Chapter 10: Muscle Tissue Flashcards
Motor Unit
Consists of a somatic motor neuron plus all the skeletal muscle fibers it stimulates.
Myogram
Record of a muscle contraction
Unfused (incomplete) Tetanus
When a skeletal muscle fiber is stimulated at a rate of 20 to 30 times per second, it can on partially relax between stimuli.
Fused (Complete) Tetanus
When a skeletal muscle fiber is stimulated at a high rate of 80 - 100 times per second, the muscle does not relax at all.
Motor Unit Recruitment
The process in which the number of active motor units increase.
Muscle Tone
A skeletal muscle exhibits a small amount of tautness or tension in the muscle due to weak, involuntary contractions of its motor units.
Flaccid
A state of limpness in which muscle tone is lost.
Isotonic Contraction
Muscle contraction where the tension developed remains almost constant while the muscle changes length.
Concentric Isotonic Contraction
Tension generated is great enough to overcome resistance of the object to be moved, the muscle shortens and pulls on another structure such as a tendon.
Eccentric Isotonic Contraction
When the length of a muscle is increased during a contraction.
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.
Hypertrophy
Enlargement of exciting cells
Hyperplasia
An increase in the number of fibers
Pericytes
Stem cells found in association with blood capillaries and small veins.
New smooth muscles can arise from this cells.
Muscle Fibers
Most important component of skeletal muscle
Sacrolemma
Plasma membrane of muscle fiber. Muscle action potentials travel along the sarcolemma, ensures excitement.
Transverse (T) Tubules
Open to the outside the muscle fiber. Filled with interstitial fluid. Action potential travels through these.
Sarcoplasm
Within the sarcolemma. This is the cytoplasm of a muscle fiber.
Myoglobin
Red colored protein. Found only in muscle fibers. Binds in O2 molecules with interstitial fluid. Releases the O2 when its needed for ATP.
Myofibrils
Small contractile structures of skeletal muscles. Extend entire length of muscle fibers. Give muscle the striated appearance.
Sarcoplasmic Reticulum
Fluid filled membranous sac. Encircles each myofibrils. Stores Ca2+ when muscle are relaxed, releases Ca2+ through terminal cisterns when contracts.
Terminal Cisterns
Dilated end sacs of SR. Butt against the T Tubule from both sides. These cisterns releases Ca2+ when SR triggers muscle contractions.
Triad
Formed from 2 terminal cisterns and T tubule.
Thick Filament
Composed of protein myosin
Thin Filament
Composed of protein actin.
Sarcomeres
Basic functional unit of myofibrils. Compartments arranged from filaments inside the myofibril. Organized in bands and zones.
Tropomyosin
Regulatory Protein. Component of thin filament. When muscle is relaxed, covers myosin. This prevents myosin from binding with actin, thus preventing contraction.
Troponin
Regulatory Protein. Component of thin filament. Ca2+ changes shape when binds with troponin. This moves tropomyosin away from myosin. Muscle contractions begin to bind with actin.
Structural Proteins
Proteins that keep thick and thin filaments of myofibrils in proper alignment.
Titin
Structural protein. Connects Z disc to M line. Stabilizes thick filaments
A-actinin
Structural protein of z discs. Attaches to actin of thin filaments.
Myomesin
Structural proteins forms M line. Binds to thin filaments and connects to adjacent thick filaments.
Nebulin
Structural protein. Wraps around entire length of thin filaments.
Dystropnin
Link thin filaments of sarcomere to integral proteins to sarcolemma. Helps reinforce sarcolemma.
Myosin
Contractile Proteins. Makes up thick filaments.
Contains a tail and 2 heads. Binds to actin of thin filaments during a muscle contraction.
Actin
Contractile proteins. Make up thin filaments. Contains myosin binding site where myosin bind during muscle contraction.
Regulatory Protiens
Proteins that help switch muscle contractions on and off.
Why Smooth Muscle Lack Straintions
Contain both thin/thick filaments and intermediate filaments. None of these are arranged in sarcomeres.
Muscle Tissue
Skeletal
Cardiac
Smooth
Skeletal Muscle
Move bones of skeleton
Striated; dark and light protein bands
Voluntary: control by neurons.
Cardiac Muscle
Only found in the heart, forms heart wall.
Striated: dark and light bands of proteins.
Involuntary: alternating contractions and relaxations of heart is not continuously controlled. Autonomic.
Contains autorhythmicity.
Autorhythmicity
Build in heart rhythm
Smooth Muscle
Located in walls of hallow internal structures
Blood vessels, airways, organs in abdpelvic cavity. Also in skin attached to hair follicles.
Non striated: autorphythpmic
Involuntary: regulated by neurons of autonomic division
Functions of Muscle Tissue
- Producing body movement: movement of whole body. Relies on function of skeletal muscles, bones and joints.
- Stabilizing body positions: skeletal muscle contractions stabilize joints and help maintain positions such as standing.
- Storing and moving substances within the body: Sphincters of smooth muscle prevent out flow of contents of hallow organs. Cardiac muscle pumps blood throughout body. Smooth muscle contraction/relaxation in blood vessels help adjust blood flow. Skeletal muscle promote flow of lymph and return of blood in veins.
- Generate heat: muscle tissue produces heat (thermogenesis). Heat produced is used to maintain body temp.
Properties of Muscle Tissue
- Electrical Excitability: ability to respond to retain stimuli by producing electrical signals called muscle action potential.
- Contractility: ability to contract forcefully when stimulated by action potential.
- Extensibility: ability to stretch within limits without being damaged.
- Elasticity: Ability to return to its original shape after contraction or extension.
Electrical Excitability
Both a property of muscle and nervous tissue
Ability to respond to certain stimuli by producing signals called muscle action potentials.
2 types:
1. Electrical: autorphytmic
2. Chemical: neurotransmitters released both by neurons or hormones in blood
Contractility
Ability of muscular tissue to contract forcefully when stimulated by an action potential
Example: smashing food
Extensibility
Ability of muscle tissue to stretch within limits without being damaged. CT within the tissue keeps it in range.
Smooth muscle is subject to the greatest amount of stretching.
Elasticity
The ability of muscular tissue to return to its original length and shape after contraction.
Muscle Fiber Ormyocytes
100-1000 cells that male up skeletal muscle cells
Fibers have elongated shapes
Fascia
Dense sheet of irregular CT
Lines body walls and limbs
Supports and surrounds muscles and organs
Connective Tissue Layer of Skeletal Muscles
Extend from the fascia to protect and strengthen skeletal muscles
1. Epimysium
2. Perimysium
3. Endomysium
All these layers of CT extend beyond muscle fibers to form rope like tendon that attaches a muscle to periosteum of bone.
Epimysium
Dense Irregular CT
outer layer, encircles the entire muscle
Perimysium
Dense irregular CT
Surrounds groups of 10-100 muscle fibers into bundles. These muscle bundles are known as fascicles.
Fascicles
Bundles of fibers that are formed by the Perimysium
Give meat its grain
Endomysium
Reticular fibers
Penetrates the interior of each fascicle
Separates individual muscle fibers from one another
Somatic Motor Neurons
Nerves that stimulate skeletal muscles to contract.
Capillaries In Tissue
Plentiful in muscular tissue, each muscle fiber is in close contact to capillaries
Level of Organization of Skeletal Muscle
- Skeletal Muscle: made of fascicles that contain muscle fibers, blood vessels and nerves wrapped in Epimysium.
- Fascicle: Bundle of muscle fiber wrapped in Perimysium.
- Muscle Fiber (Cell): cell covered by Endomysium and sacrolemma. Contain nuclei and organelles. Striated appearance.
- Myofibril: thread like contractile element within sarcoplasm of muscle fibers composed of filaments
- Filaments (myofilaments): Contractile protein within myofibril. 2 types: thick filaments and thin filaments
Thick Filaments
Composed of myosin
Thin Filaments
Composed of actin
Z Disc
Occurs at the boarder of a sarcomere. Narrow region of dense material that separate one sarcomere from the next.
A Band
Dark middle part of sarcomere that extend the entire length of the thick filament. Includes the parts of thin filaments that overlap thick filaments.
I Band
Lighter, dense area of sarcomere that contains remainder of thin filaments but no thick filaments. Z disc passes through center of each I Band.
H Zone
Narrow region in center of each A Band that contain thick filaments but not thin filaments.
M Line
Region in center of H Zone that contains proteins that hold back myosin tail.
Muscle Metabolism
Muscle fibers produce ATP in 3 ways:
1. From creatine phosphate
2. Anaerobic glycolysis
3. Aerobic respiration
Creatine Phosphate
Synthesize excess ATP produced when muscles are relaxed. This is energy rich molecule is found in muscle fiber.
Anaerobic Glycolysis
Faster than aerobic but yields less ATP
Breakdown of glucose gives rise to lactic acid when O2 is absent or in low concentration.
Glycolysis occurs in the cytosol, produces a net gain of 2 ATP molecules and 2 lactic acids. Lactic acid diffuses out of muscle into blood stream.
Glycolysis also breaks down glucose molecules into 2 molecule of pyruvic acid.
Aerobic Respiration
Slower than anaerobic but yields more ATP. Requires O2. Pyruvic acid formed by glycolysis enters mitochondria where a series of O2 requiring reactions occur.
These reactions are :Krebs cycles and electron transport. These reactions produce ATP, CO2, H2O and Heat.
2 Sources of O2 for Muscles
1.O2 that diffuses into muscle fibers from blood
2. O2 released by myoglobin within muscle fibers.
Muscle Fatigue
The inability of a muscle to maintain force of a contraction after prolonged activity.
Oxygen Debt
Refers to added O2, over and above the resting O2 consumption that is taken into the body after exercise.
Payback or Restore in O2 Debt
The extra O2 must payback or restore metabolic conditions to resting levels by:
1. Convert lactic acid back into glycogen. Stored in liver
2. To resynthesizes creatine phosphate and ATP in muscle fibers
3. Replace the O2 removed from myoglobin.
Red Muscle Fibers
Skeletal muscle fibers that have a high myoglobin content. Appear darker.
White Muscle Fibers
Skeletal muscle fibers that have a low content of myoglobin. Appear lighter.
Slow Oxidative Fibers
Appear dark red due to large amount of myoglobin.
Location: postural neck muscles
Recruitment: used first
Contains: Many mitochondria and capillaries
High: ATP by aerobic respiration, fatigue resistance
Low: glucose storage, creatine kinase
Slow: ATP by hydrolysis, contraction velocity
Function: Maintaining posture during endurance activities
Fast Oxidative Glycolytic Fibers
Appear red/pink due to medium amount of myoglobin
Location: lower limb muscles
Recruitment: used second
Contains: Many mitochondria and capillaries
Intermediate: ATP by aerobic/anaerobic respiration, fatigue resistance, creatine kinase, glycogen stores
Fast: ATP hydrolysis, contraction velocity
Function: walking, sprinting
Fast Glycolytic Fibers
Appear white/pale due to small amount of myoglobin
Location: extracellular muscles
Few: mitochondria, capillaries
Low: ATP by anaerobic glycolysis, fatigue resistance
Fast: ATP hydrolysis, contraction velocity
High: creatine kinase, glycogen stores
Function: rapid intense movement of short duration
Intercalated Discs
Irregular transverse thickenings of sarcolemma
Unique to cardiac muscles.
Connect the ends of cardiac muscles to one another.
Visceral (Single Unit) Muslce Tissue
More common type of smooth muscle
Found in skin, blood vessels and hallow organs: stomach, intestines, uterus, bladder
Multi Unit Muscle Tissue
Second type of smooth muscle
Consists of individual fibers with its own motor neuron terminals
Sarcoplasm of Smooth Muscle
Contains:
Thick/thin filaments
Intermediate filaments
Coveolae
No tubules
Caveolae
Found in Smooth Muscle
Small pouch like invaginations of the PM
Contains extracellular Ca2+ used for muscle contraction
Calmodulin
Smooth muscle regulatory protein enzyme
Regulates contractions and relaxations
Binds to Ca2+ in sarcoplasm, activates myosin
Works slowly
