Olfactory Nerve Cranial Nerve I

Damage to which cranial nerves could result in death ...

Of the numerous organs which constitute the human body , the most complex and least understood is the brain . Though much of the brain’s function remains a mystery where human mental capacity and capabilities are concerned, physiologists and surgeons have been able to isolate the discrete regions of the brain responsible for eyesight, language, emotions, taste and smell. Each of these regions has appended to it a specific nerve that serves as a conduit for sensory data from the environment. Located in a vertical orientation along the underside of the brain, the cranial nerves, so called because they originate in the cranium, branch out to the areas of the face and body that correspond to the functions processed in the brain. In this respect, as part of the sympathetic nervous system, the cranial nerves may be thought of in a similar way to the cables which connect peripheral devices like a Webcam or a microphone to a computer’s central processing unit (CPU).

The brain houses a total of 12 cranial nerves that are noted in Roman numerals beginning with the olfactory nerve (I) at the very front. The olfactory nerve carries information about odors and smells and is attached to epithelium of the nose. The optic nerve (II), as the name implies, is responsible for visual processing. It is attached to the retina at the back of the eye’s aqueous humor and extends up into the brain shortly beyond. Cranial nerve III is the oculomotor nerve, which relates to the functional movements of the eyes. This includes the eyes’ rotation up, down, right and left as well as the contraction and dilation of the iris and the rarefaction and compression of the eyes’ crystalline lenses. The trochlear nerve (IV) connects to the large muscle that surrounds each eye like a disk. This nerve moves the eyebrows and eyelids and allows such behaviors as squinting. Cranial nerve (V) is the largest of the 12, and is called the trigeminal nerve in reference to its three component appendages that connect to all regions of the face including the jaws and inside of the mouth. This is the nerve associated with chewing, but it also carries sensory information from the forehead, the cavity behind the nose, as well as the cheeks.

The abducens nerve (VI) functions as the motor pathway for the eye’s lateral rectus muscle. The facial nerve (VII) is the sensory conduit for part of the tongue as well as the face as a whole. The facial nerve is also the motor source for facial movements and expressions. The eighth cranial nerve (VIII) is the vestibulocochlear nerve, and it is associated with the component organs of the ear canal and auditory capabilities. The glossopharyngeal nerve (IX) provides sensory information and motor faculties to the rear of the tongue and throat muscles while also regulating the heart’s sympathetic reflex. The vagus nerve (X) is the longest of all the nerves, reaching down the throat and esophagus and collecting sensory information from the digestive tract, while also providing sensory motor resources to the voice box, respiratory system and outer ear. Cranial nerve XI is the spinal accessory nerve, which branches off into the throat, where it plays a role in the swallowing reflex, and into the spine, providing motor resources for the head, neck and shoulders. The final cranial nerve, the hypoglossal nerve (XII), exclusively provides motor faculties to the tongue muscles.

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