Muscles & Integument Notes PDF

Anatomy and Physiology I The Muscular System Muscle is one of the four basic tissues in the body. It is made up of cells that can shorten and lengthen. Muscles carry out the orders of the nervous system. However, in cardiac and smooth muscle no nerve input is required to perform...

Anatomy and Physiology I The Muscular System Muscle is one of the four basic tissues in the body. It is made up of cells that can shorten and lengthen. Muscles carry out the orders of the nervous system. However, in cardiac and smooth muscle no nerve input is required to perform their basic function; instead this activity is preprogrammed. The nervous system adjusts and modifies the activity of cardiac and smooth muscle, but does not start the basic activity. Three types of muscle: Skeletal muscle is under voluntary control and moves the skeleton. Cardiac muscle is only found one place. It is involuntary muscle. Smooth Muscle is found all over the body, in places like the eye, lung, stomach, intestines, urinary bladder and reproductive tract. It is also involuntary muscle. Myo- refers to muscle generally ex. myositis is inflammation of muscle Sarco- refers to the muscle cell ex. sarcoplasm is the cytoplasm of the muscle cell Skeletal muscle Skeletal muscle can be controlled be the conscious mind, but also has a “cruise control” that allows an animal to not constantly think about functions like breathing or maintaining upright posture. Gross anatomy The belly is the muscle refers to the thick, central, contractile portion of the muscle Tendons are fibrous connective tissue bands that connect muscle to bone Aponeuroses are broad fibrous tissue bands that attach muscle to bone or muscle to other muscle o The linea alba “white line” runs lengthwise between muscles on the ventral midline and connects abdominal muscle from each side.  Origin the most stable of the two attachment points of the muscle, usually proximal and usually does not move during contraction Insertion the attachment point that moves when the muscle is contracted, usually more distal Muscle action Movement is caused by pulling on attachment points Prime movers (or agonists) describes the muscles that make the primary movement happen Antagonist is the muscle that directly opposing the action of the prime mover, they help smooth out movement or can contract at the same time to cause rigidity and lack of movement Synergist muscle is one the contracts at the same time as the primary mover and helps in movement Fixator muscles stabilize joint to allow for other movements Muscle names Flexors bend joints Extensors straighten joints Shape may determine the name, ex. Deltoid Location, ex. Biceps brachii on the brachium Direction of the fibers, ex. rectus means straight Number of heads or divisions, ex. Cephal meaning head in the biceps with two heads, triceps with three or quadriceps with four Attachment sites- origin and insertion sites can be used for the name ex. sternohyoideus Microscopic anatomy Skeletal muscle cells are very long and thin, and are usually called skeletal muscle fibers Multinucleated cells with the nucleus located just under the sarcolemma which is the muscle cell membrane Myofibrils make up most of the interior of a muscle fiber. They are packed together lengthwise and are made of thousands of even tinier protein filaments Between the myofibrils within the cell are the organelles  o Mitochondria o A network of sarcoplasmic reticulum (like the endoplasmic reticulum) o Network of transverse tubules (T tubules) Myofibrils made up of thousands of contractile protein filaments o Actin thin contractile filaments o Myosin thick contractile filaments A band is the large dark band made up of thick myosin filaments I band is the large light band made up of thin actin filaments Z band is the dark line in the center of the light I band Sarcomere is the area from one Z line to the next Z line. It is the basic contracting unit of the skeletal muscle. Sarcomeres are lined up end to end so that each of their small contractions yield considerable muscle fiber shortening Connective tissue layers Because of the force exerted during contraction, muscles must be secured together and to the structures they move Each individual muscle fiber is surrounded be a delicate, reticular connective tissue layer called the endomysium Groups of skeletal muscle fibers called fascicles are bound together by tough connective tissue layer called the perimysium. Groups of fascicles are surrounded by a fibrous tissue layer called epimysium All three connective tissue layers are continuous with the tendons and aponeurosis, so that the muscle is held together and to its attachment point. Connective tissue layers also contain blood vessels, nerves and fat. Neuromuscular junction The site where the ends of the motor nerve fibers connect to muscle fibers They are not actually attached, but rather are separated by a small synaptic space  The end of the nerve fiber contains small sacs called synaptic vesicles that contain the chemical neurotransmitter acetylcholine This neurotransmitter initiates the process of muscle contraction Acetylcholine is quickly broken down by acetylcholinesterase Each nerve fiber innervates more than one muscle fiber. A motor unit describes one nerve fiber and all the muscle fibers it innervates. Physiology of muscle contraction 1. The nerve impulse causes the release of acetylcholine into the synaptic space 2. Acetylcholine binds to receptors on the surface of the sarcolemma 3. This starts an impulse that travels along the sarcolemma and then through the T tubules to the interior of the cell 4. When the impulse reaches the sarcoplasmic reticulum stored Ca++ ions are released into the sarcoplasm 5. The Ca++ diffuses into the myofibrils and starts the contraction process 6. The contraction is fueled by ATP 7. Immediately after the Ca++ is released it is pumped back into the sarcoplasmic reticulum, also using ATP to pull Ca++ out of the myofibril stopping the contraction Mechanics of contraction During a relaxed phase actin and myosin overlap a small amount During contraction lever-like cross bridges on the myosin filaments ratchet back and forth to pull actin filaments toward the center of the myosin filament, thus shortening the sarcomere. Characteristics of contraction There is no partial muscle fiber contraction, contraction follows the all-or-nothing principle Fine, controlled movements are produced by controlling the number of muscle fibers that are stimulated to contract “Muscle memory” is the training of the nervous  system to control these stimulations precisely A single muscle fiber contraction is called a twitch which is divided into three phases o The latent phase is the slight delay (milliseconds) between the nerve stimulus and the contraction o The contracting phase o The relaxation phase The coordination of the timing of the twitches of individual fibers also for smooth, sustained contraction Chemistry of muscle contraction The sliding contraction of the actin and myosin filaments is powered with ATP produced by the abundant mitochondria in the muscle fiber The energy of ATP is released when the molecule loses a phosphate group and becomes ADP (adenosine diphosphate) The ADP can then be recharged into ATP by adding back a phosphate group The phosphate group that recharges ADP to ATP is from creatine phosphate (CP) The breakdown, or catabolism, of nutrients (using glucose and oxygen) supplies the energy to create ATP and CP Glucose is stored in the muscle in the form of glycogen Oxygen is stored in the muscle by a large protein called myoglobin When the oxygen supply is good, no myoglobin is used- this is aerobic metabolism When the oxygen supply is depleted or demand is too high, muscle fibers shift to anaerobic metabolism A by-product of anaerobic metabolism is lactic acid Heat production Muscle contraction produces heat Excessive heat is dispersed with sweating or panting Shivering to contract the muscles is one way the body reacts to hypothermia  Cardiac Muscle Microscopic anatomy Cardiac muscle cells are much smaller then skeletal muscle cells Cardiac muscle cells contain only one nucleus per cell Cells have multiple braches that are securely attached to each other by intercalated discs o Fasten the cells together o Transmit impulses form cell to cell o Allows cardiac muscle cells to contract together in a coordinated way Cardiac muscle physiology Cells contract without any external stimulus Groups of cardiac cells adopt the contraction rate of the fastest cell in the group The impulse that coordinate cardiac muscle contraction spreads from one cell to the next through the intercalated disks like a wave The impulse conduction system consists entirely of cardiac muscle cells The impulse that starts each wave of contraction starts in the “pacemaker”, the sinoatrial (SA) node Nerve supply to cardiac muscle Though no outside nerve stimulation is needed to initiate the contraction of cardiac muscle, the cardiac nerve supple can modify the cardiac muscle activity Nerves to the heart are from both portions of the autonomic nervous system: sympathetic and parasympathetic o Sympathetic fibers cause the heart to beat stronger and faster- the fight or flight response o Parasympathetic fibers cause the heart to beat more slowly and with less force- rest and digest response Smooth muscle Gross anatomy  Visceral smooth muscle- Found in sheets of cells in the walls of some hollow organs Multiunit smooth muscle- Found in small discrete groups of cells Microscopic anatomy Small spindle shaped cells with tapered ends and a single nucleus in the middle Actin and myosin filaments are not arranged in parallel so there is no striated appearance The actin and myosin filaments of smooth muscle crisscross the cell and attach at both ends to dense bodies that correspond to the Z lines of skeletal muscle This arrangement causes the cell the ball up when the contractile units shorten Individual smooth muscle cells can shorten more than cardiac or skeletal muscle cells Physiology of smooth muscle Visceral smooth muscle Has large, rhythmic waves of contractions No need for external stimulation to initiate contractions Reacts to stretching by contracting more forcefully- this does not happen in the uterus as the fetus grows because of inhibition by the hormone progesterone and others During parturition progesterone levels drop, and there is increased levels of other hormones, including oxytocin and estrogen that help to initiate labor Autonomic innervation o Sympathetic nervous system decreases smooth muscle activity o Parasympathetic nervous system increases smooth muscle activity Multiunit smooth muscle  Small and delicate for small delicate contractions Iris and ciliary body of the eye In the walls of small blood vessels Around small airways in the lungs Require specific input from the autonomic nerves to contract 6  Anatomy and Physiology I The Integument and Related Structures Integument The integument is one of the largest and most extensive organ systems in the body o Composed of all four tissue types o Protects and covers o The skin, combined with its related structures forms the integumentary system The integumentary system This system involves every inch of the external animal o Hooves, hair, horns, claws and skin related glands o Contiguous with mucous membranes that line mouth, nostrils and anus Though derived from living germinal layers- everything you see is dead cells o Cells give up their organelles and nuclei to make room for keratin o During keratinization the cell dies Involved in vitamin D synthesis Skin Two layers, epidermis and dermis (also known as the corium) Layers are separated by the epidermal basement membrane o A wavy layer, sometimes with upward projections called dermal papillae that helps to cement the epidermis to the dermis The epidermis is formed of keratinized stratified squamous epithelium The dermis is a tough layer formed of fibroelastic connective tissue Only the dermis contains blood vessels The hypodermis or subcutaneous layer is composed  primarily of adipose tissue Epidermis Contains four primary cell types o Keratinocytes make up the majority of the cells ▪ Produce keratin ▪ Young cells along the basement membrane are nourished by the dermis ▪ As they age they are pushed away from the blood supply ▪ They lose their nuclei, cytosol and organelles and fill with keratohyaline granules ▪ In humans, an entirely new epidermis forms every 7-8 weeks o Melanocytes make the pigment in the skin ▪ Found in the deepest epidermal layers ▪ Octopus-like and has long projections that extend outward to all the keratinocytes in the basal layer ▪ Produce melanin pigment stored in membrane bound granules called melanosomes ▪ Released into the intracellular space and absorbed by keratinocytes ▪ Used to protect the keratinocytes from UV damage o Langerhans cells are macrophages specific to the epidermis ▪ Originate in the bone marrow ▪ Phagocytize microinvaders and help to stimulate the immune response o Merkel cells aid in the sensation of touch ▪ At the epidermal-dermal junction ▪ Associated with the sensory nerve ending ▪ The half-dome shape of the Merkel cell together with the half-dome shaped sensory nerve ending is called a Merkel disk Layers of the epidermis 1. Stratum basale/stratum germinativum a. Consists of a single layer of keratinocytes b. Actively dividing c. Merkel cells, melanocytes and keratinocytes all  found in the basal layer 2. Stratum spinosum a. Spiny layer, fixed cells resemble sea urchins b. Contains several layers held together with desmosomes c. Less cellular division d. Langerhans cells present in this layer 3. Stratum granulosum a. Granular layer b. The middle layer of the skin c. 2-4 layers of diamond shaped keratinocytes d. Cytoplasm contains keratohyaline and lamellated granules e. Lamellated granules release glycolipids important in waterproofing the skin 4. Stratum lucidum a. Clear layer b. Found in only very thick skin c. Few rows of flattened, dead cells 5. Stratum corneum a. Outmost layer dominates the epidermis b. Makes up ¾ of total epidermal thickness c. Composed 20-30 layers of dead keratinocytes d. In crossed-section paper thin, hexagonal viewed from above Epidermis of hairy skin Haired skin usually consists of three layers- stratum basale, stratum spinosum, stratum corneum Covered with scale like folds Hair emerges from beneath the scales and in is arranged in groups of 3 follicles Tactile elevations knoblike elevations in the epidermis usually associated with a tactile or trylotrich hairs o Important in the perception of touch Dermis Makes up the greatest portion of the integument  Highly fibrous composed of dense irregular connective tissue with collagen, elastic and reticular fibers Hair follicles, nerve endings, glands, smooth muscles This layer binds the superficial dermis to the underlying tissues Two layers o Papillary layer lies beneath the epithelial layer and is composed of loose connective tissue and contains the dermal papillae that cement the epidermis to the dermis. Meissner’s corpuscles are touch receptors in the papillary layer o Reticular layer 80% of the dermis composed of dense irregular connective tissue. Fibrous bundles in this layer run in the direction of tension ▪ The direction of tension is important as wounds that are perpendicular to tension lines gap, and incisions should be made along the lines of tension to prevent gapping Subcutaneous layer A thick layer of loose areolar tissue Many blood and lymphatic vessels Has deep touch receptors called pacinian corpuscles Pigmentation Caused by the presence or absence of melanin granules Dispersion of melanin granules is controlled by melanocyte-stimulating hormone The keratinocytes arrange the melanin on the side of the cell that receives the greatest amount of sun exposure Paw pads Composed of all five epidermal layers including a very thick stratum corneum Fat and connective tissue form the pads that bear the weight of the animal Carpal pads are those located on the caudal surface of the carpus Metacarpal and metatarsal pads are the primary weight bearing pads Digital pads protect each digit  The pad also has exocrine sweat glands Nasal planum Also known as the planum nasolabiale in horses and cattle to describe the muzzle Polygonal plates packed together Composed of only three epidermal layers: stratum basale, stratum spinosum and stratum corneum Despite the wetness of a dog’s nose, there are no glands in the dermis and epidermis of the planum nasale Sheep, cattle and goats have tubular glands in their planum nasolabiale Ergots and chestnuts Chestnuts are vestigial remnants of the carpal and tarsal pads of the first digit o Found on the medial side of the carpus and tarsus Ergots are vestiges of the second and fourth digits Though the evolutionary process horses lost digits to become faster runners Cutaneous pouches Present in sheep Infoldings of skin filled with fine hairs, sebaceous and oil glands o Infraorbital- in front of the eye o Interdigital- in between the digits o Inguinal- in the flank folds o Metatarsal- lateral metatarsal of camelids Hair Hair is essential for survival for most animals. Hair helps to maintain body temperature, acts as camouflage and physical protection. In most species fur is thickest over the exposed portions of the body. Hair strands and follicles The shaft is the portion of the hair that occurs above the level of the skin The portion that occurs within the skin is called the root  The hair is anchored in the skin by the follicle that extends through the epidermis, dermis and sometimes deep into the hypodermis Hair bulb The deepest portion of the hair follicle At the base of the bulb is a mound of dermal cells called the papilla The papilla is covered with rapidly dividing epithelial cells called the matrix These epithelial cells are pushed away from their blood supply as the divide and become keratinized becoming part of the growing hair Root hair plexus A web of sensory nerve that envelope the hair root Acts as a touch receptor Compound follicles Multiple hair strands emerge from a single epidermal orifice Each strand of hair has its own follicle and bulb In compound follicles there is usually a single, long primary hair surrounded by shorter secondary hairs In most dogs 3 compound follicles are grouped together to emerge from the same epidermal fold The Hair Formed in three concentric layers The central core of the hair is formed of 2-3 layers of loosely arranged cells called the medulla The next layer is composed of a hard, thick layer of hard keratin called the cortex Finally, the outside surface of the hair is composed of a single layer of hard keratin arranged like roof shingles and called the cuticle Usually, the cuticle is smooth enough to prevent the hairs from sticking together and forming a matt. Hair growth cycles Hair grows and falls out in a continuous cycle In outside animals, spring and fall is the time of heaviest shedding  Hormones can influence hair loss, the term for losing a large volume of coat at one time is call telogen effluvium Anagen is the growth phase when more cells are added to the hair root Catagen phase is the transitional time between anagen and telogen phases Telogen is the quiescent period after hair reaches its maximum length and anagen has stopped Hair color Determined by pigment in the cortex and medulla from genetically programed melanocytes at the hair base Color variation produced by the amount of melanin produced Dogs produce two types of melanin o Pheomelanin produces yellow or reddish colors o Tyrosine melanin produces brownish-black colors Horse color variation produced by the amount and location of melanin- not different types With age the melanin production decreases and the hair turns gray Types of hair Three primary types: 1. Guard hairs/primary hairs- longer, straighter thicker hairs 2. Secondary hairs are shorter and softer, wavy or bristled 3. Tactile hairs have lots of nerve endings, commonly known as whiskers though they are mixed throughout the coat ▪ Also known as sinus hairs because of the large blood sinus in the follicle Arrector pili muscles Hairs slope head to tail, this angle is the implantation angle When animals are frightened or cold they can make their hair stand up beyond the normal implantation angle through contraction of the arrector pili muscle The muscle is also associated with a sebaceous gland  that forces sebum onto the skin’s surface to keep the integument moist and supple The contraction of the arrector pili muscle causes goose bumps in people Glands of the skin Sebaceous glands Found in almost all parts of the body Have a single duct that empties into the hair follicle or onto the surface of the skin Glandular epithelium produces an oily, lipid substance composed of glycerides and free fatty acids Glands eventually become so full they rupture and release sebum In sheep the sebaceous glands produce lanolin Arrector pili muscles contract and eject sebum from the gland Sebum traps moisture and has antibacterial and antifungal properties Excessive sebum clogs the opening of the hair follicle and causes “whiteheads” and over time turns black and causes “blackheads”, and comedones Sweat glands Found over all over the body, but only horses produce profuse sweat Two types: o Eccrine sweat glands ▪ single coiled tube connected to the surface by a long duct ▪ in dogs they are found in deep layers of fat and in the connective tissue of the foot pads o Apocrine sweat glands ▪ Coiled gland with excretory duct that empties into the hair follicle instead of onto the skin surface ▪ In dogs these glands are in the ear canals ▪ Dogs with long hair have more sebaceous and apocrine glands in their ear canals than dogs with short hair They are more prone to otitis externa Tail glands  An oval gland at the dorsal base of the tail Assists in recognition and identification Recognizable by course oily hairs, sensitive to changes in sex hormones Anal glands Musk/scent glands located at 5 and 7 o’clock around the anus Connected to the anus by a single small duct Gland is lined with apocrine and sebaceous glands and acts as a reservoir for these secretions Usually expressed through the pressure caused during defecation or fear Can become clogged or infected Animals with anal gland problems often drag their bottoms or repeatedly lick their anus 10