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Physio Exam 3 (chapters 12-16) > Skeletal Muscle (physiology) > Flashcards

Skeletal Muscle (physiology) Flashcards

(51 cards)

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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

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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

Study These Flashcards
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?

24
Q

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

Study These Flashcards
A
  • shortens with contraction

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

25
When a muscle undergoes relaxation, what is the movement of Ca2+?
- 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
What is a muscle twitch?
-a single contraction/relaxation cycle in a muscle fiber and produces tension (force)
27
What is the latent period during the muscle twitch?
-time from start of muscle action potential to start of muscle tension development =time required for excitation-contraction coupling to occur
28
The tension of a muscle twitch depends on what?
-sarcomere length: the more # of cross bridges(myosin binding with actin)=increase in tension
29
What is the optimal sarcomere operating length?
-80%-120% of resting length
30
How is the optimal sarcomere length maintained?
-CNS maintains resting muscle length near optimal by maintaining a muscle tone
31
Describe the summation of muscle twitches
-occurs when successive stimuli arrive before the relaxation phase has been completed
32
When does incomplete (unfused) tetanus occur during a muscle twitch?
-when the muscle fiber relaxes slightly between stimuli and tension increases
33
When does a complete (fused) tenanus occur during a muscle twitch?
- when a muscle fiber doesn’t relax between stimuli and reaches max tension development - relaxation phase is eliminated
34
What are the characteristics of a slow twitch muscle fiber(type I)?
- most used - dark red (myoglobin) - oxidative;aerobic - slow - fatigue resistant
35
What are the characteristics of fast twitch muscle fibers (type II)?
- least used (jumping, quick, fine movements) - glycoltic (more anaerobic) - pale color - fast - large in diameter - short contractions - easily fatigued
36
What is a motor unit?
- a motor neuron that innervates a group of muscle fibers
37
What is fatigue?
-when muscle can’t generate/sustain power output
38
What are the 2 types of fatigue
-central and peripheral fatigue
39
What does the new research say about the cause of muscle fatigue?
- failure of Exictation-contraction coupling | - lactate accumulation is no longer the cause of fatigue
40
What are the two types of contraction mechanics?
- isotonic contraction | - isometric contraction
41
What happens to the muscle during a isotonic contraction?
-muscle contracts, shorts and creates enough force to move a load
42
What happens to the muscle during an isometric contraction?
-the muscle contracts but does not shorten. The force created cannot move the load
43
Voluntary movements can be divided into what 3 phases?
1) Planning 2) initiation 3) execution
44
Where are the muscle spindles (proprioceptors) found ?
-buried among the extrafusal fibers of the muscle
45
What is the function of the muscle spindles (proprioceptor)?
- 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
What is the function of the golgi tendon organs (proprioceptor)?
-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
What are the 2 somatic motor reflexes?
- monosynaptic reflex | - polysynaptic reflex
48
What are the connections of the monosynaptic reflex?
-has a single synapse between the afferent and efferent neurons
49
What are the connections of the polysynaptic reflex?
-has two or more synapses. This somatic motor reflex has both synapses in the CNS
50
Describe the patellar tendon (knee jerk) reflex
-is a monosynaptic stretch reflex and reciprocal inhibition of the antagonistic muscle
51
Describe the crossed extensor reflex
- a flexion reflex in one limb causes extension in the opposite limb. - The coordination of reflexes with postural adjustments is essential for maintaining balance

Physio Exam 3 (chapters 12-16) (10 decks)

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