The Synapse

Sarin/VX

Commonly use organophosphates, which inhibit acetylcholinesterase and allow acetylcholine to build up in the synaptic terminal.

Atropine

Competitive antagonist to acetylcholine, which means it competes with its binding without actually activating the receptor itself.

Pre-synaptic Terminal

Contains much of the specialized molecular machinery needed for the synapse to work.

Postsynaptic function

Contains two types of receptors: metabotropic and ionotropic.Postsynaptic activity can vary hugely.

chemical synapses

Electrical signals arrive at the nerve terminal, carried from the cell body down the axon.This signal gets translated into chemical signals causing the release of neurotransmitters into the synapse. Post synaptic receptors are activated via binding of neurotransmitters.

Bungarotoxin

From snakes blocks AChRs.

Polarized Cells

Have one portion of the cell specialized for receiving inputs and another portion specialized for sending outputs.

Electron microscopes

Have wavelengths that are a hundred thousand times shorter than that of visible light, and thus allow the visualization of much smaller structures. Modern electron microscopes can resolve objects that are hundreds of picometers, while the best that a light microscope can do is several hundred nanometers.

Ionotropic Receptor

Ligand gated ion channels that open to let in ions and depolarize the neuron when a ligand, such as a neurotransmitter, binds.

Omega Bodies

Named for the shape formed by vesicles that have fused with the membrane of the pre-synaptic terminal and released its chemical payload into the synaptic cleft.

Model system

Neuromuscular junction is where the ending of a nerve attaches to a muscle fiber to actually carry out motor commands from the brain. It is one of the best studied synapses, but actually is not very representative of neural synapses.

Postsynaptic Neuron

Neuron that receives the signal.

Presynaptic function

Neurotransmitter release

SNARE Hypothesis

Provides the molecular link between calcium sensitivity and vesicle release.

Chemical Synapse

Rather than simply passing along an electrical signal from one cell to another, the action potential travels to the end of axon and causes a chemical, known as a neurotransmitter, to be released into a very small space between the two neurons called the "synaptic cleft". Such a chemical step is slower than transmission across an electrical synapse, but it opens up an enormously diverse repertoire of different and more complex kinds of signaling.

Target SNARES/t- SNARES

SNARE proteins on the membrane. SNAP-25 and Syntaxin are the main t-SNARES.

Electrical Signaling

Simplest way to pass a signal from one neuron to the next, here two neurons simply connect together and rely on the electrical properties of the conjoined cells to carry the signal from cell to cell.

Vesicles

Small hollow spheres located in the presynaptic terminal that are made out of the same stuff as the cell membrane, whose job is hold a small quantity of signalling molecules.

Metabotropic Receptor

Stimulate a secondary molecular cascade downstream the signaling pathway. In some cases altering gene expression within the cell.

Dendrites

The parts of the cell that are specialized for receiving inputs from other cells. The word "dendrite" comes from the Greek word "dendron", meaning tree, and as you can see the dendrites have a branching, tree-like shape.

Neuromuscular Junction/NMJ

The place where a nerve attaches to a muscle. The NMJ has many features that are very similar to the junctions in the central nervous system, with the added benefit that a muscle fiber is a lot easier to record from using simple electrodes than a downstream nerve.

Synaptic Cleft

The space between the presynaptic and postsynaptic neuron. It is usually only 20-40 nanometers in distance and is tightly regulated space whose geometry is governed by a complex infrastructure of adhesion molecules.

Tetanus toxin/Clostridium tetani

Very similar in structure to botulinum toxin, but selectively interferes with release of neurotransmitters in inhibitory neurons. It has spores everywhere, which is why tetanus shots are necessary after stepping on a rusty nail.

v-SNARES

Vesicle-associated SNARE proteins. Synaptobrevin is the main v-SNARE

Calcium (Ca++)

Voltage gated calcium entry couples the electrical signal to actual secretion of the vesicles.

Bernard Katz

Was a electrophysiologist & biochemist who conducted some deceptively simple experiments in the 1950's where he investigated the mechanism of release of neurotransmitters from vesicles that were fundamental to our understanding of signal transduction.

Quantal hypothesis

When you stimulate a motor neuron's axon and measure the potential inside the downstream motor fiber, you get two confounding interactions -- one is the action potential generated from the stimulation itself, and the other is the actual stimulation generated just by the chemicals binding to the postsynaptic terminal.

Presynaptic Neuron

Where the action potential enters from.

Botulinum toxin

Works on the SNARE complex to inhibit release of acetylcholine, an excitatory neurotransmitter that causes muscle contraction. It is the main ingredient in Botox injections-- used to paralyze muscles and reduce wrinkles.

Neostigmine

blocks acetylcholinesterase, the enzyme which breaks down acetylcholine. Thus it allows a given dose of acetylcholine to have a stronger effect.

Neuron doctrine

nervous system is composed of discrete cells, each with its own specific electrical activity.

Reticular theory

neurons are connected in a way such that it is one giant, continuous network.

Receptor

A molecular machine whose job is to bind to a very specific molecule, or class of molecules, and as a result effect some change in the post-synaptic neuron when they bind their signaling molecule of interest. There are many different kinds of receptors, which can exert different kinds of influences on the downstream cell.

Electrical Synapse

A physical pore that allows ions to flow through, creating an intercellular current from the upstream neuron to the downstream neuron. The depolarization in the downstream neuron caused by this current, if it reaches threshold, can then cause a propagation of the action potential down the downstream neuron. The main advantage of this system is that it is very fast. For this reason, it is often used in reflex circuits such as escape reflexes that require very fast conduction in a multi-neuron circuit. Another feature that being physically connected allows is bidirectional signaling.

Otto Loewi

A physiologist in the 1920's noticed that he could extract a substance from a nerve near the heart of a frog, squirt that substance on a different beating heart and cause that heart to slow down. This was a landmark discovery proving the existence of neurotransmitters.

Neural communication

A signal received by a dendrite is passed to the cell body. If there's a sufficient depolarization of the cell body membrane to initiate an action potential, then an action potential is sent down the axon. The axon then carries the propagating action potential to another neuron, where its dendrite is waiting to receive the signal.

Gap junctions

Allow direct ion flow. Small connections maintaining cytosol continuity so depolarization affects neighboring cell -- not the same as a syncytial synapse where the cytoplasm is fused.

Bidirectional

Allowing for synchronization of many cells, such as heart muscle.

SNARE proteins

Are synapse associated proteins that are highly conserved in structure and function across many vastly different organisms, suggestive of its evolutionary importance. Interactions between SNARE proteins on the vesicle and on the presynaptic membrane, modulated by calcium, lead to vesicle fusion.

Curare

Blocks acetylcholine receptors and prevents acetylcholine from activating postsynaptic receptors.

Synapse

Boundary between two neurons, between the axon of an "upstream" neuron and the dendrite of the "downstream" neuron.

SNAREs

Calcium modulates the interactions between the SNARE proteins on the vesicle and presynaptic membrane. This vesicle fusion is what releases the neurotransmitters into the synaptic cleft.