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APK2105C > CH 12, Part 1-6 > Flashcards

CH 12, Part 1-6 Flashcards

1
Q

Connective Tissue

A

EPIMYSIUM
- outside layer of connective tissue
- surround the muscle

PERIMYSIUM
- middle layer of connective tissue
- surround fascicles

ENDOMYSIUM
- inside layer of connective tissue
- surround individual muscle fibers

all different components of connective tissue merge together to form the TENDON at the ends of a whole muscle

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2
Q

Basic Anatomy of Muscle Fibers

A

MYOFIBRIL
- contractile organelle that runs the length of the myocyte
- what makes a cell unique
- most common organelle within muscle fibers (thousands)
- very very very small
- 80-90% of muscle fiber is made up of cylinder-shaped structure (myofibril)
- made of repeating segments called sarcomeres (actin and myosin)

SARCOMERES
- functional unit of organization of the myofibril and its overlapping arrangement of actin and myosin give a striated appearance
- length goes from z-disc to z-disc (shaped in form of Zs)
- in center is m-line
- coming off of z-disc is thin filament (actin)
- coming off of the m-line is the thick filament (myosin)
- slightly overlaps actin on both sides

T-TUBULE
- where plasma membrane enters into the muscle fiber
- “transverse tubule”
- on left and right side is sarcoplasmic reticulum (SR) which stores calcium

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3
Q

Anatomy of Actin Filament

A
  • made up of globular proteins called G actin
    • all globular actins have a myosin-binding site
  • will come together to form a strand called F actin
  • two F actin strands wrapped together in a double helix creates an actual actin filament
  • strand like proteins called tropomyosin covers up all myosin binding sites on all globular actin
  • combination of proteins is called troponin
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4
Q

Troponin

A
  • a combination of proteins that have the capacity to bind calcium, tropomyosin, and actin
  • when calcium levels are elevated inside a muscle fiber, they will bind to tropomyosin
  • troponin pushes tropomyosin stands off of myosin binding sites on actin
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5
Q

Tropomyosin

A
  • strand-like proteins that cover up all myosin binding sites on all globular actin
  • pushed off of binding sites by troponin
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6
Q

Anatomy of Myosin Filament

A
  • thick filament that comes off m-line
  • made up of myosin proteins
  • one tail and two heads
    • tails are parallel with actin
    • heads have ATPase site and actin-binding site
    • heads are slightly upward and perpendicular to actin filaments
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7
Q

Crossbridge Cycle

A
  • how myosin heads and actin interact with each other
  • dephosphorylation reaction of the myosin head

Two requirements:
(a) calcium must be elevated inside of muscle fiber
(b) must have ATP
- when cycle occurs, 1 ATP is consumed

Cycle:
(1) Rigor State
- myosin is actively bound to one globular
- stuck and cannot unbind
(2) ATP comes and binds to myosin head, causing it to release from actin
- ATP is hydrolyzed and broken down into ADP and inorganic phosphate
- head has been phosphorylated
- head is provided with energy from breakdown
(3) heads move upward
(4) Powerstroke
- head binds to a new portion of globular actin
- inorganic phosphate is released
- allows head to cycle forward and pull actin toward the m-line
(5) ADP is released

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8
Q

Force from interaction of Myosin and Actin

A
  • interaction of myosin and actin cause a contraction of the muscle fiber
  • muscle fiber contraction generates force which is relayed onto the endomysium
  • endomysium is continuous with the tendon so relays force onto tendon
  • tendon is attached to bone so force relayed to bone
  • bone moves to create joint action and movement
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9
Q

Primary Motor Cortex

A

area of gray matter that controls all of the skeletal muscles in the human body
- lays in front of central sulcus
- valley that separates front half of cerebrum from back half
- made up of cell bodies and dendrites
- myelinated axons travel into core of cerebrum –> spinal cord –> nerve –> muscle

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10
Q

Alpha Motor Neurons

A
  • primary motor neurons release glutamate (excitatory neurotransmitter) from axon terminals
  • glutamate is released onto alpha motor neurons that travel out cervical nerve to muscle fibers
    • glutamate receptors are actually sodium recptors
    • sodium shoots in and heads to axon hillock to get it to threshold so an action potential can be generated
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11
Q

Action Potential Passage

A
  • plasma membrane of skeletal muscle fiber meets AMN at neuromuscular junction
  • AP travels down AMN opening voltage-gated sodium channels and sodium drives up to +30 mV
  • calcium shoots into AMN button triggering exocytosis of neurotransmitter acetylcholine (ACh) into synaptic cleft
  • ACh will bind to receptors (ligand-gated channels) in the motor end plate causing them to open
    • ACh receptors are sodium channels that increase permeability
  • sodium shoots into muscle fiber causing depolarization (+ 20 mV)
  • voltage gated sodium channels throughout entire length of plasma membrane open and an AP is generated
  • travels down entire length of axon driving up from -90 mV –> +20 mV
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12
Q

Excitation Contraction Coupling

A
  • series of events that link the end-plate potential to muscle contraction
  • voltage-gated sodium channels exist on plasma membrane of skeletal muscle fiber –> must exists on t-tubule region (-90 mV)
  • AP will enter into t-tubule and depolarize that region
  • voltage-gated sodium channels will open, sodium will shoot in -90 mV –> +20 mV
  • on left and right of t-tubule, voltage-gated calcium channels
    • open when action potential arrives
    • DHP receptor (dihydropyridine)
  • open channels do NOT allow calcium in
    • DHP receptors attached to RyR channel (ryanodine receptors) attached to SR
  • when DHP receptors open, tug on RyR receptors causing them to open
  • calcium will flood out of SR into the intracellular fluid and bind to troponin
  • action potentials have one purpose → to release calcium
    • indirectly causes skeletal muscle fibers to contract through release of calcium
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13
Q

Muscle Fiber Relaxation

A
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14
Q

Muscle Fiber Twitch

A
  • when a muscle fiber generates a submaximal force
  • occurs when calcium gets taken up too fast by the SR’s SERCA pumps and not enough binds to troponin
  • because not all calcium can be bound to troponin, muscle fiber is unable to produce maximal force
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15
Q

Tetanus

A
  • when all available troponin binds to all available calcium (all available myosin binds to all available actin)
  • maximal force
  • can never truly happen
  • to get a greater force in the whole muscle, need multiple AMNs to generate APs so more muscle fibers will contracts (activating more AMNs)
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16
Q

Size Principle

A
  • if PMC neurons generate 10 AP per sec and synapse with 3 different AMNs, will release same amount of neurotransmitter onto each
  • smaller neurons easier to get to threshold because have less volume so less sodium needed to drive up membrane potential
  • same amount of sodium going into each AMN to get it to threshold
    • enough sodium to get smallest AMN to threshold –> generate AP
    • slow twitch muscle fibers
  • PMC neuron will increase frequency by which generates APs
    • second largest AMN will generate AP
    • transitioning to fast twitch variety
    • harder to get to threshold by synapse with more muscle fibers which are bigger
  • PMC neuron will increase frequency by which generates APs again
    • largest AMN will be able to reach threshold
    • muscles will be able to generate more force due to contractions of muscle fibers
17
Q

Force Velocity Relationship

A
  • muscles produce the most amount of force during isometric contraction
  • as soon as shortening velocity increases, the less force it can produce
    • as muscle fibers shorten faster –> myofibrils and sarcomeres shorten faster
      • actin is moving over myosin faster
      • decreases amount of myosin heads that can be bound to actin at a time –> less force produced
18
Q

Slow Twitch Muscle Fibers

A
  • myosin heads cycle at lower frequencies
  • shorten muscle fiber slowly
  • good at utilizing systems that need oxygen
    • produce ATP slowly
  • tons of blood vessels going to them (receive lots of blood and oxygen
  • lower ATP demand which can easily be met with supply
19
Q

Fast Twitch Muscle Fibers

A
  • myosin heads cycle faster –> actin is being pulled towards the m-line faster
  • shorten muscle fibers faster
  • consume much much much more ATP than slow
    • significantly high ATP demand because each cycle needs 1 ATP (for both fast and slow fibers)
  • phenomenally good at running phosphagen system and anaerobic glycolysis (system that can reduce ATP over time)
  • do NOT receive much blood –> not much oxygen
  • fatigue very easily (~10 sec) because can exceed ATP supply
20
Q

Concentric Contractions

A

muscle contraction involving a shortening of the muscle

21
Q

Eccentric Contractions

A

muscle contraction in which the muscle length increases

22
Q

Isotonic Contractions

A

muscle contraction in which the muscle generates a constant (iso) tension (tonic) greater than any forces opposing it, and its muscle length changes
- Two Types:
(1) Concentric
(2) Eccentric

23
Q

Isometric Contractions

A

muscle contraction in which a muscle creates tension but maintains the same (iso) length (metric) because the load is greater than the force generated by the muscle

APK2105C (14 decks)

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