PhysiologyWeb Logo  Search
PhysiologyWeb Loading...

Glossary of Physiology Terms
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Search

There are 34 glossary search results for:   Neuro




Definition:
Neurohormones are chemical messenger molecules that are released by neurons, but enter the bloodstream where they travel to distant target sites within the body. Therefore, neurohormones share characteristics with both neurotransmitters and hormones. Similar to neurotransmitters, neurohormones are released by neurons. Similar to hormones, neurohormones travel in the bloodstream.

Two well-known examples of neurohormones are oxytocin and the antidiuretic hormone (also referred to as vasopressin).

Related glossary terms/phrases:
Hormone
Neurotransmitter



Definition:
Posterior pituitary gland

Related glossary terms/phrases:
Hypophysis
Adenohypophysis



Definition:
Neurotoxins are chemical molecules that have an adverse effect on neuron function and, thus, disrupt the normal function of the nervous system. Neurotoxins could be small molecules or peptides and can be derived from a variety of invertebrate and vertebrate animals, as well as plant species.

The following is a short list of some examples of neurotoxins:

α-Bungarotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.

Chlorotoxin: A peptide neurotoxin that inhibits chloride channels.

α-Conotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.

δ-Conotoxin: A peptide neurotoxin that inhibits voltage-gated sodium channels.

w-Conotoxin: A peptide neurotoxin that inhibits N-type voltage-gated calcium channels.

Picrotoxin: Inhibits GABAA receptor chloride channels.

Tetrodotoxin: Inhibitor of neuronal voltage-gated sodium channels.



Definition:
Chemical messenger molecules released by neurons into the synaptic cleft.

Neurotransmitter molecules may be small molecules such as glutamate, γ-aminobutyric acid (GABA), acetylcholine, dopamine, norepinephrine, serotonin (5-hydroxytryptamine), and glycine. These are referred to as classic neurotransmitters. A neuron generally releases only one type of small classic neurotransmitter.

Neurotransmitters may also be peptide molecules, such as substance P, opioids, and somatostatin. These are referred to as neuropeptides.

Gas molecules, such as nitric oxide (NO), may also act as neurotransmitters.



Definition:
The absolute refractory period refers to a period during the action potential. This is the time during which another stimulus given to the neuron (no matter how strong) will not lead to a second action potential. The absolute refractory period starts immediately after the initiation of the action potential and lasts until after the peak of the action potential. Following this period, the relative refractory period begins.

Related glossary terms/phrases:
Relative refractory period

See also:
Neuronal Action Potential - Refractory Periods



Abbreviation:
ACh

Definition:
Acetylcholine (ACh) is a chemical neurotransmitter used by the central nervous system (CNS) as well as the peripheral nervous system (PNS). Acetylcholine is a classical neurotransmitter and, in fact, it was the first of the classic neurotransmitters to be discovered. It was discovered in 1914 by Henry Hallett Dale while conducting experiments on the heart.

Acetylcholine is the neurotransmitter used by the somatic division of the nervous system at the neuromuscular junction (where a somatic motor neuron makes synaptic contact with a skeletal muscle cell). Acetylcholine is also used extensively by both branches of the autonomic nervous system; sympathetic and parasympathetic. It is the primary neurotransmitter released in autonomic ganglia by preganglionic autonomic neurons. It is also the primary neurotransmitter released by parasympathetic postganglionic neurons. A few sympathetic postganglionic neurons also release acetylcholine. The diverse actions of acetylcholine are exerted via the activation of nicotinic and muscarinic ACh receptors.

Other resources:
Acetylcholine (Wikipedia)



Definition:
The action potential is a rapid and reversible reversal of the electrical potential difference across the plasma membrane of excitable cells such as neurons, muscle cells and some endocrine cells. In a neuronal action potential, the membrane potential rapidly changes from its resting level of approximately -70 mV to around +50 mV and, subsequently, rapidly returns to the resting level again. The neuronal action potential forms an important basis for information processing, propagation, and transmission. In muscle cells, the action potential precedes, and is necessary to bring about, muscle contraction. Some endocrine cells also exhibit action potentials, where the excitation leads to hormone secretion.

The action potential is also referred to as the electrical impulse or nervous impulse.

Related glossary terms/phrases:
Graded potential

See also:
Neuronal Action Potential



Definition:
Leading toward a region or structure of interest.

In the nervous system, afferent fibers (i.e., neurons) transmit information from a peripheral receptor to the spinal cord or the brainstem. Afferent neurons are also referred to as sensory neurons.

In the kidneys, the afferent arteriole carries blood to the glomerular capillaries.

Related glossary terms/phrases:
Efferent



Definition:
Moving along an axon away from the neuronal cell body toward the axon terminal.

Related glossary terms/phrases:
Retrograde



Definition:
Atropine is a blocker (i.e., inhibitor) of muscarinic acetylcholine receptors. Therefore, atropine blocks the action of postganglionic parasympathetic neurons.



Definition:
The region of the neuron cell body from which the axon originates. The axon hillock is generally the site of action potential initiation. It is also referred to as the initial segment.



Definition:
Refers to neurons, synapses, or receptors where acetylcholine is used as the neurotransmitter.

For example, cholinergic neurons release acetylcholine as their neurotransmitter.

In cholinergic synapses, acetylcholine is released from the presynaptic neuron, and it acts on acetylcholine receptors in the plasma membrane of the postsynaptic cell.

Cholinergic receptors are those that respond to acetylcholine as the physiological ligand. The two major types are nicotinic and muscarinic cholinergic receptors (may also be referred to as nicotinic and muscarinic acetylcholine receptors).

Cholinergic drugs are compounds that mimic the action of acetylcholine by binding to and activating cholinergic receptors.



Definition:
A potent blocker of nicotinic cholinergic receptors (nicotinic acetylcholine receptor, nAChR) found at the neuromuscular junction. At small doses, curare can lead to muscle weakness. At high doses, curare can lead to paralysis of skeletal muscles, which would also result in asphyxiation (and ultimately death) due to paralysis of the diaphragm. Curare was commonly the active agent of poison arrow.

Other resources:
See Wikipedia



Definition:
Leading away from a region or structure of interest.

In the nervous system, efferent fibers (i.e., neurons) transmit information from the central nervous system to peripheral effector organs (i.e., muscles or glands). Therefore, the cells bodies of efferent neurons reside within the central nervous system, whereas their axonal projections exit the central nervous system to make synaptic contact with effector organs in the periphery. Efferent neurons are also referred to as motor neurons.

In the kidneys, the efferent arteriole carries blood away from the glomerular capillaries.

Related glossary terms/phrases:
Afferent



Definition:
Electrophysiology is the study of the electrical properties of biological macromolecules, cells, tissues, and organs. Electrical signals such as voltage and/or current are generally measured. Examples include measuring changes in the membrane voltage of excitable cells (e.g., neurons, muscle cells, and some endocrine cells) during an action potential. The current carrried by ions as they permeate the pore of ion channels can also be measured - both at the single-channel level (single-channel current), as well as the macroscopic current resulting from the activity of a population of channels. As another example, electrical measurements may involve recording voltage changes at the surface of the skin that result from the activity of skeletal muscles (electromyogram, EMG), cardiac myocytes (electrocardiogram, ECG), or neurons in the brain (electroencephalogram, EEG).



Definition:
Refers to the ability of some cells to be electrically excited resulting in the generation of action potentials. Neurons, muscle cells (skeletal, cardiac, and smooth), and some endocrine cells (e.g., insulin-releasing pancreatic β cells) are excitable cells.

See also:
Resting Membrane Potential - Introduction



Abbreviation:
GABA

Definition:
GABA is an inhibitory amino acid neurotransmitter in the central and peripheral nervous systems. It is the most abundant inhibitory neurotransmitter in the nervous system. During embryonic development, GABA acts as an excitatory neurotransmitter at some central synapses. GABA is a classical neurotransmitter. Its action is exerted via the activation of GABAA, GABAB, and GABAC receptors. GABAA and GABAC receptors are ligand-gated chloride channels, whereas GABAB receptors are G protein coupled receptors. At GABAergic synapses, the action of GABA is terminated by GABA transporters (GAT), which transport GABA from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.



Definition:
Glutamate (Glu, E) is one of the standard twenty (20) amino acids used by cells to synthesize peptides, polypeptides, and proteins. It has a molecular weight of 147.13 g/mol. Its side chain has a pKa of 4.07 and, therefore, glutamate has a net negative charge at physiological pH.

In the nervous system, glutamate is an excitatory amino acid neurotransmitter. In fact, glutamate is the most abundant excitatory neurotransmitter in the nervous system. Glutamate is a classical neurotransmitter. Its action is exerted via the activation of glutamate receptors (GluR), some of which are ligand-gated ion channels (ionotropic receptors), and some are G protein coupled receptors (GPCRs, metabotropic receptors). At glutamatergic synapses, the action of glutamate is terminated by glutamate transporters (EAAT, excitatory amino acid transporter), which transport glutamate from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.



Definition:
Glycine (Gly, G) is one of the standard twenty (20) amino acids. At a molecular weight of 75.07 g/mol, it is the smallest of the 20 amino acids used by cells to synthesize peptides, polypeptides, and proteins.

In the nervous system, glycine is also an inhibitory amino acid neurotransmitter. Glycinergic synapses are most commonly found in brain stem and spinal cord circuits. Glycine is a classical neurotransmitter. Its action is exerted via the activation of ionotropic glycine receptors (GlyR), which are ligand-gated chloride channels. At glycinergic synapses, the action of glycine is terminated by glycine transporters (GlyT), which transport glycine from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.



Definition:
The Hodgkin cycle represents a positive feedback loop in neurons, where an initial membrane depolarization from the resting value (∼ −70 mV) to the threshold value (∼ −50 mV) leads to rapid depolarization of the membrane potential to approach the equilibrium potential for Na+ (VNa ≈ +60 mV). The voltage-gated Na+ channels of neurons are responsible for the Hodgkin cycle.

See the figure depicting the Hodgkin cycle.

See also:
Important Features of the Neuronal Action Potential



Definition:
Lidocaine is a local anesthetic and an antiarrhythmic drug. It is a commonly used local anesthetic for minor surgery and in dental procedures. Lidocaine is also used topically to relieve itching, burning, and pain from skin inflammations.

Lidocaine's mechanism of action is to block fast voltage-gated Na+ channels of neurons and cardiac myocytes.

Other names used for lidocaine are xylocaine and lignocaine.

See also:
Pharmacological Inhibition of Na+ and K+ Channels

Other resources:
Lidocaine (Wikipedia)



Definition:
A motor unit is composed of a motor neuron and all of the muscle fibers (i.e., muscle cells) it innervates.

Alternatively, a motor unit is a group of muscle fibers innervated by a single motor neuron.



Definition:
Refers to the action potential of neurons. It is also referred to as the nervous impulse.

Related glossary terms/phrases:
Action potential

See also:
Neuronal Action Potential



Definition:
Refers to the action potential of neurons. It is also referred to as the nerve impulse.

Related glossary terms/phrases:
Action potential

See also:
Neuronal Action Potential



Definition:
Refers to cells that do not generate action potentials. With the exception of neurons, muscle cells, and some endocrine cells, all cells in the body are non-excitable.

See also:
Resting Membrane Potential - Introduction



Abbreviation:
K+

Definition:
The main cation (positively charged ion) of the intracellular fluid.

Potassium (K+) plays an important role in the action potential of neurons and muscle cells.

The extracellular concentration of K+ is about 4 mM. The intracellular concentration of K+ is about 150 mM.



Definition:
A local topical anesthetic.

Procaine's mechanism of action is to block fast voltage-gated Na+ channels of neurons.

See also:
Pharmacological Inhibition of Na+ and K+ Channels

Other resources:
Procaine (Wikipedia)



Definition:
The voltage difference across a cell plasma membrane in the resting or quiescent state. It is also simply referred to as the resting potential (Vrest). The value of the resting membrane potential varies from cell to cell. Depending on the cell type, it can range from −90 mV to −20 mV.

For example, Vrest is −90 mV in skeletal and cardiac muscle cells as well as in astrocytes. In a typical neuron, Vrest is approximately −70 mV. In many non-excitable cells, Vrest ranges from −60 to −50 mV. In photoreceptors, Vrest is about −20 mV.

See also:
Resting membrane potential



Definition:
Moving from the axon terminal back toward the neuronal cell body.

Related glossary terms/phrases:
Anterograde



Definition:
Secretion refers to cellular release of substances (ions and small and large molecules) to the external environment of the cell. Secretion may be accomplished by exocytosis (fusion of transport vesicles with the plasma membrane and release of vesicle contents to the external environment), by transport of molecules across the plasma membrane (via the activity of transport proteins such as pumps, transporters, and channels), or by simple diffusion of fat-soluble molecules through the plasma membrane out of the cell.

For example, endocrine cells secrete hormone molecules that then enter the bloodstream. Neurons release (i.e., secrete) neurotransmitter molecules into the synaptic cleft. Some neurons secrete neurohormones; which similar to hormones, travel in the bloodstream to reach distant target cells. Epithelial cells secrete molecules in luminal spaces, such as digestive enzymes secreted into the digestive tract by various cell types.

See also:
Excretion



Abbreviation:
Na+

Definition:
The main cation (positively charged ion) of the extracellular fluid.

Sodium (Na+) plays an important role in several physiological processes such as the action potential of neurons and muscle cells, secondary active, sodium-coupled transport of ions, nutrients, neurotransmitters across the plasma membrane of cells, and many other processes.

The extracellular concentration of Na+ is about 145 mM. The intracellular concentration of Na+ is about 15 mM.



Definition:
Refers to the rapid depolarization of the membrane early in the action potential. In neuronal, skeletal muscle, and cardiac muscle action potentials, the Hodgkin cycle is responsible for the spike phase of the action potential.

See figure.

See also:
Important Features of the Neuronal Action Potential



Abbreviation:
TTX

Definition:
Inhibitor of fast voltage-gated sodium (Na+) channels of neurons and muscle cells. It is an extremely potent and toxic neurotoxin.

See also:
Pharmacological Inhibition of Na+ and K+ Channels

Other resources:
Tetrodotoxin (Wikipedia)



Definition:
The membrane voltage that must be reached in an excitable cell (e.g., neuron or muscle cell) during a depolarization in order to generate an action potential. At the threshold voltage, voltage-gated channels become activated. Threshold is approximately −50 to −40 mV in most excitable cells.

Related glossary terms/phrases:
Sub-threshold
Supra-threshold

See also:
Neuronal Action Potential - Introduction









Posted: Sunday, March 31, 2013
Last updated: Friday, August 28, 2015