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
T tubules
Drive propagation of an action potential
Carry action potential via voltage-gated Na+ and K+ channels
Sarcoplasmic reticulum (SR)
membrane -bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other cells. The main function of the SR is to store calcium ions (Ca 2+).
Three types of muscle
Smooth muscle
Cardiac muscle
Skeletal muscle
Cardiac muscle
Location: Only in heart
Function: Pump blood
Characteristics
- Striated
- branched cells
- ends connected via intercalated discs
- Contains sarcomeres
- Activity is involuntary
Smooth muscle
Location: Intestines, arteries
Function: Essential to function of lungs, blood vessels, digestive system, urinary bladder and reproductive system
Characteristics
- organized in thin sheets
- unbranched, unstriated and lack myofibrils
- action is involuntary and does not require a signal from motor neuron
Skeletal muscle
Location: Attached to skeleton
Function: Move skeleton
Cell characteristics
- Multinucleate
- Striated
- Unbranched
- Contains sarcomeres
- Activity is voluntary
- attach to antagonistic pairs to bones
Intercalated
discs
critical to flow of electrical signals from cell to cell to coordinate heartbeat (involuntary
First step in the process of an action potential triggering muscle contraction
ACh released into the synaptic cleft is bound by receptors on the muscle cell. This stimulates opening of ligand-gated ion channels, which causes initial depolarization of the muscle cell.
In muscle cells, myosin molecules continue moving along actin molecules as long as
ATP is present and the intracellular Ca2+
concentration is high.
During contraction, what change in appearance is observed in the sarcomere?
The light band narrows.
Why is the dark band in a sarcomere dark and the light band light?
The dark band includes thin filaments as well as thick filaments; the light band consists of thin filaments only.
One way your body increases blood pressure is to contract muscles in large veins. What muscle tissue type will be responsible for this function?
Smooth muscle as it is responsible for blood pressure
What causes myosin head to release form the action
Binding of ATP to myosin
What causes the actin and myosin filaments to slide past one another during muscle contraction?
Release of inorganic phosphate from myosin as it causes the myosin head to pivot inward, pulling the thin filaments inward toward the center of the sarcomere.
Sliding filament theory
- ATP binds to myosin head and releases actin
- ATP hydrolyze into inorganic phosphate and ADP and causes the head to pivot to new actin subunit
- When inorganic phosphate is released the head pivots to its original position and moves thin filament towards sarcomere
- ADP is released and cycle is ready to repeat
What is the molecular basis of muscle contraction
The interaction of myosin and thin filaments (actin)
What does the motor neuron release into synapse to open channel in plasma membrane of muscle fiber to allow sodium ions into cell to trigger action potential
The neurotransmitter AT
What happens in the power stroke of the sliding-filament model
occurs when the myosin head pivots, causing the actin filament to slide past the myosin filaments
Characterized by when the phosphate ion is released and causes myosin head to move back to its original position
What is the effect of the action potential on the T-tubules
causes T tubules to depolarize, which stimulates the sarcoplasmic reticulum to release calcium ions into the muscle cell.
