nerves

[sv3]

I'm using TPR and Ek and neither talk about nerves much (the 12 cranial and 31 spinal). Anyone know how these are actually connected to the brain, spine, and where they go? (they do leave the CNS right?)

Perhaps it just isn't that important, I'm not sure. On that note, are any of you memorizing what the different parts of the brain and cortex do? I'm just not sure how far to go with memory work on bio..........

thanks in advance
steve

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[loveoforganic]

first question - dont have the slightest

second question - I'm not memorizing every part, but when I happen to read that this part of the brain does that, I reread it a few times and try to commit it to memory. figure it could come up as a discrete

 

[sv3]

first question - dont have the slightest

second question - I'm not memorizing every part, but when I happen to read that this part of the brain does that, I reread it a few times and try to commit it to memory. figure it could come up as a discrete

thanks. after going through TPR's section i was like "holy shi!" but then I looked at the AAMC topics list and its quite small for something like the nervous system. Or who really knows what "organization of nervous system" really means......they sure do leave a ton of room for interpretation. But I think your right about just trying. Also, if something pops up a few times then i also make sure to note that.

As for nerves thats on the back burner for now. I'm still bothered by not knowing what causes an initial depolarization. The books sure do tell you how one cell transmits it to another, but how does the initial cell get triggered eh? I got so many questions after reading about the nervous system but I'm not even going to bother.......something tells me I would actually need to be a researcher for half the answers.

 

[loveoforganic]

I'm pretty sure the inital depolarization has to be triggered by sensory receptors. e.g. a mechanoreceptor (for touch) would depolarize with pressure.

 

[Bernoull]

thanks. after going through TPR's section i was like "holy shi!" but then I looked at the AAMC topics list and its quite small for something like the nervous system. Or who really knows what "organization of nervous system" really means......they sure do leave a ton of room for interpretation. But I think your right about just trying. Also, if something pops up a few times then i also make sure to note that.

As for nerves thats on the back burner for now. I'm still bothered by not knowing what causes an initial depolarization. The books sure do tell you how one cell transmits it to another, but how does the initial cell get triggered eh? I got so many questions after reading about the nervous system but I'm not even going to bother.......something tells me I would actually need to be a researcher for half the answers.

The 12 pairs of cranial nerves originate from the lower brain and connect to parts of the head, neck and truck. 1 pair originates from the cerebellum and the rest from the brain stem. These nerves have varied functions from enabling chewing and facial expressions to facilitating the sensations of light, smell and sound.

The 31 pairs of spinal nerves originate from the spinal cord and innervate parts of the limbs, neck and trunk.

Initial depolarization is most intuitive when u consider sensory neurons. These neurons either have specialized receptor ends at their dendrite tips or they innervate receptor cells. Either way, the receptor cell essentially transduces a physical stimulus into an electrical impulse. Once the impulse is generated, it propagates towards the CNS and the rest I'm sure u know...

 

[sv3]

The 12 pairs of cranial nerves originate from the lower brain and connect to parts of the head, neck and truck. 1 pair originates from the cerebellum and the rest from the brain stem. These nerves have varied functions from enabling chewing and facial expressions to facilitating the sensations of light, smell and sound.

The 31 pairs of spinal nerves originate from the spinal cord and innervate parts of the limbs, neck and trunk.

Initial depolarization is most intuitive when u consider sensory neurons. These neurons either have specialized receptor ends at their dendrite tips or they innervate receptor cells. Either way, the receptor cell essentially transduces a physical stimulus into an electrical impulse. Once the impulse is generated, it propagates towards the CNS and the rest I'm sure u know...

Hey thanks very much for the reply. It definitely helped. Just some clarification: So all axons that exit the spinal cord, they can be found in one of the 31 pairs of spinal nerves? Can they not go it alone and must be part of this bundle of axons that is a nerve?
I'm just trying to connect the dots in terms of what goes in and out of a nerve.

cheers

 

[sv3]

The 12 pairs of cranial nerves originate from the lower brain and connect to parts of the head, neck and truck. 1 pair originates from the cerebellum and the rest from the brain stem. These nerves have varied functions from enabling chewing and facial expressions to facilitating the sensations of light, smell and sound.

The 31 pairs of spinal nerves originate from the spinal cord and innervate parts of the limbs, neck and trunk.

Initial depolarization is most intuitive when u consider sensory neurons. These neurons either have specialized receptor ends at their dendrite tips or they innervate receptor cells. Either way, the receptor cell essentially transduces a physical stimulus into an electrical impulse. Once the impulse is generated, it propagates towards the CNS and the rest I'm sure u know...

The bolded statement above is what I'm wondering about. How does that happen? How does the physical stimulus actually depolarize a neuron? For example I know how one electical impluse can electrically or electrochemically induce another, but I don't know the mechanistic steps of the physical-electrical path - or is this just not needed for the MCAT?

thanks

 

[Bernoull]

The bolded statement above is what I'm wondering about. How does that happen? How does the physical stimulus actually depolarize a neuron? For example I know how one electical impluse can electrically or electrochemically induce another, but I don't know the mechanistic steps of the physical-electrical path - or is this just not needed for the MCAT?

thanks

The biochemical and/or biophysical mechanism of signal transduction is definitely NOT required for the MCAT!!! It will be sufficiently explained in a passage if it shows up.

My understanding is that sensory transduction is similar to neural propagation across chemical synapses. Ion channels are involved. We all know that movement of charged particles represents electricity so if you couple the opening of an ion channel to a physical stimulus, voila u generate a receptor potential. This potential is transient since it's depends on the presence of the stimulus and if its magnitude exceeds the threshold potential at the axon hillock u generate an action potential. Invariably, the receptor potential tells the brain the "spatial origin" of the stimulus and its intensity.

Generally the sensory receptor is activated by heat, light or chemicals. The activated receptor may be part of an ion channel complex and undergo conformational change to open/close the channel. This is ionotropic sensory detection. Another way has the activated receptor activate a G-protein (2nd messenger system) and a cascade results in the ultimate opening/closing of an ion channel. This is called metatropic sensory detection. Photoreceptors use a rhodopsin-mediated 2nd messenger system that ultimately closes Na+ channels and hyperpolarizes the cell (rod)..

I analogize hair cells - transduce sound to electricity -to piezoelectric materials, in other words I try to relate sound transduction to a physical/mechanical analog that I understand.

If u still want more detail, here's a book u can read...

http://www.sinauer.com/detail.php?id=1716

 

[sv3]

hey Bernoull,

thanks alot. That cleared it all up!

 

[Bernoull]

hey Bernoull,

thanks alot. That cleared it all up!

Excellent question as usual. Actually I'm like you in the sense that I like to understand the underlying physical/chemical principle that accounts for a biological phenomena. Although my undergrad is Biology, I tend to think of it less as an independent science and more as applied physics & chemistry to living systems. Appreciating these dimensions enriches ur understanding but do keep in mind what's cool to know and what's beyond the MCAT..

I'm also amazed at how much foundational material the MCAT covers - material that can explain the basis of diseases/therapies etc.. I remember reading up cortisol and I was amazed that its property as an immunologic suppressant is exploited by pharmaceuticals in making corticosteroids etc to treat autoimmune and tissue transplant. I happen to have an immunologic condition and do use a corticosteroid occasionally. Everything came full circle!!!