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Light from a single point of a distant object and light from a single point of a near object being brought to a focus. The accommodation reflex (or accommodation-convergence reflex) is a reflex action of the eye, in response to focusing on a near object, then looking at a distant object (and vice versa), comprising coordinated changes in vergence, lens shape (accommodation) and pupil size.
Reflex arc demonstrated. When a reflex arc in an animal consists of only one sensory neuron and one motor neuron, it is defined as monosynaptic, referring to the presence of a single chemical synapse. In the case of peripheral muscle reflexes (patellar reflex, achilles reflex), brief stimulation to the muscle spindle results in contraction of ...
Schematic diagram of the human eye. It shows a horizontal section through the right eye. The eye is made up of three coats, or layers, enclosing various anatomical structures. The outermost layer, known as the fibrous tunic, is composed of the cornea and sclera, which provide shape to the eye and support the deeper structures.
Virtual eye showing the contribution to focus of different components. Due to the nature of optics the focused image on the retina is always inverted relative to the object. Different animals live in different environments having different refractive indexes involving water, air and often both. The eyes are therefor required to bend light ...
The simplest reflex is initiated by a stimulus, which activates an afferent nerve. The signal is then passed to a response neuron, which generates a response. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs via neural pathways in the nervous system called reflex arcs.
The optokinetic reflex (OKR), also referred to as the optokinetic response, or optokinetic nystagmus (OKN), is a compensatory reflex that supports visual image stabilization. [1] The purpose of OKR is to prevent motion blur on the retina that would otherwise occur when an animal moves its head or navigates through its environment.
The two different types of near response are caused by different underlying disease processes. Adie's pupil is caused by damage to peripheral pathways to the pupil (parasympathetic neurons in the ciliary ganglion that cause pupillary constriction to bright light and with near vision). The pathophysiologic mechanism which produces an Argyll ...
Different species are able to see different parts of the light spectrum; for example, bees can see into the ultraviolet, [55] while pit vipers can accurately target prey with their pit organs, which are sensitive to infrared radiation. [56] The mantis shrimp possesses arguably the most complex visual system of any species. The eye of the mantis ...