Topic 25: The Nervous System

The nervous organisation is built upward of specialized cells, which nosotros dealt amongst when nosotros studied histology (the written report of tissues).  You tin terminate review it here.  Scroll downwards to "nervous tissue".

Information is carried through the nervous organisation along neurons.

The direction of data menstruum inwards a neuron is e'er from the dendrite to the axon.

We say that the "nerve impulse" carries the information.  An impulse is genuinely a modify inwards the cell's accuse (an electrical signal).  Neurons pick out a resting potential of -70mV.  This is the accuse of the prison theatre cellular telephone when no data is beingness sent along it.  When a strong plenty impulse arrives, the voltage gated sodium channels establish inwards the cell's membrane open.  This causes the within of the axon to piece of employment to a greater extent than positive than the outside.

Na-channel opening

The positive accuse causes the neighbouring sodium channels to open, allowing the accuse modify to motion along the axon.  Once the initial modify inwards accuse has occurred, the sodium channels unopen together with potassium gates open.  Potassium is pumped out of the prison theatre cellular telephone to pick out the accuse dorsum to -70mV.  The portion where this occurs is called the refractory portion together with a novel impulse cannot spill out at that spot until it has returned to the resting potential.

Impulse conduction along the axon

At this point, at that spot are to a greater extent than sodium ions within the prison theatre cellular telephone together with to a greater extent than potassium exterior the cell.  The sodium-potassium ticker plays a business office inwards balancing the deviation together with equally good inwards maintaining a resting potential of -70mV

All of what has but been explained is called the ACTION POTENTIAL, which is shown below inwards its graphical form.

On the graph, numbers 1 together with iv stand upward for the resting potential, when the prison theatre cellular telephone is non transmitting whatever information.  When the sodium channels open, the accuse of the prison theatre cellular telephone apace becomes positive equally sodium ions rush in.  This is called depolarization.  Once the sodium channels unopen together with the potassium channels open, the potassium rushes out, causes the accuse to piece of employment negative again.  This is repolarization.  The provide from hyperpolarization (the dip below -70mV) together with the maintance of the resting potential is carried out past times the sodium-potassium pump.

This video is a overnice explanation of the activity potential.  

Saltatory conduction refers to the rapid conduction of the impulse downwards a myelinated axon, where channels opening together with closing solely occurs inwards the nodes of Ravier.

Neurons pick out spaces betwixt them.  They never genuinely behaviour upon the neighbouring cell.  The axon comes upward but about the neighbouring cell's dendrite, but a infinite remains, which is the synapse.

Information crosses across the synapse inwards chemic form.  These chemicals are called neurotransmitters.  The neurotransmitter is released from the axon, it crosses across the crack (space) together with binds to a receptor on the dendrite.

The attachment to the receptor causes the activity potential to laid about together with overstep along the adjacent cell, transmitting the impulse further.