Transcript Chapt12 Lecture 13ed Pt 2

Human Biology
Sylvia S. Mader
Michael Windelspecht
Chapter 12
Muscular
System
Lecture Outline
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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
Orbicularisor is:
“kissing” muscle
Pectoralis major:
brings arm
forward and
across chest
Serratus
anterior:
pulls the scapula
(shoulder blade)
forward, as in
pushing or
punching
External
oblique:
compresses
abdomen;
rotation of
trunk
Quadriceps femoris:
straightens leg at
knee; raises thigh
Tibialis anterior:
turns foot upward, as
when walking on heels
Extensor digitorum
longus:
raises toes; raises foot
a.
Masseter:
a chewing muscle;
clenches teeth
Deltoid:
brings arm away
from the side of
body; moves arm
up and down in
front
Trapezius:
Raises scapula, as
When shrugging
shoulders; pulls head backward
Latissimus dorsi:
brings arm down
and backward
behind the body
Biceps brachii:
bends forearm at
elbow
Rectus abdominis:
Bends vertebral
column;
compresses
abdomen
Flexor carpi
group:
bends wrist
and hand
Triceps brachii:
straightens
forearm at elbow
Extensor carpi
group:
straightens wrist
and hand
Extensor
digitorum:
straightens
fingers and wrist
Adductor longus:
moves thigh toward
midline; raises
Gluteus maximus:
extends thigh back
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
Limbs
Arm: above the elbow
Forearm: below the
elbow
Thigh: above the knee
Leg: below the knee
Figure 12.5 The major skeletal muscles of the human body.
Biceps femoris:
bends leg at knee;
extends thigh back
Gastrocnemius:
turns foot downward,
as when standing on toes;
bends leg at knee
Achilles tendon
b.
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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.
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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.
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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
T tubule sarcoplasmic
reticulum
one sarcomere
Z line
nucleus
A myofibril has many sarcomeres.
6,000×
(myofi bril): © Biology Media/Photo Researchers, Inc.
Figure 12.6 The structure of a skeletal muscle fiber.
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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.
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12.2 Skeletal Muscle Fiber Contraction
The sarcomere
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crossbridge
myosin
actin
H band
Sarcomeres are relaxed.
Z line
A band
I band
Sarcomeres are contracted.
Figure 12.6 The structure of a skeletal muscle fiber.
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12.2 Skeletal Muscle Fiber Contraction
The beginning of muscle contraction:
The sliding filament model
1. Nerve impulses travel down a motor neuron to
a _____________________.
2. _______________ (ACh) is released from the
neuron and binds to the muscle fiber.
3. This binding stimulates the fiber causing
____________ to be released from the
sarcoplasmic reticulum.
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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
folded
sarcolemma
synaptic cleft
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 12.7 Motor neurons and skeletal muscle fibers join neuromuscular junctions.
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12.2 Skeletal Muscle Fiber Contraction
Muscle contraction continued…
4. Released calcium combines with ___________,
a molecule associated with actin.
5. This causes the ______________ threads
around actin to shift and expose myosin binding
sites.
6. _______ heads bind to these sites forming crossbridges.
7. ______ binds to the myosin heads and is used
for energy to pull the actin filaments towards the
center of the sarcomere – contraction now
occurs.
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12.2 Skeletal Muscle Fiber Contraction
Visualizing the roles of calcium and
myosin in muscle contraction
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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 12.8 The role of calcium ions and ATP during muscular contraction.
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