Neurons and Nervous Systems

1. Neurons and Nervous Systems

2. Nervous System Function sensory input integration central nervous system motor output peripheral nervous system

3. Organization of Nervous Systems correlated with body symmetry cnidarians and echinoderms nerve net flatworms, annelids, vertebrates exhibit cephalization nerve cord ganglia vs. brain

6. Nervous Tissue neuron cell body axon myelin sheath nodes of Ranvier dendrite synapse neurotransmitter

10. Nervous Tissue glial cells blood-brain barrier

12. Functional Organization sensory neurons interneurons motor neurons

13. Vertebrate Nervous System central nervous system brain and spinal cord peripheral nervous system

14. Nervous Tissue cell bodies in the CNS are termed nuclei cell bodies in the PNS are termed ganglia nerve fibers in the CNS are termed tracts nerve fibers in the PNS are termed nerves

15. Electrical Properties of Cells voltage ions carry electrical charges across membranes

16. Electrical Properties of Cells membrane potential resting potential action potential

17. Ion Pumps and Channels selective pumps or channels responsible for generating resting and action potentials Na+/K+ pump voltage-gated channels chemically gated channels

20. Equilibrium Potential electrochemical potential is dependent on: concentration of ion species inside a cell are different from those outside ion channels are selectively permeable to ions

21. Equilibrium Potential concentration of ions inside cell differs from outside cell permeant ions diffuse down their concentration gradient creates an electromagnetic force that pulls ion in opposing direction because of an imbalance in charges membrane potential that balances the diffusion of a permeant ion and the emf

24. Nernst Equation used to predict the equilibrium potential for one ion

25. Alteration of Membrane Potential depolarization hyperpolarization

27. Electrical Transmission changes in membrane potential at one site on the membrane causes changes along adjacent regions creates flow of electric current doesn’t typically travel far because membranes are permeable to ions

28. Action Potential all-or-none response threshold level of depolarization needed to trigger an action potential reflects the need to trigger the opening of the voltage-gated sodium channels

29. Action Potential rising phase (depolarization) as sodium channels open, Na+ ions flow into cell, depolarizes the cell more and more sodium channels open opening of sodium channels drives the membrane potential to a peak of the Nernst equilibrium potential for Na+

30. Action Potential peak action potential peaks at around +55 mV = Nernst equilibrium potential for Na+

31. Action Potential falling phase (repolarization) membrane potential returns to resting potential Na+ channels move into an inactive state go to an inactivated state after 1-2 msec after first opening inactivated = can NOT be reopened delayed voltage-gated K+ channels open open after about 1-2 msec of threshold depolarization cause the hyperpolarization after the action potential because open K+ channels make the K+ permeability higher than at rest and membrane more (-) on inside hyperpolarization causes K+ channels to close

33. Refractory Period 1. absolute refractory period Na+ channels are inactive and CAN NOT be opened no matter how much the membrane is depolarized at this time- another action potential can not be generated 2. relative refractory period as membrane repolarizes, triggers the Na+ channels to move from an inactive state to a closed state once Na+ channel is in the closed state can be opened again with depolarization

34. Conduction of Action Potential Why is the event all-or-nothing? depolarization in one area causes depolarization along adjacent regions travels unidirectionally because previous part of membrane is in refractory period

37. Saltatory Conduction impulse propagation where depolarization occurs only at the nodes of Ranvier ion channels are located at the nodes depolarization occurs at one node spreads to the next node where another depolarization event occurs speeds the transmission of the impulse

40. Synapses chemical presynaptic cell ? neurotransmitter ? postsynaptic cell neurotransmitter release dependent on Ca2+ channels

43. Summation integration via combining EPSP and IPSP EPSP depolarize IPSP hyperpolarize

46. Synapses electrical neurons connected by gap junctions speed of transmission enhanced, but no ability to integrate

47. Neurotransmitters released into synaptic cleft action depends on receptor it binds