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Chapter 28Locomotion and Support

Systems

Animal Skeletons Support, Move, and Protect the Body

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28.1 Animal skeletons can be hydrostatic, external, or internal

Hydrostatic Skeleton - In animals that lack a hard skeleton, a fluid-filled gastrovascular cavity or coelom Offers support and resistance to contraction of muscles for mobility

Example: Earthworms - When muscles contract, segments become thinner and elongate, like a squeezed balloon

Exoskeleton – Molluscs and arthropods have rigid exoskeletons In molluscs and arthropods it supports the animal and provides a

location for muscle attachment Example: The jointed and movable exoskeleton of arthropods allows

protection and flexible movements Endoskeleton - Echinoderms and vertebrates have an internal

skeleton Supports weight of a large animal without limiting the space for

internal organs and offers protection to vital internal organs, but itself is protected by the soft tissues around it

Example: The vertebrate endoskeleton is also jointed, allowing for complex movements such as swimming, jumping, flying, and running

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Figure 28.1A The well-developed circular and longitudinal muscles of an earthworm push against a segmented, fluid-filled coelom

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Figure 28.1B A starfish has an endoskeleton

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28.2 Mammals have an endoskeleton that serves many functions

Bones protect the internal organs Rib cage protects heart and lungs; skull protects brain; and vertebrae

protect spinal cord Bones provide a frame for the body

Our shape is dependent on bones, which also support the body Bones assist all phases of respiration

Rib cage lifts up and out and the diaphragm moves down, expanding the chest

Bones store and release calcium Calcium ions play a major role in muscle contraction and nerve conduction

Bones assist the lymphatic system and immunity Bone marrow produces white blood cells that defend the body against

pathogens and cancerous cells Bones assist digestion

The jaws contain sockets for the teeth, which chew food, that breaks it into pieces small enough to be swallowed and chemically digested

The skeleton is necessary to locomotion Our jointed skeleton allows us to seek out and move to a suitable

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Figure 28.2 Graceful movements are possible because muscles act on bones

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The Mammalian Skeleton Is a Series of Bones

Connected at Joints

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28.3 The bones of the axial skeleton lie in the midline of the body

Axial skeleton - bones in the midline of the body Appendicular skeleton - limb bones and their girdles

The Skull - cranium and the facial bones form the skull, which protects the brain In newborns, cranial bones are joined by membranous regions called

fontanels (“soft spots”) Major bones of the cranium have the same names as the lobes of the brain

At base of the skull, spinal cord passes upward through an opening called foramen magnum and becomes brain stem

The Vertebral Column - head and trunk are supported by vertebral column, which also protects the spinal cord and the roots of the spinal nerves Twenty-four vertebrae make up the vertebral column Intervertebral disks, composed of fibrocartilage between the vertebrae, act

as padding and prevent vertebrae from grinding against one another and absorb shock

The Rib Cage - twelve pairs of ribs The rib cage protects the heart and lungs Also swings outward and upward upon inspiration and then downward for

expiration 28-9

Figure 28.3A The human skeleton

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Figure 28.3B Bones of the skull

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Figure 28.3C The rib cage

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28.4 The appendicular skeleton consists of bones in the girdles and limbs

The Pectoral Girdle and Upper Limbs Components loosely linked together by ligaments allowing arm

to move freely Single long bone in upper arm, the humerus, has a smoothly

rounded head that fits into a socket of the scapula Susceptible to dislocation

The Pelvic Girdle and Lower Limbs Two heavy, large coxal bones (hipbones) are joined at the pubic

symphysis Coxal bones are anchored to the sacrum, and together these

bones form the pelvic cavity Weight of the body is transmitted through the pelvis to the lower

limbs and then onto the ground28-13

Figure 28.4A Bones of the pectoral girdle and upper limb

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Figure 28.4B Bones of the pelvic girdle and lower limb

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

28.5 Avoidance of osteoporosis requires good nutrition and exercise

While a child is growing, the rate of bone formation by bone cells called osteoblasts is greater than the rate of bone breakdown by bone cells called osteoclasts

Osteoporosis - bones are weakened due to a decrease in the bone mass Skeletal mass increases until ages 20 to 30 Formation and breakdown of bone mass are equal Between 40 and 50 reabsorption begins to exceed formation, and

total bone mass slowly decreases Everyone can take measures to avoid osteoporosis

Males and females require 1,000 mg of calcium per day until age 65 and 1,500 mg per day after age 65

Exercise can build or maintain bone mass, but it must be weight-bearing exercise, such as dancing, walking, running, jogging, and tennis—activities that require you to be on your feet 28-16

Figure 28.5 Exercise can help prevent osteoporosis

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28.6 Bones are composed of living tissues

Anatomy of a Long Bone Cavity usually contains yellow bone marrow, which

stores fat Thin shell of compact bone and a layer of hyaline

cartilage, called articular cartilage when it occurs at joints

Compact bone makes up the shaft of a long bone Contains many osteons where osteocytes derived from

osteoblasts lie in tiny chambers called lacunae Spongy bone provides strength and is filled with red

bone marrow, a specialized tissue that produces blood cell

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Figure 28.6 Anatomy of a long bone

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28.7 Joints occur where bones meet

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

28.8 Joint disorders can be repaired

Arthroscopic Surgery - Surgeons remove cartilage fragments, repair ligaments, or repair worn cartilage Small instrument bearing a tiny lens and light source is inserted into a

joint, as are the surgical instruments Arthroscopy is much less traumatic than surgically opening the joint

with a long incision Replacing Cartilage - Tissue culture can be used so that a

person’s own hyaline cartilage can regenerate in the laboratory Autologous chondrocyte implantation (ACI) - a piece of healthy hyaline

cartilage from the patient’s knee is removed surgically Chondrocytes, living cells of hyaline cartilage, are grown outside the

body A pocket is created over the damaged area using the patient’s own

periosteum, the connective tissue that surrounds the bone Once the cartilage cells are firmly established, the patient still faces a

lengthy rehabilitation period

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Figure 28.8 Arthroscopic surgery

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Animal Movement Is Dependent on Muscle Cell Contraction

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28.9 Vertebrate skeletal muscles have various functions

Skeletal muscles support the body Skeletal muscle contraction opposes the force of gravity and allows

us to remain upright Skeletal muscles make bones move

Muscle contraction accounts for movements of the arms and legs the eyes, facial expressions, and breathing

Skeletal muscles help maintain a constant body temperature Muscle contraction causes ATP to break down, releasing heat that is

distributed about the body Skeletal muscle contraction assists movement in cardiovascular

veins The pressure of skeletal muscle contraction keeps blood moving in

cardiovascular veins Skeletal muscles help protect internal organs and stabilize joints

Muscles pad the bones, and the muscular wall in the abdominal region protects the internal organs

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Figure 28.9 Selected human muscles and their functions

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28.10 Skeletal muscles contract in units

Skeletal Muscles Work in Pairs Skeletal muscles move the bones of the skeleton with the

aid of bands of tendons that attach muscle to bone Prime mover - The one muscle that does most of the work

of moving a bone

A Muscle Has Motor Units A motor unit is composed of all the muscle fibers under

the control of a single motor axon and obeys an “all-or-none law”—it either contracts or does not

Simple muscle twitch - When a motor unit is stimulated by a single stimulus

Tetanus - maximal sustained contraction due to summation

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Motor unit

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Figure 28.10A Antagonistic muscles

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Figure 28.10B A single stimulus and a simple muscle twitch

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Figure 28.10C Multiple stimuli with summation and tetanus

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

28.11 Exercise has many benefits

Exercise programs improve muscular strength, muscular endurance, flexibility and cardiorespiratory endurance

Exercise also seems to help prevent certain kinds of cancer: colon, breast, cervical, uterine, and ovarian cancer

Physical training with weights can improve the density and strength of bones and the strength and endurance of muscles Helps prevent osteoporosis because it promotes the activity of

osteoblasts Helps prevent weight gain, because as a person becomes more

muscular, the body is less likely to accumulate fat Exercise relieves depression and enhances the mood

Makes people feel more energetic Some people sleep better at night after exercising. Particularly if

they exercise in the late afternoon. Vigorous exercise releases endorphins, hormone-like chemicals

that are known to alleviate pain and provide a feeling of tranquility 28-31

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28.12 A muscle cell contains many myofibrils

A muscle cell has a slightly different structure from other cells Sarcolemma - the plasma membrane Sarcoplasmic reticulum - modified endoplasmic

reticulum Serve as storage sites for calcium ions, which are essential

for muscle contraction

Myofibrils - long, cylindrical organelles which are the contractile portions of muscle cells Myofibril contains many contractile units called sarcomeres

that lie between two visible boundaries called Z lines

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Figure 28.12 Components of a muscle cell

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28.13 Sarcomeres shorten when muscle cells contract

Striations of skeletal muscle are due to the placement of protein filaments in sarcomeres Sarcomere contains thick filaments made up of myosin and

thin filaments made of actin Sliding Filament Model

ATP provides the energy for muscle contraction Each myosin head has a binding site for ATP, and the heads

have an enzyme that splits ATP into ADP and P This activates the heads, making them ready to bind to actin.

ADP and P remain on the myosin heads while the heads attach to actin, forming cross-bridges

Power stroke - Release of ADP and P bends crossbridge sharply

Rigor mortis occurs because ATP is needed in order for the myosin heads to detach from actin filaments

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Figure 28.13A Contraction of a sarcomere

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Figure 28.13B Role of ATP in muscle contraction

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28.14 Axon terminals bring about muscle contraction

Muscle cells (fibers) contract only because they are stimulated by motor axons

Neuromuscular junction contains a synaptic cleft where the neurotransmitter acetylcholine (ACh) is released

Sarcolemma of a muscle cell contains receptors for Ach molecules When these molecules bind to the receptors, a

muscle action potential begins

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Figure 28.14 Neuromuscular junction (green = ACh)

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28.15 Muscles have three sources of ATP for contraction

Creatine Phosphate (CP) Pathway CP is a molecule that contains a high-energy phosphate and is

only formed when a muscle cell is resting Simplest and most rapid way for muscle to produce ATP is to

transfer the high-energy phosphate to ADP Fermentation

Produces two ATP from the anaerobic breakdown of glucose to lactate

Fast-acting, but it results in the buildup of lactate that causes muscle soreness

Also results in oxygen debt - oxygen required to complete metabolism of lactate and restore cells to original energy state

Cellular Respiration Muscle cells have a rich supply of mitochondria where cellular

respiration supplies ATP Usually from the breakdown of glucose when oxygen is available

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28.16 Some muscle cells are fast-twitch and some are slow-twitch

Fast-Twitch Fibers Usually anaerobic and good for strength because their motor

units contain many fibers Provide explosions of energy and are most helpful in activities

such as sprinting Light in color because they have fewer mitochondria, little or no

myoglobin, and fewer blood vessels than slow-twitch fibers Develop maximum tension more rapidly than slow-twitch fibers can,

and their maximum tension is greater Slow-Twitch Fibers

Slow-twitch fibers have a steadier tug and more endurance, despite having more units with a smaller number of fibers

Most helpful in sports such as long-distance running Produce energy aerobically and tire only when fuel supply is

gone Have many mitochondria and are dark because they contain

myoglobin Have a low maximum tension and are highly resistant to fatigue 28-41

Figure 28.16 Fast- and slow-twitch muscle fibers

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Connecting the Concepts:Chapter 28

The skeleton is easily observable at the macro level We learned the names of the bones making up the axial and

appendicular portions of the skeleton We considered the tissues of the bones and joints (compact bone,

spongy bone, cartilage, fibrous connective tissue) We learned the names of various muscles and how they operate

when we intentionally move our bones We can’t understand how skeletal muscles contract and move the

bones until we study skeletal muscles at the cellular level A muscle cell is suited to its task because it contains

contractile organelles called myofibrils Myofibrils contain the filaments (actin and myosin) that account

for muscle contraction Without knowing how muscles contract at the cellular

level, our understanding of muscles would be incomplete

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