Anatomy+of+a+skeletal+muscle+cell+1

__**Myofibril**__ - these are cylindrical structures that run lengthwise through the muscle cell and are made of two (2) smaller structures: __1.) thin myofilaments__ - actin protein __2.) thick myofilaments__ - myosin protein

__**Sarcolemma**__ - the outer surface of a muscle cell

__**Sarcolplasmic Reticulum**__ - a network of tubes running the length of the cell (looks like smooth endoplasmic reticulum). Inside this structure calcium ions, Ca2+, are stored, which are used to produce muscle contractions.

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__**Sarcomere**__ - these are the functional units of the muscle. There can be up to 100,000 of these in one myofibril.

__**Z-disc**__ - these are zones that seperate sarcomeres

__**A-band**__ - a dark area in a sarcomere made up mostly of thick myofilaments (myosin)

__**I-band**__ - a lighter colored area of the sarcomere that is only composed of thin myofilament (actin).

__**H-zone**__ - the center area of the A-band that only contains thick myofilaments (myosin), no thin (actin).

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