Name:______

Activity 2.2.2: The Secret to Signals

Introduction

The secrets of neuron communication have been studied by scientists for centuries. We have learned that chemical and electrical factors work together to send signals. We know that the brain and spinal cord team up to deal with all the messages that are sent around the body on a minute to minute and often a second to second basis. We also know that all body functions depend on these messages to keep us at homeostasis both physiologically and psychologically. We know a lot, but many mysteries of the brain still have to be solved before we can effectively help people with serious nervous system injuries or diseases.

Electrical messages are sent to and from the brain and the spinal cord at an amazing speed. Some of these signals can travel as fast as 250 miles per hour. It is no wonder that you are able to react to stimuli very quickly. Neurons work together to send messages in a hurry: allowing a race car driver to react while driving at intense speeds or a tennis player to return the lightning-fast serve of an opponent. We have looked at the structure of a neuron and we know that the nerve cell can generate and send an electrical signal.This signal travels down the long axon of a neuron and calls out for the next neuron in the line. Nerve cells do not actually touch one another; yet, they are able to pass signals down the line. So how does this biological relay race really happen? Let’s zoom in on the neuron and unlock the secret to these signals.

Procedure

Complete the activity “Action Potential” found at Life Sciences/HHMI Outreach Programhttp://outreach.mcb.harvard.edu/animations/actionpotential_short.swf

Follow the directions to generate an electrical impulse down the axon of a neuron and answer the following questions.

  1. What do we call electrical messages that are sent down the axon of a neuron?
  1. In one sentence, describe how the electricity in an action potential is generated.
  1. In the diagram of the cell membrane of the axon. Label the following on your drawing:, Na+ channels, K+ channels, Na+/K+ pump, Na+ ions, and K+ ions.

  1. The main component of cell membranes are fats called phospholipids. Use the Internet to research the structure of a phospholipid. Label a phospholipid on your diagram.
  1. What do these terms hydrophilic and hydrophobic mean and how do they relate to the structure of a cell membrane? Look them up if you don’t know!!!!
  1. Return to your cell membrane diagram #3. Use a blue marker or colored pencil to color the parts of a phospholipid that are hydrophilic. Use a red marker or colored pencil to color in the parts of the molecules that are hydrophobic.
  1. In the following diagram, add Na+ and K+ ions to your cell membrane drawing to show the placement of ions when the cell is at rest. Think about which side will have more K+ and which side will have more Na+.

  1. How does the location of these ions relate to the overall membrane potential (charge) at this point? Place (-) signs on the side that is now negative and (+) signs on the side that is now positive (in #7).
  1. The Na+/K+ pump pumps 3 Na+ ions out of the cell for every 2 K+ ions it brings into the cell. Is this specialized protein working via active or passive transport? Explain your reasoning.
  2. What causes the inside of the membrane to reverse charge and begin the action potential?
  1. Which membrane protein is responsible for restoring the original concentration of Na+ and K+?
  1. What happens when the action potential reaches the end of the axon at the axon terminals?