Protection, Support, and Movement PDF

PROTECTION, SUPPORT, AND MOVEMENT INTEGUMENTARY SYSTEM This organ system includes the skin and all the structures associated with it such as the hairs, claws, feathers, scales, glands, nerves, etc. and functions primarily to protect the body from the outside environment. *Integument...

PROTECTION, SUPPORT, AND MOVEMENT INTEGUMENTARY SYSTEM This organ system includes the skin and all the structures associated with it such as the hairs, claws, feathers, scales, glands, nerves, etc. and functions primarily to protect the body from the outside environment. *Integument The term which refers to the outer covering of the body. It is a protective wrapping that includes the skin and all the structures derived from and associated with the it such as hairs, setae, scales, feathers, horns, claws, etc. Functions of the Integumentary System  Protection The skin is composed of several layers of cells which prevent the entry of pathogenic or disease-causing microorganisms. This also houses certain kind of skin cells called melanocytes which produce melanin (a brown or black pigment) in response to sun exposure. The production of this pigment in the skin renders a protective function as it protects the organism from the damaging action of the ultraviolet radiation of the sun. The skin also contains sebaceous glands or oil glands which produce an oily substance (called sebum) that forms sebum membrane on the skin surface and protects the body from excessive water loss (dehydration or desiccation), absorbing the external shock and healing wounds.  Thermoregulation (regulation of body temperature) The sweat glands in the skin perform a homeostatic or regulatory mechanism which maintains body temperature. When it is hot, the sweat glands in the skin become active in producing sweat which leaves the skin through skin pores. As sweat hits the air, the air makes it evaporate together with the body heat hence, cools down the body. In contrast, when it is cold, sweat glands become inactive. This means body heat is not released and is conserved hence counteracting the coolness of the outside environment  Excretion The skin plays a role in excretion through the production of sweat by sweat glands. Sweating eliminates excess water and salts, as well as a small amount of urea, a byproduct of protein catabolism.  Sensation The skin is the body's largest sensory organ and its sensory (or afferent) nerve receptors detect a number of different stimuli: mechanical, such as pressure or stretching; and thermal, in terms of heat and cold.  Synthesis of Vitamin D The skin synthesizes vitamin D when exposed to UV radiation. In the presence of sunlight, a form of vitamin D3 called cholecalciferol is synthesized from a derivative of the steroid cholesterol in the skin. The liver converts cholecalciferol to calcidiol, which is then converted to calcitriol (the active chemical form of the vitamin) in the kidneys.  Performs respiratory functions (for some animals) Cutaneous respiration, or cutaneous gas exchange, is a form of respiration in which gas exchange occurs across the skin or outer integument of an organism rather than gills or lungs. Cutaneous respiration may be the sole method of gas exchange, or may accompany other forms, such as ventilation. Cutaneous respiration occurs in a wide variety of organisms, including insects, amphibians, fish, sea snakes, turtles, and to a lesser extent in mammals. In frogs, the skin is highly vascular (several blood vessels) which allows gas exchange. Because of their skin, the frogs must live in moist environments and secrete mucous from their skin to avoid desiccation. Cutaneous respiration also allows for the frog to remain almost completely submerged under water for long periods of time, while still oxygenating their blood. Earthworms do not have lungs. They breathe through their skin. Oxygen and carbon dioxide pass through the earthworm's skin by diffusion. For diffusion to occur, the earthworm's skin must be kept moist.  Performs reproductive functions (for some animals) In some animals the integument is used in some reproductive processes like courtship and finding a mate. In peacock for instance, their impressively sized, patterned and brightly colored feathers or plumage that they fan out for display purposes is not a sign of vanity but a way of attracting a mate, hence a form of courtship ritual.   Use in both defense from predators and offense to prey Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle. Avoidance of detection and escaping when caught are among these anti-predator adaptations. Avoidance of detection can be accomplished by different protective coloration processes such as camouflage, mimicry and countershading. o Camouflage is a process in which the animals Camouflage resemble the background against where they live. o Mimicry is a process in which some animals resemble other animals or related species. o Countershading is a process in which the surfaces of the animal that are habitually turned toward the light are dark and those on the undersides are pale. This is commonly observed in fishes and many other animals. The ability of an animal organism to undergo this coloration process is attributed to integumentary Mimicry pigments (collectively called biochromes) which are encapsulated in large cells with branching processes called chromatophores of different types: o Melanophores- contain the black pigment melanin. o Xantophores- contain the yellow, orange and red colors collectively called carotenoids. (Note: ommochromes and pteridines are yellow pigments present in mollusks and reptiles) o Iridophores- contain crystals of guanine or some purine, rather than pigments. These Countershading produce silvery, metallic effect by reflecting light. It is important to note that the plumage of birds, especially peacocks, is not because of biochromes but rather this color (called structural color) is produced by the physical structure of the surface tissue which reflects certain light wavelengths and eliminates others. This is responsible for the beautifully iridescent and metallic hues found in the animal kingdom. Integument of Different Organisms  Unicellular- the plasma membrane serves as their outer covering.  Invertebrates- the epidermis serves as their principal outer covering. Examples:  roundworms- have a thick, flexible cuticle, covered by an epicuticle.  annelids- have a thin, horny cuticle pierced by pores through which epidermal glands secrete mucus.  mollusks- its epidermis is delicate and soft containing mucous glands, some of which secrete the CaCO3 of their shells.  arthropods – have the most complex of invertebrate integuments. Its integument does not only provide protection but even skeletal support. It consists of a single layer of cells which is called hypodermis which secretes a complex cuticle.  Vertebrates – the skin is the outer covering of their body. SKIN The skin technically refers to the vertebrate integument. It has the same basic structure in all vertebrates including fish, reptiles, birds, and humans and other mammals. It is the largest organ with respect to surface area of the vertebrate body. Layers of Skin:  Epidermis o The outermost layer of skin which is composed of stratified squamous epithelium capable of keratinization (accumulation of a tough protein called keratin) o It gives rise to most integument derivatives such as the hairs, feathers, claws, hooves, beaks, nails, scutes, and setae.  Dermis o It is thicker than the epidermis and is made up of dense connective tissues. o Contains blood vessels, nerves and glands. o Some of its derivatives are scales of fishes and antlers of deer.  Hypodermis o Layer below the epidermis which is made up of loose connective tissues and adipose tissues. o Considered not part of the skin, but it does anchor the skin to the underlying organs. Serves as shock absorber and insulates the deeper tissue from extreme temperature changes in the body. o This is also responsible for the curves that are more a part of a woman's anatomy than a man's. Layers of the Epidermis: 1. stratum basale lowermost layer of the epidermis; composed of a single layer of cells which receive adequate nutrition and oxygen from the tissues below; composed of cells that are actively dividing. 2. stratum spinosum composed of several layers of flattened and irregular cells with spine like projections; cells are still capable of mitosis. 3. stratum granulosum composed of 2 to 3 layers of cells; keratinization begins here. 4. stratum lucidum thin translucent band; only found in thick areas of epidermis: soles of feet and palms of hands. 5. stratum corneum thickest of all cell layers in the epidermis (about 3/4 of the epidermis); composed of dead and water-resistant cells which are completely keratinized. Note: The stratum basale is made up of cells that are active mitotically, they renew the layers of cells that lie above. As the outer layers of cells are displaced upward by the new generations of cells beneath, an exceedingly tough, fibrous protein called keratin accumulates in the interior of the cells. Gradually, keratin replaces all metabolically active cytoplasm. The cell dies and eventually shed, lifeless and scale like. This process is called keratinization. These keratinized or cornified cells are highly resistant to abrasion and water diffusion. They are the ones that comprise the stratum corneum. This layer becomes especially thick in areas exposed to persistent pressure/ friction such as calluses and human palms and soles. Layers of Dermis 1. Papillary Layer the upper dermal layer which contains pain receptors (free nerve endings) and touch receptors (Meissner's corpuscles) Uneven with fingerlike projections called the dermal papillae. 2. Reticular Layer the deepest skin layer which contains blood vessels, sweat and oil glands, and deep pressure receptors (Pacinian Corpuscles). Integumentary Glands  Sweat glands (sudoriferous glands) - simple, tubular, highly coiled glands that occur over much of the body in most mammals which function in regulating body temperature.  Scent glands - present nearly in all mammals which are used in communication with members of the same species to mark territorial boundaries, for warning, or for defense.  Sebaceous glands (oil glands) - intimately associated with hair follicles, albeit, some are free and open directly onto the surface. - cells of which become distended with fatty accumulation, then die, and are expelled as sebum into the hair follicle. - found all over the body. In humans, these are numerous in the scalp and on the surface.  Mammary glands - this provides the name of mammals. - occur in all females and in rudimentary form in males. - secrete milk which nourish the young.  Mucous glands - Present in many animals like earthworms and amphibians which function to keep the skin moist. References: Books: 1. Campbell, N.A. 1996. Biology, 4th ed. The Benjamin Cummings Publishing Company, Inc. California. 2. Hickman, P.C; Roberts, L.S; A. Larson. 1993. Integrated Principles of Zoology, 9 th ed. Mosby Year Book, St. Louis,  Missouri. 3. Marieb, Elaine N. 2002. Essentials of Human Anatomy and Physiology, 6th ed. Pearson Education Asia Pte Ltd. Singapore. Internet Sources: 1. https://courses.lumenlearning.com/wm-biology2/chapter/vitamin-d-synthesis/ 2. http://www.biospectrum.com/shop/page.html?id=164 3. https://mrbarlow.wordpress.com/2011/11/13/ 4. https://en.wikipedia.org/wiki/Cutaneous_respiration#:~:text=Cutaneous%20respiration%2C%20or%20cutaneous %20gas,other%20forms%2C%20such%20as%20ventilation. 5. https://slideplayer.com/slide/6493540/ 6. https://web.extension.illinois.edu/worms/anatomy/anatomy10.html 7. https://animalrespriation.weebly.com/frog.html 8. http://justfunfacts.com/interesting-facts-about-peacocks/ 9. https://www.123rf.com/photo_85511086_praying-mantis-on-the-green-leaf-camouflage.html 10. https://biologywise.com/understanding-batesian-mimicry-with-examples 11. https://fishionary.fisheries.org/countershading/ 12. http://gurneyjourney.blogspot.com/2013/01/countershading.html SKELETAL SYSTEM The skeletal system includes all of the bones and joints in the body. Each bone is a complex living organ that is made up of many cells, protein fibers, and minerals. The skeleton acts as a scaffold by providing support and protection for the soft tissues that make up the rest of the body. The skeletal system also provides attachment points for muscles to allow movements at the joints. New blood cells are produced by the red bone marrow inside of our bones. Bones act as the body’s warehouse for calcium, iron, and energy in the form of fat. Finally, the skeleton grows throughout childhood and provides a framework for the rest of the body to grow along with it. Functions of the Skeletal System Support and Protection to softer tissues The skeletal system’s primary function is to form a solid framework that supports and protects the body’s organs and anchors the skeletal muscles. For example, the rib cage acts as a hard shell to protect the internal organs—such as the brain and the heart—from damage caused by external forces. rib cage Locomotion or Movement The bones of the skeletal system act as attachment points for the skeletal muscles of the body. Almost every skeletal muscle works by pulling two or more bones either closer together or further apart. Joints act as pivot points for the movement of the bones. The regions of each bone where muscles attach to the bone grow larger and stronger to support the additional force of the muscle. In addition, the overall mass and thickness of a bone increase when it is under a lot of stress from lifting weights or supporting body weight. Hematopoiesis (production of RBC and WBC) Red bone marrow produces red and white blood cells in a process known as hematopoiesis. Red bone marrow is found in the hollow space inside of bones known as the medullary cavity.  Storage of minerals The skeletal system stores many different types of essential substances to facilitate growth and repair of the body. The skeletal system’s cell matrix acts as our calcium bank by storing and releasing calcium ions into the blood as needed. Proper levels of calcium ions in the blood are essential to the proper function of the nervous and muscular systems. Bone cells also release osteocalcin, a hormone that helps regulate blood sugar and fat deposition. The yellow bone marrow inside of our hollow long bones is used to store energy in the form of lipids. Finally, red bone marrow stores some iron in the form of the molecule ferritin and uses this iron to form hemoglobin in red blood cells. Skeleton o an internal or external framework of bone, cartilage, or other rigid material supporting or containing the body of an organism. Types of Skeleton 1. Hydrostatic Skeleton- a mass or plastic parenchyma enclosed within a muscular wall to provide the support necessary for antagonistic muscle action; for example, parenchyma in acoelomates and perivisceral fluids in pseudocoelomates serve as hydrostatic skeleton. 2. Rigid Skeleton- differs from hydrostatic skeleton in consisting rigid elements usually jointed to which muscles can attach. Provide the anchor points required by opposing sets of muscles such as flexors and extensors. Types of rigid skeletons: a. Exoskeleton a supporting structure secreted by ectoderm or epidermis; external not enveloped by living tissue, as opposed to endoskeleton. this is typical for mollusks and arthropods. this may be mainly protective, but it may also perform a vital role in locomotion. may take the form of shell, a spicule, or a calcareous, proteinaceous or chitinous plate. it may be rigid, as in mollusks, or jointed and movable as in arthropods. unlike the endoskeleton, which grows with the animal, it is often limiting coat or armor that must be periodically molted to make way for an enlarged replacement. b. Endoskeleton- a skeleton that is formed inside the body and is composed of bone and cartilage, which are forms of dense connective tissue. Characteristics of echinoderms and vertebrates. Elements of Rigid Skeleton: 1. Cartilage is the major skeletal element of some vertebrates e.g. jawless fishes, lampreys (agnathans), elasmobranchs (sharks, skates, and rays) soft, pliable, characteristically deep- lying tissue. composed of cartilage cells (chondrocytes) surrounded by firm complex protein gel. blood vessels are virtually absent. hyaline cartilage makes up the articulating surfaces of many bones and joints of most adult vertebrates and the supporting tissues present in tracheal, laryngeal, and bronchial rings. the principal supporting and connective tissue present in the nose and external ear. Cartilaginous skeleton of sting ray Shark Skeleton 2. Notochord semi rigid axial rod of the earliest chordates (protochordates) and vertebrate larvae and embryos and also supportive tissue in a few vertebrates. a stiffening device, preserving body shape during locomotion. except in the jawless vertebrates (lampreys and hagfishes), this is surrounded and replaced by the backbone during embryonic development.  3. Bone a living tissue that differs from other connective and other connective tissues by having significant deposits of inorganic calcium salts to laid down in an extracellular matrix. it differs from cartilage in that it is a vascular tissue, in which no bone cell is more than 0.1 mm. away from a blood capillary. its intercellular substance is permeated with canaliculi (tiny canals) that connect lacunae with each other. Microscopic Structure of Bone Canaliculi tiny canals serving to connect the bone cells (osteocytes) with the blood capillaries. filled with fluids making them effective medium for the diffusion of nutrients from the blood to the bone cells and also facilitates gas exchange between the bone cells and the blood, so that the cells remain alive although they are surrounded by calcified intercellular matrix called lamellae Osteocyte Term of the bone cell within the Lacunae. Lacunae spaces where osteocytes are housed. Haversian system (osteon) the unit of structure of a compact bone. Composed of a canal (haversian canal) and concentric lamellae. Types of Bone (according to shape) Long bones are longer than they are wide and work as levers. The bones of the upper and lower extremities (ex. humerus, tibia, femur, ulna, metacarpals, etc.) are of this type. Short bones are short, cube-shaped, and found in the wrists and ankles. Flat bones have broad surfaces for protection of organs and attachment of muscles (ex. ribs, cranial bones, bones of shoulder girdle). Irregular bones are all others that do not fall into the previous categories. They have varied shapes, sizes, and surfaces features and include the bones of the vertebrae and a few in the skull.  Sesamoid bones These are bones embedded in tendons. Since they act to hold the tendon further away from the joint, the angle of the tendon is increased and thus the leverage of the muscle is increased. Examples of sesamoid bones are the patella and the pisiform (is a small knobbly, pea-shaped wrist bone). The patella also known as the knee cap or kneepan. is a thick, circular-triangular bone which articulates with the femur and covers and protects the knee joint. It is the largest sesamoid bone in the human body. Types of bone tissue (according to texture)  Compact bone consists of closely packed osteons or haversian systems. dense, hard, and forms the protective exterior portion of all bones.  Spongy (cancellous) bone is lighter and less dense than compact 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. Types of bone (according to development) Intramembranous bone It is a kind of bone that developed from fibrous membranes. Examples are the flat bones of the skull, the mandible and the clavicles. Endochondral bone It is a kind of bone that developed from hyaline cartilage. All of the bones of the body, except for the flat bones of the skull, mandible, and clavicles, are endochondral bones. Three types of cells that contribute to bone homeostasis: osteoblasts are bone-forming cells. osteoclasts resorb or break down bone. osteocytes are mature bone cells. Note: An equilibrium between osteoblasts and osteoclasts maintains bone tissue. Gross Structure of Long Bone Shaft (diaphysis) consists mainly of compact bone, although the innermost layer is spongy/cancellous. Medullary cavity large space at the central portion of diaphysis which contains the bone marrow. Types of Bone Marrow: Yellow marrow - present only in the medullary cavity of long bones and consists largely of adipose tissue. Red marrow - found in the bodies of vertebrate, the diploe of cranial bones, sternum, ribs, clavicle, scapula, and the proximal epiphyses of femurs and humerus. Epiphyses at the end of the long bone (capping the diaphyses) Epiphyseal disk cartilaginous which divides the epiphysis and the diaphysis. closes when the growth of the bone is completed. Periosteum outside covering of the bone which is composed of fibrous membrane. Articular cartilage found on the outer surface of the epiphysis. It forms a smooth, shiny surface that decreases friction within a joint. Because a joint is also called an articulation, this cartilage is called articular cartilage. Plan of Vertebrate Skeleton The skeletal system in an adult human body is made up of 206 individual bones. These bones are arranged into two major divisions: the axial skeleton and the appendicular skeleton. The axial skeleton runs along the body’s midline axis and is made up of 80 bones while the appendicular skeleton is made up of 126 bones. Two Main Divisions 1. Axial skeleton  includes the skull, vertebral column, sternum and the ribs. 2. Appendicular Skeleton  composed of the pectoral girdle, pelvic girdle, upper extremities and lower extremities. Axial Skeleton a) Skull – the structure which frames the head and consists of the following bony structures: Cranium- brain box 3 pairs of sense capsules for the nose, eyes and ears Visceral skeleton which provides the jaw and support of the tongue. * fontanelle (or fontanel) is an anatomical feature on an infant's skull. soft spots on a baby's head which, during birth, enable the bony plates of the skull to flex, allowing the child's head to pass through the birth canal. The ossification of the bones of the skull causes the fontanelles to close over by a child's second birthday. The closures eventually form the sutures of the neurocranium. b) Vertebral column – commonly called backbone which is differentiated into the following types of vertebrae: Cervical (neck) 7 Thoracic (chest) 12 Lumbar (back) 5 Sacral (pelvic) 5 Caudal (tail) 4 33 Note: Atlas and Axis are the terms for the first and second cervical vertebrae, respectively. Note: The sacral vertebrae are actually composed of fused vertebrae called Sacrum, while the caudal vertebrae are composed of four fused vertebrae called Coccyx which is thought to be the remnant of the tail of the ape. c) Ribs – attach to the vertebrae. e.g. primates – 13 pairs humans – 12 pairs Types of ribs: True ribs- the first 7 pairs that are attach to the sternum by separate costal cartilages. False ribs- the remaining 5 pairs. 8th 9th have cartilages that are attach to 10th the costal cartilage above 11th unattached in front and are called 12th free or floating ribs  d) Sternum a flat, dagger shaped bone located in the middle of the chest. Parts: Manubrium- also called the "handle", is located at the top of the sternum and moves slightly. It is connected to the first two ribs. Body- also called the "blade" or the "gladiolus", is located in the middle of the sternum and connects the third to seventh ribs directly and the eighth through tenth ribs indirectly. xiphoid process- also called the "tip", is located on the bottom of the sternum. It is often cartilaginous (cartilage), but does become bony in later years. Note: Thoracic basket (or rib cage) - composed of the 12 pairs of ribs and the sternum. II. APPENDICULAR SKELETON Shoulder or pectoral girdle Clavicle Scapula Forelimb Humerus Radius and ulna Carpals Metacarpals Phalanges Pelvic or hip girdle pubis ischium ilium Hindlimbs femur tibia and fibula tarsals metatarsals phalanges JOINTS (articulations) places in which two or more bones are connected. the point of contact between two bones. Types: Immovable joints or synarthroses characterized by edge–to-edge sutures that interlock the bones to another. Amphiarthroses - partially movable joints Movable joints or Diarthroses or synovial joints allow freedom of movement between bones. Types of diarthroses joints:  Ball and socket joint – the rounded head of one bone sits within the cup of another, such as the hip joint or shoulder joint. Movement in all directions is allowed.  Saddle joint – this permits movement back and forth and from side to side, but does not allow rotation, such as the joint at the base of the thumb.  Hinge joint – the two bones open and close in one direction only (along one plane) like a door, such as the knee and elbow joints. This is like hinge on a door. This allows movement in only two directions namely flexion and extension (backward or forward). Examples of hinge joints are the knees, elbows and the outer joints of the fingers.  Condyloid joint (or ellipsoid joint) – this permits movement without rotation, such as in the jaw or finger joints.  Pivot joint – one bone swivels around the ring formed by another bone, such as the joint between the first and second vertebrae in the neck. The radius and ulna, wrist and ankle joints are all pivot joints.  Gliding joint (or plane joint) – smooth surfaces slip over one another, allowing limited movement, such as the wrist joints. This is the joint in which nearly flat surfaces glide across each other as in the vertebrae or the spine. This joint enables the torso to bend forward, backward, sideways as well as rotate. radial-carpal joint Allows movement in wrist bones (e.g. wrist) References: Books: 1. Campbell, N.A. 1996. Biology, 4th ed. The Benjamin Cummings Publishing Company, Inc. California. 2. Hickman, P.C; Roberts, L.S; A. Larson. 1993. Integrated Principles of Zoology, 9 th ed. Mosby Year Book, St. Louis, Missouri. 3. Marieb, Elaine N. 2002. Essentials of Human Anatomy and Physiology, 6th ed. Pearson Education Asia Pte Ltd. Singapore. 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MUSCULAR SYSTEM The muscular system is composed of specialized cells called muscle fibers whose predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction. Exceptions to this are the action of cilia, the flagellum on sperm cells, and amoeboid movement of some white blood cells. The integrated action of joints, bones, and skeletal muscles produces obvious movements such as walking and running. The integrated action of joints, bones, and skeletal muscles produces obvious movements such as walking and running. Skeletal muscles also produce subtler movements that result in various facial expression, eye movements, and respiration. In addition to movement, muscle contraction also fulfills some other important functions in the body, such as posture, joint stability, and heat production.  Posture, such as sitting and standing, is maintained as a result of muscle contraction. The skeletal muscles are continually making fine adjustments that hold the body in stationary positions.  The tendons of many muscles extend over joints and in this way contribute to joint stability. This is particularly evident in the knee and shoulder joints, where muscle tendons are a major factor in stabilizing the joint.  Heat production, to maintain body temperature, is an important by-product of muscle metabolism. Nearly 85 percent of the heat produced in the body is the result of muscle contraction. Kinds of Animal Movement: 1. Amoeboid movement - a crawling-like type of movement accomplished by protrusion of cytoplasm of the cell involving the formation of pseudopodia. - is a form of movement especially characteristic of amoebas and other unicellular forms; it is also found in many wandering cells of higher animals, such as white cells, embryonic mesenchyme, and numerous other mobile cells that move through the tissue spaces. 2. Ciliary movement - it is a form of movement that is done by the locomotory structures, the cilia and flagella, characteristic to the ciliates and flagellates, respectively.  Cilia – are minute, hair like processes that extend from the surfaces of the cells of many animals (Paramecium caudatum)  Flagella – whip like structure usually present single or in small number at one end of a cell (e.g. euglena, sperm cell, and sponges). 3. Muscular movement – a form of animal movement performed by the muscular tissues (cells of which are specialized for contractility). Types of Vertebrate Muscles: 1. Skeletal muscles 2. Smooth muscles 3. Cardiac muscles Parts of Skeletal Muscle:  Origin – end of the skeletal muscle that is relatively more fixed point of attachment.  Insertion – end that is freely movable. This is pulled to the origin during contraction.  Belly or body – portion of the muscle between the origin the insertion. Connective tissue wrappings:  Epimysium – covers the muscle tissue.  Perimysium –surrounds the bundles of muscle fibers (fascicles)  Endomysium – surrounds each muscle fiber. Structure of Muscular Tissue (Striated Muscle)  Muscle cells – also called muscle fibers.  Fascicles (fasciculus) – bundles of muscle fibers.  Sarcolemma – term of the muscle cell’s plasma membrane.  Sarcoplasm – the muscle fiber’s cytoplasm. Contains the following:  sarcosomes – its mitochondria  sarcoplasmic reticulum – term for tits endoplasmic reticulum.  myofibrils – account for the characteristic banding patterns of striated muscles.  granulated inclusions THE MYOFIBRIL  accounts for the characteristic banding patterns of striated muscles. Two Bands of Myofibril:  A- band or anisotropic band – dark-staining bands.  I-band or isotropic band – light-staining bands.  Note: Each I-band is crossed by a narrow dark Z line from the German word “zwischen” (meaning between bands) and a pale band can be seen passing through the center of the A-band. This is called the H-band. The Sarcomere  the segment between 2 consecutive Z lines.  the structural unit of a myofibril. The Myofilaments  much smaller parallel units of a single myofibril. Two kinds:  myosin filaments - thick myofilaments that are confined to the A-band region (11 nanometers or 110-150 angstroms).  actin filaments - thin myofilaments that are located in the I-band region but extend some distance to A-band region (5 nanometers or 50 angstroms). STIMULATION OF CONTRACTION  Muscle contracts in response to nerve stimulation.  If the nerve supply to the muscle is severed, the muscle atrophies, or wastes away. MOTOR UNITS  Group of skeletal muscle fibers which is innervated with a single neuron. All- or- none law - states that if all muscle cells except for one (in a motor unit) are cut, the remaining one uncut muscle fiber never shortens even if it is stimulated at increasing intensity reaching its threshold. This means to say that muscle fibers respond to a single stimulus maximally or not at all.  As the motor neuron approaches the muscle fibers within a motor unit, it splays out into many terminal branches. Each branch attaches to a muscle fiber at a special area, A SYNAPSE, called the myoneural junction.  At the junction is a tiny gap, called synaptic cleft that thinly separates a nerve fiber (motor neuron) and a muscle fiber.  In the vicinity of the junction, the neuron stores a chemical transmitter, called acetylcholine, in minute vesicles known as synaptic vesicles. Myoneural junction. 1.Presynaptic terminal 2. Sarcolemma 3. Synaptic vesicles 4. Nicotinic acetylcholine receptor 5. Mitochondria ACETYLCHOLINE  A chemical transmitter or mediator that diffuses across the junction and acts on muscle fiber membrane to generate an electrical depolarization.  This is released from the synaptic vesicles when a nerve impulse reaches a synapse (myoneural junction) which is a special chemical bridge that couples together the electrical activities of nerve and muscle fibers. SLIDING FILAMENT THEORY (a theory of muscular contraction)  proposed by A.F. Huxley & H.E. Huxley (English physiologists).  states that muscle contraction involves the sliding movement of the thin filaments (actin) past the thick filaments (myosin).  states that the myosin filaments have cross bridges that are able to swing back and forth and hook into the binding sites of the actin filaments. In other words, the thick and thin filaments are linked together by molecular cross bridges which act as levers to pull the filaments to pass each other. According to this theory:  myosin filaments  are composed of 2 polypeptide chains with globular head and slender tail. The double heads of each myosin molecule face outward from the center of the filament.  actin filaments  are globular and are arranged into the intertwined chains (two actin filaments twisted together forming double helix). They contain active binding sites where the heads of the myosin molecules are attached during contraction.  Moreover, actin filaments are surrounded by 2 regulator proteins (troponin and tropomyosin) which prevent the binding of the myosin to actin filaments. Overview of the Sliding Filament Theory ENERGY FOR CONTRACTION  ATP – is the immediate source of energy for the muscular contraction.  Creatine phosphate - a source of energy for muscular contraction that contains even more free bond energy than ATP.   Glycogen – the major source of carbohydrate in muscle. This is also a source of energy for muscular contraction because this compound could be readily converted into glucose-6-phosphate (the starting material of cellular respiration that ultimately leads to the generation of ATP). PHASES OF CONTRACTION  Latent period – interval between the initial stimulus and shortening.  No mechanical change that occurs within the muscle but there is liberation of energy required for contraction.  Lasts for about 0.01 second  Contraction period – the time from the beginning of mechanical response to its peak.  Lasts for about 0.04 second  Relaxation period – the time from the peak of contraction to return to original length.  Lasts for about 0.05 second.  Tetanus – single sustained muscular contraction because of the extreme rapidity in the application of successive stimuli. In here, the muscles cannot relax between successive stimuli. Note: If tetanic contraction is maintained too long, fatigue will result.  Tonus – partial contraction of the muscles.  Muscle fatigue – results when there is accumulation of lactic acid due to the depletion of stored energy or insufficiency of oxygen leading to the conversion of the glycolytic product, pyruvic acid, into lactic acid. References: Books: 1. Campbell, N.A. 1996. Biology, 4th ed. The Benjamin Cummings Publishing Company, Inc. California. 2. Hickman, P.C; Roberts, L.S; A. Larson. 1993. Integrated Principles of Zoology, 9 th ed. Mosby Year Book, St. Louis, Missouri. 3. Marieb, Elaine N. 2002. Essentials of Human Anatomy and Physiology, 6 th ed. Pearson Education Asia Pte Ltd. Singapore. Internet Sources: 1. https://training.seer.cancer.gov/anatomy/muscular/ 2. http://csmbio.csm.jmu.edu/biology/garrisne/Physiology/C/sld017.htm 3. https://www.quora.com/What-are-cilia-flagella-and-pseudopodia 4. https://www.pinterest.ph/pin/380976449697953953/  5. http://fig.cox.miami.edu/~cmallery/150/neuro/myofibril.htm 6. https://psychology.wikia.org/wiki/Myofibril 7. https://www.unm.edu/~lkravitz/Exercise%20Phys/motorunitrecruit.html 8. https://human-memory.net/neuromuscular-junction/ 9. https://www.isd2135.k12.mn.us/cms/lib/MN01001544/Centricity/Domain/54/Muscle%20Physiology-2.pdf Prepared and compiled by: ADAM ROY V. GALOLO, PhD Faculty, Biology Department College of Mathematics and Natural Sciences Caraga State University Ampayon, Butuan City, Philippines