Unit 7 Reflection: Muscles

Our muscle video:

Muscles are composed of actin and myosin fibers and are classified into three groups: skeletal, cardiac, and smooth. Muscles have four properties: excitability, contractility, extensibility, and elasticity. Contractility is the ability for muscle tissue to shorten when stimulated. Extensibility is the opposite or the ability for muscles tissues to be stretched. Elasticity is the muscle tissue's ability to recoil back to resting length. Connective tissue components include the fascia, which hold muscle fibers together. The perimysium separates muscles into bundles. Tendons connect muscle to bone.

Muscles have many roles and vary in size and function. Masseter elevates the mandible and the temporalis elevates and retracts the mandible. The trapezius extends the hand and can adduct, elevate, or depress the scapula. The latissimus dorsi can extend, adduct and rotate the arm medially. The biceps brachii can flex the elbow joint while the triceps brachii can extend the elbow joint. The Brachioadiatis flexes the forearm at the elbow and is responsible for supination and pronation. The rectus abdominus can flex the abdomen while the external oblique can compress the abdomen. External intercostals elevate ribs while internal intercostals depress ribs. The hamstring group includes the biceps femoris, which flexes the lower leg, the semimembranosus, the most medial of hamstring muscles and extends the thigh, and the semitendonosus, which is anterior and medial to the semimembranosus on the inside of the thigh. Quadriceps muscles include the rectus femoris, vastus intermedius, vastus medialis, and the vastus lateralis.


Slow twitch fibers, or slow oxidative, are relatively slow and are aerobic. They have a low number of glycogen stores and are red in color, as they have a lot of oxygen. They are best suited for long distances and have high amounts of myoglobin, mitochondria, and capillaries. Fast twitch a fibers are relatively fatigue resistant while fast twitch b fibers fatigue quickly. FTa fibers are red to pink in color while FTb fibers are white or pale in color. An example of a concentric contraction is a bicep curl and an example of an isometric contraction is holding a weight out in front of you. An example of an eccentric contraction is walking. The ratio of muscle fibers varies between individuals and depends on genetics and exercise. Active exercise can result in hypertrophy (cells increase in size/volume due to an increase in myofibrils) and hyperplasia (cells remain the same size but increase in number).

Performance enhancing substances are manufactured products for oral ingestion, intranasal application or inhalation containing compounds that are intended to increase performance, promote muscle growth or induce weight loss. Health risks for men include shrinking of testicles, low sperm count, impotence, breast growth, and an enlarged prostate. Health risks for females include breast shrinkage, facial hair growth, issues with menstrual periods, and an enlarged clitoris. However, not all performance enhancements are bad for you (read more in my last blog post).

Because college decisions are coming out and I have been more busy, I haven't been able to keep up with my New Years resolutions as much as I'd like. My first goal of sleeping more has not been working out as well as I had hoped, but I want to start setting a timer whenever I do work to maximize efficiency. This will help me accomplish my second goal of studying anatomy notes every night as well. If I manage my time by setting a personal deadline, I know I will be able to catch up to what I originally had hoped.