Division
Midbrain
Also called Mesencephalon
The top of the brainstem: eye reflexes, hearing relays and dopamine factories.
The midbrain is the short top section of the brainstem, right under the center of the brain. It is small but packed. It holds hubs for eye movements and hearing, and the dopamine-making cells that fuel movement and motivation. A narrow canal runs through it, carrying brain fluid down to the lower brainstem.
Where it is
At the top of the brainstem, deep in the center of the head, just below the thalamus and above the pons.
What it does
Eye control
It houses control centers for most eye movements and for the pupil's reaction to light.
Reflexes to sights and sounds
Four small bumps on its back, the colliculi, turn your eyes and head toward sudden sights and sounds.
Movement and motivation
Its dopamine cells, in the substantia nigra and the VTA, help you move smoothly and feel driven to chase goals.
Pain control
A ring of gray matter around its fluid canal can turn pain down and trigger freezing when you are frightened.
Think of it as a busy crossroads town: tiny on the map, but full of important businesses, from eye control to dopamine factories.
Inside the midbrain
- Substantia nigraThe "black substance": dark dopamine cells whose loss causes Parkinson's disease.
- Red nucleusA rosy, iron-rich hub in the midbrain linking the cerebellum to movement.
- Ventral tegmental areaA dopamine hub for reward and motivation, firing when life beats your expectations.
- Superior colliculusThe midbrain's "look over there!" center, snapping your eyes toward things.
- Inferior colliculusThe hearing hub of the midbrain, a key relay for sound signals on their way up.
Works with
- Substantia nigraThis dark band inside the midbrain supplies dopamine for smooth movement.
- Ventral tegmental areaThis small cluster is the heart of the brain's reward and motivation system.
- Oculomotor nerve (III)This nerve leaves the midbrain to move most of the eye muscles and to shrink the pupil.
- Trochlear nerve (IV)This thin nerve exits the back of the midbrain to work an eye muscle that helps you look down.
- Cerebral aqueductThis narrow fluid channel runs right through the midbrain.
- ThalamusHearing signals pass through the midbrain on their way up to the thalamus.
When it goes wrong
Parkinson's disease
Loss of the dopamine cells in the midbrain's substantia nigra causes the tremor, stiffness and slowness of Parkinson's disease.
Blocked fluid canal
If the narrow canal through the midbrain gets blocked, fluid can build up inside the brain. This is called hydrocephalus, and surgeons can often treat it by giving the fluid another way out.
Trouble looking up
Pressure on the top of the midbrain, for example from a nearby tumor, can make it hard to look upward. This is known as Parinaud syndrome.
For learning only, not medical advice. If you have a health concern, talk to a doctor.
Surprising facts
- The four bumps on its back are called the corpora quadrigemina, Latin for "quadruplet bodies".
- When a doctor shines a light in your eyes, they are partly checking your midbrain, which controls the pupil reflex.
- The trochlear nerve is the only cranial nerve that leaves from the back of the brainstem.
Where the name comes from
Its scientific name, mesencephalon, is Greek for "middle brain". It grows from the middle of three bulges in the brain of an early embryo.
Learn it in a lesson
- The brainstem and cranial nervesLife support and the nerves of the head. A short guided lesson in 3D.
Quick quiz
3 questions. Your answers are saved and come back in your daily review.
Which of these is a job of the midbrain?
Show the answer
Eye control. It houses control centers for most eye movements and for the pupil's reaction to light.
Eye control. It houses control centers for most eye movements and for the pupil's reaction to light.
The midbrain is part of which larger structure?
Show the answer
Brainstem. It belongs to the brainstem.
Brainstem. It belongs to the brainstem.
Which part fits this description? "Like a busy crossroads town: tiny on the map, but full of important businesses, from eye control to dopamine factories."
Show the answer
Midbrain. It is the midbrain. The top of the brainstem: eye reflexes, hearing relays and dopamine factories.
Midbrain. It is the midbrain. The top of the brainstem: eye reflexes, hearing relays and dopamine factories.
These parts now come back in your daily review, just before you would forget them.
Practice these parts in 3DSources
- Neuroanatomy, Mesencephalon Midbrain, StatPearls, NCBI Bookshelf
- Neuroanatomy, Cranial Nerve 4 (Trochlear), StatPearls, NCBI Bookshelf
- Neuroanatomy, Cerebral Aqueduct (Sylvian), StatPearls, NCBI Bookshelf
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Explore the midbrain in 3D
Turn it around, zoom inside and see how it connects to the rest of the brain, then test yourself with quick quizzes.
Open it in 3D