ELECTROCHEMICAL NEUROTRANSMISSION

There are 100 trillion neurons Each of them connect, interact with as many as 1,000 other neurons across a gap called the SYNAPSE So maybe there are 100 quadrillion synapses in the brain!! A synaptic gap is about 20 A wide; 1A is mm—it’s very small

ANATOMY OF A NEURON DENDRITE CELL BODY NUCLEUS AXON HILLOCK AXON MYELIN SHEATH NODES OF RANVIER AXON 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 DENDRITES AS 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.