Lecture 5.pptx

Introduction to Neuroscience Lecture 5 Electrical Signals Are the Vocabulary of the Nervous System  Electrical Signals Are the Vocabulary of the Nervous System Electrical Signals Are the Vocabulary of the Nervous System The Road Ahead: Id...

Introduction to Neuroscience Lecture 5 Electrical Signals Are the Vocabulary of the Nervous System  Electrical Signals Are the Vocabulary of the Nervous System Electrical Signals Are the Vocabulary of the Nervous System The Road Ahead: Identify the two physical forces that make neurons more negatively charged inside than outside. Understand the changes in a neuron’s membrane that produce a large electrical signal called an action potential. Explain the changes in channels and movement of ions that underlie the action potential. Electrical Signals Are the Vocabulary of the Nervous System Neurophysiology is the study of life processes of neurons. A resting neuron is polarized, meaning there is a difference in electrical charge between the inside and the outside of the cell. Ions—electrically charged molecules Anions are negatively charged. Cations are positively charged.  Electrical Signals Are the Vocabulary of the Nervous System Ions are dissolved in the intracellular fluid and the extracellular fluid. A microelectrode inserted into a resting cell will show that the interior is more negative than the exterior. This resting potential is –50 to –80 millivolts (mV)—the negative sign indicates that the cell’s interior is more negative than the outside. Figure 2.1 Measuring the Resting Potential Electrical Signals Are the Vocabulary of the Nervous System Ion channels are proteins that span the membrane and can allow ions to pass through. Some are gated, opening and closing in response to signals. Others stay open all the time, such as the one in neurons that allows only potassium ions (K+) to cross the membrane. Neurons show selective permeability in allowing K+, but not Na+, to enter and leave the cell freely. Figure 2.2 The Distribution of Ions Inside and Outside a Neuron Electrical Signals Are the Vocabulary of the Nervous System Two opposing forces drive ion movement: Diffusion causes ions to spread towards a uniform concentration, along a concentration gradient. Electrostatic pressure causes ions to flow towards oppositely charged areas. Figure 2.3 Ionic Forces Underlying Electrical Signaling in Neurons (Part 1) Figure 2.3 Ionic Forces Underlying Electrical Signaling in Neurons (Part 2) Figure 2.3 Ionic Forces Underlying Electrical Signaling in Neurons (Part 3)  Electrical Signals Are the Vocabulary of the Nervous System Neurons use energy to operate sodium-potassium pumps. Pumps three sodium ions (Na+) out for every two K+ ions pumped in K+ ions accumulate inside the cell and diffuse out through the membrane. Negative charge builds up inside the cell, exerting electrostatic pressure that pulls the K+ ions back in. Figure 2.4 The Ionic Basis of the Resting Potential (Part 1) Figure 2.4 The Ionic Basis of the Resting Potential (Part 2) Electrical Signals Are the Vocabulary of the Nervous System The equilibrium potential is the electrical charge that balances two opposing forces—the concentration gradient and electrostatic pressure—and corresponds to the resting potential. Figure 2.4 The Ionic Basis of the Resting Potential (Part 3) Activity: Animation 2.3: The Resting Membrane Potential (in your digital resources)