Cranial nerve, second: The second cranial nerve is the optic nerve, the nerve that connects the eye to the brain and carries the impulses formed by the retina — the nerve layer that lines the back of the eye, senses light and creates the impulses — to the brain which interprets them as images.
The cranial nerves emerge from or enter the skull (the cranium), as opposed to the spinal nerves which emerge from the vertebral column. There are twelve cranial nerves.
In terms of its embryonic development, the optic nerve is a part of the central nervous system (CNS) rather than a peripheral nerve.
The word “optic” comes from the Greek “optikos”, pertaining to sight.
Aside from the optic nerve, the eye has a number of other components. These include the cornea, iris, pupil, lens, retina, macula, and vitreous.
The cornea is the clear front window of the eye that transmits and focuses light into the eye.
The iris is the colored part of the eye that helps regulate the amount of light that enters the eye.
The pupil is the dark aperture in the iris that determines how much light is let into the eye.
The lens is the transparent structure inside the eye that focuses light rays onto the retina.
The retina is, as mentioned, the nerve layer that lines the back of the eye, senses light and creates impulses that go through the optic nerve to the brain.
The macula is a small area in the retina that contains special light-sensitive cells and allows us to see fine details clearly.
The vitreous humor is a clear, jelly-like substance that fills the middle of the eye.
In sum, the optic nerve is uniquely a part of both the eye and the brain. It is embryologically the brain’s envoy to the eye and functionally the eye’s envoy to the brain.
- Cranial nerve, seventh
Cranial nerve, seventh: The seventh cranial nerve is the facial nerve, a mixed nerve that has fibers both going out and coming in (both efferent and afferent fibers). It supplies the muscles of facial expression. Paralysis of the facial nerve causes a characteristic picture with drooping of one side of the face, inability to wrinkle […]
- Cranial nerve, tenth
Cranial nerve, tenth: The tenth cranial nerve, and one of the most important, is the vagus nerve. All twelve of the cranial nerves, the vagus nerve included, emerge from or enter the skull (the cranium), as opposed to the spinal nerves which emerge from the vertebral column. The vagus nerve originates in the medulla oblongata, […]
- Cranial nerve, sixth
Cranial nerve, sixth: The sixth cranial nerve is the abducens nerve. It is a small motor nerve that has one task: to supply a muscle called the lateral rectus muscle that moves the eye outward. Paralysis of the abducens nerve causes inward turning of the eye (internal strabismus) leading to double vision. The cranial nerves, […]
- Cranial nerve, third
Cranial nerve, third: The third cranial nerve is the oculomotor nerve. The cranial nerves emerge from or enter the skull (the cranium), as opposed to the spinal nerves which emerge from the vertebral column. There are twelve cranial nerves. The oculomotor nerve is responsible for the nerve supply to muscles about the eye: The upper […]
- Cranial nerves
Cranial nerves: The nerves of the brain, which emerge from or enter the skull (the cranium), as opposed to the spinal nerves, which emerge from the vertebral column. There are 12 cranial nerves, each of which is accorded a Roman numeral and a name: Cranial nerve I: the olfactory nerve Cranial nerve II: the optic […]