Part Fundamentals of Physiology Part II Food, Energy, and Temperature

1. Part Fundamentals of Physiology • Part II Food, Energy, and Temperature • Part III Integrating systems • Part IV Movement and Muscle • Part V Oxygen, Carbon dioxide, and Internal Transport • Part VI Water, Salts and Excretion

2. Part III Integrating System • Chp 11 Neurons • Chp 12 Synapses • Chp 13 Sensory processes • Chp 14 Nervous system organization and biological clocks • Chp 15 Endocrine and Neuroendocrine Physiology • Chp 16 Reproduction • Chp 17 Integrating Systems at Work: Animal Navigation

3. Chp12Synapse Integrating System

4. http://trc.ucdavis.edu/biosci10v/bis10v/week10/08nervevolution.htmlhttp://trc.ucdavis.edu/biosci10v/bis10v/week10/08nervevolution.html

6. Vertebrate nervous system

7. Synapses: electrical or chemical

8. Electrical synapses • Signals are transmitted instantly • Can be transmitted both ways • Found in simpler animals: squid, crayfish

9. Chemical synapse: characteristics • Synapses have a discontinuity • Complex series of events • Post-synaptic response can be modulated • Can be excitatory or inhibitory • Can amplify signal • Only one way • Are plastic (can be modified) • Various processes: • Ionotropic • metabotropic

10. Synaptic excitability • If Na+ channels open: membrane potential less negative  excitation  EPSP • If K+ channels open: membrane potential more negative inhibition IPSP • Signals can add up in time (temporal summation) • Or in space (spatial summation) • Synapses are present on the dendrites (axodendritic) or on the soma (axosomatic)

11. Synaptic events • AP reached axon terminal • Voltage gated Ca++ channels open  Ca++ rush in • They activate enzymes which promote vesicle fusion and opening at the cell membrane  neurotransmitter empties into the synapse • The neurotransmitter binds to the receptors located on the post synaptic neuron • The channels open (most often Na+) triggering a less negative voltage • In case of a neuromuscular junction, the muscle fiber depolarizes • Neurotransmitter, still present in the synapse, must be degrades quick if the synapse s to be responsive  neurotransmitter is degraded or taken back (reuptake)

13. AP - EPSP - IPSP

14. The neurotransmitter is broken down and recycled

15. The pre-synaptic neuron releases vesicles full of neurotransmitter

16. Neurotransmitters • Small-molecule neurotransmitters • Cholinergic • Noradrenergic • Neuroactive peptides • Dale’s law: a differentiated neuron releases only one kind of neurotransmitter

17. Neurotransmitter’s characteristics • 1- present at the pre-synaptic terminal (along with the synthetic machinery) • 2- released in the synapse upon pre-synaptic stimulation • 3- if added, it mimics the pre-synaptic stimulation • 4- a mechanism for removal should exists • 5- effects of some drugs should mimic the potential neurotransmitter

18. Vertebrate neurotransmitters • Most CNS synapses use amino acid neurotransmitters • Glutamate for EPSPs • Glycine, GABA for IPSPs • Biogenic amine (Ach, Ne, Dopamine, serotonin) are present in few neurons but these neurons project widely • Peptides are released with other neurotransmitters and modulate the signal • Different post-synaptic receptors (for the same neurotransmitter) will induce different effects • Peptide neurotransmitters are synthesized in the body of the neuron, not the axon terminal – can be depleted • Ach, GABA, glutamate, dopamine, serotonin also found in invertebrates

19. Types of receptors • Ionotropic • Fast – channel • Ach nicotinic (ex: neuromuscular synapse, ray electric organ • Metabotropic

20. Receptors

21. Ionotropic receptors

22. Metabotropic receptors • Act via cAMP and protein kinase • Can act through IP3 and DAG, calmodulin • Modulate post-synaptic permeability and pre-synaptic inhibition

23. Synaptic plasticity • Change in synaptic strength over time • Learning and memory • Synaptic facilitation: increase in amplitude of postsynaptic potential in response to successive pre-synaptic impulses • Synaptic antifacilitation or depression: opposite • Especially present in hippocampus and cerebral cortex

24. Aplysia • Habituation: decrease in intensity of a reflex response to a stimulus when the stimulus is presented repeatedly • Sensitization: prolonged enhancement of a reflex response to a stimulus which results from the presentation of a second stimulus that is novel or noxious

25. Non-associative conditioning • Habituation: after many stimulation, there is less neurotransmitter released by the presynapticneuron decreased EPSP on the postsynaptic neuron • The smaller signals are due to inhibition of calcium channels less calcium released • Sensitization due to a shock on the neuron from the head  increased EPSPs • More calcium released in facilitation

27. Classical conditioning • A conditioning signal triggers a response after a series of stimulus (ex: Pavlov’s dog and the bell) • Learning areas in vertebrates: hippocampus and cerebral cortex: • Long term potentiation LTP: long lasting enhancement of synaptic transmission following intense stimulation

28. LPT • Receptors: NMDA AMPA receptors • NMDAs, activated by glutamate, work only if the cell is depolarized • In resting state, it is blocked by Mg++ • The EPSP depends on activation of the AMPAs • During depolarization, the Mg++ is released, NMDAs are unblocked • Ca++ enters and activate various kinase

29. Memory • The LTP leads to increase numbers of AMPA receptors on the membrane increased response • Similarly, low Ca++ leads to removal of AMPA receptors  Long Term Depression • These changes induces protein synthesis from gene transcription • Also, effects at the level of the synapses themselves with changes in the dendrites