Speed Of The Nerve Impulse Flashcards
What is the nerve impulse
The transmission of an action potential along the axon of a neurone
What factors affect the speed at which action potential passes along an axon
The myelin sheath - it acts as an electrical insulator, preventing an action potential forming in the part of the axon covered in myelin. It does jump from one node of ranvier to another (saltatory conduction). This increases the speed of conductance.
The diameter of the axon- the greater the diameter the faster the speed of conductance (less leakage of ions from a large axon)
Temperature- higher temp faster the nerve impulse. Allows enzymes to function rapidly for respiration to produce energy for active transport
Whats the all or nothing principle
There is a particular level of stimulus that triggers an action potential. At any level above this threshold, a stimulus will trigger an action potential that is the same regardless of the size. Below the threshold, no action potential is triggered
How can an organism perceive the size of a stimulus
By the number of impulses passing in a given time. Larger the stimulus the more impulses generated in a given time
By having different neurones with different threshold values. The brain interprets the number and type of neurones that pass impulses as a result of a given stimulus and thereby determines its size
What is the refractory period
The period of time it is impossible for a further action potential to be generated
What 3 purposes does th refractory period serve
It ensures that action potentials are propagated in one direction only - can only pass from an active region to a resting region. They cannot be propagated in a region that is refractory, which means that they can only move in a forward direction
It produces discrete impulses- a new action potential cannot be formed immediately behind the first one. Ensuring action potentials are separated from one another
It limits the number of action potentials- as they are separated from one another this limits the number of action potentials that can pass along an axon in a given time, and thus limits the strength of stimulus that can be Detected
Explain how the refractory period ensures that nerve impulses are kept separate from one another
During the refractory period the sodium voltage gates channels are closed so no sodium ions can move inwards and no action potential is possible. This means there must be an interval between one impulse and the next
