VF: Week 4 Propagation of electrical impulses and synapses

What are the two main types of synapses?

Electrical and chemical synapses.

What is the function of an electrical synapse?

It allows direct communication between cells via gap junctions.

What is the function of a chemical synapse?

It uses neurotransmitters to relay signals between neurons.

Where are electrical synapses commonly found?

In the heart and smooth muscle of the intestine.

What is the role of connexons in electrical synapses?

They form channels that allow ions to pass directly between cells.

What is the main neurotransmitter used at neuromuscular junctions?

Acetylcholine (ACh).

What triggers neurotransmitter release in chemical synapses?

The influx of calcium ions (Ca²⁺).

What is the effect of myelination on impulse conduction?

It increases conduction speed by allowing saltatory conduction.

What is saltatory conduction?

The jumping of action potentials between nodes of Ranvier.

What is continuous conduction?

The slow propagation of action potentials along unmyelinated axons.

What ion is responsible for depolarization during an action potential?

Sodium (Na⁺).

What ion is responsible for repolarization?

Potassium (K⁺).

What prevents an action potential from traveling backward?

The refractory period.

What is the role of voltage-gated Na⁺ channels?

They initiate and propagate action potentials.

What is the effect of a larger nerve fiber diameter on conduction speed?

It increases conduction speed.

What type of conduction occurs in unmyelinated axons?

Continuous conduction.

What disease is associated with demyelination in the central nervous system?

Multiple sclerosis.

What disease is associated with demyelination in the peripheral nervous system?

Guillain-Barré syndrome.

What are the gaps in the myelin sheath called?

Nodes of Ranvier.

What type of glial cells produce myelin in the CNS?

Oligodendrocytes.

What are the three main steps in neurotransmitter release?

Depolarization

Ca²⁺ influx

exocytosis of neurotransmitters.

What proteins are involved in neurotransmitter exocytosis?

SNARE proteins (synaptobrevin, SNAP-25, syntaxin).

What is the role of synaptobrevin in neurotransmitter release?

It helps dock vesicles to the presynaptic membrane

What is the role of SNAP-25?

It facilitates vesicle fusion and neurotransmitter release.

How do neurotransmitters cross the synaptic cleft?

By diffusion.

How do neurotransmitters exert their effects?

By binding to receptors on the postsynaptic membrane

What happens to neurotransmitters after they are released?

They are degraded, reabsorbed, or diffuse away

What enzyme breaks down acetylcholine?

Acetylcholinesterase (AChE).

What is the effect of acetylcholinesterase inhibition?

Increased acetylcholine concentration in the synaptic cleft.

What is an example of a drug that inhibits acetylcholinesterase?

Organophosphates.

What is an EPSP?

An excitatory postsynaptic potential.

What ion influx causes an EPSP?

Sodium (Na⁺).

What is an IPSP?

An inhibitory postsynaptic potential.

What ions are involved in IPSPs?

Potassium (K⁺) and chloride (Cl⁻).

What is spatial summation?

When multiple synapses fire at the same time.

What is temporal summation?

When one synapse fires repeatedly in a short time.

What neurotransmitter is primarily inhibitory in the brain?

GABA.

What neurotransmitter is primarily excitatory in the brain?

Glutamate.

What neurotransmitter is involved in pain perception?

Substance P.

What neurotransmitter is associated with mood regulation?

Serotonin.

What does botulinum toxin do at the synapse?

It blocks acetylcholine release, causing paralysis.

What does tetanus toxin do at the synapse?

It blocks inhibitory neurotransmitter release, causing spastic paralysis.

What neurotransmitter is affected by Parkinson’s disease?

Dopamine.

What is an example of a GABA receptor agonist?

Benzodiazepines.

What is an example of a drug that blocks glutamate receptors?

Ketamine.

What is the effect of norepinephrine reuptake inhibitors?

Increased norepinephrine concentration in the synaptic cleft.

What enzyme degrades norepinephrine?

Monoamine oxidase (MAO).

What is an example of an MAO inhibitor?

Selegiline.

What happens if α2-adrenoceptors are activated?

Norepinephrine release decreases.

What neurotransmitter is synthesized from tyrosine?

Norepinephrine.

What is the general concept of continuous conduction?

Think of action potential as a one way street only moving forward along a nerve axon or muscle fibers.

How does continuous conduction occur?

The impulse in one area causes local currents to flow, depolarizing the adjacent area to the threshold and generating a new action potential. Conduction requires more energy.

Why is continuous condition unidirectional?

The conduction is unidirectional because the upstream region is in its refractory period.

What is the effect of the nerve fiber diameter of continuous conduction?

The speed of action potential conduction is faster in larger diameter fibers because they have lower electrical resistance than small diameter fibers.

What is myelin in saltatory conduction?

Myelin consists of a glial cell plasma membrane concentrically wrapped around the nerve, creating tight insulation.

What is an interupted insulation in saltatory conduction?

In the peripheral nerves, the myelin sheath is strategically interrupted at regular intervals by in covered Nodes of Ranvier.

Why is it saltatory?

AP are rapidly propagated from node to node by saltatory conduction because voltage-gated Na channels are only expressed at the nodes of Ranvier.

What type of electrical impulse conduction is faster?

Saltatory conduction in the myelinated axon.

What are electrical synapses?

The type of communication between cells through gap junctional pores allowing bidirectional flow of current between them without the release of neurotransmitters into a synaptic cleft.

Where are electrical synapses located?

Found in specific structures of the body

Heart: coordinated contractions of the cardiac muscles.

Smooth Muscle: facilitate the rhythmic contractions that move food along the digestive tract.

What are the mechanisms of Electrical synapses?

Connexons

What are Connexons?

Ion channels that are triggered by depolarization of the cell membrane allowing ionic flow to the neighboring cell.

What are the seven steps of chemical synapses

1. AP depolarize the presynaptic membrane

2. OPens Ca channels

3. Ca dependent exocytosis. (fusing of vesicles with the membrane to release neurotransmitter)

4. Diffusion

5. Released neurotransmitter binds to its postsynaptic receptor

6. Postsynaptic Na channels open

   1. Neurotransmitter is removed form the synaptic cleft, and the channels close

What type of condition does tetanus cause?

Spastic paralysis

What is spastic paralysis?

A lack of inhibitory neurotransmitter release in the spinal cord leading to overstimulation of the muscles

What neurotransmitter does tetanus inhibit?

Glycine

How does the neurotransmitter action terminate?

NTs are taken into the cell

NTs are broken down

NTs diffuse away from synapses

What are the type types of postynaptic potentials?

Excitatory postsynaptic potential

Inhibitory postsynaptic potential

What does EPSP do?

Na currents depolarize the membrane

What does IPSP do?

K or Cl currents hyper polarize the membrane

What ion influx causes an inhibitory postsynaptic potential?

Chloride

What are the two groups of neurotransmitters?

Small Molecule

Neuropeptides

What are the three ways that a neurotransmitter exert their cellular actions?

Ionotropic

Metabotropic

Both

How does Ionotropic action work?

Neurotransmitters can either open or block ion channels causing changes in the membrane potential

How does Metabotropic action work?

Other neurotransmitters act like hormones produced and released to the bloodstream by endocrine cells.

Act like G-proteins coupled receptors and modify the membrane potential

What are the 4 different types of Small Molecule Neurotransmitters?

Acetylcholine

Amino Acids

Biogenic Amines

Gases

Where does Acetylcholine bind?

The CNS and PNS

Where does Amino Acids consist of?

CNS

Glutamate (excitatory)

Gamma-aminobutyric acid

GABA (inhibitory)

Where does Biogenic Amines consist of?

Catecholamines (dopamine, norepinephrine, epinephrine)

Serotonin

Where do the small molecule gases consist of?

Nitric oxide

What are the three types of Neuropeptides?

Enkephalins

Endorphines and Dynorphins

Substance P

Where does Enkephalins do?

CNS

Potent Analgesic effect

Where does the Endophins and Dynorphins do?

CNS

Control of BT and reproduction

What does Substance B do?

Transmission of peripheral pain signals and it is one of the several neurotransmitter involved in emesis.

What the the two inhibitory neurotransmitter?

GABA

Glycine

What does Tyrosine synthesize into from amino acids?

Norepiephrine

Where is Norepinephrine stored?

Vesicles and degraded by MAO and intracellular CAMT

Drugs can modulate the release of norepinephrine from the presynaptic membrane. What is the consequence of the intravenous injection of a selective a2-adrenocepor agonist?

It leads to a decrease in norepinephrine concentration in the synaptic cleft

Acetylcholine is released into the synaptic cleft and attaches to what receptor

Cholinergic receptord

What breaks down ACh in the synaptic cleft into Choline and Acetate?

Acetylcholinestrase

Where does Choline go after being made by ACh?

Transported back into the presynaptic terminal for the synthesis of new ACh.

What is the consequence of the acetylcholinesterase inhibition?

Increase of Acetylcholine concentration in the synaptic cleft

What Neurotransmitter attaches to the postsynaptic receptors?

Glutamate

What neurotransmitter is transported back into the presynaptic terminal?

Glutamate

Where is glutamate repackaged in the synaptic vesticles

Presynaptic Terminal

What converts glutamate in glutamine?

Astrocytes

What is glutamine used for in neurons

Used to synthesize new glutamate

What type of neurotransmitter is glutamate in the CNS?

Excitatory

What are the consequences of blocking the postsynaptic glutamate receptor? Do you know any drugs that works on glutamate receptors? Does the CNS outflow increase or decreases considering the glutamate is an excitatory neurotransmitter?

Ketamine

The outflow decreases

What neurotransmitter is made from glutamate by glutamate decarboxylase>

GABA