Mechanisms of the Nervous System to Guide Axonal Growth and to Determine the Survival of Neurons - Essay Example

?The various mechanisms used by the nervous system to guide axonal growth and to determine the survival of neurons The nervoussystem is consisted of a network of specialised cells known as neurons, which coordinate the actions of a living animal as well as transmitting signals between different parts of the body. In human beings, the nervous system is consisted of the brain, the spinal cord and the retina (63).1 The peripheral nervous system in human beings is constituted by ganglia and nerves that join each ganglion to the central nervous system and sensory neurons (63).2 Complex neural pathways interconnect these regions. An axon, which is also known as a nerve fiber, is a nerve cell’s extension from the neuron’s body and conducts electrical impulse. The nervous system provides precise paths that are used by the axons to reach the correct targets in a process referred to as axon guidance or axon path finding (62).3 This essay is a discussion of various mechanisms that the nervous system uses to guide axonal growth and to determine the survival of neurons. Axonal growth is topic of interest in the medical science because the damage to the nervous system and especially the spinal cord is impossible to repair (62).4 It is also important because this growth continues even after a baby is born and; therefore, it is possible to ascertain how postnatal environment influence axon growth and behavioral patterns in an individual. In vertebrates, the embryonic development comprises the differentiation of neurons from stem cell that propels immature neurons from their birth places to their destinations (43).5 It also comprises the outgrowth of axons from neurons and guidance of motile growth cone through the embryo to the postsynaptic partners, the generation of synapses between the axons and their partners as well as the continual synaptic changes in the memory and learning (43).6 The growth of the axon is guided by the mechanism of a growth cone, which is a small area at the tip of a growing axon. When an axon is growing, the growth cone moves forward and add new material to the cell membrane of the axon bringing about its extension. In addition, there is also new axonal membrane, which is added at other points along the axon, but this happens to a much lesser extent (62).7 In its forward movement, the growth cone moves through the extra cellular matrix because it is pulled and pushed. There are several types of axonal pathway that have been studied in model systems in a bid to understand the mechanisms of axon guidance (63).8 The growth of axons is important to the development of the nervous system because axons are primary constituents of neurons in the nerves. The nervous system is most likely to have defects in various ways resulting from genetic defects, physical injury, trauma, infections of aging impact. The neurons that constitute nerves reside within the brain, the peripheral ganglia, and the central cord. The mechanisms that lead to the growth of axons, therefore, lead to a microcosmic growth and development of the nervous system. During the growth of axon, a thin membrane extension called filopodia pulls its growth cone thus initiating the growth. The filopodium synthesises actin microfilaments, which are able to contract just like muscles. As microfilaments contract so does the filopodia and pulls the rest of the growth cone along. Moreover, nervous system uses another mechanism known as microtubule formation to guide axonal growth. The synthesis of microtubules pushes the growth cone and the cell body pushes the cone at the arrival of material transported along the axon thus, bringing about the growth of axons. One component of guidance in microtubule formation is adhesion, which is illustrated by an experiment using a culture tissue (63).9 In this experiment, it is observed that neurons extend neuritis because axons are very similar to dendrites at their leading edges. The growth cones are also observed to adhere strongly to some substances like laminin and guide post cells (65).10 In this way, growth cones enable the growth of axons by responding to proximal and distance cues (66).11 Neurons divide at a very high rate in early life, but at some stage, some cells stop dividing (67).12 It reaches a time when proliferation of neurons stops and cells are no longer able to divide. This hesitation of axons growth is significant to the neural system because axon proliferation is wasteful, and over 50% of neuron blast dies before they achieve their intended function (67).13 An experiment carried out to investigate the relationship between the size of target tissue in chick embryos and the size of a group of neurons that innerated it leads to two hypotheses. The first hypothesis is that the number of neurons in the neuron pool is reduced or increased to match their size (68).14 Secondly, the neurons that obtains enough alexir, which are secreted by targets and received by innerating neurons at synapsis, stay alive. On the other hand, evidence has it that in mice, cell death occurs in two phrases during development, and one of these phrases is at the period of inneration (68).15 Therefore, neuron survival is determined by programmed death called apoptosis or by normal damage, injury or stroke among other means (69).16 In conclusion, the nervous system uses several mechanisms to guide axonal growth and to determine the survival of neurons. It is evident that in guiding axonal growth, the nervous system uses growth cones, which grow by moving forward and adding new material to the cell membrane and by the growth cones filopodia that brings about growth by pulling or synthesizing actin microfilaments, which initiates growth y contraction. Since axons are primary parts of neurons in the nerves, the growth of axons is significant to the development of the neural system. Although axons rate of growth is very high at the early age, it reaches appoint and axons stop growing. This enables the neural system to avoid wastage during the proliferation of axons, which leads to multiplication of cells. The chick embryos experiment proves that neurons stay alive if they receive sufficient alexir. However, neuron survival can be determined by programmed death called apoptosis of by any other cause that can lead to the death of cells. The growth, survival and death of axons are controlled by the nervous system through various mechanisms depending on the function inherent in the organism biological function. Notes Read More