Anatomical Review of Muscle Cell anatomy

1. Anatomical Review of Muscle Cell anatomy

2. Fig. 12.1 Whole muscle = many muscle cells + CT

3. Fig. 12.15 Individual Muscle Cell—Anatomy Review

4. Fig. 12.6 Organization of actin and myosin filaments --Alternating and overlapping

5. Fig. 12.7 Organization of a sarcomere

6. Muscular System • Skeletal Muscles and associated connective tissue • Skeletal muscle cells=muscle fibers FUNCTIONS • Produces movement • (through contraction of cells) • Important in verbal and non-verbal communication • Stabilizes joints and maintains posture • (through contraction of cells) • Produces body heat • (through high levels of cellular respiration)

7. OVERVIEW OF SKELETAL MUSCLE ACTIVITY BrainMotor Neurons, synaptic activity--ACh Action Potential & propagation Ca+ channel activity ATP production/consumption sliding of actin & myosin filaments production of force and movement (sometimes)

8. CONTROL OF SKELETAL MUSCLES

9. Voluntary Motor Activity Originates in Frontal Lobe of cerebral cortex

10. Voluntary Muscle Contraction: • Neuron Activity Begins Frontal Lobe: • Upper motor neuron • Decussates in medulla (~80%) • Travels down spinal cord through anterior or lateral corticospinal tracts to lower motor neuron • Synapse with lower motor neuron • Lower motor neuron travels through nerve to effector muscle • Forms synapse—Neuromuscular Junction—with muscle • NT= Ach binds to nicotinic receptors

11. Neurological Control of Skeletal Muscle • CNS (brain and spinal cord): generate motor commands that will signal muscle cells to contract • Voluntary Activity • Frontal lobe: initiates voluntary muscle activity • Basal nuclei: coordinates voluntary muscle activity • Thalamus: involved with coordination of voluntary muscle activity • substantianigra: coordinates muscle activity (inhibits antagonistic muscles) • Cerebellum: coordinates muscle activity (makes adjustments based on current body position) • Cranial reflexes • Generate involuntary, reflexive muscle use to specific stimuli. Integrating center is in brain • Spinal Cord • Spinal reflexes • Generate involuntary, reflexive muscle use to specific stimuli. Integrating center is in spinal cord • Lower motor neurons (PNS) directly innervate muscle cells • CNS initiated commands are relayed (through synapses) to lower motor neurons which carry A.P.s from CNS to the individual muscle cells they innervate.

12. Neurological Control of Skeletal Muscle • All Skeletal Muscle cells are directly innervated by a motor neuron • Neuromuscular Junction: • The chemical synapse between a motor neuron and a muscle fiber (cell) • Chemical synapse, always excitatory • Motor Units: a motor neuron and all the muscle cells it innervates • Multiple fibers innervated by same neuron • They contract together as a unit

13. Fig. 12.4 This neuron is also a lower motor neurons

14. Fig. 12.3

15. Key NMJ concepts Chemical synapses (as described in neuron physiology unit) Neurotransmitter: ACh Receptor: nicotinic Receptor Action: ACh opens ligand gated Na+ channel, Na+ enters cells depolarizing itend plate potential Short-lived due to action of ACh’ase NMJ are always excitatory A single AP almost always releases enough ACh to bring the motor end plate/muscle cell to threshold

16. Structure and events that occur at a NMJ

17. Another representation of the events at a neuromuscular junction

18. EXCITATION-CONTRACTION COUPLING: from AP formation at synapse to actin-myosin interaction • AP propagates across PM (sarcolemma of muscle cell) • VG Na+ channels • Just like an AP in axon • AP travels down T-tubels • VG Ca+ channels (aka DHP receptors) open • DHP receptors are coupled/linked to Ca+ release channels • Ca+ release channels (aka ryanodine receptors) open • Ca+ floods into cytoplasm • Ca+ binds actin filament allowing actin-myosin interaction

19. Fig. 12.16 Visual representation of excitation-contraction coupling

20. Fig. 12.17 Flow Chart of excitation-contraction coupling events

21. REVIEW OF MYOFILAMENT ANATOMY AND FUNCTION

22. Fig. 12.13 ACTIN FILAMENTS Covers up binding sites for myosin heads, can move to expose binding sites Ca+ binds Has binding sites of myosin head, will be bound by myosin during interaction/contraction

23. Fig. 12.10 MYOSIN FILAMENT STRUCTURE • Myosin Head: • Binds Actin • Have binding site for ATP • Will grab, pull on, and detach from actin

24. Fig. 12.9 • Filament Interaction: • Myosin grabs and pulls on actinfilaments slide across one another • Zone of filament overlap increases • Sarcomeres get shorter cell shortens=contraction

25. FILAMENT INTERACTION: SLIDING FILAMENT THEORY OF MUSCLE CONTRACTION • Myosin and actin filaments interact • Myosin pulls on actin • Filaments slide past one another increasing zone of overlap • Sarcomeres get smaller • Results in contraction of muscle and production of tension (i.e., pulling force)

26. Fig. 12.14

27. When Ca+ binds troponin, tropomyosin moves to expose myosin binding sites as shown in diagram NOTE: This is show as if you were viewing the filaments along their short axis—different perspective then other diagram

28. Fig. 12.10

29. Fig. 12.11

30. Fig. 12.12

31. Table 9.02

32. Table 12.2

34. Figure 9.12

36. Production and Control of Tension • Contraction produces pulling force known as tension

37. Twitch: a single contraction. The result of a single AP/excitation contraction coupling event • Latent: • AP propagation, Ca release, Ca build up in sarcoplasm • Contraction: • Active cross bridging/contraction, Ca+ available • Relaxation: • Ca+ decreasing in sarcoplasm, diminished and eventual lack of crossbridging/contraction

38. Figure 9.41 Relationship between time of stimulus, AP, and tension

39. Factors that influence tension (i.e., strength of contraction) • Action Potential (stimulus) frequency • Number of active fibers/number of motor units activated • Fiber length (amount of actin-myosin overlap)

40. Figure 9.19 Green: single twitches, complete relaxation between Orange: partial relaxation between two stimuli stimuli wave summation—second contraction stronger than first Purple: two stimuli with no relaxation between contraction stronger than that with a single stimulus

41. Summation (temporal/frequency) • Increased stimulation rate  increased tension/strength • Build up/availability of Ca+ in cytoplasm • Incomplete/unfused tetanus—stimulation frequency allows partial contractions • Complete/fused tetanus – stimulation frequency does not allow any relaxation phase.

42. Figure 9.20

43. Recruitment = strength of contraction proportional to number of motor units activated • E.g., ↑ motor unit = ↑ tension/strength • Rotating through motor units allows prolonged contraction with reduced fatigue

44. Optimal resting length = optimal overlap of filaments  ↑ cross bridging  ↑ tension • Too long = too little overlap  not enough crossbridging  ↓ tension • Too short = no room left to contract & fiber mis-alignment  ↓ tension ˃˂↑↓

45. Energetics

46. Energetics ATP needed for: • Energizing head • Detaching head from myosin • Power Ca+ pumps that transport Ca+ into SR (from cytoplasm) ATP production through: • Aerobic respiration • Anaerobic respiration • Creatine Phosphate

47. Stored energy sources and how much muscle contraction they can sustain.

48. Resting Muscle • Primary substrate plasm fatty acids • ATP production ˃ ATP consumption/demand • Surplus ATP used to: • Creatine  CP • Glucose  glycogen ˃˂↑↓

49. Fig. 12.24

50. Moderate activity • Substrates = plasm fatty acids & glucose/glycogen • ATP production can meet ATP consumption/demand • Aerobic respiration dominates