L10: Earthworm Action Potential Experiment Flashcards
What influences the median fibre threshold value in the practical experiment?
Experimental factors such as pin placement and variability in biological preparations.
Why is Earthworm Ringer Solution used instead of water?
To match the osmolarity and ion concentration of the earthworm’s internal environment, preventing water movement that could damage cells.
What happens if the Earthworm Ringer solution contains too much liquid?
It could conduct current, causing electrical interference and reducing the accuracy of measurements.
Why is the median fibre’s threshold lower than the lateral fibre’s?
The median fibre has a larger diameter, which reduces the threshold for action potential initiation.
Why does the median fibre’s action potential arrive before the lateral fibre’s?
The median fibre has a higher conduction velocity due to its larger diameter.
What is the “all-or-none” principle of action potentials?
An action potential is either triggered completely when the threshold is reached, or not at all.
How does stimulus duration affect the threshold value for action potentials?
Increasing the stimulus duration reduces the amplitude required to reach the threshold.
What determines conduction velocity in neurons?
Axon diameter, temperature, and presence of myelin.
How does mammalian conduction velocity compare to earthworms’?
Mammals generally have higher conduction velocities due to myelination and warmer body temperatures.
What is the absolute refractory period caused by?
Inactivation of voltage-gated sodium channels.
What is the relative refractory period?
A period when a stronger-than-normal stimulus is required to trigger another action potential due to hyperpolarisation.
How does lidocaine affect action potentials?
It blocks voltage-gated sodium channels, preventing the propagation of action potentials.
Why is myelination critical for nerve function?
Myelination increases conduction velocity without requiring larger axons, saving space.
What adaptation compensates for the lack of significant myelination in earthworms?
Earthworms rely on larger axon diameters to achieve faster conduction.
What practical adjustments could influence earthworm conduction velocity?
Changing the environmental temperature.
Why is biological and experimental variability important in research?
It highlights the need for statistical analysis to identify real patterns and minimize the impact of variability.
What happens if the ion concentrations in the Ringer solution are incorrect?
An imbalance may lead to water entering cells via osmosis, causing them to swell and potentially burst.
How do action potentials in the earthworm experiment relate to the presence of ions in the Ringer solution?
Proper ion concentrations are essential for maintaining cell membrane permeability and generating action potentials.
Why does the Ringer solution’s ionic content need to be specific to the species?
Different species have varying physiological requirements, so their Ringer solutions must match their internal environments.
Why is it important to keep the earthworm damp but not submerged during the experiment?
To avoid creating a conductive pathway for electrical current outside the worm, ensuring accurate stimulation and recording.
What is the role of stimulation electrodes in the practical?
They create an electrical stimulus to depolarize the membrane and initiate action potentials.
How does fibre diameter influence conduction velocity?
Larger diameter fibres have lower internal resistance, allowing faster conduction of action potentials.
What does the difference in timing between median and lateral fibre responses demonstrate?
It shows that larger diameter axons conduct signals faster than smaller ones.
Why don’t action potentials increase in size with greater stimulus strength?
Action potentials are governed by the all-or-none principle; their size remains constant once the threshold is reached.
How does stimulus amplitude affect reaching the threshold at different durations?
Shorter durations require higher amplitudes, while longer durations can reach the threshold with lower amplitudes.
What is the relationship between charge and stimulus duration in reaching the threshold?
The total charge required is constant, whether achieved by a high amplitude or a longer duration stimulus.
What unit conversion errors were commonly observed during the conduction velocity experiment?
Confusion between millimetres, seconds, and their respective metric conversions (e.g., metres per second).
Why is the conduction velocity of mammalian nerves higher despite smaller axons compared to earthworms?
Mammals have extensive myelination, which compensates for smaller axon diameters and increases conduction velocity.
How does temperature affect conduction velocity?
Higher temperatures increase conduction velocity, while colder temperatures slow it down.
What would happen if the earthworm’s axons were not as large?
Without large axons or myelination, the earthworm would have slower nerve conduction and less efficient neural function.
How does lidocaine demonstrate evolutionary similarities in sodium channels across species?
Its effect on earthworm and human sodium channels shows a shared evolutionary mechanism for action potential generation.
What is the functional significance of the refractory period in neurons?
It ensures unidirectional propagation of action potentials and prevents continuous firing of the neuron.
Why is accurate unit conversion critical in experiments like conduction velocity measurement?
Errors in units can lead to inaccurate data interpretation and incorrect conclusions about biological properties.
What did the experiment teach about the importance of axon diameter versus myelination?
While axon diameter influences conduction velocity, myelination is more critical for rapid signal transmission in vertebrates.
What does the earthworm experiment illustrate about neuron structure and function?
It highlights the relationship between physical and physiological properties, such as axon diameter and conduction velocity.
What is the importance of statistical analysis in group data collection?
It helps identify class means and variability to make meaningful conclusions from experimental results.
Why is it unlikely to observe ions leaving cells during the earthworm practical?
Cell membranes are only permeable to ions through specific channels, which are not always open.
How does the external Ringer solution help maintain the earthworm’s cellular integrity?
By matching internal ionic concentrations, it prevents osmotic imbalance and protects cells.
What role do stimulation thresholds play in identifying fibre responses?
Different axons have distinct stimulation thresholds due to variations in diameter and properties.
How does the lateral fibre differ in threshold from the median fibre?
The lateral fibre usually has a higher stimulation threshold due to its smaller diameter.
Why do lateral fibres sometimes show similar thresholds to median fibres?
Close placement of electrodes near the lateral fibres can mimic the threshold level of the median fibre.
What factors influence variability in experimental outcomes during practicals?
Biological differences, pin placement, and external conditions like temperature contribute to variability.
What does the presence of two peaks in the action potential graph signify?
It represents the sequential activation of the median and lateral fibres due to differences in conduction velocity.
How does the Ringer solution prevent electrical interference?
By controlling its volume, the conductive properties of the solution are minimized to avoid short-circuiting.
What happens to conduction velocity if the earthworm’s temperature is increased?
Conduction velocity increases due to faster ionic movements at higher temperatures.
Why is action potential size unaffected by stronger stimuli?
Once threshold is reached, the action potential size remains constant due to the all-or-none response.
What limits the minimum stimulus value even as duration increases?
The stimulus must still provide enough charge to cross the membrane threshold despite long durations.
How do earthworm conduction velocities compare to those in squid axons?
Squid axons are faster due to their extremely large diameters, which reduce internal resistance.
What practical challenge arises from measuring conduction velocity in earthworms?
Accurate placement of electrodes and proper unit conversions are critical for reliable measurements.
Why is myelin so beneficial for vertebrate nerve conduction?
It allows for rapid conduction velocities in smaller axons, conserving space and energy.
What experimental factor could impact the accuracy of measuring refractory periods?
Stimulus timing and intensity must be precise to differentiate between absolute and relative refractory periods.
How does lidocaine illustrate the function of voltage-gated sodium channels?
By blocking these channels, it demonstrates their critical role in generating and propagating action potentials.
Why do larger axon diameters result in faster conduction velocities?
Larger diameters reduce axial resistance, allowing ions to move more easily and signals to propagate faster.
What are the consequences of incorrect electrode placement in the earthworm practical?
It can lead to missed or misinterpreted action potential recordings, affecting data reliability.
How do the experimental results demonstrate the importance of maintaining precise environmental conditions?
Variations in temperature, solution composition, or setup can significantly alter conduction velocity and action potential characteristics.
