Muscular System
•Stabilize Joints
•Generate Heat
• Skeletal- voluntary, striated,
• Cardiac- involuntary, striated,
• Smooth- involuntary, not
striated, visceral
Anatomy of Skeletal Muscle
• Muscle fiber (cell) is wrapped by endomysium
• Several wrapped fibers are bundled and
wrapped by perimysium
• Each bundle is called a fascicle
• Many fascicles are wrapped by tough
• Epimysium ends in a cord like tendon or a
sheet like aponeuroses
Muscle Fiber (Cell)
• Made of many myofibrils
covered by a plasma
membrane called the
• Each myofibril has contractile
units called a sarcomere
• Alternating dark (A) bands and
light (I) bands
• Z disc- midway in (I) band
• H zone midway in (A) band
• M line- center of H zone
• 2 types of protein filaments:
–Thick filaments= myosin
–Thin filaments= actin
• Cross bridges on myosin
filaments connect the two
Sliding Filaments
• Thin fibers are pulled to center of the
sarcomere by myosin head cross bridge
• Triggered by rise in Ca ++ which attaches to
myosin head to pull it back
• ATP releases the head and it springs forward
and pushes the thin filaments over the thick
filaments = Muscle Shortens
Skeletal muscle must be stimulated
by a nerve
• Motor Unit = one neuron and all the
muscle cells it stimulates
• More fibers stimulated by one
neuron, the greater the force
• Less fibers stimulated by one neuron
than the finer the movement
Glucose is necessary to provide
• Muscle can store glucose as
• Muscle contains myoglobin
which will bind oxygen
3 pathways to ATP production
• 1. Creatine phosphate (CP) good for minutes
• 2. Aerobic respiration=
C6H12O6 + O2  CO2 + H2O + ATP
95% of all ATP produced (38 ATP / glucose)
• 3. Anaerobic glycolysis= without oxygen,
glucose is broken into 2 pyruvate acid,
releases 2 ATP and a by product lactic acid,
causes muscle soreness
Types of muscle contraction
• Isotonic – contraction occurs and results in
• Isometric- the myosin filaments try to contract
but the muscle is against something
• Muscle tone- even when the muscle is
relaxed, few of the muscle fibers continue to
contract and make the muscle firm
Exercise effect
• Aerobic- endurance
– does NOT increase size
– DOES resist fatigue
– more blood hemoglobin, more mitochondria,
more glycogen
• more myoglobin- holds oxygen
Exercise effect continued
• Isometric- resistance
– Does increase size and strength
– more myofilaments
– more connective tissue
• larger cells
5 Golden Rules
• 1. muscles cross at least one joint
• 2. the bulk of the muscle lies proximal to the
• 3. all muscles have at least two attachments: --origin and insertion
• 4. muscles can only pull; never push
• 5. during contraction, the insertion moves
towards the origin
Naming Muscles
• 1. Directions of fibers: Rectus,
• 2. Relative size: Maximus, Minimus
• 3. Location over bone: Frontalis,
• 4. Number of origins: Biceps,
• 5. Location of origin and
• 6. Shape: Deltoid
• 7. Action: adductor, flexor
• Prime Mover- major responsibility
for move
• Antagonist- when prime mover is
contracted, it is relaxed
• Synergist- helper to prime mover
• Fixator- special synergists that hold a
muscle stable
Shapes of Muscles
Circular- sphincters
Convergent- fan shaped
Parallel- strap like
Fusiform- special parallel with big
• Pennate- feather like
Muscles of the Head
Frontalis- raises eyebrows
Orbicularis oculi- blinking, squinting
Zygomaticus- smile
Depressor anguli oris- frown,
(antagonists= smile / frown)
• Lavator labii superioris- disgust
• Depressor labii- pout
Chewing (Mastication)
• Masseter- prime mover (from
zygomatic to ramus of mandible)
• Temporalis- synergist
• Buccinator- holds food between
teeth/ sucking
• Platysma- tenses skin of neck during
• Digastric- open mouth- depress
• Mylohyoid- forces bolus into
• Pharyngeal constrictors- propels
bolus to esophagus
• Sternocleidomastoid- head flexion,
neck flex, rotate head towards
opposite shoulder
• Scalenes- flex and rotate neck
Shoulder Joint
• Trapezius- depress shoulder/
adducts scapula
• Pectoralis major- prime mover
of arm flexion, adducts arm,
rotates medial
Shoulder continued
• Latissimus dorsi- prime mover of
arm extension, arm adductor brings
arm down in hammering,
swimming, rowing
• Deltoid- antagonist of pectoralis
major, and latissimus dorsi, prime
mover of arm abduction, swinging
arm movement while walking
Shoulder (rotator cuff)
• Supraspinatus- prevents downward
dislocation, assists in abduction
• Infraspinatus- rotates humerus laterally
• Teres major- medial rotation of humerus,
• Also: Coracobrachialis• coracoid – humerus, flexion and
adduction of humerus
Elbow Joint
• Triceps brachii- antagonist to forearm
flexors, strong forearm extensor,
stabilizes shoulder
• Biceps brachii- flexes elbow,
supinates forearm, lifts radius
• Brachialis- forearm flexor, lifts ulna
• Brachioradialis- synergist to forearm
Back Trunk
• Erector Spinae- prime mover of back
extension- made of 3 muscles: Iliocostalis,
Longissimus, and Spinalis
• Bending forward at the waist touching fingers
to the floor they are relaxed ( held together by
ligaments!) that is why lifting can be problem
Thorax (breathing)
• External intercostals- synergist to
diaphragm in inspiration, elevates rib
• Diaphragm- prime mover of
• Internal intercostals- aid in
expiration, depress the rib cage
Thorax continued
• Serratus anterior- “boxer’s
muscle” raises the point of the
shoulder, abduction and
raising the arm, pushing,
Abdominal Girdle
• Rectus Abdominus- pubic crest to xiphoid
process, flex and rotate lumbar vertebrae
• External oblique- diagonal fibers, “sit-up” flex
• Internal oblique- under external oblique
• Transverse abdominus- runs across under
Hip and Knee
• Iliopsoas- prime mover of hip flexion
• Sartorius- strap like, superficial, flexes and
laterally rotates thigh, flexes knee, “cross leg
• Adductor magnus:
• Adductor longus: adducts thigh
• Adductor brevis:
• Gracilis- adducts thigh, medial rotation when
Quadriceps group (ant. Thigh)
• All extend knee:
• Rectus Femoris: also flexes hip
on thigh
• Vastus lateralis
• Vastus intermedius
• Vastus medialis
Hip and Thigh posterior
• Gluteus Maximus- major, powerful,
extensor of the thigh, (rising from
chair, stairs, running)
• Gluteus medius- injection site
• Gluteus minimus- adducts thigh
Hamstring group
• Posterior thigh, sciatic nerve runs
through, powerful knee flexors, extends
• Biceps Femoris- extends thigh, flexes
knee, lateral rotation of leg when knee is
• Semitendinosus
• Semimembranosus
Lower Leg
• Gastrocnemius- prominent belly
forms proximal curve of the calf,
plantar flexion, large Achilles Tendon
• Soleus- lies under gastrocnemius,
also plantar flexor