30 Questions
Which type of cells are connected by gap junctions to form syncytial tissues?
Epithelial cells
Where are electrical synapses common?
In invertebrates
What is the function of electrical synapses?
To increase/decrease smooth muscle contraction
What is the molecular-weight cutoff for gap junctions?
~1000 Da
What happens when cell Ca++ levels decrease?
Gap junctions close
Which type of cells release enzymes into the gut?
Epithelial cells
What is the purpose of synapses?
To alter the activity of postsynaptic neurons
Which type of synapse involves the opening of postsynaptic ion channels?
Chemical synapses
Which of the following can result from transmitter binding to postsynaptic receptors?
All of the above
Which neurotransmitter is inhibitory at the heart?
Acetylcholine
Which neurotransmitter is derived from tyrosine and acts as a circulating hormone?
Epinephrine
Which neurotransmitter is the major inhibitory transmitter in the spinal cord?
GABA
Which mechanism decreases the concentration of transmitter-receptor complexes in the synaptic cleft?
All of the above
Which toxin permanently poisons synapses by preventing vesicle release of acetylcholine from motor neurons?
Botulinum toxin
Which type of synapse is the most common in the nervous system?
Neuron-neuron
What is the minimum amount of transmitter released in a vesicle?
One quantum of transmitter
What process is responsible for the uptake of molecules into a cell?
Endocytosis
What controls synaptic release at the presynaptic terminal?
Opening of voltage-dependent Ca++ channels
What is the critical dependence for synaptic release?
Extracellular [Ca++]
What causes a decrease in synaptic release?
Hypocalcemia
What is the main factor contributing to the synaptic delay in chemical synapses?
Time required for Ca++ to signal start of exocytosis
Which toxin is almost as lethal as botulinum and permanently poisons GABA neurons by preventing vesicle release?
Tetanus toxin
Which spider venom causes uncontrolled dumping of synaptic vesicles and depletion of synaptic vesicles?
Black-widow spider venom
Which substance blocks the uptake of choline into presynaptic nerve terminals of cholinergic neurons?
Hemicholinium
Which type of paralytic poison paralyzes by binding to nicotinic ACh receptors, preventing EPP?
Succinylcholine
Which substance blocks muscarinic-type ACh receptors, affecting the heart, glands, and iris of the eye?
Atropine
Which depolarizing paralytic binds to nicotinic ACh receptors and produces sustained and large amplitude EPPs?
Succinylcholine
Which class of drugs inhibits acetylcholinesterase at cholinergic synapses, preventing hydrolysis of ACh?
Cholinesterase inhibitors
Which drug is used clinically for the treatment of myasthenia gravis?
Cholinesterase inhibitors
Which substance is used as an antidote for poisoning by cholinesterase inhibitors?
Atropine
Study Notes
Cell Connections and Syncytial Tissues
- Muscle cells and nerve cells are connected by gap junctions to form syncytial tissues.
- Electrical synapses are common in neural networks, such as the cerebral cortex and the retina.
Function of Electrical Synapses
- The function of electrical synapses is to allow rapid transmission of electrical signals between cells.
Gap Junctions
- Gap junctions have a molecular-weight cutoff of approximately 1 kDa, allowing small molecules to pass through.
- When cell Ca++ levels decrease, gap junctions close, preventing the passage of molecules.
Cellular Functions
- Exocrine cells release enzymes into the gut to aid in digestion.
Synaptic Functions
- The purpose of synapses is to allow communication between cells through the transmission of signals.
- Ionotropic synapses involve the opening of postsynaptic ion channels, allowing ions to flow into the postsynaptic cell.
- Transmitter binding to postsynaptic receptors can result in depolarization, hyperpolarization, or modification of the postsynaptic cell.
Neurotransmitters
- Acetylcholine (ACh) is an inhibitory neurotransmitter at the heart.
- Epinephrine (adrenaline) is derived from tyrosine and acts as a circulating hormone.
- Glycine is the major inhibitory transmitter in the spinal cord.
Synaptic Transmission
- The process of synaptic transmission involves the release of neurotransmitters from the presynaptic terminal, binding to postsynaptic receptors, and the subsequent response of the postsynaptic cell.
- The mechanism of synaptic transmission is controlled by the concentration of transmitter-receptor complexes in the synaptic cleft, which can be decreased through the process of diffusional dissociation.
Toxins and Synapses
- α-Latrotoxin permanently poisons synapses by preventing vesicle release of acetylcholine from motor neurons.
- Botulinum toxin is a potent inhibitor of synaptic release, causing paralysis by blocking vesicle release.
- Tetrodotoxin (TTX) is a potent inhibitor of voltage-gated sodium channels, blocking action potential propagation.
- Black widow spider venom causes uncontrolled dumping of synaptic vesicles and depletion of synaptic vesicles.
- Hemicholinium-3 blocks the uptake of choline into presynaptic nerve terminals of cholinergic neurons, reducing ACh synthesis.
- α-Bungarotoxin paralyzes by binding to nicotinic ACh receptors, preventing end-plate potentials (EPPs).
- Atropine blocks muscarinic-type ACh receptors, affecting the heart, glands, and iris of the eye.
- Succinylcholine is a depolarizing paralytic that binds to nicotinic ACh receptors, producing sustained and large amplitude EPPs.
- Anticholinesterase drugs, such as neostigmine, inhibit acetylcholinesterase at cholinergic synapses, preventing hydrolysis of ACh.
- Pyridostigmine is used clinically for the treatment of myasthenia gravis.
- Pralidoxime is used as an antidote for poisoning by cholinesterase inhibitors.
Test your knowledge on the mechanisms of synaptic transmission with this quiz. Learn about excitatory and inhibitory neurotransmitters, the role of ion channels, and the analogy of a door to understand the process.
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