Name: 【TED-Ed】How do nerves work? - Elliot Krane
Uploaded: 2015-01-03T08:46:35.000Z
Duration: 5 min
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

that conduct electricity, like the wires in the walls of your home

but the reality is that nerves have a much more complex job in the body.

They are not just the wires, but the cells that are the sensors,

detectors of the external and internal world,

the transducers that convert information to electrical impulses,

the transistors that gate the information

and finally, the activators that take that information

and cause it to have an effect on other organs.

Consider this. Your mother gently strokes your forearm

Or a spider crawls on your forearm and you startle and slap it off.

Or you brush your forearm against a hot rack while removing a cake from the oven

Light touch produced pleasure, fear, or pain.

How can one kind of cell have so many functions?

Nerves are in fact bundles of cells called neurons

and each of these neurons is highly specialized to carry nerve impulses,

in response to only one kind of stimulus, and in only one direction.

The nerve impulse starts with a receptor,

One nerve's receptor might be a thermal receptor,

designed only to respond to a rapid increase in temperature.

Another receptor type is attached to the hairs of the forearm,

detecting movement of those hairs, such as when a spider crawls on your skin.

Yet another kind of neuron is low-threshold mechanoreceptor,

Each of these neurons then carry their specific information:

And that information is projected to specific areas of the brain

The inside of a nerve is a fluid that is very rich in the ion potassium.

It is 20 times higher than in the fluid outside the nerve

while that outside fluid has 10 times more sodium than the inside of a nerve.

This imbalance between sodium outside and potassium inside the cell

results in the inside of the nerve having a negative electrical charge

This is called the nerve's resting potential.

But in response to that stimulus the nerve is designed to detect,

pores in the cell wall near the receptor of the cell open.

These pores are specialized protein channels

that are designed to let sodium rush into the nerve.

The sodium ions rush down their concentration gradient,

and when they do, the inside of the nerve becomes more positively charged-

While this happens, initially in the nerve right around the receptor,

if the change in the nerve's electrical charge is great enough,

the nearby sodium ion channels open, and then the ones nearby those,

so that the positivity spreads along the nerve's membrane

and then along the nerve's long, thread-like extension, the axon.

and the membrane voltage returns to normal.

the nerve is resistant to further depolarization- it is refractory,

which prevents the nerve electrical impulse from traveling backwards.

Then, ion pumps pump the sodium back back out of the nerve,

restoring the nerve to its normal resting state.

The end of the nerve, the end of the axon,

This target will be other nerves in a specialized area of the spinal cord,

to be processed and then transmitted up to the brain.

Or the nerve's target may be another organ, such as a muscle.

When the electrical impulse reaches the end of the nerve,

small vesicles, or packets, containing chemical neurotransmitters,

are released by the nerve and rapidly interact with the nerve's target.

This process is called synaptic transmission,

because the connection between the nerve and the next object in the chain

is called a synapse. And it is here, in this synapse,

that the neuron's electrical information can be modulated,

or translated to another informational process.