The Muscle System I

1. The Muscle System I Structure and Function

2. Functions • Contraction (shortening) – the result of which is body movement, posture. • Thermogenesis – generation of heat ATP ADP + P + energy (work and heat)

3. Structure • Each skeletal muscle has four layers of CT • Each skeletal muscle is comprised of muscle cells called muscle fibers • The muscle fibers are organized into bundles called fascicles

4. Structure • Fascia – CT surrounding each muscle and separating muscles from each other

5. Structure • Epimysium – dense CT that surrounds the entire muscle…. just deep to the fascia • Perimysium – CT that surrounds and separates the fascicles • Endomysium – CT that surrounds each muscle fiber (muscle cell)

6. Structure of Muscle Fiber (cell) • Myofibrils – bundles of myofilaments • Myofilaments – actin and myosin….contractile proteins

7. Neuromuscular Junction (NMJ) • One of the properties of muscle is excitability or responsive to input • Nerve cells (neurons) provide the input that causes a muscle cell (fiber) to respond (contract) • The interface between the muscle fiber and the neuron is the NMJ • Every muscle fiber has a branch of a neuron that is control of it.

8. NMJ • How does a nerve impulse cause excitability in a muscle?

9. NMJ • Nerve releases neurotransmitters into synaptic cleft • Neurotransmitters bind to receptors on surface of muscle fibers and cause contraction of muscle • Acetylcholine (ACh) is the most common neurotransmitter

10. Muscle Terminology • Every muscle has 2 Attachments • Origin and insertion • When the muscle shortens one attachment moves and the other one doesn’t • Origin – the attachment that does not move • Insertion – the attachment that does move

11. Muscle Terminology • Agonist – the one muscle in a group of muscles that produces the most forceful reaction • Synergist – the other muscles that “help” the agonist do the same movement • Antagonist – a muscle whose action opposes that of another muscle.