Overview and Passive Membranes

Sketch of Cerebellar Neurons by Santiago Cajal (1899) A: Purkinje cells B: Granule cells How do these cells work?

A Single Neuron A stained neuron with an extensive dendritic tree

A Population of Neurons Several stained and possibly interconnected neurons

C. Elegans Wikipedia 302 neurons, 56 glial cells contained in head and tail ganglia and a spinal cord-like ventral nerve

Grasshopper Nervous System Nerve cells in ganglia,, connected by a spinal cord-like structure

The Leech

Leech Ganglia

Crab Pyloric Network From the Eve Marder lab, Brandeis University Contained within the stomatogastric ganglion, which has about 30 neurons that comprise two central pattern generators, the pyloric network and the gastric mill network

Structure of a Neuron

Communication via a Chemical Synapse

Communication via a Chemical Synapse Electron micrograph showing a chemical synapse. From Lodish, 4th edition.

Neuronal Action Potential

Electrical Impulses are Ubiquitous

Pioneers of Modern Neuroscience Alan Hodgkin (1914-1998) Andrew Huxley (1917-2012)

Atomic Model of an Ion Channel The bacterial KcsA K+ channel

Ion Flow Through an Ion Channel Only the K+ ions get through, the Cl- stays put. The membrane acts as a semipermeable membrane.

Electrodiffusion Through a Semipermeable Membrane Diffusion – flow of atoms down the K+ concentration gradient Electrical drift – flow of ions due to electrical potential Electrodiffusion – flow of ions due to combination of diffusion and electrical drift

Nernst Potentials Relative locations of Nernst and resting potentials

The Plasma Membrane

An Equivalent Circuit

A Capacitor A capacitor is like a moat surrounding a castle: it separates inside from outside. A deep moat is like a small Dielectric, making it hard to pass from one side to the next. In the membrane, the dielectric reflects the lipids.

Membrane Time Constant