1. The Muscular System Structure & Function

2. Skeletal Muscle Functions
Produce movement
Maintain posture
Stabilize joints
Generate heat

3. The Muscular System
Muscles are responsible for all types of body movement
3 muscle types are found in the body
Skeletal muscle
Attached to bone & skin, some facial muscles
Produce movement, stabilize joints, provide posture & generate heat
Cardiac muscle
Walls of the heart
Protect the heart & produce contractions of the heart walls
Smooth muscle
Walls of hollow visceral (i.e, stomach) organs (except heart)
Protect organs & produce slow contractions

4. Comparison of Skeletal, Cardiac & Smooth Muscles

5. Characteristics of Muscles
Skeletal & smooth muscle cells are elongated (muscle cell = muscle fiber)
Contraction of muscles is due to the movement of microfilaments
All muscles share some terminology
myo & mys refer to “muscle”
sarco refers to “flesh”

6. Smooth Muscle Characteristics
Lacks striations
Spindle-shaped cells
Single nucleus
Involuntary—no conscious control
Contractions happen very slowly
Found mainly in the walls of hollow organs
Stomach, urinary bladder, respiratory passages

7. Cardiac Muscle Characteristics
Striations
Usually has a single nucleus
Branching cells
Joined to another muscle cell at an intercalated disc
Involuntary
Contractions happen slowly
Found only in the heart

8. Skeletal Muscle Characteristics
Most are attached by tendons to bones
Cells are multinucleated
Striated—have visible banding
Voluntary—subject to conscious control
Contractions happen slow to fast
Muscles are either contracted or relaxed
Contracted the muscle exerts pulling force = muscle shortens
Since muscles can only pull (not push), they work in pairs (antagonistic muscles)
Example: Biceps & Triceps
Muscle that bends joint is called the flexor muscle
Muscle that straightens joint is called the extensor muscle
Which is the flexor muscle?
Extensor muscle?

9. EXAMPLE

10. The Muscular System Skeletal Muscle Structure & Contractions

11. Connective Tissue Wrappings & Attachments of Skeletal Muscle
Cells are surrounded & bundled by connective tissue
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
Tendons—cord-like structures
Mostly collagen fibers
Attach muscle to bone
Figure 6.1

12. Microscopic Anatomy of Skeletal Muscle
Sarcolemma—specialized plasma membrane
Myofibrils—long organelles inside muscle cell

13. Microscopic Anatomy of Skeletal Muscle
Sarcomere—contractile unit of a muscle fiber
Organization of the sarcomere
Myofilaments
Thick filaments = myosin filaments
Thin filaments = actin filaments
Figure 6.3b

14. Microscopic Anatomy of Skeletal Muscle
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
Figure 6.3b

15. Microscopic Anatomy of Skeletal Muscle
Thick filaments = myosin filaments
Composed of the protein myosin
Myosin filaments have heads (extensions, or cross bridges)
Myosin & actin overlap somewhat (A-band)
Thin filaments = actin filaments
Composed of the protein actin
Anchored to the Z disc
Figure 6.3c

16. The Nerve Stimulus & Action Potential
Skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract
Motor unit— one motor neuron & all skeletal muscle cells stimulated by that neuron
Figure 6.4a

17. The Nerve Stimulus & Action Potential
Neuromuscular junction
Association site of axon terminal of motor neuron & muscle
Neuromuscular Junction Animation

18. The Nerve Stimulus & Action Potential
Figure 6.5a
Action Potentials & Muscle Contraction

19. The Nerve Stimulus & Action Potential
Synaptic cleft
Gap between nerve & muscle
Do not make contact
Filled with interstitial fluid

20. Transmission of Nerve Impulse to Muscle
Neurotransmitter—chemical released by nerve upon arrival of nerve impulse
Skeletal muscle – acetylcholine (ACh)
ACh attaches to receptors on sarcolemma
Sarcolemma becomes permeable to sodium (Na+)

21. Transmission of Nerve Impulse to Muscle
Na+ rushes into cell, generating an AP
Once started, muscle contraction cannot be stopped

22. The Sliding Filament Theory of Muscle Contraction
Activation by nerve causes myosin heads (cross bridges) to attach to binding sites on thin filament
Myosin heads then bind to next site of thin filament & pull them toward center of sarcomere
Continued action causes a sliding of the myosin along actin
Result – muscle is shortened (contracted)

23. The Sliding Filament Theory
Myofilament Contraction animation
Figure 6.8a

24. The Sliding Filament Theory
Figure 6.8b

25. The Sliding Filament Theory
Sarcomere Contraction animation
Figure 6.8c

26. 5 Golden Rules of Skeletal Muscle Activity

27. Muscles & Body Movements
Movement is attained due to a muscle moving an attached bone
Muscles are attached to at least 2 points
Origin
Attachment to moveable bone
Insertion
Attachment to immovable bone

28. Types of Muscle Contractions
Isotonic contractions
Myofilaments are able to slide past each other during contractions
Muscle shortens & movement occurs
Ex: lifting a dumbbell
Isometric contractions
Tension in muscles increases
Muscle is unable to shorten or produce movement
Ex: pushing on a wall

29. Effect of Exercise on Muscles
Exercise increases muscle size, strength & endurance
Aerobic (endurance) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigue
Makes body metabolism more efficient
Improves digestion, coordination
Resistance (isometric) exercise (weight lifting) increases muscle size & strength

30. The Muscular System Skeletal Muscles to Identify

31. Types of Muscles
Prime mover—muscle with major responsibility for a certain movement
Antagonist—muscle that opposes or reverses a prime mover
Synergist—muscle that aids a prime mover in a movement & helps prevent rotation
Fixator—stabilizes origin of a prime mover

32. Naming Skeletal Muscles
By direction of muscle fibers
Examples
Rectus (straight)
Transverse (horizontal)
Oblique (angle)
By relative size of the muscle
Maximus (largest)
Minimus (smallest)
Longus (longest)
By location of the muscle
Examples
Temporalis (temporal bone)
Occipitalis (occipital bone)
By number of origins
Triceps (3 heads)
Biceps (2 heads)
Quadriceps (4 muscles in group)

33. Naming Skeletal Muscles
By location of the muscle’s origin & insertion
Example
Sternocleidomastoid (on the sternum)
By shape of the muscle
Examples
Deltoid (triangular)
Trapezius (trapezoid)
By action of the muscle
Examples
Flexor (flexes a bone)
Extensor (extends a bone)
Abductor (abducts a limb)
Adductor (adducts a limb)

34. Head & Neck Muscles Facial muscles Chewing muscles
Frontalis—raises eyebrows
Orbicularis oculi— closes eyes, squints, blinks, winks
Orbicularis oris— closes mouth & protrudes lips
Buccinator—flattens cheek, chews
Zygomaticus—raises corners of mouth
Chewing muscles
Masseter—closes jaw & elevates mandible
Temporalis—synergist of masseter, closes jaw

35. Head & Neck Muscles Neck muscles
Platysma—pulls corners of mouth inferiorly
Sternocleidomastoid—flexes neck, rotates head

36. Muscles of Trunk, Shoulder & Arm
Anterior muscles
Pectoralis major— adducts & flexes humerus
“Pecs”
Intercostal muscles
External intercostals— raise rib cage during inhalation
Internal intercostals— depress rib cage to move air out of lungs when you exhale forcibly

37. Muscles of Trunk, Shoulder & Arm
Posterior muscles
Trapezius—elevates, depresses, adducts & stabilizes scapula
Latissimus dorsi—extends & adducts humerus
Deltoid—arm abduction

38. Muscles of Trunk, Shoulder & Arm
Muscles of the abdominal girdle
Rectus abdominis— flexes vertebral column & compresses abdominal contents (defecation, childbirth, forced breathing)
External & internal obliques—flex vertebral column; rotate trunk & bend it laterally
Transversus abdominis— compresses abdominal contents

39. Muscles of the Upper Limb
Biceps brachii—supinates forearm, flexes elbow
Brachialis—elbow flexion
Brachioradialis—weak muscle
Triceps brachii—elbow extension (antagonist to biceps brachii)

40. Muscles of the Lower Limb (Pelvis, Hip, Thigh)
Gluteus maximus—hip extension
Gluteus medius—hip abduction, steadies pelvis when walking
Iliopsoas—hip flexion, keeps upper body from falling backward when standing erect
Adductor muscles—adduct thighs

41. Muscles of the Lower Limb
Muscles causing movement at the knee joint
Hamstring group— thigh extension & knee flexion
Biceps femoris
Semimembranosus
Semitendinosus

42. Muscles of the Lower Limb (Pelvis, Hip, Thigh)
Muscles causing movement at the knee joint
Sartorius—flexes thigh
Quadriceps group—extends knee
Rectus femoris
Vastus muscles (3)

43. Muscles of the Lower Limb
Muscles causing movement at ankle & foot
Tibialis anterior— dorsiflexion & foot inversion
Extensor digitorum longus—toe extension & dorsiflexion of foot
Fibularis muscles— plantar flexion, everts foot
Soleus—plantar flexion
Gastrocnemius— plantar flexion

44. Superficial Muscles: Anterior
You should
be able to
identify
these
superficial
muscles
for your
Quiz
NEXT WEEK!

45. Superficial Muscles: Posterior
You should
be able to
identify
these
superficial
muscles
for your
Quiz
NEXT WEEK!