PHYS 115 Ad Hoc Project
Introduction to Biological Neuroscience
The Nervous System
Have you ever wondered what makes you… you? There is truly no singular way to approach this question, but it is one of the foundational questions of neuroscience, or the study of the nervous system.
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Your nervous system is comprised of two primary sections: your central nervous system (your brain and spinal cord) and your peripheral nervous system (everything else). Among many other supporting structures and cells, the primary unit of both of these sections is called the neuron.
The Neuron
Neurons are specialized cells that have a unique way of communicating with each other through electrical signals. They are comprised of four basic sections:
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Dendrites, where a signal is received from a neighboring neuron
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Soma, or cell body, where the nucleus and other vital organelles are contained
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The axon, where signals are transmitted
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The axon terminals, where signals are passed onto another cell
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Like other cells, neurons are comprised of a cellular membrane that prevents certain molecules (particularly charged ions such as potassium/K+ and sodium/Na+). Therefore, they require specialized membrane proteins called channels to move them from one side to another
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The Action Potential and Signal Propagation
When a neuron receives a sufficient signal in its dendrites, it triggers what is known as an action potential (AP). APs are characterized by extremely fast, but temporary changes in charge within the cell, known as the membrane potential (Vm). For example, many positive ions such as K+ leads to a higher positive Vm, while more negative ions such as Cl- leads to a more negative Vm.
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These temporary changes in Vm during an action potential are caused by the movement of ions across the cell membrane. When an AP is triggered, sodium ion channels are opened in the cell membrane, allowing Na+ to flow into the cell. This causes an increase in membrane potential, or depolarization. After a short period of time, these Na+ channels begin to close while K+ channels begin to open. This leads to an efflux of K+ ions, leading to less positive charge and a more negative membrane potential, or hyperpolarization.
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This process continues along the entire length of the axon, repeating this process of depolarization and hyperpolarization until the signal reaches the axon terminals. This causes calcium ion channels to open, which then bind to vesicles containing neurotransmitters. These vesicles fuse with the cell membrane, releasing their neurotransmitter contents onto the dendrites of another neuron. If sufficient signal is created from this, another AP is triggered in the next neuron, propagating the electric signal.
K+ Leak Channel
These channels always allow only K+ ions to travel across the cell membrane (normally inside to outside)
Na+ V-Gated Channel
These channels allow only Na+ ions to pass through (normally from outside to inside) when Vm is very positive
K+ V-Gated Channel
These channels allow only K+ ions to pass through (normally from inside to out) when the Vm is very positive
Na+/K+ Pump
This channel uses energy from a molecule called ATP to move Na+ ions out of the cell and K+ ions into the cell to restore Vm after an action potential