the optic nerve is located at primary visual nuclei in the brain.
the optic nerve is located at primary visual nuclei in the brain.
where is the optic nerve located in the brain?
primary visual nuclei
the lateral geniculate nucleus (lgn) is a sensory relay nucleus in the thalamus of the brain. the lgn consists of six layers in humans and other primates starting from catarhinians, including cercopithecidae and apes. layers 1, 4, and 6 correspond to information from the contralateral (crossed) fibers of the nasal retina (temporal visual field); layers 2, 3, and 5 correspond to information from the ipsilateral (uncrossed) fibers of the temporal retina (nasal visual field). layer one (1) contains m cells which correspond to the m (magnocellular) cells of the optic nerve of the opposite eye and are concerned with depth or motion. layers four and six (4 & 6) of the lgn also connect to the opposite eye, but to the p cells (color and edges) of the optic nerve. by contrast, layers two, three and five (2, 3, & 5) of the lgn connect to the m cells and p (parvocellular) cells of the optic nerve for the same side of the brain as its respective lgn. spread out, the six layers of the lgn are the area of a credit card and about three times its thickness. the lgn is rolled up into two ellipsoids about the size and shape of two small birds' eggs. in between the six layers are smaller cells that receive information from the k cells (color) in the retina. the neurons of the lgn then relay the visual image to the primary visual cortex (v1) which is located at the back of the brain (posterior end) in the occipital lobe in and close to the calcarine sulcus. the lgn is not just a simple relay station but it is also a center for processing; it receives reciprocal input from the cortical and subcortical layers and reciprocal innervation from the visual cortex.
visual system
the optic nerve can be damaged when exposed to direct or indirect injury. direct optic nerve injuries are caused by trauma to the head or orbit that crosses normal tissue planes and disrupts the anatomy and function of the optic nerve; e.g., a bullet or forceps that physically injures the optic nerve. indirect injuries, like blunt trauma to the forehead during a motor vehicle accident, transmit force to the optic nerve without transgressing tissue planes. this type of force causes the optic nerve to absorb excess energy at the time of impact. the most common site of injury of the optic nerve is the intracanalicular portion of the nerve. deceleration injuries from motor vehicle or bicycle accidents account for 17 to 63 percent of cases. falls are also a common cause, and optic neuropathy most commonly occurs when there is a loss of consciousness associated with multi-system trauma and serious brain injury. in less than three percent of patients, an orbital hemorrhage after an injection behind the eye (retrobulbar block) can cause injury to the optic nerve, but this is readily manageable if it does not involve direct optic nerve injury and is caught early. the role of high-dose steroids and orbital decompression in treating these patients is controversial and, if administered, must be done very soon after injury with minimal effects. in patients with an orbital fracture, vomiting or nose blowing can force air into the orbit and possibly compromise the integrity of the optic nerve.
optic neuropathy