Nerve Impulses

1. Nerve Impulses

2. How does an impulse travel along a nerve pathway? Review “Best of”, filling in your notes as you go. Effector Interneuron Motor neuron Receptor Sensory neuron Stimulus C B F D E A

3. Nerve impulses have a domino effect. Through a chain of chemical events, the dendrites pick up an impulse that’s shuttled through the axon and transmitted to the next neuron.

4. The entire impulse passes through a neuron in about 7 milliseconds- faster than a lightning strike. Introductory animation

5. NaK pumps in the cell membrane actively transport 3 Na+ ions out of the cell for every 2 K+ ions pumped into the cell The result- the interior of the cell is negatively charged with respect to the exterior- polarization Resting potential animation and quiz Step 1Resting Potential(the nerve fiber is not sending a signal)

7. A threshold stimulus is received. (the stimulation level that must be exceeded to elicit a nerve impulse) Na+ channels in the membrane open and Na+ diffuses inward depolarizing the membrane Step 2 Depolarization

8. What charge are sodium ions? • + • What will happen to the charge inside of the neuron? • It will become more + Depolarization animation

9. K+ channels in the membrane open K+ diffuse outward, repolarizing the membrane Repolarizing animation Step 3Repolarization

10. The resulting action potential causes a local bioelectric current that stimulates adjacent portions of the membrane The wave of action potential travels the length of the nerve fiber as a nerve impulse Action potential propagation animation Step 4Action Potential

11. Summary of Nerve Impulse • Nerve impulse summary video

12. Dramatizing an Action Potential 2. What happens to the charge during an action potential? 1. What is the name of the stimulus that causes an action potential? +++ ------- +++ ---- +++ ---- Threshold stimulus!!!! +++ ------+++------++++ +++ ------- +++ ---- +++ ---

13. Dramatizing an Action Potential 3. During rest, what is the charge on the outside of the cell membrane? Resting 1. What part of the neuron does this rectangle represent? Neuron Cell Body +++ ++++ +++ ++++ +++ 2. What branch is this? Axon +++ ++++ +++ ++++ +++ ++

14. Complete Nerve Impulse Homework

15. The Synapse • A synapse or synaptic cleft is a gap that separates the axon of one neuron and the dendrites of the next neuron. • *Neurons do not touch. • Chemicals carry messages across the synapse.

16. Structures of the synapse 1 Presynaptic cell 2 Synaptic knob 3 7 8 4 6 5 Postsynaptic cell Axon, Dendrite, Mitochondria, Neurotransmitter, Receptor site, Synaptic cleft, Synaptic knob, Synaptic vesicle

17. What’s happening? Arrival of the nerve impulse

18. Arrival of the nerve impulse Opening of the calcium channels Binding of Ca2+ to synaptic vesicles, neurotransmitter released into the gap Neurotransmitter binds to receptor Na+ enter the Ligand-gated channel Action potential generated in postsynaptic neuron

20. The synapse animation

21. Synaptic transmission Excitatory • “+” charged ions are released into postsynaptic neuron • May trigger a nerve impulse Inhibitory • “-” charged ions are released into postsynaptic neuron • Less likely a threshold stimulus will be reached

22. Something else to think about….. The synaptic knobs of a thousand or more neurons may communicate with the dendrites and cell body of a single postsynaptic neuron. What will happen if both excitatory and inhibitory signals are received?

23. Dramatize it! Dendrite neurotransmitters receptor Na+ receptor Axon synapse Dendrite Cell Body Cell Body Cl- • Needed: • Presynaptic Neuron • Dendrite (1 student) • Cell Body (1 student) • Axon (Row 3) • Calcium (1 student) • Synaptic Vesicles (4 students) • Neurotransmitters (2 students) Synaptic knob • Postsynaptic Neuron • Receptors (4 students) • Sodium Ion (1-2 students) • Chlorine Ion (1-2 student) • Dendrite Branch (3 students) • Cell body (1 student)