The Nervous System - Signal Transmission - Student Lesson Outline 

In my 2-Minute Neuroscience videos I explain neuroscience topics in 2 minutes or less. In this video, I discuss synaptic transmission. I describe the synapse, synaptic cleft, release of neurotransmitter and its interaction with receptors, and the ways neurotransmitter is cleared from the synaptic cleft.

For a more in-depth 10-minute video on synaptic transmission, watch this 10-Minute Neuroscience video: https://youtu.be/k5RafiYXieo

For more neuroscience articles, videos, and a complete neuroscience glossary, check out my website at www.neuroscientificallychallenged.com !

TRANSCRIPT:

Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics in 2 minutes or less. In this installment I will discuss synaptic transmission.

Most communication between neurons occurs at a specialized structure called a synapse. A synapse is an area where two neurons come close enough to one another that they are able to pass chemical signals from one cell to another. The neurons are not actually connected, but are separated by a microscopically small space called the synaptic cleft. The cleft is less than 40 nanometers wide; by comparison a human hair is about 75,000 nanometers.

The neuron where the signal is initiated is called the presynaptic neuron, while the neuron that receives the signal is called the postsynaptic neuron. In the presynaptic neuron, there are chemical signals called neurotransmitters that are packaged into small sacs called vesicles. Each vesicle can contain thousands of neurotransmitter molecules. When the presynaptic neuron is excited by an electrical signal called an action potential it causes these vesicles to fuse with the presynaptic membrane and release their contents into the synaptic cleft. 

Once they are in the synaptic cleft, neurotransmitters interact with receptors on the postsynaptic membrane. They bind to these receptors and can cause an action to occur in the postsynaptic cell as a result. This action may involve increasing the likelihood that the postsynaptic cell will become activated and itself fire an action potential, or decreasing it (inhibition). 

Eventually, the neurotransmitter molecules must be cleared from the synaptic cleft. Some of them will simply drift away in a process called diffusion. In some cases, the neurotransmitter is taken back up into the presynaptic neuron in a process called reuptake. Once back inside the presynaptic neuron, the neurotransmitter can be recycled and reused. In other cases, enzymes break down the neurotransmitter within the synapse. Then the component parts can be sent back into the presynaptic neuron to make more neurotransmitter.

REFERENCE:

Purves D, Augustine GJ, Fitzpatrick D, Hall WC, Lamantia AS, McNamara JO, White LE. Neuroscience. 4th ed. Sunderland, MA. Sinauer Associates; 2008.

2-Minute Neuroscience: Synaptic Transmission

This video demonstrates the development of myelin in the peripheral nervous system and the propagation of action potential along a myelinated axon. The video was completed by Marziah Karch as her 2008 sabbatical project from the script and voiceover of Professor Marilyn Shopper. 

This is close captioned, but in some cases a few of the words were left out to make it possible to read it at all.

The Schwann Cell and Action Potential

The sodium-potassium pump is a protein pump that is critically important to the function of neurons. It helps to stabilize membrane potential, and thus is essential in creating the conditions necessary for the firing of action potentials. In this video, I discuss the general function of the sodium-potassium pump.

For an article (on my website) explaining the sodium-potassium pump, click this link: https://neuroscientificallychallenged.com/posts/know-your-brain-sodium-potassium-pump

TRANSCRIPT:

The sodium-potassium pump is a protein pump found in the cell membrane of all animal cells. Its main function is to transport sodium ions out of the cell and potassium ions into the cell. This serves a number of purposes, but is critically important to the function of neurons as it helps to maintain a higher concentration of sodium ions outside the cell, and a higher concentration of potassium ions inside the cell. Preserving these differences in ion concentrations helps to stabilize the cell’s membrane potential. This is critical for the neuron to be able to fire an action potential, which is the basis of the electrical signaling of neurons.

The sodium-potassium pump is a large membrane-associated enzyme that uses the energy of adenosine triphosphate, or ATP, to transport sodium and potassium ions across the cell membrane. All of the details of how this is achieved are not yet fully clear, but the general process involves the binding of ATP to the pump, which promotes the binding of 3 sodium ions and the release of 2 previously bound potassium ions. ATP is broken down and transfers a chemical group known as a phosphate group to the pump, which prompts the pump to undergo a conformational change, or a change in its shape. This causes the bound sodium ions to be released into the extracellular fluid. At the same time, the pump binds 2 potassium ions, which also prompts another conformational change that returns the pump to its previous configuration and the cycle begins again. Each cycle of the pump causes 3 sodium ions to move out of the cell and 2 potassium ions to move into the cell. Because there is one more positive charge leaving the cell than entering, there is a net loss of positive ions, which makes the resting membrane potential of the cell slightly more negative.

References:

Mordecai PB, Yao JPY, Matteson DR. Cellular Physiology and Neurophysiology. 4th ed. St. Louis, MO. Elsevier; 2020.     

Purves D, Augustine GJ, Fitzpatrick D, Hall WC, Lamantia AS, Mooney RD, Platt ML, White LE, eds. Neuroscience. 6th ed. New York. Sinauer Associates; 2018.

Thanks to Nicole Lookfong for help with fact-checking the script for this video.

2-Minute Neuroscience: Sodium-Potassium Pump

This animation demonstrates the behavior of a typical neuron at its resting membrane potential, and when it reaches an action potential and fires, transmitting an electrochemical signal along the axon. It shows how the various components work in concert: Dendrites, cell body, axon, sodium and potassium ions, voltage-gated ion channels, the sodium-potassium pump, and myelin sheaths. It also shows the stages of an action potential: Polarization, depolarization, and hyperpolarization.

The animation was co-developed by Harvard Extension School's Office of Digital Teaching and Learning, and instructors for the courses in neurobiology and human anatomy.

Learn more about Harvard Extension School:  https://www.extension.harvard.edu/?utm_source=youtube&utm_medium=social&utm_campaign=ext_action-potential-in-the-neuron&utm_content=description

Action Potential in the Neuron

In this video, I describe the mechanisms underlying neurotransmitter release. I discuss how calcium influx is thought to play a role in mobilizing and preparing synaptic vesicles for neurotransmitter release, and I cover the hypothesized mechanism by which vesicles fuse with the cell membrane of the neuron to empty their contents into the synaptic cleft.

TRANSCRIPT:

Neurotransmitters are stored in the axon terminals of a neuron in small sac-like structures called synaptic vesicles. When an action potential travels down the neuron and reaches the axon terminal, it causes depolarization of the neuron. This change in membrane potential causes voltage-gated ion channels, which are ion channels that open in response to changes in membrane potential, to open and allow calcium to enter the cell. Calcium seems to be involved with mobilizing vesicles to prepare them for neurotransmitter release. One way this occurs is through an interaction between calcium and a protein called synapsin, which attaches vesicles to the cytoskeleton of the cell. Calcium activates an enzyme that causes synapsin to separate from the vesicles, mobilizing them for release. 

After mobilization, a family of proteins called SNARE proteins are involved with getting the vesicle ready to fuse with the cell membrane of the neuron. Synaptobrevin (also called VAMP) is a SNARE protein found in the membrane of vesicles, while syntaxin and SNAP-25 are two  SNARE proteins found in the cell membrane. These three proteins are thought to form a complex, which helps to bring vesicles in contact with the cell membrane, allowing the two membranes to fuse together. This process is thought to be facilitated by another protein called munc18. The role of munc18 in vesicle fusion is not completely understood, but it seems to bind to syntaxin and be necessary for fusion to occur. Another protein found in synaptic vesicles known as synaptotagmin is thought to act as a calcium sensor, which aims to promote vesicle fusion only when calcium levels in the cell are high. When the vesicle fuses with the cell membrane, it empties its contents into the synaptic cleft. After neurotransmitter release, the SNARE complex is disassembled with the help of proteins called NSF and SNAP, and the vesicle is recycled so it can be used again.


References: 

Südhof TC. A molecular machine for neurotransmitter release: synaptotagmin and beyond. Nat Med. 2013 Oct;19(10):1227-31. doi: 10.1038/nm.3338.

Südhof TC, Rothman JE. Membrane fusion: grappling with SNARE and SM proteins. Science. 2009 Jan 23;323(5913):474-7. doi: 10.1126/science.1161748.

2-Minute Neuroscience: Neurotransmitter Release

BAHHHHHH! Did I scare you? What exactly happens when we get scared? How does our brain make our body react? Just what are Neurotransmitters? In this episode of Crash Course Psychology, Hank takes us to the simplest part of the complex system of our brains and nervous systems: the neuron.   
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Want more videos about psychology? Check out our sister channel SciShow Psych at https://www.youtube.com/scishowpsych! 
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Chapters:
Introduction: Brain Chemicals 00:00
Neurons 1:31
Parts of a Neuron 2:07
Synapses 3:08
Neurotransmitters 3:58
Excitatory Neurotransmitters 4:48
Inhibitory Neurotransmitters 5:10
More Neurotransmitters 5:30
Hormones 6:08
Nervous vs. Endocrine Systems 6:44
Endocrine System Glands 7:19
The Pituitary Gland 7:58
How the Nervous & Endocrine Systems Work Together 8:33
Credits 9:33

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The Chemical Mind: Crash Course Psychology #3

The Nervous System - Signal Transmission - Exit Ticket 

The Nervous System - Signal Transmission - Student Presentation 

The Nervous System - Signal Transmission - Teaching Presentation 

The Nervous System - Signal Transmission is a lesson by Teach Science with Fergy, containing engaging videos, presentations and activities to help develop students' science knowledge.

The Nervous System - Signal Transmission - Student Lesson Outline

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