture of the head throughout the course of a day and have some of the greatest endurance of any muscles in the body.
The clavicular head of the sternocleidomastoid muscle
The clavicular head of the sternocleidomastoid muscle is the more lateral and posterior of the two heads of origin of the sternocleidomastoid muscle. It connects the skull to the clavicle and allows the head to flex or rotate. The sternocleidomastoid is clinically significant as an anatomical landmark. Minor strain injuries are common in this muscle, due to overexertion.
Anatomy of the clavicular head of the sternocleidomastoid muscle
The sternocleidomastoid muscle, or SCM, is one of the larger and more superficial muscles in the neck, making it an important and easily identifiable anatomical landmark. It arises from two origins: the sternal head arises from the superior border of the manubrium of the sternum, while the clavicular head arises from a wide band on the superior edge of the clavicle. From these origins, the heads extend obliquely posteriorly and laterally across the neck where their fibers fuse into a single muscular body. The unified SCM continues to run posteriorly and laterally to insert at the mastoid process, a small mass of bony tissue on the temporal bone of the skull. The course of the SCM can be traced through palpation of the neck by turning one’s head to the side and feeling for a bulging muscle running from the sternum and clavicle and ending posterior to the ear.
Compared to the sternal head, the clavicular head is thinner and wider, as it has a much larger origin along the medial third of the clavicle. Its muscle fibers run almost vertically compared to the oblique fibers of the sternal head.
Physiology of the clavicular head of the sternocleidomastoid muscle
The sternocleidomastoid muscles produce several motions within the neck, depending on whether one or both muscles are operating. When one SCM muscle contracts, it pulls the mastoid process towards its origins, pivoting of the head and turning the face toward the opposite side of the body. Both SCM muscles working together draw both mastoid processes towards the origins, resulting in flexion of the head toward the chest.
The sternocleidomastoid muscles can also work with the scalene muscles as muscles of deep respiration. When other muscles of the neck hold the head steady, the SCM muscles can pull the sternum and ribcage superiorly toward the neck. This elevation of the ribcage increases its volume, pulling more air into the lungs.
Strains of the SCM are common minor muscle injuries. Turning the head suddenly, whiplash, or sleeping with the neck in a strained position are some of the factors that can lead to SCM strain. While painful, this condition is not usually serious and can be treated with rest, massage, stretching, and NSAIDs.
The Depressor Anguli Oris Muscle
The depressor anguli oris is a muscle that originates from the mandible and inserts on angles of the mouth to depress the angle of the mouth.
The Depressor Labii Inferioris Muscle
The depressor labii inferioris muscle is a muscle of the face that draws the lower lip down and slightly laterally, as in the expression of irony.
The Frontal Belly of Epicranius Muscle (Frontalis Muscle)
The frontal belly of epicranius muscle (also known as the frontalis muscle), with assistance from the occipital belly, pulls the scalp back so that the eyebrows are lifted and the forehead can wrinkle. The epicranius muscle is a wide musculofibrous layer that wraps around one entire side of the vertex of the skull, from the occipital bone to the eyebrow. It's made up of two muscles: the occipitalis and the frontalis.
The frontalis muscle takes on a thin, quadrilateral form. This muscle is wider than the occipitalis and its fibers are lighter in color and longer. There are no bony attachments. The medial fibers are connected with those of the Procerus; the corrugator and the orbicularis oculi mix with its immediate fibers. Its lateral fibers also mix with the latter muscle over the zygomatic process of the frontal bone.
At these attachments, the fibers move up and join the galea aponeurotica beneath the coronal suture. The medial margins of the frontales move together for a while above the root of the nose; however, between the occipitales there is a significant, though changing interval taken up by the galea aponeurotica.
The galea aponeurotica
The galea aponeurotica is a muscle that covers the upper part of the cranium (skull). Its attachment to the frontal and occipital bellies (muscles on the brow at the front and on the upper back of the head) allows it to move the scalp freely over the underlying skull bone. The occipital and frontal bellies work together with this muscle to draw back the scalp, raise the eyebrows, and wrinkle the forehead in an expression of surprise.
The levator labii superioris alaque nasi muscle
The levator labii superioris alaque nasi muscle raises the upper lip and dilates the nostril. The zygomaticus minor is a small bundle of muscle fibers lying in the area of the cheek. The levator labii superioris arises from the upper lip, carrying it a little forward. These three muscles, working together, form the nasolabial furrow, from the side of the nose to the upper lip, which is deepened in expressions of sadness. When these muscles work together with the levator anguli oris the furrow deepens into an expression of contempt or disdain. The zygomaticus major is larger than the minor, but it also lies in the cheek area and extends down to the mouth. It draws the angle of the mouth upward and backward in laughing.
The levator labii superioris muscle
The levator labii superioris muscle arises from the upper lip, carrying it a little forward. The zygomaticus minor is a small bundle of muscle fibers lying in the area of the cheek. The levator labii superioris alaeque nasi raises the upper lip and dilates the nostril. These three muscles, working together, form the nasolabial furrow, from the side of the nose to the upper lip, which is deepened in expressions of sadness. When these muscles work together with another tongue-twister, the levator anguli oris, the furrow deepens into an expression of contempt or disdain. The zygomaticus major is larger than the minor, but it also lies in the cheek area and extends down to the mouth. It draws the angle of the mouth upward and backward in laughing.
The masseter muscle
The masseter muscle is a thick quadrilateral muscle located in the cheek. It is needed for mastication (chewing) and performs when it closes the jaws. It is made up of two parts: superficial and deep. The larger, superficial portion comes up by a wide tendinous aponeurosis from the zygomatic process of the maxilla, and from the anterior two-thirds of the bottom lower border and deep surface of the zygomatic arch. Its fibers extend down and back and fit into the angle and bottom half of the lateral surface of the ramus of the mandible.
The second part, the deep portion, is a lot smaller and has a texture that is more muscular. This part comes from the posterior third of the lower border and by way of the whole of the medial surface of the zygomatic arch. The fibers go down and forward and fit into the top half of the ramus and the lateral surface of the coronoid process of the mandible. This portion of the masseter muscle is only partially covered by the superficial portion in front. It is concealed by the parotid gland behind. The fibers of both the deep and superficial portions are continuous at their insertion.
The masseter lifts the mandible and assists in protracting it. The nerve comes from the mandibular nerve. The name for this muscle means the chewer muscle.
The mentalis muscle
The mentalis muscle elevates and protrudes the lower lip and wrinkles the skin of the chin.
The nasalis muscle
The nasalis muscle depresses the cartilaginous part of the nose.
The occipital belly of epicranius muscle (the occipitalis muscle)
The occipital belly of epicranius muscle (also known as the occipitalis muscle) helps extend the scalp so that the eyebrows can come up and the forehead may wrinkle. This, along with the frontalis muscle is one of two parts, or bellies, of the epicranius. The epicranius is a musculofibrous layer that is wide and spreads across one entire side of the vertex of the skull, from the occipital bone to the eyebrow. The occipital belly is close to the occipital bone. This muscle takes on a thin, quadrilateral form and begins with tendinous fibers at the lateral two-thirds of the superior nuchal line of the occipital bone, and from the mastoid part of the temporal bone. The occipitalis ceases in the galea aponeurotica. The occipital belly exchanges information with the frontal belly by an intermediate tendon.
The omohyoid muscle
The omohyoid muscle (omohyoideus) depresses the hyoid bone.
The orbicularis oculi muscle
The orbicularis oculi muscle is a ringlike band of muscle, called a sphincter muscle, that surrounds the eye. It lies in the tissue of the eyelid and causes the eye to close or blink. At the same time, it compresses the nearby tear gland, or lacrimal gland, aiding the flow of tears over the surface of the eye. Contraction of the muscle also causes the appearance of folds or crow's feet that radiate out from the outer corner of the eye.
The orbicularis oris muscle
The orbicularis oris muscle is a sphincter muscle that encircles the mouth. It lies between the skin and the mucous membranes of the lips, extending upward to the nose and down to the region between the lower lip and chin. It is sometimes called the kissing muscle because it causes the lips to close and pucker.
The platysma muscle
The platysma muscle is a broad sheet of muscle arising from the pectoral (chest) and deltoid (shoulder) muscles and rises over the collarbone (clavicle), proceeding upward in a slanting manner along the sides of the neck. The muscle draws the lower lip and corner of the mouth sideways and down, partially opening the mouth, as in an expression of surprise or fright. When all the fibers work to their maximum, the platysma increases the diameter of the neck as well, as may be seen during the intensive breathing of a sprinting runner.
The risorius muscle
The risorius muscle draws the angle of the mouth outward and is commonly called the laughing muscle.
The scalene muscles
The scalene muscles are lateral vertebral muscles that begin at the first and second ribs and pass up into the sides of the neck. There are three of these muscles. (1) The scalenus anterior muscle, which, when the neck is fixed, elevates the first rib to aid in breathing; or when the rib is fixed, bends the neck forward and sideways and rotates it to the opposite side. (2) The scalenus medius is similar to the scalenus anterior and raises the first rib from above or bends to slightly rotate the neck from below. (3) The scalenus posterior raises the second rib or bends and slightly rotates the neck. This muscle may be absent or may extend to the third rib. When the scalene muscles are fixed from above, they elevate the first and second ribs to become respiratory muscles for breathing. Acting from below, they bend the spinal column to the same side or, if muscles act on both sides, the spinal column is slightly flexed.
The semispinalis capitis muscle
The semispinalis capitis muscle is a broad, sheet like muscle extending up from the vertebrae in the neck and thorax to the occipital bone. It functions to extend the head, bend it to one side, and rotate it.
The splenius capitis muscle
The splenius capitis muscle is a broad, strap like muscle located in the back of the neck. It connects the base of the skull to the vertebrae in the neck and upper thorax. When one muscle acts singly, it causes the head to rotate and bend toward one side; together, these muscles bring the head into an upright position.
The sternal head of the sternocleidomastoid muscle
The sternal head of the sternocleidomastoid muscle (also known as the sternocleidomastoideus), along with the clavicular head, assist one another to stretch the cervical portion of the spinal column and the head at the atlanto-occipital joint. It's part of a long neck muscle called the sternocleidomastoid that goes from the mastoid process at the mastoid bone to the sternum and clavicle. This muscle rotates the head and neck.
The sternal head comes from the upper part of the anterior surface of the manubrium sterni, and is instructed to flow up, laterally, and back. It is a rounded fasiculus that is fleshy in back and tendinous in front. This and the other head, the clavicular head originate separately at a triangular interval. They eventually come together a little lower than the middle of the neck. This muscle gets worked into the lateral half of the superior nuchal line of the occipital bone. This occurs when the two heads merge into a thick muscle that gets tucked in to the lateral surface of the mastoid process, from its apex to its superior border, and by a thin aponeurosis by way of a strong tendon.
The temporalis muscle
The temporalis muscle (or temporal muscle) is one of the mastication muscles; if you clench and unclench your jaw, you can see and feel it contracting at the temples on both sides of your head. It's attached to the mandible (jaw) and to the skull's temporal bone, or temporal fossa. The temporal fascia is a strong, fibrous investment that covers the temporal muscle. Contracting the temporalis muscle lifts the jaw, while the muscle's rear fibers (which are almost horizontal) cause the jaw to retract.
The zygomaticus major muscle
The zygomaticus major muscle is one of two zygomaticus muscles, the zygomaticus minor and zygomaticus major, which are two facial muscles that aid in articulation of the mouth, nose, and cheeks. The zygomaticus minor is a small bundle of muscle fibers lying in the area of the cheek. Together with two other muscle bundles, it forms the nasolabial furrow, from the side of the nose to the upper lip, which is deepened in expressions of sadness. The zygomaticus major is larger than the minor, but it also lies in the cheek area and extends down to the mouth. It draws the angle of the mouth upward and backward in laughing.
The zygomaticus minor muscle
The zygomaticus minor muscle is one of two zygomaticus muscles, the zygomaticus minor and zygomaticus major, which are two facial muscles that aid in articulation of the mouth, nose, and cheeks. The zygomaticus minor is a small bundle of muscle fibers lying in the area of the cheek. Together with two other muscle bundles, it forms the nasolabial furrow, from the side of the nose to the upper lip, which is deepened in expressions of sadness. The zygomaticus major is larger than the minor, but