presynaptic neuron

(noun)

The neuron that releases neurotransmitters into the synaptic cleft.

Related Terms

Examples of presynaptic neuron in the following topics:

  • The Synapse

    • The neuron conducting impulses towards the synapse is called presynaptic neuron.
    • At a synapse , the presynaptic neuron sends information and postsynaptic neuron receives the information.
    • Most neurons, function as both as presynaptic and postsynaptic neurons.
    • In a chemical synapse, the plasma membrane of the signal-passing neuron (the presynaptic neuron) comes into close apposition with the membrane of the target (postsynaptic) cell.
    • The presynaptic neuron contains a chemical called a neurotransmitter that is packaged into synaptic vesicles clustered beneath the membrane in the axon terminal.

  • Peripheral Motor Endings

    • A neuromuscular junction is the synapse or junction of the axon terminal of a motor neuron with the motor end plate, as shown in Figures 1 and 2.
    • Upon the arrival of an action potential at the presynaptic neuron terminal, voltage-dependent calcium channels open and Ca2+ ions flow from the extracellular fluid into the presynaptic neuron's cytosol.
    • 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.
    • The affects of myasthenia gravis illustrate the importance of effective and functioning neuromuscular junctions for communication between neurons and muscles to allow contraction and relaxation of muscle fibers.
    • Detailed view of a neuromuscular junction: 1) Presynaptic terminal; 2) Sarcolemma; 3) Synaptic vesicle; 4) Nicotinic acetylcholine receptor; 5) Mitochondrion.

  • Autonomic Ganglia

    • The axons of dorsal root ganglion neurons are known as afferents.
    • The first neuron in this pathway is referred to as the preganglionic or presynaptic neuron.
    • This second neuron is referred to as the postganglionic or postsynaptic neuron.
    • The axons of presynaptic parasympathetic neurons are usually long.
    • The pathways of the ciliary ganglion include sympathetic neurons (red), parasympathetic neurons (green), and sensory neurons (blue).

  • Postganglionic Neurons

    • At the synapses within the ganglia, the preganglionic neurons release acetylcholine, a neurotransmitter that activates nicotinic acetylcholine receptors on postganglionic neurons.
    • The postganglionic neurons of sweat glands release acetylcholine for the activation of muscarinic receptors.
    • Presynaptic nerves' axons terminate in either the paravertebral ganglia or prevertebral ganglia.
    • Because paravertebral and prevertebral ganglia are relatively close to the spinal cord, presynaptic neurons are generally much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations.
    • The axons of presynaptic parasympathetic neurons are usually long.

  • Ionotropic and Metabotropic Receptors

    • Metabotropic receptors on the presynaptic membrane can inhibit or more rarely facilitate neurotransmitter release from the presynaptic neuron.

  • Function and Physiology of the Spinal Nerves

    • Acetylcholine is the preganglionic neurotransmitter for both divisions of the ANS, as well as the postganglionic neurotransmitter of parasympathetic neurons.
    • In the parasympathetic system, ganglionic neurons use acetylcholine as a neurotransmitter to stimulate muscarinic receptors.
    • At the adrenal medulla, there is no postsynaptic neuron.
    • Instead the presynaptic neuron releases acetylcholine to act on nicotinic receptors.
    • Upper motor neurons release acetylcholine.

  • Adrenergic Neurons and Receptors

    • Negative feedback in the neuronal synapses—presynaptic inhibition of noradrenalin release in CNS.

  • Types of Neurotransmitters by Function

    • Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse.
    • Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane in the axon terminal on the presynaptic side of a synapse.
    • Acetylcholine-releasing neurons are also found in the central nervous system (CNS).
    • Additionally, some motor neurons of the ANS release catecholamines like NE.
    • Chemical synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands.

  • Postsynaptic Potentials and Their Integration at the Synapse

    • Chemical synapses are either excitatory or inhibitory depending on how they affect the membrane potential of the postsynaptic neuron.
    • This is an excitatory postsynaptic potential (EPSP) as it brings the neuron's potential closer to its firing threshold (about -50mV).
    • Neurotransmitter binding at inhibitory synapses reduces a postsynaptic neuron's ability to generate an action potential.
    • A single EPSP at one synapse is generally far too small to trigger an action potential in the postsynaptic neuron.
    • This figure depicts the mechanism of temporal summation in which multiple action potentials in the presynaptic cell cause a threshold depolarization in the postsynaptic cell.

  • Parasympathetic (Craniosacral) Division

    • The motor root carries presynaptic parasympathetic nerve fibers (general visceral efferent fibers) that terminate in the ganglion by creating a synapse for the postsynaptic fibers traveling to target organs.
    • The parasympathetic division has craniosacral outflow, meaning that the neurons begin at the cranial nerves (CN3, CN7, CN9, CN10) and the sacral spinal cord (S2–S4).