Chapter 14 Flashcards
Muscle can be broken down into macro and micro structure. What differentiates the two?
Macrostructure can be seen without a microscope.
List and describe the elements of a muscle, including the connective tissue surrounding specific parts.
Muscle, surrounded by the Epimysium, is made up of may different fascicles. The different fascicles, surrounded by the perimysium, are made up of several muscle fibres. Muscle fibres, each surrounded by the endomysium, are comprised of myofibrils bundled together. Each myofibril is comprised of myofilaments bundled together. The myofilament is made of of sarcomeres which are placed end to end.
What is deemed the functional unit of a muscle?
The sarcomere, as it is the smallest fully functioning component of muscle.
What is the sliding filament theory?
The act of performing work by muscles is called the sliding filament theory (applying force, causing the muscle unit to displace). This is achieved at the level of the sarcomere, with interactions between the actin and myosin filaments.
Myosin will grab onto actin and pull, which generates force. If the filaments slide, there is a change in displacement, therefore the force generated performs work.
What comprises a sarcomere?
Within a sarcomere, there are two sets of myosin filaments and two sets of actin filaments.
The two sets of myosin filaments are held together in the middle by the M-line (one set sticks out on the left of the M-line and one on the right).
The actin filaments are on either end of the sarcomere.
Actin filaments from one sarcomere, are held to actin filaments of the adjacent sarcomere by the Z-disk.
Describe the interaction between myosin and actin during muscle contraction.
Myosin, called the “thick filament” has heads that protrude out. The myosin heads grab onto an actin filament, firing a cross-bridge (each cross-bridge formed can generate force, thus more cross-bridges means more force can be produced). Once the cross-bridge is formed, the myosin head will pull on the actin filament causing a power-stroke.
If the actin slides in the direction that the myosin head is pulling, that is a concentric contraction (can also have eccentric and isometric)
How big is a single sarcomere?
Between 1 and 4.5 micrometers
What four regions comprise a force-length relation graph?
1 - ascending limb I
2 - ascending limb II
3 - Plataeu region
4 - Descending limb
Describe the plateau region of the force-length relationship.
In the plateau region, the actin and myosin filaments are overlapped so that all myosin heads can form cross-bridges with the actin filaments. At this length, the maximum number of cross-bridges can be formed and thus the sarcomere can generate maximum force.
What is happening to the sarcomere on the descending limb?
The sarcomere lengthens, with the Z-discs moving away from the M-line. The myosin and actin filaments do not completely overlap, and less cross-bridges can form. The further they lengthen apart, the less force can be produced.
What is happening to the sarcomere on the ascending limb II?
As the sarcomere shortens, the Z-discs move closer to the M-line. Although all of the myosin filaments can form cross-bridges, the actin filaments start to bunch up and push outward against each other. As a result, less force is produced.
What is happening to the sarcomere on the ascending limb I?
Eventually, the Z-discs get so close to the M-line that the Z-discs themselves will push against the myosin filaments, further reducing the force that can be generated by the sarcomere.
True or false: The force generating capability is maximized for each uncle in anatomical position.
False. Sarcomere length in anatomical position varies by muscle. Thus force-generating ability may not be optimal in anatomical position. (Some on ascending or descending limb ect).
Where are the gastrocnemius and soleus located on the force-length relation in anatomical position?
Both the gastrocnemius and the soleus are located on the plateau region in anatomical position, meaning they are strongest in a neutral position.
Why is it less effective to train calf-raises on a flat surface?
Because, training is limited to the ascending limb. Strengthening the calf muscles from a dorsiflexed position is more effective and targets both the ascending and descending limbs.
Where are the major hand and finger flexors on the force-length relation in anatomical position?
They are on the short end of the plateau region (corner of plateau and ascending limb) in anatomical position. As the wrist extends, the muscles are stretched and slide along the long end of the plateau region (towards the descending limb).
When is grip strength strongest?
With fingers only slightly flexed and the wrists slightly extended (hook grip).
Why are most gripping tasks not suitable for human anatomy?
Manny gripping tasks require the fingers to be in considerable flexion - eg barbells, dumbbells. This is also the case with many hand tools.
Thus, many individuals who regularly perform weight training do not have a particularly strong grip, because training on the ascending limb is less effective.
Describe the vasti muscles in relation to the force-length relationship in anatomical neutral versus other positions.
In anatomical position, the vasti muscles are on the descending limb, meaning the sarcomeres are too short for a forceful contraction.
As the knee goes into flexion, the sarcomeres lengthen, reaching their plateau from 60-90 degrees of knee flexion , before sliding down the ascending limb.
because the vasti muscles are used over a large range of motion, their starting point on ascending limb 1 allows them to exert 80% or more max strength throughout knee flexion ROM
Why is the psoas major unique?
It is the only muscle that attaches to the lower extremity and the lumbar spine.
Where is the psoas major in terms of the force-length relationship, in anatomical neutral and other positions?
In anatomical neutral, the psoas major is on the descending limb (too long). Thus flexing the lumbar spine or hip bring the psoas major closer to its plateau (ability to generate maximum force).
In the 1970’s, it was proposed that performing sit-ups with knees bent would lessen the involvement of the psoas major, allowing for more focus on the abdominal muscles. Why is this idea wrong?
The psoas major is stretched out and unable to contribute to spine flexion movements as much. It is more likely to contribute/generate more of the force, when the hip is flexed. This is because when the hip is flexed, the psoas major is at an optimal length.
How should sit-ups be done to target the abdominals?
They should be done in an extended position. The sit-up should only be a partial crunch, as to not flex the hip too much.
Training the psoas major in what ROM is most effective?
Something that moves through hip flexion near 90 degrees.
