Chapter 4 Electrical communication(1)

Introduction to Neurons and Behavior

• Psychology in Everyday Life: Discusses how understanding brain functions can impact behavior.

• Neurons: Essential elements for transmitting electrical signals and forming the basis of communication in the nervous system.

Research Exploration of Neural Activity

• René Descartes (1664): Formulated key questions regarding how sensory stimuli are perceived and how responses are commanded from the brain.

  • How do nerves detect and convey sensory information?

  • How does the brain decide on responses?

  • How does the brain coordinate muscle movements?

Clinical Focus: Understanding Epilepsy

• Epilepsy: A neurological condition characterized by recurrent seizures due to excessive neural synchrony.

  • Prevalence: 50% of cases have identifiable neural causes; 50% have unknown causes.

  • Seizure Management: Various treatments including medication, dietary changes, deep brain stimulation, and surgical interventions.

The Action Potential

• Graded Potentials: Incorporate excitatory (EPSPs) and inhibitory (IPSPs) changes summated spatially and temporally.

  • Threshold: Action potentials occur when the summed voltage exceeds a critical level.

Exploring Electrical Activity in the Nervous System

• Early Studies:

  • Stephen Gray (1731): Suggested electricity as a messenger in the nervous system.

  • Luigi Galvani: Found electrical stimulation to induce muscle contraction.

  • Gustav Fritsch & Eduard Hitzig: Demonstrated that stimulating the neocortex elicits movement.

  • Roberts Bartholow (1874): First to explore human brain stimulation impacts.

Basics of Electricity and Neuroscience

• Electrical Current: Movement of electrons from regions of high to low charge.

• Microelectrodes: Enable recording and stimulation of neuronal activity at the cellular level.

• Potential:

  • Electrical potential: Measured in volts; represents the capacity to perform work due to stored electrical energy.

Historical Electrical Recording Studies

• Richard Caton: Made early measurements of brain electrical currents using external electrodes.

• Electroencephalogram (EEG): A representation of electrical activities reflecting graded potentials across neuron populations.

The Role of Ions in Neuronal Function

• Ion Types:

  • Cations: Positively charged ions (e.g., Na+, K+).

  • Anions: Negatively charged ions (e.g., Cl−).

• Factors Influencing Ion Movement:

  • Diffusion: Movement from regions of higher concentration to lower concentration.

  • Concentration Gradient: How much an ion is present in different areas.

  • Voltage Gradient: Differences in charge influence ion movements.

Electrical Activity at Neuronal Membranes

• Resting Potential: The electrical charge across neuron membranes at rest, typically around -70 mV.

• Ion Distribution: Uneven distribution across membranes contributes to resting potential, facilitating signal transmission.

Membrane Features Maintaining Resting Potential

• Ionic Channels and Pumps: Essential for maintaining charged state and facilitating the selective passage of ions (especially K+ and Na+).

• Balance of Ion Concentrations: Sodium higher outside, potassium higher inside, contributing to the resting potential.

Action Potentials: Generation and Propagation

• Characteristics: A rapid reversal of the neuron's membrane potential lasting about 1 millisecond.

  • Threshold: The critical level of depolarization required to trigger an action potential, approximately -50 mV.

• Voltage-Activated Channels: Channels sensitive to changes in electrical potential, critical for the propagation of action potentials along axons.

Summation of Inputs and Neural Integration

• Postsynaptic Potentials (PSPs): EPSPs and IPSPs combine (summation) to determine whether an action potential is generated.

  • Temporal Summation: Summation over time.

  • Spatial Summation: Summation across different locations on the neuron.

Nerve Impulses and Muscle Contraction

• Mechanism: Motor neurons release neurotransmitters at the synapse onto muscle cells, triggering action potentials that lead to contraction.

• Acetylcholine Release: Key neurotransmitter in muscle contraction pathways.

Advanced Topics in Neuronal Function

• Optogenetics: A cutting-edge technique involving light-sensitive ion channels to control neuronal activity in live tissue.

• Multiple Sclerosis (MS): Disease characterized by loss of myelin, greatly affecting neuron signaling and function.

• Saltatory Conduction: Depolarization jumps between nodes of Ranvier in myelinated axons, increasing conduction speed and efficiency.