Sarcoplasm shown with a muscle fiber

Cytoplasm of a muscle cell.

- Sarcoplasm

25 related topics


Muscle cell

Also known as a myocyte when referring to either a cardiac muscle cell , or a smooth muscle cell as these are both small cells.

General structure of a skeletal muscle cell and neuromuscular junction: 1. Axon

2. Neuromuscular junction

3. Skeletal muscle fiber

4. Myofibril
Diagram of skeletal muscle fiber structure

The cytoplasm in a muscle cell is termed the sarcoplasm; the smooth endoplasmic reticulum of a muscle cell is termed the sarcoplasmic reticulum; and the cell membrane in a muscle cell is termed the sarcolemma.


Smallest functional unit of striated muscle tissue.

Image of sarcomere
Muscle contraction based on sliding filament theory

The concentration of calcium within muscle cells is controlled by the sarcoplasmic reticulum, a unique form of endoplasmic reticulum in the sarcoplasm.


Cell membrane of a muscle cell.

Skeletal muscle fiber, with sarcolemma labeled at upper left.

A special feature of the sarcolemma is that it invaginates into the sarcoplasm of the muscle cell, forming membranous tubules radially and longitudinally within the fiber called T-tubules or transverse tubules.


Part of the cardiac cycle during which some chambers of the heart muscle contract after refilling with blood.

The cardiac cycle at the point of beginning a ventricular systole, or contraction: 1) newly oxygenated blood (red arrow) in the left ventricle begins pulsing through the aortic valve to supply all body systems; 2) oxygen-depleted blood (blue arrow) in the right ventricle begins pulsing through the pulmonic (pulmonary) valve en route to the lungs for reoxygenation.
Electrical waves track a systole (a contraction) of the heart. The end-point of the P wave depolarization is the start-point of the atrial stage of systole. The ventricular stage of systole begins at the R peak of the QRS wave complex; the T wave indicates the end of ventricular contraction, after which ventricular relaxation (ventricular diastole) begins.
The cardiac cycle at beginning of atrial systole: The left (red) and right (blue) ventricles begin to fill during ventricular diastole. Then, after tracing the P wave of the ECG, the two atria begin contracting (systole), pulsing blood under pressure into the ventricles.
A Wiggers diagram, showing various events during systole (here primarily displayed as ventricular systole, or ventricular contraction). The very short interval (about 0.03 second) of isovolumetric, or fixed-volume, contraction begins (see upper left) at the R peak of the QRS complex on the electrocardiogram graph-line. + Ejection phase begins immediately after isovolumetric contraction—ventricular volume (red graph-line) begins to decrease as ventricular pressure (light blue graph-line) continues to increase; then pressure drops as it enters diastole.

These cells are activated spontaneously by depolarization of the electrical potential across their cell membranes, which causes voltage-gated calcium channels on the cell membrane to open and allow calcium ions to pass through into the sarcoplasm (cytoplasm) of cardiac muscle cells.

Skeletal muscle

Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system that are mostly attached by tendons to bones of the skeleton.

A top-down view of skeletal muscle
3D rendering of a skeletal muscle fiber
Muscle types by fiber arrangement
Types of pennate muscle. A – unipennate; B – bipennate; 
C – multipennate
ATPase staining of a muscle cross section. Type II fibers are dark, due to the alkaline pH of the preparation. In this example, the size of the type II fibers is considerably less than the type I fibers due to denervation atrophy.
Structure of muscle fibre showing a sarcomere under electron microscope with schematic explanation.
Diagram of sarcoplasmic reticulum with terminal cisternae and T-tubules.
Human embryo showing somites labelled as primitive segments.
When a sarcomere contracts, the Z lines move closer together, and the I band becomes smaller. The A band stays the same width. At full contraction, the thin and thick filaments overlap.
Contraction in more detail
(a) Some ATP is stored in a resting muscle. As contraction starts, it is used up in seconds. More ATP is generated from creatine phosphate for about 15 seconds. (b) Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to lactic acid. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle. (c) Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria.
Exercise-induced signaling pathways in skeletal muscle that determine specialized characteristics of slow- and fast-twitch muscle fibers
Jogging is one form of aerobic exercise.
In muscular dystrophy, the affected tissues become disorganized and the concentration of dystrophin (green) is greatly reduced.
Prisoner of war exhibiting muscle loss as a result of malnutrition.

The cell membrane is called the sarcolemma with the cytoplasm known as the sarcoplasm.


Myofilaments are the three protein filaments of myofibrils in muscle cells.

Muscle fiber showing thick and thin myofilaments of a myofibril.

Calcium ions are then released from the sarcoplasmic reticulum into the sarcoplasm and subsequently bind to troponin.

Albert von Kölliker

Swiss anatomist, physiologist, and histologist.

X-ray of Kölliker's hand, made by Röntgen on 23 Jan 1896

Albert L. Lehninger asserted that Kölliker was among the first to notice the arrangement of granules in the sarcoplasm of striated muscle over a period of years beginning around 1850.

Strength training

Strength training or resistance training involves the performance of physical exercises that are designed to improve strength and endurance.

A gym environment where various forms of strength training are being practiced. Identified from left to right, the exercises are: overhead presses, battle ropes, planking, and kettlebell raises.
The bodyweight squat is effective at strengthening the legs and core. It requires no equipment and can be performed almost anywhere. A person stands with their arms by their sides, and then squats down moving their arms out ahead of themselves, and then stands up again while moving their arms back to their sides, and so forth.
A back extension
Using a wrist strap
A woman doing strength training using weights at a health club with her coach standing behind her.
Arthur Saxon performing a Two Hands Anyhow with an early kettlebell and plate-loaded barbell

Exercises of 6–12 reps cause hypertrophy of the sarcoplasm in slow-twitch and high-twitch muscle fibers, contributing to overall increased muscle bulk.

Beta-Hydroxy beta-methylbutyric acid

Naturally produced substance in humans that is used as a dietary supplement and as an ingredient in certain medical foods that are intended to promote wound healing and provide nutritional support for people with muscle wasting due to cancer or HIV/AIDS.

Top: β-Hydroxy β-methylbutyric acid
Bottom: β-Hydroxy β-methylbutyrate
A commercially available formulation of HMB. Each size 000 gelatin capsule contains 1 gram of HMB-Ca and an unspecified amount of microcrystalline cellulose and magnesium stearate.
This graph shows the plasma concentration of HMB (in units of micromoles per liter of blood plasma) over time following ingestion of a 1 gram dose of the calcium or free acid form of HMB.
First synthetic routes to β-hydroxy β-methylbutyric acid
Later synthetic routes to β-hydroxy β-methylbutyric acid

The average concentration of HMB in the intramuscular fluid of healthy men of ages 21–23 has been measured at 7.0 μM.

Wilhelm Krause

German anatomist born in Hanover.


"Krause's membranes": defined as isotropic bands in striated muscle fiber that consist of disks of sarcoplasm and connect the individual fibrils. Also known as Z-Disc or Dobie's line.