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Neurons Structure and Conduction of a Nerve Impulse

Neurons Structure and Conduction of a Nerve Impulse. Two coordinating systems which respond to environmental stimuli. Nervous System & Endocrine (hormone) System Begin with Nervous System (data processing system) 3 interconnected functions  input / integration / output.

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Neurons Structure and Conduction of a Nerve Impulse

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  1. NeuronsStructure and Conduction of a Nerve Impulse

  2. Two coordinating systems which respond to environmental stimuli Nervous System & Endocrine (hormone) System Begin with Nervous System (data processing system) 3 interconnected functions  input / integration / output

  3. Basic Organization sensory receptor (sensory input)  integration  (motor output)  effector • Sensory Input triggered by stimuli • conduction of signals to processing center • Integration • interpretation of sensory signals within processing centers • Motor output • conduction of signals to effector cells (i.e. muscles, gland cells)

  4. Neuron • Dendrite - conducts “signal” toward the cell body -- [input zone] • often short, numerous & highly branched • signal comes from sensory cell or neighboring neuron • Axon - usually a single fiber -- [conducting zone] • conducts signal away from cell body to another neuron or effector cell • Axon Ending • a cluster of branches (100’s to 1000’s) • each with a bulblike synaptic knob • relays signal to next neuron / effector cell

  5. Generation - Conduction of Neural Impulses • Dependent on concentration gradients of Na+ & K+ • Na+ 14x greater outside • K+ 28x greater inside • Membrane permeability • lipid bilayer bars passage of K+ & Na+ ions • protein channels and pumps regulate passage of K+ & Na+ • at rest more K+ move out than Na+ move in • K+ ions diffuse out leave behind excess negative charge • Sodium-potassium pump • Na+ out - K+ in (more Na+ out than K+ in • contributes to loss of (+)

  6. Overview of Neural Impulse

  7. Maintenance of negative charge within neuron • resting membrane potential about -70 millivolts • [5% voltage of AA battery] • Dissolved organic molecules [negative charge] kept inside • Na+ - K+ balance

  8. Stimulus causes opening of Na+ gates & closing of K+ gates - • Threshold [~ +30 mV] • all - or - nothing response • Action potential localized electrical event • Changes permeability of region immediately ahead • changes in K+ & Na+ gates • domino effect • propagation of signal • Intensity of stimuli (i.e. pinch vs. punch) = number of neurons firing • Speed on impulse based on diameter of axon & amount of myelination [wire for internet]

  9. Myelin Sheath • Resembles chain of beads • Prevents ions from flowing through membranes • Na+ channels highly concentrated at nodes • Allows signal to travel faster because impulse “jumps” from node of Ranvier to node of Ranvier (with myelin sheath (225 mph / without 11 mph) • MS  destruction of mylin sheath by own immune system (progressive loss of signal conduction, muscle control & brain function)

  10. Neurons Communicate at Synapses • Electrical [no synapse] • common in heart & digestive tract - maintains steady, rhythmic contraction • All cells in effector contain receptor proteins for neurotransmitters • Chemical - skeletal muscles & CNS • presence of gap (SYNAPTIC CLEFT) which prevents action potential from moving directly to receiving neuron • ACTION POTENTIAL (electrical) converted to CHEMICAL SIGNAL at synapse (molecules of neurotransmitter) then generate ACTION POTENTIAL (electrical) in receiving neuron

  11. Overview of Transmission of Nerve Impulse • Action potential synaptic knob opening of Ca+ channels • neurotransmitter vesicles fuse with membrane • release of neurotransmitter into synaptic cleft • binding of neurotransmitter to protein receptor molecules on receiving neuron membrane • opening of ion channels • triggering of new action potential • Neurotransmitter is broken down by enzymes & ion channels close -- effect brief and precise

  12. Nerve Impulse • Presynaptic neuron • Vesicles • [Calcium channels] • Synaptic cleft • Postsynaptic neuron • Neurotransmitter receptor

  13. Nerve Impulse • Action potential  synaptic knob  opening of Ca+ channels • neurotransmitter vesicles fuse with membrane • release of neurotransmitter into synaptic cleft Ca2+

  14. Nerve Impulse • Action potential • neurotransmitter vesicles fuse with membrane • release of neurotransmitter into synaptic cleft

  15. Action potential • binding of neurotransmitter to protein receptor molecules on receiving neuron membrane • opening of sodium channels • triggering of new action potential

  16. Neurotransmitters • Catecholamine Neurotransmitters • Derived from amino acid tyrosine • Dopamine [Parkinson’s], norepinephrine, epinephrine • Amine Neurotransmitters • acetylcholine, histamine, serotonin • Amino Acids • aspartic acid, GABA, glutamic acid, glycine • Polypeptides • Include many which also function as hormones • endorphins

  17. Transmission of signals based on MULTIPLE STIMULI • combined excitatory & inhibitory neurons • Inhibition in Pre-synaptic neuron • Ca+ channels blocked • stops release of neurotransmitter • Inhibition in Post-synaptic neuron • opens Cl- channels • makes interior more [-] • increase permeability of K+ ions • makes interior more [-]

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