2.4 Neural Firing
5 min read•december 19, 2022
Megan Revello
Dalia Savy
Haseung Jun
Megan Revello
Dalia Savy
Haseung Jun
Vocabulary
Neural Firing
Parts of the Neuron
Neurons are our body’s nerve cells which make up the nervous system. For a neuron to fire, or communicate with another neuron, information must first be gathered in by the dendrites of the receiving neuron. From there, the information passes through the cell body to the axon.
| Part of the Neuron | Function |
| Dendrite | Receives information📖 and transfers it to the cell body |
| Cell Body | The neuron's support center❤️ |
| Axon | Passes messages to its terminal branches. The neural impulse goes through the axon and is an electrical signal⚡ |
| Myelin Sheath | A layer of tissue that covers the axon and speeds up neural impulses. Without a myelin sheath, there is a loss of muscle control💪 |
| The Axon's Terminal Branches | Pass on chemical messages✉️ to other cells and parts of the body |
Image Courtesy of Open Source Textbook
Action Potential
Action potential must occur for the message to continue to travel down the axon. This only occurs if the neuron’s threshold has been met - meaning it has received enough stimulation🔋 from the original sending neuron. If this threshold is met, the action potential occurs and the message travels down the axon via a process of depolarization. If the threshold is not met, nothing happens. Neurons have an all-or-none response - they either fire or they don’t.
This action potential occurs through the relocation of ions. At resting state, the neuron has a negative (-70mv) ➖charge. The negative ions are inside the neuron, while positive ions are outside the neuron. Then, specific neuron receives neurotransmitters (more of this explained later: think of it as a signal). When enough of this signal is received, meeting the threshold, the membrane of the neuron becomes permeable, allowing the positive ions to rush into the neuron, bringing the charge of the cell to about +40mv ➕. When the charge changes, a series of signaling occurs within the neuron like a bullet 💣💨(the speed of this electric message firing is actually 120 m/s, which is about 270 mph!! 😵).
Image Courtesy of Teach Me Physiology
Though you are not required to memorize the complicated steps of action potential (that's more AP Biology material!), try to know what each step of the graph means, because it can come up as a MCQ! Just understand what each section of the graph means (its signficance) and you'll be good to go!
Basically, the action potential is associated with depolarization. Depolarization is the process that carries the neural impulse through the axon, action potential is what must happen for the process to occur.
There are two types of signals / neurotransmitters:
Excitatory -- Pushes neuron's "accelerator"🚦; makes a neuron more likely to reach action potential and fire
Inhibitory -- Pushes a neuron's "brake"🛑; makes it less likely for a neuron to reach action potential
Terminal Branches
Remember those neurotransmittors? Well once the message has passed through the axon, it reaches the terminal branches. The terminal branches of a neuron contain neurotransmitters which are then released. These neurotransmitters cross the synaptic gaps between neurons and are gathered in by dendrites of a new neuron, continuing the communication process📩
Image Courtesy to Wikipedia
The synapse is where two neurons meet and neurotransmitters are released into it. There is both an electrical synapse, which relays quick🐆 messages to another cell, and a chemical synapse, which sends messages slowly🦥 to another cell.
Neurotransmitters are stored in vesicles in the axon terminal. When there is a neural impulse, the vesicle binds with the edge of the axon terminal and the neurotransmitters are released into the synaptic cleft.
Neurotransmitters that do not find a home on the dendrites of a neuron are absorbed back into the original neuron through a process called reuptake.
Neurotransmitters
Neurotransmitters often act as agonists or antagonists in our body. An antagonist neurotransmitter binds to the dendrites of a neuron and prevents or blocks🙅 its response. An example of this is the poison, Botulin. Botulin causes paralysis because it blocks the release of acetylcholine, an important neurotransmitter in muscle action.
Agonists, on the other hand, bind to receptor sites and mimic the effects of a specific neurotransmitter. Opiates are an example of an agonist as they mimic the effects of endorphins in our body (which is why they produce a morphine-like effect).
Drugs trick our brains into thinking that they are neurotransmitters. As mentioned above, drugs mimic the effects of endorphins so much to the point that our brain stops producing natural endorphins. This is why there is such a withdrawal when people stop trying to take drugs💊. The brain of a long-term drug user just cannot produce something significant for your health anymore because of the way drugs trick our brain.
Here is a chart of the functions of some key neurotransmitters. It is good to memorize this since it is sometimes tested on.
| Neurotransmitter | Function | Examples of Malfunctions |
| Acetylcholine (ACh) | Enables muscle action, learning, and memory. | With Alzheimer's disease, ACh-producing neurons deteriorate. |
| Dopamine | Influences movement, learning, attention, and emotion. | Oversupply --> schizophrenia Undersupply --> tremors and decreased mobility in Parkinson's disease |
| Serotonin | Affects mood, hunger, sleep, and arousal. | Undersupply --> depression. Antidepressant drugs raise serotonin levels |
| Norepinephrine | Helps control alertness and arousal | Undersupply can depress mood. |
| GABA | A major inhibitory neurotransmitter | Undersupply --> seizures, tremors, and insomnia. |
| Glutamate | A major excitatory neurotransmitter; involved in memory | Oversupply --> over stimulates the brain --> migraines and seizures (why lots of people avoid MSG in their food) |
| Endorphins | Diminishes the perception of pain and acts as a natural sedative | Undersupply --> can cause depression, anxiety and moodiness |
Table and Content Courtesy of Myers' Psychology for AP - 2nd edition
After Firing
After a neuron fires and reaches action potential, it goes into its refractory period, where it cannot fire. This period of rest😴 prevents one signal from combining with another. The neuron becomes slightly more negative than -70mv during this period. After its refractory period, the neuron comes back to -70mv, and the neuron reaches the resting potential, where the cell is polarized and ready to fire again once it reaches threshold.
🎥Watch: AP Psychology - Neurons and Neurotransmitters
Key Terms to Review (27)
Acetylcholine (ACh)
: A type of neurotransmitter involved in many functions including muscle stimulation, memory formation and learning.Action Potential
: Action potential is an electrical charge that travels along an axon when a neuron transmits information.Agonist
: An agonist is a substance that initiates a physiological response when combined with a receptor. In terms of neuroscience, it mimics the action of a naturally occurring substance.All-or-None Response
: The all-or-none response refers to how neurons either fire completely or they don't fire at all; there's no such thing as partial firing.Antagonist
: In psychology, an antagonist is a substance that blocks or inhibits the function of a neurotransmitter in the brain.Axon
: An axon is the long threadlike part of a nerve cell along which impulses are conducted from the cell body to other cells.Cell Body
: The cell body, or soma, is the part of a neuron that contains the nucleus. It's responsible for maintaining the life of the cell and it's where most protein synthesis occurs.Dendrites
: Dendrites are the branched projections of a neuron that act to conduct the electrical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project.Depolarization
: Depolarization is when there's a shift in a neuron's electrical charge that allows an action potential (nerve impulse) to occur.Dopamine
: Dopamine is a type of neurotransmitter, which is a chemical messenger that transmits signals in the brain and other areas of the body. It plays several important roles in the body, and it's found in high levels in certain parts of the brain.Endorphins
: Endorphins are neurotransmitters produced by your brain and nervous system during times of stress or pain. They interact with opiate receptors in your brain reducing your perception of pain and triggering positive feelings.Excitatory Signals
: Excitatory signals are electrical signals that increase the likelihood that a neuron will fire an action potential.GABA (Gamma-Aminobutyric Acid)
: GABA is a neurotransmitter in the central nervous system that inhibits or slows down brain signals and activity.Glutamate
: Glutamate is an excitatory neurotransmitter that increases brain activity and plays a key role in learning and memory.Inhibitory Signals
: These are signals in the nervous system that decrease the likelihood of a neuron firing an action potential, or "message."Myelin Sheath
: The myelin sheath is an insulating layer around nerves, including those in the brain and spinal cord. It allows electrical impulses to transmit quickly along the nerve cells.Neuron
: A neuron is a nerve cell that is the basic building block of the nervous system. It transmits information to other nerve cells, muscle, or gland cells.Neurotransmitters
: Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron (nerve cell) to another 'target' neuron, muscle cell, or gland cell.Norepinephrine
: Norepinephrine is both a hormone and neurotransmitter involved in stress response; it increases heart rate, releases glucose from energy stores, and increases blood flow to skeletal muscle.Refractory Period
: The refractory period is a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.Resting Potential
: Resting potential refers to the state of a neuron when it's not being stimulated or sending signals. It's the difference in electric charge between the inside and outside of a neuron's cell membrane.Reuptake
: Reuptake is the process by which neurotransmitters are taken back into the synaptic vesicles of a neuron after they have performed their function of transmitting a neural impulse.Serotonin
: Serotonin is another neurotransmitter that has many functions throughout the body. In the brain, it helps regulate mood, appetite, sleep cycle, memory and learning.Synapse
: A synapse is a tiny gap at which nerve cells (neurons) communicate with each other. Information from one neuron flows to another neuron across this small space.Terminal Branches
: Terminal branches are the tiny, tree-like ends of a neuron that send messages to other neurons.Threshold
: The threshold is the minimum level of stimulation required to trigger a neural impulse.Vesicles
: Small membrane-bound sacs inside neurons that store various neurotransmitters that are released at the synapse.2.4 Neural Firing
5 min read•december 19, 2022
Megan Revello
Dalia Savy
Haseung Jun
Megan Revello
Dalia Savy
Haseung Jun
Vocabulary
Neural Firing
Parts of the Neuron
Neurons are our body’s nerve cells which make up the nervous system. For a neuron to fire, or communicate with another neuron, information must first be gathered in by the dendrites of the receiving neuron. From there, the information passes through the cell body to the axon.
| Part of the Neuron | Function |
| Dendrite | Receives information📖 and transfers it to the cell body |
| Cell Body | The neuron's support center❤️ |
| Axon | Passes messages to its terminal branches. The neural impulse goes through the axon and is an electrical signal⚡ |
| Myelin Sheath | A layer of tissue that covers the axon and speeds up neural impulses. Without a myelin sheath, there is a loss of muscle control💪 |
| The Axon's Terminal Branches | Pass on chemical messages✉️ to other cells and parts of the body |
Image Courtesy of Open Source Textbook
Action Potential
Action potential must occur for the message to continue to travel down the axon. This only occurs if the neuron’s threshold has been met - meaning it has received enough stimulation🔋 from the original sending neuron. If this threshold is met, the action potential occurs and the message travels down the axon via a process of depolarization. If the threshold is not met, nothing happens. Neurons have an all-or-none response - they either fire or they don’t.
This action potential occurs through the relocation of ions. At resting state, the neuron has a negative (-70mv) ➖charge. The negative ions are inside the neuron, while positive ions are outside the neuron. Then, specific neuron receives neurotransmitters (more of this explained later: think of it as a signal). When enough of this signal is received, meeting the threshold, the membrane of the neuron becomes permeable, allowing the positive ions to rush into the neuron, bringing the charge of the cell to about +40mv ➕. When the charge changes, a series of signaling occurs within the neuron like a bullet 💣💨(the speed of this electric message firing is actually 120 m/s, which is about 270 mph!! 😵).
Image Courtesy of Teach Me Physiology
Though you are not required to memorize the complicated steps of action potential (that's more AP Biology material!), try to know what each step of the graph means, because it can come up as a MCQ! Just understand what each section of the graph means (its signficance) and you'll be good to go!
Basically, the action potential is associated with depolarization. Depolarization is the process that carries the neural impulse through the axon, action potential is what must happen for the process to occur.
There are two types of signals / neurotransmitters:
Excitatory -- Pushes neuron's "accelerator"🚦; makes a neuron more likely to reach action potential and fire
Inhibitory -- Pushes a neuron's "brake"🛑; makes it less likely for a neuron to reach action potential
Terminal Branches
Remember those neurotransmittors? Well once the message has passed through the axon, it reaches the terminal branches. The terminal branches of a neuron contain neurotransmitters which are then released. These neurotransmitters cross the synaptic gaps between neurons and are gathered in by dendrites of a new neuron, continuing the communication process📩
Image Courtesy to Wikipedia
The synapse is where two neurons meet and neurotransmitters are released into it. There is both an electrical synapse, which relays quick🐆 messages to another cell, and a chemical synapse, which sends messages slowly🦥 to another cell.
Neurotransmitters are stored in vesicles in the axon terminal. When there is a neural impulse, the vesicle binds with the edge of the axon terminal and the neurotransmitters are released into the synaptic cleft.
Neurotransmitters that do not find a home on the dendrites of a neuron are absorbed back into the original neuron through a process called reuptake.
Neurotransmitters
Neurotransmitters often act as agonists or antagonists in our body. An antagonist neurotransmitter binds to the dendrites of a neuron and prevents or blocks🙅 its response. An example of this is the poison, Botulin. Botulin causes paralysis because it blocks the release of acetylcholine, an important neurotransmitter in muscle action.
Agonists, on the other hand, bind to receptor sites and mimic the effects of a specific neurotransmitter. Opiates are an example of an agonist as they mimic the effects of endorphins in our body (which is why they produce a morphine-like effect).
Drugs trick our brains into thinking that they are neurotransmitters. As mentioned above, drugs mimic the effects of endorphins so much to the point that our brain stops producing natural endorphins. This is why there is such a withdrawal when people stop trying to take drugs💊. The brain of a long-term drug user just cannot produce something significant for your health anymore because of the way drugs trick our brain.
Here is a chart of the functions of some key neurotransmitters. It is good to memorize this since it is sometimes tested on.
| Neurotransmitter | Function | Examples of Malfunctions |
| Acetylcholine (ACh) | Enables muscle action, learning, and memory. | With Alzheimer's disease, ACh-producing neurons deteriorate. |
| Dopamine | Influences movement, learning, attention, and emotion. | Oversupply --> schizophrenia Undersupply --> tremors and decreased mobility in Parkinson's disease |
| Serotonin | Affects mood, hunger, sleep, and arousal. | Undersupply --> depression. Antidepressant drugs raise serotonin levels |
| Norepinephrine | Helps control alertness and arousal | Undersupply can depress mood. |
| GABA | A major inhibitory neurotransmitter | Undersupply --> seizures, tremors, and insomnia. |
| Glutamate | A major excitatory neurotransmitter; involved in memory | Oversupply --> over stimulates the brain --> migraines and seizures (why lots of people avoid MSG in their food) |
| Endorphins | Diminishes the perception of pain and acts as a natural sedative | Undersupply --> can cause depression, anxiety and moodiness |
Table and Content Courtesy of Myers' Psychology for AP - 2nd edition
After Firing
After a neuron fires and reaches action potential, it goes into its refractory period, where it cannot fire. This period of rest😴 prevents one signal from combining with another. The neuron becomes slightly more negative than -70mv during this period. After its refractory period, the neuron comes back to -70mv, and the neuron reaches the resting potential, where the cell is polarized and ready to fire again once it reaches threshold.
🎥Watch: AP Psychology - Neurons and Neurotransmitters
Key Terms to Review (27)
Acetylcholine (ACh)
: A type of neurotransmitter involved in many functions including muscle stimulation, memory formation and learning.Action Potential
: Action potential is an electrical charge that travels along an axon when a neuron transmits information.Agonist
: An agonist is a substance that initiates a physiological response when combined with a receptor. In terms of neuroscience, it mimics the action of a naturally occurring substance.All-or-None Response
: The all-or-none response refers to how neurons either fire completely or they don't fire at all; there's no such thing as partial firing.Antagonist
: In psychology, an antagonist is a substance that blocks or inhibits the function of a neurotransmitter in the brain.Axon
: An axon is the long threadlike part of a nerve cell along which impulses are conducted from the cell body to other cells.Cell Body
: The cell body, or soma, is the part of a neuron that contains the nucleus. It's responsible for maintaining the life of the cell and it's where most protein synthesis occurs.Dendrites
: Dendrites are the branched projections of a neuron that act to conduct the electrical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project.Depolarization
: Depolarization is when there's a shift in a neuron's electrical charge that allows an action potential (nerve impulse) to occur.Dopamine
: Dopamine is a type of neurotransmitter, which is a chemical messenger that transmits signals in the brain and other areas of the body. It plays several important roles in the body, and it's found in high levels in certain parts of the brain.Endorphins
: Endorphins are neurotransmitters produced by your brain and nervous system during times of stress or pain. They interact with opiate receptors in your brain reducing your perception of pain and triggering positive feelings.Excitatory Signals
: Excitatory signals are electrical signals that increase the likelihood that a neuron will fire an action potential.GABA (Gamma-Aminobutyric Acid)
: GABA is a neurotransmitter in the central nervous system that inhibits or slows down brain signals and activity.Glutamate
: Glutamate is an excitatory neurotransmitter that increases brain activity and plays a key role in learning and memory.Inhibitory Signals
: These are signals in the nervous system that decrease the likelihood of a neuron firing an action potential, or "message."Myelin Sheath
: The myelin sheath is an insulating layer around nerves, including those in the brain and spinal cord. It allows electrical impulses to transmit quickly along the nerve cells.Neuron
: A neuron is a nerve cell that is the basic building block of the nervous system. It transmits information to other nerve cells, muscle, or gland cells.Neurotransmitters
: Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron (nerve cell) to another 'target' neuron, muscle cell, or gland cell.Norepinephrine
: Norepinephrine is both a hormone and neurotransmitter involved in stress response; it increases heart rate, releases glucose from energy stores, and increases blood flow to skeletal muscle.Refractory Period
: The refractory period is a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.Resting Potential
: Resting potential refers to the state of a neuron when it's not being stimulated or sending signals. It's the difference in electric charge between the inside and outside of a neuron's cell membrane.Reuptake
: Reuptake is the process by which neurotransmitters are taken back into the synaptic vesicles of a neuron after they have performed their function of transmitting a neural impulse.Serotonin
: Serotonin is another neurotransmitter that has many functions throughout the body. In the brain, it helps regulate mood, appetite, sleep cycle, memory and learning.Synapse
: A synapse is a tiny gap at which nerve cells (neurons) communicate with each other. Information from one neuron flows to another neuron across this small space.Terminal Branches
: Terminal branches are the tiny, tree-like ends of a neuron that send messages to other neurons.Threshold
: The threshold is the minimum level of stimulation required to trigger a neural impulse.Vesicles
: Small membrane-bound sacs inside neurons that store various neurotransmitters that are released at the synapse.
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