anatomy muscular test

indirect attachment

the epimysium of the skeletal muscle extends as a TENDON which then anchors the skeletal muscle to the periosteum surrounding the bone

direct attachment

skeletal muscles attach directly to the bone when the epimysium fuses directly with periosteum surrounding the bone

which way of attachment is more common in the human body and why?

indirect attachment - tendon occupies a smaller bone surface

A band

contains thin and thick filaments

Z line

anchor thin filaments in myofibril

H zone

middle region of the A band

M line

bisects the H zone

I band

regions of thin filaments

according to the sliding filament mechanism, which structures shorten?

the H zone and I band

according to the sliding filament mechanism, which structures remain the same?

the A band and length of thin filaments

what is the function of triads in skeletal muscle contraction?

primary site for excitation-contraction coupling, cause rapid calcium release from sarcoplasmic reticulum to trigger muscle contraction

what is a motor unit?

a motor neuron and all the skeletal muscle fibers it innervates in a skeletal muscle via its axon terminals.

how does the size of a motor neuron affect skeletal muscle contraction?

larger motor units generate more force in a skeletal muscle than smaller motor units

neuromuscular junction

where a motor neuron terminal communicates with a skeletal muscle fiber

what is a motor end plate?

the highly folded region of the sarcolemma of the muscle fiber at the neuromuscular junction that expresses acetylcholine receptors

what is the function of acetylcholinesterase?

terminates nerve impulses by hydrolyzing acetylcholine

how does an acetylcholinesterase inhibitor affect the strength of skeletal muscle contraction?

an acetylcholinesterase inhibitor would increase the strength of skeletal muscle contraction.

discuss how Botox affects skeletal muscle contraction

the muscle no longer contracts blocks the release of acetylcholine

name the 3 proteins in a thin filament in a skeletal muscle fiber

actin

tropomyosin

troponin

actin

contain the binding sites for the myosin globular heads

troponin

a three-polypeptide complex

tropomyosin

spirals around the actin and blocks myosin binding sites on actin in a relaxed skeletal muscle

what are the 3 subunits of troponin

TnC, TnT, TnI

what does TnC bind to?

calcium ions (Ca2+)

what does TnT bind to?

binds to tropomyosin

what does TnI bind to?

actin

what are activated globular heads?

myosin heads are in a high-energy, ready-to-bind state during muscle contraction when myosin heads are attached ADP + Pi

what are cross bridges?

the physical linkages formed when activated myosin globular heads bind to actin filament

sliding filament theory

myosin filaments pull actin filaments inward to shorten the sarcomere

what is the powerstroke?

when attached myosin globular heads undergo a change of orientation, changing from a right angle to a bent, smaller angle. Pulling thin filaments inward into the H zone, toward M line

what is the consequence of the power stroke?

the sarcomere shortens and the muscle contractions

how does cross bridge detachment occur in skeletal muscle fibers?

new ATP molecules bind to the attached myosin heads, causing them to break the link with actin.

discuss the role of ATP in muscle contraction

it binds to myosin heads to allow for detachment from actin. Provides energy for pumping calcium back into the sarcoplasmic reticulum for relaxation.

what are the 4 sources of ATP in skeletal muscle fibers

stored ATP

creatine phosphate

anaerobic catabolism of glucose

aerobic catabolism of glucose

stored ATP

used first - supports 5 seconds of skeletal muscle activities

creatine phosphate

ATP from the phosphorylation of ADP using enzyme creatine kinase - supports 10 seconds of skeletal muscle activities

anaerobic catabolism of glucose

produces 30 seconds to 60 seconds of skeletal muscle activities

aerobic catabolism of glucose

produces more ATP to support skeletal muscle activities for hours

what is the function of creatine kinase?

catalyzes the phosphorylation of ADP by creatine phosphate to create ATP and creatine

what is muscle fatigue?

physiological inability of a stimulated skeletal muscle to contract due to ATP deficit - skeletal muscle demand for ATP is greater than ATP produced by the body

what is rigor mortis?

ATP synthesis ceases, and myosin and actin are irreversibly cross-linked - permanent depletion of ATP

what are the 4 factors that affect the strength of skeletal contraction?

size of motor units activated

number of motor units activated

frequency of skeletal muscle activation

length of sarcomeres prior to contraction

how does a stretched sarcomere prior to contraction affect the strength of skeletal muscle contraction?

results in decreased force. reduced overlap between actin and myosin limits cross-bridge formation

how does a shortened sarcomere prior to contraction affect the strength of skeletal muscle contraction?

results in decreased force. the sarcomere is too compact, reducing further cross-bridge formation

how does a contracted skeletal muscle relax?

cross-bridge detachment

Do fast oxidative skeletal muscle fibers have more mitochondria than slow oxidative skeletal muscle fibers? Explain why.

No, fast oxidative skeletal fibers do not have more mitochondria than slow oxidative skeletal muscle fibers. It is the opposite. The reason for this is because slow oxidative fibers are designed for endurance and sustained contractions, which require more energy.

do fast glycolytic skeletal muscle fibers have larger diameter than slow oxidative skeletal muscle fibers? Explain why.

Yes, a larger size allows for more storage of glycogen and anaerobic contraction.

are slow oxidative skeletal muscle fibers recruited before fast oxidative skeletal muscle fibers?

yes, they’re recruited first because their motor neurons are smaller and easier to activate.

are the slow oxidative skeletal muscle fibers surrounded by more capillaries than fast glycolytic skeletal muscle fibers? Explain why

yes. because they depend on oxygen for sustained ATP production

which type of skeletal muscle is fatigable and why?

fast glycolytic fibers are fatigable because they produce ATP very rapidly and don’t have that many mitochondria

which type of skeletal muscle fiber is fatigue-resistant?

slow oxidative fibers are fatigue-resistant because they contain high levels of mitochondria

Which type is also known as red fibers and why?

slow oxidative muscle fibers because they contain high concentrations of myoglobin

Which type is also known as white fibers and why?

fast glycolytic fibers because they contain low concentrations of myoglobin

discuss how aerobic exercises increase stamina

aerobic exercises increase stamina by increasing the amount of capillaries, mitochondria, and myoglobin, which improve endurance. Improved endurance increases stamina

discuss how resistance-type exercises increase the strength of skeletal muscles

increase the size of skeletal muscle (hypertropy) and glycogen content. Bulky muscles generate more force which increase muscle strength.

name and define the two major phases (categories) of skeletal muscle contraction.

isometric contraction & isotonic contraction

isometric contraction

increasing at a constant muscle length (ex. plank)

isotonic contraction

muscle length changes

what are the two divisions of isotonic contraction?

concentric - skeletal muscle shortens

eccentric - skeletal muscle lengthens

name the subtype of contraction described by the Sliding Filament Mechanism

concentric contraction

skeletal muscle

striations, long cylindrical cells called muscle fibers, multinucleate cells

cardiac muscle

striations, branching cells with intercalated discs; uninucleate cells

smooth muscle

no striations, spindle-shaped cells; uninucleate cells

which type of muscle is considered a “blend” and why?

cardiac muscle because it contains elements of both skeletal and smooth muscle (ex. involuntary movement and striations)

What is the calcium-induced calcium release (CICR) mechanism?

calcium ions enter the smooth muscle cells from the extracellular fluid in the caveolae and to induce the release of more calcium from the poorly-developed sarcoplasmic reticulum

name the type of muscles that use the CICR mechanism and explain why they have to use this mechanism to increase intracellular calcium.

smooth and cardiac muscle use the CICR mechanism. they must use it because the sarcoplasmic reticulum (SR) in cardiac and smooth muscle does NOT store/release enough Ca²⁺ on its own

how does calcium channel blockers affect the contraction of muscles that use the CICR mechanism?

they reduce the effect of muscle contraction by preventing entry of extracellular calcium

discuss the role of increased intracellular Ca+ in skeletal muscle contraction

Initiates skeletal muscle contraction by exposing actin binding sites through binding troponin

discuss the role of increased intracellular Ca+ in smooth muscle contraction

initiates contraction by initiating the phosphorylation of myosin light chains, which initiates cross bridge formation

discuss the role of increased intracellular Ca+ in cardiac muscle contraction

initiates cardiac muscle contraction by exposing actin binding sites through binding troponin (NEEDS CICR)

how does excitation-contraction coupling in single-unit smooth muscle differ from skeletal muscle?

Skeletal muscle: Ca²⁺ comes only from the sarcoplasmic reticulum (SR)

Single-unit smooth muscle: Ca²⁺ comes from both extracellular fluid AND the SR

How is the excitation-contraction coupling in single-unit smooth muscle similar to cardiac muscle?

both single-unit smooth muscle and cardiac muscle rely on extracellular Ca²⁺ influx to trigger contraction

What is the function of pacemaker cells?

generate spontaneous electrical activity that initiates and regulates contraction without external input.

name structures present in skeletal muscle fibers that are absent from smooth muscle cells

sarcomeres, t-tubules, terminal cisternae, troponin

t-tubules

invaginations of the sarcolemma into the sarcoplasm that carry the electrical signal (action potential) from the surface of the muscle cell deep into the interior

terminal cisternae

enlarged sacs at the ends of the sarcoplasmic reticulum (SR) that sit right next to T-tubules. they store large amounts of calcium ions (Ca²⁺) and release them quickly when the muscle cell is stimulated

name structures present in smooth muscle cells that are absent from skeletal muscle fibers; discuss the functions of these structures in smooth muscle

calmodulin (instead of troponin), caveolae (instead of T-tubules), dense bodies (instead of z lines)

calmodulin

calcium-binding protein in smooth muscle

caveolae

small indentations in the cell membrane in smooth muscle that help spread electrical signals into the cell

dense bodies

anchor actin filaments in smooth muscle

what are intercalated discs?

cell junctions that connect cardiac muscle cells

what are electrically-coupled cells?

cells connected by gap junctions that allow for direct ion flow between cells

what is functional syncytium?

single-unit smooth muscle cells all contract at the same time

Name the types of muscles that exhibit functional syncytium and why.

single-unit smooth muscle and cardiac muscle because they have gap junctions

what division of the peripheral nervous system innervates skeletal muscles?

somatic nervous system

what division of the peripheral nervous system innervates smooth and cardiac muscles?

autonomic nervous system

how does activation of the parasympathetic nervous system affect smooth muscle in the walls of the bronchioles?

causes narrowing of the airways (bronchoconstriction)

how does activation of the sympathetic nervous system affect smooth muscle in the walls of the bronchioles?

causes widening of the airways (bronchodilation)

explain why sympathomimetic drugs are used in the management of asthma.

asthma causes airway inflammation. Sympathomimetic drugs open airways by relaxing bronchial smooth muscle.

how does activation of the sympathetic nervous system affect cardiac muscle contraction?

increases heart rate, increases force of contraction

how does activation of the parasympathetic nervous system affect the cardiac muscle?

decreases heart rate, decreases force of contraction

what are varicosities?

bulbous swellings of autonomic fibers that form junctions with smooth muscle called diffuse junctions

does activation of the autonomic system always lead to smooth muscle contraction? Explain your answer.

no it leads to contraction or relaxation. depends on alpha or beta receptors and the branch of ANS activated

does activation of the somatic nervous system always lead to skeletal muscle contraction?

yes

 How does cross bridge detachment occur in skeletal muscle fibers

ATP binding to myosin

how does cross bridge detachment occur in smooth muscle fibers

requires ATP binding to myosin, but myosin must be phosphorylated

how does cross bridge detachment occur in cardiac muscle fibers

ATP binding to myosin, depends on CICR for extracellular Ca2+

discuss how calcium channel blockers directly affect the strength of skeletal muscle

no direct effect

discuss how calcium channel blockers directly affect the strength of smooth and cardiac muscle

decreased force of contraction (inhibits cardiac muscle contraction)