Nervous Flashcards
What are neurons
The functional unit of the nervous system. It is an elongated cell with three parts
How does the nervous system function? How does the transmission occur?
By the almost instantaneous transmission of electrochemical signals. The means of transmission are highly specialized cells knows as neurons.
What are the three major parts of the neuron
Dendrites, cell body, axon
How many dendrites does the typical neuron have
Many
What do dendrites look like
Thin branches extending from the cell body
What does the cell body of the neuron contain
Nucleus and organelles
How many times longer is the axon than the rest of the neuron
Can be thousands
What is the axon
A single, long projection extending from a cell body
What does the axon end in
Several small branches known as axon terminals
How are neurons connected/not connected
They are often connected in chains and networks, yet they never actually come in contact with one another: the axon terminals of one neuron is separated from the dendrites of an adjacent neuron
What separates the axon terminals of one neurons from the dendrites of an adjacent neuron
A small gap known as a synapse
Where does the electrical impulse moving through a neuron begin
The dendrites
Where does the electrical impulse move after the dendrites
It passes through the cell body and then along the axon
What does the impulse always do
Follow the same path from dendrite to cell body to axon
What happens when the electrical impulse reaches the synapse at the end of the axon
It causes the release of specialized chemicals known as neurotransmitters
What do the neurotransmitters do after the electrical impulse activated them
They carry the signal across the synapse to the dendrites of the next neuron, starting the process again in the next cell
What is the cell at when there is no impulse traveling through a neuron? What is the charge of the cell?
The cell is at its resting potential and the inside of the cell contains a negative charge in relation to the outside
To keep the cell negatively charged inside, what does it require
Energy: it is an active process
What protein does the cell membrane of the neuron contain
Na+/K+ ATPase
What does Na+/K+ ATPase do (the sodium potassium pump)
Uses the energy provided by one molecule of ATP to pump three positively charged sodium ions out of the cell, while simultaneously taking into the cell two positively charged potassium ions.
What does the sodium potassium pump build up outside and inside the cell
Outside: a high concentration of sodium ions
Inside: an excess of potassium ions
What is one of the special properties of phospholipid cell membranes and what does that mean for the concentrations that the sodium potassium pump created
The special property is that they bar passage to ions unless there is a special protein channel that allows a particular ion in or out. This means that all of the ions can’t diffuse across the membrane to regularize the distribution like they want
Does a special protein channel exist for the sodium that is built up
For the sodium that is built up outside the cell, there is no channel
Does a special protein channel exist for the potassium that is built up inside the cell
Yes- there are potassium leak channels that allow some of the potassium ions to flow out of the cell
What does the difference in ion concentrations create
A net potential difference across the cell membrane of approximately -70 mV or millivolts ( the value of the resting potential )
What is the value of the resting potential
-70 mV
What do most cells have
Some sort of resting potential from the movement of ions across their membranes
Neurons are among only a few types of cells in that they can also form a ____
An action potential
What is the action potential
The electrochemical impulse that can travel along the neuron
(Comprehensive) what does the neuron membrane contain
Sodium potassium pump and potassium leak channel proteins as well as voltage gated proteins
What do voltage gated proteins do
Respond to changes in the membrane potential by opening to allow for certain ions to cross that would not normally be able to do so
What channels does the neuron contain
Voltage gated sodium channels and voltage gated potassium channels that open under different circumstances
Where does the action potential begin
When chemical signals from another neuron manage to depolarize, or make less negative, the potential of the cell membrane in one localized area of the neuron cell membrane, usually in the dendrites
What happens if the neuron is stimulated enough so that the cell membrane potential in that area manages to reach as high as -50 mV (from the resting potential of -70 mV)
The voltage gated sodium channels in that region of the membrane open
What is the threshold potential
The voltage at which the voltage gated channels open
What happens when the voltage gated channels open and why
The sodium ions follow the concentration gradient and Rush into the cell because there is a large concentration of positive sodium ions just outside the cell membrane that have been pumped out by the sodium potassium pump
What happens with the flood of positive ions
The cell continues to depolarize, or become less negative
What happens when the membrane potential gets as high as +35 mV
The voltage gated sodium channels close and the voltage gated potassium channels open, letting the positive potassium ions concentrated in the cell rush out of the neuron, repolarizing the cell membrane to its negative resting potential
As the potassium ions rush out of the neuron, what happens
The membrane potential continues to drop beyond -70 mV until the voltage gated potassium channels close once again around -90 mV
With the voltage gated proteins closed what happens
The sodium potassium pump and the potassium leak channels work to restore the membrane potential to its original polarized state of -70 mV.
How long does the whole process with the pump take to occur
Approximately one millisecond
The action potential does not occur in one localized area of the neuron and then stop (t/f)
True