1. Fibers: composed of myofibrils
Myofibrils composed of protein filaments:
Myosin: thick filaments
Actin: thin filaments

2. Muscle structure:
Actin
Muscle
Muscle fiber
Myofibril
Myosin

3. Muscle Structure

4. Sarcomere: the muscle contraciton unit

5. Sarcomere Components A Band: area of myosin filaments
I Band: area between the “A” bands – both actin and myosin
H Zone: thickened area of myosin
Z line: center of the I band
Z to Z: equals one sarcomere

6. Muscle Contraction Components

7. Motor Unit: muscle fiber and motor neuron
1. Motor Neurons: cells of the nervous system – pass impulse from brain or spinal cord
Motor Unit: muscle fiber and motor neuron

8. 2. Sarcolemma: the cell membrane of muscle fibers

9. 3. Transverse Tubule: deep invaginations, enfoldings of the sarcolemma

10. 4. Sarcoplasmic Reticulum: network of muscle contractions tubules that carry the muscle impulse

11. 5. Mitochondria: cellular organelle which synthesizes adenosine triphosphate (ATP)

12. 6. Tropomyosin: a protein attached to the actin filament which blocks myosin-binding sites

13. 7. Troponin: a protein complex located on the tropomyosin
-Receives calcium from the sarcoplasmic reticulum

14. 8. Myosin Cross Bridge: portion of the myosin filament which binds to the actin binding site

15. 9. Calcium: ions released from sarcoplasm – bind to troponin – clear the myosin binding sites

16. 10. Acetylcholine (ACh): the neurotransmitter released by the motor neurons

17. Neuromuscular Junction

18. Sliding Filament Contraction Theory
General Sequence of Events:
-neural response is sent to the sarcoplasmic reticulum
-thin filament (actin) slides past the thick filament (myosin)
“I” band becomes smaller
Actin/myosin slide back and forth

19. Sliding Filament Contraction Theory
Detailed Sequence of Events: 8 steps 1. Neural impulse (polarization/depolarization) from motor neuron moves to the synaptic knob and releases acetylcholine (ACh) 2. ACh carries the impulse across the synaptic cleft to the sarcolemma

20. Sliding Filament Contraction Theory
ACh carries the impulse along the sarcolemma to the transverse tubules. The ACh enters the transverse tubule to the sarcoplasmic reticulum.
ACh activates the sarcoplasmic reticulum to release Ca++ (calcium ions)
Ca++ binds to the troponin, moving the tropomyosin off of the binding sites on actin

21. Sliding Filament Contraction Theory
Cross bridge of myosin connects to actin
The cross bridge performs a “power stroke” – which shortens the sarcomere
-ATP  ADP is the energy source
8. Myosin grabs actin and pulls – the muscle contracts

22. Relaxation Impulse stops – no ACh
ACh in tubules breaks down by acetylcholine esterase (AChE)
Ca++ reabsorbed by sarcoplasmic reticulum
Sarcomere lengthens and relaxes

23. Smooth Muscle:
FX: 1. move food through intestine 2. adjust the eye for light 3. move blood through vessels 4. moves babies from uterus through birth canal

24. Characteristics/Location
Muscle in hollow organs (except heart)
Digestive, urinary, circulatory and reproductive
One nucleus per myocyte
No striations/sarcomeres/ “T” tubules
Fusiform shape
lay in sheets at right angles
Alternating contraction/relaxation of sheets causes elongation – peristalsis
Ca++ comes from extra-cellular fluid

25. Cardiac Muscle:
-makes up most of the heart -has striations like skeletal muscle -myocytes branched and interconnecting -each myocyte stimulates its neighbor – chain reaction

26. Cardiac Muscle: Large T-tubules admit more Ca++ for contraction
Sino-Atrial node: bundle of nervous tissue that stimulates contraction