Braaaiins!!!!! Part II: It's electric boogie woogie woogie

So in part I I told you that ion channels on the cell membrane control which electrically charged particles (ions) can enter or leave the cell. Some ions such as sodium (Na2+) or potassium (K+) are positively charged while others such as chloride (Cl-) are negatively charged. As some of you may remember ions flow from areas of high concentration to areas with low concentration. Ion pumps use energy to maintain the cell in an unbalanced state; at rest the cell maintains a negative charge inside the cell of about -70 mV and the concentration of sodium ions is much higher outside the cell than inside.Communication between cells occurs at the synapse.

The cell that is doing the talking releases neurotransmitter which binds onto the receptors of ion channels of the cell that is receiving the message. Depending on the type of neurotransmitter that is released and the type of ion channel that binds the receptor this acts to make the inside of the cell more positive (depolarized) or more negative (hyperpolarized). When the membrane reaches a certain level of depolarization this causes voltage gated sodium channels to open and sodium rushes into the cell resulting in more sodium channels opening which results in the generation of an electrical signal called an action potential. Sodium channels close and other channels open to restore the inside of the cell to its original resting state. The firing of action potentials is an all or none phenomenon. Action potentials propagate to synapses where they cause voltage gated calcium to open to result in the release of neurotransmitter which then influences the electrical charge on the inside of the next cell.  The ability of the brain to process sensory information and generate motor output is dependent on the physical connections between neurons (ie who is talking to who). Memories are formed through the strengthening of existing connections or the formation of new ones. The brain is unendingly complex but its function comes down to the properties of ion channels which control the flow on ions across a membrane and the pattern of connectivity between neurons. New techniques have given neuroscientists more powerful tools to visualize and record from many neurons at the same time in order to get a better understanding of how brain regions are connected and develop models of information processing.

My favorite part of this story is that a pair of scientists Hodgkin and Huxley worked out how the flow of ions generates an action potential by studying the squid giant axon (no not the giant squid axon). This is an axon in the squid that rapidly generates an escape reflex and its large size allowed these scientist to stick electrodes in it an measure currents across the membrane.

Picture by Tom Kleindinst