Inferior oblique muscle
The inferior oblique muscle or obliquus oculi inferior is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. The inferior oblique is an extraocular muscle, is attached to the maxillary bone and the posterior, lateral surface of the eye; the inferior oblique is innervated by the inferior branch of the oculomotor nerve. The inferior oblique arises from the orbital surface of the maxilla, lateral to the lacrimal groove. Unlike the other extraocular muscles, the inferior oblique muscle does not originate from the common tendinous ring. Passing lateralward and upward, between the inferior rectus and the floor of the orbit, just underneath the lateral rectus muscle, the inferior oblique inserts onto the scleral surface between the inferior rectus and lateral rectus. In humans, the muscle is about 35 mm long; the inferior oblique is innervated by the inferior division of the oculomotor nerve. Its actions are extorsion and abduction of the eye. Primary action is extorsion.
The field of maximal inferior oblique elevation is in the adducted position. The inferior oblique muscle is the only muscle, capable of elevating the eye when it is in a adducted position. While affected by palsies of the inferior division of the oculomotor nerve, isolated palsies of the inferior oblique are quite rare. "Overaction" of the inferior oblique muscle is a observed component of childhood strabismus infantile esotropia and exotropia. Because true hyperinnervation is not present, this phenomenon is better termed "elevation in adduction". Surgical procedures of the inferior oblique include: loosening, marginal myotomy, denervation and extirpation, it is encountered and identified in lower lid blepharoplasty surgeries. This article incorporates text in the public domain from page 1023 of the 20th edition of Gray's Anatomy Anatomy figure: 29:01-08 at Human Anatomy Online, SUNY Downstate Medical Center lesson3 at The Anatomy Lesson by Wesley Norman Image at childrenshospital.org
Superior tarsal muscle
The superior tarsal muscle is a smooth muscle adjoining the levator palpebrae superioris muscle that helps to raise the upper eyelid. The superior tarsal muscle originates on the underside of levator palpebrae superioris and inserts on the superior tarsal plate of the eyelid; the superior tarsal muscle receives its innervation from the sympathetic nervous system. Postganglionic sympathetic fibers originate in the superior cervical ganglion, travel via the internal carotid plexus, where small branches communicate with the oculomotor nerve as it passes through the cavernous sinus; the sympathetic fibres continue to the superior division of the oculomotor nerve, where they enter the superior tarsal muscle on its inferior aspect. The superior tarsal muscle works to keep the upper eyelid raised after the levator palpebrae superioris has raised the upper eyelid. Damage to some elements of the sympathetic nervous system can inhibit this muscle, causing a drooping eyelid; this is seen in Horner's syndrome.
The ptosis seen in Horner's syndrome is of a lesser degree than is seen with an oculomotor nerve palsy. The muscle derives its name from Greek ταρσός, meaning'flat surface' used for drying; the term Müller's muscle is sometimes used as a synonym. However, the same term is used for the circular fibres of the ciliary muscle, for the orbitalis muscle that covers the inferior orbital fissure. Given the possible confusion, the use of the term Müller's muscle should be discouraged unless the context removes any ambiguity. Heinrich Müller
In human anatomy, the head is at the top of the human body. It is maintained by the skull, which itself encloses the brain; the human head consists of a fleshy outer portion. The brain is enclosed within the skull; the head rests on the neck, the seven cervical vertebrae support it. The human head weighs between 5 and 11 pounds The face is the anterior part of the head, containing the eyes and mouth. On either side of the mouth, the cheeks provide a fleshy border to the oral cavity; the ears sit to either side of the head. The head receives blood supply through the external carotid arteries; these supply the area outside of the inside of the skull. The area inside the skull receives blood supply from the vertebral arteries, which travel up through the cervical vertebrae; the twelve pairs of cranial nerves provide the majority of nervous control to the head. The sensation to the face is provided by the branches of the trigeminal nerve, the fifth cranial nerve. Sensation to other portions of the head is provided by the cervical nerves.
Modern texts are in agreement about which areas of the skin are served by which nerves, but there are minor variations in some of the details. The borders designated by diagrams in the 1918 edition of Gray's Anatomy are similar but not identical to those accepted today; the cutaneous innervation of the head is as follows: Ophthalmic nerve Maxillary nerve Mandibular nerve Cervical plexus Dorsal rami of cervical nerves and others are in picture which show following in upper column The head contains sensory organs: two eyes, two ears, a nose and tongue inside of the mouth. It houses the brain. Together, these organs function as a processing center for the body by relaying sensory information to the brain. Humans can process information faster by having this central nerve cluster. For humans, the front of the head is the main distinguishing feature between different people due to its discernible features, such as eye and hair colors, shapes of the sensory organs, the wrinkles. Humans differentiate between faces because of the brain's predisposition toward facial recognition.
When observing a unfamiliar species, all faces seem nearly identical. Human infants are biologically programmed to recognize subtle differences in anthropomorphic facial features. People who have greater than average intelligence are sometimes depicted in cartoons as having bigger heads as a way of notionally indicating that they have a "larger brain". Additionally, in science fiction, an extraterrestrial having a big head is symbolic of high intelligence. Despite this depiction, advances in neurobiology have shown that the functional diversity of the brain means that a difference in overall brain size is only to moderately correlated to differences in overall intelligence between two humans; the head is a source for many metaphors and metonymies in human language, including referring to things near the human head, things physically similar to the way a head is arranged spatially to a body and things that represent some characteristics associated with the head, such as intelligence. Ancient Greeks had a method for evaluating sexual attractiveness based on the Golden ratio, part of which included measurements of the head.
Headpieces can signify status, religious/spiritual beliefs, social grouping, team affiliation, occupation, or fashion choices. In many cultures, covering the head is seen as a sign of respect; some or all of the head must be covered and veiled when entering holy places or places of prayer. For many centuries, women in Europe, the Middle East, South Asia have covered their hair as a sign of modesty; this trend has changed drastically in Europe in the 20th century, although is still observed in other parts of the world. In addition, a number of religions require men to wear specific head clothing—such as the Islamic Taqiyah, Jewish yarmulke, or the Sikh turban; the same goes for Christian nun's habit. A hat is a head covering. Hats may be worn as part of a uniform or used as a protective device, such as a hard hat, a covering for warmth, or a fashion accessory. Hats can be indicative of social status in some areas of the world. While numerous charts detailing head sizes in infants and children exist, most do not measure average head circumference past the age of 21.
Reference charts for adult head circumference generally feature homogeneous samples and fail to take height and weight into account. One study in the United States estimated the average human head circumference to be 55 centimetres in females and 57 centimetres in males. A British study by Newcastle University showed an average size of 55.2 cm for females and 57.2 cm for males with average size varying proportionally with height Macrocephaly can be an indicator of increased risk for some types of cancer in individuals who carry the genetic mutation that causes Cowden syndrome. For adults, this refers to head sizes greater than 58 centimeters in men or greater than 57 centimeters in women. Human body Head and neck anatomy 8. Human head Campbell, Bernard Grant. Human Evolution: An Introduction to Man's Adaptations, 4th edition
Lateral rectus muscle
The lateral rectus muscle is a muscle on the lateral side of the eyeball in the orbit. It is one of six extraocular muscles; the lateral rectus muscle is responsible for lateral movement of the eyeball abduction. Abduction describes the movement of the eye away from the midline, allowing the eyeball to move horizontally in the lateral direction, bringing the pupil away from the midline of the body; the lateral rectus originates at the lateral part of the annulus of Zinn known as the annular tendon or common tendinous ring, inserts into the temporal side of the eyeball. The annulus of Zinn is a tendinous ring that surrounds the optic nerve and serves as the origin for five of the six extraocular muscles, excluding the inferior oblique muscle, it is the only muscle supplied by the abducens nerve, cranial nerve VI. The abducens nerve exits the brainstem from the pons-medullary junction, travels through the superior orbital fissure to innervate the lateral rectus muscle; the lateral rectus muscle is innervated through the tectospinal tract.
This tract begins in the tectum region of the midbrain, crosses to the contralateral side of the midbrain. The tectospinal tract descends through the brainstem to the upper spinal cord, but goes no further than the neck; this tract is involved with both upper and lower motor neurons, as well as in the reflex of turning the head in response to visual and auditory stimulus. Part of the descending tracts carry motor signals down spinal cord. A sixth nerve palsy known as abducens nerve palsy, is a neurological defect that results from a damaged or impaired abducens nerve; this damage can stem from stroke, tumor and infection. Damage to the abducens nerve by trauma can be caused by any type of trauma that causes elevated intracranial pressure; this defect can result in reduced lateral movement. The lateral rectus muscle will be denervated and paralyzed and the patient will be unable to abduct the eye. For example, if the left abducens nerve is damaged, the left eye will not abduct fully. While attempting to look straight ahead, the left eye will be deviated medially towards the nose due to the unopposed action of the medial rectus of the eye.
Proper function of the lateral rectus is tested clinically by asking the patient to look laterally. Depending on the underlying cause of the lateral rectus palsy, some improvement may occur over time. While the prognosis for a lateral rectus palsy onset by a viral illness is positive, the prognosis for an onset of trauma or tumor is quite poor. Nerves are not good at regenerating or healing themselves, so if the damage is severe there will be permanent damage. In addition, another disorder associated with the lateral rectus muscle is Duane Syndrome; this syndrome occurs when the sixth cranial nerve which controls the lateral rectus muscle does not develop properly. The reason why the nerve does not develop is not understood. Anatomy figure: 29:01-05 at Human Anatomy Online, SUNY Downstate Medical Center "6-1". Cranial Nerves. Yale School of Medicine. Archived from the original on 2016-03-03
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
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
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