Chapter 12 - Nervous Tissue - Study Guide - Testing Your Comprehension - Page 473: 2

Hyperkalemia, which is an excess of potassium (K+) in the extracellular fluid, can have significant effects on the resting membrane potentials of cells in the nervous system and can alter neural excitability. Here's how it impacts these aspects: 1. **Resting Membrane Potential**: - The resting membrane potential (RMP) is the electrical charge difference across the cell membrane of a neuron when it is not actively transmitting a signal. It is typically around -70 millivolts (mV) in neurons. - The RMP is primarily determined by the concentration gradients of ions, especially potassium (K+), sodium (Na+), and chloride (Cl-), as well as the permeability of the cell membrane to these ions. 2. **Effect of Hyperkalemia on RMP**: - Hyperkalemia results in an elevated extracellular potassium concentration. This increase in extracellular K+ disrupts the normal potassium concentration gradient across the cell membrane. - With excessive extracellular K+, there is a reduced concentration gradient favoring K+ efflux (outward movement) from neurons during the resting state. - As a result, the resting membrane potential becomes less negative (moves closer to zero mV) and may even depolarize (become more positive) compared to the usual -70 mV. This shift is called depolarization of the resting membrane potential. 3. **Effect on Neural Excitability**: - Changes in the RMP affect neural excitability. When the RMP is depolarized due to hyperkalemia: - Neurons become closer to their threshold for firing an action potential, making them more excitable. - It takes less stimulation to reach the threshold and initiate an action potential. - Neurons may even exhibit spontaneous firing without external stimuli, which can lead to excessive or inappropriate neural signaling. 4. **Consequences for Nervous System Function**: - Hyperkalemia-induced changes in RMP and increased neural excitability can result in abnormal neural function. - Symptoms of hyperkalemia affecting the nervous system may include muscle weakness, tingling sensations, and, in severe cases, muscle paralysis. - In extreme cases, excessive depolarization of neuronal membranes can lead to a phenomenon known as depolarization block, where neurons are no longer able to generate action potentials. In summary, hyperkalemia disrupts the normal potassium concentration gradient across neuronal cell membranes, leading to a depolarization of the resting membrane potential. This depolarization increases neural excitability and can result in abnormal neuronal function. The specific effects and symptoms can vary depending on the severity and duration of hyperkalemia, as well as individual variations in neural responses to changes in potassium levels.

Hyperkalemia, which is an excess of potassium (K+) in the extracellular fluid, can have significant effects on the resting membrane potentials of cells in the nervous system and can alter neural excitability. Here's how it impacts these aspects: 1. **Resting Membrane Potential**: - The resting membrane potential (RMP) is the electrical charge difference across the cell membrane of a neuron when it is not actively transmitting a signal. It is typically around -70 millivolts (mV) in neurons. - The RMP is primarily determined by the concentration gradients of ions, especially potassium (K+), sodium (Na+), and chloride (Cl-), as well as the permeability of the cell membrane to these ions. 2. **Effect of Hyperkalemia on RMP**: - Hyperkalemia results in an elevated extracellular potassium concentration. This increase in extracellular K+ disrupts the normal potassium concentration gradient across the cell membrane. - With excessive extracellular K+, there is a reduced concentration gradient favoring K+ efflux (outward movement) from neurons during the resting state. - As a result, the resting membrane potential becomes less negative (moves closer to zero mV) and may even depolarize (become more positive) compared to the usual -70 mV. This shift is called depolarization of the resting membrane potential. 3. **Effect on Neural Excitability**: - Changes in the RMP affect neural excitability. When the RMP is depolarized due to hyperkalemia: - Neurons become closer to their threshold for firing an action potential, making them more excitable. - It takes less stimulation to reach the threshold and initiate an action potential. - Neurons may even exhibit spontaneous firing without external stimuli, which can lead to excessive or inappropriate neural signaling. 4. **Consequences for Nervous System Function**: - Hyperkalemia-induced changes in RMP and increased neural excitability can result in abnormal neural function. - Symptoms of hyperkalemia affecting the nervous system may include muscle weakness, tingling sensations, and, in severe cases, muscle paralysis. - In extreme cases, excessive depolarization of neuronal membranes can lead to a phenomenon known as depolarization block, where neurons are no longer able to generate action potentials. In summary, hyperkalemia disrupts the normal potassium concentration gradient across neuronal cell membranes, leading to a depolarization of the resting membrane potential. This depolarization increases neural excitability and can result in abnormal neuronal function. The specific effects and symptoms can vary depending on the severity and duration of hyperkalemia, as well as individual variations in neural responses to changes in potassium levels.