It is important to know both the general principles that govern the pattern and the rates of myelination of different regions of the brain.
Midget[ edit ] Midget retinal ganglion cells project to the parvocellular layers of the lateral geniculate nucleus. Histology thalamus cells are known as midget retinal ganglion cells, based on the small sizes of their dendritic trees and cell bodies. They receive inputs from relatively few rods and cones.
They have slow conduction velocityand respond to changes in color but respond only weakly to changes in contrast unless the change is great Kandel et al.
They have simple center-surround receptive fieldswhere the center may be either ON or OFF while the surround is the opposite. Parasol[ edit ] Parasol retinal ganglion cells project to the magnocellular layers of the lateral geniculate nucleus.
These cells are known as parasol retinal ganglion cells, based on the large sizes of their dendritic trees and cell bodies. They receive inputs from relatively many rods and cones.
They have fast conduction velocity, and can respond to low-contrast stimuli, but are not very sensitive to changes in color Kandel et al. They have much larger receptive fields which are nonetheless also center-surround.
Bistratified[ edit ] Bistratified retinal ganglion cells project to the koniocellular Histology thalamus of the lateral geniculate nucleus. Bistratified retinal ganglion cells have been identified only relatively recently.
Koniocellular means "cells as small as dust"; their small size made them hard to find. They receive inputs from intermediate numbers of rods and cones.
They have moderate spatial resolution, moderate conduction velocity, and can respond to moderate-contrast stimuli.
They may be involved in color vision. They have very large receptive fields that only have centers no surrounds and are always ON to the blue cone and OFF to both the red and green cone. Photosensitive ganglion cell[ edit ] Photosensitive ganglion cellsincluding but not limited to the giant retinal ganglion cells, contain their own photopigmentmelanopsinwhich makes them respond directly to light even in the absence of rods and cones.
They project to, among other areas, the suprachiasmatic nucleus SCN via the retinohypothalamic tract for setting and maintaining circadian rhythms.
Other retinal ganglion cells projecting to the lateral geniculate nucleus LGN include cells making connections with the Edinger-Westphal nucleus EWfor control of the pupillary light reflexand [[giant retinal ganglion cells Physiology[ edit ] Most mature ganglion cells are able to fire action potentials at a high frequency because of their expression of Kv3 potassium channels.
For a reference source, please consult "Connecting the Retina to the Brain" by Erskine et al. Then, RC growth will sweep out ventrally and peripherally from there, in a wave-like pattern. The cell soma will pull towards the RPE, undergo terminal differentiation, and then migrate backwards towards the inner limiting membrane.
It will then extend an axon in the retinal ganglion cell layer. This process is likely mediated by Slit-Robo signaling, which controls the retraction of the apical process of the RGC. Slit signaling also plays a role, preventing RGCs from growing into layers beyond the optic fiber layer.
Once differentiated, they are bordered by an inhibitory peripheral region and a central attractive region, thus promoting extension of the axon towards the optic disc. CSPGs exist along the retinal neuroepithelium surface over which the RGCs lie in a peripheral high-central low gradient.
Shh is expressed in a high central, low peripheral gradient, promoting central-projecting RGC axons extension via Patched-1, the principal receptor for Shh, mediated signaling.
This morphogen initially attracts RGC axons, but then, through an internal change in the growth cone of the RGC, Netin-1 becomes repulsive, pushing the axon away from the optic disc. RGCs will grow along glial cell end feet in the optic nerve.
These glia will secrete repulsive Semaphorin 5a and Slit in a surround fashion, covering the optic nerve which ensures that they remain in the optic nerve.
Vax1, a transcription factor is expressed by the ventral diencephalon and glial cells in the region where the chiasm is formed, and it may also be secreted to control chiasm formation.
Building the repulsive outline of the chiasm[ edit ] Once RGCs reach the chiasm, the glial cells supporting them will change from an intrafascicular to radial morphology.An understanding of cerebral vascular territories is important in understanding stroke and complications from surgery and endovascular procedures.
Although one could be excused for thinking that within the brain, such a carefully organised orga. SSB HISTOLOGY Nervous Tissue. SELF-ASSESSMENT QUESTIONS. NOTE: The following questions are designed for introductory drill. They do not necessarily represent the quality of questions which will appear on the Unit evaluation.
Thalamus The internal medullary lamina is a thin sheet of white matter that runs longitudinally through the thalamus, separating it into medial and lateral nuclear masses. Wheater's Nervous tissues and Central nervous system. Text. Ross and Pawlina (6th ed), Chapter 12 Nerve Tissue.
The medial surface of the section is the posterior portion of the thalamus and a small portion of the cerebral peduncle. Look at the margins of the ventricle at higher magnification and note that it is entirely lined by. Cerebellar ataxia. Cerebellar ataxia can be either acute or chronic.
Chronic ataxia is sometimes referred to as cerebellitis, and is seen in people with multiple sclerosis (MS). Cerebellar ataxia is a form of ataxia that originates from abnormalities such as inflammation in the occipital and temporal lobes of the leslutinsduphoenix.com cerebellum is found at the back of the brain, below the cerebrum.
A retinal ganglion cell (RGC) is a type of neuron located near the inner surface (the ganglion cell layer) of the retina of the leslutinsduphoenix.com receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine leslutinsduphoenix.com amacrine cells, particularly narrow field cells, are important for creating functional subunits within the ganglion cell layer and.