The Nervous System
The Neuron
A neuron is built to send and receive information within the body. This means that the neuron cell is built to maximize this effect. Many neurons act together within the body to communicate messages by sending and receiving signals. Neurons can communicate with only one cell, or with many cells. The shape of the neuron depends on the number of cells a neuron communicates with.
Parts of the Neuron
The Cell Body: The
main body part of the cell, which contains most of the cells organelles, or
"small organs" that sustain its life.
The Axon: Extends from the cell that transmits signals, or sends out communication signals. There is only one on the cell, and it can be extremely long. The very end of it branches out. Dendrites: Many branches that extend from the cell. These help the cell body receive signals from other cells. Myelin Sheath: This isn't a part of the actual neuron, but it surrounds the axon of a neural cell. It is basically insulation that surrounds the axon so the signals can flow more quickly down the axon. Myelin layers are often made by Schwann cells. The Myelin Sheath is made up of layers of Myelin. Schwann Cells
Schwann
cells surround the axons of neural cells in the peripheral nervous system (as
opposed to the central nervous system, which is the brain and spinal cord), or
all nerve cells that are not found in the brain or spinal cord. These cells
produce the myelin sheath that also surrounds the axons of neural cells. They
are also one of the layers that make up the myelin sheath.
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Action Potential
A major factor in producing the signals that travel along a neuron is the potential of the cell membrane. The inside of the cell membrane is a different charge than the outside, and this difference is because of the different ions on the inside and outside of the cell. An ion either has a positive charge or a negative charge, and if there are more positively charged ions on the inside of the membrane than on the outside, the inside of the membrane is overall positively charged.
Hyper-Polarization
When positive ions flow out of the cell, or when negative ions flow in to the cell. This increases membrane potential. Potassium ions flowing out are often responsible for hyper-polarization.
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Depolarization
When positive ions flow in to the cell, or when negative ions flow out of the cell. This decreases membrane potential. Sodium ions flowing in to the cell are often responsible for this.
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Sodium and potassium ions don't just flow in and out of the cell on their own, because they are not able to flow through the membrane alone. So, in order to change their levels within the cell, they must flow through protein gates that are embedded within the membrane. These gates aren't always open though, and must be turned on or off in various ways so the ions can flow through. Also, each ion can only flow through one specific gate.
If you didn't understand the video....
Active Potential is basically just a massive change in the membrane voltage due to a great shift
in membrane potential due to depolarization. When a membrane potential
depolarizes enough, the change in voltage causes both sodium ion gates and
potassium ion gates to open. (Remember, sodium ion gates allow sodium ions to
flow in, causing depolarization, and potassium ion gates allow potassium ions
to flow out, causing hyperpolarization.)
However, sodium ion gates open first, causing an initial overall depolarization. Then, as they start to close, potassium ion gates open, causing hyperpolarization. The hyperpolarization signals the end of the action potential. However, the initial depolarization causes adjacent regions to open ion gates and allow for more action potentials, which spread down the nerve cell.
As the neuron cell is very long, different parts of the cell can have different charges. For example, along the axon, one section might be depolarized, while a section next to it could be hyperpolarized.
However, sodium ion gates open first, causing an initial overall depolarization. Then, as they start to close, potassium ion gates open, causing hyperpolarization. The hyperpolarization signals the end of the action potential. However, the initial depolarization causes adjacent regions to open ion gates and allow for more action potentials, which spread down the nerve cell.
As the neuron cell is very long, different parts of the cell can have different charges. For example, along the axon, one section might be depolarized, while a section next to it could be hyperpolarized.
Synapses
Messages typically get from cell to cell by crossing over things called synapses, which are basically gaps between nerve cells. There are two types of synapses, electrical and chemical synapses.
Electrical Synapses
A gap that allows for a direct flow of information from cell to cell. These aren't very common.
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Chemical Synapses
An actual gap between the cells that conveys messages through chemical messengers (neurotransmitters).
When an action potential arrives at the end of the cell's axon, it triggers the release of calcium ions, which triggers the release of the neurotransmitter (chemical messenger). The messenger is received by the cell on the other side of the gap, and triggers certain ion gates to open. Depending on which ion gates are opened, the region of the new cell is either depolarized (which would be the beginning of an action potential system), or hyperpolarized (which would inhibit any action potential). |
Dopamine
An example of a neurotransmitter is dopamine. It is released from cells in the brain, and acts as an excitatory neurotransmitter (excitatory means that when it's received by another cell, it activated the ion channels that result in depolarization, so the action potential system is started). So, when the an action potential arrives at the end of one of the dopamine-producing neurons in the brain, it triggers the in flow of calcium ions, which also triggers the release of dopamine molecules, which flow across the gap and bind onto the adjacent neuron, which cause certain ion gates to open and triggers another sequence of action potentials.
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The Human Brain
There are many parts to the brain, but they all originated as either the forebrain, midbrain, and hindbrain. These three sections are found in the brain as an embryo, but eventually develop in to the different specialized parts.
There are four main parts, the cerebrum, cerebellum, brainstem, and diencephalon.
There are four main parts, the cerebrum, cerebellum, brainstem, and diencephalon.
The Cerebrum
This is the largest part of the brain, and is divided into left and right cerebral hemispheres. The right hemisphere controls and receives information from the left side of the body, and the left hemisphere receives and controls information from the right side of the body. Overall, the cerebrum controls skeletal muscle contraction, and helps with learning, perception, emotion, and memory. It also has the cerebral cortex, which is needed for perception, voluntary movement, and learning. It originated as a part of the forebrain. It is connected to neurons in the eyes, and receives information from them.
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The Cerebellum
This is necessary for movement, balance, and motor skills. It receives information from the hearing and visual systems, as well as information about joints and muscles. It uses this information to carry out functions. For example, this is vital to our hand eye coordination. It might receive information from the eyes about an upcoming obstacle, and coordinate the muscles so that you could walk around it. The cerebellum originally rose from the hindbrain.
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The Diencephalon
This has three parts, the thalamus, hypothalamus, and epithalamus. The thalamus basically receives and sorts information from the senses, and then sends the information to the cerebrum. The thalamus is responsible for maintaining a constant internal temperature and the body's biological clock. It also regulates things like hunger and thirst. The hypothalamus deals a lot with neuro-hormone production. It receives information from the surroundings and responds appropriately by producing certain hormones. For example, if it receives information that it is breeding season, it would start producing reproductive hormones. The epithalamus mainly controls melatonin release. The diencephalon originally rose from the forebrain.
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The Brainstem
This also has three parts: the pons, the midbrain, and the medulla oblongata. The midbrain obviously rose from the midbrain originally, and it mainly receives and sends sensory information. For example, it is responsible for some visual reflexes. The pons and medulla oblongata originally rose from the hindbrain. The pons and medulla both help a lot with transferring information from any nerves outside of the brain and spinal cord to within the brain and spine. Also, the medulla is responsible for many of our automatic functions, like breathing.
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Emotion:
As opposed to being controlled by one region of the brain, emotion is controlled by many parts. These parts are found outside of the brainstem, and are together called the limbic system. Information from emotions, like emotional experiences, are not stored in the same place as other memories. These emotional experiences are stored in the amygdala.
As opposed to being controlled by one region of the brain, emotion is controlled by many parts. These parts are found outside of the brainstem, and are together called the limbic system. Information from emotions, like emotional experiences, are not stored in the same place as other memories. These emotional experiences are stored in the amygdala.