"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.
"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.
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.
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.
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.
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.
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.
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.
Cranial Nerve Exam
This gives an excellent way to look at the brainstem and the posterior fossa structures.
Essentially an examination of the cerebellum, which is another posterior fossa structure.
Examination of the two ascending sensory systems which gives "y" as well as "x" values.
Examinations of the corticospinal tract as well as the lower motor neuron nerve and muscle which again gives "y" and "x" values.
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.
Each of the following modules will focus on one of the 6 components of the neuro exam. The format of each will be as follows:
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.