Muscular System

1. MuscularSystem Functions • Voluntary Movement • Maintain Posture • Maintains normal body temperature • Generates 85% of body heat • Compensates for cold by shivering

2. 1 2 Skeletal Skeletal 4 3 Cardiac Smooth

3. Skeletal Voluntary Attached to bones Cylindrical Striated Multi-nucleated Nuclei near membrane Tight Junctions Form Motor Units Cardiac Involuntary Heart Cylindrical/Branched Striated Single Nucleus Central Nucleus Gap Junctions – intercalated discs Figure 8 shaped Pacemaker Muscle Cell Characteristics

4. Smooth Muscle Involuntary Surrounding walls of hollow organs and glands Spindle shaped Not striated Single nucleus Central nucleus Gap Junctions Single and Multi-unit Muscle Cell Characteristics

5. Muscle Cell Anatomy • Myofiber – muscle cell • Sarcolemma – specialized cell membrane of muscle cell (actively transports Na+ and K+ • Sarcoplasm – cytoplasm of muscle – has most mitochondria of any cell • Sarcoplasmic Reticulum – specialized SER for storing and releasing and actively transporting Ca++

7. Muscle Cell Anatomy Cont. • Transverse Tubules – special passages for Na+ that pass over SR • Myofibrils – cylindrical organelles that contain the myofilaments needed for muscle contraction • Myofilaments – protein fibers • Thick filaments – myosin • Thin filaments – actin • Sarcomere – functional unit of contraction – part of a myofibril

10. Sarcomere Anatomy • Z Line – membrane that marks the end of the sarcomere – actin is attached here • A Band – Dark part of sarcomere – contain myosin (some parts have overlapping actin) • H zone – very center of A band – a little lighter than rest of A band since only contain myosin – no overlapping actin • M line – membrane in the center of the sarcomere • I band – at edges of sarcomere – light band – contains only actin • I band disappears during contraction and so does the H zone as actin is pulled in over myosin

15. Muscle Anatomy • Fiber – cell • Endomysium – fibrous sheath around each muscle cell or fiber • Fasicle – bundle of muscle cells surround by the perimysium fibrous sheath • Muscle – bundle of fasicles covered in the epimysium • Tendon – fibrous proteins attaching the muscle to the bone

20. MUSCLE INNERVATION • Motor Unit – One nerve and all of the muscle cells or fibers that it innervates • All of None Principle – when you contract a motor unit, ever fiber or cell in the motor unit contracts and each contracts to the fullest extent • How can you get different strengths of contraction in the same muscle??? • # OF MOTOR UNIT ACTIVATE!

22. Neuromuscular Junction • Sarcolemma – cell membrane • Motor end plate – specialized part of sarcolemma with neurotransmitter receptors – part where muscle membrane meets the nerve • Axon – cytoplasmic extension of the nerve cell that meets the muscle • Acetylcholine (Ach) – neurotransmitter that sets off contraction • Synaptic Cleft – space in between axon and motor end plate where Ach is dumped • T-Tubule – when Ach binds to receptors on motor end plate – opens T-tubule channels and allows Na+ to flow in

25. Components of Muscle Contraction • Myosin – thick filament that pulls actin in to cause contraction • Actin – thin filament/has binding sites for myosin • Tropomyosin – a rope like protein that wraps around actin covering the active sites on actin so that myosin can’t bind to the actin • Troponin – small proteins that attach to the tropomyosin– has a Ca++ binding site – when Ca++ binds it changes shape and in turn causes the tropomyosin to swivel off of the active sites on actin

26. Contraction • Ach is released from the axon into the synaptic cleft • Ach binds to receptors on the motor end plate • This opens the T tubules – Na+ flow in through the T-tubules

27. Steps of Contraction • Na+ flowing in through the T-tubules causes channels in SR to open releasing Ca++ • Ca++ attaches to troponin causing it to change shape • The troponin shape change causes the tropomyosin to swivel off of the actin active sites • Activated myosin heads pop up and grab on to actin and swivel forward (power stroke) dragging the actin inward

28. Contraction • Many myosin heads are popping up and grabbing on all at once – they are staggered so that some are always attached • This continues as long as there is Calcium present and ATP to power the process (usually don’t run out of the ATP)

29. How to Stop a Normal Contraction • This is not exhaustion – just normal stopping • Destroy the Ach • Pump out the Na+ • Pump all of the Ca++ back into the SR

30. Motions Muscles Make • Flexion – decreasing angle in the joint – bringing bones closer together • Extension – increasing the angle in the joint – straightening the joint • Hyperextension – straightening more than 1800 • Abduction – movement of a limb away from the midline of the body • Adduction – movement of a limb toward the midline

31. Motions Continued • Rotation – movement of a bone around its axis without medial or lateral displacement • Circumduction – movement of distal portion around stationary proximal portion of the bone • Pronation – turning the palms down (special kind of rotation) • Supination – turning the palms up (also rotation)

32. Motions Continued • Inversion – turning the sole of the foot in • Eversion – turning the sole of the foot out • Dorsiflexion – pulling the toes up toward the tibia • Plantar Flexion – pointing toes – pushing them downward

33. Muscle TwitchA single muscle contraction • Latent period – Ach is released, Na+ rushes in, Ca++ is released, active sites are uncovered on actin, myosin binds to actin • Contraction period – myosin is pulling actin inward • Relaxation period – Ca++ is being sucked up by the SR, tropomyosin is recovering active sites on actin, myosin can no longer bind to actin, Na+ is also pumped out and Ach is destroyed in the synaptic cleft

34. Energy Usage • Creatine phosphate – enzyme transfers phosphate from creatine to ADP – make ATP quickly for a few seconds • Glycolysis/Fermentation – only make 2 ATP/glucose – ineffective but don’t need oxygen • Aerobic Cellular Respiration – make 38 ATP/glucose – only efficient way to make enough ATP for sustained muscle contraction

35. Aerobic Respiration • Needs a lot of oxygen to burn glucose this way and make ATP • Myoglobin – red protein in muscle that binds oxygen and stores it • Why need oxygen? • Make ATP aerobically • Replenish creatine phosphate • Reload myoglobin Oxygen debt – can’t get enough , can’t make enough ATP – feel fatigued, breathe heavily

36. Fast vs. Slow Twitch Muscles • Fast Twitch Muscles • Contract faster • White/Little myoglobin • Bigger SR/Faster Ca++ release • Slow Twitch Muscles • Take longer to contract but can sustain the contraction • Red/Lots of myoglobin • More mitochondria

37. Isotonic Muscle Contractions – muscle shortens – force of muscle is greater than the load • Isometric – muscle doesn’t shorten – force of load > force of muscle • Muscle Tone – some motor units are contracted but not enough to move the muscle • Hypertrophy – muscle cells increase in size by increasing the amount of actin and myosin, SR, and mitochondria due to stress on muscle • Atrophy – shrinkage of a muscle because each muscle cell gets smaller – loses actin and myosin due to disuse • Rigor Mortis – after death, calcium leaks out of SR and the troponin/tropomyosin complex is moved from actin active sites – myosin binds but not ATP is being produced to unattach it so muscle becomes rigid – as tissue starts to break down after a day, it goes away

38. Cardiac Muscle • No neurons innervating cells, no motor units – one pacemaker and then conductive protein fibers to carry the impulse to other cardiac cells • Gap junctions (intercalated discs) cause ions to flow from cell to cell to get a coordinated contraction • Impulse starts in atria and then travels through ventricles so atria contract and then ventricles • The cardiac muscle cells have the same arrangement of actin and myosin (striations) but only have one nucleus and have bigger mitochondria and only 1 T-Tubule • Contracts slower – takes more time for calcium to diffuse • Contracts about 70 times/min. • Long Refractory period so there is no tetanus even when the hear is beating fast

39. Smooth Muscle • Contracts slower and longer (takes longer for Ca++ to diffuse and to be pumped back into the SR) • Actin and myosin different from cardiac and skeletal – actin is attached to dense bodies and membrane but myosin still pulls it in – just pulls in in every direction • No motor units – instead most are single unit junctions – a nerve synapses with one smooth muscle cell and the impulse spreads thru gap junctions so it all contracts in a wave • In pupil – multi-unit – each smooth muscle cell has its own nerve