Three principal kinds of movement:– ameboid– ciliary and flagellar– muscular

Lecture 3. Movement

– amebas and other unicellular forms– white blood cells– embryonic mesenchyme cells– other mobile cells

Ameboid Movement

Fig. 11.5a

Fig. 11.5c

Consensus model to explain extension and withdrawal of pseudopodia and ameboid crawling:

1. hyaline cap appears

Consensus model to explain extension and withdrawal of pseudopodia and ameboid crawling:

2. endoplasm flows toward hyaline cap

Consensus model to explain extension and withdrawal of pseudopodia and ameboid crawling:

3. actin subunits attach to regulatory proteins

Consensus model to explain extension and withdrawal of pseudopodia and ameboid crawling:

4. endoplasm fountains out to the periphery

Consensus model to explain extension and withdrawal of pseudopodia and ameboid crawling:

5. actin subunits released and polymerized

Consensus model to explain extension and withdrawal of pseudopodia and ameboid crawling:

6. microfilaments cross-linked

Consensus model to explain extension and withdrawal of pseudopodia and ameboid crawling:

7. Ca2+ activate actin-severing protein

Consensus model to explain extension and withdrawal of pseudopodia and ameboid crawling:

8. myosin associate with and pull on microfilaments

Cilia– minute, hairlike, motile processes– occur in large numbers– ciliate protistans– found in all major groups of animals– move organisms through aquatic environment– propel fluids and materials across surfaces

Ciliary and Flagellar Movement

Flagella– whiplike– present singly or in small numbers– occur in unicellular eukaryotes– animal spermatozoa– sponges

Ciliary and Flagellar Movement

• both cilia and flagella have the same ultrastructure

– a core of microtubules sheathed by the plasma membrane

• both cilia and flagella have the same ultrastructure

– “9 + 2” pattern– flexible “wheels” of proteins connect outer doublets to

each other and to the core

• both cilia and flagella have the same ultrastructure

– outer doublets are connected by motor proteins

– anchored in the cell by a basal body

• The bending of cilia and flagella is driven by the arms of a motor protein, dynein.

• Addition to dynein of a phosphate group from ATP and its removal causes conformation changes in the protein.

• Dynein arms alternately grab, move, and release the outer microtubules.

• Protein cross-links limit sliding and the force is expressed as bending.

• A flagellum has an undulatory movement– force is generated parallel to the flagellum’s axis

• Cilia move more like oars with alternating power and recovery strokes– generate force perpendicular to the cilia’s axis

Invertebrate MuscleBivalve molluscan muscles– 2 kinds of fibers:• fast muscle fibers = striated, can contract rapidly• smooth muscle = capable of slow, long-lasting

contractions

Invertebrate MuscleInsect flight muscles (fibrillar muscle)– wings of small flies operate at 1000 beats/sec– limited extensibility; shorten only slightly

Vertebrate Muscle

Types1. Striated2. Smooth3. Cardiac

Structure of Striated Muscle

Sliding Filament Model

• Actin filaments at both ends of sarcomere– one end of each filament attached to a Z-plate at one end

of the sarcomere– other end suspended in sarcoplasm

Sliding Filament Model

• Myosin filaments suspended in between Z-plates– myosin filaments contain cross-bridges which pull the actin filaments

inward– causes Z-plates to move toward each other– shortens sarcomere– sarcomeres stacked together in series and cause myofiber to shorten

Sliding Filament Model

• Working muscles require ATP – myosin breaks down ATP– sustained exercise• requires cellular respiration• regenerates ATP

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Muscle Innervation

• Neuromuscular junction– the synaptic contact between a nerve fiber and a

muscle fiber– nerve impulses bring about the release of a

neurotransmitter that crosses the synaptic cleft– signals the muscle fiber to contract

Human Muscular System

• Skeletal muscles– attached to the skeleton by cable-like fibrous

connective tissue called tendons– arranged in antagonistic pairs

• can only contract, cannot push• when one muscle contracts, it stretches its

antagonistic partner• a muscle at “rest” exhibits tone (minimal

contraction)• a muscle in tetany is at maximum sustained

contraction

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Muscle Performance

– slow oxidative fibers (red muscles)• for slow, sustained contractions without

fatigue• contain extensive blood supply•high density of mitochondria•abundant stored myoglobin• important in maintaining posture in terrestrial

vertebrates

Muscle Performance

fast fibers1. fast glycolytic fiber (white muscles)• lacks efficient blood supply•pale in color• function anaerobically• fatigue rapidly

2. fast oxidative fiber• extensive blood supply•high density of mitochondria and myoglobin• function aerobically• for rapid, sustained activities

Energy for Contraction

– ATP, immediate source of energy– glucose broken down during aerobic metabolism– glycogen stores can supply glucose– muscles have creatine phosphate, an energy

reserve– slow and fast oxidative fibers rely heavily on

glucose and oxygen– fast glycolytic fibers rely on anaerobic glycolysis– muscles incur oxygen debt during anaerobic

glycolysis