Lecture Notes: Membrane Transport and Membrane Potential

Introduction

• Topic: Membrane transport leading to nerve signal transmission.
• Aim: Understanding how neurons create and transmit electrical signals.

Membrane Potential

• Definition: Charge difference between extracellular fluid and intracellular fluid (ICF).
• Measurement: Using probes and a voltage meter, showing the inside of the cell more negative than the outside.
• Charge Separation: Phospholipid bilayer acts as a voltage separator, maintaining ion separation (sodium, potassium, chloride).

Resting Membrane Potential (RMP)

• Range: -60 to -90 millivolts.
• Reference Point: Charge is always referenced to the inside of the cell.
• Key Equations: Nernst equation, Goldman-Hodgkin equation (consider factors like temperature, concentration).
• Abbreviations:
  • VM: Membrane potential.
  • RMP: Resting membrane potential.
  • Average for neurons: -70 mV; skeletal muscle: -90 mV.

Excitable Cells

• Cells with membrane potential include neurons, muscle cells (cardiac, smooth, skeletal), and certain sensory epithelia.
• Changes in the membrane potential can trigger changes in cell behavior.

Ions and Gradients

• Major Ions: Sodium (Na+), Potassium (K+), Chloride (Cl-), Calcium (Ca2+), and large anions.
• Ion Distribution:
  • Sodium: Higher outside than inside.
  • Potassium: Higher inside than outside.
  • Chloride: Higher outside than inside.
• Gradients:
  • Concentration Gradient: Based on ion concentration.
  • Electrical Gradient: Based on charge attraction/repulsion.
  • Electrochemical gradients influence ion movement.

Leak Channels and Ion Movement

• Leak Channels: Allow passive ion movement (more K+ out, Na+ in). Minimal effect but crucial for maintaining concentration gradients.

Sodium-Potassium Pump

• Role: Maintains resting voltage by moving ions against their gradients.
• Mechanism: Uses ATP (active transport).
  • Moves 3 Na+ out for 2 K+ in.

Nervous System Pathways

• Neurons Involved: Sensory (unipolar), interneurons, motor neurons.
• Autonomic vs. Somatic: Pathways differ; autonomic involves two neurons, somatic one.

Next Steps

• Focus: Graded potentials, action potentials, synaptic transmission.
• Autonomic Physiology: Understand receptor roles in sympathetic/parasympathetic responses.

Study Recommendations

• Revisit notes, draw diagrams, read up on the upcoming topics like graded potentials, action potentials, and synaptic transmission.