Nervous System Flashcards
What happens when a stimulus is applied to the axon?
The permeability of the membrane to sodium ions increases as sodium ion channels start to open.
What is the threshold level for generating an action potential?
-55mV
What occurs if the threshold level is not reached?
The sodium ion channels close and resting potential restores quickly.
What is the term for the rapid influx of sodium ions into the cell when the threshold is reached?
Depolarization
What is the action potential’s change in potential difference?
From -70mV to +40mV
What does the all or nothing law state regarding action potentials?
The action potential is either generated if the threshold level is reached or not if it isn’t.
How is the strength of a stimulus differentiated?
By the number of action potentials per second.
How does the action potential move along an axon?
In a wave of depolarization.
What is the role of local circuits in action potential propagation?
The depolarization of part of the membrane acts as a stimulus for the next part.
What is the function of myelin in myelinated neurons?
It acts as an electrical insulator.
What is the phenomenon called when action potentials jump from one node to the next?
Saltatory conduction
What is the conduction speed of myelinated neurons?
100m/second
What is the conduction speed of unmyelinated neurons?
1m/second
What advantage do myelinated neurons have regarding ATP usage?
Less ATP is used because sodium potassium pumps only operate at the nodes.
Where are voltage-gated channels found in myelinated neurons?
Only at the nodes of Ranvier.
How does the diameter of an axon affect action potential transmission?
The wider the diameter, the less resistance there is, allowing faster transmission.
What is a famous example of an organism with giant axons?
Squid
What effect does higher temperature have on transmission speed?
Increases transmission speed as diffusion happens faster.
How is resting potential maintained?
Sodium-potassium pumps actively transport sodium ions out and potassium ions ions into the neurone (3NA+ out for each 2K+ in) and required ATP
What happens when the threshold (-55mv) is reached?
The change in the voltage across the axon membrane opens the NA+ channels so that sodium ions flood in (influx of NA+) and then depolarises the axon to about +40 mV (this is the action potential)
What is the function of dendrites?
Short, branched extensions of the cell body that receive nerve impulses from other neurones
What is the function of the cell body?
The region of the neurone that contains the organelles, notably the nucleus and the RER
What is the function of the axon?
A long fibre that conducts nerve impulses away from the cell body
What is the function of the myelin sheath?
An electrically insulating layer consisting of the membranes of Schwann cells and it increases the speed of nerve impulses
