As it contracts it
-causes movement
-maintains posture
-stabilizes joints
-and generates heat.

Skeletal muscle (voluntary)
 muscle attached to the skeleton
 cells are long, striated, and multinucleate
 Connective tissue coverings (endomysium, perimysium,
and epimysium) enclose and protect the muscle fibers and
increase the strength of skeletal muscles.

Smooth muscle (involuntary)
 cells are uninucleate, spindle-shaped, and arranged in
opposing layers in the walls of hollow organs.

Cardiac muscle (involuntary)
 cells are striated, branching and fit closely together
arranged in spiral bundles in the heart.
Connective
Tissue
Wrappings
*endomysium: forms a
sheath around a fiber
*perimysium: coarse
membrane that surrounds
several sheathed fibers
*fascicle: bundle of fibers
covered in perimysium
*epimysium: tough
overcoat that surrounds
several fascicles that make
a muscle

Skeletal muscles attach to bone using
tendons or aponeuroses.
 Tendons: stong, cord-like structures
▪ Can cross bony projections
▪ Used to stabilize joints
 Aponeuroses: sheet-like structures that attach
muscle indirectly
Microscopic
Anatomy
•sarcolema- plasma
membrane that serves as
the “muscle husk”
•myofibrils- long ribbon-
like organelles which
nearly fill the cytoplasm.
•Alternating light (I) and
dark (A) bands give the
striped appearance.
•Midsection of the light
band is the Z disc
•Midsection of the dark
band is the H zone
Microscopic
Anatomy, Cont.
•sarcomere- unit of a
myofibrile that stretches
from one Z to the next Z.
•Myofilamentsthreadlike protein
structures within the
sarcomere
•Myosin- thick fibers that
split ATP to generate
power.
•Heads or cross bridges
link filaments during
contraction.
•Actin- thin fibers that are
anchored to the Z disc

During contraction:
 Myosin heads pull on
actin filaments.
 Actin filaments slide
toward the center of the
sarcomere.
 Light zones disappear.

Irritability
 Ability to receive and respond to stimuli

Contractility
 Ability to forcibly shorten
Motor unit: one
neuron and all muscle
it stimulates.
 Neuromuscular
junction: where nerve
fiber ends (axon
terminals) at skeletal
muscle.
 Synaptic cleft: gap
between axon
terminals and
sarcolema.







Nerve impulse to axon
Chemical release of
neurotransmitter.
ACh crosses synaptic cleft
and attaches to receptors.
Muscle becomes
permeable to Na+.
Inward rush of Na
generates electrical
impulse, Action Potential.
AP travels over muscle
causing contraction.

Direct phosphorolation of ADP by creatine
phosphate.

ATP
transfer of phosphate group from CP to
ADP
ATP
 Lasts about 20 seconds. (makes 1 ATP)

Aerobic Respiration
 C6H12O6
CO2 + H2O + energy (ATP)
 Yields 36 ATP.
 Requires oxygen.

Anaerobic Glycolysis and lactic acid
formation.
 Glucose
pyruvic acid + 2 ATP
 Without oxygen, pyruvic acid converts to lactic
acid.
 Fast process. Good for 30-60 seconds of energy.
 Lactic acid accumulation causes muscle fatigue
and soreness.
Types and Names

Origin
 Attachment to the immovable or less movable
bone

Insertion
 attachment to the movable bone
**When a muscle contracts, the insertion moves
toward the origin.
Example:
During
contraction
of the
biceps, the
insertion
moves
toward the
origin.

Flexion
 Movement that decreases
the angle of a joint.
 Bringing two bones closer
together

Extension
 Increases the distance or
angle between two bones.
 If extension is >180
degrees, it is called
hyperextension.

Rotation
 Movement of a bone
around its
longitudinal axis.
▪ Lateral: away from
midline
▪ Medial: toward
midline

Abduction
 away from central
axis of the body

Adduction
 closer to central axis
of the body

Circumduction
 Common in ball and
socket joints
 Proximal end of limb is
stationary while distal
end moves in a circle.
SPECIAL MOVEMENTS OF THE
FOOT.
UP AND DOWN MOVEMENTS
AT THE ANKLE.
MOVEMENTS OF THE RADIUS
AROUND THE ULNA.
MOVEMENT OF THE THUMB.

Prime mover
 Muscle that has the major responsibility for
causing a movement.

Antagonist
 Muscles that oppose or reverse a movement

Synergyst
 Help prime movers

Fixator
 Special synergists
 Stabilize the origin of the prime mover
Homeostatic Imbalance


In the fetus, muscles are laid down in
segments and then segments are invaded by
nerves.
Occurs very early in the pregnancy.

Muscular Dystrophy
 Congenital muscle-destroying disease
 Duchenne: usually diagnosed between age 2-6
▪ Normal child begins to fall, lose coordination.
▪ Wheel chair by age 12
▪ Generally do not live beyond teens

Myastenia gravis
 Happens in adults
 Shortage of acetylcholine receptors at neuromuscular
junctions results in generalized muscle weakness.

Nerve Damage
 Destruction of nerve supply to muscle causes the
muscle to lose tone and become paralyzed.
 Over time, the muscle with become soft and
atrophy.