How Do Nerve Cells Work, and Why is It Important for Psychologists to Know This - Essay Example

Download file to see previous pages 1. How Nerve Cells Work Nerve cells process and transmit information by electrical and chemical signalling. Chemical signalling occurs via synapses, in a process known as synaptic transmission. This is a process where the axon terminal of one cell impinges upon a dendrite or soma of another [or less commonly to an axon]. Nerve cells can have over 1000 dendritic branches, making connections with tens of thousands of other cells; other nerve cells, such as the magnocellular nerve cells of the supraoptic nucleus, have only one or two dendrites, each of which receives thousands of synapses. Synapses can be excitatory or inhibitory and will either increase or decrease activity in the target nerve cell. Some nerve cells also communicate via electrical synapses, which are direct, electrically-conductive junctions between cells [1]. In a chemical synapse, the process of synaptic transmission is as follows: When an action potential reaches the axon terminal, it opens voltage-gated calcium channels, allowing calcium ions to enter the terminal. Calcium causes synaptic vesicles filled with neurotransmitter molecules to fuse with the membrane, releasing their contents into the synaptic cleft. The neurotransmitters diffuse across the synaptic cleft and activate receptors on the postsynaptic nerve cell. The fundamental process that triggers synaptic transmission is the action potential, a propagating electrical signal that is generated by exploiting the electrically excitable membrane of the nerve cell. Each nerve cell maintains voltage gradients across their membranes by means of metabolically driven ion pumps, which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium. Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels. If the voltage changes by a large enough amount, an all-or-none electrochemical pulse called an action potential is generated, which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives [2]. The electrical aspect depends on properties of the nerve cell's membrane. Like all animal cells, every nerve cell is surrounded by a plasma membrane, a bilayer of lipid molecules with many types of protein structures embedded in it. A lipid bilayer is a powerful electrical insulator, but in nerve cells, many of the protein structures embedded in the membrane are electrically active. These include ion channels that permit electrically charged ions to flow across the membrane, and ion pumps that actively transport ions from one side of the membrane to the other. Most ion channels are permeable only to specific types of ions. Some ion channels are voltage gated, meaning that they can be switched between open and closed states by altering the voltage difference across the membrane. Others are chemically gated, meaning that they can be switched between open and closed states by interactions with chemicals that diffuse through the extracellular fluid. The interactions between ion channels and ion pumps produce a voltage difference across the membrane, typically a bit less than 1/10 of a volt at baseline. This voltage has two functions: First, it provides a power source for an assortment of voltage-dependent protein machinery that is embedded in the ...Download file to see next pagesRead More