Orbicularis oris muscle
In human anatomy, the orbicularis oris muscle is a complex of muscles in the lips that encircles the mouth. Until it was misinterpreted as a sphincter, or circular muscle, but it is composed of four independent quadrants that interlace and give only an appearance of circularity, it is one of the muscles used in the playing of all brass instruments and some woodwind instruments. This muscle puckers the lips when it contracts; the orbicularis oris is not a simple sphincter muscle like the orbicularis oculi. It consists of fibers derived from the other facial muscles which are inserted into the lips, of fibers proper to the lips. Of the former, a considerable number are derived from the buccinator and form the deeper stratum of the orbicularis; some of the buccinator fibers—namely, those near the middle of the muscle—decussate at the angle of the mouth, those arising from the maxilla passing to the lower lip, those from the mandible to the upper lip. The uppermost and lowermost fibers of the buccinator pass across the lips from side to side without decussation.
Superficial to this stratum is a second, formed on either side by the caninus and triangularis, which cross each other at the angle of the mouth. In addition to these, fibers from the quadratus labii superioris, the zygomaticus, the quadratus labii inferioris intermingle with the transverse fibers above described, have principally an oblique direction; the proper fibers of the lips are oblique, pass from the under surface of the skin to the mucous membrane, through the thickness of the lip. Fibers occur by which the muscle is connected with the maxillæ and the septum of the nose above and with the mandible below. In the upper lip, these consist of two bands and medial, on either side of the middle line; the interval between the two medial bands corresponds with the depression, called the philtrum, seen on the lip beneath the septum of the nose. The additional fibers for the lower lip constitute a slip m. incisivus labii inferioris on either side of the middle line. Babies are born without one or both sides of this particular muscle, resulting in a slight droop to the affected side of the face.
This article incorporates text in the public domain from page 384 of the 20th edition of Gray's Anatomy Anatomy figure: 23:02-03 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. Facial Muscles - BBC Picture of the circular-shaped muscle Facial Muscles - BBC Animation of movements of the muscle
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
Medial rectus muscle
The medial rectus muscle is a muscle in the orbit. As with most of the muscles of the orbit, it is innervated by the inferior division of the oculomotor nerve; this muscle shares an origin with several other extrinsic eye muscles, the anulus tendineus, or common tendon. It is stronger than the other orbital recti muscles. Anatomy figure: 29:01-06 at Human Anatomy Online, SUNY Downstate Medical Center lesson3 at The Anatomy Lesson by Wesley Norman Diagram at howstuffworks.com
Dilator naris muscle
The dilator naris muscle is a part of the nasalis muscle. It is divided into anterior parts; the dilator naris posterior is placed beneath the levator labii superioris. It arises from the margin of the nasal notch of the maxilla, from the lesser alar cartilages, is inserted into the skin near the margin of the nostril; the dilator naris anterior is a delicate fasciculus, passing from the greater alar cartilage to the integument near the margin of the nostril. This article incorporates text in the public domain from page 382 of the 20th edition of Gray's Anatomy Mann DG, Sasaki CT, Fukuda H, Mann DG, Suzuki M, Hernandez JR. "Dilator naris muscle". Ann. Otol. Rhinol. Laryngol. 86: 362–70. PMID 869439
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
Levator labii superioris
The levator labii superioris is a muscle of the human body used in facial expression. It is a broad sheet, its medial fibers form the angular head which arises by a pointed extremity from the upper part of the frontal process of the maxilla and passing obliquely downward and lateralward divides into two slips. One of these is inserted into skin of the nose; the intermediate portion or infraorbital head arises from the lower margin of the orbit above the infraorbital foramen, some of its fibers being attached to the maxilla, others to the zygomatic bone. Its fibers converge, to be inserted into the muscular substance of the upper lip between the angular head and the levator anguli oris; the lateral fibers, forming the zygomatic head arise from the malar surface of the zygomatic bone behind the zygomaticomaxillary suture and pass downward and medialward to the upper lip. Its main function is to elevate upper lip. Levator labii superioris alaeque nasi This article incorporates text in the public domain from page 383 of the 20th edition of Gray's Anatomy PTCentral
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