Functions of (Skeletal) Muscles

1. Functions of (Skeletal) Muscles • Movement • 2. Posture and Muscle Tone • 3. Heat Production

2. Movement Muscles move bones by pulling on them • Length of skeletal muscle shortens as muscle fibers • contract moves bones (levers) • Usually only insertion (more movable) bone moves • at end of muscle • Shortening of muscle pulls insertion bone towards • origin (more stationary) bone • Origin bone stays in place while insertion bone moves towards it. • Origin and Insertion can change depending on activity

6. Voluntary Muscle Movement Smooth Results from muscles working in pairs Prime Movers, and Synergists / Antagonists Prime Mover  main muscle responsible for mvmt Synergists  help prime movers Antagonists  work opposite of prime movers & synergists

7. As prime movers & synergists contract opposing antagonists relax When antagonist muscles contract, they produce movement opposite to prime movers & synergists

8. Example: biceps brachii (prime mover) brachialis (synergist/helper) triceps brachii (antagonist) Example: triceps brachii (prime mover) biceps brachii & brachialis (antagonists) Combined movement  smooth

9. Posture Muscle tone maintains posture through Tonic Contractions  don’t move body parts but keeps them in position Few muscle fibers shorten, muscle as a whole doesn’t shorten so no mvmt occurs Good posture  body parts help in position that favor best function Good posture: good appearance head/chest held high chin, abdomen, buttocks in knees slightly bent

10. Heat Production Important for body to maintain constant Body Temperature Metabolic Rxs / Cellular Fxs  maintain homeostasis Hypothermia ↓ BT Fever/Hyperthermia↑ BT Affects cellular activity/homeostasis (enzyme/protein Fx impaired) Muscle contraction produces most of heat required to maintain BT Sweat releases heat *integument Sudoriferous/Eccrine sweat glands

11. Motor Unit = motor neuron + muscle cells attached to it Muscle cells stimulated by nervous impulse that enters muscle fiber through motor neuron Neuromuscular Junction: Point of contact between motor neuron & muscle fiber Nerve impulses pass through neuromuscular junction and cause release of neurotransmitters (chemicals) that cause muscle to shorten/contract The contractile system for muscles is organized into a number of distinct parts, each of which is controlled by a single motor neuron and each motor neuron controls a large number of muscle fibers.

12. Action potential/impulse

13. Fatigue When muscles stimulated repeatedly w/out adequate rest  strength of contraction ↓ Prolonged periods of exercise ATP stores are depleted O2 can’t keep up, muscles produce lactic acid through (anaerobic respiration/glycolysis) O2 debt repaid by rapid breathing

14. Systems that play an essential role in movement Respiratory Circulatory Excretory Nervous Muscular Skeletal Muscle functions rely on other systems. No part of the body lives by or for itself! Now, can you explain HOW?

15. Muscle Stimulus Muscle cell stimulated contracts completely ALL OR NONE All cells in a muscle don’t contract simultaneously Principle of Graded Response Sub-minimal Stimulus  no contraction Minimal or Threshold Stimulus  strength of contraction ↑ according to graded response Maximal Stimulus  every muscle cell/fiber in entire muscle responds (from all or none) ??Supramaximal Stimulus  no additional effect on contraction b/c all muscle fibers already contracting

16. 5 Types of Skeletal Muscle Contraction 1. Tonic Contraction  muscle tone & posture (no movement)

17. Isometric Contraction  ↑ tension w/in muscle but no ↓ in muscle length • Results in larger muscles No movement No muscle shortening But ↑ internal tension

18. 3. Isotonic Contraction  Produces movement at joint and muscle shortens Ex. walking, running, breathing, lifting, twisting Insertion end of muscle moves toward point of origin (except for facial isotonic contractions)

19. Twitch Contraction  quick, jerky contraction • 1/10th second delay in response to stimulus • Muscles don’t shorten at stimulation but fraction of a second later • Reaches peak contraction then gradually resumes former length • Steps of a Twitch Contraction • stimulus  latent delay  contraction  relaxation

20. Tetanic Contractions (tetanus) • More sustained than twitch • Produced by series of stimuli bombarding muscle in rapid succession (~ 30 / minute) • Bacteria from puncture wound  tetanus or “lock jaw” results in severe cramping, almost continuous tetanic muscle contractions • Clostridium tetani (gram + bacillus, anaerobic)