BIO 004 · Human Anatomy
The Brainstem
Block 5 · Module 3: The Central Nervous System, the Brainstem
A reference for the brainstem video and lab. This page covers the three regions of the brainstem, the midbrain, the pons, and the medulla oblongata, the structures within each, and the reticular formation that runs through them. The focus is on the structures and the job each one does.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level depth for this course.
- Name the three regions of the brainstem and locate each one.
- Identify the key structures of the midbrain, the pons, and the medulla oblongata.
- Describe the reticular formation and the reticular activating system.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
The brainstem in profile
Add a labeled midsagittal section showing the midbrain, pons, and medulla oblongata.
The dorsal brainstem
Add a labeled posterior view showing the colliculi and the cerebellar peduncles.
Cranial nerve attachments
Add a view showing where cranial nerves III to XII attach to the brainstem.
The Brainstem, an Overview
The brainstem connects the cerebrum, the diencephalon, and the cerebellum to the spinal cord. Every ascending and descending tract passes through it, and it holds the nuclei for ten of the twelve cranial nerves.
- Brainstemthe stalk of the brain connecting the higher regions to the spinal cord; the midbrain, pons, and medulla
- Midbrainthe most superior region of the brainstem, also called the mesencephalon
- Ponsthe middle region of the brainstem, a bridge to the cerebellum
- Medulla oblongatathe most inferior region of the brainstem, continuous with the spinal cord
- Cranial nerve nucleithe clusters of gray matter in the brainstem that give rise to or receive cranial nerves III through XII
- Passing tractsthe brainstem carries every ascending sensory tract and descending motor tract between the brain and the cord
The Midbrain
The midbrain, or mesencephalon, is the short, most superior region of the brainstem. It surrounds the cerebral aqueduct.
- Tectumthe roof of the midbrain, made of four rounded bumps called colliculi
- Superior colliculithe upper pair of colliculi; centers for visual reflexes, such as turning the eyes and head toward a sight
- Inferior colliculithe lower pair of colliculi; centers for auditory reflexes, such as turning toward a sound
- Cerebral pedunclesthe paired stalks on the front of the midbrain that carry descending motor tracts
- Substantia nigraa darkly pigmented midbrain nucleus that helps regulate movement, working with the basal ganglia
- Cerebral aqueductthe narrow channel through the midbrain that carries cerebrospinal fluid from the third to the fourth ventricle
- Cranial nerve nucleithe midbrain holds the nuclei for CN III, the oculomotor nerve, and CN IV, the trochlear nerve
The Pons
The pons is the rounded, middle region of the brainstem. Its name means bridge.
- Ponsthe middle region of the brainstem; a bridge between the medulla, the midbrain, and the cerebellum
- Pontine nucleiclusters of gray matter that relay motor information from the cerebral cortex to the cerebellum
- Middle cerebellar pedunclesthe thick stalks that carry signals from the pontine nuclei into the cerebellum
- Fourth ventriclethe cerebrospinal fluid space that lies behind the pons and the upper medulla
- Cranial nerve nucleithe pons holds the nuclei for CN V (trigeminal), CN VI (abducens), CN VII (facial), and CN VIII (vestibulocochlear)
The Medulla Oblongata
The medulla oblongata is the most inferior region of the brainstem. It is continuous with the spinal cord at the foramen magnum and contains centers that keep the body alive.
- Medulla oblongatathe most inferior region of the brainstem; it merges into the spinal cord
- Pyramidsa pair of ridges on the front of the medulla formed by the descending corticospinal motor tracts
- Decussation of the pyramidsthe crossover point where most corticospinal fibers pass to the opposite side; it is why one hemisphere controls the opposite side of the body
- Cardiac centerthe medullary center that adjusts the rate and force of the heartbeat
- Respiratory centerthe medullary center that sets the basic rhythm of breathing
- Vasomotor centerthe medullary center that adjusts the diameter of blood vessels, and so blood pressure
- Cranial nerve nucleithe medulla holds nuclei for CN VIII (cochlear), CN IX, CN X, CN XI, and CN XII
The Three Regions Compared
Each region of the brainstem has its own structures and its own set of cranial nerve nuclei. Compare them.
| Region | Key structures | Cranial nerve nuclei |
|---|---|---|
| Midbrain | the tectum, with superior colliculi for visual reflexes and inferior colliculi for auditory reflexes; the cerebral peduncles carrying descending motor tracts; the substantia nigra | III and IV |
| Pons | a bridge between the medulla, midbrain, and cerebellum; contains the pontine nuclei that relay motor information to the cerebellum | V, VI, VII, and VIII |
| Medulla oblongata | contains the pyramids, where the corticospinal tracts decussate; holds the vital centers for heart rate, breathing, and blood vessel diameter | VIII through XII |
The Reticular Formation
The reticular formation is not one structure. It is a net of gray matter cell bodies woven through the white matter of the entire brainstem.
- Reticular formationa network of gray matter neurons spread through the core of the brainstem
- Reticular activating systemthe RAS, the ascending part of the network; it keeps the cortex awake, alert, and attentive
- Functions of the RASmaintaining consciousness and arousal, holding attention, and filtering out unimportant incoming stimuli so the brain is not overloaded
- Descending componentthe part that helps set the muscle tone of resting skeletal muscle and coordinates motor activity with autonomic reflexes
- Loss of RAS activitywhen the ascending system is shut down the result is sleep, and severe damage can cause coma
See also: The Brain and The Spinal Cord, and The Cranial Nerves for the nerves whose nuclei sit here.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Name the three regions of the brainstem from superior to inferior.
- For each brainstem region, name one structure or function it is known for.
- Explain why damage to the brainstem is far more dangerous than damage to a single cerebral lobe.
- Describe where the brainstem sits relative to the cerebrum and the spinal cord.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.