1. Chapter 6
Muscular System

2. Muscle is a Contractile Organ
There are three types of muscular tissue
Skeletal muscle, cardiac muscle, smooth muscle
Skeletal muscle is part of the skeleto-muscular system
Functions to move bones
In general, each skeletal muscle has a
Belly – the middle portion of the muscle
Origin - an end that remains stationary when the organ shortens
Insertion - an end that moves during contraction
Knowing the origin and insertion of any skeletal muscle offers clues about its function
Skeletal muscle is composed of numerous elongated muscle cells
Spanning from origin to insertion, one nested inside another
Muscle cells also are called muscle fibers
Muscle cells must shorten, creating tension
Connective tissue structurally supports skeletal muscle

3. Skeletal Muscle Characteristics
Most are attached by tendons to bones
Cells are multinucleate
Striated—have visible banding
Voluntary—subject to conscious control

4. Skeletal Muscle Most skeletal muscles work in pairs Synergistic pairs
Work together to cause movement in the same direction
i.e., muscles of the quadriceps or muscles of the hamstrings
Antagonistic pairs
Cause movement in opposite directions, opposite to one another
i.e., biceps and triceps

5. Fascicle (wrapped by perimysium)
Muscle fiber (cell)
Blood vessel
Perimysium
Epimysium
(wraps entire
muscle)
Fascicle (wrapped by perimysium)
Endomysium (between fibers)
Tendon
Bone
Figure 6.1

6. Connective Tissue Wrappings of Skeletal Muscle
Endomysium—encloses a single muscle fiber
Perimysium—wraps around a fascicle (bundle) of muscle fibers
Epimysium—covers the entire skeletal muscle
Fascia—on the outside of the epimysium

7. Structure of Skeletal Muscle

8. Microscopic Anatomy Sarcolemma Myofibril Nucleus Light (I) band
Dark (A) band
(a) Segment of a muscle fiber (cell)

9. Microscopic Anatomy Sarcolemma—specialized plasma membrane
Myofibrils—long organelles inside muscle cell
Sarcoplasmic reticulum—specialized smooth endoplasmic reticulum
Myofibrils are aligned to give distinct bands
I band = light band
Contains only thin filaments
A band = dark band
Contains the entire length of the thick filaments

10. Sarcomere: contractile unit of Muscle
Thick filaments = myosin filaments
Composed of the protein myosin
Has ATPase enzymes
Myosin filaments have heads (extensions, or cross bridges)
Myosin and actin overlap somewhat
Thin filaments = actin filaments
Composed of the protein actin
Anchored to the Z disc

11. Neuromuscular Junctions
Skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract
Motor unit—one motor neuron and all the skeletal muscle cells stimulated by that neuron
Neuromuscular junction
Association site of axon terminal of the motor neuron and muscle

12. Neuromuscular Junction- Initiation of Contraction
Neurotransmitter—chemical released by nerve upon arrival of nerve impulse in the axon terminal
The neurotransmitter for skeletal muscle is acetylcholine (ACh)

13. Muscle Contraction Cycle- sliding filament theory

14. Energy for Muscle Contraction
Initially, muscles use stored ATP for energy
ATP bonds are broken to release energy
Only 4–6 seconds worth of ATP is stored by muscles
After this initial time, other pathways must be utilized to produce ATP

15. Creatine Phosphate
Direct phosphorylation of ADP by creatine phosphate (CP)
Muscle cells store CP
CP is a high-energy molecule
CP transfers a phosphate group to ADP, to regenerate ATP
Produces: 1 ATP is created per CP molecule
Duration: 15 seconds
Oxygen use: none

16. Aerobic Respiration C6H12O6 + 6O2  6CO2 + 6H2O + 32 ATP
Products: 32 ATP, carbon dioxide, water
Occurs: in the mitochondria
Requires continuous oxygen
Slow

17. Anaerobic Glycolysis Pyruvic acid is converted to lactic acid
Oxygen Use: No
Produces: 2 ATP, lactic acid
Occurs: cytoplasm
Duration: 40 s
Not as efficient, but is fast
Huge amounts of glucose are needed
Lactic acid produces muscle fatigue

18. There are Three Types of Muscle Cells
Fast Twitch (or fast glycolytic)
Anaerobic, fatigue quickly
Provide a short burst of extreme energy and contraction power
Thicker, contain fewer mitochondria, usually contain larger glycogen
Responsible for hypertrophy
Because short bursts of power come from these fibers, exercises that continuously require bursts of power will enlarge them
Weight training puts demands on fast twitch fibers, resulting in the hypertrophy (muscle enlargement) we associate with body-building
Intermediate (or fast oxidative-glycolytic)

19. Three types of muscle cells
Slow Twitch (or slow oxidative)
Appear red, have a large blood supply, have many mitochondria within their sarcolemma, and store an oxygen-carrying protein called myoglobin
Are sometimes called nonfatiguing or aerobic cells
Distance running and other aerobic sports stimulate these cells
Efficiency and strength come not from increasing mass but from using oxygen more efficiently
Although training can alter the functioning of both red (slow twitch) and white (fast twitch) fibers, it does not change their proportions
The percentage of fast and slow twitch fibers is genetically determined

20. Muscle Fatigue and oxygen debt
When a muscle is fatigued, it is unable to contract even with a stimulus
Common cause for muscle fatigue is oxygen debt
Oxygen must be “repaid” to tissue to remove oxygen deficit
Oxygen is required to get rid of accumulated lactic acid
Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

21. Types of muscle contractions
Isotonic contractions
Myofilaments are able to slide past each other during contractions
The muscle shortens and movement occurs
Example: bending the knee; rotating the arm
Isometric contractions
Tension in the muscles increases
The muscle is unable to shorten or produce movement
Example: push against a wall with bent elbows

22. Types of Body Movements
Flexion
Decreases the angle of the joint
Brings two bones closer together
Extension
Opposite of flexion
Increases angle between two bones
Extension beyond 180° is hyperextension

23. Rotation
Movement of a bone around its longitudinal axis
Common in ball-and-socket joints
Example is when you move atlas around the dens of axis (shake your head “no”)

24. Abduction
Movement of a limb away from the midline
Adduction
Opposite of abduction
Movement of a limb toward the midline
Circumduction
Combination of flexion, extension,
abduction, and adduction
Common in ball-and-socket joints

25. Dorsiflexion
Lifting the foot so that the superior surface
approaches the shin (toward the dorsum)
Plantar flexion
Depressing the foot (pointing the toes)
“Planting” the foot toward the sole

26. Inversion
Turn sole of foot medially
Eversion
Turn sole of foot laterally
Supination
Forearm rotates laterally so palm faces
anteriorly
Radius and ulna are parallel
Pronation
Forearm rotates medially so palm faces
posteriorly
Radius and ulna cross each other like an X

27. Opposition
Move thumb to touch the tips of other fingers on the same hand

28. Naming muscles By location of the muscle’s origin and insertion
By direction of muscle fibers
Example: Rectus (straight), oblique (angle)
By relative size of the muscle
Example: Maximus (largest), minimus (small)
By location of the muscle’s origin and insertion
Example: Sterno (on the sternum)
By shape of the muscle
Example: Deltoid (triangular), trapezius
By action of the muscle
Example: Flexor and extensor (flexes or extends a bone)

29. Head and Neck Muscles

30. Facial muscles
Frontalis—raises eyebrows, wrinkles forehead
Orbicularis oculi—closes eyes, squints, blinks, winks
Orbicularis oris—closes mouth and protrudes the lips
Buccinator—flattens the cheek, chews
Zygomaticus—raises corners of the mouth, smiling muscle
Chewing muscles
Masseter—closes the jaw and elevates mandible
Temporalis—synergist of the masseter, closes jaw

31. Neck muscles
Platysma—pulls the corners of the mouth inferiorly, sag in mouth
Sternocleidomastoid—flexes the neck, rotates the head to one side, “prayer muscle”

32. Muscles of arm and trunk

33. Anterior muscles
Pectoralis major—adducts and flexes the humerus
Intercostal muscles
External intercostals—raise rib cage during inhalation
Internal intercostals—depress the rib cage to move air out of the lungs when you exhale forcibly

34. Muscles of the abdominal girdle
Rectus abdominis—flexes vertebral column and compresses abdominal contents (defecation, childbirth, forced breathing)
External oblique—flex vertebral column; rotate trunk and bend it laterally
Internal oblique—flex vertebral column; rotate trunk and bend it laterally
Transversus abdominis—compresses abdominal contents

35. Posterior muscles
Trapezius—elevates, depresses, adducts, and stabilizes the scapula
Latissimus dorsi—extends and adducts the humerus
Erector spinae—back extension
Deltoid—arm abduction

37. Muscles of the upper limbs
Biceps brachii—supinates forearm, flexes elbow
Brachialis—elbow flexion
Brachioradialis—weak muscle; elbow flexion
Triceps brachii—elbow extension (antagonist to biceps brachii)

39. Gluteus maximus—hip extension
Gluteus medius—hip abduction, steadies pelvis when walking
Iliopsoas—hip flexion, keeps the upper body from falling backward when standing erect
Adductor muscles—adduct the thighs

40. Hamstring group—thigh extension and knee flexion
Biceps femoris
Semimembranosus
Semitendinosus
Sartorius—flexes the thigh
Quadriceps group—extends the knee
Rectus femoris
Vastus muscles (medialis and lateralis)

42. Tibialis anterior—dorsiflexion, foot inversion
Extensor digitorum longus—toe extension and dorsiflexion of the foot
Fibularis muscles—plantar flexion, foot eversion
Soleus—plantar flexion
Gastrocnemius- “toe dancers muscle”, plantar flexion

43. Sites of IM (Intramuscular) Injection
Deltoid: less than 5 mL Gluteus medias: over 5 mL Vastus lateralis: infant