NucleusOne nucleus, sometimes two, lies near the center.
StriationsCross stripes made by the lined-up sarcomeres.
Intercalated discJoins two cells end to end and passes signals between them.
BranchThe cell divides at its end to join two neighbors.
Sarcolemma (cell membrane)The cell membrane of a muscle cell.
MitochondriaThey supply the cell's energy. A cardiac muscle cell has many.
MyofibrilA rod of contractile proteins running the length of the cell.
CapillaryA tiny blood vessel beside the cell.
How this list was compiled: Every name checked on 2026-10-01 in at least two of these, in our own words. (1) Wikipedia, Cardiac muscle, sections Cardiac muscle cells, T-tubules and Intercalated discs. (2) Wikipedia, Intercalated disc, section Structure. (3) Yale School of Medicine, Histology lab on muscle, pre-lab reading on cardiac muscle. (4) Henry Gray, Anatomy of the Human Body, 20th edition, 1918 (public domain), The Heart, on the cardiac muscular tissue. (5) Sit, Gutmann and Iskratsch, Costameres, dense plaques and podosomes, Journal of Muscle Research and Cell Motility, 2019. (6) Wikipedia, T-tubule. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry. Own original drawing; nothing is traced or copied. Licence: own work
How it works
To label the cardiac muscle cell, write a name on the line for each number. Eight numbers are on one branching cell and the capillary beside it. The close-up of the intercalated disc is on the labeled diagram.
Read the full guide
Cardiac muscle cell word bank
In alphabetical order, to copy onto the board: branch, capillary, intercalated disc, mitochondria, myofibril, nucleus, sarcolemma, striations.
The numbers that get swapped
Striations and myofibril: the striations are the fine cross lines over the whole cell, and the myofibril is the one long striped rod along its lower edge. Sarcolemma and intercalated disc: the sarcolemma is the outline of the cell, and the disc is the dark stepped line where the cell meets its neighbor. The line from number 4 ends on the upper arm itself, not on the barred oval beside it.
When marking, accept cell membrane for sarcolemma. It is the same part.
Questions and answers
Is cardiac muscle striated?
Yes. Its myofibrils are built of sarcomeres set in line, which gives the cell a striped look under a microscope. The darker stripes are A bands, mainly myosin, and the lighter ones are I bands, mainly actin.
Is cardiac muscle voluntary or involuntary?
Involuntary. It contracts without being told to, and its rate and force cannot be set at will. The autonomic nervous system and hormones influence both.
Why do cardiac muscle cells branch?
A branched end lets one cell join more than one neighbor, so the cells make a three-dimensional network and not separate parallel rows. Intercalated discs join them, and the electrical signal spreads through the network, so the muscle contracts together.
Does the cardiac muscle cell worksheet have an answer key?
Yes. The key prints the cell with its numbers and lists the eight names in order, from nucleus to capillary.