Synthetic Review: Visual topographic maps - Arielle Allentoff
One central question in developmental neurobiology is how neuronal growth cones and axons are guided along precise pathways to the right target area, and how they establish appropriately ordered connections within their targets. Topographic mapping is the idea that projecting neurons map onto a target field so that the spatial arrangement of the neurons is preserved in the spatial order of their axonal connections. The projection of retinal ganglion cells (RGCs) to the optic tectum (birds, fish, amphibians) and to the superior colliculus (its counterpart in mammals) has been the major model for studies on the construction of topographic maps. Sperry (1963) proposed the chemoaffinity theory of topographic mapping in which there are labels in gradients across the projecting and target fields and axons are able to locate their target location by matching up the labels. Since then evidence from a variety of studies including tissue grafting and ablation, axon tracing, and in vitro axon guidance assays have supported the idea of complementary retinotectal mapping labels (Goodman and Shatz, 1993; Tessier-Lavigne, 1995; Garrity and Zipursky, 1995).
Prior to these studies, immunocolocalization studies indicated that Eph receptors are present on developing axon tracts, providing the first indication that the Eph receptor family may play a role in axon guidance (Pasquale et al. 1992; Henkemeyer et al. 1994; Soans et al. 1994). In 1994, the first ephrin, ephrin-A1, was discovered (Bartley et al. 1994). Shortly after, ELF-1 (Ephrin-A2) was identified as a GPI-anchored ligand that binds to Sek and Mek4 receptors (Cheng and Flanagan, 1994). Following identification of the ligands, m...
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...ugh their results do not fit with mapping solely specified by counterbalanced gradients, there could be additional gradients at play. It is also conceivable that some degree of topographic order could be found in the absence of labels, via mechanisms based on the timing of axon growth and arrival. Additionally, their surprising finding that the ephrins are involved in dorso-ventral mapping leads to two possible models whereby either the dorsoventral mapping phenotype is a primary effect of the loss of dorsoventral labels, or is a secondary effect of the loss of anteroposterior labels. Future studies could investigate the role of EphB receptor tyrosine kinases and their ephrin-B ligands using loss-of-function and gain-of-function techniques. Additionally double knockouts of EphB and EphA receptors or ligands could be carried performed to help differentiate effects.
Stone, J. (1972). Morphology and physiology of the geniculocortical synapse in the cat: The question of parallel input to the striate cortex. Investigative Ophthalmology & Visual Science, 11, 338-46.
The two artworks I decided to discuss are A thousand peaks and myriad ravines by Wang Hui for the Chinese artwork and View of Kojima Bay by Ike Taiga as the Japanese artwork. Both these share a few similarities including the subject of the artwork being the landscape and naturalism. In A thousand peaks and myriad ravines by Wang Hui you can notice very clear detailing and lining from the top trees of the mountains to the very small fishers and scholars portrayed towards the bottom and center of the artwork. Primarily, this artwork emphasizes the detail. The portrait is mostly taken up by the mountains and that around it. The range of colors used in this hanging scroll consist of the grey scale and a golden bronze done with a very thin brush.
...e in the brain to deliver electrical stimulation to targeted areas that control movement (mayoclinic.com, 2013).
Hubel and Wiesel’s research surrounding area V1 of the primary visual cortex provided one of the first descriptions of the receptive fields in mammals. By flashing various lines along the receptive field, Hubel and Wiesel were able to classify cortical neurons into two distinct groups; simple and complex (Hubel & Wiesel, 1963). The use of manually mapping the receptive fields with simple dots, lines and edges meant that they not only discovered orientation tuning in single neurons, but also described the columnar organisation of ocular dominance and orientation preferences in the cerebral cortex (Ringach, 2004). Although Hubel and Wiesel’s findings were an extreme advance in our understanding of the visual cortex (Wurtz, 2009), it became apparent that there were cells in the visual system that responded to stimuli far more complicated than orientated lines meaning that the cells in area V1 were much more modifiable than Hubel and Wiesel had suggested. In this essay, Hubel and Wiesel’s classic receptive field shall be discussed along with reasons as to why it can no longer offer us a satisfactory explanation into visual perception. First to be discussed are the specific types of cells which were defined in Hubel and Wiesel’s classic experiment into the striate cortex.
The Vinland Map is believed to predate Christopher Columbus’ expedition by almost 50 years as it has realistic cartography of the island of Vinland, thought to be a part of Canada or even Northeastern America. The map could potentially provide evidence that the Norse explorers were the first Europeans to visit America and map it. However, there is doubt surrounding the origins and age of the map. These issues have divided scientists into two groups devoted to proving the authenticity or lack thereof of the map. Recent research has used several chemical analyses which have examined specifically the paper and the ink present on the map. The most recent methods used to test the map have been carbon dating and Raman spectroscopy. It is thought that the map was written on paper which has origins in pre-Columbus days. However, several analyses of the ink have revealed the presence of anatase, a form of TiO 2, which was not developed until the first part of the 20 th Century. This clearly would contradict the evidence that the paper is authentic. However, these two claims do not necessarily contradict one another.
...t has been noted that the gate control theory proposed by Melzack and Wall in 1965 formed the foundation of understanding the process of pain signal transmission. The dorsal horn of the spinal cord is the region of the CNS that controls the passage of pain signals by means of opening and/or closing the gate. Pain can only be perceived if reaches the brain. Events that cause excitation such pain signals and the release of excitatory or facilitatory chemicals cause the gate to open whereas inhibitory events such as competing nerve impulses caused by rubbing trigger closure of the gate. The gate can also be closed due to descending inhibition enhanced by relaxation or the use of pain-relieving medication such as morphine. The brain stem is responsible for controlling the transmission of pain signals via the ascending and descending pain pathways.
9)Organization of amygdaloid projections to brainstem dopaminergic, noradrenergic and adrenergic cell groups in the rat, Brain Res Bull, 1992, volume 28, pp 447-454, Very detailed info
Let’s say that there is a mechanical sense. If someone touched your hand, your somatosensory system will detect various stimuli by your skin’s sensory receptors. The sensory information is then conveyed to the central nervous system by afferent neurons. The neuron’s dendrites will pass that information to the cell body, and on to its axon. From there it is passed onto the spinal cord or the brainstem. The neuron's ascending axons will cross to the opposite side either in the spinal cord or in the brainstem. The axons then terminates in the thalamus, and on into the Brodmann Area of the parietal lobe of the brain to process.
Sperry, R. W. (1963, October 15). Chemoaffinity in the Orderly Growth of Nerve Fiber Patterns and Connection. Natioanl Academy of Science, 50(4), 703-710.
There are two main basic cells: afferent neurons and efferent neurons. Afferent neurons act as the cells that gather the information or stimuli from sensory receptors and take it back to the spinal cord. Efferent neurons do just the opposite. The send a response that is triggered by the spinal cord or brain back to the proper muscles or cells to generate a response. Ef...
Neurons and glia (cells that support neurons) are specialized cells for electrical signaling over long distances. Understanding neuronal structure is important for understanding neuronal function.
Chick embryo studies provide a relatively good model for defining the effects of ethanol at many organizational levels of neurogenesis, cell death, neuronal migration and differentiation, cell to cell connectivity, and synaptic function When ethanol is administered to embryos on days one to three of development, the cholinergic neuronal phenotypes were markedly decreased possibly in the sparing of catecholaminergic phenotypes which were increased. This differential sensitivity of these two early neuroblast populations to ethanol may also reflect the difference in their ontogenesis: cholinergic elements are reported to be expressed as early as the primitive streak, whereas catecholaminergic elements appear later (3).
Acetylcholine is possibly the most widely used neurotransmitter in the body, and all axons that leave the central nervous system (for example, those running to skeletal muscle, or to sympathetic or parasympathetic ganglia) use acetylcholine as their neurotransmitter. Within the brain acetylcholine is the transmitter of, among other neurons, those generating the tracts that run from the septum to the HIPPOCAMPUS, and from the nucleus basalis to the CEREBRAL CORTEX -- both of whbasalis to the CEREBRAL CORTEX -- both of which seem to be needed to sustain memory and learning. It is also the neurotransmitter released by short-axon interneurons of the BASAL GANGLIA.
When people think of geology, they usually think of rocks and fossils. However, geology is actually a very large field of study. The knowledge of geologists ranges from rocks and fossils to the moon and other planets (Hammonds 7-8). Geologists use a variety of subjects in their work, but the sciences and math are the most important. Some of the sciences geologists study are physics and chemistry (12). English is also a subject that geologists use when communicating with other scientists, the media, and the public (12) . Because of these tasks, it is important for geologists to have a wide knowledge of these different subjects.
The world we live in today is always changing, whether it be technology or the land. As these changes take place, society must adapt to them. Many things begin to change as a result of this and society beings to turn into something completely different. One of the most overlooked changes that takes place is that of the environment and landscape. The landscape is one of the most important parts of our society’s culture and has a great effect on how we live. It seems that nowadays, many individuals are taking advantage of the land and nothing appreciating it for every thing that it is worth. Its true that not everyone is going to look at the environment and landscape in the same way, however that is no excuse to disrespect it. Then again, a whole new argument can start from that, as different individuals are going to have different views on what disrespecting the land. Many positive things have come from taking advantage of the land, and also, there have been many negative things to come as a result of this. It all depends on how you look at it. One thing is for sure though, no matter what the case is, the land and environment we live in plays a huge part in each of our everyday lives.