Nerve Impulses

1. Nerve Impulses

2. Neuron Physiology Sending neuron impulses = action potential • change in electrical charge in cell membrane • depends on electrolytes • Sodium (Na+) highly concentrated outside of cells • Potassium (K+) highly concentrated inside cells • Ion movement • Move from high concentration to a low concentration passively • Na+/K+ moves ions actively using ATP

3. Creating a Resting Potential • Protein pumps • open and close • let ions through • Active pumps • against a gradient • Use ATP to work • Passive pumps • with the gradient • High to low concentration

4. Resting Potential (-70mV) #1. Resting Potential

5. Depolarization and Threshold Potential #2.) Depolarizing neuron (-62mV) Sodium rushes in when channels open which are stimulated by neurotransmitters #3.)Threshold is reached once enough sodium rushes in (-55 mV)

6. #4.) Neuron continues to depolarize as sodium continues to rush in. #5.) Repolarization occurs as K+ channels open and K+ moves outward causing inside of membrane to become negative again. Na+ Na+ 0mV to +20mV K+ Potassium channels open -70mV

7. Action Potential

9. A Nerve Impulse- a series of action potentials Nodes, myelin and action potentials: http://www.youtube.com/watch?v=DJe3_3XsBOg&feature=related

10. What happens when the nerve impulse reaches the end of the axon? • axon terminals • next to another neuron (as shown) or a muscle or gland • Gap called a synapse http://www.hhmi.org/biointeractive/neuroscience/molecular_mech.html Action Potential

11. Synapse

12. Neurotransmitters released at synapse

13. Saltatory nerve impulse conduction The action jumps large distances from node to node (1mm), a process that is called saltatory propagation.

14. Myelinated vs. unmyelinated neurons

15. Speed of a Nerve impulse • Temperature - higher the temperature=faster speed. Warm-blooded animals have faster responses than cold-blooded. • Axon diameter - larger the diameter=faster speed. Marine invertebrates, (who live at temperatures close to 0°C), developed thick axons to speed up their responses. This explains why squid have their giant axons. • Myelin sheath - Only vertebrates have a myelin sheath surrounding their neurons. The voltage-gated ion channels are found only at the nodes of Ranvier, and between nodes myelin sheath acts as a good electrical insulator. Increases the speed of propagation dramatically. • unmyelinated neurons –travel at about of 1 m/s • myelinated neurons-travel at about 100 m/s.

16. All or None Response The strength of a response of a nerve cell or muscle fiber is not dependent upon the strength of the stimulus. If a stimulus is above a certain threshold, a nerve or muscle fiber will fire. full response or no response at all. "The all-or-none law guarantees that once an action potential is generated it is always full size, minimizing the possibility that information will be lost along the way."

17. Refractory Period For a short period after the passage of an impulse, the threshold for stimulation is raised, so it limits the frequency of impulses and ensures uni-directional travel of impulse.