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    Why will a man with cystic fibrosis may be infertile?
    What is the role of the myelin sheath surrounding the axon?
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    Interesting question! I'm really surprised that either of these questions are under 'GCSE' though... I mean myelination is something that I only learnt in class 2 weeks ago! (And I'm doing my A2's)

    Ok, I'm not sure how much to simplify my answer, but I'll try my best:

    'Why will a man with cystic fibrosis may be infertile?'

    Most (I can't remember specifics but it's really close to 100%) men with cystic fibrosis will be infertile because of the absence of the vas deferens (it's a sort of duct (actually two ducts) that passes sperm (spermatozoa) from the testes to the urethra. This essentially means that people with cystic fibrosis (well the almost 100%) won't have sperm in their semen, hence will be infertile.

    Just for your information, the absence of the vas deferens is known more formally as:
    Congenital (from birth) bilateral (both ducts) absence of the the vas deferens

    Onto the second question:
    'What is the role of the myelin sheath surrounding the axon?'

    The straightforward answer is 'To increase nervous conduction'. I hesitate to go much further than that, but in simple terms:
    1. Myelin is a fatty, white substance
    2. Fats are good insulators
    3. Having layers of myelin (fatty substance) surround the axon adds an insulating layer around it
    4. Fats do not conduct electricity well (poor electrical conductor/good electrical insulator)
    5. So action potential can travel much faster.

    The bit more complicated view:
    1. Myelin doesn't surround the whole axon, it sort of surrounds it in chunks, with gaps in between each myelin 'sheath'
    something like an axon: =-=-=-= where the = represents the myelin and the - is where there is no myelin.
    Following my terrible diagram, the - are known as 'Node's of Ranvier' - essentially sites where there is no myelin.

    The reason myelination speeds up nervous conduction, besides insulating the electrical charge, is that the action potential can in effect 'jump' across the Node's of Ranvier since in between the Node's of Ranvier the 'positive charge' can diffusion across to the next Node rather than take time depolarising each part of the membrane.

    Sorry if my explanations aren't clear, but I hope its helped at least a tiny bit!
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    (Original post by Spectral)
    Interesting question! I'm really surprised that either of these questions are under 'GCSE' though... I mean myelination is something that I only learnt in class 2 weeks ago! (And I'm doing my A2's)

    Ok, I'm not sure how much to simplify my answer, but I'll try my best:

    'Why will a man with cystic fibrosis may be infertile?'

    Most (I can't remember specifics but it's really close to 100%) men with cystic fibrosis will be infertile because of the absence of the vas deferens (it's a sort of duct (actually two ducts) that passes sperm (spermatozoa) from the testes to the urethra. This essentially means that people with cystic fibrosis (well the almost 100%) won't have sperm in their semen, hence will be infertile.

    Just for your information, the absence of the vas deferens is known more formally as:
    Congenital (from birth) bilateral (both ducts) absence of the the vas deferens

    Onto the second question:
    'What is the role of the myelin sheath surrounding the axon?'

    The straightforward answer is 'To increase nervous conduction'. I hesitate to go much further than that, but in simple terms:
    1. Myelin is a fatty, white substance
    2. Fats are good insulators
    3. Having layers of myelin (fatty substance) surround the axon adds an insulating layer around it
    4. Fats do not conduct electricity well (poor electrical conductor/good electrical insulator)
    5. So action potential can travel much faster.

    The bit more complicated view:
    1. Myelin doesn't surround the whole axon, it sort of surrounds it in chunks, with gaps in between each myelin 'sheath'
    something like an axon: =-=-=-= where the = represents the myelin and the - is where there is no myelin.
    Following my terrible diagram, the - are known as 'Node's of Ranvier' - essentially sites where there is no myelin.

    The reason myelination speeds up nervous conduction, besides insulating the electrical charge, is that the action potential can in effect 'jump' across the Node's of Ranvier since in between the Node's of Ranvier the 'positive charge' can diffusion across to the next Node rather than take time depolarising each part of the membrane.

    Sorry if my explanations aren't clear, but I hope its helped at least a tiny bit!

    you sir, are a God
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    (Original post by uzma.29)
    Why will a man with cystic fibrosis may be infertile?
    What is the role of the myelin sheath surrounding the axon?
    (Original post by Spectral)
    Interesting question! I'm really surprised that either of these questions are under 'GCSE' though... I mean myelination is something that I only learnt in class 2 weeks ago! (And I'm doing my A2's)

    Ok, I'm not sure how much to simplify my answer, but I'll try my best:

    'Why will a man with cystic fibrosis may be infertile?'

    Most (I can't remember specifics but it's really close to 100%) men with cystic fibrosis will be infertile because of the absence of the vas deferens (it's a sort of duct (actually two ducts) that passes sperm (spermatozoa) from the testes to the urethra. This essentially means that people with cystic fibrosis (well the almost 100%) won't have sperm in their semen, hence will be infertile.

    Just for your information, the absence of the vas deferens is known more formally as:
    Congenital (from birth) bilateral (both ducts) absence of the the vas deferens

    Onto the second question:
    'What is the role of the myelin sheath surrounding the axon?'

    The straightforward answer is 'To increase nervous conduction'. I hesitate to go much further than that, but in simple terms:
    1. Myelin is a fatty, white substance
    2. Fats are good insulators
    3. Having layers of myelin (fatty substance) surround the axon adds an insulating layer around it
    4. Fats do not conduct electricity well (poor electrical conductor/good electrical insulator)
    5. So action potential can travel much faster.

    The bit more complicated view:
    1. Myelin doesn't surround the whole axon, it sort of surrounds it in chunks, with gaps in between each myelin 'sheath'
    something like an axon: =-=-=-= where the = represents the myelin and the - is where there is no myelin.
    Following my terrible diagram, the - are known as 'Node's of Ranvier' - essentially sites where there is no myelin.

    The reason myelination speeds up nervous conduction, besides insulating the electrical charge, is that the action potential can in effect 'jump' across the Node's of Ranvier since in between the Node's of Ranvier the 'positive charge' can diffusion across to the next Node rather than take time depolarising each part of the membrane.

    Sorry if my explanations aren't clear, but I hope its helped at least a tiny bit!
    Good response.

    However, just to add to the cystic fibrosis question, cystic fibrosis is a condition where the cystic fibrosis transmembrane conductance regulator (CFTR) does not work properly. The CFTR is a channel protein which is present in ciliated epithelial cells which allows ions such as Cl- ions to pass from the epithelial cells through the membrane into the lumen. This is due to a genetic mutation, most commonly a deletion of three nucleotides which results in the loss of phenylalanine. Since ions such as Cl- and SCN- cannot cross the membrane, there is a lower water potential inside the epithelial cells than in the lumen and so water will not enter the lumen by osmosis and so the mucus becomes very thick and sticky.

    The reason a man who has cystic fibrosis is infertile is due to these thick secretions which block the vas deferens which eventually leads to the destruction of the vas deferens. Sperm is still produced and may be retrieved from the epididymis directly, it's just that the sperm cannot transported to the accessory glands and so is not present in sperm as the vas deferens is blocked or missing (as correctly stated, this is known as congenital bilateral absence of the of the vas deferens).

    Hopefully this helps you out a bit on the first question.
 
 
 
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