Preview Questions: ...I know there is a lot of them, and they are elaborate descriptions of how the brain works.
Please spread these out into a couple sessions and take your time working through them. I think it will very much help you understand this most amazing organ (and also most difficult one to understand) better.
I'm working every day trying to 'outsmart' my brain in order to better understand it...I hope these descriptions can help you with yours!
18.1. Before we reach into the brain and dissect it, let’s talk a little more about pathways. As we discussed, the brain receives sensory stimuli that tell it what’s going on both inside and outside of our body. It then continually interprets all those impulses and comes up with an appropriate response or reaction. Let’s say you’re driving down the freeway and all a sudden, some f*#⚡︎#*g jerk cuts you off and you have to maneuver out of the way almost having an accident. Think of all the information your brain receives and needs to process extremely fast in order for you not to potentially perish! Your hands and feet for sure need to react very quickly; those motor outputs go straight to skeletal muscles. If you then wait for a moment, a sudden jittery feeling arises, like if you drank too much coffee. This is the adrenalin, which is actually a hormone that is ordered by the brain to be released into the blood stream. This way it will stay around in the system for a while and can make sure the body is ready to deal with potential injuries as well as possible. The brain’s impulses going to the muscles are said to be conscious. On the other hand, the other processes that make sure your body’s internal milieu is optimized are largely unconscious. What do we call that part of the nervous system?
18.2. As described in the last chapter, the brain is very delicate and requires ‘super’ protection. The skull is like a football helmet. Underneath we have multiple membranes helping to cushion the brain. An outer one feels tough like leather; it holds everything together. Below that, our brains are protected by a more delicate one that actually has tiny ‘finger-like’ projections reaching internally ‘touching’ the innermost membrane, which is a very thin layer adhering to the brain itself. Collectively, these ‘finger-like’ projections softly hold the brain in place and like an army of little springs prevent excessive movements. Cool, right? The watery substance described in the last chapter (17.14) surrounds the brain in the same space, effectively tacking 97% of its weight off the forces of gravity. This way the brain is protected from shock and gravity. Wouldn’t you also like to be held in such a cozy way? I would. What are these 3 membranes called?
18.3. The nervous system starts developing in an embryo within 3 weeks of being conceived – that’s early! At that point, we are kind of like a flat leaf with a stem going up it’s middle. That centrally laying structure folds in on itself and becomes the neural tube. It will ultimately grow into the spinal cord with the brain on its top end. The brain then grows heavily early in life. At what age does the brain almost reach it’s full weight?
18.4. If we look at a brain from the outside, it looks like a ball of wiggles and grooves with a stem coming out at the bottom. The convolutions are called gyri; they increase the surface area of the brain greatly. It is in this outer area where most neural cell bodies are located. Internally, the brain is primarily made up of pathways for impulses to be sent along. These fibers, as they are also called, have myelin (fatty, hydrophobic, phospholipid bi-layer) coverings that insulate them from one another, and also speed up the electrical impulse. Fatty stuff looks somewhat white making that area of the brain be called the white mater. What do we call the ‘mater’ where the cell bodies are found?
18.5. Looking at a brain again from the outside makes us appreciate that there is a deep groove, or fissure as it is called, that separates the brain largely into a right and left hemisphere. Both sides of the brain are mirrored. In terms of sensory impulses and motor commands, the body is largely controlled by the opposite side of the brain. The brain hemispheres are also impacted when it comes to thinking. The left is said to be ’more logical’, and the right ’more creative’. As these generalizations are dangerous, especially if they are used as excuses of why we are not good at math or language, they are also quite interesting. For example, patients with strokes in the area of language creation (Broca’s area its called) can have language come back somewhat when they have songs from their childhood sung to them. This apparently activates the mirrored part of the brain in the other half. Since these 2 hemispheres are largely separated from one another, how can they communicate with one another? Cell phone technology?...No, of course not. If you reach deep in between the hemispheres, you notice a structure a the bottom. Those are pathways connecting the two. What is that structure, that is actually said to be more developed in the female brain, called?
18.6. Looking at the superficial, cellular layer of the brain, called the cerebrum, we are talking about the conscious part of our ‘computer’. We can identify 5 different lobes with different functions in them. 4 of them are named after the skull plate covering them. The fifth one is hidden. Can you name it?
18.7. The frontal lobe is concerned with sending motor commands through the body. All other lobes have more sensory, or integrative functions. Let’s say you want to walk; the initiating command sent to your muscles comes from the frontal lobe, actually specifically the primary motor cortex, which is an area of cell bodies that are located in the precentral gyrus (the wiggle in front of the central sulcus, which is beneath one’s hairline on the forehead). The entire body is actually mapped out on that gyrus. When we artificially stimulate an area, the corresponding body part moves. The frontal lobe is also the main ‘thinking’ area of the brain, where we solve problems and judge situations. A famous region in the frontal lobe is known as Broca’s area. What function does it hold?
18.8. The parietal lobes process incoming, sensory information coming from the body. Sensations such as superficial or deep touch, temperature, or also pain travel from the body up the spine, through a structure in the center of the brain called the thalamus (more of it later). From there, nerve fibers send the body sensations to the postcentral gyrus, which is where the primary somatosensory cortex lies. Wowowo, what’s up with all those big words? Well, soma- means body (as in bodily sensations), and -sensory means that it is incoming information. A primary area is the part of a lobe where information is first sent to. Association areas surround them to process the information and help the brain understand what is meant by a sensation. All the processing going on within those areas ultimately create responses, some of which are sent to the association areas of the frontal lobe for motor processing, and possible motor execution. Do you start seeing of how some of the pathways could work their way around in your head? Each area of the brain does have a specific function; although the coolest thing is, that it is so moldable (neuroplasticity), that one part can take over tasks of another. Blind people, for example, fill their visual cortex with touch sensations, so that they can experience the world more fully without the visual input. What general function do the primary cortexes of the occipital and temporal lobes possess?
18.9. The hidden lobe, the one that’s like an island hidden behind the other ones on the sides of the brain, the insula has a few functions associated with it. It is where we consciously feel self-aware. It is also, where the primary vestibular cortex lies. What function would we find there?
18.10. The superficial cortex is where most cell bodies lie that integrate information. Most deeper brain structures are pathways connecting those integrating cells with one another. Some neural cell bodies, however cluster within the deeper brain; we generally call them nuclei. One of them concerns itself with bodily movement. Movement patterns are stored here. Remember when you learned driving? You had to pay full attention to every detail, gas pedal, clutch, break, steering wheel, and more. Now, never mind…you can drink your coffee in the car, listen to the news, or possibly even put on your make-up, watch a game, or read the paper (*!but do never even think of texting while you drive!). Anyway, what is the structure called where all that automated movement pattern stuff is located?
18.11. Evolutionarily speaking (you know that nifty thing God created to help life adapt to ever changing environments) early animals relied heavily on smell to understand their outside world. They used that sense to detect danger, and also more pleasant things such as food. We still process smell different than any other sensory input. It bypasses any filter and connects straight to our emotional brain. What do we call that part of the brain that deals with emotions?
18.12. The emotional brain is where we process feelings and have emotional reactions. A very important pathway within it, is the one that gets activated when we freak out and loose it. The amygdala is a structure that is heavily responsible for how we assess danger; it is where we react to fear. This is where much of our automatic reactivity and outbursts come from; remember the last time you had a tantrum? We could call it an ‘amygdala hijack’! The amygdala works unconsciously, that is outside of our control of being able to think about the danger, nor influence how we react to it. Many of us ‘live’ large parts of our lives in this ‘mental prison’, where we react to things, but have no control over what is going on. If we want to be more in control of our reactions, we have to figure out of how to make them more conscious; we have to stimulate pathways that bring the experience more into the frontal cortex, where we can consciously and hopefully more realistically assess a situation (remember, question 18.7. says that the ‘main thinking’ area of our brain is beneath the forehead). The amygdala also sends signals to another structure that is going to involve the autonomic nervous system and the hormonal endocrine system, which then ‘tell’ the whole body about the danger the brain experiences and prepare it to deal with it. A brain that is under real or perceived continued threat will keep the entire body constantly alert, which, over time will wear it out and we develop what are called ‘psycho-somatic’ illnesses. This is why calming the mind and learn ‘realistic’ threat assessment helps the body be healthier. Oi vei, that was a lot of info. At least now you know why I think meditation, or having a loving relationship with ourselves, is so crucial. Ups, yes, the question…what is the brain structure called that connects the emotional brain to the rest of the body?
18.13. Another interesting structure that lies within the emotional brain has to do with long-term memory, you know, the place where you’d like to store all that anatomy information that seems so hard to remember. Working memory, which we use to solve problems, is located in the frontal cortex. Once we solve a problem and understand a concept, and we want to ‘commit it to memory’, the information has to be transferred to this structure, which is located in the temporal lobe, beneath the ear. The way we create this memory is by repeatedly stimulating the pathway. That’s why I advocate flashcards and retrieval exercises, they focus on that process; having to ‘remember’ some previously understood names and concepts is the fastest way I know to make the ‘stuff’ stick, even though it ‘hurts’ a little in the head when we feel the neurons ‘grow’. Can you tell me the name of this structure, it’s got a really cool name?
18.14. Lastly, another named gyrus is active when we use gestures to express our emotions. If you see someone moving their arms around a lot when they speak, you know their ________cortex is quite active.
18.15. I swear, the rest of this material is less esoteric and hopefully easier to understand. Although, it is fascinating of how the brain works, isn’t it? Now, we are reaching deeper into the brain, which gets us more to automated processes that are unconsciousness. Reaching deep into the longitudinal fissure (the one that separates the hemispheres) has us first touch the corpus callosum, the structure connecting the two sides of the brain with one another. Beneath that is the diencephalon, an area that is evolutionarily older than the cerebral cortex. This is a brain region with the absolute coolest structures in it. The answer to 18.12. is one of them. Another one is an egg-shaped cluster of cell bodies that deals with practically all sensory information; pretty much all incoming nerves terminate here. Neurons from there then send the sensory inputs onto the different cortexes, which is where the information becomes conscious and we can process it that way. What structure am I describing?
18.16. We mentioned before that the brain is surrounded by liquid that protects it and helps it be weightless (see 17.14 & 18.2). That liquid, called cerebrospinal fluid, or CSF, also nourishes the brain. It is secreted from the blood by specialized cells called choroid plexus. The CSF moves through internal chambers (hollow, CSF filled spaces deep inside the brain), and then also surrounds the brain. Can you name the four internal, CSF filled chambers?
18.17. From the diencephalon, we move further into the brain stem, which is considered evolutionarily at the level of a salamander. Most of what we find in this part of the brain are automated, visceral body reactions and neural pathways connecting the brain to the spinal cord, and therefore the rest of the body. The midbrain is the first of the three brainstem structures. Within it, we find one interesting set of nuclei (remember…they are clusters of cell bodies). They are responsible for making us move our head when we see or hear something around us. Collectively, they are called corpora quadrigemini, or ‘four bodies’. What do we call the two ‘bodies’ that deal with visual stimuli? What about the one’s dealing with auditory inputs?
18.18. Other nuclei we find in the midbrain concern themselves with influencing body movements. As you can imagine, a large portion of the brain concerns itself with having us be able to stand on two legs, move us around in the world and manipulate it in various ways. That is why we can see incredible brain growth once a baby learns how to walk; and on the other hand, when someone becomes bedridden, or is a couch potato for that matter, their mental cognitive capacity declines…stop binge-watching yet another Netflix series is the message, I guessJ. Can you name the two midbrain nuclei listed that concern themselves with body movement?
18.19. The brain stem also filters incoming visual, auditory, and other body sensory stimuli (touch, temperature, pain), and decides if our conscious mind needs to know about them or not. Those nuclei keep us alert, or on the other hand, help us be unconscious and asleep. Do you know what structure I’m describing?
18.20. Inferior to the midbrain, we find the pons. It is mostly filled with nerve fibers, at that point called nerve tracts, that connect the brain to the spinal cord, but also to another part of the brain, that sort of stands by itself, almost like a mini-brain endearingly referred to as the ‘cauliflower’ brain. A large portion of what it concerns itself with is balance and movement coordination. It helps us balance on one leg, or not fall down if trip. What is this part of the brain called?
18.21. Good job! Almost done. This last brain stem structure is the connection point to the spinal cord. Remember, I told you that the body is controlled by the opposite part of the brain (18.5)? Well, the motor commands going from the brain to skeletal muscles cross here; they call that fancily the decussation of pyramidal tracts. Rudimentary visceral control centers for breathing and cardiovascular functions are found here. Can you tell me what structure this is?
Please send me the answers you came up with to those questions before the class meets to [email protected] Thank you.