1. The Muscular System
Produce movement or tension via shortening (contraction)
Generate heat - body temp
3 types:
Skeletal - moves bone, voluntary
Smooth
Cardiac
Essential function is to shorten, so they are responsible for all types of body movement. Muscles move bones together. AND produce tension: keep things static. Ex. Posture, blood vessel diameter constant despite changes in pressure. Tension - forces equal and opposite.
Muscle makes up almost half of our body mass.
Movement - gross motor, fine motor, internal organs of urinary and digestive, circulatory systems.
Posture - constantly maintaining balance agst gravity. Including when seated. Wheelchairs have belts and braces to help patients w/out muscle control.
Stabilize joints - esp important in areas where bones do not fit together well or are not anchored together well. Ex. Shoulder.
Generate heat to maintain body temp. Mostly done by skeletal muscle, as that is the majority of muscle within the body.. 3/4 of heat is from muscle.
Muscle cells are elongated (muscle cell = muscle fiber) Elongated fibers true for skeletal and smooth muscle, not cardiac.
Contraction of muscles is due to the movement of microfilaments, In all 3 types of muscle, contraction based on sliding microfilaments
terminology
Prefixes mys, myo refers to muscle
Prefix sarco refers to flesh Ex. Sarcoplasm refers to cytoplasm of a muscle cell.

2. Skeletal Muscle Characteristics
Voluntary
Most are attached by tendons to bones
Synergistic: groups work together
Antagonistic: groups oppose each other
Origin, insertion points on opposite sides of joints
Cells are multinucleate, striated
Skeletal muscle makes up at least 40% of body mass.
Tendons are tough connective tissue (collagen fibers). Withstand stress applied by muscle fibers; can rub agst rough bone without tearing; smaller than muscle, so more tendons can connect around joint.
Muscles move bones, usly attached at origin to stable bone (not much movement) and at insertion (bone that moves closer). Muscles go across joints. When a muscle contracts its insertion is pulled towards its origin.
Multinucleate (fusion), some nearly 1 foot long.
Striated - due to arrangement of filaments within cells, overlapping of fibers = band.
Voluntary - respond to conscious control, but also contract “automatically” in reflexes.
Structure - responsible for power of muscles, prevents tearing of fairly delicate cells.

3. Muscle Structure Whole muscle
Fascicles: bundles of cells, CT covering on each one
Muscle cells = fibers
Whole muscle - various lengths: 1mm to 30 cm (quadricep). Every Ind’l cell extends entire length. Surrounded by tough connective tissue (CT) Epimysium - tougher membrane, more collagen fibers, blends into a connective tissue attachment. I.e., tendon.
Sites of muscle attachment
Bones
Cartilages
Connective tissue coverings
skin (smiling)
fascicles; more fibrous membrane, tougher. = Perimysium. From dozens to 1000’s of cells per fascicle.
cell = muscle fiber. W/ Endomysium - fairly delicate covering
Tendon – cord-like structure
Aponeuroses – sheet-like structure
Figure 6.3

4. Microscopic Anatomy of Skeletal Muscle
Muscle cells
multinucleate, striated –visible banding
Myofibril - bundles of filaments
4. Myofibril - clump/cylinder of actin and myosin filaments.
Sarcolemma - with channels that penetrate into cell, between myofibrils. Important in communication
Sarcoplasmic reticulum - (smooth ER) wrapped around each myofibril, ; filled w/ Ca++ ions, used in contraction of myofibrils.
Figure 6.3a

5. Skeletal Muscle Contractile Unit
Sarcomere
Actin and myosin
Z Lines: attachment points for sarcomeres
5. Sarcomere - basic unit of contraction.
Extends from one Z to next Z line.
All sarcomeres of a cell shorten together. Up to 100K. Each works the same way. Sum is muscle shortening.
Actin - thinner filaments attached to Z line
Myosin - thicker filaments interspersed btw actin. Cross section shows distribution pattern: each myosin surrounded by actins, and vice versa.
At rest, there is a bare zone that lacks actin filaments
Sarcoplasmic reticulum (SR) – for storage of calcium. Extends throughout filaments, network of pipes that releases and takes up Ca++ as needed. Part of contraction mechanism.
Figure 6.5

6. Nerve Stimulus to Muscles
Skeletal muscles must be stimulated by a nerve to contract
Motor unit
One neuron
Muscle cells stimulated by that neuron
If muscle cells not stimulated, they will atrophy, or waste away. Eventually replaced by connective tissue, which is irreversible once complete. Use it or lose it. Problem for sedentary patients, couch potatoes, immobilized body parts.
Figure 6.4a

7. Nerve Stimulus to Muscles
Neuromuscular junctions – association site of nerve and muscle
Muscle fiber and neuron do not touch .. Synaptic cleft - gap
Neurotransmitter for skeletal muscle is acetylcholine
Neurotransmitter attaches to receptors on the sarcolemma
Sarcolemma becomes permeable to sodium (Na+)
Sodium rushing into the cell generates an action potential
Once started, muscle contraction cannot be stopped
Figure 6.5b

8. Nerve Activation of Muscle Cells
Acetylcholine released from motor neuron
Electrical impulse transmitted along T tubules
Calcium released from sarcoplasmic reticulum
Figure 6.6

9. Troponin, tropomyosin are bound to actin filament in relaxed muscle fiber, covering binding sites for myosin.
When Ca++ is released from sarcoplasmic reticulum, Ca++ binds to troponin, thus altering its shape and making it shift position such that binding sites on actin are revealed to myosin heads. So myosin heads bind, bend, and release.

10. Calcium Initiates the Sliding Filament Mechanism
Thick filaments: myosin
Thin filaments: strands of actin molecules
Contraction = formation of cross bridges between thin and thick filaments
Calcium released from sarcoplasmic reticulum
Calcium binds to troponin
Troponin-tropomysin complex shifts position
Myosin binding site exposed
Myosin heads form cross-bridges with actin
Actin filaments pulled toward center of sarcomere
Figure 6.7

11. Mechanism of Muscle Contraction (cont.)
Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament
Myosin heads then bind to the next site of the thin filament
This continued action causes a sliding of the myosin along the actin
The result is that the muscle is shortened (contracted)
Figure 6.8

12. Troponin, tropomyosin are bound to actin filament in relaxed muscle fiber, covering binding sites for myosin.
When Ca++ is released from sarcoplasmic reticulum, Ca++ binds to troponin, thus altering its shape and making it shift position such that binding sites on actin are revealed to myosin heads. So myosin heads bind, bend, and release.

13. Muscle Relaxation Nerve activation ends, contraction ends
Calcium pumped back into sarcoplasmic reticulum
Calcium removed from troponin
Myosin-binding site covered
No calcium = no cross-bridges
Note that cycle ends when ATP binds to myosin and myosin attachment to actin is released.
Rigor mortis = stiffness of muscles in a dead person, usly sets in about 4 hours after death.Why? Ca++ leaks out of sarcoplasmic reticulum (membrane falls apart without constant effort to maintain it. Ca++ interacts with troponin-tropomyosin complex and reveals binding sites on actin filaments. Myosin, already charged with ATP, binds to actin and will contract. But no more ATP available for binding to myosin again and allowing relaxation. So, muscles stay contracted and rigid.

14. Energy Required for Muscle Activity
Principle source of energy: ATP
ATP replenished by:
Creatine phosphate
Stored glycogen
Aerobic metabolism of glucose, fatty acids, and other high-energy molecules
Anaerobic use of glucose
Bonds of ATP are broken to release energy
Only 10 seconds worth of ATP is stored by muscles
CP supplies are exhausted in about 30 seconds
No oxygen needed for CP to work. Direct phosphorylation
Muscle cells contain creatine phosphate (CP) CP is a high-energy molecule CP regenerates ATP
Aerobic respiration - Slower reaction than direct phosphorylation. Generates more ATP per glucose.
Can use many dift molcs in this pathway, including fatty acids, amino acids from proteins, sugars.
So, muscles must switch to this after ATP runs out, sec.
Anaerobic resp. - Anaerobic glycolysis
Glucose is broken down to pyruvic acid to produce some ATP
Pyruvic acid is converted to lactic acid
Oxygen not needed. Not very efficient. Little of the energy of glucose is captured as ATP, usable by the cells. This reaction is fast. Runs out of glu in about sec.
Huge amounts of glucose are needed
Lactic acid produces muscle fatigue. Stretch after exercise to help metabolize lactic acid. Usly gone w/in minutes.

15. Aerobic metabolism 3 stages to convert energy of glucose to ATP
High-energy electrons carried by NADH
High-energy electrons carried by NADH
GLYCOLYSIS
ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
GLYCOLYSIS
KREBS CYCLE
ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
Glucose
Pyruvic acid
KREBS CYCLE
Glucose
Pyruvic acid
See Ch 3 Fig 24.
Note step of O2 use in ET Chain.
CO2 production
Cytoplasmic fluid
Cytoplasmic fluid
Mitochondrion
Mitochondrion

16. Muscle Fatigue and Oxygen Debt
A fatigued muscle is unable to contract
anaerobic metabolism produces lactic acid
Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less
Oxygen is required to get rid of lactic acid
GLYCOLYSIS
Ability to deliver O2 then affects athletic performance. So, some will have their own blood withdrawn several weeks before competition, then dope up with their own RBCs to increase oxygen capacity.
Lance Armstrong - heart is able to pump about 5-7 times more blood per minute than typical person. Gets more O2 to muscles, allows him to push in endurance contests.
2 Pyruvic acid
2 Lactic acid
Glucose

17. Contraction of a Skeletal Muscle
Muscle fiber contraction is “all or none”
Within a skeletal muscle, not all fibers may be stimulated during the same interval
Graded responses due to:
- number of muscle cells in each motor unit
- number of muscle cells stimulated
- frequency of muscle stimulation
Muscle force depends upon the number of fibers stimulated.
Motor unit = nueron + many muscle firbers, 10 to 1000s. Fine moter control vs. gross movements with strength.
Degree of nerve activation influences force
Muscles can continue to contract unless they run out of energy
The more fibers contracting, the more tension created. Ie stronger.

18. Muscle Contraction: Myogram
Latent period
Contraction
Relaxation
Summation vs. tetanus
Diagram represents what happens during contraction of sgl fiber. Motor unit.
Latent period while Ca++ floods out of sarcoplasmic reticulum.
Contraction as sarcomeres shorten,
relaxation. Filiaments slide back to original position.
Summation - if stimulated again before full relaxation, get more force from muscle cell.
Tetantic - if repeatedly stimulated, no relaxation at all. Muscle will likely fatigue.
Figure 6.10

19. Types of Muscle Contractions
Isotonic contractions
Myofilaments slide past each other
muscle shortens
Isometric contractions
Tension in muscles
muscle is unable to shorten
Some fibers are contracted even in a relaxed muscle
Different fibers contract at different times to provide muscle tone
The process of stimulating various fibers is under involuntary control
Type of exercise causes different results in muscle tissue:endurance training vs bodybuilding
Origin vs insertion cn be dept on which movement is being done. Ex. Raise hand vs doing chinups on a bar.
Results of increased muscle use
Increase in muscle size
Increase in muscle strength
Increase in muscle efficiency
Muscle becomes more fatigue resistant

20. Muscle Activity Slow twitch vs. fast twitch fibers
Slow twitch: endurance, long duration contraction, contain myoglobin
Jogging, swimming, biking
Fast twitch: strength, white muscle, short duration contraction
Sprinting, weight lifting, tennis
Every muscle is a combination of both types. Athletes good at certain types of activity can have predominantly one form or another.
Slow twitch - dark meat of the turkey. Legs. These cells rely on aerobic metabolism, have lots of mitochondria and use Oxygen readily. So, plenty of blood vessels, myoglobin = dark, reddish color.
Fast twitch - able to break down ATP more quickly, hence, fast twitch. short duration contractions, but very forceful. Not so aerobic, able to get by for brief periods without O2. Little myoglobin, fewer blood vessels. = white meat muscle.

21. Exercise Training Strength training Resistance training
Short, intense
Builds more fast-twitch myofibrils
Aerobic training
Builds endurance
Increases blood supply to muscle cells
Target heart rate at least 20 minutes, three times a week
Strength training - challenge muscles with short, intense workload. Builds more fast tw. Myofibrils, but NOT more muscle cells. Muscles can bulk up (but not necessarily) as myofibrils increase in number.
Aerobic training - endurance. So number of mito increases, number of blood vessels increases, amount of myoglobin (which stores O2 in cells) increases, but not much increase in muscle mass.

22. Features of Cardiac and Smooth Muscles
Activation of cardiac and smooth muscles
Involuntary
Specialized adaptations
Speed and sustainability of contractions
Arrangement of myosin and actin filaments
Involuntary: no conscious control. Both types will contract without nervous stimulus. Intrinsic rhythm of contraction. They DO respond to autonomic nervous system. Capacity to do this is due to gap junctions, which allow passage of electrical stimulation directly from cell to cell.
Cardiac cells w’ some faster ones = pacemakers. Rest of cells follow. Intercalated discs at ends of short cells, w/ many gap junctions. So cells can stimulate each other, w/out neuron.
Skeletal muscles require neuron. So, spinal cord injury will incapacitate skeletal muscle, but not smooth muscle.
2. Speed and sustainability - fastest - skeletal; med - cardiac; slowest - smooth.
Each suited to its purpose. Smooth always partially contracted, as it moves slowly, doesn’t run out of ATP. Allows blood vessel diameter to be maintained at all times. Cardiac has periods of recovery which allow sustainability.
3. Filament arrangement - next pages

23. Smooth Muscle Characteristics
Has no striations
Spindle-shaped cells
Single nucleus
Involuntary – no conscious control
Found mainly in the walls of hollow organs
No striations, b/c filaments are not parallel, but crisscross cytoplasm, attach to cell membrane at dift angles. Produces a lumpy slug when contracted.
Cells contract more slowly than skeletal muscle cells. Can produce ATP at rate to support its contractions.
Arranged in sheets in 2 directions around organs, w/ axis parallel and circumnavigating the organ. Diag. Allows pushing of substances along length of organ. Ex. Food thru digestive tract, and bowel movements to empty colon.
Blood vessels, urinary system
Figure 6.2a

24. Cardiac Muscle Characteristics
Has striations
Branched cell with a single nucleus
Joined to another muscle cell at an intercalated disc
Involuntary
Muscle bundles wrapped around heart
Striations reflect filament arrangement within cells.
Intercalated disc enables close coordination, fast communication btw cells. Direct stimulation of adjacent cells, such that heart muscle will continue rhythmnic contractions without outside stimulus.
Pacemaker cells at one position - contraction initiates here.
Involuntary, keeps beating without thought. Can also respond to CNS and beat faster.
Bundles wrapped around heart in a way that allows power of contraction to push blood thru chambers in a coordinated way.
Figure 6.2b

25. Diseases and Disorders of the Muscular System
Muscular dystrophy
Tetanus
Muscle cramps
Pulled muscles
Fasciitis
Muscular dystrophy - lack of a protein, dystrophin, which limits leakage of Ca++ into muscle cells. Eventually damages, kills cells. So, loss of muscle fibers, including cardiac, death in 30s. No cure
Tetanus - bacterial infection that produced toxin which constantly stimulates muscle. Max contraction = tetanus. Often associated w jaw muscles,” lockjaw”. Respiratory failure, fatigue.
Muscle cramps - imbalance of ions, probably K+, when muscle is used. Reflex-mediated muscle contractions. Fix by massage, helping to move fluids around muscle. Rehydrate.
Pulled muscles. Stretch a muscle too far, tear some of the fibersl. Bleeding, swelling, pain.
Fasciitis - inflammation of connective tissue around muscle. Often in sole of foot, around heel. Slow to heal, as w/ ligamnets, tendons.

26. Superficial Muscles: Anterior
Figure 6.21

27. Superficial Muscles: Posterior
Figure 6.22

28. Body Movements Flexion Extension Rotation
Flexion - decreases the angle of the joint. 2 bones closer together
Extension - inc angle btw bones. More than 180 is hyperextension
Rotation - movement around a bone’s axis.
Page 113 in text Johnson 3rd ed.
Figure 6.13a–c

29. Body Movements Abduction Adduction Circumduction
Abduction - moving a part away from the midline. Includes spreading apart of fingers, toes.
Adduction - moving TOWARD the midlinel.
Circumduction - combo of several such that circle is described.
Figure 6.13d