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The diagnostic exam of the nervous system evaluates specific functions, many while taking the history and examining the body by regions. When nervous system malfunction is encountered, a complete, systematic neurologic examination is required. The first objective is to identify all cognitive, sensory, motor, and coordination deficits. From this inventory, the site(s) and mechanism(s) of injury are hypothesized using the following general principles:

  1. Deficits of intellect, memory, and/or higher brain function imply lesions of the cerebral hemispheres.

  2. Deficits of consciousness indicate a brainstem reticular activating system lesion or bilateral cerebral damage.

  3. Paralysis with loss of deep tendon reflexes indicates a lower motor neuron (LMN) lesion interrupting the reflex arc 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 increased reflexes after hours to days.

  4. Paralysis with accentuated deep tendon reflexes (spasticity) indicates an UMN lesion in the cerebral hemisphere, brainstem, or spinal cord.

  5. Unilateral loss of touch and position sensation and contralateral loss of temperature and pain sensation indicate a unilateral spinal cord lesion ipsilateral to the sensory loss. This happens because the ascending tracts for touch and position decussate in the medulla, whereas the ascending tracts for pain and temperature sensation cross near their entry into the spinal cord.

  6. Paralysis is contralateral to lesions above the medulla and ipsilateral below because the descending motor tracts, like the tracts for discriminative sense, decussate in the medulla.

  7. Lower motor neuron paralysis accompanied by anesthesia in an appropriate distribution usually indicates a peripheral nerve lesion, many nerves carrying both motor and sensory fibers. Spinal root and segmental cord lesions sometimes produce similar signs.

  8. Muscle wasting with fasciculation indicates a lower motor neuron lesion. Without fasciculation, wasting is often attributable to intrinsic muscle disease.


A comprehensive understanding of the anatomy and functional organization of the nervous system is required to interpret neurologic exam findings. The reader should consult anatomy and neurology texts for detailed discussions of neuroanatomy and functional physiology.

Anatomic Organization of the Nervous System:

For diagnostic purposes, the nervous system is divided anatomically into the brain, spinal cord, spinal roots, and peripheral nerves. The brain is encased within the rigid skull and the spinal cord within the spinal canal of the vertebral column. The ganglia, plexuses, and nerve trunks are inaccessible to physical exam since they lie deep to the muscles and bones of the spine, chest, abdomen, and pelvis. The peripheral nerves, however, course with their corresponding arteries and veins in neurovascular bundles and may be palpable where they exit the trunk and in the extremities.

Central nervous system (CNS)

The brain consists of the cerebrum, brainstem, and cerebellum. The cerebrum performs cognitive functions, is the site of emotion and mood formation, ...

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