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Midbrain: Definition, Function & Structures

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  • 0:01 Neural Information…
  • 0:40 What is the Midbrain?
  • 1:43 Structures of the Midbrain
  • 5:40 Lesson Summary
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Lesson Transcript
Instructor: Sarah Phenix
In this lesson, we'll explore the midbrain, including where it's located, what structures compose it, and what its role is in the functions of your brain.

The Neural 'Information Superhighway'

Have you ever heard the Internet referred to as the 'information superhighway'? It's a bit of a dated term now, but it was coined in the late '70s, during the advent of fast, cable-based communication. That's right, way back in the days of the dial-up modem!

You might be asking, what does this have to do with the midbrain? Well, the midbrain is the biological equivalent of the Internet; it's a vital aspect of our neural 'information superhighway,' which transfers visual and auditory input to the brain and motor (movement) information from the brain.

What is the Midbrain?

The human brain
Midbrain

The midbrain is an area of the brain that, as you might have guessed, is in the middle of two other regions: the forebrain and the hindbrain. The forebrain is the 'front' (fore) brain and is composed of the cerebral cortex, the area that most people think of as the 'brain'; it's the 'supercomputer' of the human body. The hindbrain, or 'back' (hind) brain, is composed of the cerebellum and the pons and the medulla oblongata (or medulla, for short) of the brainstem; it is evolutionarily the oldest part of our brain, controlling primal instincts and automated actions of the body, such as our 'fight or flight' response and heart rate.

The midbrain, on the other hand, acts most notably as the information superhighway connecting these two regions. It enables your brain to integrate sensory information from your eyes and ears with your muscle movements, thereby enabling your body to use this information to make fine adjustments to your movements.

Structures of the Midbrain

The midbrain is formed by three main structures: the cerebral peduncle (peduncle meaning 'foot' or 'base' of the cerebrum), the corpora quadrigemina (meaning 'quadruplet bodies' since it has four mound or hill-like structures), and the cerebral aqueduct, which is a canal dividing the two structures. Now that we know the structures, let's take a moment to look at them individually so we can get a better understanding of their unique roles.

Cerebral Peduncle

The main function of the cerebral peduncle is to transfer motor signals from the brain down to the brainstem. It's made up of a thick bundle of nerve fibers, called the corticospinal tracts, which carry motor signals from your brain to your muscles. Don't be fooled, though; the cerebral peduncle isn't just a 'truck driver,' carrying its 'cargo' of motor signals from one location to another; it also communicates with the cerebellum and, in doing so, helps to fine tune your motor movements.

What's important to remember is that the cerebellum, while not a portion of the midbrain, does communicate with the cerebral peduncles through something called the red nucleus. This communication results in the fine-tuning of your motor movements by way of something called your sense of proprioception. Proprioception is your body's sense of self in the environment, meaning that, even with a blindfold on, you can sense things like where your hands, arms, and feet are relative to one another or if you're upside down or right-side up. It's a pretty cool feature, and, in its absence, we would be really clumsy and completely graceless in our surroundings. If motor signals came straight from our brains, without passing through the 'refining' midbrain, you could say good-bye to dance competitions because we'd all be really terrible!

In addition to all of this, you have two pair of cranial nerves (cranial nerves 3 and 4) that originate in the cerebral peduncle. Cranial nerves, unlike spinal nerves, are nerve bundles that exit directly from your brain rather than your spinal cord. These two nerve bundles both innervate specific muscles of your eyes, anchoring your vision and enabling you to rotate your eyes in their sockets rather than having to turn your head when you want to look at something.

Corpora Quadrigemina

Structures of the corpora quadrigemina
Corpora Quadrigemina

The corpora quadrigemina is a structure located on the back side of the brainstem and hidden by the cerebellum. It's actually a funny-looking little structure because, if you were to flip the cerebellum down, it would almost look as if the brain were 'mooning' you! The corpora quadrigemina has four little 'mounds', or colliculi: two superior colliculi (meaning 'above' or 'top' mounds) and two inferior colliculi (or 'lower' or 'bottom' mounds).

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