Nerve impulse

1. Nerve impulse • Action potential travels along an axon • Information passes from presynaptic neuron to postsynaptic cell

2. General properties of synapses • Electrical • Rare • Pre- and postsynaptic cells are bound by interlocking membrane proteins

3. General properties of synapses • Chemical synapses • More common • Excitatory neurotransmitters cause depolarization and promote action potential generation • Inhibitory neurotransmitters cause hyperpolarization and suppress action potentials

4. Cholinergic synapses • Release acetylcholine (ACh) • Information flows across synaptic cleft • Synaptic delay occurs as calcium influx and neurotransmitter release take appreciable amounts of time • ACh broken down • Choline reabsorbed by presynaptic neurons and recycled • Synaptic fatigue occurs when stores of ACh are exhausted

5. Figure 12.19 The Function of a Cholinergic Synapse PLAY Animation: Overview of a cholinergic synapse Figure 12.19.1

6. Figure 12.19 The Function of a Cholinergic Synapse Figure 12.19.2

7. Other neurotransmitters • Adrenergic synapses release norepinephrine (NE) • Other important neurotransmitters include • Dopamine • Serotonin • GABA (gamma aminobutyric acid)

8. Neuromodulators • Influence post-synaptic cells response to neurotransmitter • Neurotransmitters can have direct or indirect effect on membrane potential • Can exert influence via lipid-soluble gases PLAY Animation: Synaptic potentials, cellular integration, and synaptic transmission

9. Figure 12.21 Neurotransmitter Functions Figure 12.21a

10. Figure 12.21 Neurotransmitter Functions Figure 12.21b

11. Figure 12.21 Neurotransmitter Functions Figure 12.21c

12. Information processing • Simplest level of information processing occurs at the cellular level • Excitatory and inhibitory potentials are integrated through interactions between postsynaptic potentials

13. Postsynaptic potentials • EPSP (excitatory postsynaptic potential) = depolarization • EPSP can combine through summation • Temporal summation • Spatial summation • IPSP (inhibitory postsynaptic potential) = hyperpolarization • Most important determinants of neural activity are EPSP / IPSP interactions

14. Figure 12.22 Temporal and Spatial Summation Figure 12.22a

15. Figure 12.22 Temporal and Spatial Summation Figure 12.22b

16. Figure 12.23 EPSP – IPSP Interactions Figure 12.23

17. Presynaptic inhibition • GABA release at axoaxonal synapse inhibits opening calcium channels in synaptic knob • Reduces amount of neurotransmitter released when action potential arrives

18. Figure 12.24 Presynaptic Inhibition and Facilitation Figure 12.24

19. Presynaptic facilitation • Activity at axoaxonal synapse increases amount of neurotransmitter released when action potential arrives • Enhances and prolongs the effect of the neurotransmitter

20. Figure 12.24 Presynaptic Inhibition and Facilitation Figure 12.24

21. Rate of generation of action potentials • Neurotransmitters are either excitatory or inhibitory • Effect on initial membrane segment reflects an integration of all activity at that time • Neuromodulators alter the rate of release of neurotransmitters

22. Rate of generation of action potentials • Can be facilitated or inhibited by other extracellular chemicals • Effect of presynaptic neuron may be altered by other neurons • Degree of depolarization determines frequency of action potential generation

23. You should now be familiar with: • The two major divisions of the nervous system and their characteristics. • The structures/ functions of a typical neuron. • The location and function of neuroglia. • How resting potential is created and maintained.

24. You should now be familiar with: • The events in the generation and propagation of an action potential. • The structure / function of a synapse. • The major types of neurotransmitters and neuromodulators. • The processing of information in neural tissue.