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The adrenal medulla is the principal site of the conversion of the amino acid tyrosine into the catecholamines; epinephrine, norepinephrine, and dopamine. Because the ANS, specifically the sympathetic division, exerts direct control over the chromaffin cells , the hormone release can occur rather quickly. [ 2 ]
The human eye is a sensory organ in the visual system that reacts to visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and keeping balance. Arizona Eye Model. "A" is accommodation in diopters. The eye can be considered as a living optical device.
The fovea centralis is a small, central pit composed of closely packed cones in the eye.It is located in the center of the macula lutea of the retina. [1] [2]The fovea is responsible for sharp central vision (also called foveal vision), which is necessary in humans for activities for which visual detail is of primary importance, such as reading and driving.
The eye is essentially a derivative of the ectoderm from the somatic ectoderm and neural tube, with a succession of inductions by the chordamesoderm. Chordamesoderm induces the anterior portion of the neural tube to form the precursors of the synapomorphic tripartite brain of vertebrates, and it will form a bulge called the diencephalon.
It is important in mediating saccadic eye movements. [2] It is probably not involved in smooth pursuit. [2] The PPRF generates excitatory bursts that are delivered to the ipsilateral abduecens nucleus to drive ipsilateral saccades (inhibitory saccadic stimuli are meanwhile delivered to the abducens nucleus from the contralateral medulla oblongata).
With this simple geometrical similarity, based on the laws of optics, the eye functions as a transducer, as does a CCD camera. In the visual system, retinal , technically called retinene 1 or "retinaldehyde", is a light-sensitive molecule found in the rods and cones of the retina .
The lateral line in fish and aquatic forms of amphibians is a detection system of water currents, consisting mostly of vortices. The lateral line is also sensitive to low-frequency vibrations. It is used primarily for navigation, hunting, and schooling. The mechanoreceptors are hair cells, the same mechanoreceptors for vestibular sense and hearing.
The accommodation reflex refers to the swelling of the lens of the eye that occurs when one looks at a near object (for example: when reading, the lens adjusts to near vision). [1] The eye's blind spot is a result of the absence of photoreceptors in the area of the retina where the optic nerve leaves the eye. [1]