3020 Lecture 9
Amber Stokes・46 minutes read
Action potentials move efficiently down axons in one direction, influenced by axon diameter and myelination for faster signal transmission. Neurotoxins like TTX block sodium channels, leading to paralysis, with snakes developing resistance through genetic changes in sodium channel genes due to exposure to TTX-producing prey.
Insights
- The movement of action potentials in neurons is unidirectional, akin to traffic flow on a highway, ensuring efficiency and preventing confusion.
- Neurotoxins like Tetrodotoxin (TTX) block voltage-gated sodium channels, causing paralysis by halting action potentials, with resistance in snakes evolving through genetic changes in sodium channel genes due to exposure to TTX-producing prey like newts.
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Recent questions
How do action potentials move in neurons?
Action potentials move in one direction from the cell body to axon terminals for efficiency. The axon acts like a highway with traffic moving in one direction to avoid confusion and inefficiency. Sodium drifting down the axon triggers action potentials, ensuring movement in one direction. Inactivation gate closure and hyperpolarization prevent action potentials from moving in the wrong direction. Propagation speed is influenced by the axon diameter, with larger diameters leading to faster velocities. Myelination insulates axons, allowing for faster signal transmission by skipping segments.
What factors influence the speed of signal transmission in neurons?
The speed of signal transmission in neurons is influenced by the axon diameter and myelination. Larger axon diameters and myelination significantly affect propagation speed, leading to faster velocities. The relationship between axon diameter and myelination plays a crucial role in determining the speed of signal transmission in neurons.
How do neurotoxins affect neuron function?
Neurotoxins commonly inhibit neuron function by blocking ion channels or altering synaptic communication. They can affect ion control or synaptic communication, leading to disruptions in normal neuronal activity. Neurotoxins like Novocaine and Botox are used in medicine as anesthetics to temporarily disable neurons and prevent pain sensation.
What is the role of Tetrodotoxin (TTX) in paralysis?
Tetrodotoxin (TTX) is a neurotoxin found in various organisms like pufferfish, snails, and octopuses. It blocks voltage-gated sodium channels in skeletal muscle and nerves, leading to paralysis. TTX does not affect sodium channels in the heart or brain, focusing on causing skeletal muscle paralysis. The paralysis induced by TTX can be dangerous, particularly affecting the diaphragm muscle and potentially leading to asphyxiation.
How do garter snakes develop resistance to Tetrodotoxin (TTX)?
Garter snakes develop resistance to Tetrodotoxin (TTX) through genetic changes in the sodium channel genes, specifically in the amino acid sequence of the pore region where TTX binds. The more amino acid changes in the sodium channel genes, the higher the resistance to TTX, indicating a genetic basis for resistance. Resistance to TTX in snakes evolved through convergent evolution, with populations developing resistance independently based on exposure to TTX-producing prey like newts. This illustrates the dynamic interplay in natural toxin interactions between predators and prey.
Related videos
Summary
00:00
"Action Potential: Axon Efficiency and Speed"
- Action potential process involves steps down to the movement of ions, membrane potential, and open/closed channels.
- Hyperpolarization period is crucial due to the inactivation gate for voltage-gated sodium channels.
- Action potentials move in one direction from cell body to axon terminals for efficiency.
- Axon acts like a highway with traffic moving in one direction to avoid confusion and inefficiency.
- Action potentials move down the axon in a wave-like fashion, with segments being stimulated.
- Sodium drifting down the axon triggers action potentials, ensuring movement in one direction.
- Inactivation gate closure and hyperpolarization prevent action potentials from moving in the wrong direction.
- Propagation speed is influenced by the axon diameter, with larger diameters leading to faster velocities.
- Myelination insulates axons, allowing for faster signal transmission by skipping segments.
- Myelination and axon diameter affect propagation speed significantly, with larger diameters and myelination leading to faster velocities.
23:05
Neurotoxins: Impact on Neuron Function
- The relationship between axon diameter and myelination affects signal speed
- Action potential frequency determines signal strength
- Closer action potentials result in stronger signals
- Synapses are how neurons communicate
- Electrical synapses are fast but less common, using gap junctions for direct transmission
- Chemical synapses are slower but more common, using neurotransmitters in the synaptic cleft
- Steps of chemical synapse transmission: action potential arrival, vesicle movement, calcium influx, neurotransmitter release, binding to receptors, sodium or chloride entry
- Excitatory post-synaptic potential (EPSP) results from sodium entry, while inhibitory post-synaptic potential (IPSP) results from chloride entry
- Neurotoxins inhibit neuron function by affecting ion control or synaptic communication
- Neurotoxins often inhibit neuron function by blocking ion channels or altering synaptic communication.
51:36
Neurotoxins in Medicine: Anesthetic and Paralyzing
- Neurotoxins are commonly used in medicine as anesthetics to temporarily disable neurons and prevent the feeling of pain.
- Novocaine and Botox are examples of neurotoxins used for their anesthetic properties.
- Botox is injected into the forehead to relax muscles and reduce wrinkles cosmetically.
- It is crucial to choose a skilled professional for Botox injections to avoid potential risks and complications.
- Tetrodotoxin (TTX) is a neurotoxin found in various organisms, including pufferfish, snails, octopuses, and amphibians.
- TTX blocks voltage-gated sodium channels in skeletal muscle and nerves, leading to paralysis.
- TTX does not affect sodium channels in the heart or brain, focusing on skeletal muscle paralysis.
- Paralysis caused by TTX can be dangerous, particularly affecting the diaphragm muscle and leading to asphyxiation.
- TTX binds to voltage-gated sodium channels, preventing sodium entry and halting action potentials.
- Garter snakes are resistant, not immune, to TTX, with studies dating back to the late 80s measuring their resistance through speed tests after TTX injections.
01:12:37
Evolution of Snake Resistance to TTX
- To measure the impact of TTX on snake speed, a dosage is injected, and after 30 minutes, the post-injection speed is recorded and divided by the baseline speed to calculate resistance.
- Resistance to TTX in snakes is determined by genetic changes in the sodium channel genes, specifically in the amino acid sequence of the pore region where TTX binds.
- The more amino acid changes in the sodium channel genes, the higher the resistance to TTX, indicating a genetic basis for resistance.
- Resistance to TTX in snakes evolved through convergent evolution, with populations developing resistance independently based on exposure to TTX-producing prey like newts.
- An arms race exists between newts producing TTX and garter snakes developing resistance, with increasing TTX levels in newts pressuring snakes to enhance resistance, and vice versa, illustrating the dynamic interplay in natural toxin interactions.
