4. Transmission 1. innervation - cell body as integrator 2. action potentials (impulses) - axon hillock 3. myelin sheath

5. 4. Voltage-gated ion channels - large concentration in hillock - found along the axon

6. Neuron signaling 1. afferent vs. efferent 2. interneurons 3. circuits

7. 4. synapses - presynaptic terminal - postsynaptic terminal - neurotransmitters - ligand-gated ions channels on postsynaptic membrane

8. Nervous System A. Organization of neurons 1. circuits for stimulus-response 2. exchange of information Figure 7.1

9. Central Nervous System 1. brain 2. nerve cord - ganglia associated

12. 3. axons project to and from the body (CNS  PNS) 4. cell bodies in CNS except some in ganglia

13. Support cells (neuroglia) - more abundant than neurons - more mitotic capability

14. Membrane Potentials A. Measured across the cell membrane 1. use internal and external electrodes - reference electrode and recording microelectrode

15. 2. measure potential difference between ICF and ECF (voltage) 3. determines V m (membrane potential) - intracellular potential relative to extracellular potential - extracellular potential considered zero

16. B. Resting potential V rest 1. steady state negative potential of ICF - usually between -20 and -100 mV 2. reflects an electrical gradient (energy)

17. Electrical Properties of Membranes A. Conductance (g) 1. conferred by ion channels 2. is inversely related to resistance

18. 3. Ohm’s law: ∆V m = ∆I x R ∆V m = change in voltage across the membrane ∆I = current across the membrane (in amps) R = electrical resistance of the membrane (in Ohms)

19. Electrical Properties of Membranes B. Capacitance (ability to store an electric charge) 1. conferred by membrane itself bilayer is an insulating layer separating charges

20. 2. capacitative current - ability of ions to interact across the membrane without crossing the bilayer

21. - charges collect on either side of the membrane - energy of the charges “stored” by the capacitor

22. Electrochemical Potentials A. Factors responsible 1. ion concentration gradients on either side of the membrane - maintained by active transport

23. Electrochemical Potentials A. Factors responsible 2. selectively permeable ion channels

25. B. Gradients not just chemical, but electrical too 1. electromotive force can counterbalance diffusion gradient 2. electrochemical equilibrium

26. C. Establishes an equilibrium potential for a particular ion based on Donnan equilibrium

28. Assume Cl - cannot cross the membrane

29. Nernst equation (pp. 69-71) 1. What membrane potential would exist at the true equilibrium for a particular ion? - What is the voltage that would balance diffusion gradients with the force that would prevent net ion movement? 2. This theoretical equilibrium potential can be calculated (for a particular ion). E ion = RT ln [X] outside zF [X] inside

30. E Na,K,Cl = RT P K [K + ] out + P Na [Na + ] out + P Cl [Cl - ] in P K [K + ] in + P Na [Na + ] in + P Cl [Cl - ] out F _____________________________ ln ___ Goldman Equation 1. quantitative representation of V m when membrane is permeable to more than one ion species 2. involves permeability constants (P) pp 72-73

31. Resting Potential A. V rest 1. represents potential difference at non-excited state -30 to -100mV depending on cell type 2. not all ion species may have an ion channel 3. there is an unequal distribution of ions due to active pumping mechanisms - contributes to Donnan equilibrium - creates chemical diffusion gradient that contributes to the equilibrium potential

32. Resting Potential B. Ion channels necessary for carrying charge across the membrane 1. the  the concentration gradient, the greater its contribution to the membrane potential 2. K + is the key to V rest (due to increased permeability) - opening K + channels will greatly alter V rest

33. Resting Potential C. Role of active transport E Na is + 63 mV in frog muscle V m is -90 to -100mV in frog muscle