Bipolar Cell Photoreceptors

After a retinal molecule absorbs light, the normally 11-cis form of the bound retinal molecule straightens to become the 11-trans from. This change activated the opsin molecule. Opsin activates transducin which is a G protein. This G protein then activates phosphodiesterase. Phosphodiesterase is an enzyme that breaks down cyclic-GMP. The break-down of cyclic-GMP removes them from the gated sodium channels and makes the gated sodium channels inactive. Because of this, sodium ion entry into the cytoplasm decreases.

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.

Neurons respond to two different ions: potassium(Na+) and sodium(K+). There is usually a higher concentration of Na+ ions outside the cell(extracellularly) which makes the cell more positive, rather than inside the cell(intracellularly) where there is a higher concentration of K+ ions which makes the cell more negative. This is explained as the resting membrane potential of a neuron; where there is a potential deferens of ion concentration. In cells ions will move from a region of higher concentration to a region of lower concentration and that is the concentration gradient. If channels permeable to an ion, then it will allow it to diffuse to where the ion

Processing of information in the central nervous system (Interneuron or relay neuron): The sensory neuron synapse with the interneuron in the spinal cord. In the central nervous system, the responses are again graded at the synaptic junction. Now the interneuron conducts nerve impulses from the sensory neuron to a motor neuron.

It plays a significant role in many neurological functions, including brain plasticity (4), learning and memory (5), and induction of pain (6). Poor or excess release of glutamate can cause serious neurodevelopmental and neurodegenerative disorders such as autism (7-9), epilepsy (7, 10-13), schizophrenia (14), Alzheimer’s disease (14-17) and Parkinson’s disease (18, 19). Physiologically, glutamate is released from pre-synaptic vesicles into neuronal synapses in response to action potential. The concentration of glutamate within the vesicles is reported to be ~100 mmol/L (20). The action potential firing mechanism primarily involves the movement of cations (Ca2+, Na+ and K+) across the neuronal membrane. Two voltage-gated ion-channels located in the axon permit active transport of K+ and Na+, into and out of the cells (20). This ion exchange creates a potential difference of -70 mV (resting potential) through the neuronal membrane. Sudden depolarisation or action potential occurs when potential drops, allowing Na+ to flood into the cells. Action potential is terminated to restore the resting potential of the membrane. Ca2+ channels open to allow the transport of Ca2+ (2). This ultimately causes glutamate to be released from its vesicle into the area between presynaptic membrane and postsynaptic membrane of the subsequent neuron. Through this electrochemical signal

These synaptic elements are in the different levels of expressions that are formed when matching of synaptic partners occurs. For example, olfactory receptor neurons (ORNs) are expressed when specific axons isolate themselves to antennal lobe that facilitates for them to connect with dendrites interneurons, which are also known as projection neurons (PNs). These projection neurons are very important because it is the passage that distributes information from one signal to another. Also, because the synaptic specificity examines the unique polarization of neuron organism and structure, we are told that R cells, which are the cells that receive information and send them to a synapse, and the atypical Cadherin Flamingo (Fmi) which are expressed only by incoming axons, are the ones that help in the facilitation of the formation of expression to occur. Also, synaptic partners are able to match and allow the signal to pass to the specificity synaptic via place holder and guidepost cells. In these place holders, and guideposts, there are Glia which aids in the matching of synaptic partners and their connectivity to occur. However, Glia does not help the non-neurons cells signals to

At least eight to ten layer V pyramidal neurons from the visual cortex monocular region were selected from each brain for analysis utilizing light microscopy. Each of these neurons had to have an apical dendrite of at least 80μm long and exhibited full Golgi impregnation represented by a lack of floating spine heads. Each neuron underwent analysis of the apical dendrite, and following regions if present: apical oblique (branch protruding from apical dendrite), first order basilar branch (branching directly from pyramidal cell), second order basilar branch (separated from first order branch), third order basilar branch (from second order branch) and forth order basilar branch (from third order branch). A segment of at least 10μm long and at least 2μm away from bifurcations, was selected from the structures mentioned above, and analyzed based on the number of dendritic spines and morphology of dendritic spines. Each dendritic spine was categorized based on similarity to 12 categories (Figure 1) modified from those described in Irwin et al., 2002 as seen in Figure 2. All final analyses were done under 100X magnification. Length of the each segment was recorded, as well as the thickness of the segment at the starting and end points. The segment thickness was recorded to ensure that any differences in dendritic spine density was not due to differences in dendritic branch thickness.

Duong, H., & Gest, T. (2013, June 6). Visual System Anatomy. Retrieved July 8, 2015,

The inhibitory control is provided by basket cells which are GABA-ergic. The GABA release is activated by incoming glutamate activity (7). Inhibition mediated by basket cells is enhanced when excitability increases during preparation prior to movement(motor set)(7). Basket cell activity helps control the output of PC and describing the discharge pattern of these cells. Double bouquet cells(DBC) are responsible for restricting the activity of minicolumn and preventing a spread of activity(7). They also inhibit basal and apical dendrites of the CM cell (7,11). Top-down influence mediated by thalamocortical connections and cortico-cortical connections result in activation of local GABA-ergic interneurons and glutamatergic neurons, inhibition of the basket cells/chandelier/DBC results in disinhibition of the CM cells leading to the conversion of No-Go to Go (7). The position of DBC enables its role in controlling the horizontal influence of overlapping PC(7). Recent studies indicate critical role of inhibitory interneurons located in L1- a)single bouquet cell which inhibits local interneuron that has an effect on dendrites, soma, axon hillock of L5 pyramidal cell but not the pyramidal cell itself(disinhibition effect on few PC) and b) Neurogliaform cells- inhibition of apical dendrites of numerous PC(widespread inhibition)(7). The disinhibition circuit is established in the

passes along the axon and reaches the axon of the boulevard. Axon bulb produces the substance

When a P-type ganglion cell is sent from the retina, then the layers that make up the parvocellular LGN

The objective of this study is to investigate the molecular mechanisms responsible for non-image-forming visual responses, such as the coordination of the biological clock. Because retinal rod and cone cells are not required for non-image-forming visual responses, the researchers hypothesized that retinal ganglion cells (RGC) may be the light sensitive cells utilized in the non-image-forming visual response pathway. The researchers also hypothesized that if the RGCs are light sensitive, then the protein melanopsin, which is found on the surface of RGCs, is likely the photopigment that causes RGCs to respond to light.

* Retina-is the light sensitive part of the eye. The part that converts the light stimuli into neural signals to be interpreted by the cerebral cortex. I will not discuss how the photoreceptors convert the light stimuli into electrical signals, since it involves bio-chemistry, a good description can be found in any physiology book. Light must pass through the neural layers of the retina before reaching the photosensitive layer which consists of rods and cones. The neural layer consist of ganglion cells and bipolar cells. The bipolar cells take the electrical from the photoreceptors to the ganglions cell which in turn form the optic nerve that connect the eye to the brain. The optic nerve and the blood circulation apparatus leave the eye at the optic disc or the blind spot. Named so because it has not photoreceptors. A special part of the retina crucial of acute vision is which does