Neurotransmission


Neurotransmission
The presynaptic neuron (yellow) releases neurotransmitter, which activates receptors on the postsynaptic cell (green).

Neurotransmission (Latin: transmissio = passage, crossing; from transmitto = send, let through), also called synaptic transmission, is the process by which signaling molecules called neurotransmitters are released by a neuron (the presynaptic neuron), and bind to and activate the receptors of another neuron (the postsynaptic neuron). Neurotransmission usually takes place at a synapse, and occurs when an action potential is initiated in the presynaptic neuron. The binding of neurotransmitters to receptors in the postsynaptic neuron can trigger either short term changes, like changes in the membrane potential called postsynaptic potentials, or longer term changes by the activation of signaling cascades.

Nerve impulses are essential for the propagation of signals. These signals are sent to and from the central nervous system via efferent and afferent neurons in order to coordinate smooth, skeletal and cardiac muscles, bodily secretions and organ functions critical for the long-term survival of multicellular vertebrate organisms such as mammals.

Neurons form networks through which nerve impulses travel. Each neuron receives as many as 15,000 connections from other neurons. Neurons do not touch each other; they have contact points called synapses. A neuron transports its information by way of a nerve impulse. When a nerve impulse arrives at the synapse, it releases neurotransmitters, which influence another cell, either in an inhibitory way or in an excitatory way. The next neuron may be connected to many more neurons, and if the total of excitatory influences is more than the inhibitory influences, it will also "fire", that is, it will create a new action potential at its axon hillock, in this way passing on the information to yet another next neuron, or resulting in an experience or an action.

Contents

Stages in neurotransmission at the synapse

  1. Synthesis of the neurotransmitter. This can take place in the cell body, in the axon, or in the axon terminal.
  2. Storage of the neurotransmitter in storage granules or vesicles in the axon terminal.
  3. Calcium enters the axon terminal during an action potential, causing release of the neurotransmitter into the synaptic cleft.
  4. After its release, the transmitter binds to and activates a receptor in the postsynaptic membrane.
  5. Deactivation of the neurotransmitter. The neurotransmitter is either destroyed enzymatically, or taken back into the terminal from which it came, where it can be reused, or degraded and removed.[1]

Summation

Each neuron is connected with numerous other neurons, receiving numerous impulses from them. Summation is the adding together of these impulses at the axon hillock. If the neuron only gets excitatory impulses, it will also generate an action potential; but if the neuron gets as many inhibitory as excitatory impulses, the inhibition cancels out the excitation and the nerve impulse will stop there. Summation takes place at the axon hillock.[2]

Spatial summation means several firings on different places of the neuron, that in themselves are not strong enough to cause a neuron to fire. However, if they fire simultaneously, their combined effects will cause an action potential.

Temporal summation means several firings at the same place, that won't cause an action potential if they have a pause in between, but when there are several firings in rapid succession, they will cause the neuron to reach the threshold for excitation.[3]

Convergence and divergence

Neurotransmission implies both a convergence and a divergence of information. First one neuron is influenced by many others, resulting in a convergence of input. When the neuron fires, the signal is sent to many other neurons, resulting in a divergence of output. Many other neurons are influenced by this neuron.[4]

Cotransmission

Cotransmission is the release of several types of neurotransmitters from a single nerve terminal. Cotransmission allows for more complex effects at postsynaptic receptors, and thus allows for more complex communication to occur between neurons.

In modern neuroscience, neurons are often classified by their cotransmitter, for example striatal GABAergic neurons utilize opioid peptides or substance P as their primary cotransmitter.

Some neurons can release at least two neurotransmitters at the same time, the other being a cotransmitter, in order to provide the stabilizing negative feedback required for meaningful encoding, in the absence of inhibitory interneurons.[5] Examples include:

See also

References


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Look at other dictionaries:

  • neurotransmission — ● neurotransmission nom féminin Médiation chimique ; neuromédiation …   Encyclopédie Universelle

  • neurotransmission — neurotransmitter ► NOUN Physiology ▪ a chemical substance released from a nerve fibre and bringing about the transfer of an impulse to another nerve, muscle, etc. DERIVATIVES neurotransmission noun …   English terms dictionary

  • neurotransmission — noun Date: 1961 the transmission of nerve impulses across a synapse …   New Collegiate Dictionary

  • Neurotransmission — Synapse et transmission synaptique Neurosciences Niveaux d analyse Moléculaire • …   Wikipédia en Français

  • neurotransmission — /noor oh trans mish euhn, tranz , nyoor /, n. the transmission of a nerve impulse across a synapse. [1960 65; NEURO + TRANSMISSION] * * * …   Universalium

  • neurotransmission — noun nuɹoʊtrænzˈmɪʃən The transfer of impulses between neurons. Syn: synaptic transmission See Also: neurotransmitter, neurotransmissive …   Wiktionary

  • neurotransmission — SYN: neurohumoral transmission. * * * neu·ro·trans·mis·sion tran(t)s mish ən, tranz n the transmission of nerve impulses across a synapse * * * neu·ro·trans·mis·sion (noor″o trans mishґən) the process by which a neurotransmitter is… …   Medical dictionary

  • neurotransmission — neu·ro·transmission …   English syllables

  • neurotransmission — neu•ro•trans•mis•sion [[t]ˌnʊər oʊ trænsˈmɪʃ ən, trænz , ˌnyʊər [/t]] n. phl the transmission of a nerve impulse across a synapse • Etymology: 1960–65 …   From formal English to slang

  • neurotransmission — ¦n(y)ürō, u̇ ˌ noun Etymology: neur + transmission : the transmission of nerve impulses across a synapse * * * /noor oh trans mish euhn, tranz , nyoor /, n. the transmission of a nerve impulse across a synapse. [1960 65; NEURO + TRANSMISSION] …   Useful english dictionary


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