Peripheral Nervous System Flashcards
Emergency personnel arrived on the scene, they found Mr Hancock unconscious, but with stable vital signs. As paramedics placed him on a backboard to stablize his head, neck and back, they noted watery blood leaking from his roght ear. In the hospital, Mr Hancock regained consciousness and was treated for longitudinal and transverse fractures of the right petrous temporal and sphenoid bones that extended through the foramen rotundum and foramen ovale.
The following observations were recorded on Mr. Hancock’s admission:
*complete loss of hearing in the right ear
*Paresthesia (sensation of pins and needles) at the right corner of the mouth, extending to the lower lip and chin
*Numbness of the right upper lip, lower eyelid and cheek
*right eye turned slightly inward when looking straight ahead. Diplopia (double vision), particularly when looking to the right.
Mr Hancock was given a course of antibiotics, the head of his bed was elevated by 30 degrees, and he was placed under close observation.
After 24 hours, doctors noted that the right side of Mr. hancock’s face showed signs of drooping, with incomplete eye closure and asymmetric facial expressions. Mr Hancock’s right eye showed minimal tear production. The weakness and asymmetry on the right side of his face began to subside after a few days, and the leak of fluid from his ear stopped, but he continued to complain of paresthesia, diplopia, and inability to hear with his right ear.
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In addition to blood, which fluid was leaking from Mr Hancock’s right ear? Which structures must have been damaged to allow this to happen? Why would this lead Mr Hancock’s doctor to give him antibiotics? Why was the head of the bed elevated?
Cerebrospinal fluid (CSF) is leaking out of Mr Hancock’s right ear. The fracture must have torn both the dura mater and srschnoid mater. In addition, the tympanic membrane must have been ruptured. Antibiotics were administered to prevent infection by bacteria that might enter through the ruptured meninges, causing meningitis. Elevating the head of the bed decreases CSF pressure on the skull. (this allows the torn meninges to heal spontaneously in the majority of cases)
Each of the 4 observations on Mr Hancock’s chart indicates damage to a cranial nerve. Identify wach cranial nerve involved. If applicable, identify which specific branch of that nerve is involved.
The observations on Mr Hancock’s chart indicate: (a) Either damage to the CN VIII (the vestibulocochlear nerve, which transmits afferent impulses for the sense of hearing) or destruction of the cochlea ( the sensory organ for hearing). (b) Damage to the CN V3 (the mandibular division of the trigeminal nerve), which runs through the foramen ovale. This nerve conveys sensory information from the lower part of the face. )c) Damage to the CN V2 ( the maxillary division of the trigeminal nerve), which runs through the foramen rotundum. This nerve conveys sensory information from the skin of the upper lip, lower eyelid, and cheek. (d0 Damage to CN VI ( the abducens nerve), which innervates the lateral rectus muscle of the eye. Because this muscle is responsible for pulling the eye laterally (abduction), loss of tone in this muscle at rest will cause the eye to turn inward. Diplopia will worsen when looking to the right because the eye can not abduct.
The observations after 24 hours suggest that yet another cranial nerve has been damaged. Which one? How can you explain the lack of tear production in the right eye?
the facial nerve ( cranial nerve VII) is the primary motor nerve associated with facial expression. The facial nerve also contains parasym[pathetic fibers that control secretion of tear from the lacrimal glands. Damage to this nerve explains both the motor symptoms and the dryness of his eye.
