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

Video: Pumping up muscles

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: Fly wing action

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