Study "Bio psych lectures 4-10", a flashcard deck on FORKSAI.
How does the 'all-or-none law' apply to action potentials, and what does it imply about the strength of a stimulus?
The all-or-none law states that an action potential either fires completely or not at all. This means that if the threshold of excitation is reached, a full action potential of a fixed amplitude will occur. The strength of the stimulus does not affect the size or intensity of the action potential itself, only whether it is triggered.
Distinguish between the absolute and relative refractory periods following an action potential.
The absolute refractory period is a brief time after an action potential during which a second action potential cannot be generated, regardless of stimulus strength. In contrast, the relative refractory period immediately follows the absolute period, and during this time, a stronger than usual stimulus is required to initiate another action potential.
Explain the process of repolarisation during an action potential, including the ion movements involved.
Repolarisation occurs after the membrane potential has become positive due to sodium influx. During this phase, voltage-sensitive sodium channels close, preventing further Na+ entry. Simultaneously, voltage-sensitive potassium channels open, allowing K+ ions to rush out of the neuron, which restores the negative charge inside the membrane.
Why does hyperpolarisation briefly occur after an action potential, and what is its significance?
Hyperpolarisation occurs because potassium channels are slow to close, leading to an excessive efflux of K+ ions and causing the membrane potential to temporarily drop below the resting potential (-70mV). This brief period is important as it contributes to the refractory period, ensuring unidirectional propagation of action potentials and limiting the firing rate of a neuron.
How do myelinated axons achieve a much faster conduction speed for action potentials compared to non-myelinated axons?
Myelinated axons are covered by a myelin sheath, which acts as an electrical insulator. The action potential 'jumps' from one Node of Ranvier (gaps in the myelin) to the next, a process called saltatory conduction. This allows the signal to bypass the myelinated segments, significantly increasing conduction velocity compared to the continuous propagation in non-myelinated axons.
Define the role of ion transporters (pumps) in maintaining the resting membrane potential of a neuron.
Ion transporters, such as the sodium-potassium pump, are crucial for maintaining the resting membrane potential. They actively pump three Na+ ions out of the neuron for every two K+ ions pumped in, working against concentration gradients. This unequal exchange contributes to the negative charge inside the neuron and the unequal distribution of ions across the membrane.
What is the 'threshold of excitation' in a neuron, and what happens if it is not reached?
The threshold of excitation is the critical membrane potential, typically -55mV, that a neuron must reach for an action potential to fire. If the combined excitatory signals are insufficient to depolarize the membrane to this threshold, no action potential will occur, and the neuron will not transmit a signal.
Explain how excitatory and inhibitory signals interact to determine whether a neuron will fire an action potential.
Neurons constantly receive both excitatory signals, which increase the chance of firing, and inhibitory signals, which decrease it. An action potential will only occur if the cumulative effect of excitatory signals outweighs the inhibitory ones, causing the membrane potential to depolarize sufficiently to reach the threshold of excitation.
Define 'saltatory conduction' and explain why it is an evolutionary advantage for neural communication.
Saltatory conduction is the process by which action potentials jump from one Node of Ranvier to the next along myelinated axons. This is an evolutionary advantage because it dramatically increases the speed of neural signal transmission, allowing for faster processing of information and quicker responses, which is critical for survival and complex behaviors.
What is the primary function of Acetylcholine (ACh), and what neurological disorder is linked to its loss?
Acetylcholine (ACh) primarily controls muscle movement and is vital for learning, memory, and sleep. The loss of Acetylcholine-producing neurons is strongly linked to Alzheimer's disease, where reduced ACh levels contribute to cognitive decline.