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Ions in Your Life An exploration into the role ions play in your nervous system and what can affect them. Your Nervous System Controls various organs of the body directly. The brain also receives information from many organs of the body and adjusts signals to these organs to maintain proper functioning. Central Nervous System – Brain – Spinal Cord Peripheral Nervous System – Autonomic System Neurons – Somatic System Neurons Brain Cerebral Cortex Movement) (Thought, Language, Reasoning, Perception, Voluntary Corpus Callosum (Processes information between the two sides) Midbrain (Vision, Hearing, Eye Movement, Body Movement) Cerebellum (Movement, Balance, Posture) Thalamus (Sensory Processing and Movement) Brain Stem (Breathing, Heart Rate, Blood Pressure) Hypothalamus (Body Temperature, Emotions, Hunger, Thirst) Limbic System (Emotions) Hippocampus (Learning and Memory) Spinal Cord A cylinder of nerve tissue extending from the brain stem Receives sensory information and sends output motor signals The gray matter of the spinal cord consists mostly of cell bodies and dendrites. The surrounding white matter is made up of bundles of interneuronal axons (tracts). Some tracts are ascending (carrying messages to the brain), others are descending (carrying messages from the brain). The spinal cord is also involved in reflexes that do not immediately involve the brain. Nerve cell collections extending from the base of the brain to just below the last rib vertebrae. Neurons Three Modes of Nervous Signaling (Bertil Hille, 2003) Electrical to Electrical- Down axon Electrical to Chemical to Electrical- Across synapse Chemical to Multiple Electrical– Hormones showering many cells Electrical to Electrical Moving ions make electrical signals in neurons (Hodgkin & Huxley 1952) Neurons have semi permeable membranes (cell membranes) that allow some ions through necessary for functions inside and not others. Many substances in our body which are ionically bonded, are broken into ions by the water found in our body. For example: NaCl breaks into the Na+ and Cl-. Faraday (1834) recognizes ions by current flow between charged electrodes battery + – Cl– Na+ Cl– Cl– Na+ current + Na+ cation Cl– anion – Na+ Salts dissociate in water to charged anions and cations. Cations have positive charge and move to the negative electrode. Franklin (1751) defines the direction of electric current as the direction of flow of positive charge. Anions move the other way. Nernst Nernst (1888) describes equilibrium potentials first instant voltmeter = 0 at equilibrium voltmeter = EK – + IN K+ Cl– – + K + Cl – K Cl + K+ Cl– + K K Cl– K+ K+ flow Cl– Cl–K+ – K+ Cl – K+ K+ + Cl K Cl– – – + Cl Cl K K+ K+ Cl– K+ – Cl Cl– OUT Cl– Cl– K+ – K+ K+ Cl– K+ Cl K+ Cl–K+ – K+ flow+ K+ Cl + K + – – Cl K+ Cl– K – – Cl Cl K+ Suppose the membrane is permeable only to K+ ions. How does K+ move? What happens to charge? What do the other ions do? ["Permeable" means that K+ can cross the membrane by diffusion.] Mechanisms of transport across cell membranes Channels Carriers ATPase Pumps Ion Channel in a Neuron Ions pass through a gated aqueous pore, which is narrow at the selectivity filter. The voltage sensors are collections of charged residues that are dragged towards the inside of the outside as the membrane’s charge changes. They regulate gating. Flow of ions to make signals Step 1: A few Na+ ions enter cell so cell Na+ inside goes positive. Step 2: A few K+ ions leave cell so cell inside returns to rest. Other ions that are involved include Cl- and Ca+ K+ Problems with this flow of ions Limited ions in system due to high activity or low consumption Limited water in system to break down ionic bonds into ions due to high activity or low consumption Local anesthetics plug Na+ channels – No/limited excitation, no/limited pain, no/limited movement If Na+ channels open too much or K+ channels open too little… – Too much excitation occurs leading to pain epilepsy, arrhythmias, contractions Electrical to ElectricalDown Axon Electrical to Chemical to Electrical – Across Synapse Electrical impulse created by flow of ions in and out cell down the axon (Ca+) triggers the release of synaptic vesicles filled with neurotransmitters into synaptic gap/cleft. Neurotransmitters bind with specific channels on next neuron to start electrical impulse (flow of ions) down next neuron’s axon. Many neurotransmitters each that bind to different sites to send different signals to various locations to make our body function. Once neurotransmitters are used they go through reuptake channels in original neuron to be reused. Movie Neurotransmitters 50 neurotransmitters have been discovered The five most common are: – Serotonin (emotional stability, calming effect, sleep control, sensory perception) – Dopamine (pleasure, reward, euphoria) – Acetylcholine (memory and learning, mood and arousal, muscle contractions) – GABA (muscle relaxant, reduces anxiety, principle inhibitor) – Enkephalin (pain suppressant) Problems with transfer of neurotransmitters Neurotransmitters get blocked from binding with receptors to continue signal and signal is stopped. Other molecules with similar shapes bind to receptors and prevent neurotransmitters from being used. Excitation and extra excitation occurs and neurotransmitter stops being produced by the body itself. Neurotransmitters are blocked from going through reuptake transporters by original neuron. Extra excitation occurs and body stops producing neurotransmitter. For Example: One such neurotransmitter is called "dopamine." In the normal communication process, dopamine is released by a neuron into the synapse (the small gap between neurons). The dopamine then binds with specialized proteins called "dopamine receptors" on the neighboring neuron thereby sending a signal to that neuron. After the signal is sent to the neighboring neuron, dopamine is transported back to the neuron from which it was released by another specialized protein, the "dopamine transporter“. Drugs of abuse are able to interfere with this normal communication process in the brain. Cocaine, for example, blocks the removal of dopamine from the synapse by binding to the dopamine transporters. As shown in this picture, this results in a buildup of dopamine in the synapse. In turn, this causes a continuous stimulation of receiving neurons, probably responsible for the euphoria reported by cocaine abusers. Movie The Nervous System gets remodeled!!! Things that cause these problems Chemical Imbalances Alcohol Marijuana Cocaine Opiates Nicotine Amphetamines Acknowledgements: Professor Physiology and Biophysics Bertil Hille of the University of Washington School of Medicine. Professor W. N. Zagotta of the University of Washington