Structural Support and Movement

Chapter 36

Impacts, Issues

Pumping Up Muscles

Increasing muscle size and strength with drugs

such as “andro” has unwanted side effects and

can damage other organ systems

36.1 Invertebrate Skeletons

Hydrostatic skeleton

• An enclosed fluid that contracting muscles act

upon (as in sea anemones, earthworms)

Exoskeleton

• A hardened external skeleton found in some

mollusks and all arthropods

Endoskeleton

• An internal skeleton, as in echinoderms

Hydrostatic Skeleton: Sea Anemone

Hydrostatic Skeleton: Earthworm

Exoskeleton: Fly

Exoskeleton: Spider

36.1 Key Concepts

Invertebrate Skeletons

Contractile force exerted against a skeleton moves animal bodies

In many invertebrates a fluid-filled body cavity is a hydrostatic skeleton

Others have an exoskeleton of hard structures at the body surface

Still others have a hard internal skeleton, or endoskeleton

36.2 The Vertebrate Endoskeleton

All vertebrates have an endoskeleton

• Usually consists primarily of bones

• Supports the body, site of muscle attachment

• Protects the spinal cord

The vertebral column (backbone) is made up of

individual vertebrae separated by

intervertebral disks made of cartilage

Axial and Appendicular Skeleton

Axial skeleton

• Skull

• Vertebral column

• Ribs

Appendicular skeleton

• Pectoral girdle

• Pelvic girdle

• Limbs

Skeletal Elements: Fish and Reptile

The Human Skeleton

Some features of the human skeleton are

adaptations to upright posture and walking

• Foramen magnum at the base of the skull allows

brain and spinal cord to connect

• Vertebrae stacked one above the other in an S

curve

Bones of the Human Skeleton

36.3 Bone Structure and Function

Bones have a variety of shapes and sizes

• Long bones (arms and legs)

• Flat bones (skull, ribs)

• Short bones (carpals)

The human skeleton has 206 bones ranging

from tiny ear bones to the massive femur

Bone Anatomy

Bones consist of three types of living cells in a

secreted extracellular matrix

• Osteoblasts build bones

• Osteocytes are mature osteoblasts

• Osteoclasts break down bone matrix

Bone cavities contain bone marrow

• Red marrow in spongy bone forms blood cells

• Yellow marrow in long bones is mostly fat

Bone Anatomy: Long Bone

Bone Functions

Bone Formation and Remodeling

The embryonic skeleton consists of cartilage

which is modeled into bone, grows until early

adulthood, and is constantly remodeled

Bones and teeth store the body’s calcium

• Calcitonin slows release of calcium from bones

• Parathyroid hormone releases bone calcium

• Sex hormones encourage bone building

• Cortisol slows bone building

Long Bone Formation

About Osteoporosis

Osteoporosis (“porous bones”)

• When more calcium is removed from bone than is

deposited, bone become brittle and break easily

Proper diet and exercise help keep bones

healthy

Osteoporosis

36.4 Skeletal Joints—Where Bones Meet

Joint

• Area of contact or near contact between bones

Three types of joints

• Fibrous joints (teeth sockets): no movement

• Cartilaginous joints (vertebrae): little movement

• Synovial joints (knee): much movement

Synovial Joints

In synovial joints, bones are separated by a fluid-

filled cavity, padded with cartilage, and held

together by dense connective tissue (ligaments)

Different synovial joints have different movements

• Ball-and-socket joints (shoulder)

• Gliding joints (wrist and ankles)

• Hinged joints (elbows and knees)

Three Types of Joints

Three Types of Joints

36.5 Those Aching Joints

We ask a lot of our joints when we engage in

sports, carry out repetitive tasks, or strap on a

pair of high heels

Joint Injuries and Diseases

Common joint injuries

• Sprained ankle; torn cruciate ligaments in knee;

torn meniscus in knee; dislocations

Arthritis (chronic inflammation)

• Osteoarthritis; rheumatoid arthritis; gout

Bursitis (inflammation of a bursa)

36.2-36.5 Key Concepts

Vertebrate Skeletons

Vertebrates have an endoskeleton of cartilage, bone, or both

Bones interact with muscles to move the body; they also protect and support organs, and store minerals

Blood cells form in some bones

A joint is a place where bones meet; there are several kinds

36.6 Skeletal–Muscular Systems

Muscle fibers

• Long, cylindrical cells with multiple nuclei that

hold contractile filaments

Tendons attach skeletal muscle to bone

• Muscle contraction transmits force to bone and

makes it move

Muscles and bones interact as a lever system

• Many skeletal muscles work in opposing pairs

Skeletal–Muscular Action

Opposing Muscle Groups

Muscles and Tendons

Muscles and Tendons

36.6 Key Concepts

The Muscle–Bone Partnership

Skeletal muscles are bundles of muscle fibers

that interact with bones and with one another

Some cause movements by working as pairs or

groups; others oppose or reverse the action of a

partner muscle

Tendons attach skeletal muscles to bones

36.7 How Does Skeletal Muscle Contract?

Myofibrils (bundles of contractile filaments) run

the length of the muscle fiber

Myofibrils are divided into bands (striations) that

define units of contraction (sarcomeres)

• Z-bands attach sarcomeres to each other

Sarcomeres contain two types of filaments

• Thin, globular protein filaments (actin)

• Thick, motor protein filaments (myosin)

Fine Structure of Skeletal Muscle

The Sliding Filament Model

Sliding filament model

• Interactions among protein filaments within a

muscle fiber’s individual contractile units

(sarcomeres) bring about muscle contraction

• A sarcomere shortens when actin filaments are

pulled toward the center of the sarcomere by

ATP-fueled interactions with myosin filaments

The Sliding Filament Model

36.8 From Signal to Response:

A Closer Look at Contraction

Like neurons, muscle cells are excitable

• Skeletal muscle contracts in response to a signal

from a motor neuron

• Release of ACh at a neuromuscular junction

causes an action potential in the muscle cell

Nervous Control of Contraction

Action potentials travel along muscle plasma

membrane, down T tubules, to the sarcoplasmic

reticulum (a smooth endoplasmic reticulum)

Action potentials open voltage-gated channels in

sarcoplasmic reticulum, triggering calcium

release that allows contraction in myofibrils

Nervous Control of Contraction

The Roles of Troponin and Tropomyosin

Two proteins regulate bonding of actin to myosin

• Tropomyosin prevents actin from binding to myosin

• Troponin has calcium binding sites

Calcium binds to troponin, which pulls tropomyosin

away from myosin-binding sites on actin

Cross-bridges form, sarcomeres shorten, and

muscle contracts

Interactions of Actin,

Tropomyosin, and Troponin

36.9 Energy for Contraction

Multiple metabolic pathways can supply the ATP

required for muscle contraction

Muscles use any stored ATP, then transfer

phosphate from creatine phosphate to ADP to

form ATP

With ongoing exercise, aerobic respiration and

lactic acid fermentation supply ATP

Three Metabolic Pathways Supply ATP

36.10 Properties of Whole Muscles

Motor unit

• One motor neuron and all of the muscle fibers its

axons synapse with

Muscle twitch

• Contraction produced by brief stimulation of a

motor unit

Tetanus

• A sustained contraction caused by repeated

stimulation of a motor unit in a short interval

Muscle Twitch and Tetanus

Motor Units and Muscle Tension

Muscle tension

• The mechanical force exerted by a muscle

• The more motor units stimulated, the greater the

muscle tension

A load opposes muscle tension

• Isotonic contraction: muscle shorten and move

the load

• Isometric contraction: muscles tense but do not

shorten or move the load

Isotonic and Isometric Contraction

Fatigue, Exercise, and Aging

Muscle fatigue

• Decrease in capacity to generate force; muscle

tension declines despite repeated stimulation

• Aerobic exercise makes muscles more resistant

to fatigue (increases blood supply, mitochondria)

• Intense exercise increases actin and myosin

All muscle fibers form before birth; number and

size of muscle fibers decline as people age

36.11 Disruption of Muscle Contraction

Some genetic disorders, diseases, or toxins can

cause muscles to contract too little or too much

• Muscular dystrophy (X-linked disorder)

• Motor neuron disorders (polio, ALS)

• Botulism (Clostridium botulinum toxin) and

tetanus (C. tetani toxin)

Muscular Dystrophy

Muscle fibers break down, muscles fail – death

results from respiratory failure

Tetanus

C. tetani infection, preventable by tetanus vaccine

36.7-36.11 Key Concepts

Skeletal Muscle Function

Muscle fibers contract in response to signals

from a motor neuron

A muscle fiber contains many myofibrils, each

divided crosswise into sarcomeres

ATP-driven interactions between protein

filaments shorten sarcomeres, causing muscle

contraction