Unit 7 Reflection

While the last unit dealt mostly with the foundation of our body structure, the skeletal system, this unit focuses on the structure, organization, and functions of its counterpart, the muscular system. I will begin reviewing from the smallest unit of muscles, the two protein filaments that make all of our movements possible: actin and myosin.

The picture above shows the mechanism for muscle contraction at a molecular level, with the myosin heads pictured in a variety of configurations and steps in the aptly named "power stroke" process, where the fibers slide parallel to each other in opposite directions. This contracts the unit of muscle, called a sarcomere, and long chains of these sarcomeres create a myofibril. While each sarcomere can only shorten a small amount, the myofibrils combine the effectiveness additively, allowing for the powerful, macroscale movements humans and other animals are capable of (see picture below). Now, the myofibrils are lined up side by side to create a highly effective muscle that is connected, at the ends, to tendons and thus to bones.

The process of contraction (called sliding filament theory) between the actin and myosin is best described with the video below.

In the human body there are a large number of muscles. They also, however, have slight relation to animals with similar body compositions, like chickens. In this lab, I go through a dissection of a chicken (because human cadavers are in short supply) and list and describe many of the major muscles.

        I have, recently, begun weight training- with the weight god Leon Ng- and have had extended periods of muscle soreness. I would like to know the causes of this, and whether it is true that people build muscle by causing little tears in the fibers to be rebuilt stronger.

         This unit was relatively challenging for me, as a student, because of the memorization heavy aspect of the muscles and naming of things like the tropomyosin protien or acetylcholine molecules. Thankfully, however, I was able to test the effectiveness of various studying techniques, for example, short and sweet reviewing every day, or diagram memorization. Now, I don't know how effective it is until I take the test itself, and thus I'm off.

P. E. Satire

While caffeine can increase your alertness so that, for example, you can drive late at night, it has a variety of side effects. Some are short-term and come with the rush of energy you get during the first few hours afterwards, like nervousness or anxiety; however, many of these effects are also long term in effect, such as caffeine resistance or reduced fertility (for females). This is one of the few performance enhancing substances that is actually permitted (in competitions) most likely due to its lesser effects on performance and decreased severity of side effects.

Chicken Dissection Lab Analysis 3/15 (the real pi day)

We took a cleaned, sanitized, chicken cadaver and began to pick it apart using a variety of dissection instruments while labeling any muscles we came across. For example, the contraction of the pectoralis major (pictured below)

pulls on the humerus of the chicken (as it is connected with a tendon) to lift the wing up. This is nearly identical to the human use of the same muscle, which moves the (much larger scale) humerus of a human. When looking at the tendons on both ends of the muscle, the origin always seemed to have more tendons stretching out from the muscle to anchor itself to the bone. Chicken muscles, and more specifically, the artificially selected variety that we humans have bred, seem extremely unbalanced. Looking at the pectoralis major and minor, they are easily five or six times the size and mass of any other muscle, while in humans, many of our muscles are similar in size to at least a few others. Also, the fact that the pectoralis major and minor are antagonists of each other and are located close enough to touch each other is confusing, as antagonist muscles in the human body are usually separated by a bone so that one can contract while the other relaxes. Lastly, while the arm limbs of a chicken are wings, the upper limbs of a human are arms. Even with this distinct difference, the muscle groups are essentially the same, with a lookalike elbow and wrist joint.

MUSCLE PHOTOS

Sternum (bone)
Pectoralis major - pulls humerus up
Pectoralis minor - antagonist of P. major (pulls down)

Trapezius - pulls shoulder back
Latissimus dorsi - group of muscles, extends and pulls arm

Deltoid - raise upper arm (aids P. major)

Biceps Brachii - flexes arm

Triceps humeralis - antagonist to biceps brachii, extends arm

Flexor carpi ulnaris - flexes hand/wing (at wrist)

Brachioradialis - hyperextends wrist (bend backwards)

Sartorius - flexes thigh to cross legs

Iliotibialis in birds or Tensor fasciae latae, Gluteus maximus and Iliotibial tract for humans - antagonist to sartorius, extends thigh and also flexes leg (knee)

Biceps femoris - flexes leg (high power)

Semimembranosus - extends thigh

Semitendinosus - extends thigh

Quadriceps femoris in birds or Vastus lateralis, intermedius and medialis; and Rectus femoris for humans - flexes thigh and extends leg

Gastrocnemius - extends foot and flexes lower portion of leg

Peroneus longus - extends foot

Tibalis anterior - flexes foot

Reading Response 3/13

What Happens When You Stretch
From http://people.bath.ac.uk/masrjb/Stretch/stretching_2.html#SEC13

Summary/Relate and Review
The stretching of muscles has the effect like tapping a stack of papers on a desk, aligning all of them back into a workable fashion. The muscles fibers that are straightened are intra and extrafusal muscle fibers. The stretching/elongating of the muscles starts at the middle, then diffuses towards the end, which is why holding the stretch or repeating it is necessary to really get a good stretch. This actually increases your power of contraction because that is usually measured by comparing the length before and after.

Quotes
"Nuclear bag fibers...-all the way to- gradually extend under prolonged tension"
These few sentences are highly descriptive and resemble an animation playing out.
"lengthening reaction which inhibits the muscles from contracting and causes them to relax"
The golgi tendon organ is responsible for the management of muscles, tendons, and ligaments from damage by tension strain.
"as you stretch, the collagen fibers in the connective tissue align themselves along the same line of force as the tension"
This is also another scene where I can imagine an animation for, as the pulling apart/ expansion of the sarcomeres increasing the length of the muscle.