Neural Control and Coordination Test - 3

The term aperture represents a hole through which light enters the eye. It is known as pupil. Its size can be changed by iris. Iris is a thin circular structure in the eye. It controls the diameter and size of the pupil (aperture of the eye) and thus regulates the amount of light entering the pupil and reaching the retina.
So, the correct answer is 'Iris'.

Cones are the secondary photoreceptors that are stimulated by bright light and are responsible for color perception. The presence of slightly different photopigment in different cones allows them to absorb a particular wavelength more strongly than others. Rods are repolarized by dim light and are responsible for night vision. Choroid lacks rods and cones. The correct answer is A.

The retina makes up the inner layer and occupies only the posterior two-third of the eye. The retina consists of several layers of cells, including the rods and cones, the sensory cells, that respond to light. The tips of the rods and cones are embedded in a pigmented layer of cells on the back of the retina. The pigment helps prevent light from scattering in the back of the eye.

All photoreceptors share a common visual pigment: a mixture of a vitamin A-based chromophore (retinal) and a seven-transmembrane-helix apoprotein (opsin). Together, they form rhodopsin. The pigments belong to a special class of receptors called as G protein-coupled receptors, characterised by signaling through heterotrimeric G proteins. 
In vertebrates, the rhodopsin is thermally unstable, breaking down with light into the opsin and chromophore; rhodopsins are maintained by an enzymatic process. Invertebrate rhodopsins are stable, although renewal also must take place there.

If the light source in front of eye becomes bright suddenly, then the amount of light entering the eye will increase. The pupil will then adjust to regulate the amount of light entering into eye. The lens will change the focus according to the light entering the eye. The size of pupil is regulated by iris which contracts to decrease the size of pupil. This regulation of light entering the eye by adjusting the size of pupil is called accommodation.
So, the correct answer is 'Focus of lens will change'.

The retina is a layered structure with several layers of neurons interconnected by synapses. The only neurons that are directly sensitive to light are the photoreceptor cells. These are mainly of two types: the rods and cones. Rods function mainly in dim light and provide black-and-white vision, while cones support the daytime vision and the perception of colour. The third type of photoreceptor, the intrinsically photosensitive ganglion cell, is important for reflexive responses to bright daylight. Neural signals from the rods and cones undergo processing by other neurons of the retina. The output takes the form of action potentials in retinal ganglion cells, whose axons form the optic nerve. 

The change in the shape of the lens is controlled by the cilliary 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.

Rhodopsin serves as a visual purple pigment of rod cells and is responsible for night vision. Rhodopsin deficiency causes night blindness. Myopia is caused by elongation of eyeball while shortening of eyeball causes hypermetropia. The cornea is the transparent anterior window of an outer layer of the eyeball and does not have rods. Thus, the correct answer is option D.

Myopia also known as nearsightedness or short-sightedness is a condition of the eye where light focuses in front, instead of on the retina. People having myopia can see close objects clearly, but objects farther away appear blurred. It occurs if the eyeball is too long or the cornea is too curved. So, the correct answer is option B.

The vitreous cavity is located behind the lens i.e., the posterior cavity and in front of the retina. It is filled with a gel-like fluid, called as the vitreous humour.

Among many nocturnal vertebrates, the white compound guanine is found in the epithelium or retina of the eye. This provides a mirror-like surface, the tapetum lucidum, which reflects light outward and thereby allows a second chance for its absorption by visual pigments at very low light intensities at night. Tapeta lucida produces the familiar eyeshine of nocturnal animals.

At extremely low intensities of stimuli, when only rods are stimulated, the retina shows a variable sensitivity to light according to its wavelength, being most sensitive at about 5000 angstroms, the absorption maximum of the rod visual pigment, rhodopsin. There is a characteristic shift in the maximum sensitivity from 5000 angstroms for scotopic (night) vision to 5550 angstroms for photopic (day) vision, called Purkinje shift.

The yellow spot or macula is an oval yellow spot near the centre of the retina of the human eye. It has a size of 1.5 millimeters. It is specialized for seeing things with highest clearness or visual acuity. It is the area of best vision, where maximum amount of rod cells and cone cells are present.

Neuroectoderm gives rise to the following compartments of the eye: retina, epithelial lining of ciliary body and iris, optic nerves. Surface ectoderm produces the following parts: lens, corneal epithelium, skin of eyelid.

Presbyopia occurs due to decrease in the power of accommodation of the eye usually because of ageing which causes gradual weakening of the ciliary muscles and diminishes flexibility of the eye lens.

Myopia is a defect of vision in which far objects appear blurred but near objects are seen clearly. The image is focused in front of the retina rather than on it usually because the eyeball is too long or the refractive power of the eye’s lens too strong. Myopia can be corrected by wearing glasses with concave lenses these help to focus the image on the retina.

Colour blindness and haemophilia are both X-linked recessive disorders. 

Red-green colour blindness, a very common trait in humans affects between 7% and 10% of men and 0.49% to 1% of women. 

Hemophilia A, a blood clotting disorder is caused by a mutation of the factor VIII gene and hemophilia B, also known as 'Christmas disease', is a blood clotting disorder, caused by a mutation of the factor IX gene. 

The light is mapped as an image along the surface of the retina by activating a series of light-sensitive cells which are known as rod cells and cone cells. These photoreceptor cells convert the light into electrical impulses, which are transmitted to the brain via nerve fibres. The neurons of the retina are arranged in 3 main layers separated by 2 intermediate layers whose main purpose is to make connections among the various neurons. The deepest layer of neurons processes the light first. These neurons are the photoreceptors, the only cells in the retina that can convert light into nerve impulses. The photoreceptor layer then transmits these impulses to the bipolar neurons in the second layer and on to the ganglion neurons in the third layer. It is only the axons of these ganglion neurons, that exit the eye and carry the nerve impulses to the first visual relay in the brain.

There are six extraocular muscles that move the globe (eyeball). These muscles are named the superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, and inferior oblique.

The Meibomian gland (often written with a small "m" and also called tarsal gland) is a holocrine type of exocrine gland, at the rim of the eyelid inside the tarsal plate, responsible for the supply of meibum, an oily substance that prevents evaporation of the eye's tear film.

The harderian gland is a gland found within the eye's orbit, which occurs in tetrapods (reptiles, amphibians, birds and mammals) that possess a nictitating membrane. The gland can be compound tubular or compound tubuloalveolar, and the fluid it secretes (mucous, serous or lipid) varies between different groups of animals. In some animals it acts as an accessory to the lacrimal gland, secreting fluid that eases movement of the nictitating membrane.

Presbyopia is caused by an age related process. It occurs due to a gradual thickening and loss of flexibility of the natural lens inside the eye. These age related changes occur within the proteins in the lens, making the lens harder and less elastic over time. Age related changes also take place in the muscle fibers surrounding the lens. Changes in the lens curvature progressively cause diminished ability to focus on near objects. 
So, the correct answer is option C.

The term stereoscopic vision refers to the human ability to view with both eyes in similar, but slightly different ways. This allows humans to judge distance, which develops their ability to have true depth perception.

Stereoscopic vision is particularly well developed in mammals with foveas, frontal vision, hemidecussatting visual pathways, and vergence eye movements, such as felines and primates.

Stereopsis is an aspect of "normal" healthy vision. Here's how it works. First, both eyes must be accurately aimed at the same target (that's binocular vision, but it's not yet stereoscopic vision!) Then, because the two eyes are located in different positions, each takes in a unique view from its own perspective.

Pigmented connective tissue is a type of loose connective tissue. In rabbits it is found in the choroid.
Choroid is the layer of the eye behind the retina, contains blood vessels that nourish the retina.

Tears are a clear liquid secreted by the lacrimal glands (tear gland) found in the eyes of all land mammals (except for goats and rabbits).

Their functions include lubricating the eyes (basal tears), removing irritants (reflex tears), and aiding the immune system.Tears also occur as a part of the body's natural pain response.

The plica semilunaris in humans is a small fold of tissue on the inside corner of the eye. It is the vestigial remnant of the nictitating membrane, an organ that is fully functional in some other species of mammals.

Hyalocytes, also known as vitreous cells, are cells of the vitreous body, which is the clear gel that fills the space between the lens and the retina of the eye. Hyalocytes occur in the peripheral part of the vitreous body, and may produce hyaluronic acid, collagen, fibrils, and hyaluronan.

Telescopic vision is the ability to see small items at far distances with great acuity. Hawks and eagles can see a prey more than a mile away. Like a telescopic camera lens, the birds with telescopic vision tend to have elongated eyeballs to improve distance vision. An owl's eyeball is more like a tube and this increases the focal length of the eye and gives it telescopic vision.