Skeletal Muscle Structure and Function

Question 1

What do the epi-, peri- and endomysial layers of connective tissue envelop and what are they continuous with at either end of the muscle belly?

Answer 1

Endomysium – Each Muscle fibre cell

• Perimysium – Group of muscle fibers, forming a fascicle
• Epimysium – encircles all the fascicles to form a complete muscle
• Tendons

Question 2

What protein(s) is/are likely to limit the lengthening capacity of a relaxed muscle?

Answer 2

• Actin and myosin
• Tropomyosin’s
• Lack of ATP

Question 3

Describe longitudinal and lateral force transmission (what structures transmit force in each of the above)?

Answer 3

• Longitudinal – myotendinous junctions

- Lateral – myofibers to the extracellular matrix

Question 4

What is the tension generating step of x-bridge cycling? Where is the tension generated?

Answer 4

• When a sarcomere contracts, myosin heads attach to actin to form cross-bridges. Then, the thin filaments slide over the thick filaments as the heads pull the actin. This results in sarcomere shortening, creating the tension of the muscle contraction.

Question 5

What happens to series elastic elements of skeletal muscle during a heavily resisted ‘contraction’?

Answer 5

• The series elastic component (SEC), residing in the tendons, acts as a spring to store elastic energy when a tensed muscle is stretched

Question 6

10. Define the motor unit and describe the different types of motor units found in human skeletal muscle.

Answer 6

• A motor unit is made up of a motor neuron and all of the skeletal muscle fibers innervated by the neuron’s axon terminals
• FF – Fast Fatigable
• FR – Fast Fatigue Resistant
• FI – Fast intermediate
• S – Slow oxidative

Question 7

Describe how skeletal muscle force is regulated in voluntary contractions. (This is a question requires a detailed answer and is a prime candidate for a final exam question!).

Answer 7

• Skeletal muscle force is regulated by the level of neural drive delivered to the motor neuron pool from the brain and the peripheral nervous system. With an increase in drive to the motor neurons there is a progressive increase in both the number of activated motor units and their firing rates. An increase in the number of activated motor units increases force as a consequence of increasing the number of muscle fibres that generate tension. With an increase in motor unit firing rate (the number of action potentials transmitted along the motor neurone per second) consecutive twitches fuse together and summate to a greater extent because there is less series elastic slackness to overcome when less time transpires between consecutive twitches.

Question 8

Define force development

Answer 8

How fast an athlete can develop force