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Cellular neuroscience is a branch of
neuroscience Neuroscience is the scientific study of the nervous system In biology, the classical doctrine of the nervous system determines that it is a Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sens ...

neuroscience
concerned with the study of
neuron A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology Biology is the natural science that studies life and living ...

neuron
s at a cellular level. This includes
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology) In archaeology, morphology is the study of the shape of Artifact (archaeology), artefacts and ecofacts. Morphology is a major consid ...
and physiological properties of single neurons. Several techniques such as intracellular recording, patch-clamp, and voltage-clamp technique, pharmacology, confocal imaging, molecular biology, two photon laser scanning microscopy and Ca2+ imaging have been used to study activity at the cellular level. Cellular neuroscience examines the various types of neurons, the functions of different neurons, the influence of neurons upon each other, and how neurons work together.


Neurons and glial cells

Neurons A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology Biology is the natural science that studies life and living ...

Neurons
are cells that are specialized to receive, propagate, and transmit electrochemical impulses. In the human brain alone, there are over eighty billion neurons. Neurons are diverse with respect to morphology and function. Thus, not all neurons correspond to the stereotypical motor neuron with
dendrites Dendrites (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approx ...

dendrites
and myelinated axons that conduct action potentials. Some neurons such as
photoreceptor cell A photoreceptor cell is a specialized type of neuroepithelial cellNeuroepithelial cells, or neuroectodermal cells, form the wall of the closed neural tube in early embryonic development ''Embryonic'' is the twelfth studio album by experimenta ...

photoreceptor cell
s, for example, do not have myelinated axons that conduct action potentials. Other unipolar neurons found in invertebrates do not even have distinguishing processes such as dendrites. Moreover, the distinctions based on function between neurons and other cells such as cardiac and muscle cells are not helpful. Thus, the fundamental difference between a neuron and a nonneuronal cell is a matter of degree. Another major class of cells found in the nervous system are glial cells. These cells are only recently beginning to receive attention from neurobiologists for being involved not just in nourishment and support of neurons, but also in modulating synapses. For example, Schwann cells, which are a type of glial cell found in the peripheral nervous system, modulate synaptic connections between presynaptic terminals of motor neuron endplates and muscle fibers at neuromuscular junctions.


Neuronal function

One prominent characteristic of many neurons is excitability. Neurons generate electrical impulses or changes in voltage of two types: graded potentials and action potentials. Graded potentials occur when the membrane potential depolarizes and hyperpolarizes in a graded fashion relative to the amount of stimulus that is applied to the neuron. An action potential on the other hand is an all-or-none electrical impulse. Despite being slower than graded potentials, action potentials have the advantage of traveling long distances in axons with little or no decrement. Much of the current knowledge of action potentials comes from squid axon experiments by
Sir Alan Lloyd Hodgkin
Sir Alan Lloyd Hodgkin
and Sir Andrew Huxley.


Action potential

The
Hodgkin–Huxley model The Hodgkin–Huxley model, or conductance-based model, is a mathematical model A mathematical model is a description of a system A system is a group of Interaction, interacting or interrelated elements that act according to a set of ru ...
of an
action potential In physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence ...

action potential
in the
squid giant axon The squid giant axon is the very large (up to 1.5 mm in diameter; typically around 0.5 mm) axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences Despite the various En ...
has been the basis for much of the current understanding of the ionic bases of action potentials. Briefly, the model states that the generation of an action potential is determined by two ions: Na+ and K+. An action potential can be divided into several sequential phases: threshold, rising phase, falling phase, undershoot phase, and recovery. Following several local graded depolarizations of the membrane potential, the threshold of excitation is reached, voltage-gated sodium channels are activated, which leads to an influx of Na+ ions. As Na+ ions enter the cell, the membrane potential is further depolarized, and more voltage-gated sodium channels are activated. Such a process is also known as a
positive feedback Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop Feedback occurs when outputs of a system are routed back as inputs as part of a chain Image:Kettenvergleich.jpg, Roller c ...
loop. As the rising phase reaches its peak, voltage-gated Na+ channels are inactivated whereas voltage-gated K+ channels are activated, resulting in a net outward movement of K+ ions, which re-polarizes the membrane potential towards the resting membrane potential. Repolarization of the membrane potential continues, resulting in an undershoot phase or absolute refractory period. The undershoot phase occurs because unlike voltage-gated sodium channels, voltage-gated potassium channels inactivate much more slowly. Nevertheless, as more voltage-gated K+ channels become inactivated, the membrane potential recovers to its normal resting steady state..


Structure and formation of synapses

Neurons communicate with one another via
synapses In the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physi ...
. Synapses are specialized junctions between two cells in close apposition to one another. In a synapse, the neuron that sends the signal is the presynaptic neuron and the target cell receives that signal is the postsynaptic neuron or cell. Synapses can be either electrical or chemical. Electrical synapses are characterized by the formation of gap junctions that allow ions and other organic compound to instantaneously pass from one cell to another. Chemical synapses are characterized by the presynaptic release of neurotransmitters that diffuse across a synaptic cleft to bind with postsynaptic receptors. A neurotransmitter is a chemical messenger that is synthesized within neurons themselves and released by these same neurons to
communicate Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power o ...

communicate
with their postsynaptic target cells. A receptor is a transmembrane protein molecule that a neurotransmitter or drug binds. Chemical synapses are slower than electrical synapses.


Neurotransmitter transporters, receptors, and signaling mechanisms

After neurotransmitters are synthesized, they are packaged and stored in vesicles. These vesicles are pooled together in terminal boutons of the presynaptic neuron. When there is a change in voltage in the terminal bouton, voltage-gated calcium channels embedded in the membranes of these boutons become activated. These allow Ca2+ ions to diffuse through these channels and bind with synaptic vesicles within the terminal boutons. Once bounded with Ca2+, the vesicles dock and fuse with the presynaptic membrane, and release neurotransmitters into the synaptic cleft by a process known as
exocytosis Exocytosis () is a form of active transport In cellular biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, phys ...
. The neurotransmitters then diffuse across the synaptic cleft and bind to postsynaptic receptors embedded on the postsynaptic membrane of another neuron. There are two families of receptors: ionotropic and metabotropic receptors. Ionotropic receptors are a combination of a receptor and an ion channel. When ionotropic receptors are activated, certain ion species such as Na+ to enter the postsynaptic neuron, which depolarizes the postsynaptic membrane. If more of the same type of postsynaptic receptors are activated, then more Na+ will enter the postsynaptic membrane and depolarize cell. Metabotropic receptors on the other hand activate second messenger cascade systems that result in the opening of ion channel located some place else on the same postsynaptic membrane. Although slower than ionotropic receptors that function as on-and-off switches, metabotropic receptors have the advantage of changing the cell's responsiveness to ions and other metabolites, examples being gamma amino-butyric acid (inhibitory transmitter),
glutamic acid Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compound ...
(excitatory transmitter),
dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is t ...

dopamine
,
norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and ...

norepinephrine
,
epinephrine Adrenaline, also known as epinephrine, is a hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a co ...

epinephrine
,
melanin Melanin (; from el, μέλας ''melas'', "black, dark") is a broad term for a group of natural pigments found in most organisms. Melanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the ami ...

melanin
,
serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter Monoamine neurotransmitters are s and s that contain one group connected to an by a two-carbon chain (such as -CH2-CH2-). Examples are , and . All monoamines are ...

serotonin
,
melatonin Melatonin is a hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast E ...

melatonin
,
endorphins Endorphins (contracted from endogenous morphine) are endogenous opioid neuropeptide Image:Neuropeptide Y.png, Neuropeptide Y Neuropeptides are small proteins produced by neurons that act on G protein-coupled receptors and are responsible for ...
,
dynorphins Dynorphins (Dyn) are a class of opioid peptides that arise from the precursor protein prodynorphin. When prodynorphin is cleaved during processing by proprotein convertase 2 (PC2), multiple active peptides are released: dynorphin A, dynorphin B, a ...
,
nociceptin
nociceptin
, and
substance P Substance P (SP) is an undecapeptide Peptides (from Greek language πεπτός, ''peptós'' "digested"; derived from πέσσειν, ''péssein'' "to digest") are short chains of between two and fifty amino acids, linked by peptide bonds. Chain ...

substance P
. Postsynaptic depolarizations can either transmit excitatory or inhibitory neurotransmitters. Those that release excitatory vesicles are referred to as
excitatory postsynaptic potential In neuroscience Neuroscience is the scientific study of the nervous system In biology, the classical doctrine of the nervous system determines that it is a Complex system, highly complex part of an animal that coordinates its Behavior ...
(
EPSP In neuroscience Neuroscience is the of the . It is a science that combines , , , , , and to understand the fundamental and emergent properties of s, and s. The understanding of the biological basis of , , , , and has been described by ...
). Alternatively, inhibitory vesicles stimulate postsynaptic receptors such as to allow Cl ions to enter the cell or K+ ions to leave the cell, which results in an
inhibitory postsynaptic potential An inhibitory postsynaptic potential (IPSP) is a kind of synaptic potential Synaptic potential refers to the potential difference across the postsynaptic membrane that results from the action of neurotransmitters at a neuronal synapse. In other w ...
(
IPSP An inhibitory postsynaptic potential (IPSP) is a kind of synaptic potential Synaptic potential refers to the potential difference across the postsynaptic membrane that results from the action of neurotransmitters at a neuronal synapse. In other w ...
). If the EPSP is dominant, the threshold of excitation in the postsynaptic neuron may be reached, resulting in the generation of an action potential in the neuron(s) in turn postsynaptic to it, propagating the signal.


Synaptic plasticity

Synaptic plasticity In neuroscience Neuroscience is the of the . It is a science that combines , , , , , and to understand the fundamental and emergent properties of s, and s. The understanding of the biological basis of , , , , and has been described by ...
is the process whereby strengths of synaptic connections are altered. For example, long-term changes in synaptic connection may result in more postsynaptic receptors being embedded in the postsynaptic membrane, resulting in the strengthening of the synapse. Synaptic plasticity is also found to be the neural mechanism that underlies learning and memory. The basic properties, activity and regulation of membrane currents, synaptic transmission and synaptic plasticity, neurotransmission, neuroregensis, synaptogenesis and ion channels of cells are a few other fields studied by cellular neuroscientists. Tissue, cellular and subcellular anatomy are studied to provide insight into mental retardation at the Mental Retardation Research Center MRRC Cellular Neuroscience Core. Journals such as ''Frontiers in Cellular Neuroscience'' and '' Molecular and Cellular Neuroscience'' are published regarding cellular neuroscientific topics.


See also

*
Action potential In physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence ...

Action potential
* Calcium concentration microdomains *Cell biology *Cell signaling *Chemical synapse *Dendrite *Hair cells *IKK2 *Neuroendocrinology *Neuropharmacology *Pyramidal cells *Soliton model *Synaptotropic hypothesis


References

{{DEFAULTSORT:Cellular Neuroscience Cellular neuroscience,