Neuroscience Chapter 5

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synaptic transmission

The process of transferring information from one cell to another at a synapse

electrical synapse

A synapse in which electrical current flows directly from one cell to another via a gap junction.

chemical synapse

A synapse in which presynaptic activity stimulates the release of neurotransmitter, which activates receptors in the postsynaptic membrane.

gap junction

A specialized junction where a narrow gap between two cells is spanned by protein channels (connexons) that allow ions to pass directly from one cell to another.

postsynaptic potential (PSP)

A change in the postsynaptic membrane potential by the presynaptic action of an electrical synapse, or a synaptically released neurotransmitter.

secretory granule

A spherical membrane-enclosed vesicle about 100nm in diameter containing peptides intended for secretion by exocytosis; also called dense-core vesicle

dense-core vesicle

Secretory granule.

membrane differentiation

A dense accumulation of protein adjacent to and within the membrane on either side of a synaptic cleft.

active zone

A presynaptic membrane differentiation that is the site of neurotransmitter release.

postsynaptic density

A postsynaptic membrane differentiation that is the site of neurotransmitter receptors.

neuromuscular junction

A chemical synapse between a spinal motor neuron axon and a skeletal muscle fiber.

motor end-plate

The postsynaptic membrane at the neuromuscular junction.

glutamate (Glu)

An amino acid; the major excitatory neurotransmitter in the central nervous system.

gamma-aminobutyric acid (GABA)

An amino acid synthesized from glutamate; the major inhibitory neurotransmitter in the central nervous system.

glycine (Gly)

An amino acid; an inhibitory neurotransmitter at some locations in the central nervous system.

acetylcholine (ACh)

An amine that serves as a neurotransmitter at many synapses in the peripheral and central nervous systems, including the neuromuscular junction.

transporter

A membrane protein that transports neurotransmitters, or their precursors, across membranes to concentrate them in either presynaptic cytosol or synaptic vesicles.

voltage-gated calcium channel

A membrane protein forming a pore that is permeable to calcium ions and gated by depolarization of the membrane.

exocytosis

The process whereby material is released from an intracellular vesicle into the extracellular space by fusion of the vesicle membrane with the cell membrane.

endocytosis

The process by which a bit of the cell membrane is pinched off, internalized, and converted to an intracellular vesicle.

transmitter-gated ion channel

A membrane protein forming a pore that is permeable to ions and gated by neurotransmitter.

excitatory postsynaptic potential (EPSP)

Depolarization of the postsynaptic membrane potential by the action of a synaptically released neurotransmitter.

inhibitory postsynaptic potential (IPSP)

A change in the postsynaptic membrane potential by the action of a synaptically released neurotransmitter, making the postsynaptic neuron less likely to fire action potentials.

G-protein-coupled receptor

A membrane protein that activates G-proteins when it binds neurotransmitter.

G-protein

A membrane-enclosed protein that binds guanosine triphosphate (GTP) when activated by a membrane receptor. Active G-proteins can stimulate or inhibit other membrane-enclosed proteins.

second messenger

A multistep process that couples activation of a neurotransmitter receptor activation of intracellular enzymes.

metabotropic receptor

A G-protein-coupled receptor whose primary action is to stimulate an intracellular biochemical response.

autoreceptor

A receptor in the membrane of a presynaptic axon terminal that is sensitive to the neurotransmitter released by that terminal.

neuropharmacology

The study of the effects of drugs on nervous system tissue.

inhibitor

A drug or toxin that blocks the normal action of a protein or a biochemical process.

receptor antagonist

A drug that binds to a receptor and inhibits its function.

receptor agonist

A drug that binds to a receptor and activates it.

nicotinic ACh receptor

A class of acetylcholine-gated ion channel found in various locations, notably the neuromuscular junction.

synaptic integration

The process by which multiple EPSPs and/or IPSPs combine within one postsynaptic neuron, in some cases triggering one or more action potentials.

miniature postsynaptic potential

A change in postsynaptic membrane potential caused by the action of neurotransmitter released from a single synaptic vesicle.

quantal analysis

A method of determining how many vesicles release neurotransmitter during normal synaptic transmission.

EPSP summation

A simple form of synaptic integration whereby excitatory postsynaptic potentials combine to produce a larger postsynaptic depolarization.

spatial summation

The combining of excitatory postsynaptic potentials generated at more than one synapse on the same cell.

temporal summation

The combining of excitatory postsynaptic potentials generated in rapid succession at the same synapse.

length constant

A parameter used to describe how far changes in membrane potential can passively spread down a cable such as an axon or a dendrite, represented by the symbol lambda. The length constant lambda is the distance at which the depolarization falls to 37% of its original value; it depends on the ratio of membrane resistance to internal resistance.

internal resistance

The resistance to electrical current flows longitudinally down a cable or neurite, represented by the symbol ri.

membrane resistance

The resistance to electrical current flow across a membrane; represented by the symbol rm.

shunting inhibition

A form of synaptic inhibition in which the main effect is to reduce membrane resistance, thereby shunting depolarization current generated at excitatory synapses.

modulation

A term used to describe the actions of neurotransmitters that do no directly evoke postsynaptic potentials but modify the cellular response to excitatory postsynaptic potentials and inhibitory postsynaptic potentials generated by other synapses.

norepinephrine (NE)

A catecholamine neurotransmitter synthesized from dopamine; also called noradrenaline.

adenylyl cyclase

An enzyme that catalyzes the conversion of adenosine triphosphate to cyclic adenosine monophosphate (cAMP), a second messenger.

cyclic adenosine monophosphate (cAMP)

A second messenger formed from adenosine triphosphate by the action of the enzyme adenylyl cyclase.

protein kinase

A class of enzyme that phosphorylates proteins, a reaction that changes the conformation of the protein and its biological activity.

phosphorylation

A biochemical reaction in which a phosphate group is transferred from adenosine triphosphate to another molecule. Phosphorylation of proteins by protein kinases changes their biological activity.

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