Key Takeaways

There are three types of muscles: smooth, cardiac, and skeletal, with skeletal muscles being the most commonly known because they are voluntarily controlled.
There are three types of muscle contractions: isometric, isotonic concentric, and isotonic eccentric.
The nervous system powers and regulates all muscle tissue.
Balance between muscle contraction and relaxation is crucial for fluid movement and function.
The excitation-contraction-relaxation (ECR) cycle involves multiple steps and is necessary for muscle movement.

Note: These key takeaways summarize the types and process of skeletal muscle contractions. For more information about skeletal muscle contractions, check out our recommended blog content.

Muscles are soft tissue that move reflexively or voluntarily. There are three different types - 1) smooth muscle, 2) cardiac muscle, and 3) skeletal muscle. Smooth muscle controls involuntary internal movements of organs and organ lining - think food digestion. Cardiac muscle pumps the heart. Skeletal muscle moves the bones that comprise the skeleton. The most commonly thought of muscle is skeletal, likely because those muscles can be voluntarily controlled, but sometimes they can be reflexive (without control), depending on the type of skeletal muscle contraction involved. The three different types of contractions are:

1. Isometric

2. Isotonic Concentric

3. Isotonic Eccentric

An isometric contraction activates the muscle, but it does not change the length of the tissue. An isotonic contraction activates the muscle and changes the length of the tissue. A concentric contraction shortens the muscle as it gets activated. An eccentric contraction lengthens the muscle tissue as it gets activated.

Muscle movement occurs at the discretion of the brain, spinal cord, and nerves. The nervous system powers and controls all muscle tissue. Consider the neuromuscular relationship as a flashlight and batteries - without batteries, nothing happens because without power, nothing can get turned on.

Skeletal muscles contract-and-relax to allow fluid movement. With voluntary contractions of some muscles, opposites relax involuntarily. Movement requires a delicate excitation-contraction-relaxation (ECR) balance. A tip of the scale in either direction can greatly hinder function and reduce quality of life.

From start to finish, the ECR cycle takes roughly 10 steps. The following is an example of standing up from a chair.

Step 1: The brain decides to stand up out of the chair.

Step 2: The brain sends a signal to the legs.

Step 3: The nerves in the leg release neurotransmitters into the muscle.

Step 4: Action potential travels through T tubules.

Step 5: Calcium channels open.

Step 6: Calcium induces Calcium release.

Step 7: Calcium binds to troponin, exposing myosin-binding sites

Step 8: Cross-bridge cycle begins (contraction)

Step 9: Calcium is actively transported back out of the cell

Step 10: Tropomyosin blocks myosin-binding sites (relaxation)

Skeletal Muscle Contractions Simplified

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