Chapter 10: Muscular Tissue

what are two main types of stimuli that trigger action potentials

1. autorhythmic electrical signals arising in the muscular tissue itself as in the hearts pacemaker 2. chemical stimuli (neurotransmitters released by neurons , hormones distributed by the blood or even local changes in pH).

three kinds of proteins that build myofibrils

1. contractile proteins (generate force during contraction) 2. regulatory proteins (help switch the contraction process on and off) 3. structural proteins (keep think and thick filaments in the proper alignment and give the myofibril elasticity and extensibility and line the myofibrils to the sarcolemma and extracellular matrix)

properties of muscular tissue

1. electrical excitability-- stimuli trigger action potentials 2. contractility 3. extensibility 4. elasticity

functions of muscular tissue

1. producing body movements -whole body, rely on the integrated functioning of skeletal muscles, bones and joints 2. stabilizing body positions--ex: standing or sitting 3. storing and moving substances within the body-- accomplished by sustained contractions of sphincters. temporary storage of food in stomach is possible because smooth muscle sphincters close off the outlets of organs. cardiac muscles pump blood throughout the body. also move bile and enzymes through the gastrointestinal tract and push gametes through the passageways of the reproductive systems 4.generating heat-- used to maintain normal body temp

levels of organization within a skeletal muscle

1. skeletal muscle (organ made up of fascicles that contain muscle fibers (cells), blood vessels, and nerves; wrapped in epimysium) 2. fascicle (bundle of muscle fivers wrapped in perimysium) 3. muscle fiber cell (long cylindrical cell covered by endomysium and sarcolemma: contains sarcoplasm, myofibrils, amy peripherally located nuclei, mitochondria, transverse tubules, sarcoplasmic reticulum and terminal cisterns -- striated appearance) 4. myofibril (threadlike contractile elements within sarcoplasm of muscle fiber that extend entire length of fiber; composed of filaments) 5. filaments (myofilaments) (contractile proteins within myofibrils that are of two types: thick filaments composed of myosin and thin filaments composed of actin, tropomyosin and troponin

muscle fibers

thousands of cells that compose skeletal muscles in a separate organ

types of structural proteins

titin, actinin, myomesin, nebulin, dystrophin

types of regulatory proteins

tropomyosin, troponin

myosin head

two projections of each myosin molecule. project outward front he shaft in a spiraling fashion,each extending toward one of the six thin filaments that surround each thick filament

aponeurosis

when the connective tissue elements extend as a broad, flat sheet

transverse (t) tubules

within the sarcolemma, tunnel in from the surface toward the center of each muscle fiber. open to the outside of the fiber. filled with interstitial fluid

fascia

a dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body. holds muscles with similar functions together. allows free movement of muscles; carries nerves, blood vessels and lymphatic vessels and fills spaces between muscles

glycogen

a large molecule composed of many glucose molecules. used for synthesis of ATP

perimysium

a layer of dense irregular connective tissue, surrounds groups of 10 to 100 or more muscle fibers, separate them into fascicles

contractility

ability of muscular tissue to contract forcefully when stimulated by an action potential.when a skeletal muscle contrast it generates tension while pulling on its attachment points. some develop tension but don't shorten

elasticity

ability of muscular tissue to return to its original length and shape after contraction or extension

electrical excitability

ability to respond to certain stimuli by producing electrical signals called action potentials (impulses)

what nerve components are in skeletal muscle

an artery and one or two veins accompany each nerve that penetrates a skeletal muscle

sarcomeres

basic functional units of a myofibril

fascicles

bundles of muscle fibers. large enough to be seen with the naked eye

myofilaments (thin filaments)

composed mostly of the protein actin.directly involved in contractile filaments. anchored to Z discs

thick filaments

composed mostly of the protein myosin. directly involved in contractile filaments

tendon

connective tissue layer that extend beyond the muscle fibers which attach a muscle to the periosteum of a bone

cardiac muscle

contained in only the heart. striated muscle, involuntary (heart beat)regulated by neurons that are part of the autonomic (involuntary) division of the nervous system and by hormones released by endocrine glands

sarcoplasm

cytoplasm of a muscle fiber. includes glycogen, myoglobin

A Band

dark, middle part of sarcomere that extends entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments

anatomy of a muscle fiber

diameter of 10 cm. contains myoblasts

terminal cisterns

dilated end sacs of the sarcoplasmic reticulum. butt against the t tubule form both sides. release of calcium ions from here triggers muscle contractions

three layers of connective tissue from the fascia to protect and strengthen skeletal muscle

epimysium, perimysium, endomysium

sarcoplasmic reticulum

fluid fill system of membranous sacs. encircle each myofibril. contain terminal cisterns. in a relaxed muscle fiber it stores calcium ions.

triad

formed with a transverse tubule and the two terminal cisterns on either side

shivering

involuntary contractions of skeletal muscles that can increase the rate of heat production

I band

lighter, less dense area of sarcomere that contains remained of thin filaments but no thick filaments. a Z disc passes through center of each i band

myofibrils

little threads in sarcoplasm, contractile organelles of skeletal muscle. extend the entire length of a muscle fiber. striated.

smooth muscle tissue

located in the walls of hollow internal structures (blood vessels, airways and most organs in the abdominopelvic cavity), skin and attached to hair follicles. non striated. actions are involuntary and some have autorhythmicity. regulated by neurons that are part of the autonomic (involuntary) division of the nervous system and by hormones released by endocrine glands

myosin

main component of thick filaments and functions as a motor protein -- pull various cellular structures to achieve movement by converting the chemical energy in ATP to the mechanical energy of motion (production of force). 300 molecules of myosin form a single thick filament

skeletal muscle

move the bones of the skeleton. striated- alternating light and dark protein bands (striations) are seen when the tissue is examined with a microscope. most are voluntary but some are subconscious (diaphragm)

two contractile preteens in muscle

myosin and actin

H zone

narrow region in center of each A band that contains thick filaments but no thin filaments

z discs

narrow, plate shaped regions of dense material that separate one sarcomere form the next

somatic motor neurons

neurons that stimulate skeletal muscle to contract. has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscles

epimysium

outer layer, encircling the entire muscle, dense irregular tissue

endomysium

penetrates the interior of each fascicle and separates individual muscle fibers form one another. reticular fibers

blood capillaries

plentiful in muscular tissue. bring in oxygen and nutrients and remove heat and the waste products of uncle metabolism

myosin tail

points toward the M line in the center of the sarcomere. tails of neighboring myosin molecules lie parallel to one another forming the shaft of the thick filament

sphincters

prevent outflow of the contents of a hollow organ

thermogenesis

production of heat as muscular tissue contracts

actin

protein of thin filaments. individual molecules join to form an actin filament that is twisted into a helix. each molecule is myosin binding site where a myosin head can attach

regulatory proteins

proteins that help switch muscle contraction process on and off

structural proteins

proteins that keep thin and thick filaments of myofibrils in proper alignment; give myofibrils elasticity and extensibility and sink myofibrils to sarcolemma and extracellular matrix

myoglobin

red colored protein that binds to oxygen molecules that diffuse into muscle fibers form interstitial fluid. found only in muscle. releases oxygen when it is needed by the mitochondria for ATP production

M line

region in center of H zone that contains proteins that hold thick filaments together at center

tropomyosin

regulatory protein that is a component f thin filament; when skeletal muscle fiber is relaxed it covers myosin binding sites on actin molecules thereby preventing myosin from binding to actin

troponin

regulatory protein that is a component of thin filament when calcium ions bind here it changes shape;t his conformational change moves trop myosin away form myosin binding sites on actin molecules and muscle contraction subsequently begins as myosin binds to actin

subcutaneous layer (hypodermis)

separates muscle from skin. composed of areolar connective tissue and adipose tissue. provides a pathway for nerves, blood vessels and lymphatic vessels to enter and exit muscles

what are the three types of muscular tissue

skeletal, cardiac and smooth

sliding filament mechanisms

sliding of thin filaments past thick filaments produces muscle shortening within myofilaments

filaments

smaller protein structures within myofibrils. two types: thin and thick. two thin filaments for every thick filament in the regions of filament overlap

adipose tissue (of subcutaneous layer)

stores most of the body's triglycerides, serves as an insulating layer that reduces heat loss and protects muscles from physical trauma

actinin

structural protein of z discs that attaches to actin molecules of thin filament and to titian molecules

titin

structural protein that connects z disc to m line of sarcomere thereby heeling to stabilize thick filament position; can stretch and then spring back unharmed and thus accounts for much of the elasticity and extensibility of myofibrils

myomesin

structural protein that forms m line of sarcomere; binds to titian molecules and connects adjacent thick filaments to one another

dystrophin

structural protein that links thin filaments of sarcomere to integral membrane proteins in sarcolemma which are attached to proteins in connective tissue matrix that surrounds muscle fivers. help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons

nebulin

structural protein that wraps around entire length of each thin filament; helps anchor thin filaments to z discs and regulates length of thin filaments during development

extensibility

the ability of muscular tissue to stretch within limits without being damaged. smooth muscle is subject tot he greatest amount of stretching. ex: cardiac muscle stretches when the heart fills with blood

autorhythmicity

the heart beats because it has a natural pacemaker that initiates each contraction

sarcolemma

the plasma membrane of a muscle cell.muscle action potentials travel along here and through the t tubules spreading though out the muscle fiber ensuring an action potential excites all parts of the muscle fiver at the same instant

myology

the scientific study of muscles