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16 Cards in this Set
- Front
- Back
What is a sarcomere?
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- Each myofibril appears as a series of repeating dark and light bands formed by the contractile proteins actin and myosin
- The functional unit of the muscle fiber of muscle cell is the sarcomere - the sarcomere may be defined as the region of a myofibril between two successive z-lines (discs) |
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Describe the organization of a sarcomere
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- Under the light microscope, the wide A-Band represents the regino of overlap between myosin and actin
- The narrow I-band contains only actin, there is no overlap - The H-zone is the central region for each sarcomere, contains only myosin - At rest the sarcomere is between 2-3 microns in length, can be stretched to 4 microns, upon contractions is only 1 micron |
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How do the contractile proteins in muscle work?
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- a single myosin moleculeis two interwoven polepeptides possessing a tail and a globular head
- The thick myosin filament is composed of 300 myosin molecules - Actin is composed of three smaller proteins; -- g-actin -- tropomyosin -- troponin - The g-actin contains the myosin binding sites, which are covered by the tropomyosin molecule - Tropomyosin and troponin fuctino as regulatory proteins |
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Describe the interaction of myosin and actin
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- G-actin contains the binding sites for the myosin heads
- Binding sites covered with the tropomyosin protein - Associated with tropomyosin is the protein troponin - The release of intracellular calcium ions bind to troponin - Calcium binding to troponin removes the blocking function of tropomyosin |
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How is cross bridge formation accomplished?
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- Energized myosin head attaches to actin, forming a cross-bridge
- the power stroke occurs when the myosin head pivots, pulls the actin myofilament inward - Cross-bridge detachment occurs when new ATP attaches to myosin head - As ATP is hydrolyzed to ADP and P, the myosin head returns to it's high energy "cocked" position |
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Describe the internal tubules of muscle
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- Sarcoplasmic reticulum (SR) is a modified ER, contains intracellular calcium ions, essential for muscle contraction
- SR surrounds the myofibril similar to a sleeve around the arm - The transverse tubules (t-tubles) are inward extensions of the sarcolemma; will carry the action potential deep into the cell and the SR - the depolarization of the muscle cell initiates the releaseo f stored calcium ions from the SR (opens voltage gated ion channels) |
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Give an overview of the sliding filament theory
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- Interaction between myosin and actin
- Calcium ions released for the SR will expose the myosin head binding site on the g-actin subunits - ATP is necessary for the swiveling of each myosin head (power stroke) - Actin thin filament pulled inward, thus shortening the sarcomere and each individual muscle fiber (muscle contraction) |
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Describe the composition of a neuromuscular junction
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- Action potential propogates down the axon of motor neuron
- The AP eventually opens voltage-gated calcium ion channels; the influx of calcium ions will bind with the synaptic vesicles - Synaptic vesicles contain the neurotransmitter acetylcholine (ACh) - Release of the ACh through exocytosis - ACh crosses the synaptic cleft and binds to the ACh receptor on the muscle cell, resulting in the depolarization of the muscle cell |
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Describe the function of membrane potential
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- An unequal distribution of ions across the sarcolemma
- The intracellular fluid (sarcoplasm) has a higher concentration of potassium ions and a low concentration of sodium ions - The extracellular fluid has a low concentratino of potassium ions and a high concentration of sodium ions (concentration gradient exists for these two ions) - The unequal distribution of ions creates a membrane potential |
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Describe the ion flow sequence in muscle
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- At rest the inside of the cell is slightly negative (-) (-70mv), the outside is slightly positive (+)
- The opening of sodium ion channels allows sodium ions to enter the cell, as more positive ions enter the cell the polarity of the membrane changes (depolarization) - One the inside of the cell becomes positive (+20 mv) sodium channels close and potassium ion channels open - The exit of intracellular positive potassiuminos to re-establishes polarity (repolarization) |
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Describe the operation of sodium/potassium pumps
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- Repolarization restores the resting membrane potential (RMP) of the cell.
- Ion distribution has not been restored; too many sodium ions and too few potassium ions remain inside the cell. - Sodium/potassium pumps are required to transport ions across the cell membrane and against a concentration gradient (active transport) - A muscle cell has an abundance of mitochondria; generates the ATP to operate the pumps. |
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What is meant by "action potential", with respect to neurons?
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- At rest the axon is polarized across the cell membrane (+/-)
- Stimulating an axon reverses this condition, causing depolarization (-/+) - If the stiumulus (graded potential) is strong enough this triggers the opening of additional voltage gated ion channels (sodium) similar to the falling of dominos. - The events of depolarization and repolarization defines an action potential - The Na+/K+ pumps will return these ions to their proper location across the membrane |
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How is an action potential propogated?
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- The opening of the first ion channel (triggered by the graded potential) will depolarize the adjacent region of the membrane, causing a second voltage-gated sodium ion channel to open.
- The depolarization wave continues down the axon opening sodium ion channels in succession (self-propagation) - Depolarization continues at a constant velocity. As sodium ion channels are closing, potassium ino channels are opening, initiating the events of repolarization. - The action potential propagates down the axon either by continuous conduction or saltatory conduction |
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What are the three basic functions of the nervous system?
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- Sensory Input - various sensory recepts monitor changes in the internal and external environments
- Integration - involved with the processing and interpretation of incoming sensory information - Motor output - directs an appropriate response to effectors; either muscle tissue or glands |
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Describe the anatomical representation of the nervous system
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- Central Nervous System (CNS)
-- Brain -- Spinal cord - Peripheral Nervous System (PNS) -- Cranial nerves (12 pair) -- Spinal nerves (31 pair) |
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Describe the functional representation of the nervous system
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- Central Nervous system (CNS)
-- Integration (brain and spinal cord) - Peripheral Nervous System (PNS) -- Afferent Division (all sensory) -- Efferent Division (all motor) --- Somatic Nervous System (skeletal muscle) --- Autonomic Nervous System (cardiac and smooth muscle, and glands) ---- Sympathetic Division - excites or inhibits metabolic activity ---- Parasympathetic Division - restores normal function |