[Ch.10] Anatomy of a Skeletal Muscle Fiber/Cell

During a contracted state: thin myofilamets are drawn very close together and overlap; thick myofilaments are drawn closer to the Z discs

In a relaxed state: thin myofilaments are anchored to the Z lines on each side and extend towards the center of the sacromere but do not meet; thick myofilaments are in the center portion of the sacromere but do not extend anywhere near either Z disc. What happens to the myofilaments during a contracted state?

sarcoplasmic reticulum (SR)

a specialized endoplasmic reticulum (ER) that functions in the storage, release, and overall regulation of calcium ion concentration in the cytosol of muscle cells [E]

H zone (of sacromere)

central part of A bands where there are no thin filaments present, only thick [E]

thick myofilaments

composed of the protein myosin which are used to form cross-bridges between thick and thin myofilaments; (myosin functions as a motor protein in all three types of muscle tissue); the myosin heads contain an actin binding site and an ATP-binding site

thin myofilaments

composed primarily of the protein actin; associated with troponin & tropomyosin proteins which occupy the binding site on the actin when muscles are relaxed; (controversly, muscle contraction begins as myosin heads bind to the binding site on the actin)

terminal cisterns

connected to the SR; stores an abundance of excess calcium; located bilaterally of the transverse tubules

sacroplasm

cytoplasm of a muscle fiber/cell; contains myoglobin and high amounts of glycogen

A band

dark middle area of a sacromere; extends length of the thick filaments and includes parts of thin filaments that overlap the thick filaments [G]

myofibrils

elongated contractile thread-like organelles found in striated muscle cells; contain 2 types of smaller/shorter elements - thin myofilaments (composed mostly of the protein actin) and thick myofilaments (made almost entirely of the protein myosin)

transverse tubules

extensions of the sarcolemma to sarcoplasmic reticulum[2] and into the muscle fiber; filled with interstitial fluid that allows for action potentials to spread to all parts of the muscle at the same time [11]

I band

light less dense area of a sacromere where only thin filaments are present; a Z disc passes thru the center of this band [F]

M line (of sacromere)

mid-line of sarcomere; contains proteins that hold thick filaments together [H]

1. sacromeres 2. Z discs

myofilaments are arranged into compartments called ___ which are separated from each other by ___

sarcolemma

surrounds each muscle fiber; encloses fiber's cellular contents (aka the cell membrane)