How to Draw Brainstem Sections Use the arrow

How to Draw Brainstem Sections Use the arrow keys to see the animations on each slide This tutorial will teach you how to draw representative diagrams of sections from different levels of the CNS. Although the sections may look complicated, drawing their outlines is easy. Learning how to draw these diagrams has great benefits: you will be able to quickly recognize the different CNS levels, you will understand the structures that define their shapes, and you will remember the positions of the tracts and nuclei in the pathways we will study. Chris Cohan, Ph. D Jacobs School of Medicine University at Buffalo

Spinal cord Let’s start with the spinal cord. Draw a large oval for its outer shape. Now draw curved lines for the central grey area. Place a small circle near the center for the central canal.

Caudal Medulla central canal The outer shape of the caudal medulla is similar to the spinal cord, which is connected to it. It is shaped like a circle. So draw one big circle. Now draw a small circle in the center about 1/3 from the top to represent the central canal.

Rostral Medulla 4 th ventricle Inferior cerebellar peduncle Inferior olive pyramid The rostral medulla changes shape due to some new structures present at this level. It is round, but has some large structures around its surface. Draw one big circle. Now draw 2 smaller circles above (inferior cerebellar peduncles) and 2 smaller circles below (inferior olivary nuclei) as shown. Draw 2 triangles down at the bottom (pyramids). Now draw a line around the outside staying close to the larger circle as you go. That’s the basic shape of the rostral medulla.

Caudal and Mid Pons 4 th ventricle middle cerebellar peduncle basilar pons The shape of the caudal pons is a little more complicated due to its large bottom and protruding arms (peduncles). Start off by drawing a large square. Put a large circle at the top for the 4 th ventricle. Now draw a long line with a curve at the bottom and then a straight line at the top. That’s it! All the sensory structures we are studying will go in the square. The large bottom area will contain motor structures we will study later.

Rostral Pons 4 th ventricle (beginning) The snowman! The rostral pons has a simple shape – 2 intersecting ovals. Draw one smaller oval on top and a larger oval below it. Add a small circle for the start of the 4 th ventricle. That’s it! We can erase the intersecting line to make it blend. Just like the previous level, all the sensory structures we are studying will go in the upper (oval) area.

Midbrain colliculi cerebral aqueduct periaqueductal gray crus cerebri The pig (from the rear)! The midbrain has an oval shape. To begin, draw one large oval. Place 2 rectangles on the bottom for the crus cerebri. Draw a small circle near the top for the cerebral aqueduct and outline the area around it for the periaqueductal gray. Now put 2 bumps at the top for the colliculi.

Adding Pathways to Brainstem Sections You have already learned the positions of structures in the sensory pathways. Now we can add in the motor structures including: Corticospinal Tract Motor Cranial Nerves Since the corticospinal tract is a descending pathway, we’ll start at the midbrain and proceed caudally.

Rostral Midbrain VTT ALS medial lemniscus corticospinal tract CN III • CST – positioned in middle quadrant of crus cerebri • CST remains near anterior surface of brainstem until it enters the spinal cord • CN III exits at this level. Note how fibers spread through red nucleus.

Caudal Midbrain CN IV VTT ALS IV medial lemniscus corticospinal tract • CST – in middle quadrant of crus cerebri • CST – on anterior surface • CN IV nuc at this level; Nerve travels to contralateral side and exits posteriorly!

Rostral Pons VTT ALS medial lemniscus corticospinal tract • CST – in anterior (bulging/basilar) area • CST – broken into many fascicles distributed throughout anterior region

Mid Pons CN V motor nuc V ALS VTT CN V medial lemniscus corticospinal tract • CST – on anterior surface • CST – fascicles merge together on each side to form single bundles • CN V exits lateral surface of brainstem

Caudal Pons spinal trigeminal tract/nuc VI VII ALS VTT CN VII medial lemniscus corticospinal tract CN VI • CST – on anterior surface • CST – single bundle on each side • CN VI nuc in floor of 4 th ventricle. CN VI fibers pass near CST to exit near midline • CN VII nuc sends fibers around CN VI nuc to exit lateral surface of brainstem

Rostral Medulla CN XII spinal trigeminal tract/nuc XII CN IX, X NA ALS medial lemniscus VTT Pyramids (corticospinal tract) • CST – on the anterior surface • CST – called “pyramid” here due to shape • CN XII fibers pass near CST to exit • Nuc Ambiguus fibers contribute to CN IX, X

Caudal Medulla Nuc gracilis Nuc cuneatus spinal trigeminal tract/nuc ALS Pyramids (corticospinal tract) • CST – on anterior surface as pyramid

Caudal Medulla near Spinal Cord Nuc gracilis Nuc cuneatus spinal trigeminal tract/nuc ALS Pyramidal decussation • CST – crosses over to the opposite side, forming “pyramidal decussation”

Spinal Cord fasciculus gracilis fasciculus cuneatus Lateral corticospinal tract ALS CST – main component becomes the lateral corticospinal tract