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65 Cards in this Set
- Front
- Back
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3 types of muscles
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Skeletal, cardiac, smooth
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Skeletal Muscle
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Striated muscle that generates force;
Contracts only when stimulated Innervated by SOMATIC MOTOR NEURONS |
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Cardiac Muscle
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Striated; generates force
Contracts rhythmically Innervated by AUTONOMIC NERVOUS SYSTEM |
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Smooth Muscle
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NON-STRIATED: Used for pressure loads
Maintains Organ Dimensions & Functions Contracts continuously Innervated by AUTONOMIC NERVOUS SYSTEM |
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Endomysium
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Connective tissue (?) Surrounds individual muscle fibers
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Perimysium
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Connective tissue (?) that surrounds muscle fascicles
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Muscle fascicle
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Functionally discrete bundles of muscle fibers (cells)
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Epimysium
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Surrounds whole muscle (made up of groups of fascicles)
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How do nerves and blood vessels interact with muscle fibers
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Through Connective tissue
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Describe a muscle fiber...general overview.
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Single, multi nucleated cell. Has organelles and contractile structures.
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How are muscle cells made in terms of embryology?
1st step |
Myogenic precursor cells in somites generate myoblasts and satellite cells
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What do myoblasts do embyrologically?
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Several myoblasts fuse to form single muscle fiber
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What are satellite cells and what do they do?
Include pre and post natal |
Stem like cells that survive into adulthood.
Prenatally: divide and fuse with muscle fiber to ensure adequate number of nuclei. Postnatally: they can replace damaged muscle fibers. |
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Sarcolemma
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cell membrane around a single muscle fiber
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T-tubules
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Infoldings of sarcolemma
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Sarcoplasmic reticulum
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Stores and releases Ca ion (2+)...equivalent to endoplasmic reticulum
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Regions and function of Sarcoplasmic reticulum
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Sarcotubules: store Ca 2+ bound to calsequestrin
Terminal cisternae: contact T-tubules |
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Triads: T-tubule and 2 terminal cisternae
Function? |
Where action potentials trigger release of Ca 2+ from terminal SR
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Myofibrils
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Organelles of contractile myofilaments segmented into sarcomeres.
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What is the structure/ shape of a myofibril?
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Cylinders that extend the length of the muscle.
Chain of fused Sarcomeres |
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Sarcomere: shape and structure
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Cytoskeletally distinct unit containing thick and thin myofilaments: INCLUDING ACTIN and MYOSIN
Joined to each other by Z-lines Surrounded by SR |
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What makes a muscle "striated"?
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Z lines connecting sarcomeres are aligned with each other.
Regularity of sarcomere structures form striations |
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Titin (connectin) and Nebulin structure and function
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Together make flexible filamentous network thatsurrounds myofibrils:
Titin: elastic component in muscle that can stretch under tension |
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Components of Myofilaments
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THIN: Actin; Tropomyosin; Troponin
THICK: Myosin |
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Actin
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Globular protein (G-actin) polymerized into doubled strands (F-actin)
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Tropmyosin
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Covers myosin binding sites
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Troponin
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Regulatory protein bound to tropomyosin
Activated by Ca 2+ |
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Myosin structure
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Tails form tick portion of myofibril
Head and neck form cross bridges that bind to actin |
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How is a sarcomere defined structurally?
(this may be poorly worded...think letters) |
Z lines align with each other vertically to form edges
I bands are found on each side of Z band A bands are found on each side of I band H zone found in between A bands M line is in middle of H zone...center of sarcomere End to end: Z-I-A-H-M-H-A-I-Z |
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What is a motor neuron?
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Cell body in ventral horn that projects its axon out through ventral root to muscle
Contrasts with 2 cell system for sympathetic system (don't know what this means so didn't write a good question for it) |
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What is Neuromuscular Junction?
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Synapse formed by motor neuron on skeletal muscle
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How is the Neuromuscular junction formed?
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Motor neuron axons branch and synapse onto muscle end plates
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What lines the Junctional folds on a muscle cell?
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Ach receptors
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How do the motor neurons communicate with muscle cells?
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They release Ach onto neuromuscular junctions
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How does Ach facilitate an action potential?
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Increases permeability of Na+/K+ channel creating an End Plate Potential
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What kind of receptors are Ach receptors?
What can block them? |
Ionotropic nicotine receptors
Botullinum toxin (Botox) |
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What is an end Plate Potential (EPP)
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Large depolarization similar to an EPSP except greater in amplitude.
Has sufficient amplitude to exceed threshold for action potential initiation |
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How many axon action potentials are needed to initiate a muscle action potential?
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One (not sure if you can have more than one at times as well)
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How is Muscle action potential generated?
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End Plate Potentials depolarize neighboring voltage gated Na+ channels that generate muscle action potential
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What enzyme breaks down Ach and where is it?
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acetylcholinesterase...lining of skeletal muscle cell surface
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what does esterase do?
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Enhances Neuromuscular junction activity thus enhancing muscle contraction
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What ion begins muscle excitation?
Where does it come from? |
Ca 2+ is released from sarcoplasmic reticulum
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After Ca 2+ is released from SR what happens next?
First couple of steps... |
Action potential spreads along T tubule....current activates dihydropyridine (DHP) receptors.
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what is a dihydropyridine (DHP) receptor and what does it do?
Does it work the same in cardiac receptors? |
L type voltage gated Ca 2+ channel.
When activated, doesn't allow Ca 2+ flux into cell. Sends voltage to Ryanodine(RCR) receptor. No...it does permit Ca 2+ into cardiac cells |
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what is a ryanodine receptor (RCR)?
Where is it and what does it do? |
RCR is attached to the DHP in muscle cell.
It absorbs voltage of action potential directed from T-tubule through DHP. Releases Ca 2+ from the SR terminal cisternae upon voltage activation |
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Describe Ca 2+ pathway that initiates contraction.
When does it happen in terms of Action Potential? |
Ca ++ released from terminal cisternae of SR
Ca++ binds to troponin to initiate contraction. Happens DURING an action potential |
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Describe Ca++ pathway during relaxtion.
When does it happen in terms of Action Potential? |
Ca++ sequestered into longitudinal sarcotubules of the SR via Ca-ATPase
Ca++ then translocated back to terminal cisernae for subsequent release. |
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What are the two primary cofactors that facilitate contraction?
How? |
Permission:
- Ca++ released from SR & binds to troponin. -Troponin alters tropomysosin to expose actins binding sites for myosin Motivation: - ATP binds to myosin head & hydrolyzes to ADP and P -ADP & P enable myosin head to bind to actin |
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Sliding filament mechanism and contraction:
what are the 4 stages |
1. Crossbridge attachment
2. Working stroke 3. Detachment 4. ATP hydrolysis |
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Describe the process fully
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you are a superstar...tell a friend about how their muscles work :)
Seriously, you got this! |
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What conditions are required for actin to bind to myosin?
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Ca++ needs to be present.
Actin's binding site is exposed when tropomyosin is altered by Ca++ bound troponin. |
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What events trigger bending of myosin head?
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Myosin head bound to ATP. ATP hydolzes into ADP and inorganic P cocking myosin head.
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What conditions are necessary for muscle to relax?
What is meant by rigor? |
Ca++ need to return to SR
Rigor is the point at which the myosin head is most tightly bound to the actin after inorganic phosphate is released from myosin. |
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What causes myosin head to restore to its initial position?
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ADP is released from head causing "stroke" part of contraction. Then ATP binds to myosin head causing release from actin.
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Discuss difference of 2 headed myosin
Type II vs Type V Where is each one? |
Type II: Skeletal muscle- heads bind individually. 2nd head orients and stabilizes structure of motion generating head...generates maximum displacement.
Type V: intracellular organelles- two heads walk along microtubules- think vesicle toting cartoon. |
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What happens during sarcomere contraction?
What is moving and where? |
net effect of two actin molecules (Z lines) moving toward center of sarcomere...shortens sarcomere.
During continued contraction, come together eventually overlapping. |
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Can contraction occur without any overlapping of actin and myosin?
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NO!
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Range of contraction positions?
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Overextened to severe overlapping
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The sum of what 2 tensions equal total muscle tension?
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active and passive
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Passive tension
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resistance of CT in muscle tissue (elastic titin fibers)
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Active tension (isometric)
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proportional
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Motor Unit
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Group of muscle fibers innervated by branches of a single motor neuron
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Small Motor Units vs. Large Motor Units
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Small Motor Units adapted for fine and precise motor control...small motor neurons
Large Motor Units: adapted for great force...large motor neurons |
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Twitch
1. What is it? 2. How is its duration determined? 3. Twitches can be summed to generate...? |
1. Twitch is a movement of a single motor unit caused by a single action potential
2. Duration determined by level of myoplasmic Ca++ 3. Tetanus |
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What is spasm (cramp) and how is it generated?
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Sudden, involuntary contraction generated by continuous CNS activity or muscle dysfunction
Many causes |
