The brainstem is not the most impressive part of the complex organ. However, without them, our body would be like an incredible robot that cannot access its software. But the brainstem is not as simple as a power cord and plug. It is divided into three parts including the midbrain. Within the midbrain is the tectum. But what does this tiny part of our brain do?
The tectum ("roof" in Latin) is the posterior part of the midbrain, consisting of superior and inferior colliculi. The first receives information from the retina and visual cortex. The latter receives information from the auditory fibers. In short: the tectum is essential for visual and auditory processing.
The occipital lobe of the brain deals with vision. While the auditory cortex are the areas that process auditory information. But first, these signals pass through the brainstem. But the brainstem is more than a tunnel or courier for information. It potentially saves our lives in situations where we don't have time to wait for the central brain to process the situation.
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Ceiling: A small part of the brainstem
Tegmentum: The floor of the midbrain
Ceiling: A small part of the brainstem
The tectum is located in the brain stem, which connects the brain to the spinal cord. The middle brainstem is three inches long and serves as an information pathway, carrying signals from the brain to the body and back. But the brainstem also plays an essential role in other areas, including:
- facial movements
- To swallow
- regulate the heartbeat
- blood pressure regulation
The brainstem is divided into three main sections:
- Medulla oblongata (bottom section, connected to the spinal cord)
- Pons (the "bridge" and largest section)
- Midbrain (Mesencephalon, upper section, only 2 cm long)
The tectum is located in the midbrain.
Roof: The roof of the midbrain
The midbrain (midbrain) is the upper 2 cm long section of the brainstem and is divided into three parts:
- Brainstem (front of midbrain, connects brainstem to thalamus)
- Quadriminal bodies (visual and auditory reflexes)
- Cerebral aqueduct (connects the fourth ventricle to the third)
The tectum lies behind the cerebral aqueduct and forms part of the "roof" of the midbrain. Simply put, the function of the tectum is auditory and visual processing. While the area in front of the cerebral aqueduct is the tegmentum and its prominent roles are pain processing, alertness and coordination.
Ceiling: The superior and inferior colliculi
The tectum is mainly characterized by four protuberances of clusters of neurons. These "bumps" are the superior and inferior colliculi.
The superior colliculi: ocular and cervical reflexes
The superior colliculi are the first two of the "bumps" that lie below the thalamus and above the inferior colliculi (the inferior bumps). These two main groups of neurons are responsible for eye and neck reflexes.
We use these reflexes all the time without having to consciously think about it. For example, if you are at a football game and someone throws an "Ave Maria", you can follow the trajectory of the ball without conscious effort. You will track him when he leaves the quarterback and follow him until he is caught or hits the ground.
You also use this when reading a book or web page. Your eyes move effortlessly along the text to absorb the information. Your focus is on absorbing and interpreting information, not the physical action of moving your eyes word for word across the page or screen.
These reflexes can also help protect us. A flash of light from the side or a tap on the shoulder draws attention to the surprise. The neck and eyes work together without us having to consciously consider them. These instinctive actions save us time and give us the chance to save ourselves by running or fighting if necessary.
The superior colliculi's role in survival may be why they constitute a significantly large brain region in certain animals, such as birds or fish, as opposed to a much smaller region in the human brain. Fast reflexes in response to input are needed not only to avoid damage, but to successfully hunt or reach the food source as quickly as possible.
However, this is a rudimentary explanation of the superior colliculi. Nor is its role fully understood. The superior colliculus consists of many layers that receive information from different sources.
These layers have been divided into two main groups:
- deep layers
The superficial layers are mostly related to what was discussed above as most of the information they receive comes from the retina and visual cortex.
The deep layers are more complex and less understood. In addition to visual input, these deeper layers receive input from the auditory and somatosensory systems. The latter includes touches such as pressure, temperature, pain, texture and movement.
The inferior colliculi: auditory processing
The inferior colliculi are the other two "bumps" below those that make up the superior colliculi. It plays a crucial role in hearing, collecting information from all of the body's auditory pathways and sending it to the cerebral cortex. It's like "All Roads Lead to Rome", but for listening. Once the inferior colliculi have the information, it is relayed to places like the superior colliculus or the thalamus.
The inferior colliculi are divided into the areas:
- Núcleo central
- Dorsaler Kortex
- external cortex
Some knowledge of the dorsal and external cortex is lacking. Scientists know that damaging them can impair our ability to process sound, but exactly how and why is unclear. However, there is a better understanding of the central core. It is the receptor for the cochlea, superior olive nucleus and other areas.
The central nucleus also contains neural fibers that connect to the thalamus. Within the thalamus is the medial geniculate nucleus, which receives information from the central nucleus and transmits it to the auditory cortex. It's like having a mail system for your ears.
But the inferior colliculus has a more important role than being a healthy post office, collecting and distributing acoustic input. The neurons in it can determine the loudness of a sound and even distinguish how long it took for the sound to travel from one ear to the other.
At first glance, it doesn't seem like a big deal to know which ear picked up a sound first and for how long. But this information will help you to know where a sound comes from. Also, your eyes and neck react to this input, which can be vital in a dangerous situation.
Imagine a half-asleep ball whizzing toward your head in the outfield. Sound helps your eyes locate the ball you didn't realize was being hit by the batsman. Since you haven't seen the goal, your eyes can't follow the ball. This is how your auditory calculations help narrow down the possibilities of where the ball could be. Ideally, you'll spot it and pull the glove off in time to protect your face from contact.
It is this calculation that also saves people on the road. For example, you might not see the oncoming car when you pull off the curb, but your presence will be alerted to those who can hear you, allowing you to jump back.
The inferior colliculus also acts as a filter and prioritizes sounds. For example, if you're talking to others at a dinner party, it can amplify the speakers' voices and help filter out breathing and chewing noises.
Damage to the inferior colliculus can result in deafness, even when all ear mechanisms are working perfectly. This rare occurrence is the result of bilateral damage. But if the damage is one-sided, a person can still hear but have a hard time understanding where the sound is coming from.
However, damage to the tectum without damage to the rest of the brainstem or at least the midbrain is uncommon. Therefore, the precise results of damage or abnormal development of the tectum are better understood in a broader context.
Tegmentum: The floor of the midbrain
The tegmentum is considered the floor of the midbrain. In Latin it means "hood" or "cover". Its prominent roles are in alertness, coordination, and pain processing. Unlike the tectum, the tegmentum extends beyond the midbrain and down the brainstem. However, the part of the tegmentum in the midbrain that receives the most attention is:
- red core
- periaqueductal gray matter
- net-like structure
Tegment: red core
The red core of the tegmentum gets its name from its pale pink color. Why they couldn't call it "pink core" is a good question with no definitive answer. The color is thought to come from iron in the environment, primarily hemoglobin and ferritin.
The red core is divided into two main sections:
- Parvocellular red nucleus (medium-sized neurons)
- Magnocellular red nucleus (large neurons)
Parvocellular red nucleus: bipedal mammals
Between the parvocellular red nucleus and the magnocellular red nucleus, the former is the dominant structure in the human brain. However, it is less well known than the magnocellular red nucleus because it is easier to study animal brains and neurofunctions.
However, scientists know that parvocellularis is associated with motor movement. Therefore, damage to the area can cause tremors and is being studied for its possible role in Parkinson's disease.
Magnocellular Red Core: Quadrupedal Mammals
In quadrupedal animals, the magnocellular red nucleus is dominant and assists in gait and postural stability. It is also believed that coordinating all four legs and avoiding obstacles is crucial. To this end, the magnocellular red nucleus produces neurons that migrate from the nucleus to the rubrospinal tract, which plays an important role in involuntary movements and fine motor skills. From there we come to the spinal cord.
The magnocellular red nucleus is an area of the human brain that plays a more prominent role in newborns, but diminishes as we learn to walk on two legs. However, how people control their hands still seems to play a role.
Red Core: Pain and Analgesia
The red core is not just important for coordination. For example, it is believed to play a role in how we experience pain or not (analgesia). The exact role of the red nucleus in pain control is not known, but it is thought to be due to its association with the periaqueductal gray and raphe nuclei, the former of which forms part of the tegmentum.
Tegmentum: periaqueductal gray matter
The periaqueductal gray matter is often referred to as the "analgesic center" for its role in inhibiting pain, but this is far from its sole purpose. It is located in a pillar of the brainstem and surrounds the cerebral aqueduct in the midbrain. It has neurons that connect it to the medulla oblongata, including the serotonin-producing neurons known as the raphe nuclei.
However, the periaqueductal gray matter has other functions that are still being explored. Some of them are:
- heart rate regulation
- blood pressure regulation
- Bladder control and contraction
The periaqueductal gray matter is also of great interest to those studying PTSD. The midbrain contains many neurochemicals:
- amino acid
- opioid neurotransmitter
If regulation of these changes, it may alter the functional connectivity of the midbrain, including the connectivity of the periaqueductal gray matter to the amygdala. The amygdala is one of the three main brain regions affected by PTSD patients, along with the hippocampus and the medial prefrontal cortex.
Roof: A reticular formation
The reticular formation is located in the center of the tegmentum. Its web-like structure is the source of its name and it is a very intricate and complex section. It is vital for many functions, but is best known for its role in consciousness (alertness) and arousal. Both functions are performed by the reticular activating system (upward excitation system).
The reticular activating system has circuits from different areas of the brainstem. Its neurotransmitters include acetylcholine and norepinephrine, which are crucial for arousal and alertness. When pathways in this system are damaged by injury, consciousness is impaired. The greater the damage, the more consequences follow, including coma or a vegetative state.
However, this is a simplified explanation of the reticular formation. As stated above, this is a highly complex area with many functions. Furthermore, its interaction with other areas of the brain is also diverse and complicated.
The tectum is part of the midbrain that makes up the upper part of the brainstem. The tegment forms the “ground”. The full role played by these parts of the midbrain is still being explored. However, we know that the tectum is critical for our auditory and visual processing; The tegmentum is necessary for coordination, pain processing, and alertness.
- Upper and lower colliculi
- Function of the Auditory Cortex
- Motor cortex function
- What does the thalamus do?
- Diencephalon (location, function and parts)