1. Human Biology Sylvia S. Mader Michael Windelspecht
Chapter 12
Muscular System
Lecture Outline
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2. Muscles of the human body
12.1 Overview of the Muscular System
Muscles of the human body
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Orbicularis oculi:
blinking, winking,
responsible for
crow’s feet
Masseter:
a chewing muscle;
clenches teeth
Trapezius:
Raises scapula, as
When shrugging
shoulders; pulls head backward
Orbicularisor is:
“kissing” muscle
Deltoid:
brings arm away
from the side of
body; moves arm
up and down in
front
Latissimus dorsi:
brings arm down
and backward
behind the body
Pectoralis major:
brings arm
forward and
across chest
Serratus
anterior:
pulls the scapula
(shoulder blade)
forward, as in
pushing or
punching
Biceps brachii:
bends forearm at
elbow
Triceps brachii:
straightens
forearm at elbow
Rectus abdominis:
Bends vertebral
column;
compresses
abdomen
Extensor carpi
group:
straightens wrist
and hand
External
oblique:
compresses
abdomen;
rotation of
trunk
Flexor carpi
group:
bends wrist
and hand
Extensor
digitorum:
straightens
fingers and wrist
Adductor longus:
moves thigh toward
midline; raises
Gluteus maximus:
extends thigh back
Quadriceps femoris:
straightens leg at
knee; raises thigh
Sartorius:
raises and laterally rotates
thigh; raises and rotates leg
close to body; these
combined actions occur
when “crossing legs” or
kicking across, as in soccer
Biceps femoris:
bends leg at knee;
extends thigh back
Tibialis anterior:
turns foot upward, as
when walking on heels
Gastrocnemius:
turns foot downward,
as when standing on toes;
bends leg at knee
Extensor digitorum
longus:
raises toes; raises foot
Limbs
Arm: above the elbow
Forearm: below the
elbow
Thigh: above the knee
Leg: below the knee
Achilles tendon a. b.
Figure The major skeletal muscles of the human body.

3. Muscle fibers/cells Terminology for cell structure
12.2 Skeletal Muscle Fiber Contraction
Muscle fibers/cells
Terminology for cell structure
The plasma membrane is called the ___________.
The cytoplasm is called the _____________.
The SER of a muscle cell is called the ______________________ and stores calcium.

4. Muscle fibers/cells Terminology for structure within a whole muscle
12.2 Skeletal Muscle Fiber Contraction
Muscle fibers/cells
Terminology for structure within a whole muscle
Muscle fibers are arranged in ___________ called fascicles.
Myofibrils are bundles of myofilaments that run the length of a fiber.
_______________ are proteins (actin and myosin) that are arranged in repeating units.
______________ are the repeating units of actin and myosin found along a myofibril. 4

5. Visualizing muscle structure
12.2 Skeletal Muscle Fiber Contraction
Visualizing muscle structure
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A muscle contains
bundles of muscle
fibers, and a muscle
fiber has many
myofibrils.
bundle of
muscle cells
(fibers)
myofibril
sarcolemma
mitochondrion
one myofibril
sarcoplasm
skeletal
muscle
cell
(fiber)
myofilament
Z line
one sarcomere
Z line
T tubule
sarcoplasmic
reticulum
nucleus
A myofibril has many sarcomeres.
6,000×
(myofi bril): © Biology Media/Photo Researchers, Inc.
Figure The structure of a skeletal muscle fiber.

6. The sarcomere Made of 2 protein myofilaments
12.2 Skeletal Muscle Fiber Contraction
The sarcomere
Made of 2 protein myofilaments
A thick filament is composed of several hundred molecules of the protein myosin. Each myosin molecule is shaped like a ____ ____
Primarily, a thin filament consists of 2 intertwining strands of the protein actin.
These filaments _____ over one another during muscle contraction.

7. Sarcomeres are relaxed. Sarcomeres are contracted.
12.2 Skeletal Muscle Fiber Contraction
The sarcomere
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cross-
bridge
myosin
actin
H band
Sarcomeres are relaxed.
Z line
A band
I band
Sarcomeres are contracted.
Figure The structure of a skeletal muscle fiber. 7

8. The beginning of muscle contraction: The sliding filament model
12.2 Skeletal Muscle Fiber Contraction
The beginning of muscle contraction: The sliding filament model
Nerve impulses travel down a motor neuron to a _____________________.
_______________ (ACh) is released from the neuron and binds to the muscle fiber.
This binding stimulates the fiber causing ____________ to be released from the sarcoplasmic reticulum.

9. The beginning of muscle contraction
12.2 Skeletal Muscle Fiber Contraction
The beginning of muscle contraction
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skeletal muscle fiber
axon branch
axon terminal
(photo):© Victor B. Eichler
synaptic
vesicle
a. One motor axon goes to
Several muscle fibers.
synaptic
cleft
acetylcholine
(ACh)
axon terminal
synaptic vesicle
synaptic cleft
folded
sarcolemma
sarcolemma
Ach receptor
b. Asynaptic cleft exists between an axon
terminal and a muscle fiber.
c.Neurotransmitter (ACh) diffuses across synaptic cleft and
binds to receptors in sarcolemma.
Figure Motor neurons and skeletal muscle fibers join neuromuscular junctions.

10. Muscle contraction continued…
12.2 Skeletal Muscle Fiber Contraction
Muscle contraction continued…
Released calcium combines with ___________, a molecule associated with actin.
This causes the ______________ threads around actin to shift and expose myosin binding sites.
_______ heads bind to these sites forming cross-bridges.
______ binds to the myosin heads and is used for energy to pull the actin filaments towards the center of the sarcomere – contraction now occurs.

11. Visualizing the roles of calcium and myosin in muscle contraction
12.2 Skeletal Muscle Fiber Contraction
Visualizing the roles of calcium and myosin in muscle contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
actin filament
troponin
myosin-binding sites
Ca2+
Ca2+
tropomyosin
Troponin—Ca+ complex pulls tropomyosin
away, exposing myosin-binding sites.
Function of Ca2+
actin filament P
ADP
myosin
filament
cross-bridge
myosin head
1.ATP is split when myosin
head is unattached.
ATP
2. ADP+ P are bound to
myosin asmyos in head
attaches to actin.
4.Binding of fresh ATP causes myosin
Head to return to resting position.
myosin
heads
actin
3.Upon ADP + P releases,
power stroke occurs:
head bends and pulls actin.
b. Function of myosin
Figure The role of calcium ions and ATP during muscular contraction.