Nerve: Optic Nerve
The left optic nerve and the optic tracts. The optic tract is a part of the Visual system in the Brain. It is a continuation of the Optic nerve and runs from the Optic chiasm (where
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. A nerve is an enclosed cable-like bundle of peripheral Axons (the long slender projections of Neurons. The vertebrate retina is a light sensitive part inside the inner layer of the Eye. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain

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. Cranial nerves are Nerves that emerge directly from the Brain stem in contrast to Spinal nerves which emerge from segments of the Spinal cord. In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. The diencephalon (or interbrain is the region of the Brain that includes the Thalamus, Hypothalamus, Epithalamus, Prethalamus or Consequently, the fibers are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system. Origin Oligodendroglia arise during development from an Oligodendrocyte precursor cell, which can be identified by its expression of a number of Antigens, including Named after the German physiologist Theodor Schwann, Schwann cells (also referred to as neurolemmocytes) are a variety of Glial cell that mainly The peripheral nervous system ( PNS) resides or extends outside the Central nervous system (CNS which consists of the Brain and Spinal cord. 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. The meninges (singular meninx) is the system of membranes which envelops 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 The arachnoid mater is one of the three Meninges, the membranes that cover the Brain and Spinal cord. The pia mater (Latin "tender mother" itself a translation from Arabic) is the delicate innermost layer of the Meninges - the membranes surrounding the The epineurium is the outermost layer of Connective tissue surrounding a peripheral Nerve. In the Spinal cord, nerve fibers are each wrapped in a protective sheath known as the Endoneurium. The Nerve fibers are held together and supported within the Funiculus by delicate connective tissue called the endoneurium. 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, whence a major relay inputs into the primary visual cortex. The vertebrate retina is a light sensitive part inside the inner layer of the Eye. The term visual cortex refers to the primary visual cortex (also known as striate cortex or

The optic nerve is composed of retinal ganglion cell axons and Portort cells. The vertebrate retina is a light sensitive part inside the inner layer of the Eye. A ganglion cell (more correctly a retinal ganglion cell or RGC) is a type of Neuron typically located near the inner surface of the Retina 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. In Anatomy, the orbital bone is the cavity or socket of the Skull in which the Eye and its appendages are situated The optic foramen is the opening to the optic canal. The superior surface of the Sphenoid bone is bounded behind by a ridge which forms the anterior border of The optic chiasm ( Greek χίασμα "crossing" from the Greek χλαζειν 'to mark with an X' after the Greek letter ' Χ ' chi) is the Most of the axons of the optic nerve terminate in the lateral geniculate nucleus from where information is relayed to the visual cortex. An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell The lateral geniculate nucleus ( LGN) of the Thalamus is a part of the Brain, which is the primary processor of visual information received from the 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,24 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 fibres terminate in the lateral geniculate body.

From the lateral geniculate body, fibers of the optic radiation pass to the visual cortex in the occipital lobe of the brain. The optic radiation (also known as the geniculo-calcarine tract or as the geniculostriate pathway) is a collection of Axons from Relay neurons The term visual cortex refers to the primary visual cortex (also known as striate cortex or The occipital lobe is the visual processing center of the Mammalian Brain containing most of the anatomical region of the Visual cortex. 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. The optic radiation (also known as the geniculo-calcarine tract or as the geniculostriate pathway) is a collection of Axons from Relay neurons

Physiology

The eye's blind spot is a result of the absence of retina where the optic nerve leaves the eye. A blind spot, also known as a Scotoma, is an obscuration of the Visual field. This is because there are no photoreceptors in this area. Photoreceptor can refer to In anatomy/cell biology Photoreceptor cell: a photosensitive cell most commonly referring to a specialized type of neuron

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.     There is however an alternative explanation which might conceivably account for this apparent large discrepancy; as follows: (Please note that this is a highly individual view that appears to contain some physics errors. )

A theoretically possible double-mode (multiplexed) signal-transmission

Myelinated nerve fibres are very like miniature versions of coaxial cables such as those used for TV aerials or for underwater telegraph-signalling in the 1800s. In fact, neurophysiologists still use Lord Kelvin's cable formula of the 1860s in calculations concerning saltatory conduction of myelinated nerve-fibres. For Saltation definition and other use disambiguation see Saltation Saltatory conduction (from the Latin saltare, to hop or leap is Thus it seems appropriate to invoke any other theoretical peculiarities exhibited by coaxial cables.

Historical background and precedent

Kelvin's formula for trans-Atlantic cables was a simplification based on the apparently-reasonable assumption that frequencies would be fairly low (based on manual Morse-signalling) so that any inductance ("L") would be negligible. However if we do use much higher frequencies (what we would now call "Radio Frequencies"), then "L" becomes very important, thus allowing new transmission modes (effectively fibre-optics) ^[2][3] — and incidentally leading to the invention of radio as a by-product, as demonstrated by Heinrich Hertz in 1888. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Heinrich Rudolf Hertz ( February 22, 1857 – January 1, 1894) was a German physicist who clarified and expanded the electromagnetic theory Year 1888 ( MDCCCLXXXVIII) was a Leap year starting on Sunday (click on link for calendar of the Gregorian calendar (or a

Thus trans-Atlantic cables were capable of operating in two rather-different modes (and the new method was much more efficient, with a much greater "bandwidth"). However it took a prolonged effort by Oliver Heaviside to get this view accepted despite vigorous opposition from the then senior electrician of the British Post Office, Sir William Preece. Sir William Henry Preece ( February 15[[ 834]]- November 6 1913) was a Welsh Electrical engineer and Inventor. ^[4]

Application to nerve-fibre signal capacity — perhaps explaining the anomaly

For high-frequency transmission in coaxial cables, the wave-length needs to be roughly comparable to the cable diameter. For myelinated axons (with diameters mostly in the 1-to-10 micron range) this suggests that the relevant radiation will be Infra-Red rather than the familiar Radio-Frequency. In any case, this would offer ample scope for broadband facilities — though we cannot yet tell whether nature has chosen to take advantage of this opportunity. Moreover, this IR would seem to be compatible with the quantum jumps which might be expected from any biochemical "switching"-or-"commands".     Clearly if this extra mode is available, then there will be less need for pre-processing in the retina, though it is well known that some important pre-processing does take place there, and that at least some of the communication is via action-potentials.     In any case, it is most unlikely that any visible-light signals would be transmitted this way, if only because their wavelengths would be too short.

Other indirect evidence for this alternative signal-mode

There is no systematic direct evidence for this notion; but it has prompted promising unexpected solutions in other related fields, which may be seen as indicative:

• If IR is present-in-force, then it could be expected to produce a byproduct of optical interference effects in certain circumstances. That could explain how myelin geometry is regulated — a mystery since 1905 and earlier. Year 1905 ( MCMV) was a Common year starting on Sunday (link will display full calendar of the Gregorian calendar (or a Common year starting ^[5][6]
• Insects' "Sixth Sense" and Infra-Red.       P. S. Callahan and E.R.Laithwaite offered a persuasive case that when insects detect their mates at long-distance (>"100 yards"), they are using tuned IR-detection (apparently via fluorescent^[7] effects of the pheromones). Eric Roberts Laithwaite ( 14 June 1921 &ndash 27 November 1997) was an English Engineer, principally known for his development Fluorescence is a Luminescence that is mostly found as an A pheromone (from Greek φέρω phero "to bear" + ‘ορμόνη " Hormone " is a Chemical that triggers a natural This idea was supposedly killed off by a sudden-death debate in 1977; but that debate has since been shown as faulty on both sides, so it now seems clear that Callahan was essentially correct on his main point. Also 1977 (album by Ash. Year 1977 ( MCMLXXVII) was a Common year starting on Saturday (link displays ^[8]   This offers a precedent for the usefulness of IR in bio-communication.

• IR and Insect Intelligence?       There is some suggestion that insects also may have a dual-mode nervous system — but with chitin substituting for the myelin found within vertebrates. Moreover, if they are indeed directly detecting IR and partially "thinking" via IR, why bother with any intervening action-potentials?! That could explain why Callahan was unable to detect any action-potentials between his IR stimulus and the observed behavioural reaction! (though there was no such action-potential deficiency for visible light). ^[9]

Role in disease

Main article: List of eye diseases and disorders

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. This is a partial list of human Eye diseases and disorders. The World Health Organization publishes a classification of known diseases and injuries called the In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also The type of visual field loss will depend on which portions of the optic nerve were damaged. The term visual field is sometimes used as a Synonym to Field of view, though they do not designate the same thing Generally speaking:

• 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). Bitemporal hemianopsia (or Bitemporal hemianopia) is the medical description of a type of partial Blindness where vision is missing in the outer half of both the right It may occur in large pituitary adenomata. Pituitary adenomas are Tumors that occur in the Pituitary gland, and account for about 10% of intracranial neoplasms.
• 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. Leber’s hereditary optic neuropathy (LHON or Leber optic atrophy is a mitochondrially inherited (mother to all offspring degeneration of Retinal 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).

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. Glaucoma is a group of diseases of the Optic nerve involving loss of retinal ganglion cells in a characteristic pattern of optic neuropathy. A ganglion cell (more correctly a retinal ganglion cell or RGC) is a type of Neuron typically located near the inner surface of the Retina Optic atrophy is the loss of some or most of the fibers of the Optic nerve. Peripheral vision is a part of vision that occurs outside the very center of gaze

Optic neuritis is inflammation of the optic nerve. Optic Neuritis is the Inflammation of the Optic nerve that may cause a complete or partial loss of vision It is associated with a number of diseases, most notably multiple sclerosis. Multiple sclerosis (abbreviated MS also known as disseminated sclerosis or encephalomyelitis disseminata) is an autoimmune condition in which the

Anterior Ischemic Optic Neuropathy is a particular type of infarct that affects patients with an anatomical predisposition and cardiovascular risk factors.

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 and surgery of the visual pathways including the Eye, Brain Neuro-ophthalmology is the subspecialty of both Neurology and Ophthalmology concerning visual problems that are related to the Nervous system

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

MRI scan of human eye showing optic nerve.	The ophthalmic artery and its branches. The ophthalmic artery is a branch of the Internal carotid artery which supplies branches to supply the Eye and other structures in the orbit. (optic nerve is yellow)	Dura mater and its processes exposed by removing part of the right half of the skull, and the brain.	Tentorium cerebelli from above.
Superficial dissection of brain-stem. Lateral view.	Dissection of brain-stem. Lateral view.	Mesal aspect of a brain sectioned in the median sagittal plane.	Scheme showing central connections of the optic nerves and optic tracts.
The fornix and corpus callosum from below. The corpus callosum is a structure of the Mammalian Brain in the longitudinal fissure that connects the left and right Cerebral hemispheres It also facilitates	Nerves of the orbit. Seen from above.	Nerves of the orbit, and the ciliary ganglion. Side view.	The arteries of the choroid and iris. The greater part of the sclera has been removed.
The veins of the choroid.	The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section.	Human brain dura mater (reflections)

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.
2. ^ Traill, R. R. (1977/1980/2006) Towards a theoretical explanation of electro-chemical interaction in memory-use: The postulated role of infra-red components and molecular evolution; Monograph #24, Cybernetics Department, Brunel University;[[1]] — or as Part B of thesis:[[2]]
3. ^ Traill, R. Also 1977 (album by Ash. Year 1977 ( MCMLXXVII) was a Common year starting on Saturday (link displays Year 1980 ( MCMLXXX) was a Leap year starting on Tuesday (link displays the 1980 Gregorian calendar) Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Cybernetics is the interdisciplinary study of the Structure of Complex systems especially Communication processes control mechanisms and Feedback Brunel University is a University situated in West London, England. R. (1988). Year 1988 ( MCMLXXXVIII) was a Leap year starting on Friday (link displays 1988 Gregorian calendar) "The case that mammalian intelligence is based on sub-molecular coding and fibre-optic capabilities of myelinated nerve axons", Speculations in Science and Technology, 11(3), 173-181.
4. ^ See (e. g. ) Yavetz, I. (1995) From Obscurity to Enigma: The work of Oliver Heaviside, 1872-1889. Birkhäuser Verlag: Basel; pages 247-263.
5. ^ Donaldson, H. H. , and G. W. Hoke (1905). Year 1905 ( MCMV) was a Common year starting on Sunday (link will display full calendar of the Gregorian calendar (or a Common year starting "The areas of the axis cylinder and medullary sheath as seen in cross sections of the spinal nerves of vertebrates". Journal of Comparative Neurology, 15, 1-
6. ^ Traill, R. R. (2005 March). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Strange regularities in the geometry of myelin nerve-insulation — a possible single cause. Ondwelle: Melbourne. [[3]]
7. ^ Note that fluorescence requires both a suitable fluorescent material (a pheromone in this case) and a suitable radiation-source to power it. Fluorescence is a Luminescence that is mostly found as an A pheromone (from Greek φέρω phero "to bear" + ‘ορμόνη " Hormone " is a Chemical that triggers a natural Such double-requirements are one source of confusion. The issue is also complicated by olfaction: It is, of course also possible to follow a pheromone by smell in the conventional way, and that confounds the analysis for short-distance cases. Olfaction (also known as olfactics or smell) refers to the Sense of smell. However that possibility is eliminated for the long-range cases, as Laithwaite explains in some detail. See the cited report of the debate and its references.
8. ^ Traill, R. R. (2005 December). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. How Popperian positivism killed a good-but-poorly-presented theory — Insect communication by Infrared. Ondwelle: Melbourne. [[4]]
9. ^ ibid. : pp. 13-15: "(i) How might the received IR signal be processed and perhaps affect behaviour?"

External links

• The optic nerve on MRI
• BrainMaps at UCDavis optic%20nerve

• IFOND
• online case history - Optic nerve analysis with both scanning laser polarimetry with variable corneal compensation (GDx VCC) and confocal scanning laser ophthalmoscopy (HRT II - Heidelberg Retina Tomograph). BrainMaps is an NIH -funded interactive zoomable high-resolution digital brain atlas and virtual microscope that is based on more than 20 million megapixels (50 terabytes Also includes actual fundus photos.
• Norman/Georgetown lesson3 (orbit4)
• Norman/Georgetown cranialnerves (II)