Download Nerve activates contraction

Chapter 6
The Muscular System
Functions of Muscular System
1. Produce movement and manipulate the
environment
2. Maintain posture
3. Stabilize joints
4. Generate heat
Slide 6.8
The Muscular System
 Muscles are responsible for all types of
body movement
 Three basic muscle types are found in
the body
 Skeletal muscle
 Cardiac muscle
 Smooth muscle
Similarities of all Types of Muscles
 Muscle cells are elongated
(muscle cell = muscle fiber)
 Contraction of muscles is due to the
movement of microfilaments
 All muscles share some terminology
 Prefix myo refers to muscle
 Prefix mys refers to muscle
 Prefix sarco refers to flesh
Slide 6.2
Differences in the types of muscles
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.1
Differences in the types of muscles
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.1
Skeletal Muscle Characteristics
 Most are attached by tendons to bones
 Cells are multinucleate
 Striated – have visible banding
 Voluntary – subject to conscious control
 Cells are surrounded and bundled by
connective tissue
Skeletal, striated, voluntary
Skeletal Muscle Attachments
 Tendon – cord-like structure
 Aponeuroses – sheet-like structure
 Sites of muscle attachment
 Bones
 Cartilages
 Connective tissue coverings
Tendon
Aponeuroses
Cardiac Muscle Characteristics
 Has striations
 Usually has a
single nucleus
 Joined to another
muscle cell at an
intercalated disc
 Involuntary; the
heart has a
pacemaker
 Found only in the
heart
Figure 6.2b
Cardiac, striated, involuntary
Smooth Muscle Characteristics
 Has no striations
 Spindle-shaped cells
 Single nucleus
 Involuntary – no
conscious control
 Found mainly in the
walls of hollow
organs
 Arranged in layers
 2 layers
Figure 6.2a
Smooth, no striations, involuntary
Microscopic Anatomy of Skeletal Muscle
 Cells are multinucleate
 Nuclei are just beneath the sarcolemma
 Sarcolemma (organelle) – specialized
plasma membrane
Figure 6.3a
Microscopic Anatomy of Skeletal Muscle
 Sarcoplasmic reticulum (organelle)
 Specialized smooth ER that surrounds all
myofibrils
 Stores Ca ions to be able to release them
on demand
Figure 6.3a
Microscopic Anatomy of Skeletal Muscle
 Myofibril (organelle)
 Bundles of myofilaments
 Myofibrils are aligned to give distrinct bands
 I band =
light band
 A band =
dark band
Figure 6.3b
Microscopic Anatomy of Skeletal Muscle
 Sarcomere
 Chains of contractile units in myofibrils
 Two types of myofilaments
 Thick = myosin
 Thin = actin
Figure 6.3b
Microscopic Anatomy of Skeletal Muscle
 Thick filaments = myosin filaments
 Composed of the protein myosin
Figure 6.3c
Microscopic Anatomy of Skeletal Muscle
 Thin filaments = actin filaments
 Anchored to the Z disc
 Composed of the protein actin
Figure 6.3c
Microscopic Anatomy of Skeletal Muscle
 Myosin filaments have heads
(extensions, or cross bridges)
 Myosin heads link the thick and thin
during contraction
 Myosin and
actin overlap
somewhat
Figure 6.3d
Microscopic Anatomy of Skeletal Muscle
 Thick (myosin) and thin (actin) filaments
produce the striations in skeletal muscle
Figure 6.3d
Organizational levels of Skeletal Muscle
 Organ – the muscle (biceps)
 Fiber – a muscle cell
 Myofibril – organelle composed of sarcomeres
and myofilaments
 Sarcomeres – unit of myofibril
 Myofilament – actin and myosin
Skeletal Muscle Cell
 Nucleus – control center
 Sarcolemma – plasma membrane
 Sarcoplasm – cytoplasm
Skeletal Muscle Cell
 Sarcoplasmic reticulum – storage of
calcium ions to be released when
stimulated by an impulse
 T-tubules – surround the myofibrils and
assist in delivering ions
Skeletal Muscle Cell
 Mitochondria (lots) – provide energy and
ATP
 Myofibril – composed of thick and thin
filaments and many sarcomeres
Muscle Contraction
From nerve stimulus to
sarcomere contraction
Nerve Stimulus to Muscles
 1. Skeletal muscles
must be stimulated
by a nerve to
contract
 Motor unit is
composed of:
 One neuron
 All muscle cells
stimulated by
that neuron
 One nerve cell
branches into
axonal terminals
Figure 6.4a
Nerve Stimulus to Muscles
 Axonal terminals form
junctions with
sarcoplasm called
neuromuscular junctions
 Nerve and muscle do
not make contact there
is a gap
 Synaptic cleft – gap
between nerve and
muscle
 Gap is filled with
interstitial fluid
Figure 6.5b
Nerve Stimulus to Muscles
 2. Action potentials are
sent down the neuron in
response to a stimuli
 Because the two cells
do not touch, the action
potential cannot ‘jump
the gap’
Figure 6.5b
Nerve Stimulus to Muscles
 3. The neuron
communicates indirectly
with the muscle cell by
releasing a neurotransmitter
 The neurotransmitter for
skeletal muscle is
acetylcholine (ACh) and it is
stored in the axonal terminal
 4. Sarcolemma has
receptors for Ach and
causes an action potential in
muscle cell
Transmission of Nerve Impulse Wrap-up
1. How does the neurotransmitter
produced by the motor neuron cause
the skeletal muscle to contract?
2. What is the neurotransmitter in muscle
cells?
3. What is the synaptic cleft?
4. What makes up a motor unit?
5. List the steps of transmission of a
nerve impulse.
The Sliding Filament Theory of Muscle Contraction
 Put your right palm on
the back of your left
hand.
 Now slide your right
palm toward your left
elbow
 What happened to the
distance between your
elbows?
 This is how muscle
contraction works!
Figure 6.7
Slide 6.17a
The Sliding Filament Theory of Muscle Contraction
 Activation by nerve causes
calcium to be released by
the sarcoplasm reticulum
 Calcium binds to actin and
exposes myosin binding
sites where the myosin
heads attach and form a
crossbridge
 ATP is used as the energy
source
Figure 6.7
Slide 6.17a
The Sliding Filament Theory of Muscle Contraction
 The thin filament slides
past the thick filament
towards the center as
each myosin head
attaches and detaches
 Distance between Z
discs shortens as actin
moves toward the center
 The result is that the
entire muscle is
shortened (contracted)
Figure 6.7
Slide 6.17b
The Sliding Filament Theory of Muscle Contraction
 Length of the A band
(myosin and actin) stays
the same
 Length of the H zone (only
thick filaments) shortens
 Length of the I band (thin
filaments) shortens
 http://highered.mcgrawhill.com/sites/0072437316/st
udent_view0/chapter42/anim
ations.html#
Figure 6.7
Slide 6.17b
The Sliding Filament Theory
Go to figure 6.8 in your book and summarize the steps
for the sliding filament theory and explain how a muscle
contracts
Transmission of Nerve Impulse to Muscle
Contraction
1. Nerve impulse sent and received by axonal terminal
2. Neurotransmitter (acetylcholine) is released upon arrival
of nerve impulse
3. Diffuses across synaptic cleft and attaches to receptors
on the sarcolemma
4. Triggers an action potential of the muscle cell
5. The action potential causes the SR to release calcium
ions
6. The calcium ions bind with the actin filaments to open
the binding site for myosin
7. Myosin heads bind to them with the help of ATP
8. The cell contracts