1. Neurons & Nervous Systems

2. nervous systems connect distant parts of organisms; vary in complexity Figure 44.1

3. Nervous System Components neurons –obtain information –transform information into signals –transmit information –integrate (process) information –transmit responsive information

4. Nervous System Components glial cells (outnumber neurons) –provide nutrients to neurons –maintain ionic environment for neurons –remove debris –guide neuron development –insulate neurons

5. Schwann cells insulate peripheral neurons Figure 44.3

6. Nervous System Components glial cells (outnumber neurons) –provide nutrients to neurons –maintain ionic environment for neurons –remove debris –guide neuron development –insulate neurons –form blood-brain barrier

7. brains vary in complexity

8. Nervous System Components ganglia –clusters of neurons –information processing centers brain –large, dominant pair of ganglia spinal cord –with brain, forms central nervous system (CNS) of vertebrates

9. Nervous System Components peripheral nervous system –connects sensory systems to CNS –connects CNS to effectors

10. Neurons several functionally distinct parts vary in size, complexity, organization generate nerve impulses (action potentials) communicate with other cells through synapses –axon terminal plasma membrane releases neurotransmitters –target cell plasma membrane binds neurotransmitters –targets include neurons, muscle, gland cells

11. dendrites cell body axon hillock axon axon terminals Figure 44.2

12. variation in # of connections, length of transmission Figure 44.2

13. Neuronal Networks collect information, process information and respond to information consist of at least –sensory neuron –motor neuron –muscle cell most neurons form 1000’s of synapses, participate in multiple neuronal networks

14. resting potential Figure 44.4

15. Nerve impulses cytoplasm is more negative than environment voltage difference is measured across the plasma membrane –membrane potential –resting potential in unstimulated neurons -60 mV –action potential a brief reversal of membrane polarity can be transmitted along a neuronal axon

16. membrane potential electrical potential (voltage) is the tendency of charged particles to move between two locations membrane potential represents the tendency of ions to cross the membrane –ions cannot freely cross the hydrophobic membrane –ion channels and pumps enable ion flow across the cell membrane –dominant ions are Na +, Cl -, K + & Ca 2+

17. Pumps and Channels channels permit diffusion of ions across the membrane –channels are more or less selective –channels may be open or gated open channels are unrestricted voltage-gated channels respond to voltage changes chemically-gated channels respond to specific chemical signals

18. Na & K channels Figure 44.5

19. Pumps and Channels pumps actively transport ions across the membrane –sodium-potassium (Na + -K + ) pump dominant neuronal plasma membrane pump pumps Na + out, K + in maintains cytoplasmic K + higher and Na + lower than external

20. Na-K pump Figure 44.5

21. K + channels maintain resting potential Figure 44.6

22. membrane depolarization by gated Na + channels Figure 44.8

23. membrane hyperpolarization by gated Cl - channels Figure 44.8

24. Pumps and Channels gated channels can alter membrane polarity –opening Na + channels depolarizes the membrane –opening K + or Cl - channels hyperpolarizes the membrane transmission and processing of information occurs through changes in neuronal membrane potentials

25. Nerve Impulses (Action Potentials) opening gated channels results in ion flow –ion flow in a neuron dissipates over distance –ion flow cannot transmit a signal to a distant target localized ion flow can stimulate nearby voltage-gated channels –if enough Na + enters, neighboring channels will open –if each channel triggers its neighbor, a signal can travel the length of a neural axon

26. action potential Figure 44.9

27. Nerve Impulses (Action Potentials) an action potential –results from a 1-2 millisecond opening of Na + channels –membrane potential rises rapidly (spike) then returns to resting potential –Na + channels cannot open for 1-2 milliseconds following an action potential (refractory period)

28. Nerve Impulses (Action Potentials) an action potential –travels down an axon without loss of strength depolarization opens Na + gates short range current flow depolarizes nearby membrane neighboring Na + gates open

29. action potential propagation Figure 44.10

30. Nerve Impulses (Action Potentials) action potentials travel rapidly along nerves –rate of transmission is related to diameter of axon thicker axon propagates signal faster propagation rate in vertebrates is enhanced by glial cells –Schwann cells form discontinuous sheath gaps = nodes of Ranvier action potentials fire at nodes

31. nodes of Ranvier Figure 44.12

32. saltatory propagation Figure 44.12

33. Nerve Impulses (Action Potentials) action potential at a node of Ranvier –propagates by current flow to next node –current flow is supported by myelin sheath –saltatory (jumping) propagation is more rapid than continuous propagation

34. Synaptic Communication synapse –presynaptic cell membrane –postsynaptic cell membrane –synaptic cleft neuromuscular junction –motor neuron => muscle cell –one axon, many branches & axon terminals –axon terminals produce neurotransmitter

35. a neuromuscular junction Figure 44.13

36. Synaptic Communication neuromuscular junction –presynaptic membrane releases acetylcholine from vesicles by exocytosis –acetylcholine diffuses across synaptic cleft – postsynaptic membrane (motor end plate) receptors bind acetylcholine and open Na + /K + channels –motor end plate depolarizes –acetylcholinesterase degrades acetylcholine in synaptic cleft

37. acetylcholine function Figure 44.14

38. Synaptic Communication presynaptic axon –transmits a signal in response to action potential arrival –action potential triggers voltage-gated calcium channel –calcium influx causes acetylcholine vesicles to fuse with presynaptic membrane

39. Synaptic Communication postsynaptic membrane –motor end plate receives signal, opens channels, depolarizes –motor end plate does not fire action potentials (too few voltage-gated channels) –motor end plate must transmit enough Na + to spread depolarization to neighboring areas –depolarization of neighboring plasma membrane fires action potentials

40. synaptic transmission at a neuro- muscular junction Figure 44.13

41. Synaptic Communication excitatory & inhibitory neuronal synapses –different presynaptic neurotransmitters –different postsynaptic receptors excitatory synapses depolarize (EPSP) inhibitory synapses hyperpolarize (IPSP) –e.g. GABA or glycine causes Cl - channels to open

42. Information Processing Nerve Impulse (action potential) is all-or-none firing action potential depends on sum of all incoming information –axon hillock receives EPSP/IPSP from all dendrites and cell body –IPSPs oppose depolarization by EPSPs –axon hillock fires action potential when membrane depolarizes to threshold

43. Information Processing axon hillock sums EPSPs & IPSPs –spatial summation adds effects of all synapses at one time –temporal summation adds effects of synapses firing rapidly over time

44. spatial and temporal summation at the axon hillock Figure 44.15

45. Information Processing presynaptic excitation and inhibition –synapse between axon terminal of one neuron and axon terminal of another –first neuron regulates amount of neurotransmitter released by axon terminal responding to action potential

46. Information Processing neurotransmitter receptors –ionotropic receptors are ion channels –metabotropic receptors influence ion channels indirectly

47. ionotropic receptors Figure 44.17

48. a metabotropic receptor Figure 44.16

49. Information Processing electrical synapses (gap junctions) –very rapid –bi-directional –excitatory only –unable to perform termporal summation –require large membrane surface area –uncommon in nervous systems that utilize integration and exhibit learning

50. Information Processing neurotransmitters –more than 25 known –each may bind more than one receptor –response is determined by the receptor

51. Table 44.1