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level: 15.4 Speed of the nerve impulse

Questions and Answers List

level questions: 15.4 Speed of the nerve impulse

QuestionAnswer
Factors affecting the speed at which an action potential travels- The myelin sheath - The diameter of the axon - Temperature
The myelin sheath- Passage of an AP, the myelin sheath acts as an electrical insulator, preventing AP forming in myelinated parts of axon - But it does jump from 1 node of Ranvier to another (saltatory conduction) - Increasing speed of conductance
The diameter of the axon- The greater the diameter of axon, the faster the speed of conductance - This is due to less leakage of ions from a large axon (leakage makes membrane potential harder to maintain)
Temperature- Higher temp. the faster the nerve impulse, increases diff of ions - The energy for active transport comes from respiration, which is controlled by enzymes - Enzymes function more rapidly at higher temp. up to a point - Above certain temp, they denature + impulses fail to be conducted at all - Temp. also affects speed + strength of muscle contractions
All or nothing principle- Once the threshold is reached, an AP will always fire with the same V, no matter how big the stimulus is - If the threshold isn't reached, an action potential wont fire - A bigger stimulus wont cause a bigger action potential, but it will cause them to fire more frequently
How then can an organism percieve the size of a stimulus??- By the no. of impulses passing in a given time - The larger the stimulus, the more impulses that are generated - By having different neurons with different threshold values - The brain interprets the no. + tye of neurons that pass impulses as a result of given stimulus so determines its size
The refractory period meaning- After an action potential, the neuron cell membrane cant be excited again straight away - Coz ion channels are recovering + cant be made to open
The purpose of the refractory period- It ensures that APs go in one direction only - Ensures that APs are seperated - It limits the no. of action potentials
It ensures that action potentials are propagated in one direction only- APs can only pass from an active region to a resting region - Coz APs cannot be spread in a region that is refractory, so they can only move in 1 direction - Preventing APs from spreading in both direction
It limits the no. of action potentials- As APs are separated this limits no. of APs that can pas along axon in a given time - So limits strength of stimulus that can be detected