Chapter 11 Muscle Tissue

1. Chapter 11Muscle Tissue • Muscles can only do two things: contract and ________. • Study of muscles = myology

2. Introduction to Muscle • Movement is a fundamental characteristics of all living things • Types of muscle • skeletal • cardiac • Smooth

3. 5 Characteristics of Muscle • 1. Responsiveness • capable of response to chemical signals, stretch or other signals & being able to respond • 2. Conductivity • electrical excitation travels along the muscle fiber • 3. Contractility -- shortens when stimulated • 4. Extensibility -- capable of being stretched • 5. Elasticity -- returns to its original resting length after being stretched

5. MICROSCOPIC MUSCLE • 1. Skeletal muscle consists of fibers (cells) covered by a sarcolemma and contain sarcoplasm, nuclei, sarcoplasmic reticulum, and transverse tubules. • These are involved in the pathway of the excitation-contraction mechanism. • 2. Each fiber contains thin and thick myofilaments. • The filaments are compartmentalized into sarcomeres

6. Micro Muscles (Cont.) • 3. Thin filaments are composed of actin, tropomyosin, and troponin; thick filaments consist of myosin. • a. Actin and myosin are the two contractile proteins in muscle. • b. Tropomyosin and troponin are muscle's regulatory proteins. • c. Projecting myosin heads are called cross bridges and contain actin- and ATP-binding sites.

7. CONTRACTION OF MUSCLE • Sliding Filament Mechanism: • 1. During muscle contraction, myosin cross bridges pull on thin filaments, causing them to slide inward toward the H zone; • a. Z discs come toward each other and the sarcomere shortens, but the thick and thin filaments do not change in length. • b. The sliding of filaments and shortening of sarcomeres causes the shortening of the whole muscle fiber and ultimately the entire muscle. • Note: Muscles do not fold

8. I A I StrIAtions • Dark A bands alternating with lighter I bands give muscle it’s striated appearance • “A” band is thick filament (Thick letter) • “I” band is thin filament (Thin letter) • Found in ______ and ______ • Not found in ________

9. Neuromuscular Junction (Synapse) I • The Neuromuscular Junction (NMJ): • 1. A motor neuron transmits a nerve impulse (action potential) to a skeletal muscle where the nerve impulse serves as a stimulus for contraction. • 2. Excitable cells (neurons and muscle fibers) make contact and communicate at specialized region called a synapse. • At the synapse electrical energy from the neuron is converted to chemical energy (Ach) and finally resulting in mechanical energy of the muscle

10. Neuromuscular Junction II • 3. A neuromuscular junction (NMJ=synapse) refers to an axon terminal of a motor neuron and the portion of the muscle fiber sarcolemma in closeapproximation with it (motor end plate) • (NO TOUCHING, PLEASE!) • 4. Acetylcholine (ACh), released by the synaptic vesicles of a motor neuron in response to an action potential, triggers a muscle action potential.

11. Muscle Contraction • When a nerve impulse (nerve action potential) reaches an axon terminal: • The synaptic vesicles of the terminal release acetylcholine (ACh), • 1) that diffuses across the cleft and binds to chemically gated Na+ channels on the sarcolemma, • 2) Plasma membranes exhibit voltage changes in response to stimulation • ion gates open allowing Na+ to rush into cell and then K+ to rush out of cell (quick up-and-down voltage shift is called action potential)

12. Muscle Contraction (Cont.) • This then travels into the transverse tubules and causes some of the Ca2+ stored in the sarcoplasmic reticulum to be released into the sarcoplasm. • 1) This causes the relaxed filaments to interact and start pulling. • 2) The released calcium ions that combine with troponin, causing it to pull on tropomyosin to change its orientation, thus exposing myosin-binding sites on actin. • 3) This allows the myosin head to bind to actin.

13. Muscle Contraction/ Relaxation • The source of energy for muscle contraction is ATP (Adenosine triphosphate) • ATPase splits ATP into ADP + P and the released energy activates myosin cross bridges. • Relaxation is brought about when ACh is broken down by the enzyme acetylcholinesterase (AChE)

14. Motor Unit • A motor neuron & the muscle fibers it innervates • Fine control • small motor units contain as few as 20 muscle fibers per one nerve fiber • eye muscles • Strength (gross) control • gastrocnemius muscle has 1000 fibers perone nerve fiber

15. Stretching • Muscle Over-contracted causes weakness: • thick filaments can’t slide • “The longer the stronger” • Muscle over-stretched causes weakness: • No overlap of filaments- does not allow for cross bridges to form • Remedy= • Stretch after exercise “Neuromuscular Junction”

16. Recruitment • According to the all-or-none principle, individual muscle fibers contract to their fullest extent; they do not partially contract. • Muscle as a whole can have graded contractions to perform different tasks i.e lift a glass of milk versus a whole gallon of milk The process of increasing the number of active motor units is called recruitment.

17. Isometric & Isotonic Contractions • Isometric muscle contraction • develops tension without changing length • Isotonic muscle contraction • tension development while shortening = concentric • tension development while lengthening = eccentric

18. ATP Sources • All muscle contraction depends on ATP • Pathways of ATP synthesis • anaerobic fermentation (ATP production limited) • occurs without oxygen, but produces toxic lactic acid • aerobic respiration (far more ATP produced) • requires continuous oxygen supply, produces H2O & CO2

19. Muscle Fatigue and Soreness • The inability of a muscle to maintain its strength of contraction or tension is called muscle fatigue. • 1. It occurs when a muscle cannot produce enough ATP to meet its needs. • Microscopic muscle damage appears to be a major contributing factor to muscle soreness which follows bouts of strenuous exercise. • Skeletal muscle fibers cannot divide and have limited powers of regeneration

20. Muscle Tone and Arnold • Hypotonia: decreased or lost muscle tone; flaccid muscles. • Atrophy is a wasting away of muscles and may be caused by disuse or severing of the nerve supply • Hypertonia: increased muscle tone and may be expressed as either spasticity (stiffness) or rigidity • Hypertrophy refers to an increase in the diameter of muscle fibers resulting from very forceful, repetitive muscular activity. (Arnold)

21. Muscular Dystrophy • Group of hereditary diseases in which skeletal muscles degenerate & are replaced with adipose • Mainly a disease of males • rarely live past 20 years of age • Diagnosis from: myogram which isa record of a muscle contraction

22. Myasthenia Gravis • Autoimmune disease where antibodies attack NMJ and bind ACh receptors • drooping eyelids and double vision • difficulty swallowing • weakness of the limbs • respiratory failure • Treated with cholinesterase inhibitors, thymus removal or immunosuppressive agents

23. Myasthenia Gravis Drooping eyelids (ptosis) and weakness of muscles of eye movement

24. DANGER • The use of anabolic steroids by athletes to increase muscle size, strength, and endurance has been shown to have very serious side effects, some of which are life-threatening.

25. Toxins & Paralysis • Pesticides contain cholinesterase inhibitors that bind to acetylcholinesterase & prevent it from degrading ACh • spastic paralysis & possible suffocation • Tetanus or lockjaw is spastic paralysis caused by toxin of Clostridium bacteria • causes overstimulation of the muscles • Flaccid paralysis with limp muscles unable to contract caused by curare that competes with ACh • respiratory arrest

26. Rigor Mortis • Stiffening of the body beginning 3 to 4 hours after death. • peaks at 12 hours after death & diminishes over next 48 to 60 hours • Muscle relaxation requires ATP. True or False? • Why does ATP production stop with death? • Fibers remain contracted until myofilaments decay

27. ABNORMALS • Abnormal contractions of skeletal muscle include: • 1. spasm- involuntary contraction • 2. cramp- painful spasm • 3. tremor- rhythmic, involuntary, purposeless contraction • Intension tremor • Non-intension tremor • 4. fasciculation- involuntary, brief twitching, not associated with movement • ALS, MS, or normal • 5. tic- involuntary, brief movement