Skeletal Muscle (physiology) Flashcards

1
Q

Are Skeletal muscles voluntary or involuntary muscles?

A

-voluntary

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2
Q

Where do our thoughts of voluntarily movement come from?

A
  • Primary motor cortex

- sends to

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3
Q

What is the neuromuscular junction?

A
  • synapse between somatic motor neuron and skeletal muscle fiber
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4
Q

Where is the origin of the motor neuron (cell body) of the neuromuscular junction?

A
  • anterior horn of the spinal cord
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5
Q

What happens at the axon terminal directly above the muscle fiber?

A
  • relay message by

- releasing neurotransmitter (ACh) to bind on the sarcolemma

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6
Q

The sarcolemma contains what kind of tubules?

A

-transverse tubule (t-tubule)

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7
Q

What is the function of the motor end plate?

A

-increase surface area for receptors to accept the neurotransmitters (ACh) from the vesicles

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8
Q

What is the goal of the neurotransmitter (ACh) being released into the muscle fiber?

A

-excite the muscle fiber for contraction

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9
Q

What type of receptor is needed for the muscle fiber to be excited?

A
  • nicotinic cholinergic receptor

- when ACh binds, Sodium comes in , and a little K+ leaves

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10
Q

Once the muscle is excited it leads to what process?

A

-excitation-contraction coupling

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11
Q

What is the muscle fiber threshold?

A

-50mv

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12
Q

What is an end plate potential?

A
  • localized depolarization (EPP)

- due to entry of NA+ ion

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13
Q

What kind of electrical signal does End plate potential give off?

A
  • EPSP (excitatory postsynaptic potential)

- is a graded potential

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14
Q

Where is the end plate potential created?

A

Motor end plate

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15
Q

Can graded potentials be summed?

A

Yes

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16
Q

Where is the action potential created on the muscle fiber? Where does it go after?

A
  • sarcolemma

- T tubule

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17
Q

Once the action potential reaches the t-tubule, which receptor conformed (altered)?

A
  • DHP receptor (dihydropyridine) #3
    • voltage sensitive
    • linked to the sarcoplasmic reticulum
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18
Q

The DHP receptor (dihydropyridine) opens which ion channel in the sarcoplasmic reticulum?

A
  • RyR Ca2+ (ryanodine Ca2+ release channels) #4

- Ca2+ enters cytoplasm

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19
Q

Once Ca2+ is released in the cytoplasm, where do they bind to?

A
  • Ca2+ binds to troponin (of the thin filament) #5

- allows actin-myosin binding

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20
Q

Explain how the filaments are arranged in a relaxed state (not contracted)

A
  • myosin head cocked
  • tropomyosin partially blocks binding site on actin
  • myosin is weakly bound to actin

-no calcium ions are available in a relaxed state

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21
Q

Explain what happens to the filaments during the initiation of contraction

A
  • Cystolic Ca2+ increases
    • pulls on the tropomyosin, exposing binding site on actin

-Actin is able to bind to myosin head

22
Q

What is the importance of calcium ions during the initiation of contraction

A
  • pulls the tropomyosin out of the way to expose the binding site on actin, so myosin can bind
23
Q

What is the sliding filament theory?

A
24
Q

When a muscle is contracted, what happens to the sarcomere (length)?

A
  • shortens with contraction

- H zone and I band both shorten while A band remains constant

25
Q

When a muscle undergoes relaxation, what is the movement of Ca2+?

A
  • sarcoplasmic Ca2+ ATPase pumps Ca2+ back into SR. (Primary active transport) #8
  • Decrease in cystolic Ca2+ causes Ca2+ to unbind from troponin #9
  • Tropomyosin recovers binding site. When myosin heads release, elastic elements pull filaments back to their relaxed position #10
26
Q

What is a muscle twitch?

A

-a single contraction/relaxation cycle in a muscle fiber and produces tension (force)

27
Q

What is the latent period during the muscle twitch?

A

-time from start of muscle action potential to start of muscle tension development
=time required for excitation-contraction coupling to occur

28
Q

The tension of a muscle twitch depends on what?

A

-sarcomere length: the more # of cross bridges(myosin binding with actin)=increase in tension

29
Q

What is the optimal sarcomere operating length?

A

-80%-120% of resting length

30
Q

How is the optimal sarcomere length maintained?

A

-CNS maintains resting muscle length near optimal by maintaining a muscle tone

31
Q

Describe the summation of muscle twitches

A

-occurs when successive stimuli arrive before the relaxation phase has been completed

32
Q

When does incomplete (unfused) tetanus occur during a muscle twitch?

A

-when the muscle fiber relaxes slightly between stimuli and tension increases

33
Q

When does a complete (fused) tenanus occur during a muscle twitch?

A
  • when a muscle fiber doesn’t relax between stimuli and reaches max tension development
  • relaxation phase is eliminated
34
Q

What are the characteristics of a slow twitch muscle fiber(type I)?

A
  • most used
  • dark red (myoglobin)
  • oxidative;aerobic
  • slow
  • fatigue resistant
35
Q

What are the characteristics of fast twitch muscle fibers (type II)?

A
  • least used (jumping, quick, fine movements)
  • glycoltic (more anaerobic)
  • pale color
  • fast
  • large in diameter
  • short contractions
  • easily fatigued
36
Q

What is a motor unit?

A
  • a motor neuron that innervates a group of muscle fibers
37
Q

What is fatigue?

A

-when muscle can’t generate/sustain power output

38
Q

What are the 2 types of fatigue

A

-central and peripheral fatigue

39
Q

What does the new research say about the cause of muscle fatigue?

A
  • failure of Exictation-contraction coupling

- lactate accumulation is no longer the cause of fatigue

40
Q

What are the two types of contraction mechanics?

A
  • isotonic contraction

- isometric contraction

41
Q

What happens to the muscle during a isotonic contraction?

A

-muscle contracts, shorts and creates enough force to move a load

42
Q

What happens to the muscle during an isometric contraction?

A

-the muscle contracts but does not shorten. The force created cannot move the load

43
Q

Voluntary movements can be divided into what 3 phases?

A

1) Planning
2) initiation
3) execution

44
Q

Where are the muscle spindles (proprioceptors) found ?

A

-buried among the extrafusal fibers of the muscle

45
Q

What is the function of the muscle spindles (proprioceptor)?

A
  • detects stretch of muscle fibers
    • sends info to CNS
  • maintains muscle tone
    • spindles are tonically active and firing even when muscle is relaxed
  • generates muscle spindle reflex
    • can trigger a stretch reflex
46
Q

What is the function of the golgi tendon organs (proprioceptor)?

A

-responds to muscle tension during isometric contraction

  • golgi tendon reflex
    • protects the muscle from excessively heavy loads by causing the muscle to relax and drop the load
47
Q

What are the 2 somatic motor reflexes?

A
  • monosynaptic reflex

- polysynaptic reflex

48
Q

What are the connections of the monosynaptic reflex?

A

-has a single synapse between the afferent and efferent neurons

49
Q

What are the connections of the polysynaptic reflex?

A

-has two or more synapses. This somatic motor reflex has both synapses in the CNS

50
Q

Describe the patellar tendon (knee jerk) reflex

A

-is a monosynaptic stretch reflex and reciprocal inhibition of the antagonistic muscle

51
Q

Describe the crossed extensor reflex

A
  • a flexion reflex in one limb causes extension in the opposite limb.
    • The coordination of reflexes with postural adjustments is essential for maintaining balance