Tuesday, January 21, 2020
Physics of Neurons Essay -- physics neuron
The human nervous system is divided into two parts, the central nervous system and the peripheral nervous system. The central nervous system, CNS, is just the brain and spinal cord. The peripheral nervous system, PNS, includes the nerves and neurons that extend outwards from CNS, to transmit information to your limbs and organs for example. Communication between your cells is extremely important, neurons are the messengers that relay information to and from your brain. Nerve cells generate electrical signals to transmit information. Neurons are not necessarily intrinsically great electrical conductors, however, they have evolved specialized mechanisms for propagating signals based on the flow of ions across their membranes. In their inactive state neurons have a negative potential, called the resting membrane potential. Action potentials changes the transmembrane potential from negative to positive. Action potentials are carried along axons, and are the basis for "information transportation" from one cell in the nervous system to another. Other types of electrical signals are possible, but we'll focus on action potentials. These electrical signals arise from ion fluxes produced by nerve cell membranes that are selectively permeable to different ions. 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. The number of synaptic inputs recieved by each nerve cell in our (human) nervous system varies from 1-100,000! This wide range reflects the fundamental purpose of nerve cells, to integrate info from other neurons. Cellular organization of neurons resembles that of other ce... ...ive current flow. Another way to improve the passive flow is to insulate the axonal membrane with myelin. This reduces the amount of current that would otherwise leak out of the axon and increases the distance that the current can flow passively. Myelination, aka axon insulation, increases action potential conduction up to 150m/s compared to 0.5-10m/s conduction velocities of unmyelnated axons! Speedy delivery of current (information) along axons is also due to the nodes of Ranvier. Nodes of Ranvier are gaps between insulated portions of the axon. The gaps create a place where the current can flow out of the axon so an action potential can be generated. Action potentials are started at one end of the node, flow passively through the myelinated axon, and pop out the other side to jump to the next node. This jumping of action potentials is called saltatory.