Back To CourseAnatomy & Physiology: Tutoring Solution
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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.
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.
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.
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.
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).
The colliculi are little relay stations that take information from a sensory input 'station' and relay it to the thalamus, which works something like a 'mailman' in that the thalamus collects the signals and then sends them to the appropriate 'address' in the brain for processing. The superior colliculi collects visual information from the optic tract, while the inferior colliculi collects auditory information from the ear.
The cerebral aqueduct is a little canal that separates the cerebral peduncle from the corpora quadrigemina. It's part of a larger system of canals that circulates and distributes cerebrospinal fluid throughout your brain ('cerebro') and down your spinal cord ('spinal'). This fluid plays a few roles, such as removing metabolic waste and pathogens into the bloodstream for disposal and buffering and cushioning the brain, as well as helping maintain blood pressure around the brain by functioning as the inverse to it; if blood pressure drops, cerebrospinal fluid pressure increases, and vice versa.
The midbrain is located between the forebrain and the hindbrain and is comprised of three parts known as the cerebral peduncle, corpora quadrigemina, and cerebral aqueduct. The midbrain serves to refine your muscle movements by communicating with the cerebellum, resulting in your sense of proprioception, or your sense of self in the environment. The red nucleus, located in the cerebral peduncle, communicates with the cerebellum and is responsible for relaying information that leads to these minor motor adjustments, which are sent down the corticospinal tract. Within the cerebral peduncle, you also have two cranial nerves (nerves 3 and 4), which are responsible for controlling the movement of your eyes in their sockets.
The corpora quadrigemina, composed of two superior colliculi and two inferior colliculi, act as relay stations that take sensory information from the eyes and ears and relay it to the thalamus for distribution to the appropriate area of the cerebrum. The cerebral peduncle and the corpora quadrigemina are separated by a canal called the cerebral aqueduct, which distributes cerebrospinal fluid throughout the brain and spinal cord to buffer the tissue, remove wastes, and maintain cranial pressure.
|Cerebral Peduncle||Corpora Quadrigemina||Cerebral Aqueduct|
|*Transfers motor signals from the brain down to the brainstem
*Origin of cranial nerves 3 and 4 that control eye movement
| *Collects sensory input from the ears and eyes and relays it to the thalamus
*Located behind the brainstem
*Has 2 superior and 2 inferior colliculi
|* Canal that separates the cerebral peduncle from the corpora quadrigemina
*Produces cerebrospinal fluid that maintains pressure in the brain, buffers tissue, and removes waste products
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Back To CourseAnatomy & Physiology: Tutoring Solution
19 chapters | 330 lessons