Neural Transmission - Term Paper Example

Neural Transmission Neural transmission is the process by which individual cells communicate with each other. The process can be a downward transmission of impulses or a feedback from successive cells for stabilization of electric impulses. Neurons are a specialized category of cells and their anatomical structure needs to be elaborated in order to explain the various mechanisms by which they communicate. Neurons constitute the bulk of the matrix of brain and the spinal cord tissue and are supported in the matrix by glial cells. Glial cells which constitute 90% of the matrix support the neurons, digest the dead neurons, and manufacture the protective myelin sheath covering the neurons besides providing nutrition (“Brain Cells’’ 2001). Thus neurons along with their connections can be visualized as electric conductors insulated in a thick mass of glial cells. A typical neuron, like other cells has a main body in which resides the nucleus and is called soma (Fig. I). From this emanate the inward signal processing projections called the dendrites and the outward signal processing axons, or the conducting fibres (Case Presentation, January 27th, 2014). Figure I: A Typical Neuron (Picture Courtesy: http://www.enchantedlearning.com/subjects/anatomy/brain/Neuron.shtml) The point where the two neurons connect with each other is known as the synapse, the latter being the juncture where transmission of axonal information takes place (Case Presentation, January 27th, 2014). A synapse is comparable with a connecting switch which transmits current from one circuit to another. Dendrites receive the incoming signals from the preceding neuron, the signals being generated in the form of micro electric action potentials in the soma, wherein the signal processing and stabilization takes place. The axons transmit the information from the prior to the subsequent neurons. The fatty myelin sheath serves to insulate the axon thereby facilitating transmission of signals. This myelin sheath is akin to the insulation we see on electric wires. As the insulation on electric wires stops leakage of electric current thereby protecting us, similarly the myelin sheath on the neuron protects leakage of action potential to adjacent neurons so that they can send signals along the actual destined pathways for them. However, at specific intervals it exposes the neuron at junctures called ‘Nodes of Ranvier’ which are meant for increasing the speed of transmission of the onward electric signals. A typical neuron connects with 1000-1000 other neurons through synapses (“Brain Cells’’ 2001). This can be compared to a big power supply line feeding hundreds of houses for their electricity needs. Neurons maybe classified as Sensory or Bipolar in character i.e. transmitted signals from sensory organs like eyes, ears and skin, Sensory neurons can therefore be compared with a camera which gathers images through the light falling on objects and makes sensible pictures of them. Motor or Multipolar neurons which carry signals from the central nervous system to the muscles and glands in the body, and Interneurons which possess two axons with the dendrite absent and constitute the overall neuronal wiring as in an electrical circuit (“Brain Cells’’ 2001). Motor neurons can therefore be compared to a projector which sends images out towards a screen from a film which stores the information. The communication between neurons is a complex electro chemical activity in which generation of electrical signals in the form of ‘Action Potentials’ occurs under the influence of ionic ingress and outflow of specific ions and the stimulation or inhibition by specific chemical moieties which include neurotransmitters, neurohormones and neuromodulators (Case Presentation, January 27th, 2014). A simile of this can be an electrical battery which contains chemical compounds like sulphuric acid and lead electrodes which can be compared to neurotransmitters as they work chemically. The current flowing from a battery can be compared to the electrical impulses of action potentials generated from neurons. Action Potential An Action Potential is a complex physiological phenomenon wherein the flow of neurotransmitters occurs at the synapse under the influence of a series of events. Unlike electric circuits in households, where the flow of electrons is responsible for transmission of current, the neurons transmit electric signals by exchange of positively and negatively charged ions, the differential concentration of which along the neuronal cell wall is the basis for the existence of potential difference in the extracellular and the intracellular environs of the neuron (Cooper et al 2003). The major ions whose concentration defines the potential difference across the neuronal membranes include Potassium (K+), Sodium (Na+), Calcium (Ca2+) and Chloride (Cl-) ions (Cooper et al 2003). An inactive neuron in its inert state possesses a ‘Resting Membrane Potential’ and when activated by ionic fluxes across the membrane under the influence of neurotransmitters or neurohormones, generates an’ Áction Potential’. Resting membrane potential can therefore be compared to the stored energy in a battery which attains an active form or flows only when the circuit is connected. Action potential in a neuron is generated when the two main ions in the vicinity, the K+ and the Na+ ions move outside the confines of the area in which they are usually present in higher concentration (Case Presentation, January 27th, 2014). The resultant effort at stabilization of the potential difference so generated results in the outflow or inflow of neurotransmitters which are responsible for the conduction process, the latter resulting either in the excitation of neuronal signals across an established pathway, or inhibition, depending upon the nature of the involved neurotransmitter and the physiological function being altered or carried out. Ultimately, after conduction or its suppression has occurred, the affected neuron returns to its resting membrane potential. Synaptic Transmission Synaptic transmission occurs through numerous excitatory and inhibitory neurotransmitters whose function is modulated and determined according to the physiological activity desired or necessary at a particular synapse or a series of neuronal connections involving thousands to millions of neurons in a particular neuronal circuit. Neurotransmitters (NTs) usually are released at short distances between neuronal connections, neuromodulators over long distances involving particular neuronal circuits in the brain and neurohormones released from endocrine glands like the Pituitary at specifically targeted areas (Case Presentation, January 27th, 2014). Some of the excitatory NTs include Acetyl Choline, Noradrenaline, Dopamine and Glutamate and the inhibitory ones include Gamma Amino Butyric Acid (GABA), Serotonin or 5HT (5 Hydroxy Tryptamine) and numerous peptides (Case Presentation, January 27th, 2014). Neurotransmitters can therefore be considered as local authorities exercising their power in a specific locality of the town while neurohormones and neuromodulators can be considered as higher authorities like the President or the Prime Minister of a country who influence local actions through nationally applicable laws and policies. Postsynaptic Potentials Postsynaptic potentials, as the name suggests, occur at postsynaptic membranes of the neuron as a result of the excitatory or inhibitory action of NTs generated from the preceding neuron. The Excitatory Post Synaptic Potential (EPSP) occurs as a result of opening up of Na+ channels and influx of excess Na+ ions, while the Inhibitory Post Synaptic Potential (IPSP) occurs as a result of opening up of K+ channels and an efflux of K+ ions from the neuron. Postsynaptic potentials occur briefly as compared to presynaptic action potentials as the former are instrumental in the deactivation of the NTs and their reuptake by the preceding neurons to replenish stores in a homeostatic effort i.e. stabilization of neuron after the physiological function has been met. References Brain Cells, (2001) Retrieved January 28 2013 from http://www.enchantedlearning.com/subjects/anatomy/brain/Neuron.shtml Cooper, J.R., Bloom, F.E. & Roth, R.H. (2003) Cellular Foundations of Neuropharmacology, Chapter 2, The Biochemical Basis of Neuropharmacology, Eighth Edition, Oxford University Press, New York Neurotransmission Function 2, Class Presentation (January 27 2014) Read More