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Encyclopedia > Optic nerve
Nerve: Optic nerve
The left optic nerve and the optic tracts.
Optic nerve leaving the back of a calf eye (from dissection).
Latin nervus opticus
Gray's subject #197 882
MeSH Optic+Nerve

The optic nerve, also called cranial nerve II, is the nerve that transmits visual information from the retina to the brain. Image File history File links Gray773. ... The optic tract is a part of the visual system in the brain. ... Image File history File links Calf-Eye-Posterior-Outside-2005-Oct-13. ... For other uses, see Latin (disambiguation). ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... Optic Nerve is a comic book series by graphic novelist Adrian Tomine. ... A famous image of David Wojnarowicz David Wojnarowicz (September 14, 1954 - July 22, 1992) was a gay painter, photographer, writer, filmmaker, performance artist, and activist who was prominent in the New York City art world of the 1980s. ... For other uses, see Optic Nerve. ... Nerves (yellow) Nerves redirects here. ... Human eye cross-sectional view. ... The human brain In animals, the brain (enkephalos) (Greek for in the skull), is the control center of the central nervous system, responsible for behavior. ...

Contents

Anatomy

The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during embryonic development. Consequently, the fibers are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system. Similarly, the optic nerve is ensheathed in all three meningeal layers (dura, arachnoid, and pia mater) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. This is an important issue, as fiber tracks of the mammalian central nervous system (as opposed to the peripheral nervous system) are incapable of regeneration and hence optic nerve damage produces irreversible blindness. The fibers from the retina run along the optic nerve to nine primary visual nuclei in the brain, from whence a major relay inputs into the primary visual cortex. Cranial nerves are nerves which start directly from the brainstem instead of the spinal cord. ... A diagram showing the CNS: 1. ... The diencephalon is the region of the brain that includes the epithalamus, thalamus, and hypothalamus. ... Oligodendrocytes (from Greek literally meaning few tree cells), or oligodendroglia (Greek, few tree glue),[1] are a variety of neuroglia. ... Named after the German physiologist Theodor Schwann, Schwann cells are a variety of neuroglia that mainly provide myelin insulation to axons in the peripheral nervous system of jawed vertebrates. ... The Peripheral nervous system resides or extends outside the CNS central nervous system (the brain and spinal cord) to serve the limbs and organs. ... The meninges (singular meninx) are the system of membranes that envelop the central nervous system. ... The dura mater (from the Latin hard mother), or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain. ... The Arachnoid mater is one of the three layers of the meninges, interposed between the dura mater and the pia mater and separated from the pia mater by the subarachnoid space. ... [www. ... Neurolemma (spelled also neurolema, neurilemma and neurilema, and used interchangeably with epineurium) is the insulating myelin layer that surrounds an individual peripheral nerve fiber. ... In a nerve fiber, the tubular sheath of the funiculi, perineurium, is a fine, smooth, transparent membrane, which may be easily separated, in the form of a tube, from the fibers it encloses; in structure it is made up of connective tissue, which has a distinctly lamellar arrangement. ... The nerve fibers are held together and supported within the funiculus by delicate connective tissue, called the endoneurium. ... Human eye cross-sectional view. ... Brodmann area 17 (primary visual cortex) is shown in red in this image which also shows area 18 (orange) and 19 (yellow) The primary visual cortex (usually called V1) is the most well-studied visual area in the brain. ...


The optic nerve is composed of retinal ganglion cell axons and support cells. It leaves the orbit (eye) via the optic canal, running postero-medially towards the optic chiasm where there is a partial decussation (crossing) of fibers from the temporal visual fields of both eyes. Most of the axons of the optic nerve terminate in the lateral geniculate nucleus from where information is relayed to the visual cortex. Its diameter increases from about 1.6 mm within the eye, to 3.5 mm in the orbit to 4.5 mm within the cranial space. The optic nerve component lengths are 1 mm in the globe, 25 mm in the orbit, 9 mm in the optic canal and 16 mm in the cranial space before joining the optic chiasm. There, partial decussation occurs and about 53% of the fibers cross to form the optic tracts. Most of these fibers terminate in the lateral geniculate body. Human eye cross-sectional view. ... A ganglion cell (or sometimes called a gangliocyte) is a type of neuron located in the retina that receives visual information from photoreceptors via various intermediate cells such as bipolar cells, amacrine cells, and horizontal cells. ... In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. ... optical canal information ... Visual pathway with optic chiasm circled The optic chiasm (from the Greek χλαζειν to mark with an X, after the letter Χ chi) is the part of the brain where the optic nerves partially cross, those parts of the right eye which see things on the right side being connected to the... For alternate uses of time, see Time (disambiguation) or see TIME (magazine). ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... Grays FIG. 719– Hind- and mid-brains; postero-lateral view. ...


From the lateral geniculate body, fibers of the optic radiation pass to the visual cortex in the occipital lobe of the brain. More specifically, fibers carrying information from the contralateral superior visual field traverse Meyer's loop to terminate in the lingual gyrus below the calcarine fissure in the occipital lobe, and fibers carrying information from the contralateral inferior visual field terminate more superiorly.It also gives us the power to see. The geniculo-calcerine tract (known as the optic radiation) is a collection of axons carrying visual information from the lateral geniculate nucleus of the thalamus to the primary visual cortex (also called striate cortex). ... Brodmann area 17 (primary visual cortex) is shown in red in this image which also shows area 18 (orange) and 19 (yellow) The visual cortex refers to the primary visual cortex (also known as striate cortex or V1) and extrastriate visual cortical areas such as V2, V3, V4, and V5. ... The occipital lobe is the visual processing center of the mammalian brain, containing most of the anatomical region of the visual cortex. ... Right superior quadrantanopia. ...


Physiology

The optic nerve contains 1.2 million nerve fibers. This number is low compared to the roughly 100 million photoreceptors in the retina,[1] and implies that substantial pre-processing takes place in the retina before the signals are sent to the brain through the optic nerve.[citation needed]


The eye's blind spot is a result of the absence of retina where the optic nerve leaves the eye. This is because there are no photoreceptors in this area. For other uses, see Blind spot. ... A photoreceptor, or photoreceptor cell, is a specialized type of neuron found in the eyes retina that is capable of phototransduction. ...


Role in disease

Damage to the optic nerve typically causes permanent and potentially severe loss of vision, as well as an abnormal pupillary reflex, which is diagnostically important. The type of visual field loss will depend on which portions of the optic nerve were damaged. Generally speaking: This is a partial list of human eye diseases and disorders. ... In psychology, visual perception is the ability to interpret visible light information reaching the eyes which is then made available for planning and action. ... In medicine, pupil constriction (also known as the pupillary reflex) is reduction of pupil size. ... The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. ...

  • Damage before the optic chiasm causes loss of vision in the visual field of the same side only.
  • Damage in the chiasm causes loss of vision laterally in both visual fields (bitemporal hemianopia). It may occur in large pituitary adenomata.
  • Damage after the chiasm causes loss of vision on one side but affecting both visual fields: the visual field affected is located on the opposite side of the lesion.

Injury to the optic nerve can be the result of congenital or inheritable problems like Leber's Hereditary Optic Neuropathy, glaucoma, trauma, toxicity, inflammation, ischemia, infection (very rarely), or compression from tumors or aneurysms. By far, the three most common injuries to the optic nerve are from glaucoma, optic neuritis (especially in those younger than 50 years of age) and anterior ischemic optic neuropathy (usually in those older than 50). Pituitary adenomas are tumors that occur in the pituitary gland, and account for about 10% of intracranial neoplasms. ... Leber’s hereditary optic neuropathy (LHON) or Leber optic atrophy is a mitochondrially inherited (mother to all offspring) form of acute or subacute loss of central vision that may lead to degeneration of retinal ganglion cells (RGCs) and their axons; this affects predominantly young adult males. ...


Glaucoma is a group of diseases involving loss of retinal ganglion cells causing optic neuropathy in a pattern of peripheral vision loss, initially sparing central vision. A ganglion cell (or sometimes called a gangliocyte) is a type of neuron located in the retina that receives visual information from photoreceptors via various intermediate cells such as bipolar cells, amacrine cells, and horizontal cells. ... Optic atrophy is a pathological term and somewhat misleading. ... Peripheral vision is a part of vision that occurs outside the very center of gaze. ...


Optic neuritis is inflammation of the optic nerve. It is associated with a number of diseases, most notably multiple sclerosis. Optic neuritis, sometimes called retrobulbar neuritis, is the inflammation of the optic nerve that may cause a complete or partial loss of vision. ...


Anterior Ischemic Optic Neuropathy is a particular type of infarct that affects patients with an anatomical predisposition and cardiovascular risk factors. Anterior ischemic optic neuropathy (AION) is a medical condition involving loss of vision due to damage to the optic nerve from insufficient blood supply. ...


Ophthalmologists, particularly those sub specialists who are neuro-ophthalmologists, are often best suited to diagnose and treat diseases of the optic nerve. Ophthalmology is the branch of medicine which deals with the diseases of the eye and their treatment. ... A neuro-ophthalmologist is one of about 300 world-wide credentialled specialists in the combined fields of neurology and ophthalmology. ...


The International Foundation for Optic Nerve Diseases IFOND sponsors research and information on a variety of optic nerve disorders and may provide general direction.


Additional images

References

  1. ^ Jonas JB, Schneider U, Naumann GOH (1992) Count and density of human retinal photoreceptors. Graefe's Arch Clin Exp Ophthalmol 230:505-510.

External links


  Results from FactBites:
 
IX. Neurology. 5b. The Optic Nerve. Gray, Henry. 1918. Anatomy of the Human Body. (893 words)
The optic nerve is peculiar in that its fibers and ganglion cells are probably third in the series of neurons from the receptors to the brain.
The orbital portion of the optic nerve is from 20 mm.
The crossed fibers of the optic nerve tend to occupy the medial side of the nerve and the uncrossed fibers the lateral side.
  More results at FactBites »

 
 

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