Types and Structures
Of smooth, cardiac and skeletal muscle, this is the only type under voluntary control
What is skeletal muscle?
These cylindrical contractile elements run lengthwise inside a muscle fiber
What are myofibrils?
The region between two adjacent Z lines is this basic unit of contraction
What is a sarcomere?
Thick filaments are bundles of this motor protein
What is myosin?
Huxley and Niedergerke's experiments on contracting muscle led to this model, in which filaments slide past each other
What is the sliding filament model?
These cords of connective tissue attach vertebrate skeletal muscles to bones
What are tendons?
Alternating dark and light bands give skeletal muscle this microscopic appearance
What is striated?
The thin filaments are anchored to this disc in the center of each I band
What is the Z line?
The myosin head bends toward the thin filament to form this structure
What is a crossbridge?
This system of vesicles, modified from smooth ER, encircles the sarcomeres and stores calcium
What is the sarcoplasmic reticulum?
This part of the nervous system controls skeletal muscle voluntarily
What is the somatic nervous system?
Thick filaments measure 13-18 nm across; thin filaments measure this range
What is 5-8 nm?
This lighter middle region of the A band contains only thick filaments
What is the H zone?
Thin filaments contain two chains of this protein twisted into a double helix
What is actin?
Folds of the plasma membrane at the A band-I band junction form these structures, which carry the depolarization inward
What are T (transverse) tubules?
Skeletal muscle fibers are elongated cells with this feature, since each has many nuclei
What is multinucleate?
A network of blood vessels penetrates the muscle to deliver these two things to the fibers
What are nutrients and oxygen?
This disc of proteins at the center of the H zone holds the stack of thick filaments together
What is the M line?
This elongated, fibrous protein is bound to actin and blocks crossbridge formation at low Ca²⁺
What is tropomyosin?
Released at the neuromuscular junction, this neurotransmitter depolarizes the muscle cell
What is acetylcholine?
Depending on where a skeletal muscle attaches, its contraction may extend or bend body parts, or do this to one part relative to another
What is rotate it?
Sheaths of this tissue hold muscle fibers in parallel bundles and merge with the tendons
What is connective tissue?
These light bands contain only the parts of thin filaments that are not in the A band
What are I bands?
This three-subunit globular protein binds tropomyosin at intervals along the thin filament and also binds Ca²⁺
What is troponin?
In high Ca²⁺ levels, Ca²⁺ binds this protein, which displaces tropomyosin and exposes the myosin-binding sites on actin
What is troponin?