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Head and Neck Anatomy: Part III – Cranial Nerves

Course Number: 598


As mentioned earlier the neuron cell bodies are generally located in the CNS and even those outside the CNS are clustered into areas known as ganglia (singular – ganglion). Nerves, which we will be looking at in this course are constructed of axons and dendrites and associated supporting cells. It is important to realize that the cell body that controls them can be quite distant from the terminal ends of the neuron and there is a time delay in signaling due to the length of the fibers in addition to the delay caused by any synapses involved.

To use an illustration to tie all of the above together, think of the response to touching a hot surface, which is a common human error. Pain receptors in the skin of the finger create an action potential in a sensory neuron. The greater the number of receptors connected to that neuron that are stimulated the larger the action potential created. Depending on the size of the burn there may be multiple neurons involved but let us stay with just one for now. The signal is carried back to the neuron cell body located in a ganglion just outside the spinal cord. There the signal is sent into the CNS where there are multiple connections. The sensory neurons synapse with neurons in the spinal cord and the brain. The neurons in the spinal cord are connected to motor neurons in the spinal cord that control the flexor muscles of the arm causing those muscles to pull the hand back. This reflex is mediated in the spinal cord as it is a shorter distance for the signals to pass and therefore the hand sustains less damage as it is pulled away faster. The signal also passes to the brain area that receives sensory information registering the unfortunate event as a burn and then relays through other neurons in multiple areas of the brain that can process that you burned yourself using stored memories of other burns and not only registers it but stores that new burn memory also. Other sensory neuronal information will be synthesized to determine whether there are other people in the room or some other reason that you should not swear. If this information does not send sufficient inhibitory signals to overcome the urge to vocalize your displeasure, then you will use all of your favorite swear words pulled from yet another area of the brain. But note that by the time you are choosing the proper words your fingers have been away from the hot surface for some time.