lec 13 gg way

A biopsy shows long, striated muscle fibers with multiple nuclei at the cell periphery. Which muscle tissue is present?

Skeletal muscle.

What developmental process explains why one skeletal muscle fiber contains many nuclei?

Fusion of embryonic myoblasts.

A broad, flat connective tissue attachment replaces a cordlike tendon. What is this structure?

An aponeurosis.

Which bone covering receives the attachment of skeletal muscle tendons and aponeuroses?

Periosteum.

Why can a tendon enclosed in a synovial sheath slide back and forth easily?

A film of synovial fluid reduces friction.

Inflammation of a tendon sheath and its associated synovial membrane is called what?

Tenosynovitis.

Which two connective tissue types make up superficial fascia beneath the skin?

Areolar connective tissue and adipose tissue.

Which fascia reduces the rate of heat loss by storing fat under the skin?

Superficial fascia.

What type of connective tissue forms deep fascia around muscles and organs?

Dense irregular connective tissue.

Which fascia holds muscles together while allowing them to move freely?

Deep fascia.

Which connective tissue layer directly surrounds an entire skeletal muscle rather than a fascicle?

Epimysium.

A surgeon separates a bundle of muscle fibers from adjacent bundles. Which connective tissue layer surrounds that bundle?

Perimysium.

According to the notes, how many individual muscle fibers form one fascicle?

10-100 fibers.

Which covering carries the larger nerves, blood vessels, and stretch receptors within a muscle?

Perimysium.

A histology slide shows connective tissue around one muscle fiber rather than a fascicle. Which layer is it?

Endomysium.

Which connective tissue covering contains capillaries and nerve endings reaching each individual muscle fiber?

Endomysium.

A question confuses the muscle cell membrane with its connective tissue wrapping. What is the membrane called?

Sarcolemma.

If the muscle fiber cannot store Ca2+ in its specialized endoplasmic reticulum, which organelle is defective?

Sarcoplasmic reticulum.

What happens to contraction if Ca2+ is not released from the sarcoplasmic reticulum?

The Ca2+-dependent trigger for contraction is lost.

Through what membrane structure does a contraction signal quickly reach the interior of a large muscle fiber?

Transverse tubules or T-tubules.

What fluid fills T-tubules despite their location deep inside a muscle fiber?

Extracellular fluid.

What structural relationship exists between T-tubules and the sarcolemma?

T-tubules are inward folds continuous with the sarcolemma.

What specialized sarcoplasmic reticulum structures lie on either side of a T-tubule?

Terminal cisternae.

Exactly which structures combine to form one skeletal muscle triad?

One T-tubule and two terminal cisternae.

Which three proteins compose the thin filaments described in Lecture 13?

Actin, tropomyosin, and troponin.

Which protein is the primary component of thick myofilaments?

Myosin.

Approximately how many repeating sarcomeres form each myofibril, according to the slides?

Thousands.

What structures define the two ends of one sarcomere?

Z-discs or Z-lines.

A sarcomere region contains thin filaments but no thick filaments. Which band is it?

I band.

Which line passes through the center of the I band?

Z-line.

A dark sarcomere region includes the full length of the thick filaments and their overlap with thin filaments. Which band is it?

A band.

Which sarcomere region contains thick filaments without thin filaments?

H zone.

Where is the H zone located within a sarcomere?

In the center of the A band.

Which sarcomere line consists of proteins connecting adjacent thick filaments?

M-line.

During filament sliding, what changes even though thick and thin filament lengths stay constant?

The amount of overlap between thick and thin filaments.

What happens to the H zone as actin-myosin filament overlap increases during contraction?

It narrows.

What happens to the distance between adjacent Z-discs during sarcomere contraction?

It decreases.

How many intertwined polypeptide chains form the myosin molecule described in the notes?

Two.

Toward which sarcomere landmark do myosin tails point?

M-line.

Which region of myosin forms cross-bridges capable of binding actin?

Myosin heads.

Where on myosin does ATP bind to support contraction?

Myosin heads.

Which enzyme activity on a myosin head hydrolyzes ATP?

ATPase activity.

What change converts individual G-actin molecules into an actin filament?

They polymerize into F-actin.

Where on the thin filament are the myosin cross-bridge binding sites located?

On individual actin molecules.

Why do myosin heads not bind exposed actin sites in a relaxed muscle?

Tropomyosin covers the myosin-binding sites.

Which regulatory protein directly binds Ca2+ to initiate exposure of actin binding sites?

Troponin.

Exactly how many polypeptides compose troponin, according to the notes?

Three.

What happens to tropomyosin when Ca2+ binds troponin?

Troponin shifts tropomyosin away from actin's myosin-binding sites.

Which elastic structural protein connects the M-line region with the Z-disc and stabilizes thick filaments?

Titin or connectin.

What abundance rank does titin have among muscle proteins in the notes?

Third most abundant.

Which protein provides the major component of skeletal muscle elastic filaments?

Titin.

Which structural protein wraps around a thin filament and helps anchor it to the Z-disc?

Nebulin.

Which protein links actin filaments to the sarcolemma through associated proteins?

Dystrophin.

Mutations in which structural muscle protein are linked to muscular dystrophy?

Dystrophin.

Delayed-onset soreness after strenuous exercise is associated with damage to which muscle cell membrane?

Sarcolemma.

Which sarcomere boundary structures may become disrupted after strenuous exercise?

Z-discs.

In a motor unit, which muscle fibers are controlled by a single motor neuron?

All fibers innervated by that motor neuron.

How do the muscle fibers within the same motor unit respond when their motor neuron activates?

They contract at the same time.

What is the stated range of muscle fibers innervated by one motor neuron?

10-2,000 fibers.

What is the average number of fibers per motor neuron reported in the notes?

About 150 fibers.

How many fibers per motor unit are reported for laryngeal muscles controlling vocal cords?

2-3 fibers.

How many fibers per motor unit may occur in hard-working muscles such as the biceps?

Up to 2,000 fibers.

Which specialized area of the muscle sarcolemma faces a motor neuron's axon terminal at the neuromuscular junction?

Motor end plate.

What do synaptic vesicles in a motor neuron's synaptic end bulbs contain?

Acetylcholine or ACh.

Arrival of a motor neuron action potential opens channels for which ion in the axon terminal?

Ca2+.

What does Ca2+ entry into a motor axon terminal trigger?

Fusion of synaptic vesicles and ACh exocytosis.

Which receptor type binds ACh on the skeletal muscle motor end plate?

Nicotinic acetylcholine receptor.

How many polypeptide subunits make up the nicotinic ACh receptor described in the notes?

Five.

How many ACh-binding sites must be occupied for the nicotinic receptor channel to open?

Two.

What type of gating controls the nicotinic ACh receptor at the motor end plate?

Ligand-gated.

Which two ion movements occur simultaneously through an open nicotinic ACh receptor?

Na+ enters and K+ exits.

Why does Na+ entry dominate K+ exit at an open motor end plate ACh receptor?

Na+ has a steeper electrochemical gradient.

What is the resting membrane potential at the motor end plate in the professor's example?

-90 mV.

What membrane potential marks the local end-plate potential after ACh receptor activation?

-60 mV.

A voltage change stays localized at the motor end plate instead of propagating across the sarcolemma. What is it?

End-plate potential or EPP.

What threshold voltage is shown for opening voltage-gated Na+ channels in the slides?

About -55 mV.

What peak voltage is reached during the propagated skeletal muscle action potential in the slides?

About +30 mV.

Which channel type in sarcolemma adjacent to the motor end plate initiates the propagated action potential?

Voltage-gated Na+ channels.

Which ion's outward movement through voltage-gated channels drives repolarization after the action potential peak?

K+.