4-16-10 The Nervous System- Cellular aspects-color

4-16-10 The Nervous System- Cellular aspects-color -...

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Unformatted text preview: Clicker Question _________is(are) _________is(are) the generation of unregulated electrical discharges from scar tissue in the gray matter of the brain, which causes the muscles in the body to contract contract. A) Polyneuritis (beriberi) B) The voltaic piles C) Galvanism D) Pellagra E) Epilepsy Pale Blue Dot Where are we? Last Last time I discussed… the the evidence that led us to know that the nervous signal is electrical. biomechanical biomechanical and bioelectrical devices produced by bioengineers that interface with the nervous system. Thi ti This time I will discuss… di the the structure of neurons. the bloodthe blood-brain barrier. how how neurons generate the electrical message known as an action potential. multiple multiple sclerosis (MS). synapses synapses and excitatory and inhibitory postsynaptic potentials. botulism botulism and Botox. Nerves Were Observed Under the Microscope By Antony van Leeuwenhoek in 1675 Nerves are Fibrous, Not a Cavity through which the Animal Spirits Flow “I…observed, “I…observed, that after those Nerves had been but a little while cut off from the eye, the filaments, filaments, of which they are made up, did shrink up….And upon this shrinking up, a little pit comes to appear…and ‘tis this pit in all probability, that Galen took for a cavity.” Stimulated Nerves Pass an Electrical Current Emil Du BoisBoisReymond (1848), a student of Johannes Muller provided Muller, provided evidence evidence that the nervous nervous principle is electrical by showing by that stimulated nerves pass an electrical current along their length. Nerves are Made of Cells Theodor Schwann (1830s), a cofounder of the cell theory, who was also working with also working with Johannes Johannes Muller, discovered that nucleusnucleus-containing cells, now known as Schwann Schwann cells, were a component of nerves. 1 Schwann Cells The Structure of Neurons Otto Deiters (1865) found that nerves were also composed of another cell type, now known as neurons. The neurons. The neurons have two different kinds of branching processes attached to the cell tree-like body: one which was tree-like, which he called "protoplasmic extensions", and another which was more like a long fiber, which he called "axis cylinder". Wilhelm His (1889) called the treetree-like extensions, dendrites; dendrites Rudolph von Kölliker (1896) called the long projections axons axons and the cell itself was named the neuron neuron by Heinrich Wilhelm von Waldeyer (1891). Rudolf Virchow (1854), another of Johannes Muller’s students, discovered a fatty substance in the brain that he called myelin. Myelin is formed by the Schwann cells. The Dendrites, Axon and Cell Body of a Myelinated Neuron The Brain is Composed of a Giant Network of Neurons Joseph von Gerlach (1880) proposed that the recently discovered nerve impulses studied by Emil du BoisEmil du Bois Reymond propagated from cell to cell across the axons and dendrites, and that the brain was formed by giant nets made out of a large number of interconnected filaments. The The Brain is Composed of One Large Cell Camillo Camillo Golgi developed a silver stain that allowed the visualization of the internal reticular apparatus, now known as the Golgi body as the Golgi body. After After staining the brain, it seemed to Golgi, that all the cells fused to form a single cell so that the brain consisted of a continuous mass of tissue that shared a single cytoplasm. Disagreement Disagreement on the Neural Structure of the Brain Using Using Golgi’s silver stain, Santiago Ramón y Cajal was able to see that the the brain was not a single cell, but composed of individual neurons. Ramón Cajal, Ramón y Cajal, with all due respect, di disagreed with Golgi’s conclusion. Both Both Ramón y Cajal and Golgi won the Nobel Prize in 1906 despite their opposite views of the brain. Golgi Golgi got the prize for developing the techniques used to visualize the nervous system and Ramón y Cajal got the prize for describing the correct structure of the nervous system. 2 The Brain is Composed of Individual Cells (Neurons) Ramón y Cajal concluded that neurons neurons are discrete and autonomous cells that can cells interact. interac the neuron is the neuron is the basic unit of the nervous system. there there are gaps, now called synapses synapses, that separate neurons. Information Information is transmitted in one direction from dendrites to the axon. Ramón y Cajal Traced the Networks of Neurons Over Small and Large Distances Ramón y Cajal Traced the Networks of Neurons Over Small and Large Distances Books by Santiago Ramón y Cajal Blood Brain Barrier Paul Paul Ehrlich (1870s) injected various aniline dyes, produced by the new German dye industry, into the blood stream of animals and found that the dye stained everything but the brain. His His student, Edwin Goldmann (1913) injected the aniline dyes into the brain fluid and found that the brain stained, but not the rest of the body. Lina Lina Stern (1921) proposed that there was a blood-brain barrier bloodthat separated the brain from the rest of the body. 3 Blood Brain Barrier Unlike Unlike the capillaries in the rest of the body that are “leaky”, the capillaries in the brain are tight because the membranes of the epithelial cells that make up the capillaries in the brain are tightly appressed to each other. Because of this any chemical that Because of this, any chemical that leaves leaves the blood stream and enters the brain must either be nonpolar and nonpolar small enough small enough to pass through the lipid lipid bilayer or must have a specific transport transport protein to let it enter the intercellular milieu of the brain. The The blood brain barrier protects the protects the brain from viruses and toxins, but also makes it a challenge to deliver some challenge drugs to the brain. Cell Types in the Brain The bloodThe blood-brain barrier is composed of glial cells, glial called astrocytes, which help prevent many astrocytes substances in the blood from entering the brain. Oligodendrocytes Oligodendrocytes in the central nervous system (CNS), like the Schwann cells in the peripheral nervous system (PNS) are glial cells that surround the axons and make up the myelin sheath. The glial The glial cells, which mean “glue cells” have multiple functions, including structurally supporting neurons and regulating the biochemical balance of the brain. They were discovered in 1856 by Rudolf Virchow. The The dendrites and cell bodies of the neurons make up the gray matter of the brain and the axons make up gray the white matter. white The Cell Types in the Brain Electrical Transmission Along Neurons The Plasma Membrane of Neurons The Plasma Membrane Contains Receptor Proteins and Transport Proteins, Including Ion Channels, and Ion Pumps Driven by the Energy of ATP 4 Ion channels act as enzymes that reduce the enzymes activation activation energy or thermal energy that would be necessary to move a charged ion through a charged hydrophobic hydrophobic lipid bilayer. It Would Take a Lot of Heat to Move a Charged Ion Through the Lipid Bilayer. Because of Channels, Ions Can Move Through Aqueous Channels at Body Temperature The Influence of Ion Channels on the Movement of Ions Across a Membrane Hot Temperature→ Body Temperature→ An Unequal Distribution of Ions on the Two Sides of a Membrane Leads to a Voltage Across the Membrane Known as the Membrane Potential Without the channel, the ions do not have enough energy at body temperature to pass through the plasma membrane. When When the inside concentration of a positive ion is inside concentration greater greater than the outside concentration, the ion will tend to diffuse out of the cell using its thermal diffuse thermal energy. The electrical The electrical potential inside the cell will become more more negative and the membrane will be and the membrane will be hyperpolarized hyperpolarized. At At some point, the membrane potential will become so negative that the outgoing positive ions will be attracted back into the cell and the ions will be at equilibrium at equilibrium at the hyperpolarized electrical potential. electrical That is, the concentration difference driving the ions out of the cell will be equivalent to the voltage driving the ions back into the cell. Electrical Hyperpolarization of the Membrane Generation of an Electrical Potential Across the Membrane Initial Final (At Equilibrium) Assume inside of cell (1) and outside of cell is (2) inside of outside and membrane is only permeable to the positive ion (K+) as a result of the ion channels present. At equilibrium, membrane is electrically hyperpolarized. hyperpolarized 5 Hyperpolarized and Depolarized Membranes • The electrical potential outside the cell is considered to be 0 volts by definition. • When the electrical potential inside the cell is th more negative than 0 volts, the membrane is said to be hyperpolarized. • When the electrical potential inside the cell is less negative than the hyperpolarized potential, the membrane is said to be depolarized. Electrical Depolarization of the Membrane When When the outside concentration of a positive ion is outside greater greater than the inside concentration, the ion will tend to diffuse into the cell using its thermal energy. diffuse thermal If If the membrane is already electrically hyperpolarized, the electrical potential inside the cell will become the electrical potential inside the cell will become less less negative and the membrane will be depolarized. depolarized At At some point, the membrane potential will not be negative enough to attract any more positive ions into the cell and the ions will be at equilibrium at the equilibrium depolarized depolarized electrical potential. That is, the concentration difference driving the ions into the cell is equivalent to the depolarized voltage driving the ions out of the cell. Generation of an Electrical Potential Across the Membrane Initial Final (At Equilibrium) High [NaCl] High [NaCl] Low [NaCl] Na+ Na+ Low [NaCl] Walther Nernst Derived an Equation that Predicts the Equilibrium Potential Assume outside of cell (1) and inside of cell is (2) outside inside and membrane is only permeable to the positive ion (Na+) as a result of the ion channels present. At equilibrium, membrane is electrically depolarized. depolarized Nernst Equation Equilibrium Potential = (kT/ze) ln ([ion]out/[ion]in) k = Boltzmann’s constant (1.38 x 10-23 J/K) T = Absolute Temperature (in K) = 310 K for humans e = elementary charge (1.6 x 10-19 C/charge) z = valence of ion (+1 for K+ and Na+) and (kT/ze) ln ([ion]out/[ion]in) is the voltage equivalent of the concentration difference 1 Volt = 1 J/C = 1 Joule/Coulomb ln 10 = 2.3 6 The Nernst Equation (kT/ze) is always positive and equal for both K+ and and Na+ ln ln ([ion]out/[ion]in) is positive when the outside concentration is greater than the inside concentration of an ion concentration of an ion. ln ln ([ion]out/[ion]in) is negative when the outside concentration is less than the inside concentration of an ion. ln ln ([ion]out/[ion]in) is zero when the outside concentration is equal to the inside concentration of an ion (= death). Natural Logs Are Easy Ln Ln 1000 = 6.9 Ln Ln 100 = 4.6 Ln Ln 10 = 2.3 Ln Ln 1 = 0 Ln Ln 0.1 = -2.3 Ln Ln 0.01 = -4.6 Ln Ln 0.001 = -6.9 Because Because the K+ concentration is greater inside the cell than outside the cell, K+ moving out of the cell tends to hyperpolarize the membrane. The The Na+ concentration is greater outside the cell than inside the cell but since the inside the cell, but since the membrane membrane at rest is relatively impermeable to Na+, Na+ has little effect on has the electrical potential of the membrane at rest. Consequently, Consequently, the resting membrane potential is given by the equilibrium potential for K+. Resting Potential Concentrations (in mol/m3) and Equilibrium Potentials (in V) of Cations Outside Inside Equilibrium Potential K+ 20 400 -0.08 V Na+ 440 50 +0.06V Measuring Membrane Potentials In Neurons With Microelectrodes Edgar Adrian (1928) placed small glass electrodes into many kinds of neurons and measured measured the single single cell electrical variation that contributed to the whole whole nerve electrical changes that had been measured by Emil Du BoisBois-Reymond. 7 The Action Potential: A Variation in Electrical Potential The Nervous Signal is like the Morse Code “If these records give a true measure of the activity in the sensory nerve fibres it is clear that they transmit their messages to the central nervous system in a very simple way. The message consists merely of a series of brief impulses….In any one fibre the waves are all of the same form….In fact, the sensory messages are scarcely more complex than a succession of dots in the __ __ . . . . . . . Morse Code.” ADRIAN'S LAWS Neurons communicate with Neurons communicate with each other by sending a short episode of electrical electrical pulses , known as action potentials, action along their fibers. A stimulus either induces an action stimulus either induces an action potential potential in a neuron or it does not. It is an all-orall-or-none response. The The pulses do not vary in amplitude but vary vary in the frequency of the pulses. The The frequency can be as high as 1000 impulses per second. Resting Resting State Initiation of an Action Potential A stimulus causes Na+ Na channels to open and the and influx of Na influx of Na+ causes the membrane potential to depolarize (become less negative) beyond a threshold. Action Potential: Positive Feedback The membrane depolarization activates additional Na Na+ channels, whose conductance conductance is voltagevoltagedependent. This causes a lot more Na+ to enter the cell and the membrane potential depolarizes depolarizes further (and even becomes positive). 8 Action Potential: Negative Feedback Action Potential: K+ ions Once the membrane potential is depolarized by the Na+, the membrane potential is no longer negative enough to hold in the high concentration of K+ ions and the K+ ions begin to th move out of the cell through the K+ channels. This enhanced K+ efflux, combined with the inactivation of the Na+ channels channels results in a return to the resting membrane resting potential and the action action potential is over. The Na+ channels do not remain open forever, but become inactivated. This causes the membrane to inactivated become repolarized (hyperpolarized again). repolarized Voltage Clamp Experiments The activation and inactivation of The activation and inactivation of the Na Na+ channel was studied by Alan Hodgkin and Andrew Fielding Huxley using a voltage clamp. The The properties of the channel were determined by holding the axon membrane at depolarized potential membrane at a depolarized potential (V). (V). When When the membrane is held at a depolarizing potential, the Na+ channel is activated and a current (I) carried activated and current by Na+ passes. The current is proportional to the membrane conductance conductance (G). After a millisecond or so, the current stops, indicating that the channel becomes inactivated. inactivated Voltage Clamp Experiments Equivalent Circuit of Axon Membrane Membrane Membrane and channel conductance can be determined using Ohm’s Law. Ohm’s Equilibrium potentials act as batteries. batteries Channels Channels act as variable variable resistors. Lipid Lipid bilayer acts as insulator in a capacitor capacitor. Neurons Neurons are really miniature electrical devices!!!!! Ohm’s Law V = IR R = V/I G = I/V 9 The Neuron Acts as if it is Composed of Electronic Parts Some Evidence for the Ionic Theory of Action Potentials An An action potential can not be generated unless there are Na in Na+ in the external medium. Radioactive Radioactive Na+ are taken up up by the neuron during an action potential. Pharmacological Pharmacological agents that inhibit that inhibit Na+ channels, like tetrodotoxin, which is tetrodotoxin isolated from the puffer fish, puffer prevent the action potential. http://artisresistors.co.uk/gallery.html Refractory Period and Unidirectionality The The Na+ channel remains inactivated for slightly channel longer than it takes to bring the membrane back to the resting potential. Thus, Thus, the section of membrane that just finished an action potential is not able to produce another one until the Na+ channel is no longer th th inactivated. The The period of time necessary for the Na+ channel to become sensitive to a stimulus is known as the refractory period. refractory The The refractory period makes it possible for an action potential to move down a neuron in only one direction. Nodes of Ranvier Due Due to the refractory period, the action potential moves moves along the axon unidirectionally. The The membranes of the glial cells that form the myelin sheath around the axon are almost purely lipid. Since Since ions cannot pass through lipids, the myelin sheath acts as a insulator around the conducting axon. Each Each Schwann cell is separated from the next by a node of node Ranvier, where the sodium and potassium channels are. The The combination of the glial cells and the nodes of Ranvier make an electrical capacitor that causes the voltage to capacitor “jump” from node to node. node 10 Myelin Sheath Results in a High Conduction Velocity Multiple Multiple Sclerosis Multiple Multiple sclerosis is an autoimmune autoimmune disease in which the white blood cells of the body consider the oligodendrocytes that form the myelin sheath around the myelin sheath around the neurons neurons of the central nervous central system to be foreign invaders and destroy them. The The degeneration of the myelin sheath results in a slower conduction velocity of action potentials and a loss of control of neural processes. Action Action potentials move down the axon jumping from node to node at a rate of 150 m/s (= 330 mph). Without the myelin m/s 330 sheath, the action potential would travel about 5 m/s. m/s What Happens to the Electrical Impulse When it Gets to the End of the Cell? How Can an Electrical Signal Stimulate Some Cells and Inhibit Others? Stimulatory and Inhibitory Actions of Neurons When When one provokes a a reflex movement, a contraction of one contraction of muscle is accompanied by a relaxation relaxation of an opposing muscle. Since all muscles are stimulated by Since all muscles are stimulated by a depolarizing depolarizing voltage shock and all action potentials involve the transmission of a membrane depolarization, Charles Sherrington suggested that action potentials must be capable of doing at least two different things at synapses, one stimulatory stimulatory and one inhibitory. inhibitory Excitatory and Inhibitory Synapses While While working on reflexes, Sherrington discovered that the there are two types of synapses: synapses: excitatory and inhibitor inhibitory. The The same concepts of excitation and inhibition appeared again in the sympathetic sympathetic and the parasympathetic parasympathetic nervous systems. Sympathetic Sympathetic and Parasympathetic Nervous System Since Since the sympathetic and the parasympathetic nerve systems have opposite effects on cardiac muscle, there must be two different actions at their synapses: one excitatory, another one excitatory inhibitor inhibitory. No No one could figure out how an electrical message, in the form of an action potential going to the same postsynaptic element would achieve totally opposite effects, so some turned to the idea that excitatory and inhibitory chemical messengers may be involved. 11 Chemical Synapses? Thomas Thomas Elliot (1904) could mimic the excitatory effects of the sympathetic nervous system on sympathetic cardiac muscle with an extract of the adrenal adrenal medulla known as adrenaline. Henry Dale (1920s) could mimic the inhibitory Henry Dale (1920s) could mimic the inhibitory effects effects of the parasympathetic nervous system parasympathetic nervous on cardiac muscle with an extract from ergot of rye, known as acetylcholine. known Dale Dale coined the terms "adrenergic" and "cholinergic" synapses to describe the chemicals that may couple the neural stimulus to the cardiac muscular response. Henry Henry Dale By 1936, Henry Dale concluded that, "According to this relatively new evidence, a chemical mechanism of transmission mechanism of transmission is is concerned, not only with the effects of autonomic nerves, but with the whole of the efferent activities of the peripheral nervous system, whether voluntary or involuntary in function." Occam’s Razor Sliced a Little Too Close Electrophysiologists Electrophysiologists did not want to believe in chemical signals. They They invoked Occam’s Razor, Occam’s claiming that there is no need for claiming that there is no need for two two kinds of signals. In In general, as scientists, we are reductionists reductionists and try to simplify things as much as possible. But biological systems are never as simple as reductionists postulate. Graded Potential Responses John Eccles (1952) began to insert microelectrodes into the cell bodies of postpostsynaptic neurons of the CNS. After stimulating either CNS. After stimulating either excitatory excitatory or inhibitory prepresynaptic nerves, he discovered that there were two kinds of graded graded potential responses in the postpost-synaptic cell. The Excitatory Graded Potential The excitatory The excitatory response depolarized the post-synaptic postnerve cell, bringing the membrane potential closer to the threshold the threshold. This This would increase the increase probability of activating voltagevoltage-dependent Na+ channels and initiating an action potential in the post-synaptic postcell. The Inhibitory Graded Potential The inhibitory The inhibitory response hyperpolarized the postpostsynaptic nerve cell, bringing the membrane potential further from from the threshold. This This would decrease the decrease probability of activating voltagevoltage-dependent Na+ channels and initiating an action potential in the post-synaptic postcell. 12 The Excitatory (EPSP) Graded Potential Results from the Activation of Channels VoltageVoltage-Independent Na+ Channels The Inhibitory (IPSP) Graded Potential Results from the Activation of Voltage-Independent K+ VoltageChannels VoltageChannels or Voltage-Independent Cl- Channels Integration Integration by the Post-Synaptic PostNeuron The sum of all the sum excitatory excitatory (+) post synaptic potentials (EPSP) and the inhibitory (-) post synaptic synaptic potentials (IPSP) determine the probability probability of initiating an action potential in the postpostsynaptic cell. Integration by the Post-Synaptic PostNeuron: The Basis of Decision Making? When large When a large number of excitatory postpostsynaptic potentials (EPSP) and a small number of inhibitory post-synaptic potentials (IPSP) are postevoked, the post-synaptic membrane is postdepolarized and the post synaptic neuron depolarized and the post synaptic neuron becomes likely becomes likely to initiate an action potential. If If a small number of excitatory post-synaptic postpotentials (EPSP) and a large number of large inhibitory post-synaptic potentials (IPSP) are postevoked, the post-synaptic membrane becomes posthyperpolarized and the post synaptic neuron is unlikely unlikely to initiate an action potential. The PostThe Post-Synaptic Cell is an Analog to Digital Converter The PostThe Post-Synaptic Cell is also an Integrator 13 In the Post-Synaptic Cell, Postthe Majority Rules Integration Can Take Place Over Time (from a single Pre-synaptic Neuron) or Over Space (from PreMany Pre-synaptic Neurons) Pre- Excitatory and Inhibitory Neurotransmitters Whether preWhether a pre-synaptic neuron is excitatory or inhibitory depends on the neurotransmitter that is released. Excitatory Excitatory neurotransmitters include: acetylcholine (neuromuscular junction of skeletal muscle) muscle) noradrenaline noradrenaline glutamate glutamate (an amino acid) How does an action potential trigger neurotransmitter release in a neuromuscular junction? Inhibitory Inhibitory neurotransmitters include: acetylcholine acetylcholine (neuromuscular junction of cardiac muscle) glycine glycine (an amino acid) GABA GABA The membrane depolarization at the pre-synaptic premembrane due to the action potential opens calcium calcium channels. The calcium entering the cell acts as a second second messenger to trigger the secretion of secretion acetylcholine acetylcholine by exocytosis into the neuromuscular exocytosis into neuromuscular synapse. StimulusStimulus-Response in Neurons Stimulus: Action potential (membrane depolarization) Receptor: VoltageVoltagedependent Ca2+ channels Second Messenger: Ca2+ Response: Secretion of neurotransmitters Neuromuscular Junction of Skeletal Muscle Acetylcholine is Acetylcholine is the neurotransmitter released in the neuromuscular neuromuscular junction. The The acetylcholine receptor is a Na+ channel. The The activation of which causes a depolarization of the muscle cell membrane, which causes voltagevoltage-dependent Ca2+ channels to open, which causes the muscle to contract. 14 Food Poisoning: Botulism (Clostridium botulinum) Botulinum Toxin Causes Paralysis by Blocking Acetylcholine Release Every Cloud Has a Silver Lining Weight Weight for weight, botulinum botulinum toxin is the most toxic of toxins toxins. However, However, it can be used for cosmetic reasons— reasons—where it is sold under the name botox. botox Botox: Botulinum Toxin Injections Prevent Contraction of the Muscles that Result in Frowning Cosmetic Botox Injection 15 Cosmetic Botox Injections Botox Scam: Priscilla Presley Got Low Grade Silicone Instead of a “Superior Grade of Botox” The Chemical Basis of the Individual’s Mind As As I will discuss in the next lecture, there are many many different neurotransmitters, especially in the brain, that can induce either excitation or inhibition of the post-synaptic membrane. postDue to differential transcription and Due to differential transcription and alternative alternative splicing, there is a variety of variety receptors for each neurotransmitter in different postpost-synaptic neurons. Moreover, allelic allelic differences between individuals lead to geneticallygenetically-determined differences in receptors. The nearThe near-limitless combinations allow for near infinite individual variations in the chemical basis of mind. The Mind-Body Problem: Original MindThoughts Is the mind an emergent property of emergent hundreds of billions of material brain cells? If so, One day it will be possible to electrically One day it will be possible to electrically stimulate stimulate the brain with a number of electrodes in such a way as to create an original thought. One One day it will be possible to introduce a combination of chemicals into the brain and create an original thought. The Mind-Body Problem: Original MindThoughts Does the mind have its own energy that is capable of influencing the physicophysicochemical processes in the brain and induce action potentials? According According to Wilder Penfield (1975) “…there “…there is no good evidence . . . that the brain alone can carry out the work that the mind does. . . . I believe that one should not pretend to draw a final scientific conclusion, in man's study of man, until the nature of the energy responsible for mind action is discovered, as in my own opinion, it will be." Free Will “Between stimulus and response there is a space. In that space is our power space is our power to to choose our response. In our response lies our growth and our freedom.” Viktor Frankl 16 Free Will “The very serious and difficult question arises of whether…free will is compatible with our scientific knowledge, which plainly says that the concept of breach in that the concept of a breach in causal causal continuity is not acceptable. From the point of view of science, the reality of free will cannot be conceded. On the other hand, as human beings, we depend on the belief that…our actions are preceded by deliberation and choice….” Free Will “All I have to say is that free will is a fact of experience….Free will is often denied on the grounds that you can’t explain it, that it involved it that it in happenings happenings inexplicable by present-day physics presentand physiology. To that I reply that our inability may stem from the fact that physics and physiology are still not adequately developed.…” Hans Mohr John Eccles Science and Free Will I believe that we can exercise believe and develop our neurons to transform food energy into “free will energy”, which acts locally (100 nm range) and at le levels of about 10-20 - 10-19 J. of abo 10 Perhaps Perhaps “free will energy” could modify a calcium channel in the presynaptic neuron or modify a receptor in the postsynaptic neuron and cause us to do or not do something (e.g. something that takes courage). Zorba Zorba the Greek It may be that we can choose to convert our food into fat, work, or spirit. Profiles in Courage Award In whatever arena of life one may meet the challenge of courage… courage each…must decide for himself the course he will follow…. —John F. Kennedy Profiles Profiles in Courage A Profile in Courage Plant and animal cell biologist Werner Franke exposed illegal East German steroid research and the illegal doping of athletes. 17 Another Profile in Courage Dr. Dr. Ignacio Chapela is courageous in “disentangling reality from corporate advertising” in his in ecological studies at UC Berkeley. www.nature.com 18 ...
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