Muscular system

Type of Muscle 

Cells 

Contraction 

Function 

Skeletal Muscle 

The individual cells are often called muscle fibers because of their long thread-like shape. Each skeletal muscle cell forms from numerous cells fusing together during development, giving each cell multiple nuclei. These cells have alternating dark and light cross-markings called striations. 

Skeletal muscle fibers contract in response to stimuli from a nerve. These muscle fibers relax again when that stimulation stops. Movement is voluntary. 

When you initiate the movement of your head, trunk, and limbs, it is skeletal muscle that is responsible for this motion. 

Smooth Muscle 

Smooth muscle cells do not have any striations, are shorter than skeletal muscle cells, and only have one nucleus. 

Involuntary contraction in smooth muscle occurs in response to a signal from the nervous system, but we cannot consciously start or stop these contractions. 

This tissue makes up organ lining, such as that of blood vessels, the stomach, and the urinary bladder. The contractions of smooth muscle keep blood, fluids, and nutrients moving to necessary locations throughout the body. 

Cardiac Muscle 

Cardiac muscle cells are striated and branched with one or more nuclei. They are joined end to end in complex networks. 

Cardiac muscle contractions are involuntary but do not require a signal for the nervous system to initiate contraction.   

As the name implies, cardiac muscle tissue is only found in the heart. It pumps blood through the heart’s chambers and into the blood vessels. 

Origin: Between the semitendinosus muscle and the ischium bone 

Insertion: Between the semitendinosus muscle and the tibia bone 

Skeletal Muscle 

Explain how it is separated and held together: separated from nearby muscles and held in place by layers of dense connective tissue. 

Connective Tissue 

Explain fascicles and fascia: Inside every muscle tissue are bundles of muscle fibers called fascicles. The grouping of fascicle bundles is referred to as the fascia. 

Explain the three types of connective tissue: There are three types of connective tissues surrounding muscle tissues:  

• Epimysium (pictured) surrounds the entire fascia. 

• Perimysium (pictured) surrounds each fascicle. 

• Endomysium (too small to show) surrounds each tiny muscle fiber within a fascicle. 

Blood Vessels and Nerves 

Explain the role of blood vessels and nerves: Skeletal muscles have an abundant supply of blood vessels and nerves to help with muscle contraction. A skeletal muscle must receive an impulse from a nerve cell to contract. Typically, one artery and at least one vein accompany each nerve through the skeletal muscle's epimysium to the muscle fibers. 

Explain how muscle contraction occurs: 

Sarcolemma 

Explain what it is and what it is made of: The sarcolemma is the cell membrane of a muscle cell. It is made up of a plasma membrane and an outer layer of polysaccharide material that contains numerous thin collagen fibrils 

Explain the membrane’s function: The membrane receives and conducts stimuli from adjacent nerves. At each end of the muscle fiber, the surface layer of the sarcolemma fuses with a tendon fiber to form the muscle tendons that then connect to bones. 

Sarcoplasmic Reticulum 

Define sarcoplasmic reticulum and its relation to myofibril: The sarcoplasmic reticulum is a membranous network of channels that surround each myofibril.   

Explain its function: The sarcoplasmic reticulum mainly stores calcium ions, which it releases when the muscle cell is stimulated to aid muscle contraction. 

Cardiac Muscle 

Explain where is found and how it contracts: Only in the heart and contracts usually in involuntary control 

What is the function of the intercalated disk? links the cardiac cells together to allow for synchronized heartbeats. 

Using the slides, describe how this tissue looks different from other muscle tissues on this lesson page.  

Smooth Muscle 

Explain where can be found and how it contracts: Slow, weak contraction under involentary control Found in many parts of the body, including the stomach, intestines, lungs, blood vessels, bladders, uterus, and iris. No striations. 

Explain the three types of connective tissue: Colon 1x, Colon 4x, and Colon 20x 

Using the slides, describe how this tissue looks different from other muscle tissues on this lesson page.  

Skeletal Muscle 

Explain where can be found and how it contracts: Strong, quick contractions, usually under voluntary control to move body parts. Striated microscopic appearance. Found in all skeletal muscles of the body. The quadriceps of the leg and the biceps of the arm are two examples. 

Using the slides, describe how this tissue looks different from other muscle tissues on this lesson page.  

Injuries 

Tear and Strain 

Involves a stretch (sprain) or tear in the muscle, tendon, or ligament. The best way to heal this injury is using the "RICE" method: rest, ice, compression, and elevation.   

Splint 

Inflammation of the muscle due to using the muscle too much. Happens often in runners to the muscle attached to the shin.   

Tendinitis 

Happens if the tendon is inflamed repeatedly without being allowed to heal. Some cases require surgery to repair the tendon.   

Diseases 

Muscular Dystrophy 

This disorder causes muscle cell death and is highly progressive. The body breaks down muscle cells and does not reform them, leading to atrophy (or shrinking) and the inability to perform basic functions. 

Tendinosis 

Similar to tendonitis but involves the body breaking down the tendons and forming scar tissue when the tendon is repeatedly damaged. 

Tetanus 

A bacterial infection of the muscle that can cause stiffness and paralysis (the inability to move). Often prevented through vaccination and early treatment.   

© Science Photo Library / ImageQuest 2023    

 © Science Photo Library / UIG / ImageQuest 2023 

Cardiac Muscle 

Skeletal Muscle 

Smooth Muscle