Skeletal Muscle

Created by jdavis136 

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what are the characteristics of skeletal muscle tissue?

attaches to bone via tendons, striated, contracts, voluntarily controlled

what are the 3 structures of connective tissue associated w/ skeletal muscle?

epimysium, perimysium, endomysium

describe the epimysium

connective tissue layer which surrounds the entire skeletal muscle system; outter

describe the perimysium

connective tissue that surrounds the fascicle; around

what is a fascicle?

bundles of skeletal muscle fibers

describe the endomysium

connective tissue that surrounds each skeletal muscle fiber (cell) w/in a fascicle

describe skeletal muscle fiber

cellular unit of skeletal muscle

what are the 3 components of skeletal muscle fiber?

sarcolemma, transverse (T) tubules, sarcoplasm

describe sarcolemma

plasma membrane of a skeletal muscle fiber

describe transverse (T) tubules

folds of sarcolemma that extend into the interior of a skeletal muscle fiber

describe sarcoplasm

cytoplasm of a skeletal muscle fiber

what are 3 organelles found in the sarcoplasm?

nuclei, mitochondria, sarcoplasmic reticulum (SR)

describe nuclei

multinucleate- many nuclei in skeletal muscle fiber

what are myoblasts?

several fused precursor cells

describe mitochondria

produce ATP(energy); required for muscle contraction

describe sarcoplasmic reticulum (SR)

ER of skeletal muscle fiber; membraneous sac stores (Ca+2) ions- muscle relaxation & releases (Ca+2) ions into sarcoplasm to initiate muscle contraction

what are 2 molecules found in the sarcoplasm?

glycogen & myoglobin

describe glycogen

storage form of glucose; break dwn into glucose to make ATP; found in liver

describe myoglobin

reddish protein that stores O2 & releases it when needed by mitochondria to generate ATP

describe myofibrils

rodlike structures; cause skeletal muscle fiber to shorten (contraction); 2 types thick filament, thin filament

what are the 2 types of contractile filaments?

thick filament, thin filament

describe thick filaments

contain the protein myosin

describe thin filaments

contain 3 types of proteins; actin, troponin, tropomyosin

describe sarcomeres

repeating unit of myofibrils; consist of 5 regions- Z disc, A band, I band, H zone, M line

what is a Z disc?

composed of a-actin proteins; distance between 2 successive Z discs defines sarcomere

what is an A band?

dark area, extends length of thick filament; includes parts of thin filament that overlap thick filament

what is an I band?

light area, extends from Z discs on either side; includes part of thin filament that do not overlap thick filament

what is an H zone?

central part of A band; contains only thick filament, dark

what is the M line?

central part of H zone; consist of myomesin, interconnect neighboring thick filaments

what is titin?

long protein, extends from each half of sarcomere; connect Z disc to M line; flexible, stretch & snap back; structural support

what is dystrophin?

protein that links thin filaments to proteins in sarcolemma; pull sarcolemma causes skeletal muscle fiber to shorten; structural support

what is the main function of skeletal muscle?

cause movement of various parts of the body; pull on tendons, in turn pulls on the bone, causes movement

describe the structure of a thick filament

myosin molecules; 2 polypeptide chains that form a rodlike tail & double head; 2 binding site- actin-binding site & ATP-binding site

describe the structure of a thin filament

3 proteins- actin, tropomyosin, troponin

what is actin?

thin filament, form double stranded actin helix; myosin-binding site-myosin head can attach to cause contraction

what is tropomyosin?

rod-shaped protein, promotes skeletal muscle relaxation; covers myosin-binding sites on actin- prevents myosin from interacting with actin

what is troponin?

globular protein, promotes skeletal contraction; Ca+2 ions released into sarcoplasm, binds to troponin, pushes tropomyosin off myosin-binding sites on actin, interact(contraction)

describe sliding filament mechanism

myosin heads attach to & "walk" along the thin filaments at both ends of sarcomere, pulling the thin filament towards the M line; thin filament slides inwards & meet at center of sarcomere

what are the 4 steps of the contraction cycle?

ATP hydrolysis, attachment of myosin to actin, power stroke, detachment of myosin from actin

describe ATP hydrolysis

hydrolyzes ATP into ADP & phosphate group; energy generated stored in myosin head-energized

describe attachment of myosin to actin

energized myosin heads attach to myosin-binding site on actin; only 1 head binds at a time

what is a crossbridge?

myosin head attaches to actin during contraction cycle

describe the power stroke

after crossbridge is formed, myosin head pulls thin filament past thick filament towards center of sarcomere, generating tension(force); uses energy stored in myosin head

describe the detachment of myosin from actin

as ATP binds to the ATP-binding site on myosin head, it detaches from actin; myosin hydrolyzes newly bound ATP; (continues as long as ATP avaliable & Ca+2 level is high)

describe a motor unit

consist of a motor neuron & skeletal muscle fibers it innervates; motor neuron elicts A.P. all fibers contract together

what is a neuromuscular junction (NMJ)

site of communication between a motor neuron & skeletal muscle fiber (presynaptic cell & postsynaptic cell)

what are the 3 components of NMJ?

synaptic end bulbs of the motor neuron, motor end plate, synaptic cleft

describe synaptic end bulb of the motor neuron

contain synaptic vesicles filled w/ neurotransmitters (acetylcholine, ACh)

describe the motor end plate

sarcolemma of the skeletal muscle fiber; contains ACh-receptors that bind to ACh

describe the synaptic cleft

space between synaptic end bulb of motor neuron & motor end plate of the skeletal muscle fiber

what are the 4 ways synaptic transmission occurs at the NMJ?

release of acetylcholine, activation of ACh receptors, production of muscle action potentials, termination of ACh activity

describe release of acetylcholine

nerve a.p. at endbulb of motor neuron causes synaptic vesicles to undergo exocytosis, synaptic vesicles fuse w/ motor neuron's plasma mem., releasing ACh into synaptic cleft, diffuses across synaptic cleft

describe activation of ACh receptors

binding of ACh to receptor on motor end plate opens an ion channel in ACh receptor, small cations (Na+) flow across mem.

describe production of muscle A.P.

inflow of Na+, makes inside of muscle fiber more (+), change triggers muscle A.P., then propagates along sarcolemma into T tubule system, causing muscle fiber to contract

describe termination of ACh activity

ACh no longer released when A.P. in motor neuron ceases, ACh is broken down by enzyme acetylcholinesterase(AChE), prevents formation of another A.P.

what is acetylcholinesterase (AChE)?

enzyme which breaks down the molecules of ACh into acetyl & choline

what is excitation-contraction coupling?

sequence of events connecting muscle A.P. to muscle contractions

what are the 3 ways muscle fibers obtain ATP?

transfer of phosphate from creatine phosphate to ADP to form ATP, anaerobic glycolysis, aerobic (cellular) respiration

describe transfer of phosphate from creatine phosphate to ADP to form ATP

immediate source of ATP, 15 seconds;

what is creatine?

small molecule similar to an amino acid in structure; found in skeletal muscle fibers & cardiac muscle fibers

what is creatine kinase (CK)?

transfers 1 of the phosphate groups of ATO to creatine to form creatine phosphate when ATP is in excess

what is creatinine?

break down of creatine, forming a nitrogenous waste product

describe anaerobic glycolysis

source of ATP when a skeletal muscle fiber lacks O2 or doesnt have enough O2 to meet metabolic needs (weight-lifting)- 2 min

describe aerobic (cellular) respiration

source of ATP when skeletal muscle fiber has plenty of O2 (resting, walking, moderately running on treadmill)- several min to hr or more

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