[Biology Class Notes] on Optic Nerve Pdf for Exam

Prior to learning about what is optic nerve, it is imperative to know that all the movements and the responses to any kind of stimuli that the body either projects onto the outside of the body or even the chemical reactions within the body are all associated with the nervous system of our body. Now the optic nerve definition can be stated as a bundle of nerve fibres with a special coating called myelin that is produced by oligodendrocytes, and that serves as the communication cable. The communication between the eyes and the brain is mediated by the optic nerve eye. Let us find out more about what is optic nerve through the optic nerve course. In the optic nerve anatomy, we will delve deeper into the location and the optic nerve structure and its working mechanism.

Optic Nerve Anatomy 

The optic nerve location is behind the eye and is also called the cranial nerve II or the second cranial nerve. It consists of over a million nerve fibres and is made of ganglionic cells or nerve cells. 

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The optic nerve origin can be considered as it is derived from the optic stalks, an outpouching of the diencephalon. Its development commences during the seventh week. The optical nerve is composed of glial cells and retinal ganglion cell axons. It extends to the optic tract starting from the optic disc following the path to the optic chiasma and to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus. With only a limited regenerative capability the nerve is seen to be ensheathed in all three meningeal layers are the dura, arachnoid, and pia mater.

Mechanism of Working of the Optic Nerve

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The optic nerve diagram above represents the working of the optical nerve. The optic nerve anatomy can be viewed as a part of the eye and yet at the same time still considered to be a part of the central nervous system. The optical nerve that is associated with the retinal part of the eye is light sensitive or photosensitive and if that specialized attachment of the photosensitive cells is absent a blind spot is caused since there are no photoreceptors. The presence of the photoreceptors helps in creating an image and being able to view it. The fibres from the retina run along the optic nerve to nine other primary visual nuclei in the brain, which enables the formation of a major relay input into the primary visual cortex. Of course with age, its sensitivity declines and hence one loses eyesight which means one cannot view the objects. 

Functions of the Optical Nerve

• Transmission of all visual information.

• Brightness perception

• Colour perception and contrast in the visual acuity. 

• Transmits electrical impulses created by the retina in the eye.

• It conducts the visual impulses that are responsible for the light reflex and the accommodation reflex which are the two important neurological reflexes.

• The light reflex by the optic nerve occurs when light is shone into either eye that is responded to by the constriction of both pupils. 

• The accommodation reflex is a response to adjustment of the lens of the eye by swelling when one looks at a near object for instance when reading the lens adjusts to a nearer vision and contradictorily it can even shrink accommodating the eye to view the farther objects like the scenery of mountain or planes and anything that is far from the normal eyesight range.

Symptoms and Signs of Optical Nerve Damage

Depending on the extent of the damage to the optic nerve one can assume it to be the loss of vision that may or may not be treated. The damage can be to any part of the optic nerve be it the retinal ganglion cells and axons at the leaving site of the retina, optic disc, or even the cells that make the optic nerve and the optic tract. One must consult a doctor when they experience the following symptoms:

• A decline in the field of vision because both of the reflexes to the light and accommodation is lost.

• Distorted vision, as one cannot view clearly.

• Inflamed eyes always appear more red than usual.

• Temporary for a shorter period or permanent vision loss is experienced.

• Unusual symptoms include numbness or weakness of the limbs, which may be due to the property of the optic nerve being a part of the central nervous system which may be a result of a neurological disorder.

Causes of the Optic Nerve Damage

1. Coloboma of the optic nerve- it is a congenital condition where the optic nerve is incompletely formed.

2. Glaucoma- that is caused by abnormally high pressure in the eyes which is quite difficult to endure and has become the leading cause of blindness. 

3. Idiopathic intracranial hypertension- is the high pressure in the brain, the optic nerve being a part of the Central Nervous System has inconsequential effects on the eyes in any way the brain gets affected. 

4. Neuromyelitis Optica- is a Central Nervous System disorder also known as Devic’s disease.

5. Optic nerve atrophy- caused due to tumour and trauma that is a consequence of decreased blood supply a condition called ischemia or oxygen supply the condition that can be referred to as hypoxia of which the symptoms include swelling and infection.

6. Optic nerve drusen is a result of the abnormal amounts of protein and calcium that is accumulated within the optic nerve.

7. Optic nerve pit- a condition when a small amount of the tissue of the retina protrudes backwards forming a pit beside the optic nerve that can be damaging to the optic nerve fibres.

8. Optic neuritis- is the inflammation of optic nerves due to nerve disease or an infection due to it that inadvertently affects the optic nerve and causes damage. 

Ways to Keep the Optic N
erve Healthy

• Get enough key vitamins and minerals.

• Don’t forget the carotenoids which are oxidants that are essential for a good vision. 

• Stay fit through exercises that do not put pressure on the brain or the central nervous system.

• Manage chronic conditions do not prolong the infections and make light of any situation about the eye as it can lead to irreversible damage. 

• Wear protective eyewear as much as possible when stepping out or when working in front of the screens and include sunglasses as an accessory for everyday wear.

• Follow the 20-20-20 rule where the doctor suggests that one needs to look away towards a far object for 20 minutes after spending 20 minutes looking at the screen of any kind, i.e, phone, pc, television etc. this will help avoid creating eye pressure.

• Quit smoking.

Conclusion

Without the optic nerve and the photoreceptive properties, vision is absent and one cannot enjoy the sight and beauty of the world. Keeping your eye healthy by keeping the optic nerve free from pressure is crucial even for overall sensory inputs since it is the second cranial nerve that is directly associated with the central nervous system. Keep at bay from anything that is unhealthy and unsafe for the optic nerves else one has to pay a huge price in the form of loss of vision.