Chapter 6 Muscular System
I. Muscle Tissue (myo-, mys-, sarco-,
muscle prefixes)
A. Muscle Types – skeletal, cardiac,
smooth
1.Skeletal – attach to body skeleton
- shape – long, cylindrical,
multinucleated
- w/ striations
- known as striated muscle
(because appear striped)
- Voluntary muscle – consciously
controlled
a.endomysium – connective tissue
sheath surrounding each muscle
fiber.
b. Perimysium – covering several
sheathed muscle fibers forming
a bundle (fascicle).
c.Epimysium – covering over the
bundles of sheathed muscle
fibers. (covers entire muscle)
d. Tendons – strong cordlike
epimysia connecting bone to
muscle.
2.Smooth Muscle – found in walls
of hollow visceral organs
(stomach, bladder, respiratory
passages)
- no striations, involuntary (can
not consciously control)
- spindle shaped, single nucleus.
Arranged in sheets or layers.
(layers – one runs circular, the
other longitudinal)
- Contractions of these muscles
are slow and sustained
3.Cardiac Muscle – found in heart
- striated, involuntary
- arranged in spiral of figure 8 –
shaped bundles
- branching cells joined by
junctions
- uninucleated
- beats at steady state
B. Muscle Functions – produces
movement, maintains posture,
stabilizes joints, generates heat.
1.producing movement –
responsible for all locomotion
(skeletal), movement of food
through body (smooth).
2.Maintaining posture
3.Stabilizing joints (shoulder joint)
4.Generating heat – by product of
muscle activity. ¾ of ATP
escapes as heat when muscles
contract.
C. Microscopic Anatomy of Skeletal
Muscle
1.Sarcolemma – plasma membrane
in muscle cells.
2.Myofibril – nearly fill the
cytoplasm of cell-complex
organelle composed of bundles of
myofilaments.
a.have alternating light and dark
bands; give muscle cells striped
appearance
b. Z line is in the middle of light
area (blue line in book pg 159).
c.Dark band has a lighter center
called H zone.
3.Sarcomeres – chains of tiny
contractile units – aligned end to
end in the myofibril
4.Myofilaments – small structures
within sarcomeres
Types of myofilaments
a. thick filaments – myosin
filaments (contain myosin –
protein and ATPase)
ATPase- enzyme that splits
ATP to generate power. (for
muscle contraction). –cross
bridges – projections of thick
filaments. Link thick and
thin filaments together.
b. Thin filaments – composed
of actin – a contractile
protein. – also called actin
filaments. When contraction
occurs – actin filaments slide
toward each other. – each
into the center of a
sarcomere. (light areas
disappear).
 It is the precise arrangement
of the myofilaments in the
myofibrils that produce the
banding pattern or striations,
in skeletal muscle.
5.Sarcoplasmic reticulum (SR) –
specialized endoplasmic
reticulum – surround every
myofibril like a sleeve. Function
is to store calcium and release it.
Calcium provides signal for
contraction.
D. Skeletal Muscle Activity –
stimulation and contraction of a
single muscle cell.
1.irritability – ability to receive and
respond to stimuli
2.contractility – ability to shorten
(forcibly) when an adequate
stimulus is received.
3.The nerve stimulus and Action
Potential
-skeletal muscles must be
stimulated by nerve impulses to
contract. form junctions between
different muscle cells.
- motor unit – consists of one
neuron, all the muscles it
stimulates
- neuromuscular junctions – when
nerve fibers *nerve endings and
muscle cells never touch.
- Synaptic cleft – gap between
nerve and muscle (filled w/
fluid)
- Neurotransmitter – chemical
released into gap between nerve
and muscle when impulses
reaches end of nerve.
“acetylcholine” - specific
neurotransmitter for skeletal
muscle.
* when enough Ach is released,
(Na+) – sodium ions rush into the
muscle cell. There is an upset of
electrical conditions inside cell.
An electrical current is generated.
It travels over the entire surface
resulting in a contraction of the
muscle.