The Sternothyroideus is a muscle in the neck. It is wider than the sternohyoideus, beneath which it is situated, it arises from the posterior surface of the manubrium sterni, below the origin of the sternohyoideus, from the edge of the cartilage of the first rib, sometimes that of the second rib, it is inserted into the oblique line on the lamina of the thyroid cartilage. This muscle is in close contact with its fellow at the lower part of the neck, but diverges somewhat as it ascends. Doubling; this article incorporates text in the public domain from page 393 of the 20th edition of Gray's Anatomy Photo of model at Waynesburg College musclehead/sternothyroid Anatomy photo:25:03-0105 at the SUNY Downstate Medical Center - "The Muscular triangle" PTCentral
Rectus capitis posterior minor muscle
The rectus capitis posterior minor arises by a narrow pointed tendon from the tubercle on the posterior arch of the atlas, widening as it ascends, is inserted into the medial part of the inferior nuchal line of the occipital bone and the surface between it and the foramen magnum, takes some attachment to the spinal dura mater. The synergists are the rectus. Connective tissue bridges were noted at the atlanto-occipital joint between the rectus capitis posterior minor muscle and the dorsal spinal dura. Similar connective tissue connections of the rectus capitis posterior major have been reported as well; the perpendicular arrangement of these fibers appears to restrict dural movement toward the spinal cord. The ligamentum nuchae was found to be continuous with the posterior cervical spinal dura and the lateral portion of the occipital bone. Anatomic structures innervated by cervical nerves C1-C3 have the potential to cause headache pain. Included are the joint complexes of the upper three cervical segments, the dura mater, spinal cord.
The dura-muscular, dura-ligamentous connections in the upper cervical spine and occipital areas may provide anatomic and physiologic answers to the cause of the cervicogenic headache. This proposal would further explain manipulation's efficacy in the treatment of cervicogenic headache. Atlanto-occipital joint Rectus capitis lateralis Rectus capitis posterior major muscle Rectus capitis anterior muscle This article incorporates text in the public domain from page 401 of the 20th edition of Gray's Anatomy Anatomy figure: 01:07-01 at Human Anatomy Online, SUNY Downstate Medical Center Anatomy photo:01:10-0101 at the SUNY Downstate Medical Center PTCentral
The sternocleidomastoid muscle is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck; the sternocleidomastoid is innervated by the accessory nerve. It is given the name sternocleidomastoid because it originates at the manubrium of the sternum and the clavicle, has an insertion at the mastoid process of the temporal bone of the skull; the sternocleidomastoid muscle originates from two locations: the manubrium of the sternum and the clavicle. It travels obliquely across the side of the neck and inserts at the mastoid process of the temporal bone of the skull; the sternocleidomastoid is thick and narrow at its centre, broader and thinner at either end. The sternal head is a round fasciculus, tendinous in front, fleshy behind, arising from the upper part of the front of the manubrium sterni, it travels superiorly and posteriorly. The clavicular head is composed of fleshy and aponeurotic fibers, arises from the upper, frontal surface of the medial third of the clavicle.
The two heads are separated from one another at their origins by a triangular interval but blend, below the middle of the neck, into a thick, rounded muscle, inserted, by a strong tendon, into the lateral surface of the mastoid process, from its apex to its superior border, by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone. The sternocleidomastoid is innervated by the accessory nerve of the same side, it supplies only motor fibres. The cervical plexus supplies sensation, including proprioception, from the ventral primary rami of C2 and C3; the clavicular origin of the sternocleidomastoid varies greatly: in some cases the clavicular head may be as narrow as the sternal. When the clavicular origin is broad, it is subdivided into several slips, separated by narrow intervals. More the adjoining margins of the sternocleidomastoid and trapezius are in contact; this would leave no posterior triangle. The supraclavicularis muscle arises from the manubrium behind the sternocleidomastoid and passes behind the sternocleidomastoid to the upper surface of the clavicle.
The function of this muscle is to obliquely rotate the head. It flexes the neck; when both sides of the muscle act together, it extends the head. When one side acts alone, it causes the head to rotate to the opposite side and flexes laterally to the same side, it acts as an accessory muscle of respiration, along with the scalene muscles of the neck. The signaling process to contract or relax the sternocleidomastoid begins in Cranial Nerve XI, the accessory nerve; the accessory nerve nucleus is in the anterior horn of the spinal cord around C1-C3, where lower motor neuron fibers mark its origin. The fibers from the accessory nerve nucleus travel upward to enter the cranium via the foramen magnum; the internal carotid artery to reach the trapezius. After a signal reaches the accessory nerve nucleus in the anterior horn of the spinal cord, the signal is conveyed to motor endplates on the muscle fibers located at the clavicle. Acetylcholine is released from vesicles and is sent over the synaptic cleft to receptors on the postsynaptic bulb.
The ACH causes the resting potential to increase above -55mV, thus initiating an action potential which travels along the muscle fiber. Along the muscle fibers are t-tubule openings which facilitate the spread of the action potential into the muscle fibers; the t-tubule meets with the sarcoplasmic reticulum at locations throughout the muscle fiber, at these locations the sarcoplasmic reticulum releases calcium ions that results in the movement of troponin and tropomyosin on thin filaments. The movement of troponin and tropomyosin is key in facilitating the myosin head to move along the thin filament, resulting in a contraction of the sternocleidomastoid muscle; the sternocleidomastoid is within the investing fascia of the neck, along with the trapezius muscle, with which it shares its nerve supply. It is thick and thus serves as a primary landmark of the neck, as it divides the neck into anterior and posterior cervical triangles which helps define the location of structures, such as the lymph nodes for the head and neck.
Many important structures relate to the sternocleidomastoid, including the common carotid artery, accessory nerve, brachial plexus. Examination of the sternocleidomastoid muscle forms part of the examination of the cranial nerves, it can be felt on each side of the neck. The triangle formed by the clavicle and the sternal and clavicular heads of the sternocleidomastoid muscle is used as a landmark in identifying the correct location for central venous catheterization. Contraction of the muscle gives rise to a condition called torticollis or wry neck, this can have a number of causes. Torticollis gives the appearance of a tilted head on the side involved. Treatment involves physiotherapy exercises to stretch the involved muscle and strengthen the muscle on the opposite side of the neck. Congenital torticollis can have an unknown cause or result from birth trauma that gives rise to a mass or tumor that can be palpated within the muscle, it is given the name sternocleidomastoid because it originates at the manubrium of the sternum and the clavicle, has an insertion at the mastoid process of the temporal bone of the skull.
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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
Basilar part of occipital bone
The basilar part of the occipital bone extends forward and upward from the foramen magnum, presents in front an area more or less quadrilateral in outline. In the young skull this area is rough and uneven, is joined to the body of the sphenoid by a plate of cartilage. By the twenty-fifth year this cartilaginous plate is ossified, the occipital and sphenoid form a continuous bone. On its lower surface, about 1 cm. in front of the foramen magnum, is the pharyngeal tubercle which gives attachment to the fibrous raphe of the pharynx. On either side of the middle line the longus capitis and rectus capitis anterior are inserted, in front of the foramen magnum the anterior atlantooccipital membrane is attached; the upper surface, constitutes the lower half of clivus, presents a broad, shallow groove which inclines upward and forward from the foramen magnum. This article incorporates text in the public domain from page 132 of the 20th edition of Gray's Anatomy Anatomy photo:22:os-0913 at the SUNY Downstate Medical Center
Middle pharyngeal constrictor muscle
The middle pharyngeal constrictor is a fan-shaped muscle located in the neck. It is one of three pharyngeal constrictors. To the superior and inferior pharyngeal constrictor muscles, the middle pharyngeal constrictor is innervated by a branch of the vagus nerve through the pharyngeal plexus; the middle pharyngeal constrictor is smaller than the inferior pharyngeal constrictor muscle. The middle pharyngeal constrictor arises from the whole length of the upper border of the greater cornu of the hyoid bone, from the lesser cornu, from the stylohyoid ligament; the fibers diverge from their origin: the lower ones descend beneath the constrictor inferior, the middle fibers pass transversely, the upper fibers ascend and overlap the constrictor superior. It is inserted into the posterior median fibrous raphe, blending in the middle line with the muscle of the opposite side; as soon as the bolus of food is received in the pharynx, the elevator muscles relax, the pharynx descends, the constrictors contract upon the bolus, convey it downward into the esophagus.
They have respiratory mechanical effects. This article incorporates text in the public domain from page 1143 of the 20th edition of Gray's Anatomy Its role in speech: Hamaker, Ronald C.. "Botulinum Neurotoxin for Pharyngeal Constrictor Muscle Spasm in Tracheoesophageal Voice Restoration". The Laryngoscope. 113: 1479–1482. Doi:10.1097/00005537-200309000-00010. ISSN 0023-852X, its role in Hyoid bone syndrome: Ernest, Edwin A.. "Hyoid bone syndrome: A degenerative injury of the middle pharyngeal constrictor muscle with photomicroscopic evidence of insertion tendinosis". The Journal of Prosthetic Dentistry. 66: 78–83. Doi:10.1016/0022-391390357-3. ISSN 0022-3913. Lesson8 at The Anatomy Lesson by Wesley Norman
Obliquus capitis inferior muscle
The obliquus capitis inferior muscle is the larger of the two oblique muscles of the neck. It arises from the apex of the spinous process of the axis and passes laterally and upward, to be inserted into the lower and back part of the transverse process of the atlas, it lies deep to the semispinalis trapezius muscles. The muscle is responsible for rotation of first cervical vertebra, it forms the lower boundary of the suboccipital triangle of the neck. The naming of this muscle may be confusing, as it is the only capitis muscle that does NOT attach to the cranium; the obliquus capitis inferior muscle, like the other suboccipital muscles, has an important role in proprioception. This muscle has a high density of Golgi organs and muscle spindles which accounts for this, it is believed that proprioception may be the primary role of the inferior oblique allowing accurate positioning of the head on the neck. This article incorporates text in the public domain from page 402 of the 20th edition of Gray's Anatomy