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Physiology II > skeletal muscle > Flashcards

skeletal muscle Flashcards

1
Q

muscle fiber

A

synonym for muscle cell

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2
Q

sarcolemma

A

the plasma membrane of a skeletal muscle fiber that encloses cytoplasm (sarcoplasm)

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3
Q

associated with (immediately outside of) the sarcolemma is a coat of polycaccharide material in which are embedded collagen fibrils that at the fiber’s ends, fuse with the ____ of the muscle

A

tendon

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4
Q

a muscle is composed of subunits called

A

fasciculi

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5
Q

each fasciculus is a bundle of

A

cells

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6
Q

each muscle fiber is a bundle of

A

myofibrils

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7
Q

sarcomere

A

the portion of a myofibril between two adjacent Z-discs

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8
Q

thick filament

A

myosin

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9
Q

thin filament

A

actin

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10
Q

each sarcomere is composed of several thousand myofilaments called _____ filaments and _____ filaments

A

actin

myosin

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11
Q

each myosin filament is made of many myosin molecules; each myosin molecule has a tail or body (that includes two arms) and two

A

heads

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12
Q

what three proteins make up actin filaments

A

F-actin

tropomyosin

troponin complex

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13
Q

F-actin:

A

the helical backbone of the actin filament; contains many “active sites” (binding sites for myosin)

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14
Q

tropomyosin

A

lies atop F-actin and covers up the active sites when contraction is not desired

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15
Q

troponin complex (attached intermittently along tropomyosin)

A

troponin T binds tropomyosin

troponin I binds actins

troponin C binds calcium ions

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16
Q

actin filaments attach to

A

both Z discs of a sarcomere and interdigitate with myosin filaments

17
Q

the sarcomere is made up of a complete

A

A band and the 2 halves of the I bands adjacent to it

18
Q

I band

A

all actin (thin filament) in a sarcomere

19
Q

A band

A

all the myosin (thick filament)

20
Q

titin

A

a protein that maintains alignment between actin and myosin filaments and also acts like a spring between a Z disc and the end of a myosin filament (may be important in some diseases)

21
Q

stimulus –> CNS –>

A

movement

22
Q

the synapse between a motor neuron and a skeletal muscle fiber is called a

A

neuromuscular junction (NMJ)

23
Q

the tiny fluid-filled space between cells at a synapse is the

A

synaptic cleft

24
Q

molecules of transmitter in the presynaptic axon terminal are contained within

A

many synaptic vesicles, the walls of which are made of membrane

25
Q

if the synapse is a NMJ, the transmitter is always

A

acetylcholine (ACh)

26
Q

acetylcholine receptors are embedded in the plasma membrane of the

A

postsynaptic cell

27
Q

steps of traveling wave of electricity in the motor neuron leading to muscle fiber shortening

A

EVENTS IN THE NEURON

  1. action potential arrives at axon terminal
  2. calcium enters terminal
  3. acetylcholine is released from terminal

EVENTS IN THE SYNAPTIC CLEFT
4. acetylcholine diffuses across synaptic cleft, binds to receptors on sarcolemma, and is broken down by acetylcholinesterase

EVENTS IN THE MUSCLE FIBER

  1. cation channels open and cations enter
  2. fiber produces end plate potential
  3. fiber produces action potential
  4. action potential travels into interior of the fiber along transverse tubules
  5. calcium is released from sarcoplasmic reticulum
  6. troponin removes tropomyosin’s inhibition of actin-myosin binding
  7. myosin pulls on actin, shortening the sarcomere
28
Q

synaptic transmission

A

the process whereby a signal is passed between neurons or other excitable cells

29
Q

events in the neuron

A
  1. an action potential arrives at the axon terminal of the motor neuron
  2. the segment of axon terminal membrane in which the action potential is occurring is electrically positive on the inside with respect to the outside
  3. each synaptic vesicle contains about 5000 ACh molecules
  4. the arriving action potential will function to cause the release of ACh into the synaptic cleft from synaptic vesicles
  5. the depolarization of the axon terminal, that is the action potential, opens voltage-gated calcium channels and thus increases the permeability of the axon terminal membrane to Ca++
  6. calcium ions enter the axon terminal, where they allow synaptic vesicles to move to and fuse with the inside surface of the axon terminal plasma membrane; this allows the vesicle contents to be released via exocytosis
30
Q

events in the synaptic cleft

A
  1. each arriving action potential causes the discharge of about 300 vesicles (300 * 5000 = 1,500,000)
  2. the ACh binds to ACh receptors embedded in the muscle fiber sarcolemma
  3. most of the ACh is quickly removed from the synaptic cleft by being broken down by the enzyme acetylcholinesterase
31
Q

events in the muscle fiber

A
  1. the binding of 2 ACh molecules to a single ACh receptor opens an ion channel specific for cations
  2. the influx of Na+ makes the cell less negative on the inside (depolarizes the cell), thus producing a graded potential in the muscle fiber
  3. the graded potential is called an excitatory postsynaptic potential (EPSP), aka an end plate potential (EPP)
  4. the action potential travels along the sarcolemma in both directions
  5. when an action potential gets to a T tubule, it travels inward into the fiber in addition to moving along the sarcolemma; thus T tubules carry the electrical signal into the interior of the fiber
  6. T-tubule protien (dihydropyridine receptor) senses the voltage change due to the action potential and interacts with nearby sarcoplasmic reticulum protein (ryanodine receptor/calcium release channel)
  7. opening of the calcium release channels allows many calcium ions to move out of the sarcoplasmic reticulum and into the sarcoplasm surrounding the myofibrils
32
Q

bernard katz recorded miniature end plate potential (mEPPs) from the muscle fiber in the

A

absence of stimulation of the motor neuron

33
Q

each miniature end plate potential (mEPP) is caused by

A

the spontaneous discharge of 1 synaptic vesicle

34
Q

virtually every end plate potential is large enough to elicit an

A

action potential in the sarcolemma

35
Q

transverse (T) tubules

A

invaginations of the sarcolemma into the interior of the muscle fiber that lie at right angles to the myofibrils; they are made of membrane and filled with ECF

36
Q

sarcoplasmic reticulum (SR)

A

membranous structure that is adjacent and mostly parallel to the myofibrils, in contact with the T tubules, and a storage depot for calcium

37
Q

a T tubule protein called a dihydropyridine receptor “senses”

A

the voltage change due to the action potential, becomes activated, and interacts with a protein in the nearby sarcoplasmic reticulum called a ryanodine receptor/calcium release channel, which is also an ion channel specific for calcium

38
Q

excitation-contraction (EC) coupling- the traid

A

the junction between two terminal cisternae and a T-tubule

39
Q

sliding filament theory of contraction

A
  1. ADP is released from the myosin head, which clears the way for another ATP to bind
  2. ATP binds to the myosin head, which causes actin and myosin to dissociate; myosin head is “sprung” or “uncocked”
  3. ATP is hydrolyzed to ADP plus P (both remain attached to the myosin head); this causes a conformational change in myosin that “cocks” the head
  4. If and only if calcium ions are present, calcium binds to troponin C, causing troponin to “tug on” tropomyosin, which moves tropomyosin away from the active sites on myosoin
  5. the myosin head binds to actin; the head when attached to myosin is called a “cross bridge”
  6. the phosphate group is released from the myosin head, causing pivoting (that is “springing” or “uncocking” of the myosin head
  7. because myosin is attached to actin, it pulls on actin as it changes shape, and the Z disc attached to the actin myofilament is pulled along the actin
  8. this happens at both ends of the sarcomere, and thus the two Z discs are pulled toward each other, and the sarcomere shortens (ADP remains attached to myosin)
  9. myosin and actin remain attached to each other until the ADP is released from myosin and ATP binds
  10. many cycles of myosin head springing occur, ratcheting the “right” and “left” actin filaments closer and closer together

Physiology II (16 decks)

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