Chapter 10: Muscle Tissue Flashcards

1
Q

Properties of muscle tissue include:

A
  • Electrical excitability – ability to respond to a stimulis by producing an action potential that travels along the muscle sarcolemia
  • Contracility – ability to contract forcefully when stimulated by an action potential
  • Extensibility – can stretch without damage (to a certain extent)
  • Elasticity – ability to return to the original length/ shape
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2
Q

CT coverings extend from fascia & include:

A

Endomysium → surrounds individual muscle cells

Perimysium → surrounds a bundle (fascicle) of muscle cells

Epimysium → encircles entire muscle (many fascicles)

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3
Q

Muscle Organization, made up on ___ which are made up of 100s of ____ which contain even smaller structures

A
  • Muscle cell (fiber) is elongated & multinucleated
  • Cell cytoplasm (sarcoplasm) contains 100s – 1000s of threadlike myofibrils extending the length of the cell
  • Each myofibril consists of even smaller structures – myofilaments, which are the contractile proteins
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4
Q

2 types of myofiliments

A

Thick myofilaments
– composed of the protein myosin
– has a tail & 2 globular heads
– during contraction, myosin head projects towards thin filaments & forms cross bridges

Thin myofilaments
– composed of the globular protein actin & regulatory proteins (troponin & tropomyosin)
– tropomyosin blocks myosin-binding sites on actin
– troponin binds to actin, tropomyosin, & Ca2+

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5
Q

Myofilaments parts

A
  • Are organized into sarcomeres
  • Arrangement of myofilaments results in striations
  • Z discs (boundaries of sarcomere).
  • A band (region in the centre and has thick and thin myofilaments, areas with both thick/thin and then an area with only thick. The A band is the length of the thick myofiliment)
  • H zone (In the center of the myofilament where theres only the thick filament. Region that overlaps the A filament.)
  • I band (in either side of A band and only has thin filament. )
  • M line (the area where the 2 thick filiments are stiched together to form one long thick filament)
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6
Q

sarcoplasmic reticulum (SR)

A
  • specialized smooth ER
  • Functions to store & release Ca2+
  • Has a series of channels that run longitudinally along the myofibril
  • Has dilated end sacs called terminal cisterns at the A band/I band junctions
  • A T-tubule & the 2 cisterns on either side of it forms a triad
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7
Q

Complete muscle contraction

A
  1. A nerve action potential in a somatic motor neuron triggers the release of Ach
  2. Ach binds to receptors in the motor end plate, triggering muscle action potential
  3. Acetylcholinesterase destroys Ach so another muscle action potential doesn’t start unless more Ach is relased from somatic motor neuron
  4. Muscle action potential traveling alonf a transverse tubule triggers a channel in the voltage gated Ca2+ channgels that causes the Ca2+ release channels to open, allowing the relase of calcium ions into the sarsoplasm
  5. Ca2+ binds to troponin on thin filament, exposing the myosin binding site on actin
  6. Contraction. Myosin heads bind to actin, undergo power stroked and release think filament are pulled toward center of sarcomere
  7. Ca2+ relase channels close and CA2+-ATPase pumps use ATP to restore low level of Ca2+ in the sarcoplasm
  8. Tropomyosin slide back into position where it blocks the muosin-binding sites on actin
  9. Muscles releax
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8
Q

What uses more motor units, fine or overall motor skills?

A
  • Fine motor skills (move of lips for talking) = less motor units
  • overall motor skill = more motor units
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9
Q

Muscle Stimulation

A
  • Neurotransmitter acetylcholine (ACh) is used to cross the synaptic cleft
  • ACh diffuses across cleft & binds to ACh receptor sites on the muscle sarcolemma
  • Opens ligand-gated Na+ channels & Na+ diffuses into muscle cell
  • Triggers an action potential over entire surface of sarcolemma
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10
Q

Excitation-Contraction Coupling

A
  • action potential on the sarcolemma (excitation) to the muscle contraction
  • Action potential travels down T-tubules & causes SR to release Ca2+ into sarcoplasm
  • Ca2+ binds to troponin, which changes shape & in turn moves the tropomyosin away from the myosin-binding sites on actin
  • Binding sites are “freed”
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11
Q

Sliding Filament Mechanism

A

Once binding sites on actin are exposed, the following 4 steps occur:

  1. ATP hydrolysis. Myosin head has an ATP binding site & ATPase enzymes that split ATP → ADP + P
    Myosin head is reoriented & energized
  2. Cross bridge attachment. Energized myosin head attaches to the myosin binding site on actin. P is released
  3. Power stroke. Myosin cross bridge rotates toward the centre of the sarcomere & generates force. Releases ADP. Thin filament slides toward M line
  4. Cross bridge detachment. A new ATP molecule binds to the myosin head & the cross bridge detaches from actin
  • Thin myofilaments progressively slide past the thick myofilaments & the sarcomere shortens
  • Z discs come closer together
  • The amount of overlap b/t thick & thin filaments increases
  • Once nerve action potentials cease, Ca2+ channels in muscle are closed & myosin-binding sites are blocked once again by tropomyosin
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12
Q

Force of Muscle Contraction

A

A motor unit is one motor neuron & all the muscle cells it innervates
An ↑ in stimulus strength will ↑ the number of motor units responding to ↑ the force of contraction

An ↑ in stimulus frequency will ↑ the force of contraction
The muscle is partially contracted & 2nd stimulus releases more Ca2+ so contractions are summed

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