Muscular Responses

1. Muscular Responses

2. Threshold Stimulus • any stimulus strong enough to initiate action potential • minimal strength of stimulation needed to cause a contraction

3. All-Or-None Response • individual muscle cells contract to their fullest extent when exposed to stimulus of threshold strength • muscle fibers do not partially contract • if stimulus is strong enough to initiate an action potential, a nerve impulse is transmitted along entire neuron at a constant strength

4. Twitch Contraction • brief contraction of all the muscle fibers in a motor unit • lasts only a fraction of a second • response to a single action potential in its motor unit • myogram is a record of a muscle contraction

5. Myogram(single muscle twitch)

6. Myogram • latent period - delay between the time that the stimulus was applied and the time that the muscle responded • period of contraction - muscle pulls at its attachments • period of relaxation - muscle returns to its former length

7. Tetanus or Tetanic Contraction • state of smooth sustained muscle contraction • muscle is stimulated very rapidly • no evidence of relaxation • point at which the muscle is unable to relax before next stimulus • results from the addition of Ca+2 released from sarcoplasmic reticulum

8. Twitch • brief muscular contraction followed by relaxation

9. Muscle Tone (tonus) • state of continuous partial contraction • muscles are never totally relaxed • important in maintaining posture • loss of tone - body will collapse

10. Types of Muscle Contractions

11. Isotonic Contractions • same as tone or tension • myofilaments slide freely • muscles shorten - movement occurs • Example: - bending, rotating arms, smiling

12. Isometric Contractions • muscles do not shorten • myofilaments do not move freely “skidding their wheels” • muscles are unable to slide because they are trying to move something more or less immovable • Example: - pushing against a wall

13. Types of Exercise

14. Effect of Exercise on Muscles • amount of work done by a muscle is reflected in the muscle itself • inactivity leads to weakness of muscle

15. Aerobic or Endurance • results in stronger, more flexible muscles • greater resistance to fatigue due to increased blood supply to muscles • benefits body metabolism • improves digestion, elimination

16. Aerobic or Endurance(cont.) • strengthens skeleton • heart enlarges - more blood pumped • gas exchange in lungs more efficient • no increase in muscle size

17. Weight Resistance Exercises • increase muscle mass • the use of immovable or slightly movable objects • requires little time, every other day • increase muscle size - increase strength • weight lifting will not increase endurance • will increase muscle definition