Essential knowledge 3.E.2

1. Essential knowledge 3.E.2 Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses

2. The neuron is the basic structure of the nervous system that reflects function.

3. Hear about the neuron and how it functions from MIT Professor, Eric Lander, famous for heading up the Human Genome Project! (Homework: 50 minute lecture, but well worth the time.) • https://www.youtube.com/watch?v=BAldLXDPWZM

4. 1. A typical neuron has a cell body, axon and dendrites. Many axons have a myelin sheath that acts as an electrical insulator. 2. The structure of the neuron allows for the detection, generation, transmission and integration of signal information. 3. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron.

5. 1. Membranes of neurons are polarized by the establishment of electrical potentials across the membranes. 2. In response to a stimulus, Na+ and K+ gated channels sequentially open and cause the membrane to become locally depolarized. 3. Na+/K+ pumps, powered by ATP, work to maintain membrane potential. Action potentials propagate impulses along neurons.

6. An action potential can travel long distances by regenerating itself along the axon • At the site where the action potential is generated, usually the axon hillock, an electrical current depolarizes the neighboring region of the axon membrane Conduction of Action Potentials

7. Action potentials travel in only one direction: toward the synaptic terminals • Which direction does the action potential travel??

8. Fig. 48-11-1 Axon Plasma membrane Action potential Cytosol Na+

9. Fig. 48-11-2 Axon Plasma membrane Action potential Cytosol Na+ Action potential K+ Na+ K+

10. Fig. 48-11-3 Axon Plasma membrane Action potential Cytosol Na+ Action potential K+ Na+ K+ Action potential K+ Na+ K+

11. The speed of an action potential increases with the axon’s diameter • In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase • Myelin sheaths are made by glia— oligodendrocytesin the CNS and Schwann cells in the PNS Conduction Speed

12. Fig. 48-12a Node of Ranvier Layers of myelin Axon Schwann cell Schwann cell Nodes of Ranvier Nucleus of Schwann cell Axon Myelin sheath

13. Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage-gated Na+ channels are found • Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction Node of Ranvier Layers of myelin Axon Schwann cell Schwann cell Nodes of Ranvier Nucleus of Schwann cell Axon Myelin sheath

14. In most animals, transmission across synapses involves chemical messengers called neurotransmitters. • Acetylcholine • Epinephrine • Norepinephrine • Dopamine • Serotonin • GABA 2. Transmission of information along neurons and synapses results in a response. 3. The response can be stimulatory or inhibitory. The location and functions of each of these neurotransmitters will not be on the AP Exam! Transmission of information between neurons occurs across synapses.

15. At electrical synapses, the electrical current flows from one neuron to another • At chemical synapses, a chemical neurotransmitter carries information across the gap junction • Most synapses are chemical synapses Concept 48.4: Neurons communicate with other cells at synapses

16. Fig. 48-14 Postsynaptic neuron Synaptic terminals of pre- synaptic neurons 5 µm

17. The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal • The action potential causes the release of the neurotransmitter • The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell

18. Fig. 48-15 5 Na+ K+ Synaptic vesicles containing neurotransmitter Presynaptic membrane Voltage-gated Ca2+ channel Postsynaptic membrane Ca2+ 1 4 6 2 3 Synaptic cleft Ligand-gated ion channels

19. Curare is a drug that causes paralysis. As an acetylcholine antagonist, it binds to acetylcholine receptors at nerve-muscle junctions, preventing communication between nerves and muscles. • Doctors sometimes use curare to immobilize patients during extremely delicate surgery. • South American tribes have long used curare as an arrow poison. Fun Fact

20. Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell • Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential Generation of Postsynaptic Potentials

21. Postsynaptic potentials fall into two categories: • Excitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward threshold • Inhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move the membrane potential farther from threshold

22. Different regions of the vertebrate brain have different functions. Examples include: • Vision • Hearing • Muscle movement • Abstract thought and emotions • Neuro-hormone productio • Forebrain (cerebrum), midbrain (brainstem) and hindbrain (cerebellum) • Right and left cerebral hemispheres in humans

23. ✘✘ The types of nervous systems, development of the human nervous system, details of the various structures and features of the brain parts, and details of specific neurologic processes are beyond the scope of the course and the AP Exam.