1. Muscular System

3. Skeletal Muscle 3 types of muscle Voluntary Striated Muscle Tissue
Multiple nuclei

4. Cardiac Muscle Involuntary Striated Muscle Tissue
Intercalated discs: special connections between each muscle fiber, allowing for the proper muscle contraction.
ONLY in the heart.

5. Smooth Muscle: Involuntary Not striated Spindle-shaped cells
Single nuclei per cell.

6. Smooth muscle is held in position and compartmentalized by fascia.
Connective Tissues, CT
Smooth muscle is held in position and compartmentalized by fascia.
Fascia: sheet like layers of CT.

7. The CT that extends beyond the muscle to form a cord like tissue is a tendon.
Tendon: attach muscles to the periosteum of bones.

8. The CT that extends beyond the independent muscle and forms a broader fibrous sheet like covering over adjacent muscles is aponeurosis.
Aponeurosis: spans more than one muscle.

9. Structure
All the parts of skeletal muscle are enclosed in layers of CT. This forms a network that spans the entire muscular system.

10. Structure: skeletal muscle
Fascicle
Muscle fiber
Myofibril
Sarcomere

11. Each muscle has specific layers of membrane:
Epimysium (around the muscle)
Perimysium (around the fascicle)
Endomysium (around the muscle fiber)

12. Each muscle fiber is a single cell of a muscle
Each muscle fiber is a single cell of a muscle. It responds to stimulation by contracting and relaxing.

13. Immediately below the cell membrane or sarcolemma is the sarcoplasm of the fiber. This sarcoplasm contains the oval nuclei, mitochondria, and myofibrils.

14. The key to contraction Myofibrils, protein filaments
Myosin: molecules composed of protein strands with globular parts.
A band
Dark band

15. Actin: molecules composed of protein with ADP attached to its surface.
I band
Light band

16. Sarcomere The segment of a myofibril between two consecutive Z-lines.
Actin filaments are attached to the Z-lines.
This arrangement leads to the striated appearance.

17. Carrying the impulse
To carry the impulse there are membranous channels within the cytoplasm of each muscle fiber, sarcoplasmic reticulum and transverse tubules.

18. Sarcoplasmic reticulum Transverse tubules
Run parallel to the myofibril
Transverse tubules
Extend inward passing through muscle fibers.

19. The Activators
There must be a connection between the muscular system and the nervous system.
Neuromuscular junction

20. Neuromuscular Junction
Specialized connection of a nerve fiber and a muscle fiber.
Motor end plate: specialized end of the muscle fiber

21. Follow a nervous impulse…
Synaptic Clefts: cup like branches of the motor end plate specialized to receive neurotransmitter.
Follow a nervous impulse…

22. The nerves we are dealing with are called motor fibers.
One motor fiber may be connected to many muscle fibers.

23. Impulse transmission
When a motor nerve fiber transmits an impulse, all of the muscle fibers connected to it, are stimulated to contract simultaneously.

24. Motor Unit
The motor neuron and the muscle fibers controlled by it make up a motor unit.

25. How does a muscle contract?
Myosin filament globular heads form crossbridges
Actin filament attachment sites allow for attachment of these crossbridges.

26. Sliding Filament Theory
Myosin head is bent back and up to attach with an actin active site. The myosin head pulls back contracting the sarcomere.

27. The cross bridge is broken. The myosin head straightens out
The cross bridge is broken. The myosin head straightens out. A new linkage can now be formed for further contraction.

28. Stimulus for this contraction
Stimulus via neurotransmitter: Acetylcholine.
Synthesized in the cytoplasm of the motor neuron

29. Stored in synaptic vesicles at the distal end of the motor neuron.
Travel:
Diffuses across the gap, synaptic cleft.
Received by receptors on the motor end plate.

30. Stimulus = Contraction

31. Control
Troponin wants to attach to Ca
Troponin is attached to tropomyosin
Tropomyosin is attached to actin
Myosin wants to attach to actin

32. The sarcoplasmic reticulum has a high [Ca] the membrane becomes permeable to the Ca ions and they flow into the sarcoplasm of the muscle fiber.

33. Tropomyosin blocks the actin attachment sites.
Troponin on the tropomyosin has Ca attachment sites
When [Ca] goes up the troponin binds to it.

34. Tropomyosin is lifted the myosin-actin binding sites become available
 linkage
 muscle contraction

35. Reverse…
Ca ions are quickly moved from the sarcoplasm back to the sarcoplasmic reticulum by a Ca pump.
Transport?

36. Troponin and tropomyosin return to myosin
Myosin and actin attachment is broken
Myosin and actin slide apart
 relaxation of the muscle fiber

37. Acetylcholine is broken down by acetylcholinesterase
Don’t forget about…
rhigamortis
Acetylcholine is broken down by acetylcholinesterase
Botulism

38. Botulism
Prevents the release of acetylcholine.
NO muscle stimulation
NO contraction
 NO…

39. ATP is the energy source of the muscle
Regeneration of ATP requires creatine phosphate and the cellular respiration of glucose.

40. Respiration of glucose
If the muscle is lacking O
Glucose  pyruvic acid
Pyruvic acid  lactic acid
Lactic acid  muscle soreness

41. If O had become available at any time during this cycle, it could be reversed.

42. Hemoglobin carries O in the blood = red.
Hold onto the O.
Hemoglobin carries O in the blood = red.
Myoglobin holds O in the muscle = reddish brown.
This compensates for the blood lost during contraction.

43. Muscular Response
Threshold stimulus: minimal strength needed to cause contraction

44. All-or-none Response: the stimulated fiber always contracts completely, or not at all.
If stimulus is increased, recruitment occurs.

45. Recruitment: multiple fibers contracting simultaneously.

46. Types of Contraction
Twitch: a single contraction
Tetanic: sustained forceful contraction without relaxation
Muscle Tone: a continuous slight contraction

47. Muscle tone
Caused by continuous nervous impulse to a few fibers from the spinal cord (the brain is not involved)

48. Skeletal Muscle Actions
Teamwork:
Prime mover: responsible for the bulk of movement
Synergist: helpers
Antagonist: work against, move in the opposite direction

49. Cardiac Only in the heart
Intercalated discs have a very low threshold, act on impulse rapidly.
Self-exciting, responsible for the rhythmic continuous beating.

50. Slower to contract and slower to relax.
Smooth Muscle
Slower to contract and slower to relax.
Maintains force for a longer period of time with the same amount of ATP.
Force is not effected by stretch.

51. 2 Types of Smooth Muscle Multi-unit: Less organized
Contains blood vessels

52. Visceral: Sheets of spindles Hollow organs
Self-exciting wave like rhythmic contraction
Tubular organs  peristalsis