1 Protection, Support, and Movement Chapter 33

2 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

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

4 Vertebrate Skin Two layers –Upper epidermis –Lower dermis Lies atop a layer of hypodermis

5 Epidermis Stratified epithelium Grows from bottom upward Most abundant cells are keratin- producing keratinocytes Melanocytes produce the brown pigment melanin

6 Dermis Dense connective tissue with many elastin and collagen fibers Includes blood vessels, lymph vessels, and receptor endings of sensory nerves

7 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

8 Sweat Glands Arise from epidermal cells Composition of sweat –99% water, with dissolved salts, trace of ammonia (waste product) Controlled by sympathetic nerves

9 Oil Glands Also called sebaceous glands Derived from epidermal cells Secretions lubricate and soften hair and skin; also kill many surface bacteria Acne occurs when bacteria infect oil gland ducts

10 Hair Root is embedded in skin Cells near the base of the root divide and push cells above them upward Hair follicles are nourished by the dermis As cells move upward away from the dermis they die Shaft of dead cells extends above the skin surface

11 Vitamin D Steroid-like compounds that help the body absorb calcium from food Produced in the skin from a precursor molecule Reaction requires sunlight In cooler climates, dietary vitamin D is required to supplement that produced by skin

12 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

13 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

14 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

15 Skeleton A medium or structural element against which contractile cells can act Three types –Hydrostatic –Exoskeleton –Endoskeleton

16 Endoskeleton All vertebrates have endoskeletons Fins or limbs attach to skeleton at pectoral and pelvic girdles

17 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

18 Human Skeleton s sternum rib vertebral column humerus scapula clavicle ulna radius patella femur tibia fibula pelvic girdle

19 Long Bone Structure Compact bone Spongy bone Central cavity contains yellow marrow

20 Compact Bone Structure Mature compact bone consists of many cylindrical Haversian systems

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

22 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

23 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

24 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

25 Tendons Attach Muscle to Bone muscle tendon bursae synovial cavity

26 Skeletal Muscle Bundles of striped muscle cells Attaches to bone Often work in opposition biceps triceps

27 Human Skeletal Muscles TRICEPS BRACHII PECTORALIS MAJOR SERRATUS ANTERIOR EXTERNAL OBLIQUE RECTUS ABDOMINUS ADDUCTOR LONGUS SARTORIUS QUADRICEPS FERMORIS TABIALIS ANTERIOR BICEPS BRACHII DELTOID TRAPEZIUS LATISSIMUS DORSI GLUTEUS MAXIMUS BICEPS FEMORIS GASTRONEMIUS

28 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

29 Sarcomere Z band sarcomere A myofibril is made up of thick and thin filaments arranged in sarcomeres

30 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

31 Sliding-Filament Model Myosin heads attach to actin filaments Myosin heads tilt toward the sarcomere center, pulling actin with them

32 Sliding-Filament Model Sarcomere shortens because the actin filaments are pulled inward, toward the sarcomere center

33 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

34 ATP for Contraction Pathway 1 DEPHOSPHORYLATION CREATINE PHOSPHATE Pathway 2 AEROBIC RESPIRATION Pathway 3 GLYCOLYSIS ALONE creatine oxygen glucose from bloodstream and from glycogen breakdown in cells ADP + P i Relaxation Contraction

35 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

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

37 Troponin and Tropomyosin Lie in groove in actin filament When muscle is relaxed, tropomyosin blocks myosin binding site When troponin binds calcium ions, it changes shape and moves tropomyosin Cross-bridge formation and contraction can now proceed

38 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

39 Two Main Types of Contraction Isotonic contraction –Muscle visibly shortens; moves a load –Tension remains constant as the muscle changes length Isometric contraction –Muscle does not change length –Tension is insufficient to move load

40 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

41 Twitches and Tetanus peak relaxation stimulus contraction starts time number of stimuli per second tetanic contraction repeated stimulation twitch

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