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Neurophysiology Electrical Activity in the Body Review of basic principles of electricity • • • • Two types of electrical charges? Like charges_________ Opposite charges________ The difference in electrical charged areas is called____________ __________. • Electricity is measure in _______. – In your body measurements are _________. Apparatus to administer thermal stimuli and record nerve impulses. Distribution of charges in the Nerve Cell • Outside the cell – Na+ (150mM), K+ (15mM) and Cl- (120mM) • Inside the cell – Na+ (15mM), K+ (150mM) and Cl- (10mM), A(100mM) Recall the Cell Membrane and membrane transport… What molecules will diffuse based on diffusion properties? Na+/K+ Pump • http://www.brookscole.com/chemistry_d/te mplates/student_resources/shared_resources /animations/ion_pump/ionpump.html Membrane Potential • Nerve cells have differences in the concentration of ions • The membrane is electrically Polarized (more – charges on inside than the other) – Anions are more concentrated inside a cell – Cations are more concentrated outside the cell Recall a molecule that is polar…? Extracellular fluid Intracellular fluid Membrane Potential • How do we measure potential? – Milivolts • Resting state: when a nerve is inactive (not transmitting a signal) the value is –70 mV Changes in the Membrane Potential of a neuron give rise to nerve impulses • How are the membrane potentials changed? 1. Response to stimuli (ion concentrations) Ex: temperature, light, or pressure 2. Chemical stimuli (neurotransmitters) Ex: dopamine, serotonin, amino acids • http://www.biology4all.com/resources_library/s ource/63.swf Phases of an action potential 1. Resting State: Neither channel is open 2. Depolarization: Na+ channels open, K+ remain closed 3. Repolarization: Na+ channels close, K+ channels open 4. Undershoot: K+ channels remain open (slow to close) Nerve Impulse Conduction • The resulting action potential causes an electric current that stimulates adjacent portions of the membrane • Series of action potentials occurs sequentially along the length of axon as a nerve impulse Factors that determine speed of Nerve Impulses • Temperature: The higher the temperature, the faster the speed. • Axon diameter - The smaller the diameter, the faster the speed • Myelin sheath – – Only vertebrates have a myelin sheath surrounding their neurons. – The voltage-gated ion channels are found only at the nodes of Ranvier, and between the nodes the myelin sheath acts as a good electrical insulator. – The action potential can therefore jump large distances from node to node (1mm), a process that is called saltatory propagation. – This increases the speed of propagation dramatically, so while nerve impulses in unmyelinated neurones have a maximum speed of around 1 m/s, in myelinated neurones they travel at 100 m/s. Characteristics of Nerve Impulses • Refractory period • All or none response • Impulse conduction Refractory Period aka: Rest Time • For an action potential to begin, then the depolarization of the neuron must reach the threshold value, i.e. the all or nothing law. • refractory period, – After an ion channel has opened, it needs a “rest period” before it can open again/ lasts about 2 ms. • One Way Street: although the action potential affects all other ion channels nearby, the upstream ion channels cannot open again since they are in their refractory period – only the downstream channels open, causing the action potential to move one-way along the axon. Refractory Period • • The refractory period is necessary as it allows the proteins of voltage sensitive ion channels to restore to their original polarity. 2 periods of refractory period 1. absolute refractory period = during the action potential, a second stimulus will not cause a new action potential. 2. Exception: There is an interval in which a second action potential can be produced but only if the stimulus is considerably greater than the threshold = relative refractory Refractory…Why? • Limits how many action potentials may be generated Neurotransmitters • Chemicals released from pre-synaptic neuron • Act to assist, stimulate or inhibit postsynaptic neurons • Where do they come from? – Synthesized in cytoplasm of synaptic knobs – Or stored in vesicles •http://intro.bio.umb.edu/111-112/112s99Lect/neuro_anims/s_t_anim/WW36.htm • http://www.mind.ilstu.edu/flash/synapse_1. swf Acetylcholine Categories of NT • Monoamines – Epinephrin, dopomine, and serotonin • Amino acids – Glycine, glutamic acid and gamma aminobutyric acid: GABA • Peptides – Made in RER • Neuropeptide – – – – Alter response to a NT or block release of NT Act as NTs Released during stress Ex: beta endorphin: pain reliever…similar to morphine Norepinephrine aka: adrenalin • Released from brain and ANS – Adrenal gland • • • • Excitatory Sense of feeling good Monoamine Can be used to manage hypertension Dopamine • Released from brain (CNS) – hypothalamus • Receptors: heart, kidneys, bld vessels • Inhibitory • sense of feeling good • Parkinson’s Disease • amine Serotonin • Brain (CNS) • Regulates endocrine activity (hormonal controls) • Leads to sleepiness – Controls sleep/wake cycles • amine • Inadequate amounts: – Severe depression and obsessive/compulsive disorders, anger issues, and eating disorders Endorphins • • • • • Neuropeptide Produced in brain (CNS) Pain relief: inhibitory Released in times of pain or stress Elevated levels cause disease known as Addison’s disease • Structure is similar to??? – morphine Disorders Associated with NT imbalances SIDS • • • • NT: excess dopamine Symptoms: baby stops breathing Leading cause of death of infants 0-1yr Factors: smoking, sleeping on belly Insomnia • NT: deficient serotonin • Symtoms: no sleep! Alzheimer's • NT: not enough AcH • Symptoms: memory loss, depression, disorientation Parkinson’s • NT: not enough dopamine • Symptoms: tremors, muscle rigidy • Inhibitory? Excitatory? – Over stimulation of neurons controlling muscle tone Huntington’s • NT: deficient GABA • Symptoms: personality changes, loss of coordination, muscle control, death Depression • NT: serotonin • Anger, sadness, excess sleep, social isolation, short tempered….over long period of time • http://www.williams.edu/imput/introduction _main.html