ELECTROCHEMICAL NEUROTRANSMISSION

There are 100 trillion neuronsEach of them connect, interact with as many as

1,000 other neurons across a gap called theSYNAPSE

So maybe there are 100 quadrillion synapses in the brain!!

A synaptic gap is about 20 A wide; 1A is .0000001 mm—it’s very small

ANATOMY OF A NEURON

DENDRITECELL BODYNUCLEUSAXON HILLOCKAXONMYELIN SHEATHNODES OF RANVIERAXON BOUTON

DENDRITES ARE THE “RECEIVING” END OF THE NEURON

AXONS ARE THE “SENDING” END OF THE NEURON

AXON HILLCOK ADDS UP (SUMMATES) INFORMATION COMING IN TO THE RECEIVING END OF THE NEURON—THE DENDRITESAS WELL AS THE CELL BODY

THE “MESSAGES” (AT THE RECEIVING END) TELL THE NEURON TO PASS ITS CHARGE (INFORMATION) ALONG ITS AXON TO ITS “SENDING” END, OR NOT

“YES” AND “NO” MESSAGES ARE SUMMATED AT THE AXON HILLOCK; SPATIALLY, TEMPORALLY

IF/WHEN THE AXON DECIDES “YES, I’M GOING TO PASS MY MESSAGE ALONG”, THE “ELECTRO” PART OF ELECTRO CHEMICAL NEUROTRANSMISSION BEGINS

COMMUNICATION AMONG NEURONS OCCURS VIA:

ELECTRO (within the neuron)CHEMICAL (between neurons)

NEUROTRANSMISSION

“ELECTRO” PART

AXONS AT REST HAVE IONS UNEVENLY DISTRIBUTED ACROSS THEIR MEMBRANES;THAT IS, THERE ARE MORE NEGATIVELY CHARGED IONS INSIDE THE AXON THAN OUTSIDE

THIS CREATES A TENSION ACROSS THE MEMBRANE

IN ADDITION, Na+ (sodium) and K+ (potassium) ARE ALSO UNEVENLY DISTRIBUTED ACROSS THE MEMBRANE

SODIUM IS MORE HIGHLY CONCENTRATED ON THE OUTSIDE OF THE AXON MEMBRANE

POTASSIUM IS MORE HIGHLY CONCENTRATEDL ON THE INSIDE OF THE AXON MEMBRANE

WHEN THE AXON HILLOCK DECIDES, “YES, I WANT TO PASS MY MESSAGE DOWN MY AXON TO COMMUNICATE WITH OTHER NEURONS AT THE END OF MY AXON”, “MAGIC” HAPPENS

THE AXON MEMBRANES OPEN UP AND BECOME PERMEABLE TO THE UNEVEN DISTRIBUTION OF + AND – IONS AND THEY SEEK EQUILIBRIUM DOWN THEIR ELECTROSTATIC GRADIENT

IN ADDITION, K+ AND Na+ SEEK EQUILIBRIUM DOWN THEIR CONCENTRATION GRADIENT; CALLED THE SODIUM-POTASSIUM PUMP

THE EXCHANGE OF + AND – IONS AND THE EXCHANGE OF K+ AND Na+ CAUSES MOVEMENT OF THE “MESSAGE” DOWN THE LENGTH OF THE AXON

THIS OCCURS MORE QUICKLY IN MYELINATED AXONS THAN NON-MYELINATED

WHEN THIS ACTIVITY REACHES THE END BOUTON,

THE “CHEMICAL” PART OF ELECTROCHEMICAL NEUROTRANSMISSION BEGINS

NEUROTRANSMITTERS ARE:

Synthesized in cell body;

Stored in vesicles in end boutons;

Released into the synapse;

Travel across the synapse to the

Receptor on the post-synaptic neuron; and then the signal is

Terminated—either through enzymatic degradation or reuptake.