1. Nervous Systems Three Main Functions: 1. Sensory Input 2. Integration 3. Motor Output

2. Two Main Parts of Vertebrate Nervous Systems Central nervous system (CNS) –brain and spinal cord –integration Peripheral nervous system (PNS) –network of nerves extending into different parts of the body –carries sensory input to the CNS and motor output away from the CNS

3. Two Cell Types in Nervous Systems Neurons –Cells that conduct the nerve impulses Supporting Cells –Neuroglia

4. Figure 48.2x Neurons

5. Three Major Types of Nerve Cells Sensory neurons –communicate info about the external or internal environment to the CNS Interneurons –integrate sensory input and motor output –makes synapses only with other neurons Motor neurons –convey impulses from the CNS to effector cells

7. Supporting Cells - Neuroglia provide neurons with nutrients, remove wastes Two important types in vertebrates –Oligodendrocytes – myelin sheath in CNS –Schwann cells -myelin sheath in PNS

8. Myelin Sheath Formation

10. Conduction of the Nerve Impulse Membrane Potential –Voltage measured across a membrane due to differences in electrical charge –Inside of cell is negative wrt outside Resting potential of neuron = -70 mV

11. Figure 48.6 Measuring membrane potentials

13. 1. Carrier in membrane binds intracellular sodium. 2. ATP phosphorylates protein with bound sodium. 3. Phosphorylation causes conformational change in protein, reducing its affinity for Na +. The Na + then diffuses out. 4. This conformation has higher affinity for K +. Extracellular K + binds to exposed sites. 5. Binding of potassium causes dephosphorylation of protein. Extracellular Intracellular ATP ADP PiPi P + K+K+ Na + 6. Dephosphorylation of protein triggers change to original conformation, with low affinity for K +. K + diffuses into the cell, and the cycle repeats. PiPi PiPi PiPi Sodium-Potassium Pump

14. Excitable Cells Neurons & muscle cells Have gated ion channels that allow cell to change its membrane potential in response to stimuli

16. Gated Ion Channels Some stimuli open K+ channels –K+ leaves cell –Membrane potential more negative –hyperpolarization Some stimuli open Na+ channels –Na+ enters cell –Membrane potential less negative –depolarization

17. Gated Ion Channels Strength of stimuli determines how many ion channels open = graded response

18. Nerve Impulse Transmission

19. Action Potentials Occur once a threshold of depolarization is reached –-50 to –55 mV All or none response (not graded) –Magnitude of action potential is independent of strength of depolarizing stimuli Hyperpolarization makes them less likely

20. Membrane potential (mV) 2. Rising Phase Stimulus causes above threshold voltage +50 0 12 3 –70 Time (ms) 1. Resting Phase Equilibrium between diffusion of K + out of cell and voltage pulling K + into cell Voltage-gated potassium channel Potassium channel Voltage-gated sodium channel Potassium channel gate closes Sodium channel activation gate closes. Inactivation gate opens. Sodium channel activation gate opens 3. Top curve Maximum voltage reached Potassium gate opens 4. Falling Phase Potassium gate open Undershoot occurs as excess potassium diffuses out before potassium channel closes Equilibrium restored Na + channel inactivation gate closes K+K+ Na + Na + channel inactivation gate closed

21. Refractory Period During undershoot the membrane is less likely to depolarize Keeps the action potential moving in one direction

22. Propagation of Action Potential Action potential are very localized events DO NOT travel down membrane Are generated anew in a sequence along the neuron

23. Cell membrane Cytoplasm resting repolarized depolarized + + + + + + + + + – – – – – – – – – + + + + + + + + + – – – – – – – – – – – + + + + + + + + + – – – – – – – + + + + + + + – – – – – – – – – + + + + – – + + + + + – – + + – – – – – + + + + + – – + + – – – – – + + – – + + + + – – – + + – – – – + + + – – + + – – – + + + + – – + + + – – – – + + + + + + + – – – – – – – – – + + – – + + + + + + + + + – – – – – – – Na + K+K+ K+K+ K+K+ K+K+ K+K+ K+K+

24. Saltatory Conduction

25. Transfer of Nerve Impulse to Next Cell Synapse –the gap between the synaptic terminals of an axon and a target cell

26. Transfer of Nerve Impulse to Next Cell Electrical synapses –Gap junctions allow ion currents to continue Chemical synapses –More common –Electrical impulses must be changed to a chemical signal that crosses the synapse

27. Synapses

28. Neurotransmitters

29. Effects of Cocaine

30. Receptor protein Drug molecule Synapse 1. Reuptake of neuro- transmitter by transporter at a normal synapse. 2. Drug molecules block transporter and cause overstimulation of the postsynaptic membrane. 3. Neuron adjusts to overstimulation by decreasing the number of receptors. 4. Decreased number of receptors make the synapse less sensitive when the drug is removed. Neurotransmitter Transporter protein Transporter protein Dopamine Cocaine Receptor protein

31. Human Cerebrum Cerebellum Spinal cord Cervical nerves Thoracic nerves Lumbar nerves Femoral nerve Sciatic nerve Tibial nerve Sacral nerves Nerve net Nerve cords Associative neurons Brain Giant axon Mollusk Echinoderm Central nervous system Peripheral nerves Brain Ventral nerve cords Radial nerve Nerve ribs Cnidarian Flatworm Earthworm Arthropod Diversity of Nervous Systems