SKELETON

Skeleton a skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal frame to which the organs and soft tissues attach; and the hydroskeleton, a flexible internal structure supported by the hydrostatic pressure of body fluids. Vertebrates are animals with an endoskeleton centered around an axial vertebral column, and their skeletons are typically composed of bones and cartilages. Invertebrates are other animals that lack a vertebral column, and their skeletons vary, including hard-shelled exoskeleton (arthropods and most molluscs), plated internal shells (e.g. cuttlebones in some cephalopods) or rods (e.g. ossicles in echinoderms), hydrostatically supported body cavities (most), and spicules (sponges). Cartilage is a rigid connective tissue that is found in the skeletal systems of vertebrates and invertebrates. The human skeleton, composed of 206 bones, a complex system of hard, calcified tissue (bone), supported by ligaments, tendons, muscles, and cartilage, providing structural support, organ protection & muscle attachment. Bones: The primary structural elements of the skeleton, providing rigidity and support. Cartilage: A flexible, connective tissue that cushions joints and provides support in areas like the ears and nose. Ligaments: Strong, fibrous tissue that connect bone to each other, stabilizing joints. Tendons: Tough, fibrous tissues that connect muscles to bones, allowing for movement.  Muscles: Tightly woven, stretchy fibers that contract and relax to move the skeleton. Bone Composition: Inorganic Phase: Primarily composed of hydroxyapatite, a calcium phosphate mineral, which make up about 60% of bone. Organic Phase: Includes collagen, a protein that provides flexibility and strength to bone, along with other bone matrix proteins, making up about 30% of bone. Water: Account for about 10% of bone, contributing to its overall structure and function. Type of Bone Tissue: Compact (Cortical) Bone: The dense, hard outer layer of bone, providing strength and rigidity. Cancellous (Spongy) Bone: The inner, less dense, lattice-like bone, which is surrounded by bone marrow.  Skeleton Division: Axial Skeleton: Includes the skull, vertebral column (backbone), and rib cage. Appendicular Skeleton: Includes the bones of the limbs (shoulders, arms, legs, hips, and feet). in nomine Patris et FiLii et Spiritus Sancti peace be still / bone marrow contains significant amounts of calories and fat, but it also has nutrients like vitamin B12 and other vitamins and minerals, according to WebMD. 
https://www.youtube.com/watch?v=3MN-M4gsDX0
Bones for Kids | Learn about the Skeletal System for Kids
https://www.youtube.com/watch?v=f8zQel-jAUY
Skeletal anatomy introduction

Spleen the spleen filters out stiff blood cells The spleen from Anglo-Norman espleen, ult. from Ancient Greek σπλήν, is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The native Old English word for it is milt, now primarily used for animals; a loanword from Latin is lien. The spleen plays very important roles in regard to red blood cells (erythrocytes) and the immune system. It removes old red blood cells and holds a reserve of blood, which can be valuable in case of hemorrhagic shock, and also recycles iron. As a part of the mononuclear phagocyte system, it metabolizes hemoglobin removed from senescent red blood cells. The globin portion of hemoglobin is degraded to its constitutive amino acids, and the heme portion is metabolized to bilirubin, which is removed in the liver. The spleen houses antibody-producing lymphocytes in its white pulp and monocytes which remove antibody-coated bacteria and antibody-coated blood cells by way of blood and lymph node circulation. These monocytes, upon moving to injured tissue (such as the heart after myocardial infarction), turn into dendritic cells and macrophages while promoting tissue healing. The spleen is a center of activity of the mononuclear phagocyte system and is analogous to a large lymph node, as its absence causes a predisposition to certain infections. In humans, the spleen is purple in color and is in the left upper quadrant of the abdomen. The surgical process to remove the spleen is known as a splenectomy.
https://www.youtube.com/watch?v=jgJhb13JbW0
The Spleen (Structures, Function, Topography, Coverings and Ligaments) - Anatomy

Stem cells Yes, stem cells change their DNA when they differentiate into normal cells, but they don't permanently lose genetic material. DNA arrangement in stem cells, DNA is loosely arranged and working genes are present. When stem cells receive signals, they differentiate into specialized cells, such as skin, muscle, or liver cells. During differentiation, genes that are no longer needed are turned off, while genes required for the new cell type are turned on. The genetic material in differentiated cells is complete, and can be used to clone an entire animal. Stem cells have a remarkable ability to repair DNA damage and prevent it from spreading to other cells. However, DNA damage can still occur over time. Stem cell therapies are being developed to treat a variety of medical conditions, including heart failure, spinal cord injuries, and diabetes. In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can change into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell in a cell lineage. They are found in both embryonic and adult organisms, but they have slightly different properties in each. They are usually distinguished from progenitor cells, which cannot divide indefinitely, and precursor or blast cells, which are usually committed to differentiating into one cell type. In mammals, roughly 50 to 150 cells make up the inner cell mass during the blastocyst stage of embryonic development, around days 5–14. These have stem-cell capability. In vivo, they eventually differentiate into all of the body's cell types (making them pluripotent). This process starts with the differentiation into the three germ layers – the ectoderm, mesoderm and endoderm – at the gastrulation stage. However, when they are isolated and cultured in vitro, they can be kept in the stem-cell stage and are known as embryonic stem cells (ESCs). Adult stem cells are found in a few select locations in the body, known as niches, such as those in the bone marrow or gonads. They exist to replenish rapidly lost cell types and are multipotent or unipotent, meaning they only differentiate into a few cell types or one type of cell. In mammals, they include, among others, hematopoietic stem cells, which replenish blood and immune cells, basal cells, which maintain the skin epithelium, and mesenchymal stem cells, which maintain bone, cartilage, muscle and fat cells. Adult stem cells are a small minority of cells; they are vastly outnumbered by the progenitor cells and terminally differentiated cells that they differentiate into. Research into stem cells grew out of findings by Canadian biologists Ernest McCulloch, James Till and Andrew J. Becker at the University of Toronto and the Ontario Cancer Institute in the 1960s. As of 2016, the only established medical therapy using stem cells is hematopoietic stem cell transplantation, first performed in 1958 by French oncologist Georges Mathé. Since 1998 however, it has been possible to culture and differentiate human embryonic stem cells (in stem-cell lines). The process of isolating these cells has been controversial, because it typically results in the destruction of the embryo. Sources for isolating ESCs have been restricted in some European countries and Canada, but others such as the UK and China have promoted the research. Somatic cell nuclear transfer is a cloning method that can be used to create a cloned embryo for the use of its embryonic stem cells in stem cell therapy. In 2006, a Japanese team led by Shinya Yamanaka discovered a method to convert mature body cells back into stem cells. These were termed induced pluripotent stem cells (iPSCs).

Synapse In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending on the mechanism of signal transmission between neurons. In the case of electrical synapses, neurons are coupled bidirectionally with each other through gap junctions and have a connected cytoplasmic milieu. These type of synapses are known to produce synchronous network activity in the brain, but can also result in complicated, chaotic network level dynamic. Therefore, signal directionality cannot always be defined across electrical synapses. Chemical synapses, on the other hand, communicate through neurotransmitters released from the presynaptic neuron into the synaptic cleft. Upon release, these neurotransmitters bind to specific receptors on the postsynaptic membrane, inducing an electrical or chemical response in the target neuron. This mechanism allows for more complex modulation of neuronal activity compared to electrical synapses, contributing significantly to the plasticity and adaptable nature of neural circuits. Synapses are essential for the transmission of neuronal impulses from one neuron to the next, playing a key role in enabling rapid and direct communication by creating circuits. In addition, a synapse serves as a junction where both the transmission and processing of information occur, making it a vital means of communication between neurons. At the synapse, the plasma membrane of the signal-passing neuron (the presynaptic neuron) comes into close apposition with the membrane of the target (postsynaptic) cell. Both the presynaptic and postsynaptic sites contain extensive arrays of molecular machinery that link the two membranes together and carry out the signaling process. In many synapses, the presynaptic part is located on the terminals of axons and the postsynaptic part is located on a dendrite or soma. Astrocytes also exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission. Synapses (at least chemical synapses) are stabilized in position by Synaptic Adhesion Molecules (SAMs) projecting from both the pre- and post-synaptic neuron and sticking together where they overlap; SAMs may also assist in the generation and functioning of synapses. Moreover, SAMs coordinate the formation of synapses, with various type working together to achieve the remarkable specificity of synapses. In essence, SAMs function in both excitatory and inhibitory synapses, likely serving as the mediator for signal transmission. amongst the many supplements one needs for the brain is Sodium Potassium and Calcium for proper action potential neuron signaling
https://www.youtube.com/watch?v=wQCze5jbC0g
Erik Jorgensen (U. Utah / HHMI) 1: Synaptic transmission
https://www.youtube.com/watch?v=vso9jgfpI_c
Neuroscience - Long-Term Potentiation
https://www.youtube.com/watch?v=-ApzwDu9q5o
Neuroscience - Intracellular Signaling
https://www.youtube.com/watch?v=XdCrZm_JAp0
Lights, Camera, Action Potentials!
https://www.youtube.com/watch?v=fO5Xgnswl58
The Action Potential