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Neurophysiology

Learn the basics of electricity in the body, nerve impulse conduction, membrane potential, and factors affecting nerve impulse speed. Explore the characteristics of nerve impulses and neurotransmitters.

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Neurophysiology

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  1. Neurophysiology Electrical Activity in the Body

  2. 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 _________.

  3. Apparatus to administer thermal stimuli and record nerve impulses.

  4. 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?

  5. Na+/K+ Pump • http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html

  6. 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…?

  7. Extracellular fluid Intracellular fluid

  8. Membrane Potential • How do we measure potential? • Milivolts • Resting state: when a nerve is inactive (not transmitting a signal) the value is –70 mV

  9. Changes in the Membrane Potential of a neuron give rise to nerve impulses • How are the membrane potentials changed? • Response to stimuli (ion concentrations) Ex: temperature, light, or pressure • Chemical stimuli (neurotransmitters) Ex: dopamine, serotonin, amino acids

  10. http://www.biology4all.com/resources_library/source/63.swf

  11. Phases of an action potential • Resting State: Neither channel is open • Depolarization: Na+ channels open, K+ remain closed • Repolarization: Na+ channels close, K+ channels open • Undershoot: K+ channels remain open (slow to close)

  12. 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

  13. 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.

  14. Characteristics of Nerve Impulses • Refractory period • All or none response • Impulse conduction

  15. Refractory Periodaka: 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.

  16. 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 • 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

  17. Refractory…Why? • Limits how many action potentials may be generated

  18. 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 Neurotransmitters • http://intro.bio.umb.edu/111-112/112s99Lect/neuro_anims/s_t_anim/WW36.htm

  19. http://www.mind.ilstu.edu/flash/synapse_1.swf

  20. Acetylcholine

  21. 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

  22. Norepinephrineaka: adrenalin • Released from brain and ANS • Adrenal gland • Excitatory • Sense of feeling good • Monoamine • Can be used to manage hypertension

  23. Dopamine • Released from brain (CNS) • hypothalamus • Receptors: heart, kidneys, bld vessels • Inhibitory • sense of feeling good • Parkinson’s Disease • amine

  24. 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

  25. 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

  26. Disorders Associated with NT imbalances

  27. SIDS • NT: excess dopamine • Symptoms: baby stops breathing • Leading cause of death of infants 0-1yr • Factors: smoking, sleeping on belly

  28. NT: deficient serotonin Symtoms: no sleep! Insomnia

  29. NT: not enough AcH Symptoms: memory loss, depression, disorientation Alzheimer's

  30. Parkinson’s • NT: not enough dopamine • Symptoms: tremors, muscle rigidy • Inhibitory? Excitatory? • Over stimulation of neurons controlling muscle tone

  31. Huntington’s • NT: deficient GABA • Symptoms: personality changes, loss of coordination, muscle control, death

  32. Depression • NT: serotonin • Anger, sadness, excess sleep, social isolation, short tempered….over long period of time

  33. http://www.williams.edu/imput/introduction_main.html

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