Human Physiology Muscular System

1. Human PhysiologyMuscular System

2. Muscle Classification • Functionally • 1. Voluntarily • 2. Involuntarily • Structurally • 1. Striated • 2. Smooth • Combined • 1. Visceral • 2. Cardiac • 3. Skeletal

3. Sarcomere Z A Z A Z A (I) I Z Z Z

4. Categories of skeletal muscle actions • CategoriesActions • Extensor Increases the angle at a joint • Flexor Decreases the angle at a joint • Abductor Moves limb away from midline of body • Adductor Moves limb toward midline of body • Levator Moves insertion upward • Depressor Moves insertion downward • Rotator Rotates a bone along its axis • Sphincter Constricts an opening

5. Myofilaments • 1. Myosin: 110Å thick; confined to the A-band. (Mole. wt. 500,000 deltons; 200 molecules/myofilament) • A. Tail- 800Å long, composed of a double helix • B. Head (cross bridges)-600Å terminating in a globular double structure. Contains binding sites for actin & ATP

6. Myofilaments • 2. Actin: 60A thick; runs from Z-line (disc) to just inside A-band. Mole wt. 60,000 deltons. • G-actin (globular units): contracted form • F-actin (fibrous polymers): relaxed form • Actin associated proteins • A. Tropomyosin • B. Troponin

7. Mechanics of Muscle Contraction • 1. An action potential is generated by a motor nerve. • 2. This causes the release of acetylcholine from the axon terminals at the neuromuscular junctions. • 3. This Ach causes an increase in membrane permeability at the motor-end plate, causing the production of an end-plate potential (EPP).

8. Mechanics of Muscle Contraction • 4. The EPP depolarizes the fiber membrane (sarcolemma) causing a muscle action potential which spreads over the entire surface of the fiber membrane. • 5. This depolarizes the T-tubules, causing ionic conduction through their extracellular fluid, and the release of inositol triphosphate as a second messenger.

9. Mechanics of Muscle Contraction • 6. Ca++ is then released from the endoplasmic reticular fluid of the cisterns (lateral sacs) into the surrounding myofibril. • 7. Ca++ binds to the actin associated protein troponin, allowing the attachment of actin to the myosin-ATP complex to form a strong ATPase. • 8. The ATPase splits ATP, releasing the energy needed for the movement of the myosin cross bridges.

10. Mechanics of Muscle Contraction • 9. Energy from creatine phosphate replaces ADP on the myosin cross bridges, thereby breaking the A-M bond and allowing the cross bridges to relax. • 10. The Ca++ are forced back into the walls of the longitudinal tubules by active transport. • 11. This restores the inhibitory action of the troponin-tropomyosin complex.

11. A I H Z

12. Selective Terms • 1. Motor Unit: consists of all the muscle fibers innervated by terminals from a single axon. (Range from 23 - 2,000 fibers) • 2. All or None Law: at or above threshold levels; the degree of contractile response of a single muscle fiber (or motor unit) is independent of stimulus strength • 3. Tension: force exerted by a contracting muscle • 4. Load: force exerted on a muscle by the weight of an object • 5. Isotonic contraction (same tension): the tension developed by the contracting is greater than the load. Therefore, the muscle shortens.

13. Selective Terms • 6. Isometric contraction (same length): the strength of the load is greater than the tension of the muscle. Therefore, the muscle remains at the same length. • 7. Muscle spindle apparatus: a series of small spindle shaped fibers within the muscle for detecting changes in the length (stretch) of the muscle. • 8. Golgi tendon organ: tension receptors located in tendons, and activated by the pull of a contracting muscle

14. Flexor Reflex Cross Extensor reflex From stimulus source Repetitive after discharge (oscillatory circuit) Inhibitory interneuron excited inhibited Reciprocal inhibition excited Vasodilation Blood vessel Antidromic Reflex Renshaw cell Red line Red flare wheel No motor activity

15. Impulse Responses of Skeletal Muscles 1) Twitch Contraction phase (0.04 sec) Relaxation phase (0.05 sec) Latent period (0.002 sec) 2) Summation a) wave (frequency) fatigue Tetanus

16. b) Multiple motor unit (recruitment) intensity 5 1. Subthreshold 2. Threshold 3. suprathreshold 4. Maximal 5. Supramaximal 4 3 2 1 Voltage c) Treppe (staircase phenomenon) 2 stimuli/sec

17. Lactic Acid in Cellular Respiration (Glycolysis) • (LDH: Lactic Acid Dehydrogenase) 2 NADH Lactic Acid Glucose Pyruvate LDH O2 Acetyl CoA

18. Glycolysis [cont.] • Fate of Lactic Acid • 1. Used by the heart for energy: it can convert lactic acid back to pyruvate. • 2. Decarboxylation (buffering action):  CO2 which  ventilation • 3. Converted back to pyruvate then to TCA

19. Glycolysis [cont.] • Pain • 1. Bradykinin: a peptide released from damaged tissue. It excites the pain nerve endings. • 2. Ischemia: If the brachial artery is occluded & the muscles of the forearm exercised, pain will begin in 15 seconds. With no exercise it takes 4 minutes.

20. Strength-Duration Curve (Excitability Curve) Utilization time (nerve) Utilization time (muscle) Chronaxie of nerve 2.0 Chronaxie of muscle Strength of stimulus 1.5 1.0 .5 0.1 0.2 0.3 Duration of stimulus (seconds)

21. 2.25m 2.0m 1.65m 1.0 Relative tension 0.5 3.65m 1.25m 80100120 140 160 0 60 Percentage rest length 1.65 m 2.25 m 3.65 m