A&P Chapter 9 - Muscle Tissue

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what are the three types of muscle tissue?: skeletal
cardiac
smooth
what are the 5 functional characteristics?: excitability
conductivity
contractility
extensibility
elasticity
muscle excitability: respond to chemicals released from nerve cells
muscle conductivity: ability to propagate electrical signals over membrande
muscle contractility: ability to shorten and generate force
muscle extensibility: ability to be stretched without damaging the tissue
muscle elasticity: ability to return to original shape after being stretched
what are the 4 muscle tissue functions?: 1. produce body movement and body heat

2. stabilizing body positions

3. regulating organ volumes

4. movement of substances within the body
what type of tissue is skeletal muscle?: connective tissues
superficial fascia: loose connective tissue and fat underlying the skin
deef fascia: dense irregular connective tissue around muscle
connective tissue components of the muscle and their function: -epimysium-surrounds the whole muscle

- perimysium - surrounds bundles of 10-100 muscle cells

- endomysium - separates individual muscle cells
tendon: a cord of dense connective tissue that attaches a muscle to the periosteum of a bone
aponeurosis: a tendon that extends as a broad, flat layer
what supplies each skeletal muscle?: a nerve, artery and two veins
where are nerve fibers and capillaries found?: the endomysium between individual cells
motor unit: one somatic motor neuron and all the skeletal muscle cells it stimulates
how many muscle cells does a motor neuron stimulate?: 10-2,000 cells
where are muscle fibers normally scattered?: throughout the belly of muscle
sarcolemma: muscle cell membrane
T (transverse) tubules: invaginations of the sarcolemma into the center of the cell

filled with extracellular fluid

carry muscle action potentials down into cell
mitochondria: lie in rows throughout cell

use ATP during contraction
the sarcoplasm is filled with tiny threads called myofibrils, these contain what?: myoglobin and glycogen
myoglobin: red-colored, oxygen-binging protein
what does the sarcoplasmic reticulum do and what is its function?: separates and encircles each myofibril and functions in a relaxed muscle to store calcium ions
sarcomere: the contractile unit, composed of myofilaments
what creates the striations in skeletal muscle?: thick and thin filaments that overlap each other in a pattern
what is the structure of a myofibril?: contains a sarcomere that has light I bands and Dark A bands. the I bands contain thin filaments. each sarcomere is separated by Z discs. in the overlapping region, six thin filaments surround each thick filament
which supporting proteins help to anchor the thick and thin filaments in place?: M line
titin
Z discs
what three proteins build myobibrils?: z
what three types of proteins build myofibrils?: contractile proteins
regulatory proteins
structural proteins
what do regulatory proteins do?: turn contraction on and off
what do structural proteins do?: provide proper alignment, elasticity, and extensibility
what are the contractile proteins?: myosin and actin
what are the regulatory proteins?: Troponin (Tnl, TnT, TnC) and tropomyosin
what are the structural proteins?: titin
myomesin
nebulin
dystrophin
which proteins act on thick filaments?: myosin and actin
which proteins act on thin filaments?: troponin and tropomyosin
what does myosin look like?: two golf clubs twisted together, has myosin heads that cross bridges and extend toward the thin filaments
what holds myosin in place?: the M line proteins
which proteins make up thin filaments?: actin, troponin, tropomyosin
what holds thin filaments in place?: Z lines
from one Z line to the next is a ....: carcomere
what covers the myosin- binding site on each actin molecule in relaxed muscle?: tropomyosin
what is troponin responsible for?: for binding to ion and moving tropomyosin out of the way when muscle cotnracts
what does titin do?: anchors thick filaments to the M line and the Z disc
how far can the portion of the molecule between the Z disc and the end of the thick filament stretch/: to 4 times its resting length and can spring back unharmed
which protein plays a role in recovery of the muscle from being stretched?: titin
what does the M line do?: connects to titin and adjacent thick filaments
another name for M line: myomesin
nebulin: an inelastic protein that helps align the thin filaments
what does dystrophin do?: links thin filaments to sarcolemma and transmits the tension generated to the tendon
what happens in the sliding filament mechanism of contraction?: 1. myosin cross bridges and pull on thin filaments

2. thin filaments slide inward

3. Z discs come toward each other

4. sarcomeres shorten, muscle fiber shortens, muscle shortens
how does a skeletal muscle contract?: 1. nerve impulses reach an axon and synaptic vesicles release ACh

2. ACh diffuses to receptors on the sarcolemma and Na+ channels open and Na+ rushes into the cell

3. the inside of the muscle cell becomes more positive, triggering a muscle action potential that travels over the sarcolemma and down the T tubules

4. SR releases Ca+2 into the sarcoplasm

5. Ca+2 binds to troponin and casues troponin-tropomyosin complex to move and reveal myosin binding sites on actin--the contraction cycle beings
contraction cycle: repeating sequence of events that cause the thick and thin filaments to move past each other
what are the 4 steps to contraction cycle?: 1. ATP hydrolysis
2. Attachment of myosin to actin to form crossbridges
3. power stroke
4. detachement of myosin from actin
how long does the contraction cycle last?: it keeps repeating as long a there is ATP available and there is a high Ca+2 level near the filaments
how are myosin heads activated?: by ATP
what do activated myosin heads attach to?: actin
how does skeletal muscle relaxation occur?: -acetylcholinestrerase breaks down ACh within the synaptic cleft
-muscle action potential ceases
-Ca+2 release channels close
-active transport pumps Ca2+ back into storage in the sarcoplasmic reticulum
-calcium -binding protein (calsequestrin) helps hold Ca+2 in SR
-Tropomyosin-troponin complex recovers binding site on the actin
what are the 4 parts of a twitch contraction?: latent period
contraction period
relaxation period
refractory period
how long is the latent period of a twitch contraction?: 2 msec
what is happening during the latent period: Ca+2 is being released from SR and slack is being removed from elastic components
what is happening during the contraction period?: filaments slide past each other
how long is the contraction period?: 10-100 msec
how long is the relaxation period?: 10-100msec
what is happening during the relaxation period?: active transport of Ca+2 into SR
how long is the refractory period?: 5 msec for skeletal muscle and 300 msec for cardiac muscle
what is happening during the refractory period?: muscle can not respond and has lost its excitability
unfused tetanus: if stimulate is at 20-30 times/sec

there will be only partial relaxation between stimuli
fused tetanus: if stimulate is at 80-100 times/second

a sustained contraction with no relaxation between stimuli will result
what causes wave summation and both types of tetanus?: Ca+2 remaining in the sarcoplasm
why is a force of second contraction easily added to the first?: because the elastic elements remain partially contracted and do not delay the beginning of the next contraction
what are the features of muscle tone?: keeps muscle firm even though relaxed

does not produce movement
what is muscle tone used for?: essential for maintaining posture (head upright) and important in maintaining blood pressure -tone of smooth muscles in walls of blood vessels
muscle tone: involuntary contraction of a small number of motor units - alternately active and inactive in a constantly shifting pattern
isotonic contractions: contractions where a load is moved

2 types - concentric and eccentric
concentric contraction -give example: a muscle shortens and does work -ex. picking up a book or kicking a ball
eccentric contractions -give example: a muscle contracts as it lengthens
-ex. walking up a steep hill
isometric contraction -give example: no movement occurs because the muscle neither shortens nor lengthens, builds to its peak tension-producing capacity

-ex. maintaining upright posture or hold joints in stationary position - sitting in a chair, squats
when does muscle use ATP the most?: when active
how long does sarcoplasmic ATP last?: a few seconds
what are the 3 sources of ATP production within muscle?: creatine phosphate
anaerobic cellular respiration
aerobic cellular respiration (better for muscle)
how is creatine phosphate formed?: excess ATP within resting muscles is used to form it
which is more plentiful within muscle when resting? ATP or creatine phosphate? by how much?: creatine phosphate is 3-6 times more plentiful
how long is maximal contraction of muscles using creatine phosphate ?: 15 seconds - used for 100 meter dash
what happens to those athletes that tried creatine supplementation?: they gain muscle mass but they shut down the bodies own synthesis because the body says they already have high level of creatine from the supplement so there is no reason to produce more, so it shuts off.
anaerobic cellular respiration: ATP is produced from glucose breakdown into pyruvic acid during glycolysis
what happens if there is no O2 present in anaerobic cellular respiration?: pyruvic acid is converted to actic acid which diffuses into the blood
how long can glycolysis continue anaerobically to provide ATP?: 30-40 seconds of maximal activity - 200 meter race
what type of cellular respiration occurs for activity lasting over 30 seconds? how?: aerobic cellular respiration

if sufficient oxygen is available, pyruvic acid enters the mitochondria to generate ATP, water and heat

fatty acids and amino acids can also be used by the mitochondria
how much of the ATP energy is provided by aerobic cellular respiration if activity lasts more than 10 minutes?: 90% of ATP energy
what is muscle fatigue?: the inability to contract after prolonged activity
what are the factors that contribute to fatigue?: -central fatigue - feeling of tiredness and a desire to stop
-insufficient release of ach from motor neurons
-depletion of creatine phosphate
-decline of Ca+2 within the sarcoplasm
-insufficient oxygen or glycogen
-buildup of lactic acid and ADP
what happens as a muscle is stretched past optimal length?: fewer cross bridges exist and less force is produced
what does the optimal overlap of thick and thin filaments produce?: the greatest number of cross bridges and the greatest amount of tension
what happens if muscle is overly shortened- less than optimal?: fewer cross bridges exist and less force is produced

thick filaments are crumpled by Z discs
what are the red muscle fibers?: myoglobin, mitochondria and capillaries
what makes white muscle fibers: less myoglobin and less capillaries giving fibers their pale color
what causes the variation in contraction and relaxation speeds?: how fast myosin ATPase hydrolyzes ATP
what do slow oxidative or slow twitch muscle fibers look like? what is their function and where are they found?: -red in color
-prolonged, sustained contraction for maintaining posture
-found in neck, back and leg muscles
what do oxidative- glycolytic or fast -twitch A muscle fibers look like? and what is their function? what are they used for?: -red in color
-they split ATP at very fat rate
-used for walking and sprinting
what do fast glycolytic or fast-twitch B muscle fibers look like? what is their function? where are they found?: -white in color
-anaerobic movements for short duration - used in weight lifting
-found in shoulder and arm muscles
why are fast twitch muscle fibers longer?: they need more myoglobin
what do anabolic steroids do?: increases muscle size, strength and endurance
what are the side effects of anabolic steroids?: liver cancer
kidney damage
heart disease
mood swings
facial hair and voice deepening in females
atrophy of testicles and baldness in males
what are anabolic steroids most similar to?: testosterone
what are the two types of smooth muscle?: visceral - single unit and multiunit
where is visceral smooth muscle found?: int he walls of hollow viscera and small BV
what do the gap junctions of visceral muscle serve to do?: cause fibers to contract in unison
multiunit smooth muscle: individual fibers with their own motor neuron ending
where is multiunit smooth muscle found?: large arteries, large airways, arrector pili muscles, iris, ciliary body
what does smooth muscle look like?: small involuntary muscle cells tapering at the ends, single oval, centrally located nucleus, and lack T tubules and have little SR for Ca+2 storage
how do smooth muscle fibers contract? relax?: by twisting motion into a helix as it shortens and relaxes by untwisting
what is the regulator protein that binds calcium ions in the cytosol of smooth muscle?: calmodulin - it takes the place of troponin in striated muscle
what is calmodulins role in smooth muscle?: it activates the enzyme myosin light chain kinase, which facilitates myosin-actin binding and allows contraction to occur in a relatively slow rate
describe the regeneration of skeletal muscle fibers?: they cannot divide after 1 year
their growth is from enlargement of existing cells and through repair satellite cells and bone marrow produce some new cells. if there is not enough numbers - fibrosis occurs most often
describe the regeneration of muscle fibers: they cannot regenerate or divide. all healing is done by fibrosis - scar formation
describe smooth muscle regeneration: regeneration is possible
the cells can grow in size -hypertrophy. some cells like the uterus can divide - hyperplasia. new fibers can form from stem cells in BV walls
spasm: involuntary contraction of single muscle
cramp: a painful spasm
Tic: involuntary twitching of muscles normally under voluntary control - eyelide or facial muscles
tremor: rhythmic, involuntary contraction of opposing muscle groups
fasciculation: involuntary, brief twitch of a motor unit visible under the skin
muscle atrophy: wasting away of muscles
what causes muscle atrophy?: disuse (disuse atrophy) or severing of the nerve supply (denervation atrophy)
what happens in muscle atrophy?: the transition to connective tissue can not be reversed
hypertrophy: increase in the diameter of muscle fibers
what causes muscle hypertrophy?: very forceful, repetitive muscular activity and an increase in myofibrils, SR and mitochondria
rigor mortis: state of muscular rigity that begins 3-4 hrs after death and lasts about 24 hrs
what causes rigor mortis?: after death, Ca+2 ions leak out of the SR and allow myosin heads to bind to actin. since ATP synthesis has ceased, crossbridges cannot detach from actin until proteolytic enzymes begin to digest the decomposing cells

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