neurotransmitter

Examples of neurotransmitter in the following topics:

• Types of Neurotransmitters by Function

  • Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse.
  • Neurotransmitters fall into several chemical classes based on the molecular structure.
  • The major types of neurotransmitters include acetylcholine, biogenic amines, and amino acids.  
  • Acetylcholine, which acts on the neuromuscular junction, was the first neurotransmitter identified.
  • Glutamate and gamma-aminobutyric acid (GABA) are amino acid-based neurotransmitters.

• Classification of Neurons

  • Neurons can be classified by direction of travel, neurotransmitter utilized, or their electrophysiological properties.
  • A neuron releases a neurotransmitter that binds to chemical receptors on the target neuron .
  • The combination of neurotransmitter and receptor properties results in an excitatory, inhibitory, or modulatory change to the target neuron.
  • For example, the two most common neurotransmitters in the brain (90% of neurons), glutamate and GABA, have opposing actions.
  • Describe how neurons can be classified by direction of travel, neurotransmitter utilized, or their electrophysiological properties

• Postsynaptic Potentials and Their Integration at the Synapse

  • The neurotransmitters bind to receptors on the postsynaptic terminal resulting in an opening of ion channels.
  • At excitatory synapses, neurotransmitter binding depolarizes the postsynaptic membrane.
  • If enough neurotransmitter binds, depolarization of the postsynaptic membrane can reach 0mV, which is higher than threshold of -30-50mV.  
  • Neurotransmitter binding at inhibitory synapses reduces a postsynaptic neuron's ability to generate an action potential.
  • Most inhibitory neurotransmitters hyperbolize the postsynaptic membrane by making it more permeable to potassium or chloride.

• Cholinergic Neurons and Receptors

  • Acetylcholine is a neurotransmitter in the central and peripheral nervous systems that affects plasticity, arousal, and reward.
  • Acetylcholine is one of many neurotransmitters in the autonomic nervous system (ANS) and the only neurotransmitter used in the motor division of the somatic nervous system (sensory neurons use glutamate and various peptides at their synapses).
  • Acetylcholine is also the principal neurotransmitter in all autonomic ganglia.
  • However, acetylcholine also behaves as an excitatory neurotransmitter at neuromuscular junctions in skeletal muscle.
  • Acetylcholine was also the first neurotransmitter to be identified.

• The Synapse

  • The presynaptic neuron contains a chemical called a neurotransmitter that is packaged into synaptic vesicles clustered beneath the membrane in the axon terminal.
  • The neurotransmitter is released into and diffuses across the synaptic cleft, where it binds to specific receptors in the membrane on the postsynaptic side of the synapse.
  • Release of neurotransmitters usually follows arrival of an action potential at the synapse, but may also follow graded electrical potentials found in dendrites.
  • A: Neuron (Presynaptic) B: Neuron (Postsynaptic)MitochondriaSynaptic vesicle full of neurotransmitterAutoreceptorSynaptic cleftNeurotransmitter receptorCalcium ChannelFused vesicle releasing neurotransmitterNeurotransmitter re-uptake pump

• Ionotropic and Metabotropic Receptors

  • Although both ionotropic and metabotropic receptors are activated by neurotransmitters, ionotropic receptors are channel-linked while metabotropic receptors initiate a cascade of molecules via G-proteins.
  • Two types of membrane-bound receptors are activated with the binding of neurotransmitters: ligand-gated ion channels (LGICs) inotropic receptors and metabotropic G- protein coupled receptors.
  • When the neurotransmitter binds to the receptor, there is an activation via the G-protein that later activates the  secondary messengers.
  • Metabotropic receptors on the presynaptic membrane can inhibit or more rarely facilitate neurotransmitter release from the presynaptic neuron.

• Postganglionic Neurons

  • The post-ganglionic neurons are directly responsible for changes in the activity of the target organ via biochemical modulation and neurotransmitter release.
  • The neurotransmitters used by postganglionic fibers differ.
  • In the parasympathetic division, they are cholinergic and use acetylcholine as their neurotransmitter.
  • In the sympathetic division, most are adrenergic, meaning they use norepinephrine as their neurotransmitter.
  • The parasympathetic nervous system uses acetylcholine (ACh) as its chief neurotransmitter, although peptides (such as cholecystokinin) may act on the PSNS as a neurotransmitter.

• Peripheral Motor Endings

  • A neuromuscular junction exists between the axon terminal and the motor end plate of a muscle fiber where neurotransmitters are released.
  • In vertebrates, the signal passes through the neuromuscular junction via the neurotransmitter acetylcholine.
  • This influx of Ca2+ causes neurotransmitter-containing vesicles to dock and fuse to the presynaptic neuron's cell membrane, which results in the emptying of the vesicle's contents (acetylcholine) into the synaptic cleft; this process is known as exocytosis.

• Organization of the Nervous System

  • Neurons send signals along thin fibers called axons and communicate with other cells by releasing chemicals called neurotransmitters at cell-cell junctions called synapses .
  • When this signal reaches a synapse, it provokes release of neurotransmitter molecules, which bind to receptor molecules located in the the target cell.

• Parasympathetic Responses

  • The parasympathetic nervous system uses chiefly acetylcholine (ACh) as its neurotransmitter, although peptides (such as cholecystokinin) may act on the PSNS as neurotransmitters.