1
Chapter 13
Lecture Outline
See separate PowerPoint slides for all figures and tables pre-
inserted into PowerPoint without notes.
Copyright © 2016 McGraw-Hill Education. Permission required for reproduction or display.
2
Muscular System
3
Points to ponder • What are the three types of muscle tissue?
• What are the functions of the muscular system?
• How are muscles named and what are the muscles of the human body?
• How are skeletal muscles and muscle fibers structured?
• How do skeletal muscles contract?
• How do skeletal muscle cells acquire ATP for contraction?
• What is rigor mortis?
• What are some common muscular disorders?
• What are some serious muscle diseases?
• How do the skeletal and muscular system help maintain homeostasis?
• How are these two systems related to other systems in maintaining homeostasis?
4
Review: Types of muscle tissue
1. Smooth – involuntary muscle found in hollow organs and vessels
2. Cardiac – involuntary muscle found in the heart
3. Skeletal – voluntary muscle that is attached to the skeleton
13.1 Overview of the Muscular System
5
13.1 Overview of the Muscular System
Figure 13.1 The three classes of muscles in humans.
Review: Types of muscle tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Skeletal muscle
• has striated cells
with multiple nuclei.
• occurs in muscles
attached to skeleton.
• functions in voluntary
movement of body.
striation nucleus
a. b. c.
250X
Cardiac muscle
• has branching,
striated cells, each
with a single nucleus.
• occurs in the wall of
the heart.
• functions in the pumping
of blood.
• is involuntary.
Smooth muscle
• has spindle-shaped
cells, each with a
single nucleus.
• cells have no striations.
• functions In movement of
substances in lumens of body.
• is involuntary.
• is found in blood vessel walls and walls
of the digestive tract.
400X
250X
Smooth muscle cell nucleus Intercalated disk nucleus
(smooth): © The McGraw-Hill Companies, Inc. Dennis Strete, photographer; (cardiac, skeletal): © Ed Reschke;
6
What are the functions of
skeletal muscles?
1. Support the body by allowing us to stay
upright
2. Allow for movement by attaching to the
skeleton
3. Help maintain a constant body temperature
4. Assist in movement in the cardiovascular and
lymphatic vessels
5. Protect internal organs and stabilize joints
13.1 Overview of the Muscular System
7
How are skeletal muscles attached?
• Tendon – connective tissue that connects muscle to bone
• Origin – attachment of a muscle on a stationary bone
• Insertion – attachment of a muscle on a bone that moves
Figure 13.2 Connecting muscle to bone.
13.1 Overview of the Muscular System
muscle fiber
fascicle
tendon
radius
dense
connective
tissue
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
8
How do skeletal muscles work?
• Antagonistic – muscles that work in opposite pairs
• Synergistic – muscles working in groups for a common action
Figure 13.3 Skeletal muscles often work in pairs.
13.1 Overview of the Muscular System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
tendon
origin
radius
ulna
a.
biceps brachii (contracted)
triceps brachii (relaxed)
humerus
insertion
biceps brachii (relaxed)
triceps brachii (contracted)
b.
9
Examples of how skeletal muscles
are named
• Size – the gluteus maximus is the largest
buttock muscle
• Shape – the deltoid is triangular (Greek letter
delta is Δ)
• Location – the frontalis overlies the frontal bone
• Direction of muscle fiber – the rectus abdominis
is longitudinal (rectus means straight)
13.1 Overview of the Muscular System
10
Examples of how skeletal muscles
are named
• Attachment – the brachioradialis is attached to
the brachium and radius
• Number of attachments – the biceps brachii has
2 attachments
• Action – the extensor digitorum extends the
digits
13.1 Overview of the Muscular System
11
Muscles of the human body 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
Limbs
Arm: above the elbow
Forearm: below the
elbow
Thigh: above the knee
Leg: below the knee
Achilles tendon
Gastrocnemius:
turns foot downward,
as when standing on toes;
bends leg at knee
Biceps femoris:
bends leg at knee;
extends thigh back
Gluteus maximus:
extends thigh back
Extensor
digitorum:
straightens
fingers and wrist
Extensor carpi
group:
straightens wrist
and hand
Triceps brachii:
straightens
forearm at elbow
Latissimus dorsi:
brings arm down
and backward
behind the body
Trapezius:
Raises scapula, as
When shrugging
shoulders; pulls head backward
Masseter:
a chewing muscle;
clenches teeth
Deltoid:
brings arm away
from the side of
body; moves arm
up and down in
front
Biceps brachii:
bends forearm at
elbow
Rectus abdominis:
Bends vertebral
column;
compresses
abdomen
Flexor carpi
group:
bends wrist
and hand
Adductor longus:
moves thigh toward
midline; raises
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
b. a.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 13.5 The major skeletal muscles of the human body.
13.1 Overview of the Muscular System
12
Muscle fibers/cells
• Terminology for cell structure
– The plasma membrane is called the sarcolemma.
– The cytoplasm is called the sarcoplasm.
– The SER of a muscle cell is called the
sarcoplasmic reticulum and stores calcium.
13.2 Skeletal Muscle Fiber Contraction
13
• Terminology for structure within a whole muscle
– Muscle fibers are arranged in bundles called fascicles.
– Myofibrils are bundles of myofilaments that run the length of a fiber.
– Myofilaments are proteins (actin and myosin) that are arranged in repeating units.
– Sarcomeres are the repeating units of actin and myosin found along a myofibril.
13.2 Skeletal Muscle Fiber Contraction
Muscle fibers/cells
14
Visualizing muscle structure
myofilament
one myofibril
sarcolemma
mitochondrion
sarcoplasm
A myofibril has many sarcomeres.
6,000×
A muscle contains
bundles of muscle
fibers, and a muscle
fiber has many
myofibrils.
bundle of
muscle cells
(fibers)
myofibril
skeletal
muscle
cell
(fiber)
T tubule sarcoplasmic
reticulum nucleus
Z line one sarcomere Z line
(myofi bril): © Biology Media/Photo Researchers, Inc.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 13.6 The structure of a skeletal muscle fiber.
13.2 Skeletal Muscle Fiber Contraction
15
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 golf club.
– Primarily, a thin filament consists of two intertwining strands of the protein actin.
– These filaments slide over one another during muscle contraction.
13.2 Skeletal Muscle Fiber Contraction
16
The sarcomere
Figure 13.6 The structure of a skeletal muscle fiber.
13.2 Skeletal Muscle Fiber Contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
I band A band Z line
myosin
cross-
bridge
Sarcomeres are relaxed.
Sarcomeres are contracted.
H band
actin
17
The beginning of muscle contraction:
The sliding filament model
1. Nerve impulses travel down a motor neuron to a neuromuscular junction.
2. Acetylcholine (ACh) is released from the neuron and binds to the muscle fiber.
3. This binding stimulates the fiber causing calcium to be released from the sarcoplasmic reticulum.
13.2 Skeletal Muscle Fiber Contraction
18
The beginning of muscle contraction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
skeletal muscle
fiber
axon branch
axon terminal
a. One motor axon goes to
Several muscle fibers.
axon terminal
synaptic vesicle
synaptic cleft
sarcolemma
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.
Ach receptor
folded
sarcolemma
acetylcholine
(ACh)
synaptic
cleft
synaptic
vesicle
(photo):© Victor B. Eichler
Figure 13.7 Motor neurons and skeletal muscle fibers join neuromuscular junctions.
13.2 Skeletal Muscle Fiber Contraction
19
Muscle contraction continued… 4. Released calcium combines with troponin, a
molecule associated with actin.
5. This causes the tropomyosin threads around actin to shift and expose myosin binding sites.
6. Myosin heads bind to these sites forming cross-bridges.
7. ATP binds to the myosin heads and is used for energy to pull the actin filaments towards the center of the sarcomere – contraction now occurs.
13.2 Skeletal Muscle Fiber Contraction
20
Visualizing the roles of calcium and
myosin in muscle contraction
myosin head
4.Binding of fresh ATP causes myosin
Head to return to resting position.
myosin
heads
actin
b. Function of myosin
myosin
filament
actin filament
cross-bridge
3.Upon ADP + P releases,
power stroke occurs:
head bends and pulls actin.
ADP
ATP
P
1.ATP is split when myosin
head is unattached.
2. ADP+ P are bound to
myosin asmyos in head
attaches to actin.
actin filament troponin myosin-binding sites
tropomyosin
Function of Ca2+
Troponin—Ca+ complex pulls tropomyosin
away, exposing myosin-binding sites.
Ca2+
Ca2+
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 13.8 The role of calcium ions and ATP during muscular contraction.
13.2 Skeletal Muscle Fiber Contraction
21
What role does ATP play in muscle
contraction and rigor mortis? • ATP is needed to attach and detach the myosin
heads from actin.
• After death, muscle cells continue to produce ATP through fermentation and muscle cells can continue to contract.
• When ATP runs out, some myosin heads are still attached and cannot detach, causing rigor mortis.
• Rigor mortis and body temperature may be used to estimate time of death.
13.2 Skeletal Muscle Fiber Contraction
22
Terms to describe whole muscle
contraction
• Motor unit – a nerve fiber and all of the muscle
fibers it stimulates
• Muscle twitch – a single contraction lasting a
fraction of a second
• Summation – an increase in muscle
contraction until the maximal sustained
contraction is reached
13.3 Whole Muscle Contraction
23
• Tetanus – maximal sustained contraction
• Muscle tone – a continuous, partial contraction
of alternate muscle fibers causing the muscle
to look firm
13.3 Whole Muscle Contraction
Terms to describe whole muscle
contraction
24
Physiology of skeletal muscle contraction
Figure 13.9 The three phases of a single muscle twitch and how summation and tetanus increase the force of contraction.
13.3 Whole Muscle Contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fo
rce
relaxation
period
contraction
period
latent
period
Time
fatigue
tetanus
summation
Stimuli
Time
Fo
rce
b.
Stimulus
a.
25
Where are the fuel sources for
muscle contraction?
• Stored in the
muscle
– Glycogen
– Fat
• In the blood
– Glucose
– Fatty acids
0 1 2 3 4
6 0
5 0
4 0
3 0
2 0
1 0
0
Exercise time (hr)
muscle triglycerides
plasma fatty acids
blood glucose muscle glycogen
Pe
rce
nta
ge
of
en
erg
y e
xp
en
dit
ure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 13.10 The sources of energy for muscle contraction.
13.3 Whole Muscle Contraction
26
What are the sources of ATP for
muscle contraction? • Limited amounts of ATP are stored in muscle fibers.
• Creatine phosphate pathway (CP) – fastest way to acquire ATP but only sustains a cell for seconds; builds up when a muscle is resting
• Fermentation – fast-acting but results in lactate build up
• Cellular respiration (aerobic) – not an immediate source of ATP but the best long term source
13.3 Whole Muscle Contraction
27
Acquiring ATP for muscle contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Anaerobic Anaerobic Aerobic
creatine
phosphate glycogen
glycogen or
fatty acids
fermentation
O2
creatine lactate CO2 + H2O
ATP ATP ATP
a. b. c.
+ + +
Figure 13.11 The three pathways by which muscle cells produce the ATP energy needed for contraction.
13.3 Whole Muscle Contraction
28
Muscle fibers come in 2 forms
Fast-twitch fibers
• Rely on CP and fermentation (anaerobic)
• Adapted for strength
• Light in color
• Few mitochondria
• Little or no myoglobin
• Fewer blood vessels than slow-twitch
13.3 Whole Muscle Contraction
29
Muscle fibers come in 2 forms
Slow-twitch fibers
• Rely on aerobic respiration
• Adapted for endurance
• Dark in color
• Many mitochondria
• Myoglobin
• Many blood vessels
13.3 Whole Muscle Contraction
30
Types of muscle fibers
Figure 13.12 Fast-twitch and slow-twitch muscle fibers differ in structure.
13.3 Whole Muscle Contraction
31
Exercise, exercise, exercise
• Exercise increases muscle strength, endurance, and flexibility.
• It increases cardiorespiratory endurance.
• HDL increases thus improving cardiovascular health.
• The proportion of protein to fat increases favorably.
13.3 Whole Muscle Contraction
32
• Exercise may prevent certain cancers: colon, breast, cervical, uterine, and ovarian.
• It improves density of bones thus decreasing the likelihood of osteoporosis.
• Exercise enhances mood and may relieve depression.
13.3 Whole Muscle Contraction
Exercise, exercise, exercise
33
Anabolic steroids • Anabolic steroids are a group of steroids that usually
increase protein production.
• The most common side effects are high blood pressure, jaundice, acne, and greatly increased risk of cancer.
• Abuse of these drugs may also cause impotence and shrinking of the testicles.
• Anabolic steroid use may lead to increased aggressiveness and violent mood swings.
• Are they worth the risk? Should they be legal to use in athletics?
13.4 Whole Muscle Contraction
34
Common muscle disorders
• Spasms – sudden, involuntary muscle
contractions that are usually painful
• Convulsions (seizures) – multiple spasms of
skeletal muscles
• Cramps – strong, painful spasms often of the
leg and foot
13.4 Muscle Disorders
35
Common muscle disorders
• Strain – stretching or tearing of a muscle
• Sprain – twisting of a joint involving muscles,
ligaments, tendons, blood vessels, and nerves
13.4 Muscle Disorders
36
Muscular diseases
• Myalgia – achy muscles due to injury or infection
• Fibromyalgia – chronic achy muscles; not well understood
• Muscular dystrophy – group of genetic disorders in which muscles progressively degenerate and weaken
13.4 Muscle Disorders
37
Muscular diseases • Myasthenia gravis – autoimmune disorder
that attacks the ACh receptor and weakens muscles of the face, neck, and extremities
• Amyotrophic lateral sclerosis (ALS) – commonly known as Lou Gehrig’s disease; motor neurons degenerate and die leading to loss of voluntary muscle movement
• Sarcomas – cancers that originate in muscle, or the connective tissue associated with muscle
13.4 Muscle Disorders
38
Homeostasis: The skeletal and
muscular systems • Both systems are involved with movement that
allows us to respond to stimuli, digestion of food, return of blood to the heart, and moving air in and out of the lungs.
• Both systems protect body parts.
• Bones store and release calcium needed for muscle contraction and nerve impulse conduction.
• Blood cells are produced in the bone.
• Muscles help maintain body temperature.
13.5 Homeostasis
39
How the skeletal and muscular systems
interact with other body systems
13.5 Homeostasis
Figure 13.13 The muscular system’s
contributions to homeostasis.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Digestive System
Urinary System
Cardiovascular System
The muscular and skeletal systems work
together to maintain homeostasis. The
systems listed here in particular also
work with these two systems.
Muscular Systems
Reproductive System
Respiratory System
Endocrine System
Nervous System
Muscle contraction moves gametes in
oviducts, and uterine contraction occurs
during childbirth. Androgens promote
muscle growth.
Respiration provides the oxygen needed for
ATP production so muscles can contract.
Muscles assists in breathing
Growth and sex hormones regulate muscle
development. Parathyroid hormone and
calcitonin regulate Ca2+ content of bones.
The nervous system coordinates the activity
of muscles. Muscle contraction moves eyes,
permits speech, and creates facial
expressions.
The muscular system works with the skeletal
system to allow movement and support and
protection for internal organs. Muscle
contraction provides heat to warm the body;
bones play a role in Ca2+ balance. These
systems specifically help the other systems
as mentioned below.
Muscle contraction keeps blood moving in the
heart and blood vessels, particularly the veins.
Muscle contraction moves the fluid within
ureters, bladder, and urethra. Kidneys
activate vitamin D needed for Ca2+ absorption
and help maintain the blood level of Ca2+ for
muscle contraction.
Muscle contraction accounts for chewing
of food and peristaltic movement. The
digestive system absorbs ions needed for
muscle contraction.
