The diagnostic examination of the nervous system requires testing of its specific functional components, in addition to the traditional physical examination modalities of inspection and palpation.
Many nervous system components are evaluated while taking the history and examining the body by regions. The patient's speech and behavior reflect cerebral function. When examining the head, some, if not all, of the cranial nerves (CN) are tested. Muscle mass and strength are assessed by inspection and observation of gait and movement. Tendon reflexes are elicited during examination of the extremities. When evidence of nervous system malfunction is encountered, a complete, systematic neurologic examination is required.
The first objective of the systematic neurologic examination is to identify all cognitive, sensory, motor, and coordination deficits. From this inventory, the site(s) and mechanism(s) of injury can by hypothesized using the following general principles:
Deficits of intellect, memory, or higher brain function imply lesions of the cerebral hemispheres.
Deficits of consciousness indicate lesions of the brainstem reticular activating system or bilateral cerebral damage.
Paralysis with loss of deep tendon reflexes indicates a lower motor neuron (LMN) lesion interrupting the reflex arc. This can be at the spinal cord, spinal root, plexus or peripheral nerve level. Acute upper motor neuron (UMN) lesions can be associated with decreased reflexes initially, but produce increased reflexes after hours to days.
Paralysis with an accentuated deep tendon reflexes (spasticity) indicates an UMN lesion. This may reflect disease of the hemisphere, brainstem, or spinal cord.
Unilateral loss of touch and position sensation and contralateral loss of temperature and pain sensation indicate a unilateral lesion of the spinal cord ipsilateral to the loss of touch and position. This happens because the ascending tracts for touch and position sensation decussate in the medulla, while the ascending tracts for pain and temperature sensation cross near where they enter the spinal cord.
Paralysis is contralateral to lesions above the medulla and ipsilateral below. This is because the descending motor tracts, like the tracts for discriminative sense, decussate in the medulla.
An LMN paralysis accompanied by anesthesia in an appropriate distribution usually indicates a peripheral nerve lesion, because many nerves carry both motor and sensory fibers. Sometimes spinal root or segmental cord lesions cause similar signs.
Muscle wasting with fasciculation results from an LMN lesion; without fasciculation, wasting is often attributable to intrinsic muscle disease.
Interpretation of the neurologic examination requires a comprehensive understanding of the anatomy and functional organization of the nervous system. A complete description of the anatomy and the functional components of the nervous system is beyond the scope of this book. The reader should consult anatomy and neurology texts for detailed discussions of neuroanatomy and functional physiology.
For diagnostic purposes, the nervous system is divided anatomically into the brain, the spinal cord and the peripheral nerves.
The central nervous system (CNS)