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Section 3: Meat Wires
Nerve cells (neurons) and muscle cells (muscle fibers) are specialized cells whose cell membrane potential can change. These changes contribute to the basic functioning of these cells. Nerve cell processes can carry electical signals similar to how wires do.
Why is the nervous system different from skin, liver, kidneys, or spleen? The fundamental building blocks of the nervous system and muscles are electrically active cells. These cells process inputs and generate outputs.
Neurons are individual cells that form the elemental unit of every nervous structure in the body. The brain, spinal cord, peripheral nerves, and autonomic nervous system are all made up of neurons, and of glial cells, which are supporting cells for neurons.
Although they differ somewhat both morphologically and physiologically depending on where they are found and what function they serve, all neurons have a basic similar structure, illustrated in the image below (click to enlarge).
1) All neurons have a cell body, or soma. This is where the cell's nucleus and many other organelles reside. 2) Most neurons have many dendrites, branching out from the soma like the branches of a tree. These dendrites carry information (in the form of electrical signals) from other cells in towards the soma. 3) Most neurons have a single axon, which carries information (again, electrical signals) out from the soma so that it may eventually be converted into chemical signals (neurotransmitters) and delivered to other cells through specialized connections called synapses. These other cells are typically other neurons, but some neurons synapse onto muscle cells.
Muscle cells are also electrically active, and in the case of skeletal muscle, they receive information from neruons telling them when to contract.
When the cell membrane of neurons or muscle fibers is depolarized enough, they propagate a nondecremental wave of electrical polarization called an action potential. Neurons use these action potentials to quickly transmit information across distance. Muscle fiber action potentials result in a mechanical contraction of the fiber, resulting in the production of force and motion.
Terminology:
By the end of this section, make certain that you understand what each of these terms mean, and can apply them appropriately.
- Neuron
- Axon
- Dendrite
- Soma
- Myelin
- Conduction Velocity
- Temporal Summation
- Spatial Summation
- IPSP
- EPSP
Section 1: Cells are Batteries
Section 2: Why Are Cells Batteries?
Section 4: The Neuron Action Potential
Section 5: Muscle Fiber Action Potential
Section 6: Synapses and the Neuromuscular Junction (NMJ)
If you have any questions regarding this section, please ask them in the Neuroanatomy User Forum, or in the comments section at the bottom of this page.
