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Physiology Intro > Lecture 7 Muscular Physiology > Flashcards

Lecture 7 Muscular Physiology Flashcards

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0
Q

Each muscle fibre is innervated by only one neuron but one motor neuron may go on to

A

Innervate many muscle fibres

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1
Q

Each muscle fibre is innervated by how many neurons ?

A

Just one

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2
Q

1 neuron innervates _____ fibres within the same whole muscle

A

150 ave

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3
Q

Presynaptic neuron contains vesicles with nT (acetylcholine) and on the post synaptic membrane of the muscle fibre (sarcolemma), it is a region with _____ and is referred to as ______

A

ACH receptors

Motor end plate

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4
Q

After acetylcholine binds to the ACH receptors on the motor end plate of the sarcolemma what happens?

A

Chemical gates open and Na+ floods into the cell. Creating a end plate potential which is a graded potential. This EPP is always sufficient enough to cause an action potential.

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5
Q

Why is the transmission of action potential always propagated from the lower motor neuron to the muscle fibre?

A

Because a lot of ACH is released in the synaptic cleft.

And there are many ACH receptors on the motor end plate

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6
Q

One action potential from a neuron to an end plate will cause how many APs in the muscle?

A

Just one

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7
Q

When a muscle fiber is in a relaxed state what covers the myosin binding sites on actin ?

A

Tropomyosin

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8
Q

When the muscle fibre is in a state of rest is the myosin head activated ?
If so, how is it?

A

It is activated only it’s biding site is covered
The ATP on the myosin has become
ADP + Pi and NRG (stored in the myosin head) so now it is ready to bind as soon as the binding sites on actin are exposed

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9
Q

When a muscle fiber is excited
The sarcolemma is depolarized; the EPP produces an AP
When the AP propagates, where does it go and how ?

A

It propagates down the t tubules to deep within the fibre

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10
Q

The excitation of the muscle fibre sets the stage for the excitation - contraction coupling. This is going from an electrical to________ event

A

Mechanical

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11
Q

What is the next step after AP has been propagated down to the t-tubules ?

A

Calcium ions are released into cytosol (coupling agent) from terminal cisternae sarcoplasmic reticulum
This happens because the voltage sensitive tubule proteins change shape. (Voltage gates)

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12
Q

After the calcium has been released from the terminal cisternae during the EC coupling what happens

A

The calcium binds to troponin (go signal) which removes the blocking action of tropomyosin
Now the binding sites are exposed on the thin filaments

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13
Q

After the calcium has bound to troponin… Changing the shape of the tropomyosin … Exposing the binding sites on the thin filament what then will happen ?

A

Now contraction can occur
Activated myosin can attach to binding sites on actin
This is called cross bridge attachment

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14
Q

When actin and myosin form cross bridges, the energy in the myosin head is released, how does this happen

A

Myosin head pivots ( power stroke )
The ADP and organic phosphate are released
The power stroke causes actin to slide over myosin toward the center of the sarcomere

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15
Q

What action of myosin is responsible for causing the actin to slide over myosin toward the center of the sarcomere?

A

Power stroke

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16
Q

At which point is E-C coupling over ?

A

When contraction

Cross bridge cycling begins

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17
Q

The mechanical event of contraction is also called

A

Sliding filament mechanism

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18
Q

After the power stroke occurs and actin moves toward middle of sarcomere what happens to he myosin head ?

A

ATP attaches to the myosin head which releases the myosin head from actin and un-pivot occurs

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19
Q

When the myosin head is released from actin it’s called unpivot
What’s another name for this action ?

A

Recovery stroke

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20
Q

After a recovery stroke the myosin head becomes activated once again. Which means…

A

It converts the ATP to ADP and Pi and NRG

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21
Q

If after a contraction occurs via action potential in the muscle and myosin head has become activated once again (ADP Pi) if there is sufficient _______ in the ________ it can continue to bind to _________

A

Calcium
Sarcoplasm

Troponin
Then the cycle may continue to repeat many times to shorten a muscle

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22
Q

If there is sufficient enough calcium in the sarcoplasm after a contraction occurs what will happen

A

Calcium will bind to troponin
Tropomyosin will change shape and actin binding site will be exposed
Then activated myosin head will undergo powerstroke to pivot up to actin
Actin will then slide over myosin toward the middle of the sarcomere
Then an ATP will bind to myosin and release it from actin
Repeat until no more calcium to shorten muscle

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23
Q

In the sliding filament mechanism what shortens and what stays the same length

A

Myofibrils shorten / H zone and I band shortens / sarcomere shortens

Actin / myosin stay same length / A band stays same length

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24
Acetylcholine broken down by what on the motor end plate
Acetylcholinesterase
25
During relaxation ACh is broken down by ache and the sarcoplasmic reticulum takes up Ca2+ occurs via
Ca2+ - ATPase
26
During relaxation of muscle cell ____ binds to myosin heads causing
ATP binds to myosin heads causing them to activate and release from actin and tropomyosin covers actin once again
27
Thick filaments bind to what and what
Actin and ATP
28
Thin filaments bind to what and what
Myosin and calcium
29
What Are All the things ATP is used for in muscle contraction
Na+ K+ ATPase pump for maintaining gradient Activation of myosin and powerstroke Release of cross bridge Pump calcium into SR
30
What is rigor Mortis
Stiffness of body after death
31
Why do the muscles of the body remain in a contracted state shortly after death
Before death : myosin heads are activated and able to bind to actin After death: no O2 in and no ATP being produced. Calcium comes from ECF to ICF --> SR Since there is no ATP, myosin can not be released from actin and muscles remain in contracted state
32
When does rigor mortis begin and peak?
3 hours AD | 12 hrs AD
33
If extra cellular Ca2+ is low Pregnancy or lactation What happens
Na+ enters the cell and cramps happen
34
If intracellular ca2 is low
Contractions not initiated
35
What is myasthenia gravis What is it caused by Treatment ?
It is an autoimmune disease Caused by decrease in # of acetylcholine receptors Treatment: acetylchonesterase inhibitors. Increases binding of remaining acetylcholine receptors
36
What is curare poisoning ? | What can it be used for
Prevents acetylcholine from binding to receptors (no connection from lower motor neuron to skeletal muscle) Causes flaccid paralysis Used in surgeries
37
What is botulism How is it caused What does it do to acetylcholine How is it used clinically
Caused by improper canning resulting in an infection with bacterium clostridium botulinum Prevents exocytosis of acetylcholine Flaccid paralysis Used to treat crossed eyes and uncontrolled blinking Botox: cosmetic - wrinkles / sweating
38
What are the effects of nicotine in acetylcholine
Binds to receptors and mimics effect of acetylcholine | Causes muscle spasms
39
Black widow spider venom does what to acetylcholine | What is the result
Causes mass release of acetylcholine As a result muscles contract so much breathing stops Leads to initial stimulation of acetylcholine receptors Long term can cause receptor desensitization Firing of muscle can become depressed
40
What is tension
The amount of force exerted by a muscle | Determined by a total number of cross bridge attachments
41
There's different degrees of frequency of stimulation of muscle fibers: single stimulus, 2nd stimulus, rapid sequence and
High frequency
42
Single stimulus frequency in muscle fiber is not normally not seen in _________muscles Produces ____________
Skeletal muscles Produces twitch Weak contraction followed by relaxation
43
For the single stimulus the action potential lasts 1-2 seconds In muscle there's 3 phases : latent, contraction and relaxation Describe latent/ lag phase
~2 milliseconds Period between application of stimulus and muscle contraction Processes associated with exciting and coupling ***Movement of AP down T-tubule release of calcium which binds to troponin exposing myosin binding sites
44
Describe the contraction phase of the single stimulus frequency How long
~10-100 milliseconds Mechanical (time when head groups contract) Cross bridge attachment and sliding filaments Increased tension
45
Relaxation phase of the single stimulus frequency
Ca2+ pumped back kno sarcoplasmic reticulum by Ca2+ ATPase ATP attaches to myosin heads and recovery stroke Decrease in tension
46
Describe a 2nd stimulus frequency on a muscle --> tension
2nd stimulus arrives before muscle has completely relaxed Produces contraction with increased tension / no refractory period with contraction (due to Ca2+ availability) Much Ca2+ released on first stimulus but taken back into SR before all myosin heads are able to attach Second stimulus releases more Ca2+ so cytosolic concentration rises and more myosin heads able to attach
47
What is wave summation ?
The increase of tension aquired by more than 1 stimulus due to increasing calcium levels
48
Rapid sequence of stimuli on muscle ---> tension
Allows partial relaxation between contractions Tension increases (wave summation) (increased Ca2+ availability) Incomplete tension results
49
What is tetanus
Smooth sustained muscle contraction resulting from high frequency stimulation
50
High frequency of stimulation
No relaxation between contractions Sustained Highest tension results (3-4x that of a twitch) All troponin saturated with Ca2+ Fiber is warm because ATP synthesis releases heat Everything working faster , this occurs normally in the boy Complete tetanus
51
Describe fast fibers
Contract / reflex rapidly | Appear white because lack of myoglobin
52
Describe slow fibers
Contract and relax slowly Appear red because of more myoglobin - postural muscles
53
Muscle length has a lot to do with how much tension it can produce resting fiber length is is optimal, why
Max number of + bridges can be attached therefore stimulate maximum tension
54
Fiber length that is shorter than resting when stimulated ...
Thin filaments overlap and interfere with cross bridge attachment Fewer cross bridges attack and a decrease in tension results Minimum length for tension to occur is 70 % of resting
55
Sometimes when a fiber is stretched it becomes more difficult for it to accomplish tension why
Not all myosin heads are near active binding sites Fewer cross bridges attach Decreased tension The maximum length is 130% of optimal
56
The size of the fiber affects the tension How does it When it's Thicker / larger
Thickness. More Myofibrils | Larger. More tension
57
What are factors that affect tension in a whole muscle
-Number of fibres contracting (#of active motor units) -Number of fibres per motor unit (one neuron > 10 fibers - delicate contractions. One neuron : 1000- strong) Fatigue
58
A large muscle will have ____ number of fibers contracting and _____ # of fibers per motor unit
High
59
Muscle tone
Few fibers in low tension Different motor units stimulated over tjme but tone relatively constant Gives firmness to muscle
60
There are 2 types of muscle contractions isotonic and isometric Describe isotonic
Muscle changes length Tension relatively constant during contraction Tension exceeds resistance of load lifted Used for body movement and moving objects Flexion of elbow - tension greater than weight of forearm
61
Isometric contraction
Muscle length is constant Tension increases : cross bridges attached but no shortening Tension is less than required to move load Used for standing - holding a book in place
62
In the example of lifting a book to read | Where would isotonic and isometric contraction take place
Isotonic lifting | Isometric holding
63
Muscle metabolism during resting conditions (aerobic)
Fatty acids used to produce ATP Storage: of glycogen creatine phosphate and little ATP When ATP and creatine together P is cleaved off of ATP to produce ADP and creatine phosphate (c~p)
64
During short term exercise (less than a minute) --> primarily anabolic
A) creatine phosphate is used to make ATP C~P + ADP --> ATP + Creatine (via creatine kinase) C~P lasts 15 seconds b) muscle glycogen --> glucose --> pyruvic acid (Pyruvic acid then takes the anarobic pathway to create lactic acid) Lasts 30 seconds
65
During long term exercise
One minute to hours Glucose from liver is used Fatty acids used more as exercise continues ATP; from aerobic pathway Oxygen sources include hemoglobin in blood and myoglobin in muscle
66
Muscle fatigue What is it What does it do How does it protect
Not fully understood Inability to maintain tension Decreases ATP use Protective exhausting ATP would be detrimental for vital function ATO only decreases 70% of Resting if too little cross bridges can't release and contraction continues
67
What is fatigue potentially caused by
-depletion of NRG supply ( glycogen) lack of ATP normally not a problem - built up end products Failure of action potentials
68
What are the built of end products potentially causing fatigue
- -H+ from lactic acid (muscle contraction compresses blood vessels --> decrease O2 to muscle. Muscle needs to be anarobic for periods of time (potentially during long term exercise) - -phosphate (from conversion of ATP - ADP and Pi-- will bind to Ca2+ therefore less Ca2+ available to troponin - this slows the release of Pi from myosin which slows release of myosin from actin
69
Explain how failure of action potential could lead to fatigue
Concentration of K increases jn the small space of the t-tubules during rapid stimuli Disturbs membrane potential and stops ca2+ release from sarcoplasmic reticulum Long term; neurons run out of ACh --> usually not seen in a healthy person
70
Post exercise the body is in oxygen debt The increase of body temperature increases need for O2 Deep rapid breathing is happening until body returns to resting state What else is 02 used for post exercise
Replenish glycogen stores C~P O2 on hemoglobin and myoglobin To convert lactic acid to pyruvic acid permitting into Krebs cycle and to glucose in liver

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