What is the paralysis of the twelve cranial nerves referring to?
The cranial nerves are a set of twelve pairs of nerves that come out of or enter the cranium or skull. Each pair is connected to a specific brain function, serving different parts of the face and surrounding areas.
Paralysis of any of the cranial nerves has a direct impact on the function it serves. When the electrical impulse normally sent from the brain is curtailed or damaged in any way, the associated area being served is directly affected.
The twelve cranial nerves are named according to their function and are also known by a number, such as the first, second or third cranial nerves and so on. The cranial nerves are entitled olfactory (first), optic (second), oculomotor (third), trochlear (fourth), trigeminal (fifth), abducent or abducens (sixth), facial (seventh), vestibulocochlear (eighth), glossopharyngeal (ninth), vagus (tenth), spinal accessory (eleventh), and hypoglossal (twelfth).
The olfactory nerves, which send impulses of smell from the brain, may manifest in a loss of smell or an unusually intense or noxious smell sensation when paralysis occurs.
When the optic nerves are unable to function, sight is affected, as optic messages from the brain do not reach the retina. The ability to sense light and interpret images is impaired and may create double vision also known as ptosis, or a partial or total vision loss.
Muscles around the eye are served by the oculomotor cranial nerves. These work with the upper eyelids, determine direction of eye movement, and constrict or dilate pupils. Paralysis creates double vision, causes drooping eyelids, deviation of movement outwards, and dilated pupils.
The trochlear nerves are connected to the oblique muscles of the eye, dictating eye movement. Again, double vision may result from the state of dysfunction, as well as an upward or outward eyeball rotation.
The trigeminal cranial nerves play a complex and vital role in a sensory and motor capacity. Their threefold purpose includes the three divisions by which they function: ophthalmic, maxillary and mandibular. The trigeminal nerves are responsible for major facial sensations and thus a loss of sensation may occur in parts of the face, as well as in the scalp, forehead, temple, jaw, eyes and teeth. As a motor nerve involved with mastication or chewing, dysfunction makes chewing difficult. The paralysis may also cause the jaw to deviate towards the side that is paralyzed.
The abducent nerve pair serves muscles moving the eye. Inward turning of the eye or squinting and double vision are effects of paralysis in this area.
Facial expression is determined by the facial cranial nerves supplying essential nerve information to the muscles of the face. A well-known condition involving facial paralysis is Bell’s Palsy. The face droops to one side with a deviation of the mouth to the opposite side of the face, the forehead does not wrinkle and appears as unnaturally smooth, and the eye does not close.
A sense of hearing, balance and body position sense are made possible by the vestibulocochlear cranial nerves. Thus when there is a system failure, deafness or tinnitus may be experienced, as well as a sense of dizziness or vertigo. Vomiting may occur.
The glossopharyngeal nerves serve the tongue, throat and the parotid gland which is one of the salivary glands. Difficulty tasting and swallowing is the result when there is paralysis.
The vagus nerves play multiple roles, supplying nerve fibers to the pharynx, larynx, trachea, lungs, heart, esophagus and most of the intestinal tract. When the area is paralyzed the sensory information cannot reach the required area. Included in the numerously affected parts, are the impact on speaking and swallowing, which become difficult.
The spinal accessory, when affected, prevents head rotation from the damaged side. Drooping of the shoulders may take place.
Muscles of the tongue are served by the hypoglossal, the twelfth cranial nerve pair. Paralysis causes impaired speech, resulting in a thick sound. The tongue may deviate to the side that is paralyzed and may eventually atrophy. Swallowing is thus affected.
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