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The following diagram is provided as an overview of and topical guide to the human nervous system: Human nervous system. Human nervous system – the part of the human body that coordinates a person's voluntary and involuntary actions and transmits signals between different parts of the body.
Since only a small part of the eye called the fovea provides sharp vision, the eye must move to follow a target. Eye movements must be precise and fast. This is seen in scenarios like reading, where the reader must shift gaze constantly. Although under voluntary control, most eye movement is accomplished without conscious effort.
Diagram of a human eye; note that not all eyes have the same anatomy as a human eye. The mammalian eye can also be divided into two main segments: the anterior segment and the posterior segment. [10] The human eye is not a plain sphere but is like two spheres combined, a smaller, more sharply curved one and a larger lesser curved sphere.
Emmetropia is the state of vision in which a faraway object at infinity is in sharp focus with the ciliary muscle [1] in a relaxed state. That condition of the normal eye is achieved when the refractive power of the cornea and eye lens and the axial length of the eye balance out, which focuses rays exactly on the retina, resulting in perfectly sharp distance vision.
The eye's lens becomes too inflexible to accommodate to normal reading distance, focus tending to remain fixed at long distance. Glaucoma is a type of blindness that begins at the edge of the visual field and progresses inward. It may result in tunnel vision. This typically involves the outer layers of the optic nerve, sometimes as a result of ...
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina.The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric and triploblastic animals—that is, all multicellular animals except sponges and diploblasts.
The lateral rectus is the only muscle supplied by the abducens nerve (CN VI). The neuron cell bodies are located in the abducens nucleus in the pons.These neurons project axons as the abducens nerve which exit from the pontomedullary junction of the brainstem, travels through the cavernous sinus and enter the orbit through the superior orbital fissure.
The parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book. [6] The ciliary body is also known to receive sympathetic innervation via long ciliary nerves. [7] When test subjects are startled, their eyes automatically adjust for distance vision. [8]