Tube ends other sprouts are reabsorbed neuron

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Unformatted text preview: (small, myelinated) Large, myelinated ~120 m/sec Regeneration of Fibers Regeneration Damaged nerve fibers of PNS can be repaired IF soma & some neurilemma are intact neurilemma • After injury, severed distal end of axon & myelin sheath After degenerate & macrophages remove degenerate • Regeneration tube forms Regeneration (neurilemma & endoneurium) & axon stump sprouts new fiber ends until 1 finds r.tube ends • Other sprouts are reabsorbed • Neuron establishes connection Neuron w/ cells it innervated w/ CNS cannot regenerate neurons Electrophysiology of Neurons Electrophysiology How do neurons generate electrical signals & how are they How transformed into meaningful messages to next cell? transformed Electrical potentials= difference in [ions] btw 1-pt-to-another • ‘Potential energy’ (or polarized) can lead to an electrical Potential current (flow of ions) current Currents are created by movement of Na+, K+, etc. & are etc. turned on/off by gated-channels turned RMP= resting membrane potential results from 3 factors: resting • • • Diffusion of ions down [gradient] through p.membrane Diffusion [gradient] Selective permeability of p.membrane Electrical attraction of cations & anions K+ has greatest influence on RMP since plasma membrane is most permeable to it (40x more conc. inside cell) most Resting/Local Potentials Resting/Local Na+ 12x more conc. in ECF; some ions diffuse across membrane • Na-K pumps continually move ions ‘up’ [gradient] to compensate Na-K for ‘leaking’ membrane & maintain –RMP for • 3 Na+ out, 2 K+ in • Results in –70mV Pumps must continually restore equilibrium, thus, NS requires Pumps large amounts of ATP, glucose, O2 large • ~70% of ATP used in NS is by Na-K pumps Local potentials differ from AP’s (Table 12.2)• Neurons stimulated by chemicals, light, heat, mechanical Neurons distortion of plasma membrane distortion • Chemically stimulated dendrites open ligand-regulated Na-gates, Chemically ligand-regulated Na enters, ISF becomes ‘neutralized’ (charge ~0) Na • Depolarization= voltage shifts to less - charge Local Potentials Local Local potentials (cont.)• Na+ diffuse short distances along inside of plasma membrane & produce a current that travels towards trigger zone t...
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