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"Window"
to the Brain
Anatomy and pathology of the nervous system is understood by directly
visualizing it. This is best accomplished by handling the brain (or model
of the brain as the case may be) and dissecting or taking it apart for
direct examination. The purpose (for the clinician) of understanding neuroanatomy
and neurophysiology is to be able to use that knowledge to solve clinical
problems. The first step in solving a clinical problem is anatomical localization.
So, if one cannot directly inspect the patient's brain, how is this localization
accomplished? The "window" to the patient's brain is the neurological
examination. The neuro exam is a series of tests and observations that
reflects the function of various parts of the brain. If the exam is approached
in a systematic and logical fashion that is organized in terms of anatomical
levels and systems then the clinician is lead to the anatomical location
of the patient's problem.
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"x",
"y" Graph
To understand how this is done, let's first of all think of the mathematical
model of an x,y graph.
We know we can locate
a point on the graph if we have an "x" and a "y" coordinant. For example,
if we had a y=4 and x=2, then we know where that point is located on the
graph.
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"y" Values
Now let's take the brain and spinal cord and superimpose it over the
graph. We can see that the brain can be subdivided into parts along its
vertical or "y" axis.
The neurological exam
is designed to inspect the brain and spinal cord at these basic vertical
levels thus giving us a "y" value
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"x" Values
So far we have a handle on the vertical localization within the neuroaxis
but we have a very flat, one-dimensional structure. We need to have a
way to come up with "x" values. Let's rotate the neuroaxis by 90 degrees
so we can see it in the coronal plane.
Now we can appreciate
that most structures in the neuroaxis have a right, left or midline orientation
on our "x" axis.
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Longitudinal Systems
To further help us obtain "x" information, we need to add 3 basic
systems that are longitudinal in nature but which also cross the midline
during their descending or ascending course and thereby give us valuable
localizing information.
The first system we
will consider is a descending motor system, the corticospinal tract.
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Corticospinal
Tracts
Axons from the motor cortex descend on the same side of the brain until
the level of the spinomedullary junction at which time most of the fibers
cross to the opposite side and continue to descend through the spinal cord
until they reach the lower motor neuron on that side. |
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Somatosensory Tracts
Now let's add the 2 ascending sensory systems that give us important
clinical information for localizing lesions in the neuroaxis.
The first system is
the spinothalamic tract (pain and temperature) diagramed in light blue
and the second is the Dorsal Column- Medial Lemniscus system (discrimatory
touch and position sense) outlined in dark blue.
Two important anatomical
(and hence clinical) points about these two systems:
- The spinothalamic
tracts cross almost immediately upon entering the cord but the Dorsal
Column tracts don't cross until they reach the level of the medulla.
- The course of
these two sensory systems have a different "x" location until they reach
the rostal pons where they are then in close proximity to each other
for the remainder of their climb to the thalamus and on to the sensory
cortex.
The clinical importance
of these two anatomical facts will be become apparent as we discuss the
sensory exam.
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Mental Status Exam
Let's review how the neuro exam dissects or views the brain and the spinal
cord.
Mental Status Exam-
this lets us "see" the supratentorial structures of the cerebral hemispheres.
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Cranial
Nerve Exam
This gives an excellent way to look at the brainstem and the posterior
fossa structures. |
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Coordination
Exam
Essentially an examination of the cerebellum, which is another posterior
fossa structure. |
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Sensory
Exam
Examination of the two ascending sensory systems which gives "y" as well
as "x' values. |
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Motor
Exam
Examinations of the corticospinal tract as well as the lower motor neuron
nerve and muscle which again gives "y" and "x" values. |
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Gait
Exam
Gait is the last component of the neuro exam and it too can have localizing
value. All of the above systems make a contribution to gait. There are 7
basic pathological gaits that should be looked for and readily recognized
on examination. |
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Overview
Each of the following modules will focus on one of the 6 components
of the neuro exam. The format of each will be as follow:
- Anatomical review
of the level or system being examined.
- Demonstration
of that part of the neuro exam.
- Patient demonstration
of pathological findings of that particular system or level.
- Self-evaluation
quiz for that module.
At the end of the
tutorial there will be patient cases which will give you an opportunity
to put the neuro exam all together and test yourself in actually using
the exam to solve patient problems.
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Home (Exam)
MOVIES
CAN BE VIEWED ONLINE, OR DOWNLOADED.