Albia Dugger • Miami Dade College

Chapter 35Structural Support

and Movement

35.1 Muscles and Myostatin

• Skeletal muscle gets bulkier by enlarging existing cells

• Hormones such as testosterone and human growth hormone increase muscle mass

• People who do not respond normally to the protein myostatin have large muscles and unusual strength

• Bully whippets homozygous for a mutation that prevents them from making myostatin are also heavily muscled

Disrupted Myostatin Function

Disrupted and Normal Myostatin Function

36.1 Invertebrate Skeletons

• Hydrostatic skeleton• An enclosed fluid that contracting muscles act upon• Found in sea anemones, earthworms)

• Exoskeleton• A hardened external skeleton• Found in some mollusks and all arthropods

• Endoskeleton • An internal skeleton• Found in echinoderms and vertebrates

Hydrostatic Skeleton: Sea Anemone

gastrovascularcavity; the mouthcan close andtrap fluid insidethis cavity

mouth

Hydrostatic Skeleton: Earthworm

Exoskeleton: Fly

thorax

Exoskeleton: Spider

Endoskeleton: Echinoderm

Take-Home Message: What kinds of skeletons do invertebrates have?

• Soft-bodied animals such as sea anemones and earthworms have a hydrostatic skeleton—an enclosed fluid that contractile cells exert force upon.

• Some mollusks and all arthropods have a hardened external skeleton, or exoskeleton.

• Echinoderms have an endoskeleton, an internal skeleton.

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 of Early Reptile

vertebral column

pectoral girdle

skull bonesrib cage

pelvic girdle

The Human Skeleton

• Some features of the human skeleton are adaptations to upright posture and walking

• The brain and spinal cord connect through an opening in the base of the skull called the foramen magnum

• Maintaining an upright posture requires that vertebrae and intervertebral disks stack one on top of the other in an S shape, rather than being parallel to the ground

Figure 35-8a p611

Cranial bones

Facial bones

B Rib Cage

Sternum (breastbone)

Ribs (12 pairs)

C Vertebral Column

Vertebrae (26 bones)

Intervertebral disks

A Skull

Patella (kneecap)

Clavicle (collarbone)

12

345

Scapula (shoulder blade)

E Bones of the ArmHumerus (upper arm bone

Phalanges (finger bones)

Metacarpals (palm bones)

Carpals (wrist bones)Ulna (forearm bone)

F Pelvic Girdle

Femur (thighbone)

phalanges (toe bones)metatarsals (sole bones)Tarsals (ankle bones)

Fibula (lower leg bone)

Tibia (lower leg bone)

D Pectoral Girdle

G Bones of the Legs

Radius (forearm bone)

Figure 35-8b p611

thoraic vertebrae

cervical vertebrae

coccyx (tailbone)

sacrum

lumbar vertebrae

ANIMATED FIGURE: Human skeletal system

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Take-Home Message: What type of skeleton do humans and other vertebrates have?

• The endoskeleton of vertebrates usually consists mainly of bone. Its axial portion includes the skull, vertebral column, and ribs. Its appendicular part includes a pectoral girdle, a pelvic girdle, and the limbs.

• Some features of the human skeleton such as an S-shaped backbone are adaptations to upright posture and walking.

35.4 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

compact bone tissue

location of yellow marrow

nutrient canal

spongy bone tissue

Cross-section through a Femur

blood vessel

space occupied by living bone cell

one osteon

Table 35-1 p612

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

Figure 35-10 p613

Embryo:cartilage modelof bone forms

Fetus:blood vessel invadesmodel; osteoblastsstart producing bonetissue; marrowcavity forms

Newborn:remodeling andgrowth continue;secondary bone-forming centersappear at knobbyends of bone

Adult: mature bone

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

A Normal bone B Bone weakened by osteoporosis

Take-Home Message: What are the structural and functional features of bones?

• Bones have a variety of shapes and sizes.

• A sheath of connective tissues encloses the bone, and the bone’s inner cavity contains marrow. Red marrow produces blood cells.

• All bones consist of bone cells in a secreted extracellular matrix. A bone is continually remodeled; osteoclasts break down the matrix of old bone and osteoblasts lay down new bone. Hormones regulate this process.

35.5 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)

Figure 35-12a p614

fibrous jointattachestooth tojawbone

synovial joint (balland socket) betweenhumerus and scapula

synovial joint (balland socket) betweenpelvic girdle andfemur

synovial joint (hingetype) betweenhumerus and radius

artilaginous jointbetween adjacentvertebrae

cartilaginous jointbetween rib andsternum

Figure 35-12 p614

femur

fibula

tibia

menisci

cruciate ligaments

cartilage

patella

Joint Health

• 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)

Increased Risk of Knee Osteoarthritis

Take-Home Message: What are joints?

• Joints are areas where bones meet and interact.

• In the most common type, synovial joints, the bones are separated by a small fluid-filled space and are held together by ligaments of fibrous connective tissue.

35.6 Skeletal–Muscular Systems

• 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 muscle activity also generates body heat

biceps

ulna

tendons

tendon

radius

triceps

Figure 35-14 p616

Quadriceps femoris (set of four muscles) flex the thigh at the hip, extend the leg at the knee

Sartorius raises and rotates thigh; flexes leg at knee; longest muscle in the body

Rectus abdominus compresses the abdomen, bends the back

Pectoralis major draws arm forward and in toward the body

Triceps brachii straightens forearm

Biceps brachii bends forearm at elbow

Achilles tendon attaches gastrocnemiusto the heel bone

Gastrocnemius bends leg at knee; turns foot downward

Biceps femoris (one of three hamstringmuscles) extends leg straight back; bends knee

Gluteus maximus (one of three buttock muscles) extends and laterally rotates thigh at the hip

Lattisimus dorsi draws arm inward, extends arm behind back, rotates arm at shoulder

Trapezius elevates and rotates shoulder blade (scapula)

Deltoid raises arm at shoulder

Figure 35-15 p617

Take-Home Message: How do muscles and tendons interact with bones?

• Tendons of dense connective tissue attach skeletal muscles to bones.

• Small muscle movements can bring about large movements of bones.

• Muscles can only pull on a bone; they cannot push. At many joints, movement is controlled by a pair of muscles that act in opposition.

35.7 How Does Skeletal Muscle Contract?

• A muscle fiber is a cylindrical contractile cell that runs the length of the muscle

• A skeletal muscle fiber has many nuclei, and is filled with threadlike myofibrils

• Myofibrils are bundles of contractile filaments run the length of the muscle fiber

Structure of Skeletal Muscle

• 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)

Figure 35-16a-c p618

A Musclein a sheathof connectivetissue

B Bundle of musclefibers wrapped inconnective tissue

C Cross section of a muscle fiber, a multinucleated cell whose interior is crammed full of threadlike protein structures called myofibrils. (Colorized scanning electronmicrograph)

Figure 35-16de p618

D Portion ofone myfibril.

sarcomere sarcomere

Z band

sarcomere

E Each myofibril consists of many contractile units called sarcomeres arranged end to end.

Z band H zone Z band

Figure 35-16f-h p618

actin

sarcomere

myosin head

troponintropomyosin

H Thin filaments consist mostly ofthe globular protein actin, with lesseramounts of two other proteins (troponinand tropomyosin).

G Thick filaments are composedof parallel bundles of the motorprotein myosin. A myosin moleculehas a head that can bind to actinand a long tail.

F Each sarcomere has a dark Zband at either end, and alternatingrows of thick and thin proteinfilaments in between them.

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

Figure 35-17 p619

relaxed sarcomere

musclecontraction

contracted sarcomere

Figure 35-17 p619

ADP, PiADP, Pi

ATP ATPmyosin head

3

1

4

5

2

ADP ADP

ATP ATP

Take-Home Message: How does a muscle’s structure affect its function?

• Sarcomeres are the basic units of contraction in skeletal muscle. Sarcomeres are lined up end to end in myofibrils that run parallel with muscle fibers. These fibers, in turn, run parallel with the whole muscle.

• The parallel orientation of skeletal muscle components focuses a muscle’s contractile force in a particular direction.

Take-Home Message: (cont.)

• Energy-driven interactions between myosin and actin filaments cause the sarcomeres of a muscle cell to shorten and bring about muscle contraction.

• During muscle contraction, the length of actin and myosin filaments does not change, and the myosin filaments do not change position. Sarcomeres shorten because myosin filaments pull neighboring actin filaments inward toward the center of the sarcomere.

Video: How Muscles Hold Tension

ANIMATION: Muscle Contractions

35.8 Nervous Control of Muscle 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

section from spinal cord

motor neuron A signal travels along the axon of a motor neuron, from the spinal cord to a skeletal muscle.

1

Stepped Art

section from skeletal muscle

neuromuscular junction The signal is transferred from the motor neuron to the muscle at neuromuscular junctions. Here, ACh released by the neuron’s axon terminals diffuses into the muscle fiber and causes action potentials.

2

muscle fiber’s plasma membrane

one myofibril in muscle fiber

sarcoplasmic reticulum

Ttubule

Action potentials propagate along a muscle fiber’s plasma membrane down toT tubules, then to the sarcoplasmic reticulum, which releases calciumions. The ions promote interactions of myosin and actin that result in contraction.

3

Figure 35-18 p620

ANIMATED FIGURE: Nervous system and muscle contraction

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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

Role of Calcium in Muscle Contractiontropomyosintroponinactin

Ca++

exposed myosin-binding sites

B Excited muscle. Ca++ binds to troponin, which shifts andmoves tropomyosin, exposing myosin-binding sites on actin.

A Resting muscle. Calcium ion (Ca++) concentration is low andtropomyosin covers the myosin-binding sites on actin.

Motor Units and Muscle Tension

• Motor unit• One motor neuron and all of the muscle fibers its axons

synapse with

• Muscle tension• The mechanical force exerted by a muscle• The more motor units stimulated, the greater the muscle

tension

Disrupted Control of Skeletal Muscle

• Some genetic disorders, diseases, or toxins can cause muscles to contract too little or too much• Botulism (Clostridium botulinum toxin) prevents motor

neurons from releasing ACh• Tetanus (C. tetani toxin) prevent inhibition of motor

neurons• Polio virus impairs motor neuron function• Amyotrophic lateral sclerosis (ALS) also kills motor

neurons

Tetanus

Polio

ALS

Take-Home Message: How do nervous signals cause muscle contraction?

• A 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.

• An action potential results in release of calcium ions, which affect proteins attached to actin. Resulting changes in the shape and location of these proteins open the myosin-binding sites on actin, allowing cross-bridge formation.

ANIMATION: Calcium and Cross Bridge Cycles

35.9 Muscle Metabolism

• 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 Energy-Releasing Pathways

dephosphorylation of creatinephosphate

ADP + Pi

oxygenglucose from bloodstream and

from glycogen breakdown in cells

creatine

lactate fermentation

aerobic respiration

1

2 3

Types of Muscle Fibers

• Red fibers (high in myoglobin)• Have an abundance of mitochondria • Produce ATP mainly by aerobic respiration• Myoglobin allows aerobic respiration to continue even if

blood flow is insufficient to meet oxygen need

• White fibers (no myoglobin)• Have few mitochondria• Make ATP mainly by lactate fermentation

Fast and Slow Fibers

• Muscle fibers are subdivided into fast fibers or slow fibers based on the ATPase activity of their myosin

• All white fibers are fast fibers; red fibers can be fast or slow

• The mix of fiber types in each skeletal muscle varies between individuals and has a genetic basis

Effects of Exercise

• Muscle fatigue is a decrease in capacity to generate force; muscle tension declines despite repeated stimulation

• Aerobic exercise makes muscles more resistant to fatigue by increasing blood supply and number of mitochondria

• Intense exercise increases actin and myosin

• Exercise increases production of lipoprotein lipase (LPL), which allows muscle to take up fatty acids and triglycerides

Low Activity, Low LPL

Take-Home Message:What factors affect muscle metabolism?

• Muscle contraction requires ATP. When excited, muscle first uses stored ATP, then transfers phosphate from creatine phosphate to ADP to form ATP. With prolonged exercise, aerobic respiration and lactate fermentation provide ATP.

• Exercise increases blood flow to muscles, the number of mitochondria, production of actin and myosin, and the muscle’s ability to take up lipids from the blood for use as an energy source.