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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.