Muscle Tissue Flashcards
What are the universal characteristics of muscle?
- Muscle is excitable in that it can respond to chemical signals such as calcium.
- Muscles are conductive. They have the ability respond to electrical change and trigger a wave of excitation along the muscle fiber.
- Muscles are contractile. Myofibrils shorten as a result of the sliding filament theory.
- Muscles are also extensible (able to be stretched).
- Muscles are elastic. They have the ability to return to their original resting length after being stretched.
What is the responsibility of the Transverse (T) Tubules?
T Tubules penetrate through the Sarcolemma and encapsulate myofibrils. These tubular infoldings carry electric current to the myofibril’s interior.
Explain the purpose of the Sarcoplasm.
The sarcoplasm is a fluid substance that surrounds myofibrils. Glycogen and myoglobin binding oxygen is stored in the sarcoplasm for quick recruitment of energy.
What protein is considered the thick filament of the myofibril?
The thick filament is called the myosin. There are 200-500 myosin molecules in each myofibril. The myosin contains 2 entwined polypeptides that have heads on them that resemble golf clubs. These filaments are responsible for binding to the thin filament (actin) to form a cross-bridge. Once calcium floods the myofibril, the myosin heads can bind to the actin causing a pulling action or sliding of the actin over the myosin. When calcium leaves the myofibril (via the calcium pump) the myosin heads release from he actin and the sarcomere is able to return to its original resting length.
To what structure does calcium bind to in order for a cross-bridge to occur?
Calcium binds to actin; specifically, it binds to troponin located on the tropomyosin rod on each active. Once calcium binds to troponin, it releases the tropomyosin in order for the myosin head to bind to the actin filament.
Once the myosin head releases from the actin molecule, what filament is responsible for allowing the sarcomere to return to its resting length?
Connectin is the elastic protein that attaches the Z-discs to the myosin filament. When calcium is evacuated from the myofibril, the myosin heads release from the actin and the sarcomere is able to return/recoil to their original resting position.
A motor unit is defined as each motor neuron and all the muscle fibers it innervates. Each muscle has a different number of motor units. Which type of muscle would have less motor units and why…a muscle of the eye or the gastrocnemius?
The eye muscle would have fewer motor units for a couple reasons. First, the muscle itself is smaller in terms of cross-section. More importantly, the eye muscle is not a strength generating muscle AND is needs fine motor function (precision of eye movement). Therefore, it relies on few motor units so that fine motor control can be achieved.
Describe the length-tension relationship.
The length-tension relationship explains the amount of tension generated relative (or dependent) to the length of the muscle when it was initially stimulated. When a muscle is in its resting length, it can produce the greatest amount of tension; this because the most amount of cross-bridges can be formed. When the muscle is fully extending (or stretched), the myosin and actin are not overlapping as much resulting in fewer cross-bridges being formed. When the muscle is overly contracted, the thick filaments are too close to the Z discs and have no where to slide; thus decreasing the amount of tension generated.
