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| Yoga and Awakening | ||||||||
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center for Arlington, MA 02474
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Tissue Anatomy Overview As explorers of embodiment, yogis will encounter myriad sensations emanating from all the layers of the body/mind. As we dive into the miracle of aliveness and attempt to communicate our experiences with ourselves, our students and the general public, it will be helpful to have a familiar a 3 dimensional vision and language of the body. Cells and tissues are fundamental entities that begin our understanding of a living body. They combine to create organs, organ systems, and finally the fully integrated living organism. The Cell The basic unit of life is the cell, which manifests in two basic forms, prokaryotic and eukaryotic. Prokaryotes lack a membrane bound nucleus, can use other sources of energy than oxygen, and, in the form of various bacteria and the recently discovered Archaea, compose the majority of single celled organisms on the planet. Eukaryotes, dependent upon oxygen, have a distinct nucleus as well as other differentiated structures such as mitochondria, lysosomes and vacuoles. They form the basis for all multicellular life forms including plants and animals. In multicellular entities, the cells are suspended in a complex fluid/connective tissue matrix somewhat like a sponge. This living matrix is crucial to the health of the cells and the organism and will be the primary focus of our explorations. This matrix performs several necessary functions. It allows the organism to maintain a dynamic 3 dimensional shape by channeling the forces of gravity and water pressure. It provides a support structure for the surrounding blood vessels and nerves which nourish and inform the cells. And it provides a flowing, fluid ground substance that acts as a resevoir to hold electrolytes, nutrients and other chemical messengers, and help transport cellular wastes away. The human body consists of around 100 trillion eukaryotic cells, (and about 10 times that number of bacterial cells!), divided into about 210 different, specialized cell types, including cells that circulate throughout the body like blood and immune cells, cells that secrete various hormones, and cells that provide a lining to vesels and organs. Tissue The next order of complexity up from the cell is called tissue. A tissue is a collection of cells and associated intercellular materials which are specialized for a particular function. The human body is comprised of four categories of tissue: nervous, muscle, epithelial, and connective. These tissues are used in different proportions and arrangments to create the more complex organs. An organ is a group of tissues designed and organized to perform a particular function or group of functions such as the heart or the liver. Several organs can work together to form organ systems such as the cardiovascular, urinary, or reproductive systems. The living matrix interpenetrates all levels of cells, tissues, organs and organ systems and is the individual embodiment of what Buddhist teacher Thich Nhat Hanh refers to as interbeing, the realization that all of us are enmeshed in a web of interconnected relationship.
Glial (glue) cells make up 'The Other Brain' as described by R. Douglas Fields in a book of the same name. Totally different from neurons, glia have their own communication network, insulate and support the neurons and even regulate the flow of information between neurons. They also provide nourishment and other aids to neuron function. Glia come in a wide variety of shapes and sizes depending on the particular type and the study of them is one of the more exciting explorations on the frontiers of brain science. Muscle tissue
Groups of muscle fibers may form fasciculi (fasciculus = small bundle), and many fasciculi, in turn, are aggregated into units we call muscles. There are 3 major types of muscle tissue: skeletal, cardiac and smooth. Skeletal muscle is attached to bones. Cardiac muscle is found in the heart. Smooth muscle is found in vessels, ducts, skin, and internal organs. Muscle tissue is may be controlled by nerves, hormones, local chemicals, or itself depending on the type and location.
Epithelial tissue
Epithelia are classified according to the shape of the cells (squamous, cuboidal,or columnar) and the number of layers (simple, stratified,or pseudostratified). A special type of epithelium, endothelium, makes up the walls of blood and lymph vessels. Epithelial tissue is nourished by diffusion from blood vessels situated in the underlying connective tissue as no blood or lymph vessels are found in epithelium. Epithelial tissue can produce downgrowths into underlying connective tissue called glands and contain cells whose functions are secretion and excretion. There are two main types of glands, exocrine glands and endocrine glands. Exocrine glands possess ducts which convey the secretory material (mucus, enzymes, etc.) to the surface of the body or cavity lined by the epithelium. Endocrine glands have lost their connection to the epithelial lining from which they were derived and therefore lack ducts. These clumps of cells release their secretions (hormones) directly into the bloodstream, where they are distributed throughout the body. Classification of glands can be very confusing and is based on branching of the ducts (simple vs compound), shape of the secretory region (tubular, alveolar, tubuloalveolar) and by the type of secretion (mucous, serous or mixed). Cells which inhabit the connective tissues provide defense as well as produce the supportive structures. Some cells remain in the connective tissue and function in its long-term maintenance. Examples include: fibroblasts which are responsible for the formation of collagen, elastin and ground substance that comprise the extracellular component of connective tissue: mesenchymal cells (embryonic connective tissue cell commonly called stem cells) and adipose or fat storing cells. Other wandering cells enter the connective tissue in response to injury or invasion by microorganisms. Examples include mast cells, antibody secreting plasma cells and the trash collecting macrophages. Mast cells are widely distributed in connective tissue and are particularly abundant along small blood vessels. They contain many granules whose contents are responsible for preventing blood clotting and increasing the permeability of capillaries and venules, thus allowing other cells to enter the connective tissue from the blood to fight foreign invaders. Fibroblasts are the cells that secrete the fibers that give the extra cellular matrix its structure as well as the ground substance. (see below) Extracellular fibers give connective tissue its strength. There are 3 types: Collagen fibers are composed of the protein collagen. They have great tensile strength and are inelastic. Reticular fibers are very thin collagen fibers and form delicate networks around blood vessels, nerves and certain other cells. Elastic fibers are composed of the protein elastin. They stretch easily but return to their original length. They are most abundant in tissues that require flexibility, for example, the ligamentum nuchae on the back of the neck. Ground substance is the name for the amorphous, gel-like intercellular material in which the cells and fibers of connective tissue are embedded. It is composed of water, proteoglycans (large molecules which help store and regulate the movement of ions and water), other plasma constituents, metabolites and ions, and functions as a medium through which nutrients can diffuse from blood vessels to nourish the cells and the waste products can diffuse back into the blood stream. Types of Connective Tissue
Loose Connective Tissue has an abundance of cells and ground substance, but relatively few fibers. It is soft and pliable and serves as a kind of packing material between other tissues and organs. It is found between muscles, allowing one to move freely over the other and supports small blood vessels, lymphatic vessels and nerves. Dense Connective Tissue has a greater proportion of fibers, fewer cells and less ground substance than loose connective tissue. There are four types of dense connective tissue; fascia, tendons, ligaments, and aponeuroses. We will take a closer look at fascia in a moment. Cartilage is a form of connective tissue that is much firmer than dense connective tissue. It consists of a dense network of fibers embedded in a gel-like intercellular material which confers firmness but also permits flexibility. The cells of cartilage are called chrondrocytes. Cartilage has no blood vessels and the cells are entirely dependent on diffusion as the source of their nutrients and oxygen. There are three basic types of cartilage that serve different functional requirements and vary by the type of fiber embedded in the ground substance. Elastic cartilage has a large number of elastin fibers, allowing it to be very flexible and when deformed, able to immediately return to its normal position. It is found in the auricle of the ear. Hyaline cartilage, the most widely distributed type of cartilage found in the body, has very little elastin and mostly collagen. This hard, translucent tissue first appears first as the developing bones in the embryo. As growth continues, the cartilage tissue is gradually replaced by bone tissue. At maturity, hyaline cartilage remains at the end of bones where they articulate with one another. Hyaline cartilage also supports the nose, larynx, trachea and bronchi of the respiratory system. The most abundant cartilage by weight is fibrocartilage, a both tough and elastic tissue present in regions of frequent stress. Containing both elastin and collagen, fibrocartilage is found in the intervertebral discs, the menisci of the knees and the pubic symphasis. Bone is the most rigid form of connective tissue and is much firmer than cartilage. The hardness of a bone (equal to that of cast iron!) is caused by the presence of calcium phosphate; the small degree of elasticity possessed by bone is caused by the presence of organic collagen fibers. The cells of bone are called osteocytes. Unlike cartilage, bone contains small tubular canals through which the cells are nourished. Bone exists in two forms: compact and spongy. The Superficial Fascia is located directly under the subcutis of the skin. Its functions include the storage of fat and water and it also provides passageways for nerves and blood vessels. In some areas of the body, it also houses a layer of skeletal muscle, allowing for movement of the skin. The Deep Fascia is beneath the superficial fascia. It aids muscle movements and, like the superficial fascia, provides passageways for nerves and blood vessels. In some areas of the body, it also provides an attachment site for muscles and acts as a cushioning layer between them. for more information: www.fasciaresearch.com http://mywebpages.comcast.net/wnor/ (on line anatomy course with great visuals!) http://web.jjay.cuny.edu/~acarpi/NSC/14-anatomy.htm http://www.nlm.nih.gov/research/visible/visible_gallery.html
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