- Are...cells in which a change in the internal or external environment produces a nerve impulse (action potential).
- All receptors are transducers - the change energy from one form to another.
- Are...neurons that transmit nerve impulses from a sensory receptor to the central nervous system (CNS).
- The cell body is at the side of the dendron.
- The dendrites are longer than the axon.
- Has synaptic knobs.
- Are...neurons that transmit nerve impulses from the CNS to an effector (e.g. muscle or gland).
- The cell body is at the end of the axon.
- The axon is longer than the dendrites.
- Has motor end plates.
- Is...the potential difference (or voltage) across the neuron cell membrane while the neuron is at rest - not conducting a nerve impulse (= 70mV).
1. Sodium-potassium pumps in the plasma membrane actively transport 3Na+ OUT OF and 2K+ INTO the axon.
2. The membrane is relatively impermeable to the Na+ ions so they build up on the outside of the axon.
3. The membrane is permeable to K+ ions which diffuse from inside of the membrane, out of the membrane.
4. This results in the outside of the axon being positively charged compared to inside the axon.
- Are...depolarisation of the cell membrane so that the inside is more positive compared to the outside (= +40mV).
1. Stimulus is applied which exceeds the threshold value, opening Na+ channels.
2. Voltage gated Na+ channels open and Na+ ions diffuse INTO the axon, down a gradient.
3. The membrane depolarises.
4. The inside of the axon becomes more positive compared to the outside.
5. The voltage gated Na+ channels close.
6. The voltage gated K+ channels open.
7. K+ ions diffuse out of the axon, and the potential difference becomes negative.
8. Hyperpolarisation occurs - the membrane cannot depolarise.
9. Resting potential is restored.