The Eyeball

There are three layers of the eyeball. The three layers are the sclera, the choroid, and the retina. The layers can also be called tunics, but if they are called tunics they are known as the fibrous, the pigmented, and the visual. The fibrous, sclera, choroid and the pigmented are vascular; and the retina and visual are not vascular. The white part of the eye is known as the sclera. Calogen gives the sclera the white color.
The autonomic nervous system regulates the pupil's diameter. The parasympathetic nerve impulse causes the circular muscles to contract which allows less light to enter the eye. The sympathetic nerve impulse causes the muscles to dilate, allowing more light in.
The cornea has no blood vessels. The lens are made up of protein.The fovea is the focus point in the eye. Since the lens are concave as well as the cornea, the ligaments attached to the lens tighten in order to make the lens flat and loosen in order to allow the lens to be more concave. This ability helps make the object you are seeing clear.

Nerves

There are twelve pairs of cranial nerves. Cranial nerves eight and twelve are only carry afferent impulses.Olfactory nerves relay information from high in the nasal cavity. When the brain is removed the olfactory lobe on the brain gets ripped off. The olfactory foramina is where the nerves go through cranial nerve I. The ganglion is a collection of cell bodies outside the central nervous system. A cell body found inside the central nervous system is a nucleus cell. Cervical three, four, and five stimulates the breathing, they go through thoracic diagram to keep your negative and positive pressure.The median nerve controls your thumb and if it is severed you will never be able to use it again.The sciatic nerve is the largest nerve in the body it controls the back muscles of the legs.
The muscles of the eyeball stimulate the oculomotor nerves, trochlear nerves, and abducens. The trochlear nerve is the central nerve number four. The central nerve VI is the abducens it is a motor nerve, sends efferent impulses. The trochlear nerve controls the superior oblique. The ascending oblique attaches and connects to the lateral rectus. Nerve three, four, and six all pass through the superior orbital fissure. There are two parts to the autonomic nervous system, the sympathetic and the parasympathetic. The parasympathetic nerves system stimulates the muscles of the eyeball that cause the eyeball to constrict. The sympathetic nerves system stimalates the muscles of the eye to dilate.

The Circle of Willis and Cranial Nerves

The Circle of Willis is a ring of arteries at the base of the brain. The Circle of Willis contains five aortic archs, there is the posterior communicating, posterior cerebral,middle cerebal, anterior cerebral, and anterior communicating. It is the brains major blood flow and has two main arteries. The Circle of Willis has a backup artery in case one artery gets clogged and the other one will flow.
There are twelve pairs of Cranial Nerves. The twelve pairs are known as Olfactory, Optic, Oculomotor, Trochlear, Abducens, Trigeminal, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Spinal, and Hypoglossal. Three of the pairs of nerves are consider sensory: Olfactory, Optic, and Vestibulocochlear. The rest of the nerves are considered mixed. The mixed nerves have a sensory portion and motor portion, these mixed nerves have the sensory and motor part mixed together.