1. Lesson 7.6
Remember
 a muscle cell
is called a
muscle fiber

2. Muscles have three
layers of
wrappings:
1. Endomysium –
wraps an individual
muscle fiber

3. 2.Perimysium
wraps many
muscle fibers
forming bundles
called fascicles

4. 3. Epimysium
wraps the
fasciles to
form the
muscle.

5. These
wrappings
taper past
the belly
and form
the tendon.

6. Structure of muscle cell
1. Have many nuclei (skeletal)
2. Many mitochondria
3. Has endoplasmic reticulum
called sarcoplasmic reticulum

7. Structure of muscle cell
1. Have many nuclei (skeletal)
2. Many mitochondria
3. Has endoplasmic reticulum called sarcoplasmic reticulum
4. Contains myofibrils which are
the contracting unit of the cell
5. Has a Cell membrane

8. Myofibrils:
Run the length of the cell
Each cell contains dozens to
hundreds myofibrils
Composed of smaller units
called sarcomeres

9. Muscle fiber/cell
Cell membrane
Nucleus
sarcomere

10. Sarcomere:
Composed of overlapping protein
fibers
• myosin – a thick protein fiber
•actin – a thin protein fiber
overlapping of actin and
myosin makes muscle look
striated

11. Thick Myosin
protein filament
Thin Actin
protein
filament

12. How does a muscle contract
Nervous system sends a
message by the motor
neuron to the muscle fibers
stimulating them to
contract.
(Note: nerve and muscle do
not touch each other.)

14. Neuromuscular junction – place
where motor neuron and muscle
fiber meet (but don’t touch).
Neurotransmitters – chemicals
that carry a nerve impulse across
the neuromuscular junction
stimulating myofibrils to contract.

18. Muscle contraction control:
oOne motor neuron branches
and controls a few to
hundreds of muscle fibers.
oMotor neuron called a motor
unit when branches and
includes the muscle fibers it
connects with.

20. Dexterity vs. strength
oDexterity - motor unit
only branches a few times.
ex. Your eyes when you
read or thread a needle

21. Dexterity vs. strength
oDexterity
oStrength - motor unit will
branch stimulating hundreds of
muscle fibers at the same time.
ex. Lifting a heavy box