Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A&P 2024 > Lecture 12: Skeletal Muscle > Flashcards

Lecture 12: Skeletal Muscle Flashcards

Exam 2

1
Q

Skeletal muscle is the largest _____?

A
  • The largest contributor to body weight and volume in non-obese people
  • Largest container we have within the body
  • Need them to behave normally otherwise things get screwed up, very important
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How can anesthetics affect skeletal muscle?

A

We take a lot of skeletal muscles offline with anesthetics
- Volatile anesthetics - reduce amount of muscle activity
- Paralytics - take the skeletal muscles offline

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the 8 roles of skeletal muscle

A
  • Largest contributor to body weight and volume in non-obese people
  • Locomotion
  • Expression
  • Communication
  • Body temp
  • Storage of glycogen
  • “Effectors”/neural targets
  • Large store of ions, fluid, and proteins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

The vast majority of skeletal muscle cells are innervated by how many motor neurons?

A

Just one
One motor neuron can innervate multiple skeletal muscle cells, very large and branch multiple times

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

A collection of muscle fibers

A

Motor unit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is an example of a skeletal muscle cell that is innervated with more than one motor neuron?

A

ocular muscles in the eye socket

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Where are the cell bodies of motor neurons located?

A

The anterior horn of the grey matter of the spinal cord

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

A single neuron that innervates a motor unit

A

Motor Neuron
- Small mu’s=small mn’s
- Large mu’s=large mn’s

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the 2 ways to excite motor neurons?

A
  1. Descending spinal pathways originating from the brain
  2. Reflex arcs - sensory info fed into the back of the cord that results in a muscle contraction at the same level of the spinal cord (without traveling back to the brain) so that muscle contraction can occur quickly to withdraw from pain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is another name for a skeletal muscle cell?

A

Muscle fiber

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the contractile elements of skeletal muscle cells? How are they arranged?

A

Actin and myosin filaments - arranged in tube-like structures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the specialized version of the ER called in skeletal muscle cells?

A

Sarcoplasmic reticulum - sarco = muscle, more developed ER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Where do skeletal muscle cells store Ca++?

A

The sarcoplasmic reticulum - needs Ca++ for contraction (release internally)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are transverse tubules? Why are they needed?

A

An extension of the skeletal muscle cells that allows an AP to move deep into the muscle cells (enfolding); invaginations of the cell membrane
Needed because skeletal muscle cells can be very long (can be over a foot long) and are fairly wide/thick

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the 4 components of skeletal muscle cells

A
  • Sarcoplasm
  • Sarcoplasmic reticulum
  • Transverse Tubules - AKA T Tubules
  • Actin/myosin filaments
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What do we need to know for exam 2 about sarcomere anatomy?

A

Just need to know that contraction shortens the muscle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Fluid inside muscle cells (like cytoplasm)

A

Sarcoplasm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the structures noted in the picture

A

Microscopic view of skeletal muscle cells
- Each branch of motor neurons takes care of innervation for skeletal muscle fibers
- Each fiber has NMJ associated with it (balls in pic)
- Some only have one motor neuron for several skeletal muscle cells
- Have zebra-like (cross-hatch) pattern because of actin and myosin filaments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the invaginations that increase N-M junction surface area?

A

Clefts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the 2 types of clefts on the skeletal muscle cell?

A
  • Primary: only one enfolding
  • Secondary: more than one enfolding
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is located in the membrane of skeletal muscle clefts?

A

ACh receptors towards the surface of the cleft, closer to the neuron
Concentrated V-G Na+ channels on the inside of clefts and the other side of ACh-R

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What surrounds motor neurons?

A

Wrapped in myelin, maintained by Schwann cells that hang out at the terminal end of motor neurons; Schwann cells manage the myelin in the motor neuron back to the spinal cord

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the role of mitochondria in the NMJ?

A

The skeletal muscle cells and motor neurons both have a lot of mitochondria located near the NMJ

mitochondria in the presynaptic terminal produce acetate. Acetate combines with recycled choline into acetylcholine (ACh)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How many ACh-R are there? How many are activated during an AP? How much ACh is needed?

A

ACh receptors - have 5 million at each NMJ
- About 500,00 activated during a typical AP ~10%
- Need to be producing at least 1,000,000 ACh from motor neuron - usually twice that in reality

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Why is more ACh released than what is needed by the motor neuron?

A
  • Some get broken down by AChesterase before reaching receptors
  • Some bind to receptors and only have 1 ACh molecule bound and therefore can’t activate the receptor (need 2 ACh)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the function of AChesterase?

A

Breaks down ACh via hydrolysis (ACh → acetyl + choline)
Once broken down to acetyl and choline, no more effect on the ACh receptors
Limits length of depolarization from motor neuron - finite time period so resetting can happen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What does the motor neuron do with acetyl and choline after AChesterase breaks apart ACh?

A

Choline is moved back into motor neuron via choline-sodium transporter and Choline ATPase pumps
Acetyl recycled too but not as much known about mechanism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Where is AChesterase produced and housed?

A

Produced by the skeletal muscle and fastened to skeletal muscle at the NMJ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What are other ways to describe acetyl?

A

Acetate, a very small starch group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

How are acetate and choline made in the motor neuron?

A
  • Mitochondria produces acetate and ATP
  • Can store extra choline in cell wall (phosphatidylcholine)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is underneath the NMJ and clefts in the skeletal muscle?

A

Contractile elements - myosin and actin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Why doesn’t K+ want to exit the skeletal muscle cell through open ACh-R, even though it can?

A

K+ probably would want to leave via leak channels instead (easier)

33
Q

How many subunits are there on nACh-R?

A
  • 2 Alpha subunits - Both alpha subunits must bind ACh to open the ion channel
  • 1 Beta subunit
  • 1 Delta subunit
  • 1 Epsilon subunit
34
Q

What is the name of the first nACh-R antagonist? Where was it found?

A

Curare - paralytic found in rainforest, used to paralyze prey; not used clinically now
- Most non-depolarizing muscle relaxant (NDMR) paralytics are modeled after Curare MOA
- Only need one to bind to each receptor to block the channel, antagonist; stop AP from starting in the skeletal muscle

35
Q

How does ACh leave the motor neuron? What is this mediated by?

A

Exocytosis, mediated by Ca++
(SNAP and SNARE proteins)

36
Q

What are the components of skeletal muscle calcium signaling?

A
  • SR Calcium Release
  • Depolarization
  • Repolarization
  • Ryanodine (RyR) Receptors
  • SERCA pumps
37
Q

What are the different types of channels seen in a skeletal muscle cell?

A

Same as normal cell -
V-G Na+ channels
V-G K+ channels
K+ leak channels
Na+ leak channels (less than K+)

38
Q

What are the channels that cause an AP in a skeletal muscle cell?

A

Same as normal cell -
V-G Na+ channels
V-G K+ channels

39
Q

How do skeletal muscles know when to respond to an AP?

A

DHP (dihydropyridine) receptors that sense the voltage changes in the cell wall
- Not really a receptor but a sensor

40
Q

How do DHP receptors respond to a change in voltage?

A

Voltage sensor senses AP → has physical connection to Ca++ release channel on SR - tugs on attachment (looks like a spring), removing obstruction from Ca++ being released (pops the cork), liberating Ca++ to inside skeletal muscle → contraction with actin and myosin
- some Ca++ comes from outside cell too

41
Q

Where are SRs located?

A

Fairly close to the cell wall, close to T-tubules
- SR is the yellow portion surrounding the T-tubules

42
Q

Where are DHP receptors located?

A

In cell wall and in T-tubules

43
Q

Some Ca++ channel blockers are _______

A

dihydropyridine Ca++ channel blockers

44
Q

DHP receptors look a lot like what?

A

V-G Ca++ channel; lets Ca++ in from SR instead of outside of the cell
However a small amount of Ca++ comes from outside cell too

45
Q

What is the name of the Ca++ release channel on the SR?

A

Ryanodine (RyR) Receptors

46
Q

What chemicals are RyRs sensitive to?

A

ryanodine

47
Q

Are RyRs receptors?

A

Not really a receptor in function in the body because it is physically attached to DHP receptor
Called receptors because they open in response to ryanodine binding

48
Q

How does the Ca++ get put back into the SR after an AP?

A

SERCA pumps - sarcoendoplasmic reticulum calcium ATPase (SERCA) pump
- need ATP because Ca++ going against the concentration gradient

49
Q

What are the steps to skeletal muscle E-C coupling?

A
  1. Motor neuron depolarizes (from brain or reflex arcs)
  2. Ca++ influx into motor neuron (P-type Ca++)
  3. ACh vesicles fuse to presynaptic neural cell wall/membrane
  4. ACh secreted by presynaptic neuron (into NMJ)
  5. ACh interacts with nACh receptors
  6. Na+ comes in (#1); Ca++ comes in (#2)
  7. Local Na+ and Ca++ influx generates end plate potential (EPP)
  8. EPP in a physiologic “setting” always causes an action potential in skeletal muscle; Local depolarization→AP
  9. Action potential spreads down muscle fibers in both directions (←AP→) via V-G Na+ channels
  10. Muscle depolarization sensed by dihydropyridine “receptors”/sensors (DHP)
  11. Dihydropyridine sensors pull on ryanodine receptors (RyRs)
  12. Ca++ influx into sarcoplasm
  13. After AP, Ca++ tucked back into SR via SERCA, then muscle stops contracting
50
Q

When does a skeletal muscle stop contracting?

A

Once Ca++ tucked away back into SR

51
Q

What is the local depolarization that generates an AP called? Where does it occur?

A

End plate potential (EPP) - NMJ
- Occurs when nACh-R opens and allows local Na+ and Ca++ influx

52
Q

What is myasthenia gravis?

A
  • Condition where the patient’s body generates antibodies to nACh-R
  • Immune system response to inflammation or genetic anomaly with thymus gland
  • Gets worse throughout the day (better in the morning, worse in the evening)
53
Q

How does myasthenia gravis affect skeletal muscle?

A

Antibodies park themselves on top of nACh-R
- The immune system comes in and destroys receptors
- Over time, clefts become scarred over
- Fewer nACh-R and V-G Na+ channels
- Can’t fire an AP

54
Q

What are the treatments for myasthenia gravis?

A
  1. Remove thymus gland
  2. Plasmapheresis
  3. Acetylcholinesterase inhibitors (-stigmine)
55
Q

How does plasmapheresis work to treat MG and LEMS? What’s the downside?

A

Plasmapheresis removes circulating antibodies
- can’t just remove one type of antibody from blood → can be bad

56
Q

How do acetylcholinesterase inhibitors treat myasthenia gravis?

A

Inhibitor AChesterase, keeping ACh around longer, increasing the likelihood of ACh binding to receptors

57
Q

Why can’t acetylcholinesterase inhibitors be used to treat LEMS?

A

There’s no ACh in the synapse because P-type Ca++ channels are attacked, so ACh is never released from motor neuron

58
Q

What is LEMS or ELMS?

A

Lambert-Eaton Myasthenic Syndrome
- Parody of plastic (paraneoplastic) syndrome - develops after cancer (especially lung cancer)
- Antibodies to P-type Ca++ channels, preventing ACh release from vesicles

59
Q

What are the treatment options for LEMS?

A
  1. Plasmapheresis
  2. Remove lung tumor
  3. Drugs to block K+ channels
60
Q

Drugs used to treat LEMS are fairly _____

A

dangerous - V-G K+ channel blockers unsafe because not specific for muscle cells only → cardiotoxic

61
Q

________ isn’t a good K+ channel blocker

A

Amiodarone - fairly safe because not very good

62
Q

How do drugs used to block K+ channels treat LEMS?

A

K+ prevented from leaving cell → more positive membrane potential → longer depolarization of motor neuron → allows more time for Ca++ to come in through P-type Ca++ channels → increasing ACh release

63
Q

How do P-type Ca++ channels work?

A

Don’t have an inactivation gate
- Open when cell depolarized, closed when cell is repolarized

64
Q

What are the drugs that are used to treat LEMS?

A

TEA - tetra-ethyl ammonium
4,5-diaminopyrimidine

65
Q

When is LEMS treated with K+ channel blockers?

A

End stage, nothing can be done about the tumor

66
Q

Succinylcholine includes

A

2 ACh

67
Q

The two types of paralytics are

A

depolarizing and non-depolarizing

68
Q

Succinylcholine is a _______ paralytic

A

depolarizing

69
Q

How long does succinylcholine last?

A

10 min, longer than ACh

70
Q

The initial muscle twitch when giving succinylcholine is called _______

A

fasciculation
Initially, opening of nACh-R causes a depolarization wave → generating a contraction or fasciculation (initial muscle twitching/quiver), because the drug hits different parts of the muscle at different times

71
Q

Succinylcholine acts to paralyze the muscle by

A

Sustained depolarization of the skeletal muscle via binding to nACh-R and keeping them open for prolonged period of time, causing constant Na+ leaking into skeletal muscle, preventing V-G Na+ from resetting

72
Q

How does sux cause Na+ to constantly leak into the skeletal muscle?

A

All the V-G Na+ channels in the area are stuck in the inactive configuration because the activation gate won’t close, until repolarization happens

73
Q

nACh-R are only found in the ____

A

NMJ, nowhere else in skeletal muscle
Ends of the skeletal muscle farther away, so only small area of skeletal muscle is paralyzed

74
Q

Can AChesterase break down sux?

A

AChesterase is specific for breaking ester bonds in ACh, can’t destroy succinylcholine (2 ACh) in the same way

75
Q

What is different about a stroke patient’s skeletal muscle? What would be the consequences of giving sux?

A

Sustained (+) inside cell causes more K+ to leak out of cell (trying to repolarize) → leaking K+ in the blood increases by K+ levels by 0.5 mOsm/L, okay in healthy individuals

Unhealthy skeletal muscles (denervation injuries or stroke) - generate more nACh-R in places other than just the NMJ → more K+ leaking, widespread → hyperkalemia → heart problems

76
Q

Differentiate between P-type and L-type Ca++ channels

A

P-type - primarily found in the motor neurons, don’t have inactivation gate (open when depolarized, closed when repolarized)
L-type - found in the heart and smooth muscle cells, takes longer to open and close (do have them on motor neurons but not needed for ACh release)

77
Q

T/F: V-G K+ channels are required for repolarization

A

F - repolarization mostly via K+ leak channels, but V-G K+ make the process faster

78
Q

LEMS symptoms get _____ with activity

A

better

A&P 2024 (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions