This lesson will cover a micro-level view of muscle contractions, looking specifically at sarcomeres and how they act in order to produce a muscle contraction:
Muscle contractions are the shortening of fibers within muscles, which act to generate force. The sarcomere is the basic unit of contraction. Muscle contractions rely on calcium, and can occur when there's an increase in calcium ions. Calcium is either stored or released by the sarcoplasmic reticulum, which is like the endoplasmic reticulum of muscle fibers. It stores and releases the calcium necessary for these muscle contractions.
Use this diagram below to give you a general idea of what the sarcomere, or muscle fiber, looks like. Muscles contain different bundles of fibers, but a single fiber is made of a myofibril. Myofibrils have a banded appearance; when bundled together, they give muscles their striated, or striped look. Sarcomeres, the basic unit of contraction, are portions of myofibrils.
The sarcomere has three regions:
Within our sarcomere, we have something called thick and thin filaments. Those thick and thin filaments work together in order to produce a contraction. Actin is a protein that's referred to as the thin filament in a contraction, whereas myosin is the protein referred to as a thick filament.
Actin looks like a strand of beads, and the above image shows several molecules of myosin together. Just one molecule of myosin is composed of a head and a tail. The head plays an important role in contraction.
Use this diagram to visualize what's happening during a contraction; imagine this is one sarcomere. When a contraction happens, actin and myosin overlap with each other, and the Z-bands will move closer together. The top image is a relaxed muscle fiber, and the bottom is one that has contracted.
This contraction happens when myosin heads bind to actin, and this occurs when the sarcoplasmic reticulum releases calcium. Calcium prepares actin and myosin for interaction. Once myosin has bound to actin, the myosin heads will pull the actin filaments toward the center of the sarcomere.
ATP energy is also required for this to happen. When ATP is released, it will then bind to myosin, and myosin will detach from actin. The sarcomere will return to its resting state. This whole process is known as the sliding filament mechanism.
There are two types of contractions that can occur:
In other words, if a muscle twitches over and over again, it can sustain that contraction. Contractions are caused by impulses from the nervous system. An action potential is the technical term for these impulses, and a motor unit describes one motor neuron and all of the muscle fibers it innervates at once.
The sarcomere is the basic unit of contraction within muscle fibers, and is made up of myofibrils. The structure of the sarcomere includes 3 regions: Z-bands, I-bands, and A-bands; sarcomeres also have thin and thick filaments. Contractions happen when calcium is released, and myosin, the thick filament, binds to actin, the thin filament. They overlap in the A-band region, pulling the Z-bands closer together. There are two types of muscle contractions: twitch and tetanus. A twitch is a single contraction, while a tetanus is a prolonged contraction made up of multiple twitches.
Keep up the learning and have a great day!
Source: Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND
The primary energy molecule that cells use for energy; composed of adenosine and three phosphate groups; when the bonds that hold the phosphates together are broken energy is released for work.
Referred to as the thin filament of a sarcomere, creates the lighter color within a sarcomere and interacts with myosin to create movement.
The technical term for a nervous impulse; when a wave of depolarized electrical energy travels down the length of a cell/tissue.
A mineral/ion that has many physiologic uses to humans; calcium is stored in the sarcoplasmic reticulum (SR) of skeletal muscles and when released it prepares actin and myosin for interaction.
A muscle fiber generates tension, causing the muscle to shorten.
The term used to describe one motor neuron and all of the muscle fibers it innervates at once.
Referred to as the thick filament of a sarcomere, creates the darker colors within a sarcomere and contains various heads that pull on actin filaments to create movements.
The functional and contractile units of skeletal and cardiac muscles; created by a specific arrangement of myofilaments called actin and myosin; each sarcomere is bordered by a z-line.
A specialized form of smooth endoplasmic reticulum (SER) found within skeletal muscles used for calcium storage.
A theory used to describe how the microfilaments within the sarcomere interact with one another; actin and myosin cling together and slide past one another.
A term used to described a prolonged muscle contraction; often used to describe a person who has been exposed to Clostridium tetani toxin.
The way a skeletal muscle contracts, sarcomeres quickly pull inward and create a quick, jerky twitch.