1. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition Solomon Berg Martin Chapter 39 Neural Signaling

2. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Neural signaling process Reception of information by a sensory receptor Transmission by afferent neuron to the central nervous system Integration by CNS interneurons Efferent neuron transmission Action by effectors

3. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Stimulus response

4. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Glial cells Support and nourish neurons Microglia are phagocytic cells Astrocytes –Some are phagocytic –Others help regulate composition of the CNS extracellular fluid –May induce and stabilize synapses

5. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Oligodendrocytes Glial cells that form myelin sheaths around axons in the CNS Schwann cells Form sheaths around axons in the peripheral nervous system (PNS)

6. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Structure of a typical neuron A cell body contains the nucleus and most of the organelles Many branched dendrites extend from the cell body Single long axon extends from the cell body and forms branches called axon collaterals

7. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Structure of a multipolar neuron

8. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Dendrites receive stimuli and send signals to the cell body Axon transmits signals into its terminal branches that end in synaptic terminals Many axons are surrounded by an insulating myelin sheath formed of Schwann cells

9. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Nodes of Ranvier Gaps in the sheath between successive Schwann cells Nerve Several hundred axons wrapped in connective tissue Ganglion Mass of neuron cell bodies

10. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Nerve structure

11. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Neuron resting potential In a resting neuron, the inner surface of the plasma membrane is negatively charged compared with the outside Potential difference of about -70 millivolts (mV) across the membrane

12. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Differences in concentrations of specific ions—Na + (sodium) and K + (potassium)—inside the cell relative to the extracellular fluid Selective permeability of the plasma membrane to these ions Ions pass through specific passive ion channels

13. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling K + leaks out more readily than Na + can leak in Cl - (chlorine) ions accumulate along the inner surface of the plasma membrane Gradients that determine the resting potential are maintained by ATP

14. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Resting potential

15. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Sodium-potassium pumps Continuously transport three sodium ions out of the neuron for every two potassium ions transported in

16. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Voltage-activated ion channels

17. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Depolarized membrane Stimulus caused the membrane potential to become less negative Hyperpolarized membrane Membrane potential becomes more negative than the resting potential

18. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Graded potential Local response that varies in magnitude depending on the strength of the applied stimulus Fades out within a few mm of its point of origin

19. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Action potential Wave of depolarization that moves down the axon –Voltage across the membrane declines to a critical point –Voltage-activated ion channels open –Na + flows into the neuron –Action potential is generated

20. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Action potential

21. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Action potential is an all-or- none response No variation exists in the strength of a single impulse Membrane potential either exceeds threshold level, leading to transmission of an action potential, or it does not

22. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Repolarization As the action potential moves down the axon, repolarization occurs behind it During depolarization, the axon enters a refractory period –Time when it cannot transmit another action potential

23. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Resting state Depolarization

24. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Repolarization Return to resting state

25. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Continuous conduction Takes place in unmyelinated neurons Involves the entire axon plasma membrane

26. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Saltatory conduction More rapid than continuous conduction Takes place in myelinated neurons Depolarization skips along the axon from one node of Ranvier to the next

27. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Saltatory conduction

28. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Synapses Junction between two neurons or between a neuron and effector Most synapses are chemical Transmission depends on release of neurotransmitter from synaptic vesicles in the synaptic terminals of a presynaptic neuron

29. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Neurotransmitters Acetylcholine –Triggers contraction of skeletal muscle Glutamate –Main excitatory neurotransmitter in the brain GABA –Inhibitory neurotransmitter

30. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Biogenic amines –Norepinephrine –Serotonin –Dopamine –Play important roles in regulating mood –Dopamine is important in motor function

31. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Neuropeptides –Endorphinsm –Enkephalins Nitric oxide (NO) –Gaseous neurotransmitter that transmits signals from the postsynaptic neuron to the presynaptic neuron

32. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Synaptic transmission Calcium ions cause synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitter into the synaptic cleft Neurotransmitter combines with specific receptors on a postsynaptic neuron

33. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Synaptic transmission

34. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Neurotransmitter receptors Many are proteins that form ligand-gated ion channels Others work through a second messenger such as cAMP

35. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Excitatory and inhibitory signals Excitatory postsynaptic potential (EPSP) –Bring the neuron closer to firing Inhibitory postsynaptic potential (IPSP) –Move the neuron farther away from its firing level

36. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling A postsynaptic neuron integrates incoming stimuli and “decides” whether or not to fire Each EPSP or IPSP is a graded potential Varies in magnitude depending on the strength of the stimulus applied

37. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling The mechanism of neural integration is summation Process of adding and subtracting incoming signals By summation of several EPSPs, the neuron may be brought to critical firing level

38. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Temporal summation Repeated stimuli cause new EPSPs to develop before previous EPSPs have decayed Spatial summation Postsynaptic neuron stimulated at several different places

39. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Convergence Single neuron is controlled by converging signals from two or more presynaptic neurons Permits the CNS to integrate incoming information from various sources

40. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Divergence Single presynaptic neuron stimulates many postsynaptic neurons Allows widespread effect Reverberation Axon collateral synapses with an interneuron

41. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 39 Neural Signalling Reverberation