Week 6

Action potential

is propagated over the presynaptic membrane.

Depolarization

of the presynaptic terminal leads to influx of Ca²⁺.

Ca²⁺

promotes exocytosis, the fusion of vesicles with the presynaptic membrane, which releases transmitter into the cleft.

The binding of transmitter to receptor molecules

in the postsynaptic membrane opens channels, permitting ion flow and initiating an excitatory or inhibitory postsynaptic potential.

Excitatory or inhibitory postsynaptic potentials

spread passively over dendrites and the cell body to the axon hillock.

Enzyme present in the extracellular space

breaks down excess transmitter.

Reuptake of transmitter

slows synaptic action and recycles transmitter for subsequent transmission.

Transmitter binds to auto receptors

in the presynaptic membrane informing the presynaptic cell about transmitter levels.

synaptic vesicle

A small, spherical structure that contains molecules of neurotransmitter.

synaptic cleft

The space between the presynaptic and postsynaptic cells at a synapse. This gap measures about 20–40 nanometers.

calcium ion (Ca²⁺)

A calcium atom that carries a double positive charge.

synaptic delay

The brief delay between the arrival of an action potential at the axon terminal and the creation of a postsynaptic potential.

ligand

A substance that binds to receptor molecules, such as a neurotransmitter or drug that binds to postsynaptic receptors.

acetylcholine (ACh)

A neurotransmitter that is produced and released by parasympathetic postganglionic neurons, by motor neurons, and by many neurons in the brain.

neurotransmitter receptor

Also called simply receptor. A specialized protein, embedded in the cell membrane, that selectively senses and reacts to molecules of a corresponding neurotransmitter.

curare

A neurotoxin that causes paralysis by blocking acetylcholine receptors in muscle.

bungarotoxin

A neurotoxin, isolated from the venom of the many-banded krait, that selectively blocks acetylcholine receptors.

agonist

A substance that mimics or boosts the actions of a transmitter or other signaling molecule.

antagonist

A substance that blocks or reduces the actions of a transmitter or other signaling molecule.

cholinergic

Referring to cells that use acetylcholine as their synaptic transmitter.

degradation

The chemical breakdown of a neurotransmitter into inactive metabolites.

acetylcholinesterase (AChE)

An enzyme that inactivates the transmitter acetylcholine.

reuptake

The process by which released synaptic transmitter molecules are taken up and reused by the presynaptic neuron, thus stopping synaptic activity.

transporter

A specialized membrane component that returns transmitter molecules to the presynaptic neuron for reuse.

axo-dendritic synapse

A synapse at which a presynaptic axon terminal synapses onto a dendrite of the postsynaptic neuron, either via a dendritic spine or directly onto the dendrite itself.

axo-somatic synapse

A synapse at which a presynaptic axon terminal synapses onto the cell body (soma) of the postsynaptic neuron.

axo-axonic synapse

A synapse at which a presynaptic axon terminal synapses onto the axon terminal of another neuron.

dendro-dendritic synapse

A synapse at which a synaptic connection forms between the dendrites of two neurons.

knee-jerk reflex

A variant of the stretch reflex in which stretching of the tendon beneath the knee leads to an upward kick of the leg.

Exogenous

arising from outside the body

Endogenous

produced inside the body

presynaptic

Located on the “transmitting” side of a synapse.

synapse

The cellular location at which information is transmitted from a neuron to another cell.

neurotransmitter

Also called simply transmitter. A signaling chemical, released by a presynaptic neuron, that diffuses across the synaptic cleft to alter the functioning of the postsynaptic neuron.

neurotransmitter receptor

Also called simply receptor. A specialized protein that is embedded in the cell membrane, allowing it to selectively sense and react to molecules of the corresponding neurotransmitter.

postsynaptic

Located on the “receiving” side of a synapse.

reuptake

The reabsorption of molecules of neurotransmitter by the neurons that released them, thereby ending the signaling activity of the transmitter molecules.

transporter

A specialized membrane component that returns transmitter molecules to the presynaptic neuron for reuse.

ionotropic receptor

Also called ligand-gated ion channel. A receptor protein containing an ion channel that opens when the receptor is bound by an agonist.

excitatory synapse

A type of synapse that, when active, causes a local depolarization that increases the likelihood the neuron will fire an action potential.

inhibitory synapse

A type of synapse that, when active, causes a local hyperpolarization that decreases the likelihood the neuron will fire an action potential.

metabotropic receptor

A receptor protein that does not contain ion channels but may, when activated, use a second-messenger system to open nearby ion channels or to produce other cellular effects.

receptor subtype

Any type of receptor having functional characteristics that distinguish it from other types of receptors for the same neurotransmitter.

G protein-coupled receptor (GPCR)

A type of receptor that, when activated extracellularly, initiates a G protein signaling mechanism inside the cell.

Acetylcholine (Ach)

a neurotransmitter that is produced and released by the autonomic nervous system, by motor neurons, and by neurons throughout the brain

amino acid neurotransmitter

A neurotransmitter that is itself an amino acid. Examples include GABA, glycine, and glutamate.

peptide neurotransmitter

Also called neuropeptide. A neurotransmitter consisting of a short chain of amino acids.

amine neurotransmitter

A neurotransmitter based on modifications of a single amino acid nucleus. Examples include acetylcholine, serotonin, and dopamine.

gas neurotransmitter

A neurotransmitter that is a soluble gas. Examples include nitric oxide and carbon monoxide.

glutamate

An amino acid transmitter, the most common excitatory transmitter.

gamma-aminobutyric acid (GABA)

A widely distributed amino acid transmitter, the main inhibitory transmitter in the mammalian nervous system.

Co-localization

the synthesis and release of more than one type of neurotransmitter by a given presynaptic neuron

cholinergic

Referring to cells that use acetylcholine as their synaptic transmitter.

basal forebrain

A region, ventral to the basal ganglia, that is the major source of cholinergic projections in the brain.

dopamine (DA)

A monoamine transmitter found in the midbrain—especially the substantia nigra—and in the basal forebrain.

dopaminergic

Referring to cells that use dopamine as their synaptic transmitter.

substantia nigra

A brainstem structure that innervates the basal ganglia and is a major source of dopaminergic projections.

ventral tegmental area (VTA)

A portion of the midbrain that projects dopaminergic fibers to the nucleus accumbens.

serotonergic

Referring to cells that use serotonin as their synaptic transmitter.

raphe nuclei

A string of nuclei in the midline of the midbrain and brainstem that contain most of the serotonergic neurons of the brain.

serotonin (5-HT)

A synaptic transmitter that is produced in the raphe nuclei and is active in structures throughout the cerebral hemispheres.

noradrenergic

Referring to cells using norepinephrine (noradrenaline) as a transmitter.

norepinephrine (NE)

Also called noradrenaline. A neurotransmitter produced and released by sympathetic postganglionic neurons to accelerate organ activity.

locus coeruleus

A small nucleus in the brainstem whose neurons produce norepinephrine and modulate large areas of the forebrain.

lateral tegmental area

A brainstem region that provides some of the norepinephrine-containing projections of the brain.

opioid peptide

A type of endogenous peptide that mimics the effects of morphine in binding to opioid receptors and producing marked analgesia and reward.

Retrograde transmitter

a neurotransmitter that diffuses from the postsynaptic neuron back to the presynaptic neuron