1. Muscular System PCB 3703 Human Physiology S12-1 Human Physiology Muscular System

2. Muscular System PCB 3703 Human Physiology S12-2 Muscle Classification Functionally 1. Voluntarily 2. Involuntarily Structurally 1. Striated 2. Smooth Combined 1. Visceral 2. Cardiac 3. Skeletal

3. Muscular System PCB 3703 Human Physiology S12-3 Sarcomere ZZZ ZZZ I AA A (I)

4. Muscular System PCB 3703 Human Physiology S12-4 Categories of skeletal muscle actions Categories Actions 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. Muscular System PCB 3703 Human Physiology S12-5 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. Muscular System PCB 3703 Human Physiology S12-6 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. Muscular System PCB 3703 Human Physiology S12-7 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. Muscular System PCB 3703 Human Physiology S12-8 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. Muscular System PCB 3703 Human Physiology S12-9 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. Muscular System PCB 3703 Human Physiology S12-10 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 Z H

12. Muscular System PCB 3703 Human Physiology S12-12 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. Muscular System PCB 3703 Human Physiology S12-13 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. Cross Extensor reflex Flexor Reflex Inhibitory interneuron inhibited excited Reciprocal inhibition excited Repetitive after discharge (oscillatory circuit) From stimulus source Vasodilation Blood vessel Antidromic Reflex Red line Red flare wheel No motor activity Renshaw cell

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) Tetanus fatigue

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

17. Muscular System PCB 3703 Human Physiology S12-17 Lactic Acid in Cellular Respiration (Glycolysis) (LDH: Lactic Acid Dehydrogenase) Acetyl CoA Glucose Pyruvate Lactic Acid LDH 2 NADH O2O2

18. Muscular System PCB 3703 Human Physiology S12-18 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. Muscular System PCB 3703 Human Physiology S12-19 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. Muscular System PCB 3703 Human Physiology S12-20 Strength-Duration Curve (Excitability Curve) Utilization time (nerve) Chronaxie of nerve Utilization time (muscle) Chronaxie of muscle 2.0 1.5 1.0.5 0.1 0.20.3 Duration of stimulus (seconds) Strength of stimulus

21. 1.65  m 3.65  m 2.25  m 0 60 80 100 120 140 160 Percentage rest length 0.5 1.0 Relative tension 1.25  m 1.65  m 2.0  m 2.25  m 3.65  m