| 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 |
