The nasalis is a sphincter-like muscle of the nose whose function is to compress the nasal cartilages. It is the muscle responsible for "flaring" of the nostrils; some people can use it to close the nostrils to prevent entry of water. It consists of two parts and alar: The transverse part arises from the maxilla and lateral to the incisive fossa, it compresses the nostrils and may close them. The alar part arises from the maxilla over the lateral incisor and inserts into the greater alar cartilage, its medial fibres tend to blend with the depressor septi, has been described as part of that muscle. Like all the other muscles of facial expression, nasalis muscle is innervated by the seventh cranial nerve: the facial nerve. Interactive diagram at ivy-rose.co.uk
The occipitalis muscle is a muscle which covers parts of the skull. Some sources consider the occipital muscle to be a distinct muscle. However, Terminologia Anatomica classifies it as part of the occipitofrontalis muscle along with the frontalis muscle; the occipitalis muscle is quadrilateral in form. It arises from tendinous fibers from the lateral two-thirds of the superior nuchal line of the occipital bone and from the mastoid process of the temporal and ends in the epicranial aponeurosis; the occipitalis muscle is innervated by the facial nerve and its function is to move the scalp back. The muscles receives blood from the occipital artery. Occipitofrontalis muscle This article incorporates text in the public domain from page 379 of the 20th edition of Gray's Anatomy PTCentral
Levator labii superioris alaeque nasi muscle
The levator labii superioris alaeque nasi muscle is, translated from Latin, the "lifter of both the upper lip and of the wing of the nose". It has the longest name of any muscle in an animal; the muscle is attached to the upper frontal process of the maxilla and inserts into the skin of the lateral part of the nostril and upper lip. Known as Otto's muscle, it dilates the nostril and elevates the upper lip, enabling one to snarl. Elvis Presley is famous for his use of this expression, earning the muscle's nickname "The Elvis muscle". A mnemonic to remember its name is, "Little Ladies Snore All Night." Snore- because it is the labial elevator closest to the nose. The levator labii superioris alaeque nasi is sometimes referred to as the "angular head" of the levator labii superioris muscle. Levator labii superioris
Depressor septi nasi muscle
The depressor septi arises from the incisive fossa of the maxilla. Its fibers ascend to be inserted into the nasal septum and back part of the alar part of nasalis muscle, it lies between the mucous membrane and muscular structure of the lip. The depressor septi is a direct antagonist of the other muscles of the nose, drawing the ala of the nose downward, thereby constricting the aperture of the nares. Works like the alar part of the nasalis muscle; this article incorporates text in the public domain from page 382 of the 20th edition of Gray's Anatomy
In human anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is powerful in herbivores to facilitate chewing of plant matter; the most obvious muscle of mastication is the masseter muscle, since it is the most superficial and one of the strongest. The masseter is a thick, somewhat quadrilateral muscle, consisting of two heads and deep; the fibers of the two heads are continuous at their insertion. The superficial head, the larger, arises by a thick, tendinous aponeurosis from the temporal process of zygomatic bone, from the anterior two-thirds of the inferior border of the zygomatic arch, its fibers pass inferior and posterior, to be inserted into the angle of the mandible and inferior half of the lateral surface of the ramus of the mandible. The deep head is much bigger, more muscular in texture, it arises from the posterior third of the lower border and from the whole of the medial surface of the zygomatic arch. Its fibers pass downward and forward, to be inserted into the upper half of the ramus as high as the coronoid process of the mandible.
The deep head of the muscle is concealed, anteriorly, by the superficial portion. Posteriorly, it is covered by the parotid gland. Along with the other three muscles of mastication, the masseter is innervated by the anterior division of the mandibular division of the trigeminal nerve; the innervation pathway is: gyrus precentralis > genu capsula interna > nucleus motorius nervi trigemini > nervus trigeminus > nervus mandibularis > musculus masseter. The action of the muscle during bilateral contraction of the entire muscle is to elevate the mandible, raising the lower jaw. Elevation of the mandible occurs during the closing of the jaws; the masseter parallels the medial pterygoid muscle, but it is stronger and superficial fibres can cause protrusion. To perform an extraoral examination, stand near the patient and visually inspect and bilaterally palpate the muscle. Place the fingers of each hand over the muscle and ask the patient to clench his or her teeth several times; the masseter muscle can become enlarged in patients who habitually clench or grind their teeth and in those who chew gum.
This masseteric hypertrophy is soft. If the hypertrophy is bilateral, asymmetry of the face may still occur due to unequal enlargement of the muscles; this extraoral enlargement may be confused with parotid salivary gland disease, dental infections, maxillofacial neoplasms. However, no other signs are present except those involved in changes in occlusion intraorally such as pain, the enlargement corresponds with the outline of the muscle. Most patients seek medical attention because of comments about facial appearance, this situation may be associated with further pathology of the temporomandibular joint; the muscle undergoes spasm with malignant hyperthermia as do other skeletal muscles, but this one is noted, since it is on the face. Zygomasseteric system
The extraocular muscles are the six muscles that control movement of the eye and one muscle that controls eyelid elevation. The actions of the six muscles responsible for eye movement depend on the position of the eye at the time of muscle contraction. Since only a small part of the eye called the fovea provides sharp vision, the eye must move to follow a target. Eye movements must be fast; this is seen in scenarios like reading. Although under voluntary control, most eye movement is accomplished without conscious effort. How the integration between voluntary and involuntary control of the eye occurs is a subject of continuing research, it is known, that the vestibulo-ocular reflex plays an important role in the involuntary movement of the eye. Four of the extraocular muscles have their origin in the back of the orbit in a fibrous ring called the annulus of Zinn: the four rectus muscles; the four rectus muscles attach directly to the front half of the eye, are named after their straight paths. Note that medial and lateral are relative terms.
Medial indicates near the midline, lateral describes a position away from the midline. Thus, the medial rectus is the muscle closest to the nose; the superior and inferior recti do not pull straight back on the eye, because both muscles pull medially. This posterior medial angle causes the eye to roll with contraction of either the superior rectus or inferior rectus muscles; the extent of rolling in the recti is less than the oblique, opposite from it. The superior oblique muscle originates at the back of the orbit, getting rounder as it courses forward to a rigid, cartilaginous pulley, called the trochlea, on the upper, nasal wall of the orbit; the muscle becomes tendinous about 10mm before it passes through the pulley, turning across the orbit, inserts on the lateral, posterior part of the globe. Thus, the superior oblique travels posteriorly for the last part of its path, going over the top of the eye. Due to its unique path, the superior oblique, when activated, pulls the eye laterally; the last muscle is the inferior oblique, which originates at the lower front of the nasal orbital wall, passes under the LR to insert on the lateral, posterior part of the globe.
Thus, the inferior oblique pulls the eye laterally. The movements of the extraocular muscles take place under the influence of a system of extraocular muscle pulleys, soft tissue pulleys in the orbit; the extraocular muscle pulley system is fundamental to the movement of the eye muscles, in particular to ensure conformity to Listing's law. Certain diseases of the pulleys cause particular patterns of incomitant strabismus. Defective pulley functions can be improved by surgical interventions; the extraocular muscles are supplied by branches of the ophthalmic artery. This is done either directly or indirectly, as in the lateral rectus muscle, via the lacrimal artery, a main branch of the ophthalmic artery. Additional branches of the ophthalmic artery include the ciliary arteries, which branch into the anterior ciliary arteries; each rectus muscle receives blood from two anterior ciliary arteries, except for the lateral rectus muscle, which receives blood from only one. The exact number and arrangement of these cilary arteries may vary.
Branches of the infraorbital artery supply inferior oblique muscles. The nuclei or bodies of these nerves are found in the brain stem; the nuclei of the abducens and oculomotor nerves are connected. This is important in coordinating the motion of the lateral rectus in one eye and the medial action on the other. In one eye, in two antagonistic muscles, like the lateral and medial recti, contraction of one leads to inhibition of the other. Muscles show small degrees of activity when resting, keeping the muscles taut; this "tonic" activity is brought on by discharges of the motor nerve to the muscle. The extraocular muscles develop along with the fatty tissue of the eye socket. There are three centers of growth that are important in the development of the eye, each is associated with a nerve. Hence the subsequent nerve supply of the eye muscles is from three cranial nerves; the development of the extraocular muscles is dependent on the normal development of the eye socket, while the formation of the ligament is independent.
Below is a table of each of the extraocular muscles and their innervation and insertions, the primary actions of the muscles. Intermediate directions are controlled by simultaneous actions of multiple muscles; when one shifts the gaze horizontally, one eye will move laterally and the other will move medially. This may be neurally coordinated by the central nervous system, to make the eyes move together and involuntarily; this is a key factor in the study of strabismus, the inability of the eyes to be directed to one point. There are two main kinds of movement: disjunctive; the former is typical when shifting gaze right or left, the latter is convergence of the two eyes on a near object. Disjunction can be performed voluntarily, but is triggered by the nearness of the target object. A "see-saw" movement, one eye looking up and the other down, is possible, but not voluntarily. To avoi
Superior rectus muscle
The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles, it is innervated by the superior division of the oculomotor nerve. In the primary position, the superior rectus muscle's primary function is elevation, although it contributes to intorsion and adduction, it elevates and helps intort the eye. The superior rectus muscle is the only muscle, capable of elevating the eye when it is in a abducted position. Anatomy figure: 29:01-02 at Human Anatomy Online, SUNY Downstate Medical Center "Diagram". Archived from the original on March 25, 2010