neurophysiology / ATP

Neurophysiology Concepts

Introduction to Neurons

  • Neurons are responsible for initiating and conducting electrical signals throughout the body.

  • Neurons can exhibit excitatory and conduct signals due to their ability to receive and transmit signals.

Neuron Structure and Functionality

  • Neurons maintain a difference in electrical charge across their cell membranes (the concept of membrane potential).

Membrane Potential Details

Understanding Electrical Charges

  • Cells maintain a difference in electrical charge with positively charged cations outside (extracellular) and anions (negatively charged) inside (intracellular).

  • This results in an overall negative charge inside the cell due to protein anions.

Definition of Membrane Potential

  • The difference in charge across a cell membrane, referred to as the membrane potential, can be measured in millivolts and is vital for neuron excitability.

  • A typical resting membrane potential is around -70 millivolts.

Measurement of Membrane Potential

  • Membrane potential is determined by the difference in charge, and it indicates the charge on the inside surface of the membrane.

Polarized Membrane

  • A membrane that exhibits a difference in charge is labeled as polarized, representing a form of potential energy.

Resting Membrane Potential

Maintenance of Resting Potential

  • The resting membrane potential is an active process maintained by the sodium-potassium pump, which transports 3 sodium ions out and 2 potassium ions into the neuron.

  • This is an example of active transport requiring energy (ATP).

Characteristics of resting neuron

  • At rest, there are open channels that allow certain ions to move based on concentration gradients.

  • Selectively permeable nature of the membrane is important for maintaining the charge.

Action Potentials

Definition and Process

  • Action potentials occur when a neuron is stimulated sufficiently to reach a threshold, leading to an electrical impulse along the neuron's membrane.

  • This process involves the opening of gated sodium channels and results in depolarization.

  • Threshold potential is defined at around -59 mV, where voltage-gated sodium channels become activated.

Phases of Action Potential

  1. Depolarization: Sodium ions flow into the neuron, leading the membrane potential to rise quickly.

  2. Repolarization: Once the potential reaches a peak (around +30 mV), sodium channels close, and potassium channels open to flow potassium ions outside.

  3. Hyperpolarization: The membrane potential temporarily dips below resting potential before stabilizing back to -70 mV.

Importance of the Sodium-Potassium Pump

  • The sodium-potassium pump plays a crucial role in re-establishing the resting membrane potential by restoring the concentrations of sodium and potassium.

Refractory Period

Definition of Refractory Periods

  • The refractory period is the time after an action potential during which the neuron resists stimulation.

  1. Absolute Refractory Period: Lasts 0.5 to 1 ms where neuron cannot be stimulated, no matter how strong the stimulus.

  2. Relative Refractory Period: Occurs when the neuron can only be stimulated by a very strong stimulus, and only after passing through the initial absolute phase.

Implications on Neuronal Signaling

  • Understanding the refractory period is crucial for knowing how neurons respond to repeated stimuli and the implications for signal transmission frequency.

Frequency of Action Potentials

  • The frequency of action potentials encodes stimulus strength, not the magnitude of each action potential itself because action potentials are “all-or-nothing.”

Conclusion

The transcript provides a humorous glimpse into the life with a dog intermixed with an educational opportunity to delve into the fundamentals of neurophysiology, from the electrical activities of neurons to action potentials and their respective properties. The detailed explanation of resting and action potentials alongside the importance of ionic mechanisms in maintaining neuron excitability enriches the understanding of how neuronal communication is achieved.