I’m taking a Neural Biology course. I’m completely new to the area and would like a bit of info.
I always feel that I learn better when I know the “Big Picture”.
I understand how the nucleus of a neuron creates specific amino acids to convert into peptide chains.
I also understand that the resting potential of a neuron is based on the concentration of various things on either side of the cell wall, and that the potential is generally about -70.
My question is, so what. What’s the punchline? My WAG is that the perpherial nervous system responds to a stimulus causing a chemical reaction (the release of amino acids), which stimulates the electrical impulse in the neuron - that is, K+ is stimulated to exit, Na- and Cl- are stimulated to enter, causing the neuron to fire, sending the message to or from the brain.
However, this is a WAG. So, am I even close to accurate here? If not, can anyone explaine where I went wrong.
I encourage folks to dumb it down for me. I’ve never even taken a biology course (even in high-school) and I’m sort of floundering here.
THANKS!!
You’re on the right track, yet there’s a few things I can try and clarify.
The nucleus doesn’t create polypeptides, rather it sends out RNA which tells cellular ribosomes the sequence of amino acids to string together to make a polypeptide chain. Amino acids are the fundamental unit (the assorted Lego bricks, as an analogy) of which proteins are composed of. Amino acids are held together by peptide bonds. And the only difference between a polypeptide and a protein is semantics. When we say polypeptide, we imply the protein molecule is very small, but no one will be confused if you called it a protein.
Regarding the -70mV potential of the inside of the nerve relative to the outside, it’s pretty lengthy to explain how it all comes about that way. But all that complexity isn’t what makes it so interesting. The fact that there is a potential is the punchline. With an electrical potential, things can happen.
In this case we can produce a signal by allowing the potential to change momentarily to about +30mV before it changes back again to it’s original -70mV state. Like a momentary on/off. The neat thing is that this momentary change doesn’t occur everywhere at once in the nerve. It happens at one little site which causes the adjacent site to change causing its adjacent site to change, and so on all along the length of the nerve. That is how the electrical signal travels along the nerve.
Cool, huh?
What else ya got? Bring it on!
Amino acids arent usually used to stimulate excitable cells (ie. neurons). They are used to make proteins, which then go out and make smaller molecules, which are packed up and “sent” to the axon to begin the stimulus. Or the stimulus is external to begin with, like a photon of light hitting the sensory nerves in the eye, which causes certain molecules (rhodopsin?) to change conformation, which causes a chain reaction eventually leading to an axonic charge/chemical release that is interpretted by the next neurons dendrites, etc etc. The chemicals used to stimulate adjacent cells are neurotransmitters, such as acetylcholine or dopamine. These are dumped out into the synapse (the gap between the axon of one cell and the dendrite of the other) and specialized receptor proteins on the dendrite “catch” them, and causes an appropriate reaction in that cell.
The answer to “so what” is that the neuron generates an electrical charge. This charge runs along the length of the neuron and hits another neuron. In this way, the charge moves around and around the brain.
But neurons aren’t like wires. They need a certain number of charges coming in before they fire. Some incoming charges are inhibitors – the make it harder for the neuron to fire.
So it’s one amazing system which balances inibition and excitation to create movement, thought, sensation.
A lot of the detail that you are studying is about how that happens. The bigger picture is that there are 100 billion neurons, with perhaps 1000 connections to each neuron from other neurons. And the brain isn’t jello, it’s highly structured. It’s miraculous, really.
There are so many things that affect each individual neuron that it can seem a bit overwhelming at first. The walls of the neuron have ion pumps, channels, receptors – all kinds of wacky stuff. Some of these things change how the neuron fires from moment to moment, and others create long-term changes, which is how memories are formed.
Ok. So I’m kinda more clear now. Thanks.
So, lets talk about the pons. Now, I get that the pons is a bridge between this and that. My question is, why is it there at all? Apparently, it’s a throw back, ala an apendix, but I’m wondering - what did it USED to be for?
I don’t know the textbook you are using in Neurobiology, but a good one is * Neurobiology: Molecules, Cells, and Systems * by Gary G. Matthews. I believe it was published in 2001. This book states that the pons is located at the junction between the hindbrain and the midbrain and includes neurons that regulate respiration (along with the medulla oblongata).
This book states that the basic long-distance signal of the nervous system is a self-propagating depolarization called the action potential. It arises through a sequence of voltage-dependent chantges in the ionic permeability of the neuron membrane. This voltage-dependent behavior of the membrane is related to the presence of gated sodium and potassium channels. These channels are controlled by several different kinds of gates. The voltage-sensitive potassium channels are controlled by a single gate.
It also details the action potentials and notes that the influx of sodium ions is the depolarizing upstroke of the action potential. As with sodium ions, the equilibrium potential for calcium ions (with a valnce of +2) is positive. If the membrane potential is negative and a calcium channel opens, an influx of calcium will enter the cell. In the case of the sodium-dependent action potential sodium channels activated by depolarization provide the basis for the regenerative all-or-nothing depolarizing phase of the action potential. Similarly, in the case of calcium-dependent action potentials, calcium channels that open upon depolarization underlie the depolarizing phase of the action potential.
Depolarization opens calcium channels, which permite the influx of positively charged calcium ions, which in turn produces greater depolarization and opens additional calcium channels.
The increase in the intracellular concentration of calcium that results from the influx of calcium ions through voltage-dependent calcium channels represents an important cellular signal that allows depolarization of a cell to be coupled to the triggering of internal cellular events, such as the release of neurotransmitter from the presynaptic terminal. Calcium-activated potassium channels can contribute to action potential repolarization in neurons that include a calcium component in the action potential.
So you can have either voltage-activated or calcium-activated potassium channels. Calcium-activated potassium channels remain open for as long as the intracellular calcium level remains elevated after the action potential, which period can be hundreds of times longer than the undershoot produced by the voltage-dependent potassium channels.
The pons is definitely still used by the brain. You couldn’t live without it. Among other things, it keeps you awake (neurons from the pons inhibit neurons that put you to sleep).
I wouldn’t say it is like the appendix, which doesn’t serve any important function. It’s more accurate to say that the pons has been around for a very long time during our evolution.
The brain is often thought to have evolved in three parts. The first part is found in simpler animals, and this part regulates movement, respiration, and reflexes. It’s the basic stuff an animal needs to survive. This is where the pons is located. As reptiles evolved to walk on land, it is believed that the pons developed new centers within it for specialized functions, such as balance and muscle control.
The next part to evolve added on new brain tissue and it’s thought that animals developed more social behaviors. This is sometimes called the limbic brain, and it regulates emotions, memory formation, and a lot of other stuff.
Then the cortex evolved, which gave greater ability to plan ahead, and to allow the animal to regulate its own behavior. But the pons is still there doing its job.