Chapter 45 Flashcards
Movement
way for animals to respond to stimuli from
their environment
Locomotion
movements generated by muscle contraction
are key innovations in animal evolution
Muscle & skeletal systems
work together to produce movement
What is the skeletal system stimulated to contract by
Nervous system
Muscle structure
Consists of a bundle of long fibers, each a
single cell, running the length of the muscle
Each muscle fiber is itself a bundle of
smaller myofibril
Sarcomere
functional unit of muscle contraction
Bordered by z lines and made up of thin and thick filaments
Are the alternating light-dark units that produce the banded appearance of myofibrils, which are the strands that make up each muscle fiber.
Thin filaments
Consists of 2 chains of the protein actin
One end of each thin filament is bound to Z disk,
which forms end of sarcomere & anchors the filament– Other end is free to interact with thick filamen
Thick filament
Thick filaments composed of several strands of myosin
Myosin has two subunits: head & tail
What happens when actin and myosin interact
Shortening of sarcomere and muscle contraction
Process of Actin-Myosin interaction
- When Ca2^+ ions are released, they bind to the protein complexes and allow binding of the myosin head to actin
- The thin filament pulled toward the center of the sarcomere.
- When the myosin head binds ATP, it detaches from actin
- Then, the myosin head hydrolyzes ATP to ADP and Pi,
which extends the myosin head and puts it in position to bind actin once again - The result of repeated cycles is the shortening of the sarcomere, and ultimately, contraction of the muscle.
Troponin and Tropomyosin
Proteins in thin filaments that form a complex to block myosin binding sites so that the actin and myosin cannot slide past each other (muscle at rest.
When muscle contraction occurs, calcium ions are released to bind to troponin, causing a change in the troponin tropomyosin complex so that actin can interact with myosin (filaments can now slide against each other
How do neurons cause muscle contraction
Action potential moves down the T tubules, it triggers Ca2+ channels in the sarcoplasmic reticulum to open
- Ca2+ ions rush into the cytosol. and diffuse into the myofibrils, where they enable muscle contraction to begin, completing action potential
- The Ca2+ channels in the sarcoplasmic reticulum close, and Ca2+ ions are again pumped back into the sarcoplasmic reticulum.
- The cytosolic level of Ca2+ drops, Ca2+ ions diffuse out of the myofibrils, stopping muscle contraction.
Synaptic terminal
- most distal portion of neuron’s axon and is critical for neural communication
-calcium floods neuron and allows synaptic vesicles to fuse with the membrane and release stored neurotransmitters to target cells
Mitochondrian
Important sites for energy production needed to sustain normal muscle contraction.
How nervous system causes muscle contraction
- Action potential arrives at neuromuscular junction
2.. When it action potential reaches end of axon terminal, it causes release of neurotransmitter ACh from synaptic vesicles
- The ACh molecules diffuse across the synaptic cleft and bind to the muscle fiber receptors, thereby initiating a muscle contraction.
- It is initiated with the with the depolarization of the sarcolemma caused by the sodium ions’ entrance through the sodium channels associated with the ACh receptors.
- The T tubules are periodic invaginations in sarcolemma where the propagation of an action potential occurs
- T tubules carry action potential into interior of the cell and trigger opening of calcium channels in the membrane of adjacent SR causing Ca++ to diffuse out of the SR and into the sarcoplasm, where Ca++ initiates contraction of the muscle fiber by its sarcomeres
