14 Jul The brain is made up of at least one hundred billion neurons, and these neurons are assisted by a variety of supporting cells. Neurons communicate with each other via electrical
The brain is made up of at least one hundred billion neurons, and these neurons are assisted by a variety of supporting cells. Neurons communicate with each other via electrical or chemical messages; the electricity causes the release of chemicals. The electrical impulses are similar to the electricity that flows throughout your home. In your home, you must place a plug into a socket for the electricity to flow into the device you have plugged in. The body is similar to this, and yet it is very different because there are no physical connections between neurons in the brain. Instead of one neuron touching another and sending a message via a physical connection, neurotransmitters are released into a space called the synaptic cleft.
Answer the following questions:
- Describe vesicles and terminal buttons in a presynaptic neuron. How are neurotransmitters released into the synaptic cleft, and what happens to them after they are released? What must happen at the postsynaptic neuron to ensure binding?
- Neurons are released into the synaptic cleft where the neurotransmitter diffuses throughout the space. What are the advantages and disadvantages of not having neurons connected to each other?
- What role do the supporting cells play in neurotransmission? Describe the role of at least two different types of supporting cells. Are the supporting cells as important as the neurons when it comes to neural communication?
Respond to at least two of your classmates. As in all assignments, make sure to cite your sources in your work and provide references for those citations utilizing APA format.
Hormones and Drugs.html
Hormones and Drugs
Like neurotransmitters, hormones are endogenous substances (chemicals that exist in the body) that influence the body and bring about changes in organs. Unlike neurotransmitters, hormones are secreted by the endocrine glands into the bloodstream so that the hormones can spread throughout the body and make a long-distance change. You can think of a released hormone as dispersed pinecone seeds in a river after they fall from a tree. Pinecone seeds can flow with the river, go just about anywhere, and get picked up by anything that is receptive to them. Like neurotransmitters, hormones must bind to a receptor for a change to occur. However, hormones are different from neurotransmitters because the changes that hormones make are often more long-term.
Psychoactive drugs are exogenous substances that are introduced into a person's body; they are called psychoactive because they can alter the mind. Some of these substances, such as amphetamines, alter behavior by releasing neurotransmitters like dopamine when they attach to specific receptors in the brain. Other drugs such as heroin (a powerful opiate drug that can alter one's sense of mood and perception of pain) actually bind to the body's opiate receptors, mimicking the endogenous chemicals. Exogenous opiates and other drugs that have similar mechanisms of action not only bind but also can activate the receptors as if they were the neurotransmitter. When a substance can mimic the brain's neurotransmitter, it is called an agonist. Taking an agonist is like using a copy of the key that opens the door to your house. It is not the brain's natural chemical, but it acts exactly the same.
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Nerves.html
Nerves
Each of us has about one hundred billion neurons in our 3-pound brain. Neurons are responsible for sending messages within certain localized areas and they are the means of communication in the brain. All of your bodily functions, including your movements and thoughts, are dependent on neuronal functions. Let’s examine what neurons look like and how they work.
The dendrites, connected to the soma (cell body) of a neuron, receive information from other neurons. Like a tree, these dendrites have branches called dendritic arborizations (note: arbor means tree). Dendrites are the starting point for the electrical impulse that enables neurons to communicate. In addition, like a tree, neurons have something similar to a trunk. The trunk of a neuron projects from the cell body and is called an axon. The electrical signal that starts at the dendrites is propagated from the cell body down the axon to the end. Many neurons also have a coating on their axons, which is called myelin. Myelin, made by glia cells, helps the electrical current move faster down the axon. Because myelin coats the axon, it is somewhat analogous to the bark of a tree. However, myelin has breaks in the sheath, which make the electrical current move faster as it jumps from one break to another.
The last part of the tree analogy involves the roots. Similar to the roots of a tree, the axon terminals branch out, and the ends of the branches are referred to as terminal buttons (pronounced boo-tons). The neuron releases chemicals from the buttons, and the released chemicals are then able to cause reactions in other neurons.
Additional Materials
View a Pdf Transcript of Various Types of Neurons
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Various Types of Neurons
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Neurotransmitters.html
Neurotransmitters
What happens when the neurotransmitter is released from the neuron? A chemical diffuses through a fluid-filled space referred to as a synaptic cleft and other neurons that are in the vicinity have an opportunity to receive the neurotransmitter. They will receive it if it binds to a receptor on their dendrites.
Regardless of how a specific neurotransmitter works, if it is going to make a change in another neuron, it will have to bind to a receptor located on the dendrites of the receiving cell, the postsynaptic neuron. You can think of receptors as having a particular shape, and only certain neurotransmitters can fit in the receptors. It is similar to how a key fits in a lock.
Just as a key has to have the right shape to make the lock turn, a neurotransmitter has to have the proper shape to activate the receptor to cause a change. A neurotransmitter's ability to fit into the receptor and stay bound is called affinity, and its ability to activate the receptor is called efficacy.
Additional Materials
View a Pdf Transcript of Release of a Neurotransmitter
View a Pdf Transcript of Neurotransmitters and Their Functions
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Dendrites |
The receiving part of a neuron. They have branching fibers with receptors. |
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Soma |
The neuron's cell body. It contains the nucleus and other important structures. |
|
Axon |
A fiber that connects the cell body to the terminals. It is responsible for transmitting nerve impulses. |
|
Myelin |
A substance that covers some axons. It helps the action potential to move faster. |
|
Synaptic Cleft |
The place between neurons where the neurotransmitter is released into. |
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Neurotransmitters |
Chemicals released by neurons that convey messages. |
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Action Potential |
When the cell voltage changes and fires, transmitting a nerve impulse (electrical current) down a cell and causing the release of neurotransmitters. |
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Release of a Neurotransmitter
Neurotransmission depends on a neuron’s ability to create APs. APs are electrical impulses
that cause the release of neurotransmitters. Before APs are initiated, the neuron is at rest and
has an electrical voltage of –70 mV.
That voltage amount means that the inside of the cell is negative compared to the outside of
the cell.
APs cause the electrical properties of a neuron to change. During an AP, the inside of a
neuron becomes more positive.
The membrane of the neuron is responsible for the electrical state inside the neuron.
There are two layers to each membrane. The membranes have channels that go from one
side to the next.
If enough excitatory neurotransmitters bind to the dendrites of a neuron, it leads to the
depolarization of the cell, which means that positive ions rush into the cell, making the cell
more positive on the inside. Once the neuron reaches its threshold of excitation, voltage-
dependent channel doors open and the cell fires, setting off an AP.
Excitation leads to a large surge of electricity moving from the cell body to the axon terminals.
This sudden wave of electricity is the AP.
When an AP is initiated, it moves down the axon, toward the terminals.
If the axon has myelin, a substance that coats the axon, the AP jumps from one break in the
myelin, known as a node, to another. The jumping is called saltatory conduction.
When the AP gets to the end of the neuron, it causes stored neurotransmitters to be released.
Neurotransmitters are packed in vesicles in the terminal buttons. These vesicles are
positioned so that they can fuse with the membrane and dump their chemicals into the
synaptic cleft when there is an AP.
Once released into the synaptic cleft, neurotransmitters can bind to the receptors on the
dendrites of other neurons.
If it is an excitatory neurotransmitter, the depolarization process repeats and the AP continues
to move through the network.
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Neurotransmitters and Their Functions
Neurotransmitter Name and Abbreviation Examples of Functions
Dopamine (Da) Pleasure/reward and movement
Serotonin (5-HT) Sleep, pain, and mood
Norepinephrine (Na) Heart rate, sleep, and stress
Acetylcholine (ACh) Learning/memory and motor response
gamma-aminobutyric acid (GABA) Inhibitory (makes cells less likely to fire)
Glutamate Excitatory (makes cells more likely to fire)
Endorphins Pleasure and pain
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