Anatomy of a Muscle

1. Anatomy of a Muscle REC3010 – Human Movement

2. REC3010 – Human Movement Muscles in the Body • We know that there are 3 different types of muscle in the body • Smooth Muscle – Found in the organs • Cardiac Muscle – Found in the walls of the heart • Skeletal Muscle – Found attached to the skeleton • Even though all muscle moves and acts in similar fashion, we are going to focus on Skeletal Muscle

3. REC3010 – Human Movement Skeletal Muscle • The human body is made up of approximately 600 different skeletal muscles. • This number varies depends on what source is used. (350 – 650) • The muscle cells • Are striated and tubular • Have many nuclei • Are very long and have many nucleus • Are often referred to as fibres, rather than cells

4. REC3010 – Human Movement The Hierarchy of Muscle Structure

5. REC3010 – Human Movement The Hierarchy of Muscle Structure d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly

6. REC3010 – Human Movement Holding The Muscle Together • All muscle components are held together with connective tissue • Connective tissue is made up of • Epimysium • Surrounds entire muscle • Perimysium • Surrounds bundles of muscle fibers • Fascicles • Endomysium • Surrounds individual muscle fibers

7. REC3010 – Human Movement Holding The Muscle Together

8. REC3010 – Human Movement The Muscle Fibre

9. REC3010 – Human Movement The Muscle Fibre

10. REC3010 – Human Movement The Muscle Fibre – Sacromere

11. REC3010 – Human Movement The Muscle Fibre – Thin Myofilament

12. REC3010 – Human Movement The Muscle Fibre – Thick Myofilament

13. REC3010 – Human Movement Movement of the Muscle • Text

14. REC3010 – Human Movement Sliding Filament Mechanism • Myosin heads attach to actin molecules • at binding (active) site • Myosin “pulls” on actin, causing thin myofilaments to slide across thick myofilaments, towards the center of the sarcomere • Sarcomere shortens, I bands get smaller, H zone gets smaller, & zone of overlap increases

15. REC3010 – Human Movement Sliding Filament Mechanism • As sarcomeres shorten, myofibril shortens. • As myofibrils shorten, so does muscle fibre. • Once a muscle fiber begins to contract, it will contract maximally. • This is known as the “all or none” principle.

16. REC3010 – Human Movement Neuromuscular junction • Location where the neuron activates muscle to contract

17. REC3010 – Human Movement Muscle Stimulation • Muscles require large amounts of interaction with nerves and motor neurons in order to function • Involuntary muscle movements are initiated and regulated via the autonomic nervous system • Voluntary muscle movements are initiated and regulated via the somatic nervous system

18. REC3010 – Human Movement Autonomic Nervous System • Also referred to as the involuntary nervous system • Involved with unconscious sensations and actions • Controls and regulates the functions of most internal organs and stimuli responses

19. REC3010 – Human Movement Somatic Nervous System • Also referred to as the voluntary nervous system • Involved with conscious sensations and actions • Controls and regulates the functions of most skeletal muscle and movement patterns

20. REC3010 – Human Movement Causing a Muscle to Move • Skeletal muscles are made up of thousands of muscle fibers • A single motor neuron may directly control a few fibers within a muscle, or hundreds to thousands of muscle fibers • All of the muscle fibers controlled by a single motor neuron constitute a motor unit

21. REC3010 – Human Movement Causing a Muscle to Move • The size of the motor unit determines how fine the control of movement can be • small motor units  precise control • e.g. eye muscles - 1:1 muscle/nerve ratio • large motor units gross control • e.g. hamstring muscle - 300:1 muscle/nerve ratio

22. REC3010 – Human Movement Causing a Muscle to Move • Recruitmentis the ability to activate more motor units as more force (tension) needs to be generated • There are always some motor units active, even when at rest. This creates a resting tension known as muscle tone, which helps stabilize bones & joints, & prevents atrophy

23. REC3010 – Human Movement Muscle Contraction • When skeletal muscles contract, they may produce two types of contractions • Isotonic contraction • Isometric contraction

24. REC3010 – Human Movement Muscle Contraction • Isotonic contraction • As tension increases (more motor units recruited), length of muscle changes usually resulting in movement of a joint. The tension (load) on a muscle stays constant (iso = same, tonic = tension) during a movement. • Example: lifting a baby, picking up object, walking, etc. • Isometric contraction • no change in length of muscle even as tension increases. The length of a muscle stays constant (iso = same, metric = length) during a “contraction” • Necessary in everyday life to counteract effects of gravity • Example: holding a baby at arms length, pushing against a closed door