Structure and Composition of Muscle

What are the three types of muscle tissue

cardiac, smooth, and skeletal

where is cardiac muscle found

in the heart

is cardiac muscle voluntary or involuntary?

involuntary

key features of cardiac muscle?

striations, muscle fibers, intercalated disks, nucleus

where is smooth muscle found?

In walls of hollow organs

how is smooth muscle structured?

non-striated and involuntary

key features of smooth muscle?

muscle fibers, nucleus

what characterizes skeletal muscle?

striated, voluntary, long cylindrical cells, multiple nuclei

key structural connectors in muscle?

tendon and ligament

what is a tendon?

muscle to bone

what is a ligament?

bone to bone

List the muscle structure hiearchy (largest to smallest)

Muscle → Fascicle → Muscle fiber → Myofibril → Myofilaments

what are the two types of myofilaments?

thick (myosin) and thin (actin)

how many myofibrils are in one muscle fiber approximately?

about 2,000

what are the three connective tissue layers in muscle?

epimysium, perimysium, endomysium

what is the basic unit of muscle contraction?

sarcomere

what structures define a sarcomere?

2 Z-line, 1 A-band, 2 half I-bands

What are the two main contractile proteins in muscle?

myosin and actin

what subunits make up troponin?

TnI (inhibits actin-myosin), TnC (binds Ca2+), TnT (binds tropomyosin)

what does tropomyosin do in relaxed muscle?

covers actins active sites

what are two major structural proteins?

Titin and Nebulin

What is the function of Titin?

elasticity and thick filament anchoring

What is the function of Nebulin?

anchors thin filaments

Function of the sarcoplasmic reticulum (SR)

releases and reabsorbs Ca2+ to regulate contraction

What forms a muscle fiber “triad”?

1 T-tubule + 2 terminal cisternae

What is the signal pathway from outside muscle contraction

Endomysium → Sarcolemma → T-Tubule → SR → Myofibril

What is the function of T-tubules?

conduct electrical signals into the muscle fiber

What is the myofibrillar protein percentage of myosin?

43%

What is the myofibrillar protein percentage of Actin?

22%

what experimental method analyzes myofibril structure?

Helium-neon laser diffraction