what part of the neuron conveys electrical impulses from its start to its end?
Alcohol Wellness Res Globe. 1997; 21(2): 107–108.
The Principles of Nerve Cell Communication
The nerve cell, or neuron, is the central player in the activity of the nervous system. It conveys information both electrically and chemically. Within the neuron itself, data is passed forth through the movement of an electrical charge (i.e., impulse). The neuron has three master components: (one) the dendrites, sparse fibers that extend from the jail cell in branched tendrils to receive information from other neurons; (ii) the cell torso, which carries out nearly of the neuron'southward basic cellular functioning; and (3) the axon, a long, thin fiber that carries nerve impulses to other neurons.
Nervus signals ofttimes travel over long distances in the torso. For example, if you lot footstep barefooted on a abrupt object, the sensory information is relayed from your foot all the way to the brain; from there, nerve signals travel dorsum to the leg muscles and cause them to contract, drawing back the foot. Dozens of neurons tin can be involved in such a excursion, necessitating a sophisticated communication system to speedily convey signals between cells. Also, because private neurons can exist upwardly to iii anxiety long, a rapid-relay mechanism within the neurons themselves is required to transmit each point from the site where information technology is received to the site where it is passed on to a neighboring cell. Two mechanisms accept evolved to transmit nerve signals. Beginning, within cells, electrical signals are conveyed along the cell membrane. Second, for communication between cells, the electrical signals generally are converted into chemical signals conveyed by small messenger molecules chosen neurotransmitters.
Signal Manual Within Nerve Cells
The mechanism underlying point transmission inside neurons is based on voltage differences (i.e., potentials) that exist between the inside and the exterior of the jail cell. This membrane potential is created by the uneven distribution of electrically charged particles, or ions, the most important of which are sodium (Na+), potassium (Chiliad+), chloride (Cl−), and calcium (Ca2+). Ions enter and leave the cell through specific protein channels in the cell'southward membrane. The channels "open up" or "close" in response to neurotransmitters or to changes in the cell'south membrane potential. The resulting redistribution of electric accuse may alter the voltage deviation across the membrane. A decrease in the voltage departure is chosen depolarization. If depolarization exceeds a certain threshold, an impulse (i.due east., action potential) will travel along the neuron. Various mechanisms ensure that the activity potential propagates in only i direction, toward the axon tip. The generation of an action potential is sometimes referred to as "firing."
Point transmission across the synaptic crack. The binding of neurotransmitters (shown as triangles) to receptors that act as ligand-gated ion channels causes these channels to open, leading in some cases to a depolarization of the office of the membrane closest to the channel. Depolarization results in the opening of other ion channels, which in turn may generate an action potential. Neurotransmitters (shown as circles) that bind to second messenger-linked receptors initiate a complex cascade of chemical events that can produce changes in prison cell office. In this schematic, the kickoff component of such a signaling cascade is a G protein.
Signal Transmission Between Cells
Communication amid neurons typically occurs across microscopic gaps called synaptic clefts. Each neuron may communicate with hundreds of thousands of other neurons. A neuron sending a betoken (i.due east., a presynaptic neuron) releases a chemical chosen a neurotransmitter, which binds to a receptor on the surface of the receiving (i.e., postsynaptic) neuron. Neurotransmitters are released from presynaptic terminals, which may branch to communicate with several postsynaptic neurons. Dendrites are specialized to receive neuronal signals, although receptors may exist located elsewhere on the cell. Approximately 100 different neurotransmitters be. Each neuron produces and releases merely one or a few types of neurotransmitters, simply can carry receptors on its surface for several types of neurotransmitters.
To cross the synaptic cleft, the cell's electrical message must be converted into a chemical one. This conversion takes place when an action potential arrives at the axon tip, resulting in depolarization. The depolarization causes Ca2+ to enter the cell. The increase in intracellular Catwo+ concentration triggers the release of neurotransmitter molecules into the synaptic cleft.
Two large groups of receptors exist that elicit specific responses in the receptor jail cell: Receptors that human action as ligand-gated ion channels result in rapid simply short-lived responses, whereas receptors coupled to second-messenger systems induce slower merely more prolonged responses.
Ligand-Gated Channel Receptors
When a neurotransmitter molecule binds to a receptor that acts as a ligand-gated ion channel, a channel opens, assuasive ions to menstruation across the membrane (see figure). The flow of positively charged ions into the prison cell depolarizes the portion of the membrane nearest the channel. Because this state of affairs is favorable to the subsequent generation of an activity potential, ligand-gated channel receptors that are permeable to positive ions are called excitatory.
Other ligand-gated channels are permeable to negatively charged ions. An increase of negative accuse within the cell makes it more difficult to excite the jail cell and induce an activity potential. Such channels accordingly are called inhibitory.
Second Messenger-Linked Receptors
2nd messengers (e.g., G proteins) are molecules that help relay signals from the cell's surface to its interior. Neurotransmitters that bind to second messenger-linked receptors, such as dopamine, initiate a complex cascade of chemic events that tin can either excite or inhibit farther electric signals (meet effigy). The neurotransmitters also may attach to receptors on the transmitting cell's own presynaptic sites, beginning a feedback process that can affect future communication through that synaptic crack.
With so many different receptors on its jail cell surface, some of the signals the neuron receives volition accept excitatory effects, whereas others will exist inhibitory. In addition, some of the signals (due east.g., those transmitted through ligand-gated channels) will induce fast responses, whereas others (east.g., those transmitted through second messenger-linked proteins) volition trigger slow responses. The integration by the neuron of these often conflicting signals determines whether the neuron will generate an action potential, release neurotransmitters, and thereby exert an influence on other neurons.
Neurotransmitters and Alcohol
Among the neurotransmitters of well-nigh interest to booze researchers are dopamine, serotonin, glutamate, gamma-aminobutyric acid (GABA), opioid peptides, and adenosine, all of which are featured in this special section. These molecules generally autumn into three categories: (1) excitatory neurotransmitters (e.grand., glutamate), which activate the postsynaptic cell; (2) inhibitory neurotransmitters (east.g., GABA), which depress the action of the postsynaptic jail cell; and (3) neuromodulators (e.1000., adenosine), which modify the postsynaptic cell's response to other neurotransmitters. Neurons that release these substances class the ground of neural circuits that link different areas of the encephalon in a circuitous network of pathways and feedback loops. The integrated activity of these circuits regulates mood, action, and the behaviors that may underlie disorders such every bit alcoholism.
Articles from Alcohol Health and Inquiry World are provided hither courtesy of National Constitute on Alcohol Corruption and Alcoholism
Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6826821/
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