musculoskeletal system Qs!

[capn jazz]

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Which of the following structures is distal to the wrist?
A) the elbow
B) the fingers
C) the shoulder
D) the forearm


EK says it's B) the fingers. "Scientists use terms such as proximal and distal to describe 3D anatomy. Distal structures are farther away from a preset point of origin, while proximal structures are closer to a preset point of origin. For example, the elbow is distal to the shoulder, the wrist is distal to the elbow, and the fingers are distal to the wrist."

Okay, why isn't the SHOULDER the most distal from the wrist? Why the fingers? Anyone?

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From a passage: relevant info is "In nerves and skeletal muscle, only two currents, sodium and potassium generate an action potential. However, in cardiac myocytes, the electrical activity is made complicated by the involvement of channels selective for Na+, Cl-, Ca2+, and K+."

Q: Which of the following ions is involved in initiating the cardiac action potential but not the skeletal muscle action potential?
A) high concentration of extracellular Na
B) high concentration of intracellular K+
C) high concentration of extracellular Cl-
D) high concentration of extracellular Ca2+

Answer: D.
"According to the passage, skeletal muscles rely on sodium and potassium to generate an action potential. Answer choices A and B can be eliminated because the question stem asks to exclude ions involved in the excitation of skeletal muscle. FYI: Cardiac depolarization utilizes calcium ions to enter the cell and cause membrane depolarization.

Why isn't it C? I thought that ALL muscle action potentials require calcium for initiation.

In fact, in a later question, they contradict themselves:
At the neuromuscular junction, neurotransmitters cross the synaptic cleft and depolarize the cell which opens:
a) sodium gated channels
b) potassium gated channels
c) calcium gated channels
d) chloride gated channels.

The answer is C. "Muscle contraction requires a great deal of calcium which is obtained 1) from the extracellular environment via calcium-gated channels and 2) from the sarcoplasmic reticulum (muscle cell smooth ER). Sodium-gated channels open during the depolarization of nerves, while most muscle cells, including skeletal, cardiac, and smooth, rely on calcium-gated channels.

So... calcium is involved in ALL types of muscle cells. Why isn't chloride the answer for the question prior to this one??

 

[FutureInternist]

Which of the following structures is distal to the wrist?
A) the elbow
B) the fingers
C) the shoulder
D) the forearm


EK says it's B) the fingers. "Scientists use terms such as proximal and distal to describe 3D anatomy. Distal structures are farther away from a preset point of origin, while proximal structures are closer to a preset point of origin. For example, the elbow is distal to the shoulder, the wrist is distal to the elbow, and the fingers are distal to the wrist."

Okay, why isn't the SHOULDER the most distal from the wrist? Why the fingers? Anyone?

I think their explanation is a little off. Sure distal means furthest away HOWEVER all the structures use the same point of origin i.e. top of the head. Everything in the body is measured from there. So whatever you encounter first is more proximal whereas what you encounter later is more distal. Hence shoulder is proximal to elbow, wrist etc & fingers (being the most distal part of the upper extremity) are distal to the wrist.

 

[ksmi117]

Which of the following structures is distal to the wrist?
A) the elbow
B) the fingers
C) the shoulder
D) the forearm


EK says it's B) the fingers. "Scientists use terms such as proximal and distal to describe 3D anatomy. Distal structures are farther away from a preset point of origin, while proximal structures are closer to a preset point of origin. For example, the elbow is distal to the shoulder, the wrist is distal to the elbow, and the fingers are distal to the wrist."

Okay, why isn't the SHOULDER the most distal from the wrist? Why the fingers? Anyone?

Distal refers to the farthest out from the center of the body. The wrist would be distal to the shoulder but not the other way around. Since the shoulder is the point of origin for the entire arm, it would be the most proximal of anything on the arm. The tips of your fingers would be the most distal. The others, I'm not sure

 

[ksmi117]

From a passage: relevant info is "In nerves and skeletal muscle, only two currents, sodium and potassium generate an action potential. However, in cardiac myocytes, the electrical activity is made complicated by the involvement of channels selective for Na+, Cl-, Ca2+, and K+."

Q: Which of the following ions is involved in initiating the cardiac action potential but not the skeletal muscle action potential?
A) high concentration of extracellular Na
B) high concentration of intracellular K+
C) high concentration of extracellular Cl-
D) high concentration of extracellular Ca2+

Answer: D.
"According to the passage, skeletal muscles rely on sodium and potassium to generate an action potential. Answer choices A and B can be eliminated because the question stem asks to exclude ions involved in the excitation of skeletal muscle. FYI: Cardiac depolarization utilizes calcium ions to enter the cell and cause membrane depolarization.

Why isn't it C? I thought that ALL muscle action potentials require calcium for initiation.

The reason it can't be D is that an influx of Cl- would inhibit an action potential since it is a negative charge flowing in. For an action potential, you need positive ions to flow into the cell.

 

[ksmi117]

In fact, in a later question, they contradict themselves:
At the neuromuscular junction, neurotransmitters cross the synaptic cleft and depolarize the cell which opens:
a) sodium gated channels
b) potassium gated channels
c) calcium gated channels
d) chloride gated channels.

The answer is C. "Muscle contraction requires a great deal of calcium which is obtained 1) from the extracellular environment via calcium-gated channels and 2) from the sarcoplasmic reticulum (muscle cell smooth ER). Sodium-gated channels open during the depolarization of nerves, while most muscle cells, including skeletal, cardiac, and smooth, rely on calcium-gated channels.

So... calcium is involved in ALL types of muscle cells. Why isn't chloride the answer for the question prior to this one??

Yes, calcium is involved in all of them, but I don't think calcium plays a role in the action potential of skeletal muscle. It just binds to the thin filaments and such. The key here is that the question asks "depolarized cell opens what channels?" So this channels aren't involved in the depolarization itself. This calcium flows in because of the action potential and binds to the filaments creating the contraction. In cardiac, however, calcium does play a role during the depolarization.

I think... anyone wanna correct this if I'm wrong?

 

[nlax30]

Which of the following structures is distal to the wrist?
A) the elbow
B) the fingers
C) the shoulder
D) the forearm

EK says it's B) the fingers. "Scientists use terms such as proximal and distal to describe 3D anatomy. Distal structures are farther away from a preset point of origin, while proximal structures are closer to a preset point of origin. For example, the elbow is distal to the shoulder, the wrist is distal to the elbow, and the fingers are distal to the wrist."

Okay, why isn't the SHOULDER the most distal from the wrist? Why the fingers? Anyone?

When they talk about distal being further from a "preset point of origin" that's referring to being further away from the center of they body. When describing position you refer to things assuming the body in the "anatomical position". So distal doesn't refer to just distance away from something, but distance away from the center of the body. So even though there's more distance between the shoulders and wrist, than the wrist and fingers, the fingers are further away from the center of the body than the wrist while the shoulders are closer.

From a passage: relevant info is "In nerves and skeletal muscle, only two currents, sodium and potassium generate an action potential. However, in cardiac myocytes, the electrical activity is made complicated by the involvement of channels selective for Na+, Cl-, Ca2+, and K+."

Q: Which of the following ions is involved in initiating the cardiac action potential but not the skeletal muscle action potential?
A) high concentration of extracellular Na
B) high concentration of intracellular K+
C) high concentration of extracellular Cl-
D) high concentration of extracellular Ca2+

Answer: D.
"According to the passage, skeletal muscles rely on sodium and potassium to generate an action potential. Answer choices A and B can be eliminated because the question stem asks to exclude ions involved in the excitation of skeletal muscle. FYI: Cardiac depolarization utilizes calcium ions to enter the cell and cause membrane depolarization.

Why isn't it C? I thought that ALL muscle action potentials require calcium for initiation.

You may be confusing the electrical action potential with the muscle contraction. Ca2+ is involved in the actual muscle contraction but only in cardiac muscle is Ca2+ (along with Na+) part of the action potential, it's actually one of the reasons for the plateau/prolongation seen in cardiac action potentials. If you have a physio textbook it should have action potential diagrams for things like nerve fibers, skeletal muscle, and cardiac muscle with a diagram of which ion channels are involved at each portion of the action potential.

In fact, in a later question, they contradict themselves:
At the neuromuscular junction, neurotransmitters cross the synaptic cleft and depolarize the cell which opens:
a) sodium gated channels
b) potassium gated channels
c) calcium gated channels
d) chloride gated channels.

The answer is C. "Muscle contraction requires a great deal of calcium which is obtained 1) from the extracellular environment via calcium-gated channels and 2) from the sarcoplasmic reticulum (muscle cell smooth ER). Sodium-gated channels open during the depolarization of nerves, while most muscle cells, including skeletal, cardiac, and smooth, rely on calcium-gated channels.

So... calcium is involved in ALL types of muscle cells. Why isn't chloride the answer for the question prior to this one??

It's a little tricky but this question is referring to a different part of the action potential --> muscle contraction "pathway". You're right in that Calcium is involved in actual muscle contraction (troponin, actin, myosin, etc...) process, but these Ca channels open in response to an action potential that was initially caused by Na influx, which itself was caused by the neurotransmitters released into that synaptic cleft. So an action potential travels down a nerve fiber, which releases acetycholine into the snyaptic cleft at a neuromuscular junction, this then causes Na channels to open on the muscle fiber which causes an action potential to form there, this THEN causes Ca channels to open (review t tubules and sarcoplasmic reticulum) releasing Calcium and causing contraction. This last question was asking about that last part which is similar (some differences) among the different muscle types.

The 2nd question was basically asking about the step BEFORE calcium release, about what ions are involved in creating that action potential that then causes calcium release.

 

[lirpa]

ok i know this is a little random, but i just came across this thread and am taking a prereq anatomy class before i start school in may to refresh and came across some questions that are driving me crazy because they seem so simple?
I think i am just over analyzing the question and need to keep it simple

IF YOU LIFT YOUR ARM UP AWAY FROM THE SIDE OF YOUR BODY, YOUR SHOULDER IS??
A-ADDUCTED
B-ABDUCTED
C-FLEXED
D-SUPINATED

i have always felt very confident with these concepts but for some reason this question gets me, because i visualize when raising the arm yes your arm is abducting as you lift it away from the body..but wouldnt just your shoulder be adducting as it is getting closer to your head??

I feel like this is such a simple concept?

 

[nlax30]

ok i know this is a little random, but i just came across this thread and am taking a prereq anatomy class before i start school in may to refresh and came across some questions that are driving me crazy because they seem so simple?
I think i am just over analyzing the question and need to keep it simple

IF YOU LIFT YOUR ARM UP AWAY FROM THE SIDE OF YOUR BODY, YOUR SHOULDER IS??
A-ADDUCTED
B-ABDUCTED
C-FLEXED
D-SUPINATED

i have always felt very confident with these concepts but for some reason this question gets me, because i visualize when raising the arm yes your arm is abducting as you lift it away from the body..but wouldnt just your shoulder be adducting as it is getting closer to your head??

I feel like this is such a simple concept?

You're right with the abduction, beyond that don't think too much into it.
Just remember the definiton:

Abduction, in functional anatomy, is a movement which draws a limb away from the median (Sagittal) plane of the body

 

[lirpa]

You're right with the abduction, beyond that don't think too much into it.
Just remember the definiton:

so basically they are just tryimg to trick you with throwing in the shoulder part because it is the motion of the entire limb that matters?🙄

 

[capn jazz]

You may be confusing the electrical action potential with the muscle contraction. Ca2+ is involved in the actual muscle contraction but only in cardiac muscle is Ca2+ (along with Na+) part of the action potential, it's actually one of the reasons for the plateau/prolongation seen in cardiac action potentials. If you have a physio textbook it should have action potential diagrams for things like nerve fibers, skeletal muscle, and cardiac muscle with a diagram of which ion channels are involved at each portion of the action potential.

Thank you! This is exactly the part I was confusing. I forgot that Ca2+ is the plateau part of the action potential.


And thanks to everyone else also - I figured out the "distal" problem by re-looking up the definition. EK's explanation was just lacking.