Protection, Support, and Movement Chapter 37

Husky Adaptations Huskies are adapted to load pulling and long distance running in cold climates Their integument, musculature, and skeleton are specialized for this way of life

Integumentary System An animal’s outer covering Examples Chitin-hardened cuticle of many invertebrates Vertebrate skin and its derivatives

Vertebrate Skin Two layers Lies atop a layer of hypodermis Upper epidermis Lower dermis Lies atop a layer of hypodermis Figure 37.3 Page 646

Functions of Human Skin Protects the body from injury, dehydration, UV radiation, and some pathogens Helps control temperature Receives some external stimuli Produces vitamin D

Sunlight Damages Skin UV light stimulates melanin production in skin; produces a tan Tan is the body’s way of protecting itself against UV Prolonged sun exposure causes elastin fibers to clump, skin to age prematurely

Langerhans Cells White blood cells that arise in bone marrow, migrate to epidermis Engulf pathogens and alert immune system UV radiation can damage these cells and weaken body’s first line of defense

Granstein Cells Also occur in epidermis Interact with cells that carry out immune response Issue suppressor signals that keep immune response under control Less vulnerable to UV damage than Langerhans cells

Hydrostatic Skeleton Muscles work against an internal body fluid and redistribute it within a confined space Radial cells are relaxed; longitudinal ones contracted Radial cells are contracted; longitudinal ones relaxed

wing Exoskeleton pivot point Dorsal-ventral muscles contract, exoskeleton pops out, wings move up Rigid, external body parts receive the applied force of muscle contraction Dorsal-ventral muscles relax, exoskeleton pops back, wings move down In-text figure Page 649

Endoskeleton All vertebrates Fins or limbs attach to skeleton at pectoral and pelvic girdles Generalized mammal Figure 37.10c Page 650 pelvic girdle pectoral girdle

Functions of Bone Interact with muscle to enable movement Support and anchor muscles Enclose and protect internal organs Store calcium and phosphorus Produce blood cells

Human Skeleton SKULL PECTORAL GIRDLES AND UPPER EXTREMITIES cranial bones facial bones PECTORAL GIRDLES AND UPPER EXTREMITIES clavicle scapula humerus radius ulna carpals metacarpals phalanges Human Skeleton sternum RIB CAGE ribs VERTEBRAL COLUMN vertebrae intervertebral disks pelvic girdle femur patella tibia fibula tarsals metatarsals phalanges PELVIC GIRDLE AND LOWER EXTREMITIES Stepped Art Figure 37.11 Page 651

Long Bone Structure Compact bone Spongy bone Central cavity contains yellow marrow nutrient canal contains yellow marrow compact bone tissue spongy bone tissue Fig. 37.12 (1) Page 652

Compact Bone Structure Mature compact bone consists of many cylindrical Haversian systems Haversian system blood vessel outer layer of dense connective tissue spongy bone tissue compact bone tissue Fig. 37.12 (2) Page 652

Bone Marrow Yellow marrow Red marrow Fills the cavities of adult long bones Is largely fat Red marrow Occurs in spongy bone of some bones Produces blood cells

Bone Remodeling In adults, bone building and bone breakdown continue constantly Osteoblasts deposit bone Osteoclasts secrete enzymes that degrade it Remodeling adjusts bone strength and helps maintain blood calcium levels

Bone Density Exercise can increase bone density Osteoporosis is a decrease in bone density May occur when the action of osteoclasts outpaces that of osteoblasts May also occur as a result of inability to absorb calcium

Joints Areas of contact or near contact between bones Fibrous joints Short connecting fibers join bones Synovial joints Move freely; ligaments connect bones Cartilaginous joints Straps of cartilage allow slight movement

Tendons Attach Muscle to Bone bursae synovial cavity Figure 37.15 Page 654

Skeletal Muscle Bundles of striped muscle cells Attaches to bone Often works in opposition biceps triceps Figure 37.17 Page 654

Major Human Muscles triceps brachii biceps brachii pectoralis major deltoid serratus anterior trapezius external oblique latissimus dorsi rectus abdominus gluteus maximus adductor longus sartorius biceps femoris quadriceps femoris gastrocnemius tibialis anterior Figure 37.18 Page 655

Skeletal Muscle Structure A muscle is made up of muscle cells A muscle fiber is a single muscle cell Each fiber contains many myofibrils myofibril Figure 37.19a Page 656

Sarcomere A myofibril is made up of thick and thin filaments arranged in sarcomeres sarcomere sarcomere sarcomere sarcomere Z line Z line Z line Figure 37.19b Page 656

Muscle Microfilaments Thin filaments Like two strands of pearls twisted together Pearls are actin Other proteins in grooves in filament Thick filaments Composed of myosin Each myosin molecule has tail and a double head Figure 37.19c Page 656

Sliding-Filament Model Myosin heads attach to actin filaments Myosin heads tilt toward sarcomere center, pulling actin with them Fig. 37.20c-g Page 657

Sliding-Filament Model Sarcomere shortens because the actin filaments are pulled inward, toward the sarcomere center Fig. 37.20a,b Page 657

Nervous System Controls Contraction Signals from nervous system travel along spinal cord, down a motor neuron Endings of motor neuron synapse on a muscle cell at a neuromuscular junction

Role of Calcium in Contraction T tubules in the sarcoplasmic reticulum relay signal Calcium ions are released

Troponin and Tropomyosin Lie in groove in actin filament When muscle is relaxed, tropomyosin blocks myosin binding site troponin myosin binding site blocked actin Figure 37.22 Page 659

Troponin and Tropomyosin When troponin binds calcium ions, it changes shape and moves tropomyosin Cross-bridge formation and contraction can now proceed myosin head actin Figure 37.22 Page 659

Contraction Requires Energy Muscle cells require huge amounts of ATP energy to power contraction The cells have only a very small store of ATP Three pathways supply ATP to power muscle contraction

ATP for Contraction Dephosphorylation Creatine Phosphate Aerobic ADP + Pi Pathway 1 Dephosphorylation Creatine Phosphate relaxation contraction creatine Pathway 2 Aerobic Respiration Pathway 3 Glycolysis Alone glucose from bloodstream and from glycogen break down in cells oxygen Figure 37.23 Page 659

Muscle Tension Mechanical force a contracting muscle exerts on an object For a muscle to shorten, muscle tension must exceed the load that opposes it The load may be the weight of an object or gravity’s pull on the muscle

Two Types of Contraction contracted muscle can’t shorten contracted muscle can shorten isotonic contraction isometric contraction Figure 37.24 Page 660

Motor Unit One neuron and all the muscle cells that form junctions with its endings When a motor neuron is stimulated, all the muscle cells it supplies are activated to contract simultaneously Each muscle consists of many motor units

Twitches and Tetanus Figure 37.25 Page 660 peak relaxation stimulus contraction starts time number of stimuli per second number of stimuli per second tetanic contraction Figure 37.25 Page 660 twitch repeated stimulation

Muscle Fatigue An inability to maintain muscle tension Occurs after a period of tetanic contraction Different types of muscle show different fatigue patterns