Review motor end plate nmj notes

1. Review of Terminology
(the “sarco-” words)
•Sarcolemma – the cell membrane of a
muscle fiber.
•Sarcoplasm – the cytoplasm of a muscle
fiber.
•Sarcoplasmic reticulum – the endoplasmic
reticulum of a muscle fiber.
•Sarcomere – the smallest unit of
contraction within a myofibril.

2. Sarcomere
Sarcolemma
Sarcoplasmic
Reticulum
A similar picture
can be found on
page 169 of the
reading packet,
figure 8.4.
* Note that the sarcoplasmic reticulum “surrounds” each myofibril.
* Also note that the sarcoplasmic reticulum seems to form
repeating units that “surround” individual sarcomeres.
Z-line Z-line

3. Review of Terminology
(the “myo-” words)
•Myocytes – a muscle fiber or cell.
•Myofibrils – units of alternating
filamentous proteins contained within the
sarcoplasm of a muscle fiber and which
extend from end to end within the fiber.
•Myofilaments – filamentous proteins called
actin (thin) filaments and myosin (thick)
filaments.

4. sarcomere
Myofibril
* Note that a sarcomere is a
repeating unit of contraction
within the myofibril.
* The myofibril can be seen to
be made up of repeating units
of overlapping myofilaments.

5. Myofilaments
•Thick myofilament
–Myosin
•Thin myofilament
–Actin
•Arrangement is so orderly
that the muscle looks
striped or “striated”
microscopically
sarcomere
sarcomere lengthened
shortened

6. New Terminology
•T-tubules – extensions of the sarcolemma
which carry “electrical” impulses deep
within a muscle fiber.
•This allows the impulse to be brought very
close to the sarcoplasmic reticulum
throughout the fiber, and thus to get very
close to each and every sarcomere.

7. Skeletal Muscle Fiber
(Myocyte)
sarcoplasmic reticulum
(the “blue” tubes)
T-tubules
(the “purple” tubes)
Myofibril
A similar picture
can be found on
page 169 of the
reading packet,
figure 8.4.
Sarcolemma

8. Motor Unit
(page 170; figure 8.6)
•Defined as a motor
neuron and all the
muscle fibers it
innervates
•By using more motor
units, the muscle
contracts with more
force.
•A small number are
used in muscles with
fine control
•A large number are
used in muscles with
crude control

9. Neuromuscular Junction
(page 170; figure 8.5)
•This is defined as the
place where the motor
neuron axon “connects”
to the muscle fiber.
•It is also the site where
the motor neuron
stimulates the muscle
fiber to begin the
sequence known as
Action Potential and
eventually contraction.
Signal from brain
Motor end
plate

10. Axon branch of motor neuron
Motor End Plate
Neuromuscular Junction

11. Our Goals !!
•1. To define and track the sequence of “electrical”
events which happen in a phenomenon called
“Action Potential”.
•2. To define and track the sequence of
interactions between myofilaments that occur
during contraction and relaxation of muscle
tissue.
•3. To determine the connections between numbers
one and two above.