The Muscular System

        We have more than 600 muscles in your body. They do everything from pumping blood throughout your body to helping you lift your heavy backpack. You control some of your muscles, while others — like your heart — do their jobs without you thinking about them at all.

          Muscles are all made of the same material, a type of elastic tissue (sort of like the material in a rubber band). Thousands, or even tens of thousands, of small fibers make up each muscle.

         There are three types of muscle:

Skeletal muscle

• There are nearly 650 skeletal muscles in the human body!
• Skeletal muscles are attached to the skeleton
• They work in pairs: one muscle moves the bone in one direction and the other moves it back again
• Skeletal muscles are voluntary muscles - in other words we think about what movements we want to make (at least, usually!) and send messages via our nervous system to tell the appropriate muscle(s) to contract. 
• Muscle contractions can be short, single contractions or longer ones. 

Smooth muscle 

• Smooth muscle is found in our internal organs: in our digestive system, our blood vessels, our bladder, our respiratory organs and, in a female, the uterus. 
• Smooth muscle can stretch and maintain tension over extended periods 
• Smooth muscles are involuntary muscles - in other words we donot have to think about contracting them because they arecontrolled automatically by the nervous system. It would be pretty inconvenient if we had to think about digesting our food, for example!

Cardiac muscle

• As the name should tell you, cardiac muscle is found only in the heart. 
• It can stretch, just like smooth muscle, and contract like skeletal muscle. 
• It is a twitch muscle - it only does short single contractions
• Like smooth muscle, cardiac muscle is involuntary. It'd be rather dangerous if it were voluntary - we could stop our heart beating any time we wanted!

The skeletal System

Skeletal System

Skeletal system is the biological system providing support in living organisms.

The skeleton functions not only as the support for the body but also in haematopoiesis, the manufacture of blood cells that takes place in bone marrow. This is why people who have cancer of the bone marrow almost always die. It is also necessary for protection of vital organs and is needed by the muscles for movement.

A. Functions of Bones
1. Support. Provide a hard framework.
2. Protection of many vital organs.
3. Movement. Act as levers with skeletal muscles moving them. Joints control possible movements.
4. Mineral storage. Especially calcium and phosphate, critical minerals for cellular function. Continuous deposition and withdrawal. Exquisite control of Ca++ (calcium ions) levels necessary for function of nerves, muscles, blood coagulation and other functions. Most of Ca++ in body in bones. Osteoclasts & osteoblasts controlled by hormones which regulate blood levels of Ca++.
5. Blood cell formation. Certain bones have active marrow.
B. Structure
1. Compact-Dense outer layer, looks smooth and solid. Contains cylinder of concentric layers with central canals.
a. Haversian system = circles of bone (lamella) with central canal (Haversian canal)
b. Central canal contain blood vessels & nerves. Connected at right angles to network.
c. Perforating small canals - blood vessels & nerves go through lamellar bone to supply osteocytes. Connect to periosteum.
d. Osteocytes live in bone, maintain it. Live in holes called lacunae. Connect to each other and central canal via canaliculi, little canals. Pass nutrients, waste products
2. Spongy- honeycombed, open spaces. Same structure as compact but less regular.
Withstand maximum stress with least weight. In bone interiors & weird weight bearing bones like head of femur. Not organized in lamella. Trabeculae are arranged along lines of stress. Osteocytes interconnected by canaliculi. Nutrients reach osteocytes by diffusing through the canaliculi from capillaries. Osteoporosis - More bone resorption than deposition, very weak bone.

Skeletal System

A. Axial skeleton
Principal supportive structure of the body includes skull, vertebrae, sternum & ribs. Central column of the skeleton from which arms and legs & bones that help them hang.
B. Appendicular skeleton
Provides fairly freely movable frame for upper & lower limbs. Includes pectoral (shoulder) & pelvic (hip) girdles, arms, forearms, wrists, hands, thighs, legs & feet.

Joints

Bones -> framework; muscles -> power; joints provide mechanism that allows body to move
A joint is where 2 adjacent bones or cartilages or combination thereof meet.
Most joints movable, some not.



Bone cells are called osteocytes, and the matrix of the bone is made of calcium salts and collagen. The calcium salts give bones the strength for its supportive and protective functions. The function of osteocytes is to regulate the amount of calcium that is deposited in or removed from the bone matrix.
Bone is an organ, it has its own blood supply and is made up of two types of tissue; compact and spongy bone.
 The names imply that the two types of differ in density, or how tightly the tissue is packed together. There are three types of cells that contribute to bone homeostasis. Osteoblasts are bone-forming cell, osteoclasts resorb or break down bone, and osteocytes are mature bone cells. An equilibrium between osteoblasts and osteoclasts maintains bone tissue.
Compact bone consists of closely packed osteons or haversian systems. The osteon consists of a central canal called the osteonic (haversian) canal, which is surrounded by concentric rings (lamellae) of matrix. Between the rings of matrix, the bone cells (osteocytes) are located in spaces called lacunae. Small channels (canaliculi) radiate from the lacunae to the osteonic (haversian) canal to provide passageways through the hard matrix. In compact bone, the haversian systems are packed tightly together to form what appears to be a solid mass. The osteonic canals contain blood vessels that are parallel to the long axis of the bone. These blood vessels interconnect, by way of perforating canals, with vessels on the surface of the bone.
Spongy (cancellous) bone is lighter and less dense than compact bone. Spongy bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow. The canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply. It may appear that the trabeculae are arranged in a haphazard manner, but they are organized to provide maximum strength similar to braces that are used to support a building. The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes.

The Cell

The Cell

The one-celled organism amoeba proteus

A single-celled bacteria of the type: E. coli

A human red blood cell

A plant cell from the leaf of a poplar tree

         The cell is one of the most basic units of life.  There are millions of different types of cells.  There are cells that are organisms onto themselves, such as microscopic amoeba and bacteria cells.  And there are cells that only function when part of a larger organism, such as the cells that make up your body. 

The cell is the smallest unit of life in our bodies.  In the body, there are brain cells, skin cells, liver cells, stomach cells, and the list goes on.  All of these cells have unique functions and features.  And all have some recognizable similarities. 

All cells have a 'skin', called the plasma membrane, protecting it from the outside environment.  The cell membrane regulates the movement of water, nutrients and wastes into and out of the cell.  Inside of the cell membrane are the working parts of the cell.  At the center of the cell is the cell nucleus.  The cell nucleus contains the cell's DNA, the genetic code that coordinates protein synthesis.  In addition to the nucleus, there are many organelles inside of the cell - small structures that help carry out the day-to-day operations of the cell.  One important cellular organelle is the ribosome.  Ribosomes participate in protein synthesis.  The transcriptionphase of protein synthesis takes places in the cell nucleus.  After this step is complete, the mRNA leaves the nucleus and travels to the cell's ribosomes, where translation occurs.  Another important cellular organelle is the mitochondrion.  Mitochondria (many mitochondrion) are often referred to as the power plants of the cell because many of the reactions that produce energy take place in mitochondria.  Also important in the life of a cell are the lysosomes.  Lysosomes are organelles that contain enzymes that aid in the digestion of nutrient molecules and other materials.  Below is a labelled diagram of a cell to help you identify some of these structures.

Prokaryotic Organisms

The simplest of cells, and the first types of cells to evolve, were prokaryotic cells—organisms that lack a nuclear membrane, the membrane that surrounds the nucleus of a cell. Bacteria are the best known and most studied form of prokaryotic organisms, although the recent discovery of a second group of prokaryotes, called archaea, has provided evidence of a third cellular domain of life and new insights into the origin of life itself.
Prokaryotes are unicellular organisms that do not develop or differentiate into multicellular forms. Some bacteria grow in filaments, or masses of cells, but each cell in the colony is identical and capable of independent existence. The cells may be adjacent to one another because they did not separate after cell division or because they remained enclosed in a common sheath or slime secreted by the cells. Typically though, there is no continuity or communication between the cells. Prokaryotes are capable of inhabiting almost every place on the earth, from the deep ocean, to the edges of hot springs, to just about every surface of our bodies.
Prokaryotes are distinguished from eukaryotes on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack any of the intracellular organelles and structures that are characteristic of eukaryotic cells. Most of the functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili—proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and aplasma membrane; and a cytoplasmic region that contains thecell genome (DNA) and ribosomes and various sorts of inclusions.

Eukaryotic Organisms

Eukaryotes include fungi, animals, and plants as well as some unicellular organisms. Eukaryotic cells are about 10 times the size of a prokaryote and can be as much as 1000 times greater in volume. The major and extremely significant difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specific metabolic activities take place. Most important among these is the presence of a nucleus, a membrane-delineated compartment that houses the eukaryotic cell’s DNA. It is this nucleus that gives the eukaryote—literally, true nucleus—its name.
Eukaryotic organisms also have other specialized structures, called organelles, which are small structures within cells that perform dedicated functions. As the name implies, you can think of organelles as small organs. There are a dozen different types of organelles commonly found in eukaryotic cells. In this primer, we will focus our attention on only a handful of organelles and will examine these organelles with an eye to their role at a molecular level in the cell.
The origin of the eukaryotic cell was a milestone in the evolution of life. Although eukaryotes use the same genetic code and metabolic processes as prokaryotes, their higher level of organizational complexity has permitted the development of truly multicellular organisms. Without eukaryotes, the world would lack mammals, birds, fish, invertebrates, mushrooms, plants, and complex single-celled organisms.

Understanding what makes up a cell and how that cell works is fundamental to all of the biological sciences. Appreciating the similarities and differences between cell types is particularly important to the fields of cell and molecular biology. These fundamental similarities and differences provide a unifying theme, allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types.

Tissues

            Tissues are considered to be one of the very important components of the body. A Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning. 

            The study of tissue is known as histology or, in connection with disease, histopathology.

            The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, and the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of clinical diagnosis and prognosis.

            There are four types of tissues in the human body: Epithelial tissues, connective tissues, muscle tissues and nervous tissues.

       1. Epithelial 

             It is made of cells arranged in a continuous sheet with one or more layers, has apical & basal surfaces. A basement membrane is the attachment between the basal surface of the cell & the underlying connective tissue.

             The number of cell layers & the shape of the cells in the top layer can classify epithelium namely, simple, stratified, pseudostratified columnar, and glandular. 

               

            Simple Epithelium is a one cell layer.

            Stratified epithelium has two or more cell layers.

            Pseudostratified Columnar Epithelium. This is when cells of an epithelial tissue are all anchored to the basement Membrane but not all cells reach the apical surface

            Glandular Epithelium (1) Endocrine: Release hormones directly into the blood stream and (2) Exocrine - Secrete into ducts.

         2. Connective

              It contains many different cell types including: fibroblasts, macrophages, mast cells, and adipocytes. Connective Tissue Matrix is made of two materials: ground substance - proteins and polysaccharides, fiber – reticular, collagen and elastic.

              Classification of Connective Tissue:

Loose Connective - fibers & many cell types in gelatinous matrix, found in skin, & surrounding blood vessels, nerves, and organs.

Dense Connective - Bundles of parallel collagen fibers& fibroblasts, found in tendons& ligaments.

Cartilage - Cartilage is made of collagen & elastin fibers embedded in a matrix glycoprotein & cells called chondrocytes, which was found in small spaces.

Cartilage has three subtypes:

Hyaline cartilage – Weakest, most abundant type, Found at end of long bones, & structures like the ear and nose,

Elastic cartilage- maintains shape, branching elastic fibers distinguish it from hyaline. 

Fibrous Cartilage - Strongest type, has dense collagen & little matrix, found in pelvis, skull & vertebral discs.

             3. Muscle

It is divided into 3 categories, skeletal, cardiac and smooth.

• Skeletal Muscle – voluntary, striated, striations perpendicular to the muscle fibers and it is mainly found attached to bones.

• Cardiac Muscle – involuntary, striated, branched and has intercalated discs

• Smooth Muscle – involuntary, nonstriated, spindle shaped and is found in blood vessels & the GI tract.

         4. Nervous

Consists of only two cell types in the central nervous system (CNS) & peripheral nervous system (PNS):

• Neurons - Cells that convert stimuli into electrical impulses to the brain, and Neuroglia – supportive cells.
• Neurons – are made up of cell body, axon and dendrites. There are 3 types of neurons:
• Motor Neuron –  carry impulses from CNS to muscles and glands,
• Interneuron - interpret input from sensory neurons and end responses to motor neurons
• Sensory Neuron – receive information from environment and transmit to CNS.
• Neuroglia – is made up of astrocytes, oligodendrocytes, ependymal cells and microglia in the CNS, and schwann cells and satellite cells in the PNS.

All tissues of the body develop from the three primary germ cell layers that form the embryo:

• Mesoderm – develops into epithelial tissue, connective tissue and muscle tissue.
• Ectoderm - develops into nervous tissue and epithelial tissue.
• Endoderm – develops into epithelial tissue.

A tissue is like love. A simple idea but somehow complicated. :)