Superior orbital fissure
The superior orbital fissure is a foramen in the skull, although it is more of a cleft, lying between the lesser and greater wings of the sphenoid bone. A number of important anatomical structures pass through the fissure, these can be damaged in orbital trauma blowout fractures through the floor of the orbit into the maxillary sinus; these structures are: superior and inferior divisions of oculomotor nerve trochlear nerve lacrimal and nasociliary branches of ophthalmic. Abducens nerve inferior divisions of ophthalmic vein. Inferior division passes through the inferior orbital fissure. Sympathetic fibers from cavernous plexusThese include nonvisual sensory messages, such as pain, or motor nerves, they serve as vascular connections. The nerves passing through the fissure can be remembered with the mnemonic, "Live Frankly To See Absolutely No Insult" - for Lacrimal and Frontal divisions of the ophthalmic nerve, Trochlear nerve, Superior division of the oculomotor nerve, Abducens nerve, Nasociliary branch of the ophthalmic nerve and Inferior Division of the oculomotor nerve.
It is divided into 3 parts from lateral to medial: Lateral part transmits: superior ophthalmic vein, lacrimal nerve, frontal nerve, trochlear nerve, recurrent meningeal branch of lacrimal artery Middle part transmits: Superior and inferior divisions of the oculomotor nerve, nasociliary nerve and abducent nerve Medial part transmits: Inferior ophthalmic veins and sympathetic nerves arising from the plexus that accompanies the internal carotid artery The abducens nerve is most to show signs of damage first, with the most common complaints retro-orbital pain and the involvement of cranial nerves III, IV, V1, VI without other neurological signs or symptoms. This presentation indicates either compression of structures in the superior orbital fissure or the cavernous sinus. Superior orbital fissure syndrome known as Rochon-Duvigneaud's syndrome, is a neurological disorder that results if the superior orbital fissure is fractured. Involvement of the cranial nerves that pass through the superior orbital fissure may lead to diplopia, paralysis of extraocular muscles and ptosis.
Blindness or loss of vision indicates involvement of the orbital apex, more serious, requiring urgent surgical intervention. If blindness is present with superior orbital syndrome, it is called orbital apex syndrome. Foramina of skull Inferior orbital fissure Anatomy figure: 22:02-04 at Human Anatomy Online, SUNY Downstate Medical Center lesson3 at The Anatomy Lesson by Wesley Norman
Levator palpebrae superioris muscle
The levator palpebrae superioris is the muscle in the orbit that elevates the superior eyelid. The levator palpebrae superioris originates on the lesser wing of the sphenoid bone, just above the optic foramen, it decreases in thickness and becomes the levator aponeurosis. This portion inserts on the skin of the upper eyelid, as well as the superior tarsal plate, it is a skeletal muscle. The superior tarsal muscle, a smooth muscle, is attached to the levator palpebrae superioris, inserts on the superior tarsal plate as well; as with most of the muscles of the orbit, the levator palpebrae receives somatic motor input from the ipsilateral superior division of the oculomotor nerve. An adjoining smooth muscle, the superior tarsal muscle, confused to be a portion of the levator palpebrae superioris, is only attached, it is separately innervated by sympathetic fibers that originate in the cervical spinal cord; the levator palpebrae superioris muscle retracts the upper eyelid. Damage to this muscle or its innervation can cause ptosis, drooping of the eyelid.
Lesions in CN III can cause ptosis, because without stimulation from the oculomotor nerve the levator palpebrae cannot oppose the force of gravity, the eyelid droops. Ptosis can result from damage to the adjoining superior tarsal muscle or its sympathetic innervation; such damage to the sympathetic supply presents as a partial ptosis. It is important to distinguish between these two different causes of ptosis; this can be done clinically without issue, as each type of ptosis is accompanied by other distinct clinical findings. Blepharospasm Ptosis Superior tarsal muscle Anatomy figure: 29:01-01 at Human Anatomy Online, SUNY Downstate Medical Center lesson3 at The Anatomy Lesson by Wesley Norman
Inferior rectus muscle
The inferior 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 oculomotor nerve, it depresses and helps extort the eye. The inferior rectus muscle is the only muscle, capable of depressing the pupil when it is in a abducted position. Anatomy figure: 29:01-07 at Human Anatomy Online, SUNY Downstate Medical Center lesson3 at The Anatomy Lesson by Wesley Norman Diagram at mun.ca
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
Zonule of Zinn
The zonule of Zinn is a ring of fibrous strands forming a zonule that connects the ciliary body with the crystalline lens of the eye. These fibers are sometimes collectively referred to as the suspensory ligaments of the lens, as they act like suspensory ligaments; the ciliary epithelial cells of the eye synthesize portions of the zonules. The zonule of Zinn is split into two layers: a thin layer, which lines the hyaloid fossa, a thicker layer, a collection of zonular fibers. Together, the fibers are known as the suspensory ligament of the lens; the zonules are about 1–2 μm in diameter. The zonules attach to the lens capsule 2mm anterior and 1 mm posterior to the equator, arise from the pars plana region of the ciliary epithelium and pass forward related to the lateral surfaces of the ciliary process of the pars plicata; when colour granules are displaced from the Zonules of Zinn, the irises fade. In some cases those colour lead to Glaucoma Pigmentosa; the zonules are made of fibrillin, a connective tissue protein.
Mutations in the fibrillin gene lead to the condition Marfan syndrome, consequences include an increased risk of lens dislocation. The zonules of Zinn are difficult to visualize using a slit lamp, but may be seen with exceptional dilation of the pupil, or if a coloboma of the iris or a subluxation of the lens is present; the number of zonules present in a person appears to decrease with age. The zonules insert around the outer margin of both anteriorly and posteriorly; this article incorporates text in the public domain from page 1018 of the 20th edition of Gray's Anatomy Diagram at unmc.edu Diagram at eye-surgery-uk.com Diagram and overview at webschoolsolutions.com Histology image: 08011loa – Histology Learning System at Boston University
Anatomical terminology is a form of scientific terminology used by anatomists and health professionals such as doctors. Anatomical terminology uses many unique terms and prefixes deriving from Ancient Greek and Latin; these terms can be confusing to those unfamiliar with them, but can be more precise, reducing ambiguity and errors. Since these anatomical terms are not used in everyday conversation, their meanings are less to change, less to be misinterpreted. To illustrate how inexact day-to-day language can be: a scar "above the wrist" could be located on the forearm two or three inches away from the hand or at the base of the hand. By using precise anatomical terminology such ambiguity is eliminated. An international standard for anatomical terminology, Terminologia Anatomica has been created. Anatomical terminology has quite regular morphology, the same prefixes and suffixes are used to add meanings to different roots; the root of a term refers to an organ or tissue. For example, the Latin names of structures such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for "two-headed", brachii as in the brachial region of the arm.
The first word describes what is being spoken about, the second describes it, the third points to location. When describing the position of anatomical structures, structures may be described according to the anatomical landmark they are near; these landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, such as the midclavicular line from the centre of the clavicle. The cephalon or cephalic region refers to the head; this area is further differentiated into the cranium, frons, auris, nasus and mentum. The neck area is called cervical region. Examples of structures named according to this include the frontalis muscle, submental lymph nodes, buccal membrane and orbicularis oculi muscle. Sometimes, unique terminology is used to reduce confusion in different parts of the body. For example, different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals. Here, Rostral refers to proximity to the front of the nose, is used when describing the skull.
Different terminology is used in the arms, in part to reduce ambiguity as to what the "front", "back", "inner" and "outer" surfaces are. For this reason, the terms below are used: Radial referring to the radius bone, seen laterally in the standard anatomical position. Ulnar referring to the ulna bone, medially positioned when in the standard anatomical position. Other terms are used to describe the movement and actions of the hands and feet, other structures such as the eye. International morphological terminology is used by the colleges of medicine and dentistry and other areas of the health sciences, it facilitates communication and exchanges between scientists from different countries of the world and it is used daily in the fields of research and medical care. The international morphological terminology refers to morphological sciences as a biological sciences' branch. In this field, the form and structure are examined as well as the changes or developments in the organism, it is functional.
It covers the gross anatomy and the microscopic of living beings. It involves the anatomy of the adult, it includes comparative anatomy between different species. The vocabulary is extensive and complex, requires a systematic presentation. Within the international field, a group of experts reviews and discusses the morphological terms of the structures of the human body, forming today's Terminology Committee from the International Federation of Associations of Anatomists, it deals with the anatomical and embryologic terminology. In the Latin American field, there are meetings called Iberian Latin American Symposium Terminology, where a group of experts of the Pan American Association of Anatomy that speak Spanish and Portuguese and studies the international morphological terminology; the current international standard for human anatomical terminology is based on the Terminologia Anatomica. It was developed by the Federative Committee on Anatomical Terminology and the International Federation of Associations of Anatomists and was released in 1998.
It supersedes Nomina Anatomica. Terminologia Anatomica contains terminology for about 7500 human gross anatomical structures. For microanatomy, known as histology, a similar standard exists in Terminologia Histologica, for embryology, the study of development, a standard exists in Terminologia Embryologica; these standards specify accepted names that can be used to refer to histological and embryological structures in journal articles and other areas. As of September 2016, two sections of the Terminologia Anatomica, including central nervous system and peripheral nervous system, were merged to form the Terminologia Neuroanatomica; the Terminologia Anatomica has been perceived with a considerable criticism regarding its content including coverage and spelling mistakes and errors. Anatomical terminology is chosen to highlight the relative location of body structures. For instance, an anatomist might describe one band of tissue as "inferior to" another or a physician might describe a tumor as "superficial to" a deeper body structure.
Anatomical terms used to describe location
The ciliary muscle is a ring of smooth muscle in the eye's middle layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It changes the shape of the lens within the eye, not the size of the pupil, carried out by the sphincter pupillae muscle and dilator pupillae; the ciliary muscle develops from mesenchyme within the choroid and is considered a cranial neural crest derivative. The ciliary muscle receives parasympathetic fibers from the short ciliary nerves that arise from the ciliary ganglion; the sympathetic postganglionic fibers are part of cranial nerve V1, while presynaptic parasympathetic fibers to the ciliary ganglia are from the oculomotor nerve. The postganglionic sympathetic innervation arises from the superior cervical ganglia. Presynaptic parasympathetic signals that originate in the Edinger-Westphal nucleus are carried by cranial nerve III and travel through the ciliary ganglion via the postganglionic parasympathetics fibers which travel in the short ciliary nerves and supply the ciliary body and iris.
Parasympathetic activation of the M3 muscarinic receptors causes ciliary muscle contraction, the effect of contraction is to decrease the diameter of the ring of ciliary muscle. The zonule fibers relax and the lens becomes more spherical, increasing its power to refract light for near vision; the parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book. The ciliary fibers have circular and radial orientations. According to Hermann von Helmholtz's theory, the circular ciliary muscle fibers affect zonular fibers in the eye, enabling changes in lens shape for light focusing; when the ciliary muscle contracts, it pulls itself forward and moves the frontal region toward the axis of the eye. This releases the tension on the lens caused by the zonular fibers; this release of tension of the zonular fibers causes the lens to become more spherical, adapting to short range focus. Conversely, relaxation of the ciliary muscle causes the zonular fibers to become taut, flattening the lens, increasing the focal distance, increasing long range focus.
Although Helmholtz's theory has been accepted since 1855, its mechanism still remains controversial. Alternative theories of accommodation have been proposed by others, including L. Johnson, M. Tscherning, Ronald A. Schachar. Contraction and relaxation of the longitudinal fibers, which insert into the trabecular meshwork in the anterior chamber of the eye, cause an increase and decrease in the meshwork pore size facilitating and impeding aqueous humour flow into the canal of Schlemm. Open-angle glaucoma and closed-angle glaucoma may be treated by muscarinic receptor agonists, which cause rapid miosis and contraction of the ciliary muscles, opening the trabecular meshwork, facilitating drainage of the aqueous humour into the canal of Schlemm and decreasing intraocular pressure; the word ciliary had its origins around 1685–1695. The term cilia originated a few years in 1705–1715, is the Neo-Latin plural of cilium meaning eyelash. In Latin, cilia means upper eyelid and is a back formation from supercilium, meaning eyebrow.
The suffix -ary occurred in loanwords from Middle English, Old French, Latin. Taken together, cili-ary pertains to various anatomical structures in and around the eye, namely the ciliary body and annular suspension of the lens of the eye. Accommodation reflex Ciliary body Cycloplegia Presbyopia Lens, zonule fibers, ciliary muscles—SEM