II. Definitions

  1. Neuron
    1. Conducting cell of the neurologic system which receives, conducts and transmits small electrical signals
  2. Synapse
    1. Connections between Neurons in which they communicate via chemical signals (neurotransmitters)
  3. Neurologic Pathway
    1. Chain of communicating Neurons
  4. Neuraxis Tract (or fasciculus, peduncle or lemniscus)
    1. Bundle of axons in a pathway within the Central Nervous System (CNS)
  5. Nerve
    1. Bundle of axons in a pathway within the peripheral nervous system
  6. Neural Nucleus
    1. Group of Neuron cell bodies (soma) with attached group of axons (nerve tracts)
    2. Includes brain nucleii, Cranial Nerve nucleii, cerebellar nucleii and spinal cord nucleii
    3. Ganglia are the peripheral nerve versions of the CNS neural neuclei

III. Anatomy

  1. Images
    1. neuron.png
    2. nerveActionPotential.png
  2. Dendrites
    1. Tree-like structures that receive signals from other Neurons
  3. Cell Body (Soma)
    1. Nucleus
    2. Cytoplasm (Perikaryon)
  4. Axon
    1. Transmits signal from cell body to axon terminals
    2. Myelin Sheath
      1. Most axons are insulated with a thin layer of cells to conserve and speed electrical transmission
      2. Myelinated axons appear as white matter (while Neuron cell bodies appear as gray matter)
  5. Neurotransmitters
    1. Released from axon terminals to transmit a signal into Synapse (inter-Neuron space)
  6. Neuron types
    1. Sensory Neurons
    2. Motor Neurons
    3. Interneurons (interconnections between Neurons forming a pathway)
  7. Group of Neurons
    1. Peripheral nervous system
      1. Nerves
    2. Central Nervous System (interchangeable names)
      1. Nerve Tract
      2. Fasciculus
      3. Lemniscus
      4. Peduncle

IV. Physiology: Nerve Impulse (Action Potential)

  1. Neurons are specialized cells capable of tranmsitting an electrical signal
  2. Neuron resting Membrane Potential is more positive on outside of cell than on inside (e.g. -60 mv difference)
    1. sodiumPotassiumATPase.jpg
    2. Maintained by Sodium-Potassium ATP Pump (exchanges 3 Na+ moved extracellular for 2+ intracellular)
    3. Potassium leaks out of the cell more than Sodium leaks back in
  3. Depolarization
    1. Voltage gated electrical channels specific for Potassium and Sodium allow for electrical signal transmission
    2. Voltage channels are activated when there is a neutralization of resting Membrane Potential
      1. Membrane Potential decreases below a threshold (e.g. 15-35 millivolts or mv)
    3. Voltage-Gated Sodium channels suddenly open
      1. Sodium rushes into Neuron, resulting in neutralization of resting potential and depolarization
      2. Inside and outside of Neuron may have minimal difference of charge at depolarization
    4. Voltage-Gated Calcium channels may also be involved
      1. Most common in cardiac muscle (esp. Purkinje Fibers) and smooth muscle (uncommon in axons)
      2. As with Sodium, Calcium concentrations outside the cell are higher
      3. When Calcium channels open, Calcium rushes into the muscle cell
      4. However Calcium channels are slower than Sodium channels
        1. Results in an Action Potential plateau and a delayed repolarization/recovery
        2. Allows for a sustained, prolonged contraction of muscles
    5. Signal spreads along the axon via contiguous regions, each depolarizing in turn
  4. Repolarization
    1. Voltage-Gated Sodium channels close in response to neutralized Membrane Potential
    2. Voltage-Gated Potassium channels open
      1. Potassium flows rapidly out of cell
    3. Resting Membrane Potential is Restored
      1. Neuron refractory period is related to the time required to Restore the resting Membrane Potential

V. Images

  1. NeuroCellGrayBB629.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  2. NeuroCellGrayBB626.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  3. NeuroCellGrayBB625.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)

VI. References

  1. Goldberg (2014) Clinical Physiology, MedMaster, p. 36-7

Neuro Atlas (FPnotebook.com) Open in New Window

Images: Related links to external sites (from Bing)

Related Studies

Ontology: Action Potentials (C0001272)

Definition (GO) A process in which membrane potential cycles through a depolarizing spike, triggered in response to depolarization above some threshold, followed by repolarization. This cycle is driven by the flow of ions through various voltage gated channels with different thresholds and ion specificities. [GOC:dph, GOC:go_curators, GOC:tb, ISBN:978-0-07-139011-8]
Definition (CSP) a rapid self-propagating change in the electrical potential across a neuron, gland, or muscle fiber membrane primarily due to a sudden influx of sodium ions followed by an efflux of potassium ions.
Definition (MSH) Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.
Concepts Cell Function (T043)
MSH D000200
English Action Potential, Action Potentials, Potential, Action, Potentials, Action, action potential, action potentials
German Aktionspotenziale, Aktionspotentiale
French Potentiels d'action
Swedish Aktionspotentialer
Czech akční potenciály
Finnish Aktiopotentiaalit
Japanese 活動電位
Polish Potencjały czynnościowe
Portuguese Potenciais de Espiga, Potenciais de Espícula, Impulsos Nervosos, Potentiais de Pico, Potenciais de Ação
Italian Potenziali d'azione
Dutch Actiepotentiaal, Potentiaal, actie-
Spanish Potenciales de Acción

Ontology: Axon (C0004461)

Definition (FMA) Neurite which has as its direct parts an axon hillock, an axon proper, one or more axon collaterals and one or more axon terminals.
Definition (GO) The long process of a neuron that conducts nerve impulses, usually away from the cell body to the terminals and varicosities, which are sites of storage and release of neurotransmitter. [GOC:nln, ISBN:0198506732]
Definition (UWDA) Cell appendage of a neuron that consists of an axon hillock, an axon proper, axon collaterals and an axon terminal.
Definition (NCI) A projection of a neuron that conducts electrical impulses away from the neuronal cell body.
Definition (MSH) Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body.
Definition (CSP) long fiber of a neuron, that carries efferent (outgoing) action potentials from the cell body towards target cells; each nerve cell has one axon, which can be over a foot long; in the peripheral nervous system, the larger (myelinated) axons are surrounded by a myelin sheath formed by concentric layers of plasma membrane of the Schwann cell.
Concepts Cell Component (T026)
MSH D001369
SnomedCT 60436000
English Axons, axon, neuraxons, axons, neuraxon, axone, Axon structure (cell structure), Axon structure, Axon structure (body structure), Axon
French Axone, Prolongements axoniques, Axones
Swedish Nervcellsutskott
Czech axony
Finnish Aksonit
Croatian AKSONI
Latvian Aksoni
Polish Neuryty, Aksony
Norwegian Aksoner
Spanish Axonas, axón, estructura del axón (estructura celular), estructura del axón (estructura corporal), estructura del axón, Axones
German Achsenzylinder, Axone
Italian Assoni
Dutch Axon, Axonen
Portuguese Axônios

Ontology: Dendrites (C0011305)

Definition (FMA) Neurite which has as its direct parts a dendrite proper and a set of dendritic spines.
Definition (GO) A neuron projection that has a short, tapering, often branched, morphology, receives and integrates signals from other neurons or from sensory stimuli, and conducts a nerve impulse towards the axon or the cell body. In most neurons, the impulse is conveyed from dendrites to axon via the cell body, but in some types of unipolar neuron, the impulse does not travel via the cell body. [GOC:dos, GOC:mah, GOC:nln, ISBN:0198506732]
Definition (UWDA) Cell appendage of a neuron that consists of the dendrite proper and the dendritic spines.
Definition (NCI) A long, branching outgrowth or extension from a neuron, that carries electrical signals from synapses to the cell body; any structure that resembles a dendrite.
Definition (MSH) Extensions of the nerve cell body. They are short and branched and receive stimuli from other NEURONS.
Definition (CSP) one of the threadlike extensions of the cytoplasm of a neuron, which typically branch into tree-like processes; in unipolar and bipolar neurons, there is a single dendrite, which proximally resembles an axon but branches distally; in multipolar neurons there are many short, branching dendrites; dendrites compose most of the receptive surface of a neuron; called also dendron, neurodendrite, and neurodendron.
Concepts Cell Component (T026)
MSH D003712
SnomedCT 90604005
French Prolongements dendritiques, Dendrite, Dendrites
Swedish Nervcellsförgreningar
English Dendritic, Dendrites, dendrite, dendrites, Dendrite, Dendrite (cell structure), Dendrite (body structure)
Czech dendrity
Finnish Dendriitit
Latvian Dendrīti
Polish Dendryty
Norwegian Dendritter
Spanish dendrita (estructura celular), dendrita (estructura corporal), dendrita, Dendritas
German Dendriten
Italian Dendriti
Dutch Dendriet, Dendrieten
Portuguese Dendritos

Ontology: Membrane Potentials (C0025251)

Definition (MSH) The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).
Definition (NCI) The electrical potential difference across a plasma membrane.
Definition (CSP) electrical potential difference across a biological, i.e., cell or organelle, or artificial membrane.
Concepts Cell Function (T043)
MSH D008564
English Potential, Membrane, Potential, Transmembrane, Potentials, Membrane, Potentials, Transmembrane, Transmembrane Potential, Transmembrane Potentials, Difference, Transmembrane Potential, Differences, Transmembrane Potential, Potential Difference, Transmembrane, Potential Differences, Transmembrane, Transmembrane Electrical Potential Difference, Transmembrane Potential Differences, Transmembrane Potential Difference, Membrane Potential, membrane potentials, transmembrane potential, membrane potential, potential resting, resting potential, resting membrane potential, rest membrane potential, Membrane Potentials
German Transmembranpotentialdifferenz, Transmembrane elektrische Potentialdifferenz, Membranpotentiale, Transmembranpotentiale
French Potentiels transmembranaires, Différence de potentiel transmembranaire, Différence de potentiel électrique transmembranaire, Potentiels de membrane
Swedish Membranpotentialer
Czech membránové potenciály
Finnish Kalvojännitteet
Italian Potenziali transmembrana, Differenza di potenziale transmembrana, Differenza di potenziale elettrico transmembrana, Potenziali di membrana
Croatian Not Translated[Membrane Potentials]
Polish Potencjały błonowe
Japanese 静止電位, 膜電位, 膜内外電位, 静止膜電位
Norwegian Membranpotensial, Membranspenning
Dutch Membraanpotentiaal, Membraanpotentialen, Rustpotentialen, Transmembraanpotentialen
Portuguese Potenciais da Membrana, Potenciais Transmembrana
Spanish Potenciales de la Membrana, Potenciales Transmembrana

Ontology: Myelin Sheath (C0026973)

Definition (GO) An electrically insulating fatty layer that surrounds the axons of many neurons. It is an outgrowth of glial cells: Schwann cells supply the myelin for peripheral neurons while oligodendrocytes supply it to those of the central nervous system. [GOC:jl, NIF_Subcellular:sao-593830697, Wikipedia:Myelin]
Definition (FMA) Cell appendage of a Schwann cell or an oligodendroctye which wraps around a zone of an axon; it is a shared part between the axon and the glial cell (Schwann cell or oligodenrocyte).
Definition (NCI_NCI-GLOSS) The fatty substance that covers and protects nerves.
Definition (NCI) A layer of phospholipids and protein found on neuronal axons. This structure acts as an electrical insulator that allows nerve impulses to travel faster by increasing the resistance and decreasing the capacitance over that found in unmyelinated nerve fibers.
Definition (MSH) The lipid-rich sheath surrounding AXONS in both the CENTRAL NERVOUS SYSTEMS and PERIPHERAL NERVOUS SYSTEM. The myelin sheath is an electrical insulator and allows faster and more energetically efficient conduction of impulses. The sheath is formed by the cell membranes of glial cells (SCHWANN CELLS in the peripheral and OLIGODENDROGLIA in the central nervous system). Deterioration of the sheath in DEMYELINATING DISEASES is a serious clinical problem.
Concepts Cell Component (T026)
MSH D009186
SnomedCT 23879005
English Myelin Sheath, Myelin Sheaths, Sheath, Myelin, Sheaths, Myelin, Myelinated, medullary sheath, myelin sheath, myelin sheaths, myelin, Myelin sheath, Myelin sheath structure (cell structure), Myelin sheath structure, Myelin sheath, NOS, Myelin sheath structure (body structure), Myelin
Swedish Myelinskida
Czech myelinová pochva
Spanish Vaina de Mielina, estructura de la vaina de mielina (estructura celular), estructura de la vaina de mielina (estructura corporal), estructura de la vaina de mielina, vaina de mielina
Finnish Myeliinituppi
Latvian Mielīna apvalks
Polish Osłonka mielinowa, Osłonka rdzenna
Croatian Not Translated[Myelin Sheath]
Norwegian Myelinskjede
Portuguese Extrato Mielínico, Bainha de Mielina
German Myelinscheide
Italian Guaina mielinica
Dutch Myelineschede, Schede, myeline-
French Gaine de myéline

Ontology: Nerve conduction function (C0027788)

Definition (CSP) movement of a nerve impulse along a single nerve.
Definition (MSH) The propagation of the NERVE IMPULSE along the nerve away from the site of an excitation stimulus.
Concepts Organ or Tissue Function (T042)
MSH D009431
SnomedCT 22690006
LNC LP32240-1
English Conduction, Nerve, Conduction, Neural, Conductions, Nerve, Conductions, Neural, Nerve Conduction, Nerve Conductions, Neural Conduction, Neural Conductions, neural conduction, nerve conductions, nerve conduction, conduction nerve, Neural conduction, Nerve conduction, Nerve conduction (observable entity), Nerve conduction function
Swedish Nervledning
Czech nervové vedení
Spanish Conducción Nerviosa, Conducción Neural, Conducción Neuronal, conducción nerviosa (entidad observable), conducción nerviosa, Conducción del Nervio
Finnish Hermoimpulssin johtuminen
French Conduction des influx nerveux, Propagation nerveuse, Conduction de l'influx nerveux, Conduction nerveuse
Italian Conduzione nervosa, Conduzione neuronale
Japanese 神経興奮伝導, 神経刺激伝導, 神経伝導
Polish Przewodnictwo nerwowe, Zjawisko Wedenskiego
German Nervenleitung, Neurale Leitung
Dutch Geleiding, zenuw-, Zenuwgeleiding
Portuguese Condução Nervosa, Condução Neuronal

Ontology: Neurons (C0027882)

Definition (FMA) Neural cell which has as its direct parts a cell body (soma) and one or more neurites; the neuron is the structural and functional unit of the nervous system. Examples: unipolar neuron, bipolar neuron, neuron of retina.
Definition (FMA) Somatic cell which is dervied from the neuro-ectoderm or the neural crest.
Definition (MSHCZE) Základní buněčné jednotky nervové tkáně. Každý neuron sestává z těla, axonu a dendritů - výběžků neuronu. Jejich účelem je přijímat, vést a přenášet impulsy v nervovém systému.
Definition (NCI_NCI-GLOSS) A type of cell that receives and sends messages from the body to the brain and back to the body. The messages are sent by a weak electrical current.
Definition (NCI) Any of the conducting cells of the nervous system. A typical neuron consists of a cell body, containing the nucleus and the surrounding cytoplasm (perikaryon); several short radiating processes (dendrites); and one long process (the axon), which terminates in twiglike branches (telodendrons) and may have branches (collaterals) projecting along its course.
Definition (MSH) The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.
Definition (CSP) basic cellular units of nervous tissue; each neuron consists of a body, an axon, and dendrites and their purpose is to receive, conduct, and transmit impulses in the nervous system.
Concepts Cell (T025)
MSH D009474
SnomedCT 47220008
English Cell, Nerve, Cells, Nerve, Nerve Cells, nervous system cell, nerve unit, neurocyte, neurone, Neural cell, Nerve cell, Neurone, cells nervous system, cells neural, nerve cell, neurons, neural cell, nerve cells, neuron, Neuron, Neuron (cell), Neuron, NOS, Nerve Cell, Neural Cell, Neurocyte, Neurons
Swedish Nervceller
Czech neurony, nervové buňky
Finnish Hermosolut
Italian Cellule nervose, Neuroni
Croatian NEURONI
Latvian Nervu šūnas, Neironi
French Cellule nerveuse, Neurone, Cellules nerveuses, Neurones
Polish Neurocyty, Komórki nerwowe, Neurony
Japanese 神経細胞, ニューロン, ノイロン, 神経単位
Norwegian Nevroner, Nerveceller
Spanish Células Neurales, neurona (célula), neurona, Neuronas, Células Nerviosas
Portuguese Células Neurais, Células Nervosas, Neurônios
German Nervenzellen, Neuronen
Dutch Neuron, Neuronen, Zenuwcellen

Ontology: Synapses (C0039062)

Definition (MSHCZE) Specializované spojení, na němž dochází ke styku neuronu s cílovou buňkou. U klasické synapse dojde k uvolnění chemického přenašeče (transmiteru) z měchýřku presynaptického zakončení neuronu, ten je rozstříknut přes synaptickou štěrbinu na aktivovaný receptor postsynaptické membrány cílové buňky. Cílem může být dendrit, buněčné tělo nebo axon jiného neuronu nebo specializovaná oblast svalu či sekreční buňka. Neurony mohou také komunikovat cestou přímého elektrického spojení prostřednictvím ELEKTRICKÝCH SYNAPSÍ. Existují i jiná nesynaptická spojení kromě chemické a elektrické signalizace, a to cestou mimobuněčně zprostředkované interakce. r
Definition (GO) The junction between a nerve fiber of one neuron and another neuron or muscle fiber or glial cell; the site of interneuronal communication. As the nerve fiber approaches the synapse it enlarges into a specialized structure, the presynaptic nerve ending, which contains mitochondria and synaptic vesicles. At the tip of the nerve ending is the presynaptic membrane; facing it, and separated from it by a minute cleft (the synaptic cleft) is a specialized area of membrane on the receiving cell, known as the postsynaptic membrane. In response to the arrival of nerve impulses, the presynaptic nerve ending secretes molecules of neurotransmitters into the synaptic cleft. These diffuse across the cleft and transmit the signal to the postsynaptic membrane. [ISBN:0198506732]
Definition (NCI) Specialized junctions at which a neuron communicates with a target cell. At classical synapses, a neuron's presynaptic terminal releases a chemical transmitter stored in synaptic vesicles which diffuses across a narrow synaptic cleft and activates receptors on the postsynaptic membrane of the target cell. The target may be a dendrite, cell body, or axon of another neuron, or a specialized region of a muscle or secretory cell. Neurons may also communicate through direct electrical connections which are sometimes called electrical synapses.(MeSH)
Definition (NCI_NCI-GLOSS) The space between the end of a nerve cell and another cell. Nerve impulses are usually carried to the neighboring cell by chemicals called neurotransmitters, which are released by the nerve cell and are taken up by another cell on the other side of the synapse. The neighboring cell may be another nerve cell, a muscle cell, or a gland cell.
Definition (CSP) specialized junctions at which a neuron communicates with a target cell; presynaptic terminals release a chemical transmitter stored in synaptic vesicles which diffuses across a narrow synaptic cleft and activates receptors on the postsynaptic membrane of the target cell; the target may be a dendrite, cell body, or axon of another neuron, or a specialized region of a muscle or secretory cell; do not confuse with the immunological synapse, see cross reference for that concept.
Definition (MSH) Specialized junctions at which a neuron communicates with a target cell. At classical synapses, a neuron's presynaptic terminal releases a chemical transmitter stored in synaptic vesicles which diffuses across a narrow synaptic cleft and activates receptors on the postsynaptic membrane of the target cell. The target may be a dendrite, cell body, or axon of another neuron, or a specialized region of a muscle or secretory cell. Neurons may also communicate via direct electrical coupling with ELECTRICAL SYNAPSES. Several other non-synaptic chemical or electric signal transmitting processes occur via extracellular mediated interactions.
Concepts Body Space or Junction (T030)
MSH D013569
SnomedCT 69147006
French Synapse, Synapses, Jonction synaptique, Jonctions synaptiques
English synaptic junction, Synapse, neuron junction, neuron-neuron junction, Synapsis, Synaptic junction, synapses, synapse, synapsis, Synapses, Synapse structure (body structure), Synapse structure
Swedish Synapser
Czech synapse
Finnish Synapsit
Japanese 接合部-神経細胞間, シナプス, 神経細胞間シナプス
Croatian SINAPSE
Latvian Sinapses
Polish Synapsy
Norwegian Synapser, Synapse
Spanish estructura de la sinapsis (estructura corporal), estructura de la sinapsis, sinapsis, Sinapsis
German Synapsen
Italian Sinapsi
Dutch Synaps, Synapsen
Portuguese Sinapses

Ontology: Nerve fasciculus (C0549154)

Concepts Body Part, Organ, or Organ Component (T023)
SnomedCT 123168002, 57592002
English Nerve fasciculus, Nerve bundle, Nerve fiber bundle, Neural fasciculus, nerve bundle, bundle nerve, bundles nerve, Nerve bundle (body structure), Nerve bundle -RETIRED-
Spanish haz nervioso, haz nervioso (concepto no activo)

Ontology: Cell body of neuron (C0599444)

Definition (FMA) Cell body which consists of the plasma membrane and the cytoplasm surrounding the nucleus of the neuron.
Definition (GO) The portion of a neuron that includes the nucleus, but excludes cell projections such as axons and dendrites. [GOC:go_curators]
Definition (UWDA) Cell body which consists of the plasma membrane and the cytoplasm surrounding the nucleus of the neuron.
Definition (CSP) the cell body of a neuron.
Definition (GO) The portion of the cell soma (cell body) that excludes the nucleus. [GOC:jl]
Concepts Cell Component (T026)
English perikaryon, soma, Soma of neuron, Perikaryon, Cell body of neuron, neuronal cell body, neuronal cell soma, somas, cell body, body cell, bodies cell, neuron cell body, bodies cells, body cells, neural cell body, Cell Body

Ontology: Nerve Impulses (C1720744)

Concepts Cell Function (T043)
MSH D000200
English Impulse, Nerve, Impulses, Nerve, Nerve Impulses, Nerve Impulse
French Influx nerveux
German Nervenimpulse
Italian Impulso nervoso
Czech nervové impulzy, nervové impulsy

Ontology: membrane depolarization (C1816453)

Definition (GO) The process in which membrane potential changes in the depolarizing direction from the resting potential, usually from negative to positive. For example, the initial depolarization during the rising phase of an action potential is in the direction from the negative resting potential towards the positive membrane potential that will be the peak of the action potential. [Wikipedia:Depolarization]
Concepts Cell Function (T043)
English membrane depolarization

Ontology: Lemniscus of neuraxis (C2330117)

Concepts Body Part, Organ, or Organ Component (T023)
English Neuraxis lemniscus, Lemniscus of neuraxis

Ontology: Tract of neuraxis (C2330216)

Concepts Body Part, Organ, or Organ Component (T023)
English Neuraxis tract, Tract of neuraxis

Ontology: Peduncle of neuraxis (C2332863)

Concepts Body Part, Organ, or Organ Component (T023)
English Peduncle of neuraxis, Neuraxis peduncle