Three muscle types. Three connective tissue types. Use the label reveals, quick checks, and bettybroadbent.com reference pages to explore each tissue — then put your skills to the test in the Mystery Lab.
Slide the slider to reveal each labeled structure
Quick checks test understanding
Mystery Lab: identify the tissue from the image
STAIN KEY:
SKELETAL MUSCLE
STRIATED?
Yes
VOLUNTARY?
Yes
NUCLEUS POSITION
Peripheral
CELL SHAPE
Long Cylinder
UNIQUE FEATURES
Multi-nucleated
Why two views?
A muscle fiber is a long cylinder. Cut it lengthwise → long ribbons with striations visible (longitudinal). Cut it face-on → circular profiles with nucleiClusters of neurons in the CNS responsible for processing information. at the outer rim (cross-section). Same tissue, completely different image. Histologists always look at both.
Longitudinal Section — Slide 058-Thin · H&E
Look along the length of the fibers. Find the alternating dark and light cross-bands (striations) and locate the nuclei — they should be at the very edge of each fiber, never in the center.
Grab and Move the slider to reval each labeled structure
Muscle fiber
long cylindrical cell running parallel to others
Peripheral nucleusThe control center of the cell that contains DNA and directs cellular activities.
dark purple dot pressed to the outer edge of the fiber — never the center
Sarcolemma
plasma membraneThe outer boundary of a cell that controls what enters and exits. forming the outer boundary of each fiber
Striations
alternating dark (A-band) and light (I-band) bands crossing the fiber
Endomysium
delicate CT sheath separating individual fibers
Cross Section — Slide 058-T · H&E
Now you are looking at the cut face of the same cylinders. Each circle is one fiber. Find the nuclei at the rim, count the fasciclesBundles of nerve fibers within a nerve.
or
Bundles of nerve fibers within a muscle., and trace the CT wrappings from innermost to outermost.
Muscle fiber
long cylindrical cell running parallel to others
Peripheral nucleus
dark purple dot pressed to the outer edge of the fiber — never the center
Sarcolemma
plasmaThe liquid component of blood. membrane forming the outer boundary of each fiber
Striations
alternating dark (A-band) and light (I-band) bands crossing the fiber
Endomysium
delicate CT sheath separating individual fibers
Clinical Connection — Duchenne Muscular Dystrophy (DMD)
DMD results from a mutationA change in DNA sequence that can affect gene function. in the dystrophin gene. Dystrophin links the sarcolemma to the internal cytoskeleton A network of protein filaments that provide structure, shape, and movement to cells., stabilizing the membrane during contraction. Without it, the sarcolemma tears repeatedly, calcium floods the cell, and the fiber degenerates. On H&E, affected muscles show fibers of wildly variable size, centrally-relocated nuclei (a regeneration sign), and replacement by fat and CT. The peripheral nucleus you just labeled? Its position is the first thing that changes in a diseased fiber.
Quick Check
Answer: No — skeletal muscle nuclei are peripheral, pushed to the outer edge. Central nuclei indicate cardiac muscle or a regenerating/diseased skeletal fiber. If you see central nuclei in skeletal muscle, that is a diagnostic red flag.
Answer: Each fiber formed by the fusion of many embryonic cellsThe basic structural and functional units of life. called myoblasts. All their nuclei remain in the merged cell — hence dozens to hundreds of nuclei per fiber. They’re pushed to the periphery to make room for myofibrils, which occupy over 80% of the cell’s volume.
List of terms
- nuclei
- nucleus
- plasma membrane
- fascicles
- plasma
- mutation
- cytoskeleton
- cells