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4 Clinical Physiology > L8 Muscle > Flashcards

L8 Muscle Flashcards

(62 cards)

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1
Q

What determines the strength of a muscle contraction?

A
  1. Cross Sectional Area
  2. # and type of fibers within the muscle
  3. Frequency of muscle fiber stimulation
  4. Thickness of each muscle fiber
  5. Resting length of muscle fibers
  6. Velocity of movement
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2
Q

What kind of muscle design is the strongest?

A

pennate

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3
Q

Hennemann’s Size Principle

A
  1. When a weak contraction is desired, smaller motor units are recruited
  2. Stronger contraction is wanted, progressively larger motor units are recruited
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4
Q

Is this recruitment pattern the same when using electrical stimulation to cause a muscle contraction?

A

NO
activate Type 2 motor unit first

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5
Q

Multiple motor unit summation

A

different numbers of motor units are brought into play to produce gradations of strength

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6
Q

Type of muscle fibers stimulated to contract

A
  1. Muscle fiber type is determined by MOTOR NEURON
  2. Somatic motor neuron innervates only one type of muscle fibers
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7
Q

Slow Twitch Fibers

A

Type 1

High Oxidative Capacity
Resistant to Fatigue

postural control muscles are mainly type 1

motor neurons have a slower conduction rate

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8
Q

High Oxidative Capacity of Type 1

A

rich capillary supply
lots of mitochondria and aerobic enzymes
high concentration of myoglobin

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9
Q

Myoglobin

A

iron and oxygen binding protein

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10
Q

Resistant to fatigue type 1 fibers

A

postural muscle s

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11
Q

Fast Twitch Fibers

A

Type 2 Fibers, phasic

Lower oxidative capacity
Fatigue quickly

gastroc, biceps, extraocular muscles are type 2

motor neurons have faster conduction rate

conduction velocity is fast, cell body size is large

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12
Q

Lower oxidative capacity Type 2 Fibers

A

Fewer Capillaries, mitochondria

Lower concentration of myoglobin

High concentration of glycolytic enzymes and large glycogen stores

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13
Q

Subpopulations of Type 2 Fibers

A

Type 2a
Type 2b
Type 2x

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14
Q

Type 2a Fibers

A

slowest, for endurance

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15
Q

Type 2b fibers

A

don’t exist in humans

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16
Q

Type 2x fibers

A

fastest, sprint/interval activities

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17
Q

How is it determined what muscle fibers you have?

A

Specific muscle (gastroc vs core)
genetics
age
training

you cannot convert type 1 to type 2, you can convert between the type 2 subtypes

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18
Q

Structure of skeletal muscle

A

composed of fibers/cells
multinucleate

Myofilaments–> Myofibrils –> Muscle fiber

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19
Q

Myofibril

A

subunit of muscle cell that consists of successive sarcomeres

single sarcomere contains many longitudinal myofilaments

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20
Q

Sarcomere

A

Z to Z, basic unit of striated muscle contraction

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21
Q

H band

A

thick filaments, composed of myosin

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22
Q

I band

A

thin filaments, composed of actin

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23
Q

A band

A

overlap of thick and thin filaments

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24
Q

Z line/disc

A

center of each I band

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25
What happens to the sarcomere during contraction?
Distance between Z lines shortens Successive A bands move closer together I bands slide over and between H bands, decreasing length
26
Contraction Steps (ATP)
1. globular head of myosin splits ATP 2. ADP and P bound to myosin until myosin attaches to actin 3. Phosphate is released, causing myosin to perform a power stroke 4. Filaments slide 5. ADP is released when myosin binds to new ATP, breaking cross bridge 6. ATP is hydrolyzed, myosin head returns to original conformation
27
Excitation-contraction Coupling
1. Action potential travels down motor neuron to axon terminal 2. Voltage gated calcium channels open, so calcium diffuse into terminal 3. Rise in intracellular calcium causes release of AcH into NMJ 4. Ach binds to nAch receptors in motor end plate, leading to EPP 5. EPP leads to action potentials that travel into T-tubules 6. AP causes calcium to be released from SR 7. Calcium binds to troponin, allows tropomyosin to move, myosin can bind to actin
28
Motor end plate
specialized region of sarcolemma at the NMJ with increased nACH receptors binding of ACh to NaCh reeptors produces an end-plate potential, if it is enough, AP is produced
29
Terminal Cisternae
Calcium in relaxed muscle is stored within expanded portions of the SR
30
Transverse tubules
terminal cisternae are separated by a narrow gap which are the T-Tubules narrow membrane tunnels that are continuous with the sarcolemma
31
Sarcoplasmic reticulum
modified endoplasmic reticulum, consisting of sacs and tubes that surround each myofibril
32
Structure of thin filament
F actin is composed of subunits of actin called G-actin F actin are arranged in a double row and twisted to form a helix
33
Tropomyosin
protein that lies within the groove between the F-actin chains
34
Troponin
complex of 3 proteins that is attached to tropomyosin, not actin
35
Role of Ca in muscle contraction
Ca binds to troponin, which triggers tropomyosin to move. Allows actin to be revealed, causing power strokes
36
How does skeletal muscle relaxation occur?
1. Neural stimulation stops 2. ACh is broken down by actylcholinesterase within the NMJ 3. SR stops releasing calcium and immediately resequesters calcium that was just released
37
ACh is broken down...
AChE is an enzyme that metabolizes ACh into acetate and choline
38
AChEIs
drugs that inhibit acetylcholinesterase, allows ACh to stay in the synaptic cleft longer used in treatment of myasthenia gravis and alzheimer's disease
39
ADRs of AChEIs
DUMBBELSS Diarrhea Urination Miosis Bronchoconstriction Bradycardia Excitation Lacrimation Salivation Sweating
40
Muscle Fatigue
inability of a muscle to maintain the required tension for a given task or generate an expected power when a contraction is sustained most likely due to accumulation of extracellular K+
41
Moderate Exercise and Muscle fatigue
Failure at any site downstream or upstream can contribute to development of muscle fatigue
42
Fatigue is multifactorial
Increased intracellular concentration of lactate, H+, inorganic phosphate impaired Ca 2+ release increased production of fatigue reactants depletion of glycogen
43
Central Fatigue
NMJ and upstream fatiguing exercise changes brain concentrations of NTs, which decreases neural drive to muscle increase perception of effort decreased motivation high serotonin, low dopamine
44
Peripheral Fatigue
produced by changes at or distal to NMJ AI diseases that target synaptic proteins muscular dystrophies
45
Central fatigue pathological conditions
MS, guillain barre, CIDP
46
S/S of Muscle Fatigue
muscle discomfort, pain, cramping tremor in contracting muscle unintentional slowing of movement altered quality of movement decline in peak torque, EMG, MMT
47
Muscle Fatigue Treatment
No single agreed upon treatment , fatigue must be evaluated based on many variables massage, compression, NSAIDs, e-stim all treat the S/S light aerobic exercise is more effective than total rest
48
Endurance training increases...
lactate threshold means it prolongs the time until an increasing proportion of energy must be derived from anaerobic glycolysis
49
Muscle adaptations to aerobic/endurance training
1. Increases # of mitochondria and aerobic enzymes in all muscle fiber types 2. Increases # of type 2a fibers and decreases # of type 2B fibers 3. Does NOT increase size of muscles
50
Other adaptations of endurance training on muscles
improved ability to obtain ATP from OP increased size and # of mitochondria less lactic acid produced increased myoglobin increased triglyceride content increased lipoprotein lipase increased energy derived from fat Lower rate of glycogen depletion improved efficiency of O2 use decreased type 2B fibers
51
Muscle adaptations to resistance training
Hypertrophies type 2 muscle fibers Increase in size and number of MYOFIBRILS cell # increases mainly in animals, minimal in humans
52
Smooth Muscle
found in almost every organ major component of the walls of hollow organs
53
Smooth muscle contraction
-arranged in circular or longitudinal layers -lack of sarcomeres, no striations -more thin vs thick (16:1) -actin and myosin contract by unique regulatory mechanism thin filaments/actin attach to either plasma membranes, dense bodies
54
Myosin Heads of Smooth muscle fiber
arrangement of myosin heads to thin filaments is required for proper smooth muscle function can still contract at very stretched lengths must be able function when greatly stretched
55
Urinary bladder
smooth muscle cels stretch 2.5 times their resting length
56
Uterus
smooth muscle cells stretch 8 times their original length by end of pregnancy
57
Differences between smooth and skeletal muscle
1. smooth muscle cells produce graded depolarizations and contractions w/out producing APs 2. Extracellular Ca enters through special channels in smooth 3. Ca binds with calmodulin in smooth 4. Calmodulin joins with myosin kinase
58
Similarities between Smooth and Skeletal
1. Depends on sharp rise in intracellular free Ca 2. Greater the depolarization of smooth muscle, more Ca will enter the cell, stronger the contraction 3. Myosin head binds with actin 4. Relaxation occurs when Ca concentration decreases
59
Single-unit smooth muscles
Most smooth muscles many gap junctions only some cells receive ANS innervation have intrinsic electrical activity and contract in response to stretch
60
ANS innervation of smooth muscles
entire surface of a smooth muscle contains receptors ACh released along a stretch of an autonomic nerve fiber located a distance from smooth muscle cells
61
Varicosities
regions of autonomic fiber that release NT
62
Multiunit smooth muscles
contraction requires nerve stimulation few if any gap junctions arrector pili muscles in in skin ciliary muscles attached to eye lens

4 Clinical Physiology (9 decks)

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