Muscles Flashcards
What is the hierarchical structure of muscle
Sarcomeres –> Myofibril –> Fibres –> Fascicles –> Muscle
What does the endomysium surround
Inidividual muscle fibres
What does the perimysium surround
Fascicles
What does the epimysium surround
Entire muscle - continuous with the tendon
What does the z-line/disk demarcate in sarcomeres
The lateral borders of the sarcomeres
Is actin the thin or thick filament
thin
Structure of actin
Contains two twisted alpha helices
Special feature of actin filaments?
They exhibit polarity
What 2 proteins are associated with actin
Troponin & Tropomyosin
What is the function of Titin in the sarcomere
Anchors the myosin filaments to the Z-line
What is the function of CapZ in the sarcomere
Covers the positive end of actin filaments
Shape and function of troponin
Globular protein
Binding site for Calcium
Shape and function of tropomyosin
Rod-like filamentous protein
Spirals round actin to stabilise it
Seals myosin binding sites on actin
What do we learn from looking at the length-tension curve on a sarcomere scale
At resting length, there is maximum contact between filaments so maximum tension can be generated
• Any shorter, there is excessive overlap between actin filaments which reduces the contact area and minimal forces can be generated
• Any longer (due to stretch), there is no overlap so there is NO contact area & minimal forces can be generated
What are the 3 components to a length-tension curve on a whole muscle scale
Active tension
Passive tension
Total tension
What is the active tension component of the length-tension curve on a whole muscle scale
Tension generated by muscle contraction
What is the passive tension component of the length-tension curve on a whole muscle scale
Increase in tension due to stretching of connective tissues (e.g. tendons, epimysium) when contracting a muscle that has been stretched past the ideal/resting length
What is active insufficiency
Failure to produce significant/sufficient force when the muscles are too short
What is passive insufficiency
Failure to produce significant/sufficient force when the muscles are too stretched
Describe the Hill Muscle model
A contractile element is in series with an elastic element and in parallel with another elastic element
Describe the Hill Muscle model
A contractile element is in series with an elastic element and they are both in parallel with another elastic element
What does the elastic element in series represent in the Hill Muscle model
This represents the tendons and cross-bridges
What does the elastic element in parallel represent in the Hill Muscle model
Connective tissue in the muscle (epimysium, endomysium and perimysium)
What factors affect force production in muscles? (3)
Length of muscle
Velocity of shortening
Amount of stimulation
What is concentric contraction and examples
Where movement is caused by shortening of the muscle
Extending the knee
Lifting a dumbbell close to the chest
What is an isometric contraction and examples
When there is no change in muscle length and thus no movement
Holding a bicep at 90 degrees to the body
What is the relationship between moment and joint angle in concentric contraction
The moment is in the same direction as joint angle change
What is an eccentric contraction and examples
When a muscle increases in length to decelerate joint movement
Extension phase of a bicep curl
What is the relationship between moment and joint angle in eccentric contraction
The moment is in the opposite direction as joint angle change
Place the 3 types of contractions in descending order of force they are able to produce
Eccentric > Isometric > Concentric
Why is eccentric able to produce the most force ? (4)
Greater cross bridging due to greater length
Contraction time (decreased rate of cross-bridge detachments)
Passive tension in elastic components
Elastic energy stored in the actin-myosin cross bridges
How many times greater is the max eccentric tension than an isometric
1.25x greater
How does velocity of ECCENTRIC contraction affect tension
Increasing velocity increases force up to a maximum
How does velocity of CONCENTRIC contraction affect tension
Increases velocity decreases force to ZERO
a rapid concentric contraction will generate no/minimal force
