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.

Performance Enhancing Drugs: A Satirical Advertisement

Performance enhancing drugs boost athletic performance, increase muscle build, and aids in the loss of body fat. I don't have much real life experience with these drugs besides a story that my friend told me about a person she used to know. Apparently this boy was abusing steroids to get ahead on his sports team and as a result, was experiencing "roid rage." In class we learned that this is not a myth, and that steroid users do indeed have a tendency to get angry faster. Other health risks and symptoms of drug use include acne, stunted growth, high blood pressure, liver damage, risk of stroke, headaches, baldness, and risk of ligament and tendon injuries. Stimulants as seemingly harmless as caffeine can result in nervousness, irritability, dehydration, and psychological addiction. Erythropoietin, or EPO, a type of hormone used to treat anemia in people with severe kidney disease, may result in heart attack and pulmonary edema. Not all performance enhancements are drugs. Finally, carbo-loading, a tactic of increasing consumption of carbohydrates depicted in the satirical advertisement above, can result in severe weight gain. Many of these substances are safe as long as they are used in moderation, like caffeine. Strength training and high protein diets can be safe, but continuous periods of abuse will only have negative effects on the human body. Ultimately, the risks that come with abusing certain performance enhancements are not worth it.

Chicken Muscle Dissection

In the lab, we distinguished significant muscles and muscle bunches in a chicken by slicing through the skin with scissors and a scalpel. The muscles in the chicken have comparable structures and shapes as the muscles in the human body. The muscles connect the bones by a tendon, white connective tissue, so that when the muscles contract, the bones and body move. If the biceps brachii contracts, and the triceps humeralis unwinds, the tendons that connect the muscles to the humerus, ulna, and radius, would pull the bones at the elbow joints and twist the arm. The tendons are what keep the muscles and bones connected and provides movement when the muscle pulls on the tendon which moves the bone. At the origin, the tendon is fixed during muscle contraction, while at the insertion sites the tendons move during contraction to move the joints properly. The muscles in the chicken are like people, but there are several key differences. The pectoralis major and minor are both relatively bigger in the fowl than in people because they have been reared to have more meat in those areas. Another contrast would be that we have a muscle in the thigh called gluteus maximus, and the chicken has iliotibialis, despite the fact that the elements of those muscles are basically the same. Also, in comparison to chickens, humans have relatively small tibialis major.


The muscles in the chicken:

The pectoralis major is larger in birds than humans because it is developed from flying.

The pectoralis minor attaches to the shoulder muscle from right under the pectoralis major

The trapezius pulls the shoulder back during flight for birds.

The latissimus dorsi works to extend the wings on the back of the bird.

The deltoid raises the upper part of the wing on the top part of the shoulder of the bird.

The biceps brachii bends the wing on the upper area of the wing.

The triceps humeralis both bends and extends the wing in chickens. It is below the biceps brachii.

The flexor carpi ulnaris is in the lower area of the wing.

The brachioradi alis is on the lower area of the wing as well and extends from the elbow to the thumb.

The sartorius runs from the thigh to the pelvis and flexes the thigh.

The iliotibialis is on the lateral side of the thigh in birds. In humans, it is on the dorsal side and is called the gluteus maximus.

The biceps femoris functions as part of the hamstring group and is medial to the iliotibialis.

The semimembranosus is also part of the hamstring group and is inferior to the biceps femoris.

The semitendinosis is part of the hamstring group and is anterior to the semimembranosis.

The quadriceps compose much of the thigh and makes up a lot of the front and inner portions of the thigh.

The gastrocnemius is attached to the Achilles tendon and is on the back of the drumstick of the chicken.

The peronus longus extends the foot and is on the lateral side of the drumstick.

The tibialis anterior flexes the foot and is on the lateral side of the shin bone.

The tendon is the connective tissue that attaches the muscles to the bones.

What happens when you stretch?

Relate and Review:

I remember learning in class that a sarcomere is a section of a myofibril where protein fibers overlap and slide past each other during the contraction and relaxation of muscles. I thought it was interesting how the reading outlined how the muscle fiber is pulled out fully one sarcomere at a time, then the connective tissue picks up the slack. When I was recovering from scarred tissue, I remember a nurse explaining parts of this process to me. The article also confirmed that it is this realignment that helps tissues recover from scarring, as it helps realign the disorganized strips of muscle fiber by pushing it in the direction of the tension.

1. "Proprioceptors are the source of all proprioception: the perception of one's own body position and movement": I thought this was an interesting line because of how sensitive the proprioceptors actually are. Any change of tension or basic movement is detected and they reside in so many places. For example, proprioceptors are found in the nerve endings, muscles, tendons, and fibers. 
2. "When stretching, it is easier to stretch a muscle that is relaxed than to stretch a muscle that is contracting": By allowing the antagonists to relax, you can get a better stretch. In track, we learned that you can stretch out your hamstrings better by keeping your leg erect. This makes sense because keeping the muscle relaxed can provide a deeper stretch. 
3. "Some sources suggest that with extensive training, the stretch reflex of certain muscles can be controlled so that there is little or no reflex contraction in response to a sudden stretch": This is a very interesting concept because one would consider reflexes to be uncontrollable. However, for professional athletes, muscular control can actually be achieved.