The Peripheral Nervous System and Reﬂex Activity
permanently paralyzed and without sensation in both legs from
the knee down, as well as on the back of his thighs. What had
You are at a party at Mary’s house. AFer you are blindfolded, an
object (a key or a rabbit’s foot) is placed in your hand. Which
spinal tracts carry the signals to the cortex that will allow you to
diﬀerentiate between these objects, and what aspects of sensory
perception are operating?
Mr. Jake was admitted to the hospital with excruciating pain in his
leF shoulder and arm. He was found to have suﬀered a heart attack.
Explain the phenomenon of referred pain as exhibited by Mr. Jake.
ground. Days later, Harry complained that his upper limb was
numb. What was damaged in his fall?
Mr. ±rank, a former stroke victim who had made a remarkable
recovery, suddenly began to have problems reading. He
complained of seeing double and also had problems navigating
steps. He was unable to move his leF eye downward and laterally.
Which cranial nerve was the site of lesion? (Right or leF?)
One of a group of rabbit hunters was accidentally sprayed
with buckshot in both of his gluteal prominences. When his
companions saw that he would survive, they laughed and
joked about where he had been shot. Tey were horriﬁed and
ashamed a week later when they learned their friend would be
Related Clinical Terms
ability to feel pain, but without losing consciousness. An
analgesic is a pain-relieving drug.
thre-ah) Diﬃculty in articulating speech due to motor
pathway disorders that result in weakness, uncoordinated motion,
or altered respiration or rhythm. ±or example, lesions of cranial
nerves IX, X, and XII result in nasal, breathy speech, and lesions in
upper motor pathways produce a hoarse, strained voice. Not to be
, which are disorders of language
ne-ah) Impaired muscle tone.
Nerve conduction studies
Diagnostic tests that assess nerve
integrity as indicated by their conduction velocities. Te nerve
is stimulated at one point, activity is recorded at a second point
a known distance away, and the time required for the response
to reach the recording electrode is measured. Used to assess
(see entry in this list).
nerve) Sharp spasmlike pain along the
course of one or more nerves. May be caused by inﬂammation or
injury to the nerve(s) (for example, trigeminal neuralgia).
ze-ah) An abnormal sensation (burning,
numbness, tingling) in the absence of stimuli. Caused by a
sensory nerve disorder.
ah-the) Disease of the peripheral
nerves characterized by muscle weakness and atrophy, pain, and
numbness. Diabetes is a common cause. Other causes are genetic,
other metabolic disorders, infections or inﬂammation, and toxins.
lis) A slowly progressive condition
caused by deteriorating dorsal tracts (gracilis and cuneatus) and
associated dorsal roots. A late sign of the neurological damage
caused by the syphilis bacterium. Because joint proprioceptor
tracts are destroyed, aﬀected individuals have poor muscle
coordination and an unstable gait. Bacterial invasion of the
sensory (dorsal) roots results in pain, which ends when dorsal
roots have been completely destroyed.
AT T H E C L I N I C
William Hancock, a 44-year-old male,
was a passenger on the bus involved
in the accident on Route 91. When
emergency personnel arrived on the
scene, they found Mr. Hancock unconscious, but with stable vital
signs. As paramedics placed him on a backboard to stabilize his head,
neck, and back, they noted watery blood leaking from his right ear. In
the hospital, Mr. Hancock regained consciousness and was treated for
deep lacerations on his scalp and face. Head CT scans revealed both
longitudinal and transverse fractures of the right petrous temporal and
sphenoid bones that extended through the foramen rotundum and
The following observations were recorded on Mr. Hancock’s
chart on 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°, 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 an inability to hear with his right ear.
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 doctors to
give him antibiotics? Why was the head of his bed elevated?
Each of the four observations on Mr. Hancock’s chart indicates
damage to a cranial nerve. Identify each cranial nerve involved. If
applicable, identify which speciﬁc branch of that nerve is involved.
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?
(Answers in Appendix H)
Peripheral Nervous System