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Impulses
AQA A-level biology nervous system year 13
| Term | Definition |
|---|---|
| Impulse | Rapid electrical signal that travels along a neurone in response to a stimulus |
| Action potential | Self-propagating impulse that travels down the axon of a neurone and is triggered by a change in potential difference across the cell membrane. Can only be produced at the naked neurone or Nodes of Ranvier |
| Resting potential | The steady electrical charge difference across the cell membrane of a neurone when it isn’t actively transmitting a signal. Approximately -70mV |
| Structure of a motor neurone: Cell body (soma) | Main part of the motor neurone containing the Nucleus and controls the functions of the cell |
| Structure of a motor neurone: Dendrites | Thin branched extensions radiating from the cell body which receives impulses and transmits them towards the cell body |
| Structure of a motor neurone: Axon | The long, slender extensions coming from the cell body which carry nerve impulses away from the cell body towards the axon terminal. Can travel over quite a long distance |
| Structure of a motor neurone: Myelin sheath | A fatty, insulating layer surrounding the axon which speeds up the conduction of nerve impulses along the axon and stops the signal getting lost. Produced by specialised Schwann cells |
| Structure of a motor neurone: Nodes of Ranvier | Small gaps between section of the myelin sheath which facilitate the rapid propagation of nerve impulses by allowing the electrical signal to “jump” from one node to the next |
| Structure of a motor neurone: Axon terminals (synaptic endings) | Specialised branches leading off from the axon that transmit nerve impulses to the next cell in the pathway and contain neurotransmitters that help with transmission of the impulse |
| Structure of a motor neurone: Synaptic vesicles | Small sac-like structures which store and release neurotransmitters when the nerve impulse reaches the axon terminal |
| Sodium potassium pump | A vital membrane protein which actively transports sodium ions out of the cell and potassium ions into the cell which can allow for active transport and maintaining action potential |
| Conformational shape change | A specific alteration of the tertiary structure of a protein, often induced by the binding of a substrate or ion. In a pump, this might cause it to open to a different side of the cell membrane |
| Sodium potassium pump: how it functions | Sodium binds and the proteins is then phosphorylated by the action of ATP hydrolyse causing a conformational shape change resulting in lowered sodium affinity causing the sodium to be released out of the cell and higher potassium affinity |
| Electrochemical gradient | The combined action of the concentration and electrical gradient of ions as they move across a cell membrane via facilitated diffusion or active transport |
| Leaky ion channel (potassium ion example) | Protein channels through which specific ions can pass through the cell membrane. When potassium ions enter the cell, they will attempt to leave the cell through the leaky channel which lowers the charge of the cell |
| Graded potential | A small, variable change in the charge of the cell that doesn’t meet the threshold required for an action potential but serve as a basis for making neurones more excitable |
| Equilibrium potential | The electrical potential at which there is no net movement of a particular ion across a cell membrane that occurs when the concentration gradient and electrical gradient are balanced. Is different for every ion |
| Voltage gated channel | A specialised protein channel found in the cell membrane which opens or closes in response to changes in cell voltage. When the voltage reaches a certain level it undergoes a conformational shape change to allow specific ions through |
| What triggers action potential | When a neurone is depolarised to a certain threshold (-55mV) by a stimulus, voltage gated ion channels open to allow in an influx of sodium and potassium ions that steadily spreads across and depolarises the cell in a wave of ions |
| Saltatory conduction | The rapid energy-efficient of action potentials along a myelinated neurone involving the action potential “jumping” from one node to the other rather than travelling continuously along the entire length of the axon |
| How temperature affects impulses | Increased temperature increase the kinetic energy of ions meaning that depolarisation and repolarisation becomes faster and vice versa with decreased temperature. If the temperature is too high then channels and enzymes can denature |
| How size of axon affects impulses | Larger axons have a larger diameter which means they have lower resistance to the flow of ions so the impulse travels faster. Less energy is required to transmit the signals across long distances and vice versa for small axons |
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