Optical pathway

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The optical pathway collects, transforms and creates an idea of the phenomena related to the presence and manifestations of light energy. Most of the impressions from the outside world are obtained through the senses of sight. The retina, which is the receiving part of the sense pathway of vision, as well as the optic nerve during development, arise from parts of the central nervous system. The sense of sight is well developed in terrestrial vertebrates with binocular vision. Primates are already developing the ability of three-dimensional vision, and humans have seen the most perfect vision, which is especially related to the high degree of development of the cerebral cortex, especially the associative optical cortex.

The optical pathway is a system of interconnected neurons, which connect the retina to the subcortical and cortical visual centers. This time, the neurons accept and transmit the image of the observed object, enabling its understanding and spatial vision. Reflex neurons this time start from the reflex optical center (stratum griseum profundum colliculi superioris) and connect it with the motor nuclei of the spinal nerves (tractus tectospinalis), the motor nuclei of the cerebral nerves (tractus tectobulbaris), the reticular nuclei of the cerebral tract in the cerebral tract (tectocerebellar tract). These numerous connections enable many defensive reflex actions in response to stimuli caused by visual impressions (reflexive movement of the head and neck, reflexive rotation of the eyes, blinking, dilation or narrowing of the pupil, accommodation, convergence of the eyes).

The optic pathway has four neurons, three of which lie in the retina, and the fourth is located in the central nervous system. The processing of visual impulses (information) begins in the retina. [1]

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Optic nerve paired nerve that transmits visual information from the retina to the brain

The optic nerve, also known as cranial nerve II, or simply as CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.

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Optic radiation

The optic radiation are axons from the neurons in the lateral geniculate nucleus to the primary visual cortex. The optic radiation receives blood through deep branches of the middle cerebral artery and posterior cerebral artery.

Optic tract

The optic tract is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and superior colliculus.

Accommodation reflex reflex action of the eye, in response to focusing on a near object, then looking at a distant object

The accommodation reflex is a reflex action of the eye, in response to focusing on a near object, then looking at a distant object, comprising coordinated changes in vergence, lens shape (accommodation) and pupil size. It is dependent on cranial nerve II, superior centers (interneuron) and cranial nerve III. The change in the shape of the lens is controlled by the ciliary muscles inside the eye. Changes in contraction of the ciliary muscles alter the focal distance of the eye, causing nearer or farther images to come into focus on the retina; this process is known as accommodation. The reflex, controlled by the parasympathetic nervous system, involves three responses: pupil constriction, lens accommodation, and convergence.

Corticobulbar tract two-neuron white matter motor pathway

The corticobulbartract is a two-neuron white matter motor pathway connecting the motor cortex in the cerebral cortex to the medullary pyramids, which are part of the brainstem's medulla oblongata region, and are primarily involved in carrying the motor function of the non-oculomotor cranial nerves. The corticobulbar tract is one of the pyramidal tracts, the other being the corticospinal tract.

Upper motor neuron lesion occurs in the neural pathway above the anterior horn cell of the spinal cord or motor nuclei of the cranial nerves

An upper motor neuron lesion occurs in the neural pathway above the anterior horn cell of the spinal cord or motor nuclei of the cranial nerves. Conversely, a lower motor neuron lesion affects nerve fibers traveling from the anterior horn of the spinal cord or the cranial motor nuclei to the relevant muscle(s).

The pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical visual system. Through reciprocal bilateral projections from the retina, it is involved primarily in mediating behavioral responses to acute changes in ambient light such as the pupillary light reflex, the optokinetic reflex, and temporary changes to the circadian rhythm. In addition to the pretectum's role in the visual system, the anterior pretectal nucleus has been found to mediate somatosensory and nociceptive information.

The menace response is one of three forms of blink reflex. It is the reflex blinking that occurs in response to the rapid approach of an object. The reflex comprises blinking of the eyelids, in order to protect the eyes from potential damage, but may also include turning of the head, neck, or even the trunk away from the optical stimulus that triggers the reflex.

Visual pathway lesions

The visual pathway consists of structures that carry visual information from the retina to the brain. Lesions in that pathway cause a variety of visual field defects. In the visual system of human eye, the visual information processed by retinal photoreceptor cells travel in the following way:
Retina→Optic nerve→Optic chiasm →Optic tract→Lateral geniculate nucleus→Optic radiation→Primary and secondary visual cortices.

References

  1. Ilic, Aleksandar (2010). Anatomija centralnog nervnog sistema. Belgrade: Savremena administracija JSC. p. 185-190. ISBN   978-86-387-0796-6.

Further reading