2: A Brief Review of Clinical Neuroanatomy

INTRODUCTION

I. GROSS SUBDIVISIONS OF THE NEURAXIS

To interpret the neurologic examination (NE), you must have a firm grasp of basic neuroanatomy. If you just groaned, let us distinguish two types of neuroanatomy: tongue tip neuroanatomy is used on the spot in the clinic, and fingertip neuroanatomy is researched as the need arises. This chapter clearly separates the two.

A. Two main parts of the nervous system

The nervous system consists of the central nervous system and the peripheral nervous system.

1. The central nervous system (= CNS = neuraxis) consists of the brain and spinal cord. See Fig. 2-1.

2. The peripheral nervous system (PNS) consists of:

   1. Cranial nerves (CrNs) and their ganglia

   2. Spinal nerves and their ganglia and plexuses

   3. Autonomic nerves and their ganglia, plexuses, and nerves

3. To cleanly separate the PNS from the CNS, simply snip all cranial and spinal nerves at their attachment sites to the brain and spinal cord.

B. Cutting the neuraxis into its gross subdivisions

1. To separate the brain from the spinal cord: Locate the foramen magnum shown in Fig. 2-1 and sweep a scalpel transversely across the neuraxis at the level of the foramen magnum. The plane of that cut defines the medullocervical junction.

   1. The brain is rostral to the cut.

   2. The spinal cord is caudal to the cut.

2. Definition of the brain: The whole brain consists of the brainstem, cerebellum, diencephalon, and the cerebral hemispheres. Identify them in Fig. 2-1.

3. To separate the brainstem from the rest of the brain, make the following cuts:

   1. Transect the neuraxis just as the midbrain (= mesencephalon) emerges from the base of the cerebrum (Fig. 2-1). (Technically the plane of transection runs from the postmammillary sulcus to the posterior commissure.) The rostral cut surface of the midbrain abuts on the caudal cut surface of the diencephalon (Fig. 2-1).

   2. Then, to separate the cerebellum from the brainstem, slice through the cerebellar peduncles that attach it to the pons (Figs. 2-1 and 8-3). The brainstem remains.

   3. To separate the brainstem into its three parts, the midbrain, pons, and medulla, make transverse cuts at the midbrain-pontine junction and at the pontomedullary junction (Figs. 2-1 and 2-20).

   4. The diencephalon and cerebrum remain.

4. To separate the diencephalon from the cerebrum, core it out with a wire loop: The basal ganglia and deep cerebral white matter surround the diencephalon. To detach these structures from the cerebrum, insert a wire loop from the base of the cerebrum, where ...