Neural conduction and synaptic transmission

Neural conduction and synaptic transmission - Early Clues...

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Early Clues that Linked Electricity and Neuronal Activity Electrical stimulation studies Galvani (18th Century) Electrical current applied to a dissected nerve causes the muscle connected to the nerve to twitch; concluded that electricity flows along the nerve Electrical Stimulation– passage of an electrical current from the uninsulated tip of an electrode through tissue, results in the electric activity of the tissue
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Early Clues that Linked Electricity and Neuronal Activity Electrical Recording Studies von Helmholtz (19th Century) Flow of information in the nervous system is too slow to be a flow of electricity Nerve conduction: 30-40 meters/second Electricity: 3 x 10 8 meters/second It is not the charge but the wave that travels along an axon. And the wave has a chemical basis(Bernstein, 1886).
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1921: Otto Loewi experiment – Nobel Prize 1936 1. Decreased the heart rate of Frog #1 via stimulating the vagus nerve. 2. Collect the fluid from Frog#1 and bathe it in the heart of Frog #2 3. See what happens…. Father of Neuroscience Communication between neurons: electrical or chemica
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Signal transmission within a cell is electrical Signal transmission between nerve cells can be both chemical and electrical But most synapses use a chemical signal
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Questions? How electrical signal is produced? How chemical signal is produced?
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Species of ions found in the intra and extracellular fluids in the brain K + potassium Na + sodium Cl chloride Ca + calcium Proteins - The cradle of life… The cradle of mind…
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Ion An atom or a group of atoms that has acquired a net electric charge by gaining or losing one or more electrons Cations Positively charged ions Examples: Sodium (Na+), potassium (K + ) Anions Negatively charged ions Examples: Chloride (Cl - ), protein molecules (A - )
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Distribution of ions across the resting neuron membrane….is not even Molecule Na + K + Cl - Ca + A- (proteins ) Outside cell many few many many few Inside cell few many few few many Species of ion Concentratio n in cytosol (mM) Concentration in extracellular fluid (mM) K + potassium 400 20 Na + sodium 50 440 Cl chloride 52 550 Proteins - 385 - + - - +
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Using electrodes we can measure the exact difference in Using electrodes we can measure the exact difference in charge b/w outside and inside of the cell charge b/w outside and inside of the cell Hodgkin and Huxley, 1963 Nobel Prize in Medicine "for their discoveries concerning the ionic mechanisms involved in excitation and inhibition in the peripheral and central portions of the nerve cell membrane" .
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neuron… The inside of the membrane is - 70 mV relative to the outside This unequal distribution is the electric potential of a This unequal distribution is the electric potential of a neuron to produce an electric current, or to “fire”, when neuron to produce an electric current, or to “fire”, when the neuron is at rest. the neuron is at rest.
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Neural conduction and synaptic transmission - Early Clues...

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