5.1 Origin and Characteristics of Bioelectric Signals

Bioelectric signals are the foundation of our body's electrical communication system. These signals, generated by cells, drive crucial processes like heartbeats and nerve impulses. Understanding their origin and characteristics is key to grasping how our bodies function.

In this section, we'll explore membrane potentials, ion channels, and action potentials. We'll also dive into extracellular recordings, which capture these signals. This knowledge is essential for developing medical devices and understanding bioelectric phenomena.

Membrane Potential and Ion Channels

Resting Membrane Potential and Ion Channel Function

Top images from around the web for Resting Membrane Potential and Ion Channel Function

• 

  Resting Membrane Potential | Biology for Majors II View original

  Is this image relevant?

• 

  Resting Membrane Potential | Biology for Majors II View original

  Is this image relevant?

• 

  Topic 6.5: Neurones and Synapses - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

• 

  Resting Membrane Potential | Biology for Majors II View original

  Is this image relevant?

• 

  Resting Membrane Potential | Biology for Majors II View original

  Is this image relevant?

1 of 3

Top images from around the web for Resting Membrane Potential and Ion Channel Function

• 

  Resting Membrane Potential | Biology for Majors II View original

  Is this image relevant?

• 

  Resting Membrane Potential | Biology for Majors II View original

  Is this image relevant?

• 

  Topic 6.5: Neurones and Synapses - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

• 

  Resting Membrane Potential | Biology for Majors II View original

  Is this image relevant?

• 

  Resting Membrane Potential | Biology for Majors II View original

  Is this image relevant?

1 of 3

• Resting membrane potential refers to the electrical potential difference across a cell's membrane when the cell is at rest, typically around -70 mV for neurons
• Ion channels are protein structures embedded in the cell membrane that selectively allow specific ions to pass through, playing a crucial role in maintaining the resting membrane potential and facilitating changes in the potential during cell signaling
• The resting membrane potential is primarily determined by the concentration gradients of ions (sodium, potassium, chloride, and calcium) across the cell membrane and the selective permeability of the membrane to these ions
• Potassium (K+) channels are more permeable at rest compared to sodium (Na+) channels, resulting in a higher concentration of K+ inside the cell and contributing to the negative resting membrane potential

Depolarization and Repolarization in Action Potential Generation

• Depolarization occurs when the membrane potential becomes less negative or more positive, typically due to the opening of voltage-gated sodium channels and the influx of Na+ ions into the cell
• During an action potential, depolarization is triggered when the membrane potential reaches a threshold value (around -55 mV), causing a rapid and transient change in the membrane potential
• Repolarization is the process of restoring the membrane potential back to its resting state after depolarization
• Repolarization is primarily mediated by the opening of voltage-gated potassium channels and the efflux of K+ ions from the cell, as well as the inactivation of sodium channels

Action Potential Characteristics

Action Potential Propagation and Signal Amplitude

• An action potential is a rapid, transient, and all-or-none electrical signal that propagates along the membrane of excitable cells, such as neurons and muscle cells
• Action potential propagation involves the sequential depolarization and repolarization of adjacent segments of the cell membrane, allowing the signal to travel along the length of the cell (axon in neurons)
• The propagation of action potentials enables the transmission of information within the nervous system and the coordination of various physiological processes
• Signal amplitude refers to the magnitude of the change in membrane potential during an action potential, typically ranging from -70 mV at rest to around +40 mV at the peak of depolarization

Frequency Spectrum of Action Potentials

• The frequency spectrum of an action potential represents the range of frequencies present in the signal
• Action potentials are characterized by a rapid rise and fall in membrane potential, resulting in a broad frequency spectrum that typically ranges from a few Hz to several kHz
• The frequency content of action potentials is important for understanding the temporal dynamics of neural activity and the information carried by these signals
• Factors such as the duration of the action potential, the refractory period, and the firing rate of the cell influence the frequency spectrum of the recorded signal

Extracellular Recordings

Principles and Applications of Extracellular Potentials

• Extracellular potentials are electrical signals recorded from the extracellular space surrounding cells, reflecting the collective activity of multiple nearby cells
• Extracellular recordings can be performed using various techniques, such as single-unit recordings (measuring the activity of individual neurons), local field potentials (LFPs, measuring the summed activity of a population of neurons), and electroencephalography (EEG, measuring the activity of large neuronal populations at the scalp)
• Extracellular potentials provide valuable information about the activity and function of neural circuits, as well as the synchronization and coordination of neuronal ensembles
• Applications of extracellular recordings include studying sensory processing, motor control, cognitive functions, and the diagnosis and monitoring of neurological disorders (epilepsy, Parkinson's disease)
• Extracellular recordings have lower signal amplitudes compared to intracellular recordings, as the signals are attenuated by the extracellular space and the distance between the recording electrode and the signal sources