Muscle & Tendon

Question 1

Describe gross skeletal muscle and tendon structure and how muscle and tendons are arranged in the locomotor system.

Answer 1

Skeletal muscle structure:
- Muscle belly - main unit of muscle
- Connective tissue (aponeurosis) - lies across the muscle and acts as an anchor that connects to the tendon (attaches muscle to bone)
- Epimysium - membrane below the fascia
- Fascicles - bundles of muscle fibres that are surrounded by the perimysium
- Perimysium - holds the muscle fibres together
- Endomysium - thin membrane that separates single muscle fibres
- Sarcolemma - cell membrane specific to muscle fibres
- Sarcomere - found in myofibrils and made up of contractile proteins in regular bundles

• Muscle fibre = muscle cell (contains the usual intracellular components)

Question 2

Discuss the roles of muscle in the body and particularly in locomotion.

Answer 2

• Force = the push/pull on and object with mass that causes it to change velocity
• Work = force x Δdistance
• Power = rate of performing work (Δwork/Δtime)

Question 3

Compare and contrast the structure and function of skeletal, smooth and cardiac muscle.

Answer 3

Skeletal:
- Have multiple peripheral nuclei for more efficient repair (central nuclei could indicate disease)
- Voluntary
- Striated (cross-hatched appearance)
- Regular parallel bundles of fibres (irregularity could indicate disease)

Cardiac:
- Striated
- Single central nucleus
- Involuntary
- Irregular arrangement with intercalated discs (important for conducting cardiac signals)

Smooth:
- No striations
- Single nucleus
- Involuntary
- Longer contractions (eg: for digestion)

Question 4

Explain how tendons contribute to locomotion.

Answer 4

• Tendons are made of collagen (primary matrix component)
• Tendons are mainly matrix and connective tissue
• Collagen fibrils -> collagen fibre -> primary fibre bundle (subfascicle) -> tendon

Roles of tendon:
- Minimising distal limb mass
- Joins muscle to bone
- Elastic energy storage
- Energy conservation
- Power amplification

• Tendons act to store and release elastic energy, reducing the cost of movement (economical) - they expend little energy when running
• Long tendons with high elasticity = short muscle fibres (short muscle fibres do not contract much - reducing energy cost)
• Tendons act as a catapult (elastic band) as they store energy slowly and release energy quickly when recoiling - amplifying power (muscle + tendon = max power)
• Power = rate of doing work
• Stretched tendons recoil faster than muscle shortens
• Small amount of work is done over a shorter time, so the power output is higher

Question 5

Describe muscle architectural design and explain how this influences muscle function.

Answer 5

• Not all skeletal muscles look the same (size; shape; number of bellies, tendinous origins/insertions; architecture) - its design is closely linked to its function
• Muscle architecture (the arrangement of muscle fibres) is a primary deterrent of muscle function (in terms of force, work and power) - but also encompasses: muscle volume, muscle moment arms and tendons

Pennate muscles:
- Feather-like
- Support (bigger animal = shorter pennate muscle = more support)
- Angular fibres towards aponeurosis/tendon
- Increases muscle physiological cross sectional area (PCSA) - higher PCSA = higher force (due to higher density)
- Short fibres decrease the contractile distance to be more economical

Parallel muscles:
- Power
- Moves joints
- Fibres run parallel to the line of pull from the muscle
- Multiple sarcomeres to increase length of total muscle fibre shortenings - allows more potential for performing muscle work
- Work = force x distance - if force is generated quickly then can produce large amounts of power
- Provides joints with large range of motion
- Can increase velocity of contraction (since speed = distance/time)
- eg: hamstring; pectoral; latissimus dorsi