The Info List - Axon Terminal

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terminals (also called synaptic boutons or terminal boutons) are distal terminations of the telodendria (branches) of an axon. An axon, also called a nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses called action potentials away from the neuron's cell body, or soma, in order to transmit those impulses to other neurons, muscle cells or glands. Neurons are interconnected in complex arrangements, and use electrochemical signals and neurotransmitter chemicals to transmit impulses from one neuron to the next; axon terminals are separated from neighboring neurons by a small gap called a synapse, across which impulses are sent. The axon terminal, and the neuron from which it comes, is sometimes referred to as the "presynaptic" neuron.


1 Nerve impulse release 2 Mapping activity 3 See also 4 References 5 Further reading

Nerve impulse release[edit] Neurotransmitters
are packaged into synaptic vesicles that cluster beneath the axon terminal membrane on the presynaptic side of a synapse. The axonal terminals are specialized to release the neurotransmitters of the presynaptic cell.[1] The terminals release transmitter substances into a gap called the synaptic cleft between the terminals and the dendrites of the next neuron. The information is received by the dendrite receptors of the postsynaptic cell that are connected to it. Neurons don't touch each other, but communicate across the synapse.[2] The neurotransmitter molecule packages (vesicles) are created within the neuron, then travel down the axon to the distal axon terminal where they sit docked. Calcium
ions then trigger a biochemical cascade which results in vesicles fusing with the presynaptic membrane and releasing their contents to the synaptic cleft within 180 µs of calcium entry.[3] Triggered by the binding of the calcium ions, the synaptic vesicle proteins begin to move apart, resulting in the creation of a fusion pore. The presence of the pore allows for the release of neurotransmitter into the synaptic cleft.[4][5] The process occurring at the axon terminal is exocytosis, which a cell uses to exude secretory vesicles out of the cell membrane. These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane. Exocytosis
in neuronal chemical synapses is Ca2+ triggered and serves interneuronal signalling.[citation needed] Mapping activity[edit]

Structure of a typical neuron


Dendrite Soma Axon Nucleus Node of Ranvier Axon
terminal Schwann cell Myelin

Dr. Wade Regehr, a Professor
of Neurobiology
at Harvard Medical School's Department of Neurobiology, developed a method to physiologically see the synaptic activity that occurs in the brain. A dye alters the fluorescence properties when attached to calcium. Using fluorescence-microscopy techniques calcium levels are detected, and therefore the influx of calcium in the presynaptic neuron.[6] Regehr's laboratory specializes in pre-synaptic calcium dynamics which occurs at the axon terminals. Regehr studies the implication of calcium Ca2+ as it affects synaptic strength.[7][8] By studying the physiological process and mechanisms, a further understanding is made of neurological disorders such as epilepsy, schizophrenia and major depressive disorder, as well as memory and learning.[9][10] See also[edit]

Telodendron Endoplasmic reticulum Golgi apparatus Micelle Membrane nanotube Endocytosis Synaptic vesicle Vesicle (biology) Chemical synapse Vesicular monoamine transporter Axon


^ " Axon
Terminal". Medical Dictionary Online. Retrieved February 6, 2013.  ^ Foster, Sally. " Axon
Terminal - Synaptic Vesicle - Neurotransmitter". Retrieved February 6, 2013. [self-published source?][unreliable medical source?] ^ Llinás R, Steinberg IZ, Walton K (1981). "Relationship between presynaptic calcium current and postsynaptic potential in squid giant synapse". Biophysical Journal. 33 (3): 323–51. doi:10.1016/S0006-3495(81)84899-0. PMC 1327434 . PMID 6261850.  ^ Carlson, 2007, p.56[verification needed] ^ Chudler, Eric H. (November 24, 2011). "Neuroscience for kids Neurotransmitters
and Neuroactive Peptides". Archived from the original on December 18, 2008. Retrieved February 6, 2013. [self-published source?][unreliable medical source?] ^ Sauber, Colleen. "Focus October 20- Neurobiology
VISUALIZING THE SYNAPTIC CONNECTION". Archived from the original on 2006-09-01. Retrieved July 3, 2013.  ^ Regehr, Wade (1999–2008). "Wade Regehr, Ph.D." Archived from the original on February 18, 2010. Retrieved July 3, 2013. [self-published source?] ^ President and Fellows of Harvard College (2008). "The Neurobiology Department at Harvard Medical School". Archived from the original on 20 December 2008. Retrieved July 3, 2013.  ^ "NINDS Announces New Javits Neuroscience Investigator Awardees" (Press release). National Institute of Neurological Disorders and Stroke. May 4, 2005. Archived from the original on January 17, 2009. Retrieved February 6, 2013.  ^ "Scholar Awards". The McKnight Endowment Fund for Neuroscience. Archived from the original on 2004-05-08. Retrieved July 3, 2013. 

Further reading[edit]

Cragg, Stephanie J.; Greenfield, Susan A. (1997). "Differential Autoreceptor Control of Somatodendritic and Axon
Terminal Dopamine Release in Substantia Nigra, Ventral Tegmental Area, and Striatum". The Journal of Neuroscience. 17 (15): 5738–46. PMID 9221772.  Vaquero, Cecilia F; de la Villa, Pedro (1999). "Localisation of the GABAC receptors at the axon terminal of the rod bipolar cells of the mouse retina". Neuroscience Research. 35 (1): 1–7. doi:10.1016/S0168-0102(99)00050-4. PMID 10555158.  Roffler-Tarlov, Suzanne; Beart, P.M.; O'Gorman, Stephen; Sidman, Richard L. (1979). "Neurochemical and morphological consequences of axon terminal degeneration in cerebellar deep nuclei of mice with inherited purkinje cell degeneration". Brain Research. 168 (1): 75–95. doi:10.1016/0006-8993(79)90129-X. PMID 455087.  Yagi T, Kaneko A (1988). "The axon terminal of goldfish retinal horizontal cells: A low membrane conductance measured in solitary preparations and its implication to the signal conduction from the soma". Journal of Neurophysiology. 59 (2): 482–94. PMID 3351572.  LTP promotes formation of multiple spine synapses between a single axon terminal and a dendrite https://www.nature.com/articles/46574

v t e

Membrane transport

Mechanisms for chemical transport through biological membranes

Passive transport

Simple diffusion
Simple diffusion
(or non-mediated transport) Facilitated diffusion Osmosis Channels Carriers

Active transport

Uniporter Symporter Antiporter Primary active transport Secondary active transport



Efferocytosis Non-specific, adsorptive pinocytosis Phagocytosis Pinocytosis Potocytosis Receptor-mediated endocytosis Transcytosis



v t e

Nervous tissue


Tissue Types

Grey matter White matter

Projection fibers Association fiber Commissural fiber Lemniscus Funiculus Fasciculus Nerve tract Decussation Commissure

Neuropil Meninges

Cell Types


Pyramidal Purkinje Granule



Myelination: Oligodendrocyte



Radial glial cell

Ependymal cells






Root Ganglion Ramus


Root Ramus

Ramus communicans

Gray White

Autonomic ganglion
Autonomic ganglion
(Preganglionic nerve fibers Postganglionic nerve fibers)

Connective tissues

Epineurium Perineurium Endoneurium Nerve fascicle


Myelination: Schwann cell

Neurilemma Myelin
incisure Node of Ranvier Internodal segment

Satellite glial cell

Neurons/ nerve fibers





Telodendron Axon
terminals Axoplasm Axolemma Neurofibril/neurofilament


Nissl body Dendritic spine Apical dendrite/Basal dendrite


Bipolar Unipolar Pseudounipolar Multipolar Interneuron


Afferent nerve fiber/ Sensory neuron


Ia or Aα Ib or Golgi or Aα II or Aβ and Aγ III or Aδ or fast pain IV or C or slow pain

Efferent nerve fiber/ Motor neuron

GSE GVE SVE Upper motor neuron Lower motor neuron

α motorneuron β motorneuron γ motorneuron



Electrical synapse/Gap junction Chemical synapse

Synaptic vesicle Active zone Postsynaptic density

Autapse Ribbon synapse Neuromuscular junction

Sensory receptors

Meissner's corpuscle Merkel nerve ending Pacinian corpuscle Ruffini ending Muscle spindle Free nerve ending Nociceptor Olfactory receptor neuron Photoreceptor cell H