Cranial nerve II: The second cranial 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 I
Cranial nerve I: The first nerve to emerge from or enter the skull (the cranium). (There are twelve cranial nerves.) The first cranial nerve is the olfactory nerve which permits the sense of smell. See: Olfactory nerve.
- Cranial nerve III
Cranial nerve III: 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 nerve IV
Cranial nerve IV: The fourth cranial nerve, the trochlear nerve, is the nerve supply to the superior oblique muscle of the eye, one of the muscles that moves the eye. Paralysis of the trochlear nerve results in rotation of the eyeball upward and outward (and, therefore, double vision). The twelve cranial nerves, the trochlear nerve […]
- Cranial nerve IX
Cranial nerve IX: The ninth cranial nerve is the glossopharyngeal nerve. The 12 cranial nerves, the glossopharyngeal nerve included, emerge from or enter the skull (the cranium), as opposed to the spinal nerves which emerge from the vertebral column. The glossopharyngeal nerve supplies the tongue, throat, and one of the salivary glands (the parotid gland). […]
- Cranial nerve V
Cranial nerve V: The fifth cranial nerve is the trigeminal nerve. The trigeminal nerve is quite complex. It functions both as the chief nerve of sensation for the face and the motor nerve controlling the muscles of mastication (chewing). Problems with the sensory part of the trigeminal nerve result in pain or loss of sensation […]