NBIO 401

Fall 2013

Spinal Cord & Brainstem Sections
Overview: Below are transverse sections from 20 levels of the spinal cord and brainstem. The sections begin at the sacral cord and move rostrally to the rostral midbrain. Our goal is to provide an overall summary of the spinal and brainstem structures that we describe in NBIO 401. Below is a section from nearly the most caudal part of the cord. In this section and the following sections we show the level of the section with a red line on an image to the left. We also name the level of the sections in the upper left. For the cord, the section in the center is stained for fibers. The hemi-section to the right is stained for cells. (You should know the difference and be able to explain what appears dark and light in each section and why.) The brainstem sections are all stained for fibers. We label the structures that we will learn about is NBIO 401. The label for each structure is blue on the most caudal section where that structure appears and red where the same structure appears in more rostral sections. We also provide a brief summary of that structure’s function. Finally, the number in parentheses in the bottom left is the number of new structures labeled (in blue) on that section, i.e., structures not labeled on more caudal sections. For the white matter structures, labeled AXONS, you should learn in 401 where the cell body of these axons are and where the axons terminate. For the gray matter, labeled CELL BODIES you should learn in 401 where the axons run and where they terminate.

-Appendix, brainstem sections, page 1-

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-Appendix, brainstem sections, page 2-

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-Appendix, brainstem sections, page 3-

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Identifying Different Levels of the Spinal Cord On the next 2 pages we will make a brief digression to review and compare the appearance of gray and white matter art different levels of the cord. Your goal here is to be able to identify the level of the cord that a section comes based on what the section looks like. Above you see spinal cord sections that are roughly scaled to size. Imagine that these sections are in the "prone" position and that you are looking at them from their caudal surface, that is, you are looking up the CNS in the rostral direction. Thus dorsal (posterior, the back of the person) is at the top of section and the left side (of the person) is to your left. Cord sections: upper left -- cervical enlargement; upper right -- thoracic; lower left -lumbar; lower right -- sacral. Identify the gray matter and white matter groups on each

section. Note that the proportion of white to gray is greater in the cervical cord segments than in sacral segments, because all descending and ascending tracts must pass through the cervical level to reach their targets. (White matter in the sacral cord contains only descending tracts that end in gray matter in the sacral segments, and ascending tracts carrying information from sacral spinal nerves). The thoracic cord section has the least amount of gray matter compared to the cervical or lumbosacral regions. Gray matter is expanded in the cervical and lumbosacral regions to accommodate the neurons responsible for innervating the limbs.

-Appendix, brainstem sections, page 4-

NBIO 401

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The differences in the size and shape of the gray matter at different spinal levels are emphasized on the next page where we see outlines of gray matter at different spinal levels. The gray matter illustrated here was traced from a set of human spinal cord sections. Note the increase in the size and lateral extent of the gray matter (particularly in the anterior [ventral] horns) in the cervical (C5-T1) and lumbar (L2-S2) regions. These enlargements accommodate additional neurons for processing the output (and input) required for the innervation of the upper and lower extremities respectively. Note that the thoracic cord innervates the trunk, and remains much the same size from segment to segment (segments T7-T9 are not shown).

Below we return to our rostral-moving march through the brainstem beginning just above the cord, in the caudal medulla.

-Appendix, brainstem sections, page 5-

NBIO 401

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Caudal Medulla (level of pyramidal decussation)

-Appendix, brainstem sections, page 6-

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Caudal Medulla (level of most caudal inferior olive)

-Appendix, brainstem sections, page 7-

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Caudal Medulla (caudal inferior olive)

-Appendix, brainstem sections, page 8-

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Middle Medulla (still caudal inferior olive, just not so caudal)

-Appendix, brainstem sections, page 9-

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Middle Medulla (level of central inferior olive)

-Appendix, brainstem sections, page 10-

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Rostral Medulla (level of very rostral inferior olive)

-Appendix, brainstem sections, page 11-

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Caudal Pons (level of caudal pontine nuclei, posterior to trigeminal nerve)

-Appendix, brainstem sections, page 12-

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Still Caudal Pons (still caudal to trigeminal nerve at level of abducens nucleus)

-Appendix, brainstem sections, page 13-

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Middle Pons (level of sensory and motor trigeminal nuclei)

-Appendix, brainstem sections, page 14-

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Still Mid Pons (level of exit of trigeminal nerve)

-Appendix, brainstem sections, page 15-

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Rostral Pons (just rostral to trigeminal nerve exit)

-Appendix, brainstem sections, page 16-

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Rostral Pons (near rostral end of pontine nuclei at level of trochlear nerve exit)

-Appendix, brainstem sections, page 17-

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Caudal Midbrain (just rostral to pontine nuclei)

-Appendix, brainstem sections, page 18-

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Rostral Midbrain (just caudal to cerebral peduncle exit)

-Appendix, brainstem sections, page 19-

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Rostral Midbrain (rostral to cerebral peduncle exit)

-Appendix, brainstem sections, page 20-