Chapter 10-Muscle Tissue

3 Types of Muscle Tissue

Skeletal, Cardiac, and Smooth

cardiac muscle tissue

principal tissue in the heart wall

Myology

the study of muscles

neuromuscular junction

the synapse between a somatic neuron and a skeletal muscle fiber

aponeurosis

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

Myofibrils built from 3 types of proteins

1) Contractie proteins, which generate force during contraction. 2) Regulatory proteins, help switch the contraction process on and off 3) structural proteins, keep the thick and thin filaments in the proper alignment, give the myofibril elasticity and extensibility, and link the myofibrils to the sarcolemma and extracellular matrix.

4 stages of contraction cycle

1. ATP hydrolysis 2. Attachment of myosin to actin to form cross-bridges 3. Power stroke 4. Detachment of myosin from actin

2 main types of stimuli that trigger action potentials (Electrical Excitability)

1. Autorhythmic electrical signals arising in the muscular tissue itself, as in the heart's pacemaker. 2. Chemical Stimuli such as neurotransmitters released by neurons, hormones distributed by the blood or even local changes in pH.

Properties of Muscular Tissue

1. Electrical excitability 2. Contractibility 3. Extensibility 4. Elasticity

Functions of muscle tissue

1. Producing body movements. 2. Stabilizing Body Positions. 3. Storing and moving substances within the body. 4. Generating heat.

How does a nerve impulse elicit a muscle action potential?

1. release of acetylcholine 2. activation of Ach receptors. 3. production of muscle action potential 4. termination of Ach activity

3 Layers of Connective Tissue Extend from Fascia to protect and strengthen skeletal muscle

1.Epimysium 2. Perimysium 3. Endomysium

In a relaxed muscle cell, what does the SR store?

Calcium ions. Release of Ca+2 from the terminal cisterns of the SR triggers muscle contraction

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. Fascia holds muscles with similar functions together, allows free movement of muscles: carries nerve, blood vessels, and lymphatic vessels; and fills space between muscles.

Sarcoplasmic Reticulum (SR)

a fluid-filed system of membranous sacs; similar to smooth ER in non muscular cells

I band

a lighter, less dense area that contains the rest of the thin filaments but no thick filaments and a Z disc passes through the center of each I band.

nebulin

a long, nonelastic protein wrapped around the entire length of each thin filament; held anchor thin filaments to the Z discs and regulate the length of thin filaments during development

Electrical excitability

a property of both muscle and nerve cells; ability to respond to certain stimuli by producing electrical signals called action potentials.

synapse

a region where communication occurs between 2 neurons or between a neuron and target cell.

aerobic respiration

a series of oxygen-requiring reactions that produce ATP, carbon dioxide, water and heat

smooth muscle tone

a state of continued partial contraction

flaccid

a state of limpness in which muscle tone is lost

fused tetanus

a sustained contraction in which individual twitches cannot be detected

Triad

a transverse tubule and the 2 terminal cisterns on either side

oxygen debt

added oxygen, over and above the resting oxygen consumption that is taken into the body after exercise

tendon

all three connective tissue layers may extend beyond the muscle fibers to form a rope like tendon that attaches a muscle to periosteum of a bone.

creatine phosphate

an energy rich molecule that is found in muscle fibers

hyperplasia

an increase in the number of fibers

tropomyosin and troponin

apart of the thin filament; in relaxed muscle, myosin is blocked from binding to actin bc of tromyosin cover the myosin binding sites on actin. Tropomyosin strands are held in place by troponin molecules

Slow oxidative fibers

appear dark red because they contain large amounts of myoglobin and many blood capillaries; generate ATP by aerobic respiration; slow pace

Why does muscle contraction occur?

because myosin heads attach to and "walk" along the thin filaments at both ends of a sarcomere, progressively pulling the thin filaments towards the M line. Thin filaments slide inward and meet at the center of a sarcomere. Band I and H zone narrow an eventually disappear altogether when the muscle is maximally contracted. Bands remain unchanged. Thin filaments on each side of sarcomere attached to Z discs, when filaments slide inward, Z discs come closer together and sarcomere shortens. Shortening of sarcomeres causes shortening of whole muscle fiber, leads to shortening of entire muscle.

a-actinin

bind to actin molecules of the thin filament and titin

calsequestrin

bind to the Ca2+, enabling even more ca2+ to be sequestered or stored within the SR.

calmodulin

binds ca2+ in the cytosol after, activates an enzyme called myosin light chain kinase. Enzyme uses ATP to add a phosphate group to a portion of the myosin head. Once phosphate group is attached, myosin head can bind to actin, and contraction can occur.

latent period

brief delay that occurs between application of the stimulus and the beginning of contraction

contraction period

ca2+ binds to troponin, myosin binding site on actin are exposed, and cross bridges form

relaxation period

ca2+ is actively transported back into the SR, myosin binding sites are covered by tropomyosin, myosin heads detach from actin and tension in muscle fiber decreases

refractory period

characteristic of all muscle and nerve cells; duration varies with the muscle involved; skeletal muscle shorter refractory period and cardiac longer

somites

columns of mesoderm undergo segmentation in a a series of these cube-shaped structures

motor unit

consists of a somatic motor neuron plus all of the skeletal muscle fibers it stimulates

multiunit smooth muscle tissue

consists of individual fibers, each with its own motor neuron terminals and with a few gap junctions between neighboring fibers.

junction folds

deep grooves in the motor end plate that provide a large surface area for Ach

Anatomy of a Skeletal Muscle Fiber

diameter of mature skeletal muscle fiber 10-100 um; length 10 cm, 100+ nuclei, once fusion occurs, the muscle fiber loses its ability to undergo division, number of skeletal muscle fibers is set before you are born and usually last a lifetime.

Terminal Cisterns

dilated end sacs of the sarcoplasmic reticulum; butt against the T tubule from both sides

A band

extends the entire length of the thick filaments; toward each end is a zone of overlap, where the thick and thin filaments lie side by side.

neurotransmitter

first cell communicates with second cell by releasing this chemical messenger

Cardiac Muscle Tissue

forms most of the heart wall; striated; involuntary; built in rhythm of heart is autorhythmicity.

dermatome

forms the connective tissues, including dermis of the skin

myotome

forms the muscles of the head, neck, and limbs

dense bodies

functionally similar to Z discs in striated muscle fibers

sclerotome

gives rise to the vertebrae

muscle fatigue

inability of a muscle to maintain force of contraction after prolonged activity

length-tension relationship

indicates how the forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins.

acetylcholine receptors

integral transmembrane proteins to which ACh specifically binds

Perimysium

layer of dense irregular connective tissue, but it surrounds groups of 10-100 or more muscle fibers, separating them into bundles caked fascicles. Many fascicles large enough to be seen with the naked eye.

dystrophin

links thin filaments of the saromere to integral membrane proteins in the connective tissue extracellular matrix that surrounds muscle fibers; dystrophin and its associated proteins are thought to reinforce the sarcolemma and help transmit the tension generated by the sacromeres to the tendons.

Smooth Muscle Tissue

located in the walls of hollow internal structures such as blood vessels, airways, and most organs in the abdominopelvic cavity; found in the skin, attached to hair follicles; looks nonstriated; involuntary.

Fast glycolytic fibers

low myoglobin content and few blood capillaries; few mitochondria and appear white in color; contract strongly and quickly due to their inability to hydrolyze ATP rapidly

synaptic vesicles

membrane enclosed sacs suspended in the cytosol within each synaptic end bulb

mesoderm

middle primary germ layer that gives rise to connective tissues, blood and blood vessels, and muscles

2 Contractile Proteins in Muscle

myosin and actin, components of thick and thin filaments

Skeletal Muscle Tissue

named so because most skeletal muscles move the bones of the skeleton; striated; mainly work in a voluntary manner; controlled subconsciously.

Z discs

narrow, plate-shaped regions of dense protein material; separate one saromere from the next

synaptic end bulbs

neural part of the neuromuscular junction

somatic motor neurons

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

acetylcholine

neurotransmitter released at the NMJ

Muscle Fibers

organ composed of thousands of cells

Endomysium

penetrates the interior of each fascicle and separates individual muscle fibers from one another. Mostly made up of reticular fibers.

Capillaries

plentiful in muscle tissue; each muscle fiber is in close contact with one or more capillaries; blood capillaries bring in oxygen and nutrients and remove heat and the waste products of muscle metabolism esp. during contraction, the muscle fiber synthesizes and uses considerable ATP.

Strength training

price of exercising with progressively heavier resistance for the purpose of strengthening the musculoskeletal system

thermogenesis

process where muscle tissue contracts, producing heat.

myomesin

protein that forms the m line.

myogram

record of a muscle contraction

Myoglobin

red-colored protein found only in muscle, binds oxygen molecules that diffuse into muscle fibers from interstitial fluid; releases oxygen needed by the mitochondria for ATP production. Mitochondria lie in rows throughout the muscle fiber, strategically close to the contractile muscle proteins that use ATP during contraction so that ATP can be produced as quickly as needed.

motor end plate

region of the sarcolemma opposite of the synaptic end bulbs

contraction cycle

repeating sequence of events that causes the filaments to slide. 4 stages

Subcutaneous Layer/Hypodermis

separates muscle from skin, is composed of areolar connective tissue and adipose tissue. Provides a pathway for nerves, blood vessels and lymphatic vessels to enter and exit muscles. Adipose layer of subcutaneous layer stores most of body's triglycerides, serves as an insulating layer that reduces heat loss, and protects muscles from physical trauma.

synaptic cleft

separates the two cells.

sliding filament mechanism

skeletal muscle shortens during contraction because the thick and thin filaments slide past one another

Myofibrils

small structures stuffed in the sarcoplasm; the contractile organelles of skeletal muscle; extend the entire length of a muscle fiber; their prominent striations make the entire skeletal muscle fiber appear striped.

creatine

small, amino acid-like molecule that is synthesized in the liver, kidneys, and pancreas and then transported to muscle fibers

filaments

smaller protein structures within myofibrils; composed mostly of protein actin=thin. Thick=protein myosin; both directly involved in contractile process; arranged in sacromeres.

excitation-contraction coupling

steps that connect excitation to contraction

wave summation

stimuli arriving at different times cause larger contractions

M Line

supporting proteins that hold the thick filaments together at the center of the H zone; middle of the sacromere

unfused tetanus

sustained but wavering reaction

Contractility

the ability of muscular tissue to contract forcefully when stimulated by an action potential. When a skeletal muscle contracts, it generates tension while pulling on its attachment points. In some muscle contractions, the muscle develops tension but does not shorten. Ex) holding a book in an outstretched hand. Lifting book of table then muscle shortens.

Elasticity

the ability of muscular tissue to return to its original length and shape after contrition or extension.

Extensibility

the ability of muscular tissue to stretch, within limits, without being damaged. The connective tissue within the muscle limits the range of extensibility and keeps it within the contractile range of the muscle cells. Smooth muscle=greatest amount of stretching. Ex) stomach fills with food, smooth muscle wall is stretched. Also, cardiac muscle also stretched each time heart is filled with blood

Sacromeres

the basic functional units of a myofibril

anaerobic glycolysis

the breakdown of glucose gives rise to lactic acid when oxygen is absent or at low concentration

twitch cibtraction

the brief contraction of all muscle fibers in response to a single action potential in its motor neuron

H zone

the center of each A band contains a thick but not thin filaments

Sarcoplasm

the cytoplasm of a muscle fiber; includes a substantial amount of glycogen; also contains myoglobin

axon terminal

the end of the motor neuron

hypertrophy

the enlargement of existing cells

Myosin

the main component of thick filaments and functions as a motor protein in all three types of muscle tissue; motor proteins pull various cellular structures to achieve movement by converting chemical energy to ATP to the mechanical energy of motion, the production of force; 300 molecules of myosin form a single thick filament; shaped like 2 golf clubs twisted together; tail points toward M line in center of sacromere; tails of neighboring myosin parallel to one another, forming shaft of thick filament; two projections of myosin molecule are called myosin heads. Heads project outward from the shaft in a spiraling fashion, each extending toward one of the 6 thin filaments that surround each thick filament

visceral smooth muscle tissue

the more common smooth muscle tissue type; found in the skin in tubular arrangements rear form part of the walls of small arteries and veins and of hollow organs such as the stomach, intestines, uterus and urinary bladder.

Somatic motor neurons

the neurons that stimulate skeletal muscle to contract; each somatic motor neuron has an axon that extends from the brain or spinal cord to a group of skeletal muscle fibers. Axon of a somatic motor neuron typically branches many times, each branch extending to a different muscle fiber

motor unit recruitment

the number of active motor units increases

Epimysium

the outer layer, encircling the entire muscle. Consists of dense irregular connective tissue

Sarcolemma

the plasma membrane of a muscle cell

tonic contraction

the tension developed in the muscle remains almost constant while the muscle changes its length

eccentric isotonic contraction

the tension exerted by the myosin cross-bridges resists movement of a load and slows the lengthening process

isometric contraction

the tension generated is not enough to exceed the resistance of the object to be moved, and the muscle does not change its length

titin

the third most plentiful protein in skeletal muscle after actin and myosin. Name reflects it huge size; stabilizes the position of the thick filament. Accounts for much of the elasticity and the extensibility of myofibrils

ACtin

thin filaments anchored to Z discs; individual actin molecules join to form an actin filament that is twisted into a helix. On each actin molecule is a myosin-binding site, where myosin head can attach.

Transverse Tubules

thousands of tiny invaginations of the sarcolemma; tunnel in from the surface toward the center of each muscle fiber; open to the outside of the fiber, they are filled with interstitial fluid. Muscle action potentials travel along sarcolemma and through T-tubules, quickly spreading throughout the muscle fiber; this arrangement ensures that an action potential excites all parts of the muscle fiber at essentially the same instant.

concentric isotonic contraction

type of isotonic contraction; if tension generated in this is great enough to overcome the resistance of the object to be moved, the muscle shortens and pulls on another structure to produce movement and to reduce the angle at the joint

Fast Oxidative glycolytic fibers

typically the largest fibers; contain large amounts of myoglobin and many blood capillaries; can generate considerable ATP by aerobic respiration which gives them high resistance to fatigue; generate ATP by anaerobic glycolysis because their intracellular glycogen level is so high; fast because the ATPase in their myosin heads hydrolyzes ATP 3-5x faster than in SO

ca2 acting transport pumps

use ATP to move ca2+ constantly from the sarcoplasm into the SR

smooth muscle tissue

usually activated involuntarily

Ca2 release channels

when channels open, ca2 flows out of the SR into the sarcoplasm around thick and tho filaments; as a result, ca2 concentration in the sarcoplasm rises tenfold or more. Released calcium ions combine with troponin, causing it to change shape.

mesodermal cells

where smooth muscle develops from, migrate to envelop the developing gastrointestinal tract and viscera

Microscopic Organization of Skeletal Muscle

1) Embryonic development-many myoblasts fuse to form on skeletal muscle fiber. Once fusion has occurred, muscle fiber loses ability to undergo cell division, but satellite cells retain ability. 2) Sarcolemma of fiber encloses sarcoplasm and myofibrils, which are striated. 3.) Sarcoplasmic reticulum wraps around each myofibril. 4.) Thousands of transverse tubules, filled with interstitial fluid, invaginate from the sarcolemma toward the center of the muscle fiber.