15.4- SPEED OF THE NERVE IMPULSE Flashcards
Is an action potential at the end of an axon the same size as when it starts?
yes
What is the transmission of an action potential along the axon of a neurone?
nerve impulse
Factors that affect the speed at which action potentials pass along an axon? (3)
myelin sheath
diameter of axon
temperature
How does the myelin sheath affect the speed at which action potentials pass along an axon?
it acts as an electrical insulator, preventing an action potential forming in the part of the axon covered in myelin
but jumps from node to node increases speed of conductance
How does the diameter of the axon affect the speed at which action potentials pass along an axon??
greater the diameter of the axon, faster the speed of conductance
due to less leakage of ions from large axon
How does temperature affect the speed at which action potentials pass along an axon?
affects rate of diffusion of ions and so higher the temp, faster the nerve impulse
Where does energy for active transport come form?
respiration
What is respiration controlled by?
enzymes
At what temperatures do enzymes function more rapidly?
at higher temps up to a certain point
What happens to enzymes and plasma membrane proteins above a certain temperature?
enzymes + plasma membrane proteins denatured + impulses fail to be conducted at all
How does the body temperature of cold-blooded (ectothermic) vary?
varied in accordance with the environment
How does temperature affect muscle contractions?
affects speed + strength of muscle contractions
What kind of response are nerve impulses described to be?
all-or-nothing responses
What is the certain level of stimulus of a nerve impulse called?
threshold value
What does the threshold value trigger?
triggers an action potential
What is not generated below the threshold value?
no action potential, and so no impulse generated
Are all action potentials more or less the same size?
yes
As all action potentials are more or less the same size, what cannot be detected?
the strength of the stimulus cannot be detected by the size of the action potentials
How can an organism perceive the size of a stimulus? (2)
by number of impulses passing in given time- larger the stimulus, the more impulses generated in given time
by having different neurones with different threshold values- brain interprets number + type of neurones that pass impulses as a result of given stimulus + thereby determines size
Once an action potential has been created in any region of an axon, what is prevented for a period afterwards?
inward movement of sodium ions prevented as sodium voltage-gated channels closed
What is the refractory period?
time where it’s impossible for further action potentials to be generated
What three purposes does the refractory period serve?
ensures action potentials propagated in one direction only
produces discrete impulses
limits number of action potentials
How does the refractory period ensure action potentials are propagated in one direction only?
action potentials cannot be propagated in region that’s refractory, which mean they can only move in forward direction
prevents action potentials from spreading in both directions
How does the refractory period produce discrete impulses?
new action potential cannot be formed immediately behind first one
ensures action potentials separated from one another
How does the refractory period limit the number of action potentials?
as action potentials separated from one another this limits the number of action potentials that can pass along axon in given time, + so limits strength of stimulus that can be detected
