Chapter 12-01: Anatomy & Physiology in Neurology

INTRODUCTION

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)

Tracts of the 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.

Motor tracts

• Pyramidal: Corticospinal and corticobulbar tracts (Figure 12.1A)

  • - Corticospinal tracts:

    • Anatomy: Neurons in the primary motor cortex (precentral gyrus), pre-motor and supplemental motor cortex → axons descend through the posterior limb of the internal capsule → enter the brainstem (cerebral peduncle in the midbrain) → basis pontis → medullary pyramids → tract divides into two tracts at the cervicomedullary junction: the contralateral lateral spinal tract and ipsilateral anterior spinal tract → descend and synapse onto the lower motor neuron (LMN).

    • Function: Voluntary control of movement from the neck to the feet

  • - Corticobulbar tracts:

    • Anatomy: Same pathway origins, synapse onto the brainstem motor nuclei

    • Function: Voluntary control of face, head and neck movement

• Extra-pyramidal: Ventromedial bulbospinal and ventrolateral bulbospinal

Sensory Tracts

• Anterolateral: Anterior and lateral spinothalamic tracts (Figure 12.1B)

  • Anatomy: Smaller afferent fibers of the peripheral nerves enter the dorsal horn of the spinal cord → cross and ascend in the opposite anterior and lateral columns → enter the brainstem → thalamus (VPL nucleus → postcentral gyrus of the parietal cortex)

  • Function: Nociception (pain), temperature sensibility, touch

• Posterior column-medial lemniscal pathway:

  • Anatomy: Larger afferent fibers of the peripheral nerves enter the spinal cord → ascend in the ipsilateral posterior column → first synapse in the gracile or cuneate nucleus in the lower ...