the animal body and how it moves

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The Animal Body and How it Moves

Chapter 42

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Outline

• Characteristics of Epithelial Tissue• Tissue Types• Types of Skeletons• The Structure of Bone• Types of Joints• Actions of Skeletal Muscles• Sliding Filament Mechanism of Contraction• Control of Muscle Contraction• Types of Muscle Fibers• Modes of Animal Locomotion

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Organization of the Body

• Bodies of all vertebrates are basically a tube within a tube.

– all vertebrate bodies supported by internal skeleton

• Four levels of organization:– cells– tissues– organs– organ systems

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• Tissues– Groups of cells similar in structure and

function are organized into tissues. Early in development, embryo cells

differentiate into three germ layers.endodermmesodermectoderm

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Tissues

• Adult vertebrates have four primary tissues:– epithelial– connective– muscle– nerve

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• Organs and organ systems– Organs are body structures composed of

several different tissues that form a structural and functional unit.

– An organ system is a group of organs that operate to perform the major activities of the body.

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Characteristics of Epithelial Tissue

• Epithelium covers every major surface of the vertebrate body.

– derived from all three germ layers can provide a barrier that can impede

the passage of some substances while facilitating the passage of others

remarkable regenerative powers

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• Types of epithelial tissues– simple - one layer thick

squamous - lining of lungs cuboidal - lining of kidney tubules columnar - lining of stomach

– stratified - several cell layers thick and named according to features of their uppermost layers

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• Glands of vertebrates are derived from invaginated epithelium.

– exocrine glands - connection between the gland and the epithelial membrane is maintained as a duct

– endocrine glands - ductless glands - connections with the epithelium, from which they are derived, are lost during development

secrete hormones

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Connective Tissue Proper

• Connective tissues are divided into:– connective tissue

divided into loose and dense connective tissues

– special connective tissues include cartilage, bone, and blood

– extracellular material generically known as matrix

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• Loose connective tissue– cells scattered within amorphous mass of

proteins that form a ground substance strengthened by collagen, elastin and

reticulin - secreted by fibroblasts adipose cells found in loose connective

tissue

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• Dense connective tissue – regular

collagen fibers lined up in parallel tendons and ligaments

– irregular collagen fibers have many orientations

organ coverings - capsulesmuscle coverings - epimysiumnerve coverings - perineuriumbone covering - periosteum

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Special Connective Tissues

• Cartilage– specialized connective tissue in which

fibers are laid down along the lines of stress in long, parallel arrays

firm and flexible chondrocytes - cartilage cells that live

within spaces (lacunae) within cartilage matrix

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Cartilage

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• Bone– Many bones are first modeled in cartilage.

The cartilage matrix calcifies at particular locations, thus chondrocytes are no longer able to obtain oxygen and nutrients through diffusion.

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The Structure of Bone

• New bone is formed by osteoblasts that secrete collagen organic matrix in which calcium phosphate is later deposited.

– cells then encased in spaces called lacunae in the calcified matrix

• Bone is constructed in thin, concentric layers or lamellae, laid down around Haversian canals that run parallel to the length of the bone.

– contain nerve fibers and blood vessels

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The Structure of Bone

• Bone formation– flat bones - Osteoblasts located in a web of

dense connective tissue produce bone within that tissue.

– long bones - bone first “modeled” in cartilage

ends and interior composed of spongy bone

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Bone

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• Blood– classified as connective tissue because it

contains plasma and platelets erythrocytes - contain hemoglobin leukocytes - have nuclei and

mitochondria, but lack hemoglobinneutrophils, eosinophils, and

basophils lymphocytes and monocytes

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Muscle Tissue

• Muscle cells are the motors of the vertebrate body.

– three types: smooth - skeletal - cardiac– Skeletal and cardiac muscles are striated

because their cells have transverse stripes when viewed in longitudinal section.

Contraction of skeletal muscle is under voluntary control, whereas contraction in cardiac and smooth muscle is generally involuntary.

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Muscle Tissue

• Smooth muscle - found in organs of internal environment (viscera)

• Skeletal muscle - usually attached to tendons or bones, so when muscles contract causes bones to move at joints

– made up of long muscle fibers that contract by myofibrils

– made up of highly ordered arrays of actin and myosin filaments

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Muscle Tissue

• Cardiac muscles– composed of smaller, interconnected cells,

each with a single nucleus interconnections appear as dark lines

called intercalated disksenable cardiac muscles to form single

functioning unit - myocardium

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Nerve Tissue

• Cells include neurons and neuroglia (supporting cells).

– Neurons are specialized to produce and conduct electrochemical impulses.

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Nerve Tissue

• Neuroglia do not conduct electrical impulses but instead support and insulate neurons and eliminate foreign materials in and around neurons.

– myelin sheath - insulating covering of neuroglia cells wrapped around axons

nodes of Ranvier separate adjacent neuroglia cells

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Nerve Tissue

• Nervous system is divided in the central nervous system (CNS) which includes the brain and spinal cord, and the peripheral nervous system (PNS) which includes nerves and ganglia.

– Nerves consist of axons in the PNS bundled together.

– Ganglia are collections of neuron cell bodies.

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Types of Skeletons

• Hydrostatic skeletons - fluid-filled cavity encircled by muscle fibers

– As the muscles contract, fluid in the cavity moves and changes cavity shape.

• Exoskeletons - surround the body as a rigid, hard case

– must be periodically shed– limits body size as exoskeleton has to

grow increasingly thicker and heavier

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Types of Skeletons

• Endoskeletons - rigid internal skeleton to which muscles are attached

– composed of cartilage or bone– vertebrate skeleton

axial skeleton - forms axis of body and supports organs of the head, neck, and chest

appendicular skeleton - includes bones of the limbs, pectoral and pelvic girdles

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Exoskeleton and Endoskeleton

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Types of Joints

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Types of Joints

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Types of Joints

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Actions of Skeletal Muscles

• Skeletal muscles produce movement of the skeleton when they contract.

– attachment to bones made by tendons origin remains stationary during

contraction insertion attached to bone that moves

during contraction

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Actions of Skeletal Muscles

• Synergists - muscles that cause same action at a joint

• Antagonists - muscles that produce opposing actions

• Isotonic contraction - muscle and all fibers shorten in length thus force of contraction remains relatively constant

• Isometric contraction - tension is absorbed by tendons and other elastic tissue, and muscle does not change in length

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Flexor and Extensor Muscles

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Sliding Filament Mechanism of Contraction

• Each skeletal muscle contains numerous muscle fibers.

– Each muscle fiber encloses 4-20 myofibrils.

Each myofibril composed of thick and thin myofilaments.

Thick myofilaments produce A bands.Thin myofilaments produce I bands.

Each I band divided in half by disc of protein (Z band).

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Skeletal Muscle Organization

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• Sarcomere - structure of myofibril from Z line to Z line

– smallest subunit of muscle contraction• A muscle contracts and shortens because its

myofibrils contract and shorten.– Myofilaments do not shorten, but slide

deeper into the A band.

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Sarcomere Shortening

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• Electron micrographs reveal cross-bridges that extend from the thick to thin filaments.

– Each thick filament composed of many myosin proteins packed together, and every myosin molecule has a “head” region.

– Each thin filament consists primarily of many globular actin proteins twisted in a double helix.

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• Before the myosin heads bind to the actin of the thin filaments, they act as ATPase, splitting ATP into ADP and Pi.

– activates heads Once a myosin head binds to actin, it

undergoes a shape change, pulling the thin filament toward the center of the sarcomere.

allows head to detach from actin and continue cross-bridge cycle

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Control of Muscle Contraction

• Role of Ca++ in contraction– When a muscle is relaxed the myosin

head cannot bind to actin because the attachment sites are physically blocked by tropomyosin.

In order to contract a muscle, troponin must move tropomyosin away from the binding site.

complex regulated by calcium ion concentration

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• When Ca++ concentration of the muscle cell cytoplasm is low, tropomyosin inhibits cross-bridge formation and the muscle is relaxed.

• When Ca++ concentration is raised, Ca++ binds to troponin.

• When a muscle fiber is stimulated to contract, an electrical impulse travels into the muscle fiber down transverse tubules.

– triggers release of Ca++ from sarcoplasmic reticulum

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Neuromuscular Junction

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• Nerves stimulate contraction– Somatic motor neurons stimulate skeletal

muscles. Axon extends from neuron cell body and

branches to make synapses with a number of muscle fibers.

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• Somatic motor neuron stimulates contraction:– releasing acetylcholine neurotransmitter

(ACh).– impulses spread along membrane and

carried into the muscle fibers through the T tubules

– T tubules conduct impulse toward the sarcoplasmic reticulum, which releases Ca++

• Excitation-contraction coupling

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• Motor units and recruitment– set of muscle fibers innervated by all axonal

branches is defined as a motor unit division of muscle into motor units allows

muscle’s strength of contraction to be finely graded

most muscles contain motor units in a variety of sizes

recruitment - nervous system’s use of increased numbers and sizes of motor units to produce a stronger contraction

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Number and Size of Motor Units

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Types of Muscle Fibers

• Muscle fiber twitches– muscle stimulated with a single electric

shock A second electrical shock delivered

immediately after the first will produce a second twitch that may partially piggyback on the first (summation).

At a particular frequency of stimulation, there is no visible relaxation between successive twitches (tetanus).

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Summation

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• Skeletal muscle fibers can be divided on the basis of their contraction speed:

– Type I – slow-twitch fibers rich capillary supply, numerous

mitochondria, and high concentration of myoglobin pigment (red fibers)

– Type II – fast-twitch fibers fewer capillaries and mitochondria and

not as much myoglobin (white fibers)

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• Muscle metabolism during rest and exercise– Skeletal muscles at rest obtain energy from

aerobic respiration of fatty acids. Skeletal muscles respire anaerobically for

the first 45-90 seconds of moderate to heavy exercise.

Maximum rate of oxygen consumption in the body is called maximal uptake or aerobic capacity.

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• Muscle fatigue and physical training– Muscle fatigue refers to the use-dependent

decrease in the ability of a muscle to generate force.

usually correlated with the production of lactic acid by the exercising muscles

also related to depletion of muscle glycogen

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• Endurance-trained athletes have a high aerobic capacity, and thus can perform more exercise before lactic acid production and glycogen depletion cause muscle fatigue.

– Weight training (resistance training) causes muscle fibers to become thicker as a result of increased size and number of myofibrils.

cause skeletal muscles to grow by hypertrophy

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Modes of Animal Locomotion

• In large animals, active locomotion is almost always produced by appendages that oscillate (appendicular locomotion) or by bodies that undulate, pulse, or undergo peristaltic waves (axial locomotion).

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• Locomotion in water– Buoyancy reduces the influence of gravity.

The primary force retarding forward movement is frictional drag.

Swimming uses the body or its appendages to push against the water.

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Locomotion in Water

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• Locomotion on land– Mollusks slide along a path of mucus.– Vertebrates and arthropods have a raised

body and move forward by pushing the ground with a series of jointed appendages.

Vertebrates have four limbs, while arthropods have six or more.

basic walking pattern of all tetrapod vertebrates LH – LF – RH – RF

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Locomotion on Land

• Both arthropods and vertebrates achieve faster gaits by overlapping leg movements.

• The highest running speeds of tetrapod vertebrates are obtained with asymmetrical gaits.

– galloping horse never supported by more than two legs, occasionally by none

reduces friction against ground• Many vertebrates use peristaltic locomotion.• Most snakes employ serpentine locomotion.

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• Locomotion in air– Flight has evolved four times:

insects, pterosaurs, birds,and bats propulsion achieved by pushing down

against the air with wings– Raising and lowering wings is achieved by

alternate contraction of extensor muscles and flexor muscles.

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• In some insect orders, flight muscles are not attached to the wings, but rather to the stiff wall of the thorax.

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Summary

• Characteristics of Epithelial Tissue• Tissue Types• Types of Skeletons• The Structure of Bone• Types of Joints• Actions of Skeletal Muscles• Sliding Filament Mechanism of Contraction• Control of Muscle Contraction• Types of Muscle Fibers• Modes of Animal Locomotion

the animal body and how it moves

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