L10: Earthworm Action Potential Experiment

Question 1

What influences the median fibre threshold value in the practical experiment?

Answer 1

Experimental factors such as pin placement and variability in biological preparations.

Question 2

Why is Earthworm Ringer Solution used instead of water?

Answer 2

To match the osmolarity and ion concentration of the earthworm’s internal environment, preventing water movement that could damage cells.

Question 3

What happens if the Earthworm Ringer solution contains too much liquid?

Answer 3

It could conduct current, causing electrical interference and reducing the accuracy of measurements.

Question 4

Why is the median fibre’s threshold lower than the lateral fibre’s?

Answer 4

The median fibre has a larger diameter, which reduces the threshold for action potential initiation.

Question 5

Why does the median fibre’s action potential arrive before the lateral fibre’s?

Answer 5

The median fibre has a higher conduction velocity due to its larger diameter.

Question 6

What is the “all-or-none” principle of action potentials?

Answer 6

An action potential is either triggered completely when the threshold is reached, or not at all.

Question 7

How does stimulus duration affect the threshold value for action potentials?

Answer 7

Increasing the stimulus duration reduces the amplitude required to reach the threshold.

Question 8

What determines conduction velocity in neurons?

Answer 8

Axon diameter, temperature, and presence of myelin.

Question 9

How does mammalian conduction velocity compare to earthworms’?

Answer 9

Mammals generally have higher conduction velocities due to myelination and warmer body temperatures.

Question 10

What is the absolute refractory period caused by?

Answer 10

Inactivation of voltage-gated sodium channels.

Question 11

What is the relative refractory period?

Answer 11

A period when a stronger-than-normal stimulus is required to trigger another action potential due to hyperpolarisation.

Question 12

How does lidocaine affect action potentials?

Answer 12

It blocks voltage-gated sodium channels, preventing the propagation of action potentials.

Question 13

Why is myelination critical for nerve function?

Answer 13

Myelination increases conduction velocity without requiring larger axons, saving space.

Question 14

What adaptation compensates for the lack of significant myelination in earthworms?

Answer 14

Earthworms rely on larger axon diameters to achieve faster conduction.

Question 15

What practical adjustments could influence earthworm conduction velocity?

Answer 15

Changing the environmental temperature.

Question 16

Why is biological and experimental variability important in research?

Answer 16

It highlights the need for statistical analysis to identify real patterns and minimize the impact of variability.

Question 17

What happens if the ion concentrations in the Ringer solution are incorrect?

Answer 17

An imbalance may lead to water entering cells via osmosis, causing them to swell and potentially burst.

Question 18

How do action potentials in the earthworm experiment relate to the presence of ions in the Ringer solution?

Answer 18

Proper ion concentrations are essential for maintaining cell membrane permeability and generating action potentials.

Question 19

Why does the Ringer solution’s ionic content need to be specific to the species?

Answer 19

Different species have varying physiological requirements, so their Ringer solutions must match their internal environments.

Question 20

Why is it important to keep the earthworm damp but not submerged during the experiment?

Answer 20

To avoid creating a conductive pathway for electrical current outside the worm, ensuring accurate stimulation and recording.

Question 21

What is the role of stimulation electrodes in the practical?

Answer 21

They create an electrical stimulus to depolarize the membrane and initiate action potentials.

Question 22

How does fibre diameter influence conduction velocity?

Answer 22

Larger diameter fibres have lower internal resistance, allowing faster conduction of action potentials.

Question 23

What does the difference in timing between median and lateral fibre responses demonstrate?

Answer 23

It shows that larger diameter axons conduct signals faster than smaller ones.

Question 24

Why don’t action potentials increase in size with greater stimulus strength?

Answer 24

Action potentials are governed by the all-or-none principle; their size remains constant once the threshold is reached.

Question 25

How does stimulus amplitude affect reaching the threshold at different durations?

Answer 25

Shorter durations require higher amplitudes, while longer durations can reach the threshold with lower amplitudes.

Question 26

What is the relationship between charge and stimulus duration in reaching the threshold?

Answer 26

The total charge required is constant, whether achieved by a high amplitude or a longer duration stimulus.

Question 27

What unit conversion errors were commonly observed during the conduction velocity experiment?

Answer 27

Confusion between millimetres, seconds, and their respective metric conversions (e.g., metres per second).

Question 28

Why is the conduction velocity of mammalian nerves higher despite smaller axons compared to earthworms?

Answer 28

Mammals have extensive myelination, which compensates for smaller axon diameters and increases conduction velocity.

Question 29

How does temperature affect conduction velocity?

Answer 29

Higher temperatures increase conduction velocity, while colder temperatures slow it down.

Question 30

What would happen if the earthworm’s axons were not as large?

Answer 30

Without large axons or myelination, the earthworm would have slower nerve conduction and less efficient neural function.

Question 31

How does lidocaine demonstrate evolutionary similarities in sodium channels across species?

Answer 31

Its effect on earthworm and human sodium channels shows a shared evolutionary mechanism for action potential generation.

Question 32

What is the functional significance of the refractory period in neurons?

Answer 32

It ensures unidirectional propagation of action potentials and prevents continuous firing of the neuron.

Question 33

Why is accurate unit conversion critical in experiments like conduction velocity measurement?

Answer 33

Errors in units can lead to inaccurate data interpretation and incorrect conclusions about biological properties.

Question 34

What did the experiment teach about the importance of axon diameter versus myelination?

Answer 34

While axon diameter influences conduction velocity, myelination is more critical for rapid signal transmission in vertebrates.

Question 35

What does the earthworm experiment illustrate about neuron structure and function?

Answer 35

It highlights the relationship between physical and physiological properties, such as axon diameter and conduction velocity.

Question 36

What is the importance of statistical analysis in group data collection?

Answer 36

It helps identify class means and variability to make meaningful conclusions from experimental results.

Question 37

Why is it unlikely to observe ions leaving cells during the earthworm practical?

Answer 37

Cell membranes are only permeable to ions through specific channels, which are not always open.

Question 38

How does the external Ringer solution help maintain the earthworm’s cellular integrity?

Answer 38

By matching internal ionic concentrations, it prevents osmotic imbalance and protects cells.

Question 39

What role do stimulation thresholds play in identifying fibre responses?

Answer 39

Different axons have distinct stimulation thresholds due to variations in diameter and properties.

Question 40

How does the lateral fibre differ in threshold from the median fibre?

Answer 40

The lateral fibre usually has a higher stimulation threshold due to its smaller diameter.

Question 41

Why do lateral fibres sometimes show similar thresholds to median fibres?

Answer 41

Close placement of electrodes near the lateral fibres can mimic the threshold level of the median fibre.

Question 42

What factors influence variability in experimental outcomes during practicals?

Answer 42

Biological differences, pin placement, and external conditions like temperature contribute to variability.

Question 43

What does the presence of two peaks in the action potential graph signify?

Answer 43

It represents the sequential activation of the median and lateral fibres due to differences in conduction velocity.

Question 44

How does the Ringer solution prevent electrical interference?

Answer 44

By controlling its volume, the conductive properties of the solution are minimized to avoid short-circuiting.

Question 45

What happens to conduction velocity if the earthworm’s temperature is increased?

Answer 45

Conduction velocity increases due to faster ionic movements at higher temperatures.

Question 46

Why is action potential size unaffected by stronger stimuli?

Answer 46

Once threshold is reached, the action potential size remains constant due to the all-or-none response.

Question 47

What limits the minimum stimulus value even as duration increases?

Answer 47

The stimulus must still provide enough charge to cross the membrane threshold despite long durations.

Question 48

How do earthworm conduction velocities compare to those in squid axons?

Answer 48

Squid axons are faster due to their extremely large diameters, which reduce internal resistance.

Question 49

What practical challenge arises from measuring conduction velocity in earthworms?

Answer 49

Accurate placement of electrodes and proper unit conversions are critical for reliable measurements.

Question 50

Why is myelin so beneficial for vertebrate nerve conduction?

Answer 50

It allows for rapid conduction velocities in smaller axons, conserving space and energy.

Question 51

What experimental factor could impact the accuracy of measuring refractory periods?

Answer 51

Stimulus timing and intensity must be precise to differentiate between absolute and relative refractory periods.

Question 52

How does lidocaine illustrate the function of voltage-gated sodium channels?

Answer 52

By blocking these channels, it demonstrates their critical role in generating and propagating action potentials.

Question 53

Why do larger axon diameters result in faster conduction velocities?

Answer 53

Larger diameters reduce axial resistance, allowing ions to move more easily and signals to propagate faster.

Question 54

What are the consequences of incorrect electrode placement in the earthworm practical?

Answer 54

It can lead to missed or misinterpreted action potential recordings, affecting data reliability.

Question 55

How do the experimental results demonstrate the importance of maintaining precise environmental conditions?

Answer 55

Variations in temperature, solution composition, or setup can significantly alter conduction velocity and action potential characteristics.