Log inSign up for FREE
Library

01.12.21 - Graded Potentials, Synapses, and Neurotransmitters

Last updated almost 5 years ago
26 questions

Graded Potentials, Synapses, and Neurotransmitters


Objectives:
  • distinguish between action potentials and graded potentials
  • determine the parts of a neuron that play a role in messaging between cells
  • sequence the steps of a message moving from one neuron to another
  • distinguish between different types of neurotransmitters
  • explain how different types of neurotransmitters have different effects on neurons
Introduction:

In our last lesson, we learned about the action potential, or the significant change in membrane potential that occurs when a message is being sent down the axon of a neuron. In this lesson, we will be learning about how messages are sent from one cell to another.

Note: All reading segments are adapted from the openstax Anatomy & Physiology textbook
1

Warm up #1:
Without looking at any other sources, draw the change in membrane potential during an action potential on the axes below as best as you can. Label everything that you can remember.

1

Warm up #2
What do you think the term "depolarization" means? Please don't google it - break it down into parts and think about what it might mean.

Part 1: Graded Potentials

The electrical changes taking place within a neuron (action potentials!) are similar to a light switch being turned on. A stimulus starts the depolarization, but the action potential runs on its own once a threshold has been reached. The question is now, “What flips the light switch on?” Temporary changes to the cell membrane voltage can result from neurons receiving information from the environment, or from the action of one neuron on another. These special types of potentials influence a neuron and determine whether an action potential will occur or not.

Local changes in the membrane potential are called graded potentials and are usually associated with the dendrites of a neuron. The amount of change in the membrane potential is determined by the size of the stimulus that causes it. In the example of testing the temperature of the water in a shower, slightly warm water would only initiate a small change in a thermoreceptor, whereas hot water would cause a large amount of change in the membrane potential.

Graded potentials can be of two sorts, either they are depolarizing or hyperpolarizing (see figure below). For a membrane at the resting potential, a graded potential represents a change in that voltage either above -70 mV or below -70 mV. Depolarizing graded potentials are often the result of positive ions entering the cell, which causes the membrane potential to increase. Hyperpolarizing graded potentials can be caused by positive ions leaving the cell or negative ions entering the cell. If a positive charge moves out of a cell, the cell becomes more negative; if a negative charge enters the cell, the same thing happens.

Examine the model below:
Graded Potentials Graded potentials are temporary changes in the membrane voltage, the characteristics of which depend on the size of the stimulus. Some types of stimuli cause depolarization of the membrane, whereas others cause hyperpolarization. It depends on the specific ion channels that are activated in the cell membrane.

Use the reading and image above to answer questions 3-4
1

Match the following with the best description

Draggable itemCorresponding Item
the difference in charge across the cell membrane gets smaller
depolarization
the difference in charge across the cell membrane gets larger
hyperpolarization
1

Consider what you learned about action potentials. Use your understanding to categorize the following as characteristics of either graded or action potentials.

  • a large depolarization that reaches +40 mV
  • transmitted over short distances
  • transmitted over long distances
  • the change in electrical potential associated with the transmission of impulses along the membrane of a nerve cell
  • small depolarizing or hyperpolarizing changes in the membrane potential
  • a change in membrane potential that can vary in magnitude
  • Graded potentials
  • Action potentials
All types of graded potentials will result in small changes of either depolarization or hyperpolarization in the voltage of a membrane. These changes can lead to the neuron reaching threshold if the changes add together, or summate. If the total change in voltage in the membrane is a positive 15 mV, meaning that the membrane depolarizes from -70 mV to -55 mV, then the graded potentials will result in the membrane reaching threshold.

In order to gain a better understanding of summation, watch the first 2:40 of the video below. Then, answer questions 5-7:


(Stop at 2:40! You do not need to know about the types of summation!)
1

What is "threshold"?

1

If the summated graded potentials of a neuron do not depolarize a cell to -55 mV, what will happen?

1

Action potentials are often referred to as "all or nothing" events. What does this mean? Choose all correct answers.

Part 2: The Synapse

There are two types of connections between electrically active cells, chemical synapses and electrical synapses. For the purpose of this class, we will focus on chemical synapses only.

In a chemical synapse, a chemical signal—namely, a neurotransmitter—is released from one cell and it affects another cell. In an electrical synapse, there is a direct connection between the two cells so that ions can pass directly from one cell to the next. Chemical synapses involve the transmission of chemical information from one cell to the next.

An example of a chemical synapse is the neuromuscular junction (NMJ) that we learned about in the muscle unit. In the nervous system, there are many more synapses that are essentially the same as the NMJ. All synapses have common characteristics, which can be summarized in this list (think to yourself... which ones do you remember?):
  • presynaptic cell
  • neurotransmitter (packaged in vesicles)
  • synaptic cleft
  • receptor proteins
  • postsynaptic cell
  • neurotransmitter elimination or re-uptake
For the NMJ, these characteristics are as follows: the presynaptic element is the motor neuron's axon terminals, the neurotransmitter is acetylcholine, the synaptic cleft is the space between the cells where the neurotransmitter diffuses, the receptor protein is the acetylcholine receptor, the postsynaptic element is the sarcolemma of the muscle cell, and the neurotransmitter is eliminated by acetylcholinesterase. Other synapses are similar to this, and the specifics are different, but they all contain the same characteristics.

Use the reading above to answer questions 8-9
1

Examine the diagram below. Which letter represents the synapse?

1

Match the following terms with the best definition

Draggable itemCorresponding Item
presynaptic neuron
the neuron that releases neurotransmitter into a synapse (the "sending" cell)
postsynaptic neuron
The neuron that "receives" the neurotransmitter
1

Ok - it's time for us to zoom in a little bit more. Let's look at what happens between the axon terminal of one neuron and the dendrite of another neuron.

To start off, watch the video below. As you watch, think about what you know, what you don't yet know, and what you have questions about.


Now, click on the 'Show your Work' box below. Draw and label the following for an "at rest" synapse:
  • dendrite
  • axon terminal
  • synaptic cleft
  • calcium ion (Ca2+) channels
  • docking protein
  • vesicles
  • neurotransmitter
  • receptor proteins

Let's break this down a little more, shall we?

Questions 11-14 break this process into four main steps. For each step, select the words that best go in the blanks. Note that there is only one match for each letter!
1

Step 1: the action potential reaches the ( a ) of the sending cell, causing ( b ) to flow into the ( c ) cell through Ca2+ channels.

  • presynaptic
  • postsynaptic
  • calcium ion(s)
  • dendrite
  • axon terminal
  • sodium ion(s)
  • a
  • b
  • c
1

Step 2: Calcium ions entering the cell bind to the ( a ). When this happens, the vesicles are triggered to bind to the ( b ). ( c ) are then released into the ( d ).

  • synaptic cleft
  • vesicles
  • action potentials
  • neurotransmitters
  • receptor proteins
  • calcium channels
  • docking proteins
  • a
  • b
  • c
  • d
1

Step 3: Neurotransmitters find and attach to ( a ) on the membrane of the ( b ) cell, triggering a(n) ( c ).

  • docking proteins
  • presynaptic
  • graded potential
  • action potential
  • postsynaptic
  • receptor protein
  • a
  • b
  • c
1

Step 4: Neurotransmitters re-enter the ( a ). If enough neurotransmitters attach to receptor proteins, a(n) ( b ) MAY be triggered in the ( c ) cell.

  • synapse
  • postsynaptic
  • vesicles
  • action potential
  • presynaptic
  • graded potential
  • a
  • b
  • c

Part 3: Neurotransmitters

Now that we have an idea on how messages are sent from one neuron to another, let's learn a little bit about the different neurotransmitters. For a short introduction to neurotransmitters, watch the following video:

1

According to the video, neurons can send neurotransmitters to which of the following tissues?

1

As mentioned in the video, how many neurotransmitters have been discovered?

1

Match the neurotransmitters with their basic function:

Draggable itemCorresponding Item
acetylcholine
activates muscles
dopamine
increases heart rate and blood pressure
GABA
incites feelings of pleasure and reward
norepinephrine
suppresses anxiety
serotonin
promotes feeling of well being and happiness
As you probably guessed, the descriptions provided in the video above are very basic and do not describe all of the functions of the neurotransmitters mentioned.

Take a few minutes to look through the transmitters listed in the table below. Focus specifically on the neurotransmitters discussed in the video:


Use the table to answer questions 18-20
1

Neurotransmitters are either inhibitory or excitatory. They can not be both.

1

What do you think the terms "excitatory" and "inhibitory" mean?

1

Thinking about your answer for #19...

  • if there is enough, can initiate an action potential in the post-synaptic neuron
  • depolarizes post-synaptic cell
  • will prevent an action potential from occuring in the post-synaptic neuron
  • hyperpolarizes post-synaptic cell
  • excitatory neurotransmitter
  • inhibitory neurotransmitter
1

Use the table above to categorize the following neurotransmitters as being used primarily in the brain, spinal cord, or peripheral nervous system

  • glycine
  • glutamate
  • acetylcholine
  • norepinephrine
  • dopamine
  • serotonin
  • GABA
  • brain
  • spinal cord
  • peripheral nervous system
Radiolab: Seeking Patterns

Listen to the podcast below, then answer questions 22-23.

1

Which neurotransmitter is the focus of the podcast?

1

Describe the benefits and downsides of the drug that Ms. Klinestiver was prescribed. (This shouldn't be something you google, just what you get from the podcast!)

The link below is to a ten minute video on the effects of poverty on the child brain. Click on the link and watch the video, then answer questions 24-25.

How does the "toxic stress" of poverty hurt the developing brain?
1

Write a 3-4 sentence description of the news segment

1

Look once more at the table of neurotransmitters:


Considering what you heard about in the news segment about the effects of poverty on the developing brain, pick two neurotransmitters that you think might be affected by poverty in young kids. Explain your answer.

1

Wrap-Up:
Is there anything about graded potentials, synapses, or neurotransmitters that you would like for us to discuss in our next synchronous session?