Week 4 ELM 9: Synapses

Flashcards covering terminology, function, and components of electrical and chemical synapses, neurotransmitter release, and vesicle recycling. Includes information about toxins affecting synaptic transmission.

Aim of Synapse

Transmit signal from one neuron to another

Electrical Synapses

Electrical: Gap junction, direct transfer of ions, non-rectifying, fast transmission, signal often attenuated, made of 2 connexons, each connexon equals 6 connexins

Synaptic Delay

Time taken for signal to cross synapse

Vagusstoff (vagus substance)

Otto Loewi's discovery in 1921

SNARE Proteins

Synaptobrevin, SNAP-25, and syntaxin

Synaptotagmin

Vesicle protein that senses calcium

Steps of Synaptic Transmission

Neurotransmitters are synthesized and stored in vesicles; action potential arrives at the presynaptic terminal; voltage-gated Ca2+ channels open, allowing influx of Ca2+; Ca2+ allows vesicle fusion and neurotransmitter release; neurotransmitter binds to receptors, causing channels to open (or close); excitatory (or inhibitory) postsynaptic potential is generated; neurotransmitter is removed by glial uptake (or enzymatic degradation); vesicular membrane is retrieved from the plasma membrane.

1 Quantum

Amount of transmitter per vesicle

Miniature postsynaptic potentials (“mini’s”)

Occur spontaneously, even in zero extracellular Ca2+; have amplitudes that are multiples of a quantal unit; are due to release of one or a few quanta (= vesicles).

‘Quantal Content’

No of quanta released for one AP

Vesicle Cycle Stages

docking, mobilization, storage, priming calcium sensing, loading, sorting, translocation, endocytosis, fusion

Clathrin and Vesicle Recycling

Clathrin and vesicle recycling involves a coated pit, clathrin, clathrin coat, constant vesicle size, constant number of vesicles, and constant size of terminal.

ω-agatoxin IVA

Blocks P/Q-type voltage-gated calcium channels

Botulinum Toxin (Botox)

Proteolytic enzyme that cleaves SNARE proteins, stopping neurotransmitter release

ω-conotoxin MVIIC

Blocks N-type voltage-gated calcium channels

α-bungarotoxin

Blocks nicotinic acetylcholine receptors

Physostigmine (Eserine)

Acetylcholinesterase inhibitor found in the Calabar bean

Post synaptic potential

A change in the membrane potential of the postsynaptic neuron, resulting from neurotransmitter binding to receptors.

Presynaptic neuron

The neuron that releases neurotransmitters into the synaptic cleft to communicate with the postsynaptic neuron.

Postsynaptic neuron

The neuron that receives neurotransmitters from the presynaptic neuron and undergoes a change in membrane potential.

Synaptic cleft

The small gap between the presynaptic and postsynaptic neurons, where neurotransmission occurs.

One way transmission

Rectifying

Two way transmission

Non-rectifying

Chemical synapses

Synaptic delay (time taken for signal cross synapse) = .5-2 ms.

Action potential, vesicle containing neurotransmitter, uptake system for NT or breakdown products, enzyme, postsynaptic receptor (ligand gated channel)

Vesicular release: the SNARE proteins

Snare proteins are synaptobrevin, SNAP-25, syntaxin

They bind to each other, drawing the vesicle close to the membrane

When intracellular calcium concentrations rise, the vesicle fuses with the membrane and the contents (ACh) are released into the synapse

Calcium is sensed by a vesicle protein called synaptomagmin