chapter 20
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How Animals Move
Chapter 20
20.1 Impacts/Issues
Bulking Up Muscles
Exercise makes muscles bigger, not by adding
cells but by adding proteins to existing cells
Certain hormones and other molecules regulate
this process
• Testosterone and human growth hormone
increase muscle growth
• Myostatin slows muscle growth
Effects of Myostatin
A normal whippet and one homozygous for a
mutation that prevents myostatin production
20.2 The Skeletal System
Muscles bring about movement by applying
contractile force against body fluids or structural
elements, such as bones
Three categories of skeletal systems are
common in animals – hydrostatic skeletons,
exoskeletons, and endoskeletons
Three Types of Skeletons
Hydrostatic skeleton (earthworm)
• Fluid-filled chamber that muscles act on,
redistributing the fluid
Exoskeleton (fly)
• Hard external parts that muscles attach to
Endoskeleton (humans, other vertebrates)
• Hard internal parts that muscles attach to
The Human Skeleton
The human skeleton consists of skull bones, a
vertebral column, a rib cage, a pelvic girdle, a
pectoral girdle, and paired limbs
The vertebral column consists of individual
segments called vertebrae, with intervertebral
disks between them
The Vertebral Column
Vertebral column
• The backbone
Vertebrae
• Bones of the backbone
Intervertebral disk
• Cartilage disk between two vertebrae
Functions of the Vertebral Column
The spinal cord runs through the vertebral
column and connects with the brain through a
hole in the base of the skull
The shape of the human backbone is an
evolutionary adaptation to upright walking
The Pectoral Girdle and Upper Limbs
Pectoral girdle
• Scapula
• Clavicle
Upper limb bones
• Humerus
• Radius and ulna
The Pelvic Girdle and Lower Limbs
Pelvic girdle
• Six fused bones
Lower limb bones
• Femur
• Tibia and fibula
• Patella
The Human Skeleton
Fig. 20-2, p. 405
Skull
cranial bones
facial bones Pectoral Girdle
clavicle (collarbone)
scapula
(shoulder blade)
Rib Cage
sternum
(breastbone)Upper Limb Bones humerus (upper arm bone)ribs (12 pairs)
Vertebral Column vertebrae
ulna (forearm bone)
intervertebral disk (cartilage)
radius (fore-arm bone)
Pelvic Girdle (6 fused bones)
carpals (wrist bones)
metacarpals (palm bones)
Lower Limb Bonesphalanges (finger bones)
femur (thighbone)
patella (kneecap)
tibia (lower leg bone)
fibula (lower leg bone)
tarsals (ankle bones)
metatarsals (sole bones)
phalanges (toe bones)
Animation: Human skeletal system
Bone Structure and Function
Bones are collagen-rich, mineralized organs,
wrapped in connective tissue
Bones function in mineral storage, movement,
and protection and support of soft organs
• Ongoing mineral deposits and removals help
maintain blood levels of calcium and phosphorus,
and also adjust bone strength
• Some bones are sites of blood cell formation
Two Types of Bone
Compact bone
• Dense, weight-bearing bone with thin concentric
layers of matrix surrounding canals for nerves
and blood vessels
Spongy bone
• Lightweight bone with many internal spaces filled
with red or yellow marrow
Bone Marrow
Red marrow
• Bone marrow that makes blood cells
Yellow marrow
• Bone marrow that is mostly fat
• Fills cavity in most long bones such as the femur
Structure of a Femur
Fig. 20-3a, p. 406
Fig. 20-3a, p. 406
nutrient canal
location of
yellow marrow
compact
bone tissue
spongy
bone
tissue
Fig. 20-3b, p. 406
Fig. 20-3b, p. 406
spongy
bone
tissuecompact
bone tissueouter layer
of dense
connective tissueblood vessel
Fig. 20-3c, p. 406
Fig. 20-3c, p. 406
space occupied
by living bone cell
central canal
Animation: Structure of a femur
Osteoporosis
Until about age 24, people produce bone matrix
faster than they break it down – as people age,
bone density declines
Osteoporosis
• Disorder in which bones lose calcium, weaken,
and are more likely to break
• Increased by smoking, excess alcohol or cola
Where Bones Meet – Skeletal Joints
Joint
• Region where bones meet and interact
Different joints have different movements
• Ball-and-socket joint (shoulder, hip)
• Gliding joints (wrists, ankles)
• Hinge joints (elbows, knees)
Fibrous and Cartilaginous Joints
Fibrous joints hold bones tightly in place; cartilaginous joints let them move a bit
Fibrous joint
• Joint where dense connective tissue holds bones firmly in place (cranial bones)
Cartilaginous joint
• Joint where pads of cartilage hold bones together and provide cushioning, as between vertebrae
Synovial Joints
Synovial joints allow the most motion; ligaments connect bones at synovial joints
Synovial joint
• Joint such as the knee that is lubricated by fluid and allows movement of bones around the joint
Ligament
• Dense connective tissue that holds bones together at a joint
Knee Joint
A hinge-type synovial joint, held together by
ligaments, stabilized by cartilage
Fig. 20-4, p. 407
femur
patella
cartilage
cruciate
ligaments
menisci
tibia
fibula
Joint Injuries
Common joint injuries include sprained ankles,
torn cruciate ligaments, and dislocations
Sprain
• Ligaments of a joint are injured
Dislocation
• Bones of a joint are out of place
Arthritis
Arthritis
• Chronic inflammation and associated pain and
swelling of a joint
Two types of arthritis:
• Osteoarthritis typically occurs in old age when
cartilage is worn down
• Rheumatoid arthritis is an autoimmune disorder
which attacks all synovial joints
Animation: Vertebrate skeletons
Animation: Long bone formation
Video: ABC News: Taller and taller
20.3 How Bones and Muscles Interact
Muscles and bones work like a lever system
• When skeletal muscles contract, they transmit
force to a tendon that makes the bones move
Tendon
• Strap of dense connective tissue that connects a
skeletal muscle to bone
How Skeletal Muscles Move
Muscles can only pull on bones, they cannot
push them
Skeletal muscles often work as opposing pairs
• Action of one reverses the action of the other
• Example: biceps and triceps
Opposition: Biceps and Triceps
Fig. 20-5, p. 408
1biceps
radius
2
triceps
Animation: Human skeletal muscles
Animation: Structure of a sarcomere
20.4 Skeletal Muscle
Structure and Function
The internal organization of a skeletal muscle
promotes a strong, directional contraction
• Many myofibrils make up a skeletal muscle fiber
• A myofibril consists of units of sarcomeres, lined
up along its length
• Each sarcomere has parallel arrays of actin and
myosin filaments
Skeletal Muscle Structure
Myofibrils
• Threadlike, cross-banded skeletal muscle
components that consist of sarcomeres arranged
end to end
Sarcomere
• Unit of skeletal muscle contraction, containing
actin and myosin filaments
Skeletal Muscle Structure
Actin
• Globular protein
• Thin filaments of muscle fibers
• Works with myosin to contract muscles
Myosin
• Motor protein with a club-shaped head
• Thick filaments of muscle fibers
• Works with actin to contract muscles
Skeletal Muscle Structure
Fig. 20-6 (left), p. 409
Fig. 20-6 (left), p. 409
biceps
brachii
triceps
brachii deltoid
pectoralis
majortrapezius
latissimus
dorsirectus
abdominis
gluteus
maximus
biceps
femoris
quadriceps
femorisgastrocnemi
us
Achilles
tendon
Fig. 20-6 (a-c), p. 409
Fig. 20-6a, p. 409
Fig. 20-6a, p. 409
outer
sheath
of one
skeletal
muscle
one bundle of many
muscle fibers in parallel
inside the sheath
Fig. 20-6b, p. 409
Fig. 20-6b, p. 409
B one myofibril, made up of sarcomeres arranged end to end
sarcomere sarcomere
Z line Z line Z line
Fig. 20-6c, p. 409
Fig. 20-6c, p. 409
Z line Z line
C one sarcomere, with
parallel actin and
myosin filaments
actin myosin actin
Z line Z line
Animation: Structure of a skeletal muscle
Muscle Contraction
Skeletal muscles contract in response to signals
from the nervous system
Sliding-filament model
• Explains how interactions of actin and myosin
filaments shorten a sarcomere and bring about
muscle contraction
How Sarcomeres Shorten
The sliding-filament model
• Actin and myosin filaments lie close to each other
• ATP activates myosin heads in thick filaments
• Calcium is released; myosin binds to actin
• Myosin heads tilt, sliding actin toward the center;
the sarcomere contracts
• Binding of ATP releases myosin from actin; the
sarcomere relaxes
The Sliding Filament Model
Fig. 20-7a, p. 410
Fig. 20-7a, p. 410
actin myosin actin
Sarcomere between contractions
Fig. 20-7b, p. 410
Fig. 20-7b, p. 410
myosin head
one of many myosin-binding sites on actin
cross-bridge cross-bridge
Fig. 20-7c, p. 410
Fig. 20-7d, p. 410
Fig. 20-7d, p. 410
cross-bridge broken cross-bridge broken
Same sarcomere, contracted
Animation: Sliding filament model
Getting Energy For Contraction
Muscle fibers produce ATP needed for
contraction by three pathways:
• Dephosphorylation of creatine phosphate (lasts 5
to 10 seconds)
• Aerobic respiration of glycogen (another 5 to 10
minutes), then of blood glucose and fatty acids
(as long as oxygen is available)
• Lactate fermentation (when oxygen is no longer
available)
Three Metabolic Pathways of ATP
Fig. 20-8a, p. 411
pathway 1
dephosphorylation of
creatine phosphate
ADP + Pi
creatine
pathway 2
aerobic respiration
pathway 3
lactate fermentation
glucose from bloodstream and
from glycogen breakdown in cellsoxygen
Fig. 20-8a, p. 411
pathway 1
dephosphorylation of
creatine phosphate
ADP + Pi
creatine
pathway 3
lactate fermentation
pathway 2
aerobic respiration
glucose from bloodstream and
from glycogen breakdown in cellsoxygen
Stepped Art
Fig. 20-8b, p. 411
Animation: Energy sources for
contraction
Animation: Opposing muscle action
Animation: Troponin and tropomyosin
Animation: Muscle contraction overview
20.5 Properties of Whole Muscles
Motor unit
• One motor neuron and all muscle fibers that form junctions with its endings
• All fibers of a motor unit contract at the same time
• Repeated stimulation of a motor unit results in a strong, sustained contraction
• Brief stimulation causes a muscle twitch
Muscle twitch
• Brief muscle contraction and relaxation
Stimulation of a Motor Unit
Fig. 20-9, p. 411
Fo
rce relaxation starts
stimulus
A A single, brief stimulus causes a twitch.
sustained
contractiontwitch
Fo
rce
repeated stimulationTime
B Repeated stimulation results in a sustained
contraction with several times the force of a twitch.
contraction
Animation: Types of contractions
Muscle Tension
Muscle tension is a mechanical force caused by
muscle contraction
• Opposed by a load (weight of object or gravity)
Muscle tension
• Force exerted by a contracting muscle
• Affected by number of fibers recruited
Isotonic and Isometric Contraction
A muscle shortens only when muscle tension
exceeds an opposing load
• Isotonically contracting muscles shorten and
move a load
• Isometrically contracting muscles develop tension
but do not shorten or move a load
Isotonic and Isometric Contraction
Fig. 20-10a, p. 412
Fig. 20-10a, p. 412
contracted
muscle can
shorten
Fig. 20-10b, p. 412
Fig. 20-10b, p. 412
contracted
muscle cannot
shorten
Muscles and Exercise
Aerobic exercise increases blood supply and number of mitochondria – which makes muscles more resistant to muscle fatigue
Strength training stimulates formation of more actin and myosin, but muscles fatigue rapidly
Muscle fatigue
• Decrease in a muscle’s ability to contract despite ongoing stimulation
Muscles and Aging
Muscle strength decreases with age
• Muscles shrink; number of muscle fibers declines
• Injuries take longer to heal
Strength training and aerobic exercise are
helpful at any age
• Slows loss of muscle tissue, improves circulation
• Also good for the brain
Impaired Muscle Contraction
Some genetic disorders affect muscle structure
and impair muscle function
• Duchenne muscular dystrophy (X-linked)
Some diseases and toxins affect motor neurons
• Poliovirus kills motor neurons
• Tetanus, caused by toxins of Clostridium tetani,
kills by locking skeletal muscles in contraction
• Amyotrophic lateral sclerosis (ALS)
Muscular Dystrophy
Normal skeletal muscle and muscle with
muscular dystrophy
Tetanus
20.6 Impacts/Issues Revisited
Research on drugs that inhibit myostatin activity
may help slow muscle loss resulting from
muscular dystrophy, ALS, or even normal aging
Digging Into Data:
Building Stronger Bones