K103 Chapter 40: Protection, Support, and Movement (Muscle)

what are the three distinct muscle types?

skeletal, cardiac, smooth

what types of control does skeletal muscle have?

voluntary and conscious control

what types of control does cardiac muscle have?

involuntary and autoregulatory control

what types of control does smooth muscle have?

involuntary and ANS control

what is the microscopic structure of skeletal muscle?

striated, long multinucleated, fibers, bound together by connective tissue (fascia)

what is the microscopic structure of cardiac muscle?

striated, branched, uni- or binucleated, cells smaller than skeletal, specialized skeletal muscle

what is the microscopic structure of smooth muscle?

nonstriated, spindle shaped cells, sheets of cells

what animals have muscle tissues?

all metazoans except for cnidarians

what is actin?

thin filaments

what are the muscle functions?

convert chemical energy, ATP, into mechanical energy and movement (body and internally) and manipulation

what is A band?

runs length of myosin fiber (will contain actin and overlapping myosin)

what is actin?

thin myofilaments

what is an agonist?

a muscle that works with another in a particular movement

what is an antagonist?

a muscle that opposes the movement of another muscle

what is a dense body?

found in smooth muscle and is the point where actin is anchored

what is the H zone?

a region of the sarcomere that is myosin only, within A band, between actin filaments within a single sarcomere

what is the I band?

z line and attached actin only, part of 2 sarcomeres

what is the M line?

a region in the center of the H zone and it is the proteins that hold the neighboring myosin filaments together

what is a motor unit?

a nerve axon and all of the muscle fibers it innervates

what is a myofiber?

a muscle cell

what is a myofibril?

a cytoplasmic grouping of myofilaments, threadlike, runs lengthwise through sarcoplasm

what is a myofilament?

made up myofibrils and are either actin or myosin filaments

what is myosin?

thick myofilaments

what is a sarcolemma?

plasma membrane of a muscle cell

what is a sarcomere?

an individual contractile unit in skeletal muscle

what is the sarcoplasmic reticulum?

the endoplasmic reticulum in a muscle cell

what is a triad?

located in skeletal muscle cells and is the region where the T tubule runs between parts of the sarcoplasmic reticulum creating a region of SR-T tubule-SR

what is troponin?

a protein complex located on tropomyosin, it contains a calcium binding site that regulates the interaction of actin and myosin by causing tropomyosin to role away from the myosin binding site on actin

what is tropomyosin?

a protein chain that regulates the interaction of actin and myosin by covering the actin binding sites on myosin when calcium is absent and a muscle is not contracting

what is a T tubule?

transverse tubule, inward extension of the sarcolemma membrane, it runs through the cell and is in contact with the sarcoplasmic reticulum

what is the Z line?

at beginning and end of a sarcomere and the point where actin is anchored, sarcomeres connected here

what is contraction?

shortens when stimulated (electrical impulse, hormones)

what is relaxation?

elongates when stimulation occurs, actin and myosin fibers return to resting position

muscles work in ___

pairs

what are skeletal muscles composed of?

fibers (long multinucleated cells)

what does connective tissue do?

surrounds and hold groups of muscle fibers together

what connective tissues are associated with skeletal muscle?

endomysium, perimysium, epimysium

what is the endomysium around?

individual muscle fibers

what is the perimysium around?

bundles of fibers

what is the epimysium around?

an entire muscle

what do contractile proteins do?

produce tension

what do regulatory proteins do?

control when contraction occurs

what do structural proteins do?

provide myofilament structural stability

skeletal and heart muscles are ___

striated

what does it mean when something is striated?

there are repeating sarcomeres

what are myosin filaments?

two interwoven protein chains

what can each head of myosin do?

hydrolyze ATP and bind an actin monomer

label the photo

1- M line

2- Z-disc

3- H zone

4- A band

5- I band

label the photo

1- actin

2- tropomyosin

3- troponin

4- actin subunit

5- actin active site

what is shown in the photo?

a myosin filament

what are the steps of muscle contraction?

myosin is pre-energized, crossbridge formation, power stroke (contraction begins), crossbridge detachment, continues (as long as stimulation continues)

what is an activated myosin head able to do?

form a crossbridge with exposed binding site

what happens when power stroke is initiated?

contraction begins

where does a nerve impulse travel?

along sarcolemma and down T-tubule

what does a nerve impulse do?

stimulates release of Ca2+ from SR, Ca2+ then enters cytoplasm

what does released Ca2+ do?

binds site on troponin

what happens when Ca2+ binds to troponin?

troponin changes shape, causes tropomyosin to roll, exposes myosin-binding sites on actin filaments

what happens at the end of a contraction cycle?

ATP binds to myosin site and crossbridge is broken, myosin head is energized for next cycle

what must happen for the contraction cycle to continue?

stimulus continues and Ca2+ remains available

what is muscle contraction?

muscles are in a state of partial contraction

what does a sarcomere do during a contraction cycle?

shorten

what do actin and myosin filaments do during a contraction cycle?

move past one another (sliding filament model), overlap increases

what do the I band and H zone do during a contraction cycle?

decrease in length (filaments do not)

is atp on demand or stored for muscle contraction?

on demand

how is atp availability maintained?

creatine phosphate (phosphate transferred to ADP making ATP (rapidly depleted) and glycogen (stored in muscle and liver)

what happens during muscle contraction without sufficient O2?

pyruvate and lactic acid form

do muscles run out of ATP?

no, not even with exercise to the point of fatigue, most studies show only 30% of possible ATP is used

what influences development of fatigue?

levels of ATP available, intensity and duration of exercise, aerobic vs anaerobic metabolism, composition of the muscle, fitness level of the individual

what is oxygen debt?

metabolism of built-up lactic acid

what factors influence the strength of muscle contraction?

type of muscle fibers, aerobic training, strength training, number of muscle fibers contracting, frequency of fiber stimulation, amount of calcium, number of motor units recruited

what does aerobic training result in?

increased capillary density, number of mitochondria, and myoglobin content of muscle fibers

what does strength training result in?

increased number of filaments in fibers, increased muscle size (diameter)

the more muscle fibers that contract...

the greater the tension in the muscle

the longer the sarcomere...

the stronger the contraction

a ___ amount of actin and myosin overlap is ideal

moderate

what kind of control are small motor units used for?

fine control (like movement in face)

what kind of control are large motor units used for?

heavy activities (like running)

what is a single stimulus and what does it result in?

brief electrical stimulus produces a twitch, muscle contraction followed by relaxation (single, quick, simple twitch)

what is the summation of multiple stimuli?

separate stimuli arrive very close together (twitches can fuse together), stimuli happen before full relaxation

what is fused tetanus?

contraction, no opportunity for partial relaxation, no relaxation period

how long is an action potential?

1-2 msec, finished before contraction begins

what is a latent period?

time for action potential to stimulate calcium release

what is contraction time?

Ca2+ release followed by generation of tension through actin and myosin interaction (contraction)

where is smooth muscle located?

surrounds tubular (hollow) organs

where is skeletal muscle located?

attached to bones

what are some functions of smooth muscle?

air flow (diameter of bronchioles), blood pressure (diameter of arterioles), movement along digestive tract

what is the function of skeletal muscle?

whole body movement

how is smooth muscle contraction regulated?

myosin-linked, contraction initiated by change in myosin

how is skeletal and cardiac muscle contraction regulated?

actin-linked, contraction initiated by change in actin

describe initiation of contraction in smooth muscle

autonomic nerve impulse (neurogenic), self-generated action potential (myogenic), hormones

describe initiation of contraction in skeletal muscle

motor nerve impulse

does smooth or skeletal muscle have stronger contraction?

smooth

does smooth or striated muscle shorten more?

smooth

does smooth muscle have gap junctions?

yes

does skeletal muscle have gap junctions?

no

what is the calcium source in skeletal muscle?

sarcoplasmic reticulum

what is the calcium source in smooth muscle?

extracellular and sarcoplasmic reticulum

what does calcium result in in smooth muscle?

Initiates cascade leading to activation of myosin ATPase (no troponin)

what does calcium result in in skeletal muscle?

binds troponin

are sarcomeres present in smooth muscle?

no