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A&P 1 FAU > Lecture 9.4 main points > Flashcards

Lecture 9.4 main points Flashcards

1
Q

what is the functional unit of the nervous system

A

neuron

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2
Q

how does the functional unit of the nervous system communicate

A

neurons communicate via the release of neurotransmitters

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3
Q

what are the signal relaying portions of neurons called and what structure are they often bundled in

A

nerves, bundles of axons

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4
Q

what is muscle connected to

A

at least one motor nerve

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5
Q

what is a motor nerve

A

contains axons to a few or hundreds of motor neurons

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6
Q

are motor axons a singular extension or can they branch

A

can branch many times before ending at nerve terminals

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7
Q

define motor unit

A

a motor neuron and all (four to several hundred) muscle fibers it innervates (controls)

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8
Q

how are motor units arranged for fine control

A

produce small, finely controlled movements. small motor units can contain as few as 10-20 muscle fibers

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9
Q

examples of fine control motor units

A

eye muscles, larynx muscles

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10
Q

how are motor units arranged for strength control

A

produce large, strong movements. Can have as many as 2000 muscle fibers in a motor unit

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11
Q

example of strength control motor unit

A

gastrocnemius

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12
Q

how are muscle fibers of a motor unit distributed in a whole muscle

A

spread throughout the muscle

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13
Q

how does the activation of a single motor unit affect the contraction of the whole muscle

A

typically causes a weak contraction of that muscle

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14
Q

do all motor units activate at the same time or do they activate asynchronously

A

only the muscle fibers of the specific motor unit will contract when activated by the motor unit.
ASYNCHRONOUSLY

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15
Q

why is it important for motor units to activate asynchronously

A

helps prevent, or decrease, overall muscle fatigue

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16
Q

describe a motor units response to a single AP in its motor neuron

A

results in an AP in the muscle fibers connected through NMJs with that neuron, produces a short period of motor unit’s muscle fiber contraction that generates tension

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17
Q

different strength and duration of twitches in whole muscle can be observed, why does this happen

A

due to variations in metabolic properties ad enzymes between muscle fiber types, different whole muscles have differing ratios of muscle fiber types

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18
Q

what is the graphical representation of a lab - measured muscle contraction called

A

myogram

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19
Q

three phases of muscle twitch

A

latent period, period of contraction, period of relaxation

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20
Q

latent period of muscle twitch

A

events of excitation- contraction coupling. AP must reach threshold, no visible shortening or tension of the muscle during this period

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21
Q

period of contraction

A

sarcomere shortening from cross bridge formation and power stroke produce visible tension (external tension)

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22
Q

period of relaxation

A

Ca reentry into the SR, tension declines to zero

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23
Q

differentiate between speed of contraction and relaxation

A

muscle contracts faster than it relaxes

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24
Q

what does a “graded response” mean in reference to muscle contraction

A

varying strength of contraction for different demands

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25
Q

why is a graded response important in muscle contraction

A

required for proper control of skeletal movement

26
Q

how is the muscle response graded?

A
  1. changing frequency of stimulation
  2. changing strength of stimulation
27
Q

is AP strength affected by increasing stimulation strength

A

no

28
Q

if a stronger stimulus is applied, what happens in a graded muscle reponse

A

more motor units are activate more muscle fibers but the AP strength does not change

29
Q

what happens to the muscle cell once threshold is met

A

threshold stimuli produce twitch

30
Q

what does the “all or none” law of muscle contraction mean
is it 100% true? if not what can affect twitch strength?

A

contracts to its maximum or not at all
not 100% true
twitch strength depends on Ca concentration, previous stretch of the muscle, temperature, pH, and hydration

31
Q

list different time required for muscle AP and contraction

A

AP in muscle cell occurs much faster than actual contraction
2 milliseconds (AP) vs up to 100 milliseconds (contraction)

32
Q

why is the difference in time important between muscle AP and contraction

A

a second action potential may be initiated during the period of mechanical activity of the muscle fiber

33
Q

propertied of low frequency (10 stimuli/ sec) muscle stimulation, why is peak tension the same

A

each stimulation produces an identical twitch response, max tension produced from each twitch remains equal
peak tension is the same for every one bc the sarcoplasmic calcium goes back to resting levels

34
Q

properties of moderate frequency (10-20stimuli/ sec) muscle stimulation

A

each twitch has time to recover but develops more tension than the one before (treppe phenomenon)

35
Q

treppe phenomenon

A

not enough time between stimuli for sarcoplasmic calcium to return to full resting levels, therefore calcium is not completely put back into the SR
an increase in sarcoplasmic calcium concentration with each successive Ap stimulation results in longer unblocking and more cross bridge formation and power strokes resulting in increase in tension produced (to a certain point)

36
Q

wave (temporal) summation

A

increased stimulus frequency (muscle does not completely relax between AP stimuli) –> second contraction of greater force
additional Ca release from the SR with the second stimulus stimulates re -unblocking of the myosin binding sites and more shortening before full relaxation is obtained

37
Q

continued temporal stimulus frequency results in unfused incomplete tetanus

A

produces sustained, but quivering, contraction that increase in successive twitch maximum tension

38
Q

during wave (temporal) summation how is another contraction elicited during relaxation and how does that affect peak tension

A

the increase stimulus frequency does not allow the muscle cell to completely relax resulting in the second contraction of greater force
the peak tension increases with each contraction to a certain point

39
Q

what is it called if we continue to temporal stimulation frequency? how does the muscle contraction appear

A

unfused (incomplete) tetanus
sustained, quivering contraction

40
Q

how is fused (complete) tetany achieved

A

if sustained stimuli are given quickly enough then muscle reaches maximal tension, no muscle relaxation due to consistently high sarcoplasmic Ca from continued release through SR

41
Q

what type of tension is achieved through fused (complete) tetany

A

maximum tension

42
Q

through fused tetany, what will it eventually lead to is successive stimulation is continued and how does this affect tension

A

eventually leads to muscle fatigue as metabolites accumulate and ionic imbalances form, this leads to a decrease in tension towards zero due to inability for muscle to contract

43
Q

compare tetanus vs twitch for
AP
effect on sarcoplasmic reticulum
time of unblocked thin filaments
amount of cross bridges formed
effects on elastic elements and transfer of tension

A

Twitch - single AP release enough calcium to saturate troponin C and allow all of the myosin binding sites to become available, but the binding of the myosin head takes time and during that time sarcoplasmic Ca is being pumped back into the SR by ATPases and SERCA pumps, therefore the sarcoplasmic CA begins to derease allowing for re-blocking of the myosin binding sites and before many of the binding sites are even formed

Tetanus - successive AP each release calcium from the SR before much of the calcium from the previous AP can be pumped back into the SR, this results in persistent elevation of sarcoplasmic Ca concentration, keeping myosin binding sites unblocked, more cross bridge formation and power strokes

43
Q

another cause for difference between twitch and tetanus due to elasticity of muscle tendons and protein titin

A

the elasticity means that these must stretch/ compress before tension is produced from the contractile unit being transferred (like a bungee cord). Because a single twitch is so brief, the cross bridge activity is already declining before force has been fully transferred through the elastic structure

during tetanic stimulation - this is less of a factor due to the long duration of cross bridge activity and force generation

44
Q

what is recruitment and why is it important

A

multiple motor unit summation, controls force of contraction of a whole muscle. during recruitment muscle contracts more vigorously as stimulus strength increases above threshold
it is used to increase the force of a muscle contraction by activating additional motor units of that msucle

45
Q

what does it mean to have a sub-threshold stimulus

A

a stimulus too weak to illicit activation of any motor units in a muscle ( no observable contractions or tension)

46
Q

what does it mean to have a threshold stimulus

A

stimulus strength that causes first observable muscle contraction (activation of motor unit) and generation of tension

47
Q

what does it mean to have maximal stimulus

A

strongest stimulus that increases contractile force of whole muscle to its maximum (all possible motor units are turned on)

48
Q

once threshold is met, what does an increase in applied stimulus voltage mean for motor unit activation and tension generated

A

more motor units are activated therefore increasing the tension generated

49
Q

why does tension increase with additional motor unit activation

A

more active motor units results in more muscle fibers shortening and pulling therefore more force generated

50
Q

why is there no additional tension generated when the stimulus voltage is increased above maximal

A

because the maximum amount of motor units have been excited despite an increase in voltage

51
Q

what does it mean when it is stated that recruitment words on the size principle

A

motor units with the smallest muscle fibers are recruited first, if more force is required motor units with more and larger fibers are recruited, and if maximal force is required the largest motor units are activated

52
Q

are there differences in the principles of contraction for single muscle cells vs whole muscle ?

A

no, contraction produces muscle tension, so however much force is needed determines what is used
force and duration of contraction vary in response to stimuli or different frequencies and intensities

53
Q

what is muscle tension

A

the force exerted on load or object to be moved
muscle tension is produced by contraction

54
Q

does contraction always lead to a shortening of a muscle

A

no, isometric contraction does not shorten the muscle but still places tension on the muscle

55
Q

define isometric contraction

A

no shortening, muscle tension increases but does not exceed load (same length)

56
Q

define isotonic contraction

A

muscle shortens because muscle tension exceeds load (same tension, or tone, once load exceeded)

57
Q

during isotonic contraction, do the thin filaments move with respect to the thick?

A

thin filaments slide

58
Q

when is an isotonic contraction concentric

A

when the muscle shortens and does work

59
Q

when is an isotonic contraction eccentric

A

the muscle generates force as it lengthens
the negative rep

60
Q

during isometric contraction do the thin filaments move with respect to the thick?

A

no, cross bridges do form but do not move the actin filaments

61
Q

what does it mean for a muscle to have tone?

A

constant, slightly contracted state of all muscles due to spinal reflexes.
Groups of motor units are alternatively activated in response to input from stretch receptors in muscles
keeps muscles firms, healthy and ready to respond

A&P 1 FAU (15 decks)

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