Nervous system II 2/3 - Biology As Poetry

It is within the central nervous system that the majority of interneurons and integrating centers are located. It consists of the brain in terms of consciousness but also numerous unconscious control mechanisms, and the spinal cord in terms of somatic reflexes as well as serving to connect the brain to much of the peripheral nervous system.

Brain

Animal body principal control center.

The brain resides in the head and helps to define the concept of cephalization, with the major sensory organs, in vertebrates, also found in association with the head. The brain both receives sensory information from the body and acts on that information via the stimulation of motor neurons as well as the release of hormones.

The brain exerts both voluntary control and involuntary control upon the body, though involuntary control also is associated with the spinal cord (i.e., via reflex arcs). The brain in addition is the center of consciousness and free will (whatever it is that those two things really mean).

Metabolically, the brain is a very expensive organ to maintain in terms of nutritive needs, and it also is the most complex of organs. The brain primarily though not entirely is connected to rest of the body through the spinal cord. Together the brain and the spinal cord make up what is known as the central nervous system.

The above video is quite disjointed and presents a psychological emphasis. Still, it does provide interesting and informative information plus has great visuals that allow one to perhaps better appreciate the structural complexity of the brain's gross anatomy.

Gray matter

That aspect of the central nervous system that is rich in cell bodies while poor in myelin.

The gray matter contains numerous cell bodies as well as numerous associated dendrites, but is somewhat lacking in myelinated axons. The gray matter thus is the location of numerous (or "enumerable") connections between neurons in the central nervous system rather than substantial numbers of relatively long spans of axons.

Among other requirements, the gray matter has substantial oxygen needs, far out of proportion to the total brain mass made up by the gray matter (that is, the brain has substantial oxygen needs and these needs come especially from the gray matter). The outside of the prominent cerebrum of our brains, the cerebral cortex, consists of a relatively thin layer of gray matter overlying white matter.

The above video does a nice job describing gray matter as it appears in the spinal cord, but don't let the moving about soma fool you as that's done in the video solely for the purpose of emphasis (and also don't let the relative size of the cell bodies fool you as they are shown as much much larger than they in reality are).

White matter

That aspect of the central nervous system that is rich in myelin while poor in cell bodies.

White literally is the color of fat and it is the color of "fat", particularly as myelin, that provides the color to the white matter of both the brain and the spinal cord. The myelin is associated with myelinated axons and the white matter can be thought of as associated with relatively long as well as insulated pathways between cell bodies.

As central nervous system myelin sheaths are generated by oligodendrocytes, it is the color of oligodendrocytes that basically supplies the color, or lack of color, to white matter. Contrast gray matter.

Cerebrum

Part of the brain responsible for highest levels of integration of information.

The cerebrum is the largest portion of the human brain. It basically is what you probably are thinking of when you think of the concept of brain, with its numerous grooves and ridges (the latter which have the effect of increasing the amount of gray matter in the cerebrum).

The cerebrum is found at the top of the brain, though that statement too can be misleading since really all you see of the human brain when looking from the top downward is the cerebrum.

The cerebrum is split into two hemispheres, the left and the right, which are connected together by what is known as the corpus callosum. It also is the cerebrum upon which the motor homunculus and sensory homunculus are defined, and therefore from which voluntary control emanates and consciousness presumably resides (voluntary control is helped as well by the actions of the cerebellum).

In addition, the cerebrum, and particularly the cerebral cortex along with underlying axons, can be divided more or less from back to front into a series of "lobes" referred to as the occipital lobe, temporal lobe, parietal lobe, and frontal lobe. The cerebrum also contains various specialized areas such as the primary visual area, the primary auditory area, the primary sensory area, the primary motor area, and also areas devoted to speaking along with understanding language.

The cerebrum additionally is associated with various subcortical structures, subcortical meaning beneath the cerebral cortex. These include what are known as basal ganglia, the hippocampus, and the olfactory bulb.

Basal ganglia

Subcortical aspect of the cerebrum involved in control over otherwise cerebral cortex-associated motor functions.

The basal ganglia fittingly are ganglia found at the base of the cerebrum, and thus are subcortical structures. They consist of a series of complex structures that receive information from various parts of the cerebral cortex and then feed that information up to the primary motor cortex.

In this way the basal ganglia may be viewed as effecting control over the output of the motor cortex and thereby over voluntary movement. Basal ganglia defects thus are associated with loss of control over various motor outputs, e.g., such as one sees with Parkinson's disease.

The video is very short but provides a nice overview of the structure and function of the basal ganglia.

Hippocampus

Subcortical aspect of the cerebrum involved in long-term memory formation as well as spatial orientation.

Very simplistically, we can think of the hippocampus as being responsible for making sure that we keep track over the long term of where we've been and what we've experienced. That is, it converts short-term memories into long-term memories.

The memories aren't actually stored in the hippocampus, but instead in the cerebral cortex. What the hippocampus does is make sure that ultimately something is stored in the cerebral cortex, by strengthening associated synapses, rather than having those memories soon become forgotten.

The hippocampus is called the hippocampus because anatomically it resembles a seahorse: hippos means horse, in Greek, and kampos means 'sea monster'.

Cerebral cortex

Primary location of gray matter representing the surface of the forebrain.

As with the cerebrum, the cerebral cortex is probably what you think of when you think of brain. This is no contradiction, however, since the cerebral cortex literally is the surface few millimeters of the cerebrum. The cerebrum thus consists of an outer gray matter (the cerebral cortex) along with an inner white matter (it is within the latter that the corpus callosum connects).

As gray matter, it is within the cerebral cortex that high densities of cerebral neuron cell bodies are found. Indeed, the majority of the brain's cell bodies, that is, soma of its neurons, are found in the cerebral cortex. Furthermore, the majority of the skull that is adjacent to the brain is adjacent to the cerebral cortex.

Note that "forebrain" contrasts with midbrain and hindbrain. As the human and indeed mammalian forebrain is so substantially developed, it is difficult to tell superficially that in fact it is otherwise found forward in the brain, but in animals with less robustly developed cerebrums in fact this anatomical perspective is clearer. For example, do an image search on reptile forebrain.

The above video considers the brain's cortex, with emphasis on the frontal lobes.

Corpus callosum

Large bundle of axons connecting together the left and right hemispheres of the cerebrum.

Corpus refers to 'body' (here meaning structure) while 'callosum' is a description of the 'toughness' or 'firmness' of the corpus callosum, i.e., as calluses are tough and firm. This name thus provides little or no description of the function of the corpus callosum, which is to connect together the two hemispheres of the cerebrum neurologically, i.e., so that they can communicate with one another.

Remarkably, it is possible to survive without a corpus callosum as this occurs as a relatively common birth defect and also the corpus callosum can be severed (corpus callosotomy or "Split-brain procedure") in order to relieve severe seizure symptoms, i.e., since it allows seizures in one hemisphere of the brain (cerebral hemisphere) to not migrate to the other hemisphere.

Cerebellum

Region of the hindbrain that is involved predominantly in refining the control of movement.

Of brain regions, only the cerebrum in the human brain is larger than the cerebellum. When you practice movements to improve your abilities, such as in sports or in playing a musical instrument, it is the cerebellum that responds to that practice, and when you temporarily interfere with your ability to properly display refined movements due to excessive alcohol consumption, it is the cerebellum that you are affecting.

The cerebellum achieves a refinement of movement in part by receiving otherwise unconscious sensory input from the parts of your body that are involved in movement. When one says that there are parts of the body that are on "automatic pilot", including in terms of body movement so that the brain can concentrate on higher level processes, part of that movement-associated "automatic pilot" is a consequence of cerebellum functioning, as well as somatic reflexes. Higher-level processing, by contrast, is a function of the cerebrum.

The above video is a really nice introduction to the basics of what the cerebellum is all about.

Brainstem

Lower-most portion of the brain responsible for maintaining many low level but nonetheless crucial homeostatic functions of the body.

The brainstem literally is the "stem" of the brain, with the spinal cord analogously the "taproot" of the brain, and peripheral nervous system the less central "roots", Continuing with this analogy, I suppose the rest of the brain, as built on top of the brainstem, would be the "leaves" and "flowers" of the brain, or something like that.

The brainstem also can be described as the posterior portion of the brain (the superior portion is our cerebrum). Note also the somewhat equivalent concept of hindbrain.

Moving away from the spinal cord, the brainstem includes the medulla oblongata, the pons, and the midbrain or mesencephalon. As with the spinal cord, nerves also originate from the brainstem, with these nerves connecting to the face and skull.

The brainstem is involved in key, unconscious aspects of homeostasis. Basically it is responsible for "lower-level" functioning that we don't think about, such as the beating of our hearts or breathing.

The above video provides a pretty introduction to the anatomy and some of the functioning of the brainstem.

The above video provides a broad though brief introduction to the anatomy and functioning on the brain stem.

Pons	Portion of brainstem involved primarily in connecting together other regions of the brain.
	The pons actually is short for pons Varolii. "Pons" means literally "bridge" in Latin, befitting its role and anatomy of linking together many of the brain's other regions, inferior, superior, and lateral. The term "Varolii" by contrast refers to a person, Constanzo Varolio, who was a 16^th century anatomist credited with first describing the pons. This in fact is why Varolii is capitalized.

Medulla oblongata

The portion of the brainstem that is found immediately adjacent to the spinal cord.

The medulla oblongata, or simply medulla, can be thought of as existing at the lowest portion of the brain and as such possesses perhaps the lowest-level functions associated with brain.

These functions represent something more than somatic reflex, but not by much, and without the crucial need for extreme rapidity of response. This includes cardiac control and respiratory control.

Without question these functions as effected by the medulla are not under conscious control, at least as such control is initiated at that level.

The above video provides a relatively crude but nonetheless relatively well done introduction the functioning of the medulla oblongata.

Dopamine

Neurotransmitter involved, in part and crucially, in the brain's reward and motivation.

Dopamine is a key component of the mesolimbic dopamine pathway. This is the part of the brain that plays a huge role in your obtaining pleasure such that, basically, we do things in order to obtain a dopamine "reward" within our mesolimbic dopamine pathway.

We decide whether something is worth doing in order to get those rewards. We obsessively check our phones or social media sites in order to obtain this reward. We tend to not do things unless we believe that we will obtain this award. We also abuse chemical substances (i.e., drugs) in order to obtain this reward.

In short, just about anything that we do for reasons other than to avoid physical pain or emotional pain we do, at least in part, because we tend to be somewhat slaves to our mesolimbic dopamine pathway. Indeed, in an animal's natural environment, doing these pleasurable things will tend to lead to an increased potential for that animal to both survive and contribute its genes to the next generation.

Why we like music, or just about anything else, is the topic of discussion in the above video.

Serotonin

Neurotransmitter that motivates appetite, mood, and sleep as well as gut motility.

The neurons that employ serotonin as their neurotransmitter tend to be less- or inactive at night and most active when we are most awake, or excited.

Of note, the drug LSD binds to a type of serotonin receptor while the drug "ecstasy" interferes with serotonin reuptake, that is, serving as a serotonin reuptake inhibitor. Those are two routes towards increased serotonin receptor stimulation, i.e., either increased direct stimulation or decreased reduction in stimulation, respectively, the latter as obtained by inhibiting serotonin reuptake.

Here's a quick overview of the disease, depression, along with the potentially indirect role of serotonin.

Electroencephalogram

Means of visualizing the activity of the brain by measuring the electrical activity along the scalp.

The electroencephalogram, or EEG, measures the movement of ions within the extracellular environment of the cerebral cortex where such movement is a consequence of neuronal depolarization.

The greater the neuronal activity then the greater the local disruption of ions and thereby the greater the electrical activity in the adjacent area of the scalp. For such electrical activity to be detected, then many thousands or even millions of neurons must be locally depolarized and thus an EEG detects relatively substantial amounts of local brain activity.

The above video shows an EEG as it is being taken; it is not worth watching the whole thing, however.

Though deviating far from the topic EEGs, the above video does discuss EEGs and sleep at least a bit.

Spinal cord

Primary connection in vertebrates between the brain and the rest of the body.

The spinal cord together with the brain make up the central nervous system of vertebrate animals.

The spinal cord plays two roles in this scheme, serving as the connection between brain and body: carrying nerve impulses both towards the brain and away from the brain and as the control center of somatic reflexes. The spinal cord is found within the vertebrae of the spine, but is not present for the entire length of spine. It instead grows thinner until disappearing as the spinal cord progresses downward, distally towards the pelvis.

In cross section, the spinal cord possesses gray matter, which is a butterfly-shaped region possessing neuron cell bodies and which is surrounded by white matter representing myelinated axons. In addition there is a hollow, central canal filled with cerebrospinal fluid.

The above video presents spinal cord external anatomy but without getting too deep into the specifics of which nerves do what.

Cerebrospinal fluid

Material that bathes, cushions, and otherwise contributes to the homeostatic functioning of both the brain and spinal cord.

Cerebrospinal fluid is produced by the choroid plexus, along with other epithelial tissue. It is produced in large amounts (about half a liter per day), but is also continuously reabsorbed and otherwise drains into the blood such that there is a constant replenishment.

Cerebrospinal fluid bathes the brain, and spinal cord, cushions these organs against mechanical shocks, removes wastes, contributes to the immunological protection of the brain, influences blood flow to the brain, and otherwise serves to define the chemical environment within which the cells of the central nervous system function.

The ventricles, which are cavities found within the brain, are the conduits through which cerebrospinal fluid flows within the brain, and cerebrospinal fluid also flows within the central canal of the spinal cord.

Basically cerebrospinal fluid serves as a constantly replenished "river" within which the brain and spinal cord are tethered and otherwise "float".

The above video is a very short but pretty cool animation of the circulation of cerebrospinal fluid; it has no annotation or narration, however.

Vertebral column

Spinal cord protective covering and dominant endoskeletal support structure in most animals possessing spinal cord.

The vertebral column is our backbone, also known as our spine. Unlike most vertebrates, our spine is arranged vertically rather than horizontally, as befitting our upright, bipedal posture.

Note that If you look at a bird's skeleton you will see that though they are bipedal, their vertebral column, except in the neck while not flying, is not vertical but instead is horizontal; the backbone of kangaroos, by contrast, can exist almost vertically and indeed this is a normal state for tetrapod vertebrates (e.g., dogs, cats, horses, even lizards, etc.) when they rise on their hind legs and stretch upright.

Humans are rather special in terms of how we employ our backbones to habitually support our weight vertically. Most of this weight that is supported by the spine is supported in the lumbar region, that is, the lower back.

The thoracic region by contrast supports the ribs and chest while the cervical region is that of the neck. The vertebral column also is associated with the pelvis (the sacrum, which consists of fused vertebrae) and with tails, or at least what's left of ours (the coccyx).

The bones making up the vertebral column are called vertebrae and associated with much of the vertebral column is the spinal cord, while vertebrae generally are separated as well as held together via intervertebral discs.

The above video does a great job of quickly walking you through both the major structures of the vertebral column and what movement of vertebrae relative to each other entails. There is no sound, though.

Vertebrae

Individual bones making up the neck, spine, sacrum, and tailbone.

The vertebrae – or singular, vertebra – in humans are built to support compressive weight while remaining somewhat flexible, protecting the spinal cord, and allowing the ingress/egress of spinal nerves. Associated with the vertebrae bones are intervertebral discs that serve as shock absorbing padding between the vertebrae (the intervertebral discs are what you "slip" when you "slip" a disk).

The vertebrae become increasingly suited to supporting weight as one moves downward towards the pelvis, and are particularly robust for this function within the lumbar region of the spine. Alternatively, our vertebrae are less robust for supporting weight in the cervical region (the neck) as well as within the coccyx, our tailbones. Further, some vertebrae are fused, in adults, giving rise to the sacrum, which makes up the posterior (back side) of the pelvis.

The above video uses a computer model of the vertebral column to walk through the anatomy of individual vertebrae; it's not a particularly well done video but it does provide a different perspective on things than you can gather from looking at the individual bones in the previous video.

Intervertebral disc

Shock absorbing connective tissue joining the ventral bodies of vertebrae.

The intervertebral discs are responsible for holding the joints between the vertebrae of the spine together. They consist of a combination of a strong ring of fibrocartilage, forming the annulus fibrosus, and a gel-like inner region called the nucleus pulposus. While the former holds the vertebrae together, the latter helps to distribute compressive shock.

The intervertebral disc is what "slips" when one slips a disc in one's spine (prolapsed disc), which occurs particularly in the substantially weight-bearing lumbar region of the vertebral column. Intervertebral discs have no direct blood supply except prior to birth. Their degeneration with aging can lead to both back problems and, with their shrinkage, an overall shortening of one's height.

The above video provides a nice introduction to the anatomy of intervertebral discs, their role in movement, and what can go wrong.

The above video provides a more detailed introduction to the anatomy of intervertebral discs, their role in movement, and what can go wrong.

The above video provides a graphic if animated visualization of what goes wrong when intervertebral discs become damaged, and options for repair.

Central Nervous System