Axon 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
5 Further reading
Nerve impulse release
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. 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.
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. 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. 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.
neuronal chemical synapses is Ca2+ triggered and serves interneuronal
Structure of a typical neuron
Dr. Wade Regehr, a
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. 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. 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.
Vesicular monoamine transporter
Axon Terminal". Medical Dictionary Online. Retrieved February 6,
^ 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 .
^ 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,
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.
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.
LTP promotes formation of multiple spine synapses between a single
axon terminal and a dendrite https://www.nature.com/articles/46574
Mechanisms for chemical transport through biological membranes
Simple diffusion (or non-mediated transport)
Primary active transport
Secondary active transport
Non-specific, adsorptive pinocytosis
Radial glial cell
Autonomic ganglion (Preganglionic nerve fibers
Postganglionic nerve fibers)
Myelination: Schwann cell
Node of Ranvier
Satellite glial cell
Apical dendrite/Basal dendrite
Afferent nerve fiber/
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/
Upper motor neuron
Lower motor neuron
Electrical synapse/Gap junction
Merkel nerve ending
Free nerve ending
Olfactory receptor neuron