Role of Retinal Waves on Three Aspects of Visual System Develoment

25. Reticular formation is an area of neurons running through the middle of the medulla and the pons, and slightly beyond, that is responsible for selective attention.

The proper functioning of the cells allow us to act, think, learn, remember and control complex behaviors. In order to understand how the brain performs these essential functions we must first understand the different components of the cells; such as the function of neurons and their supporting cells in the nervous system. The communication from neuron to neuron, the processes involved in the production of an action potential, how an action potential is conducted along a myelinated axon; and the process of synaptic transmission will be discussed and examined.

The latest research into development and learning of babies and young children shows that early stimulation are vital to the healthy development of brain. Babies are born with 100 billion neuron cells and they need to connect together in order to function. Many of these connections are made as result of what a baby senses and experiences. Stimulation, sufficient sleep and healthy diet makes a difference in allowing connections to be made. Development of brain begins well before birth. Neurons (cells in the brain which transmit electrical impulses to other cells) are formed between the 10th and 20th week of pregnancy. These cells are critical as they will later join together to allow the brain to function properly. Electrical pulses pass between cells via dendrites and axons which causes the connection between the neuron cells. The dendrites and axons of the neurons develop and begin the process of joining up in the final two months of pregnancy. Those that have not made enough strong connections are killed off and this is one reason why some children are

Explain the visual process, including the stimulus input, the structure of the eye, and the transduction of light energy.

After being shown a picture of an elephant they eye will take the light that is reflected from the object and it will enter the eye through the pupil. Then the light will be focused by the cornea and the lens to form a sharp image of the elephant in the retina. The retina is the network of neurons that cover the back of the eye and contains the visual receptors for a person vision. The visual receptors are made up of cones and rods that contain light sensitive chemicals called visual pigments. Visual pigments reacht to light and cause a triggered electrical signals to occur. These electrical signals will then flow through a network of neurons and this network of neurons is what makes up a persons retina. After the flow through the network of neurons occurs the electrical signals will emerge from the back of the eye in the area

Focusing an image clearly onto the retina is the initial step in the process of vision, but although a sharp image on the retina is essential for clear vision, a person does not see the picture on the retina. Vision occurs not in the retina, but in the brain. Before the brain can create vision, the light on the retina must activate the visual receptors in the retina by a two-element

When it comes to vision, we see things based on the light reflected from surfaces. The reflected light waves enter the eye through the cornea at the front of the eye, it's resized at the pupil, focused by the lens, and hits the retina at the back. The light is then detected by rods and cones, photoreceptors, which alters the light into electrical signals. The optic nerve transmits those vision signals to the lateral geniculate nucleus, where visual information is transmitted to the visual cortex of the brain then converts into the objects that we see.

How do we know infants can see at birth? They can’t tell us. For this we depend on clues such as eye movement, light sensitivity and the appearance of the eye. Though an infant 's vision is present at birth the strength of their vision is far from mature. However, vision develops rapidly in infants, going from only being able to focus on images 4 to 30 inches away to a rapid ability to see details and shape (Berger, 2014). By 3 months these same infants with immature ability can see patterns color and motion. Surveys and medical research are regularly used to develop a better understanding of infant development.

There is perfect correspondence between the retinal image and the cellular encoding in V1 (striate cortex), which is completed in terms of contrast and orientation. From there, information from the retinal image is sent forward to distinct regions of the occipital lobe for more complex encoding, called extra striate cortex, including V2 (discrimination, orientation, and color), V4 (shape), and V5 (motion) “(Stevens PH.D., livestong.com)

To understand the diverse causes of RP, a basic understanding of visual perception is required. Phototransduction (conversion of light to electrical signals) occurs first, which is initiated by two types of photoreceptors: rods and cones. These two types vary in their function as rods are primarily responsible for night vision and lack sensitivity to color while cones function in color vision. Light contacts these photoreceptors, and isomerizes a retinaldehydechromophore (retinal) which is bound to varying types of opsin proteins corresponding in their reactivity to different wavelengths of light. Upon absorption of a photon of light, the chromophore 11-cis-retinal is isomerized to the all-trans confirmation, which subsequently causes a series of molecular interactions which ultimately result in the electrical response of the photoreceptors (Vugler 2010). As 11-cis-retinal is required to absorb photons of light, this compound must be regenerated, a function that is performed with the aid of nearby cells of the retinal pigment epithelium

The primate visual system is usually separated in two partially independent pathways; the dorsal pathway subserves mostly motion perception, while the ventral one subserves object feature recognition. The primary visual cortex (V1) receives most of its retinal input through the lateral geniculate nucleus (LGN). Anatomical and functional segregation of visual perception starts at the level of the retina, where parvocellular (P) ganglion cells have small receptive fields and have sustained colour-sensitive synaptic response to light, whereas magnocellular (M) ganglion cells have larger receptive fields and a faster adapting achromatic response to light [Livingston et al., 1992]. Both types of cells project to the layers 3-6 and 1-2 of the LGN, respectively, which in turn send most of their outputs to layers 4Cβ and 4Cα of V1, forming what is known as the P and M pathways [Refs].

Fig. __ Feed-forward projections from the eyes to the brain and topographic mapping. In each eye the visual field on the left and right of the fovea (the cut goes right through the fovea!) projects to different cortical hemispheres: the ipsilateral retina projects to the ipsilateral visual cortex, and the contralateral retina crosses the contralateral cortex (hemifield crossing in the optic chiasma). The first synapse of the retinal ganglion cells is in the lateral geniculate nucleus (LGN), but information from the left (L) and right (R) eye remains strictly separated. The LGN consists of six layers, layers 1 and 2 are primarily occupied by the magnocellular pathway, and 3–6 by the parvocellular. Information from both eyes comes first together

According to current research there are about 800,000 ganglion cells in the human optic nerve (J.R. Anderson, 2009,pg. 35). The ganglion cells are where the first encoding of the visual information happens. Encoding is the process of recognizing the information and changing it into something one’s brains can understand and store. Each ganglion cell is dedicated to encoding information from a specific part of the retina. The optic nerve goes then to the visual cortex and the information enters the brain cells. There are two types of cells that are subcortical, or below the cortex; the lateral geniculate nucleus and the superior colliculus. The lateral geniculate nucleus is responsible for understanding details and recognizing objects. The superior colliculus is responsible for understanding where objects are located spatially. This collection of cells working together is called the “what-where” distinction. The division of labor continues, as the information is further processes. The “what” information travels to the temporal cortex, the “where” information travels to the parietal regions of the brain.

Eye development is initiated by the master control gene Pax-6, a homeobox gene known as Andridia in humans, small eye in mouse, and eyeless in Drosophila. The Pax-6 gene locus is a transcription factor for the various genes and growth factors involved in eye formation. Eye morphogenesis begins with the evagination, or outgrowth, of the optic grooves or sulci. These two grooves in the neural folds transform into optic vesicles with the closure of the neural tube. The optic vesicles then develop into the optic cup with the inner layer forming the retina

Normal vision occurs by a coordinated synthesis of the retinal images into a single brain image. If, however, one of the eyes does not transmit a coordinated or useful image the brain may choose to ignore this image when conducting its synthesis. The region of the