In neurology, we talk about “localizing” a lesion.
Step 1: Where is the lesion that is responsible for a patient’s signs and symptoms?
Step 2: Based on the location, what are the possible etiologies of the signs and symptoms?
These steps require a clear understanding of the anatomy and pathophysiology of the central and peripheral nervous systems and blood supplies. A helpful tip is to learn to map signs and symptoms to a location (e.g., vertigo, diplopia, and nystagmus = brainstem).
CENTRAL NERVOUS SYSTEM (CNS)
The CNS includes the brain and spinal cord. It is composed of gray matter (cell bodies) and white matter (axons). The brain and spinal cord are somatotopically organized. Signals travel on “tracts” – i.e., descending motor tracts and ascending sensory tracts. Here is a summary of the main tracts.
A) The main descending motor pathways. Shown is the brain and spinal cord with a depiction of the corticospinal (maroon) and corticobulbar (red) tracts. These tracts carry motor signals from the brain to the periphery (descending). B) The main ascending somatosensory pathways. Shown is the brain and spinal cord with a depiction of the spinothalamic tract (dark blue; pain, thermal sense) and the posterior column-medial lemniscus pathway (light blue; proprioception, vibration). These tracts carry sensory signals form the periphery to the brain (ascending).