Lab 4
Approximate Time: 3 hours
Learning Objectives
-
- Concentrations of Solutes in ICF and ECF: Understand the differences in composition between intracellular fluid and extracellular fluid.
- Forces Affecting Ion Movement: comprehend the concepts of chemical force, electrical force, and electrochemical force.
- Neuron Structure and Function: Identify the basic structure of a neuron and their function.
- Graded Potentials: Understand what graded potential (GP) are and how they propagate within a neuron.
- Action Potentials: Gain a comprehensive understanding of action potentials.
- GP and AP Relationship: Understand how changes in membrane potential (Vm) caused by a GP can trigger an AP.
- Role of Na+/K+ Pump: Understand the function and importance of the sodium-potassium pump in maintaining membrane potential.
- POPS Project:
- Introduction Section due.
- Students will collaborate on the Materials and Methods for peer editing.
Activity 1: Concentration of Molecules in the ECF and ICF
Determine the location where you will find the highest concentration for the following molecules:
For each of the following, you will choose the concentration amounts as “high” or “low” comparing the ECF to the ICF.
| MOLECULE | ECF | ICF |
| Na+ | ||
| K+ | ||
| Cl- | ||
| Protein | ||
| Ca2+ | ||
| Glucose | ||
| Amino Acid | ||
| HCO3- | ||
| PO4 2- |
Activity 2: Determine the Direction of the force for Na+ and K+
Step 1: Using the cell below, draw the direction of the chemical driving force for both Na+ and K+. Molecules move down their concentration gradient. This direction is known as the chemical driving force.
Step 2: Draw the direction of the electrical driving force for both Na+ and K+. Keep in mind that electrical forces are due to the membrane potential which is Vm = -70 mV for most cells. This is due because the inside of the cell is typically more negative than the outside. This Vm (membrane potential) creates an electrical driving force for the movement of ions. Use the charge of the ion to determine the direction of the electrical force. (Hint: opposites attract and likes repel)
Step 3: Draw the direction of the electrochemical driving force for both Na+ and K+. The electrochemical driving force is total force acting on the ions. It is the combination of both chemical driving force and electrochemical driving force. When both forces go in the same direction the electrochemical driving force goes in the same direction. In contrast, when those two forces go in opposite directions, the electrochemical driving force goes in the direction of the larger force. To determine which force is larger, you need the ion’s equilibrium potential (ENa, and Ek). (Hint: if the equilibrium potential is larger in magnitude than the membrane potential, then the chemical force is larger than the electrical force, then the electrochemical driving force goes in the same direction as the chemical force. If the equilibrium potential is smaller than the membrane potential, then the electrical force is larger, the electrochemical driving force goes in the same direction as the electrical force)
Activity 3: Neuron
Draw and label the following structures of a neuron and represent where they’re going to be present in higher numbers.
- dendrites
- soma
- axon hillock
- axon
- axon terminal
- stimulus-gated channels
- leak channels
- voltage-gated Na+ channels
- voltage-gated K+ channels
- Na+/K+ pump
- Voltage-gated Ca2+ channels
Activity 4: Graded Potential
Step 1: Using arrows represent the location and the direction of a graded potential in a neuron (an arrow for stimulus, and arrows that shows the flow of current)
| CHARACTERISTICS | GRADED POTENTIAL |
| Direction of Na+
(in/out of cell) |
|
| Direction of K+
(in/out of cell) |
|
| Location in the neuron | |
| Stimulus-gated channels present
(yes/no) |
|
| Depolarization
1. does it occur with graded potentials? (yes/no) 2. If so, is it excitatory or inhibitory? |
|
| Hyperpolarization
1. does it occur with graded potentials? (yes/no) 2. If so, is it excitatory or inhibitory? |
|
| Decremental
(does the amount decrease with time or distance)- yes/no) |
|
| Leak channels present?
(yes/no) |
|
| Can summation occur?
(yes/no) |
|
| Does it have refractory periods? (remember that single graded responses are usually too small to achieve threshold and begin an AP but multiple graded potentials which overlap in time – stimulated again and again)
(yes/no) |
Activity 5: Action Potential
Step 1: Label the trigger zone of an action potential and the voltage necessary to produce an action potential in a neuron.
Step 2: Using the graph below fill out Table 3
| ACTION POTENTIAL PHASE | PHASE #
(1,2,3 or 4) |
Voltage-gated Na+ channel
|
Voltage-gated K+ channel
(open or closed) |
| RESTING STATE | activation gate
inactivation gate |
||
| DEPOLARIZATION | activation gate
inactivation gate |
||
| REPOLARIZATION | activation gate
inactivation gate |
||
| AFTER HYPERPOLARIZATION | activation gate
inactivation gate |
This Week’s focus for the POPS Project Includes:
- Abstract Section Due Next Week.
- Student responsible for the Abstract section of your POPS project should bring it to our next week lab class for peer editing. Student name is listed under the Timeline for Completion in the “Plan and Schedule Assignment”, which outlines your roles for the project.
- For additional guidance, refer to the POPS Project Materials at the end of this manual.