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Nervous coordination
topic 16 bio
| Question | Answer |
|---|---|
| Explain the structure of a myelinated neuron | axon has myelin sheaths at regular intervals which are layers of lipids folded around axon which proved insulation. Nodes of ranvier are gaps between myelination and are where depolarisation occurs. |
| What is another name for a myelin sheath? | A Schwann cell. |
| Explain membrane permeability, electrochemical gradients, and the movement of Na+ and K+ in regards to resting potential. | The outside of the axon is more positive relative to the inside |
| Explain the permeability of the membrane at resting potential. Include information on electrochemical gradients and Na+ and K+. | |
| What is depolarisation? | When the inside of the axon becomes more positive and the tissue fluid becomes more negative due to the diffusion of Na+ ions in response to stimuli |
| What is resting potential? | When the outside of the axon is more positive relative to the inside of the axon. |
| What is the charge of resting potential? | -70 millivolts |
| How does a nerve impulse travel down the axon? | self-propagates down the axon via temporary reversal of charge along cell-surface membrane |
| What is threshold? | a charge that must be reached for full depolarisation (an action potential) to occur. -55mV |
| What is the charge of an action potential? | +40mV |
| Explain the structure of a myelinated neuron | lipid rich fatty sheath (Schwann cell) wrapped around the axon - electrical insulator so no action potentials occur in this area - impulses "jump" between nodes of ranvier |
| What type of action potential propagation occurs in myelinated neurones? | saltatory conduction |
| What three factors affect the speed of propagation? | - myelination - axon diameter - temperature (diffusion rate) |
| How do action potentials show when a stimulus is more intense? | increase frequency of action potentials - NOT size |
| What is the all or nothing principle? | if below threshold no action potential and if above threshold action potential occurs - all action potentials are the same size |
| What conditions cause damage to the axon? | multiple sclerosis (MS) and spinal trauma |
| What conditions affect the myelin sheath? | celiac disease - reduce fat absorption |
| What is the refractory period? | - period after an action potential where further inward movement of sodium ions is prevented because sodium voltage gated channels are closed - no further action potentials can be generated |
| What are the three purposes of the refractory period? | - ensures action potentials only propagated in one direction - ensures action potentials discrete - gap between impulses - limits the number of action potentials in a given time to prevent overstimulation |
| What is the name of the neurotransmitter we need to know? | acetylcholine (ACh) |
| What is the name of the enzyme that hydrolyses acetylcholine? | Acetylcholinesterase (AChE) |
| What ion channels are located on the presynaptic knob? | Calcium ion voltage gated channels |
| How does the synapse reset between action potentials? | - calcium ions actively transported out of synaptic knob so conc higher outside membrane - ACh removed from receptors and hydrolysed to acetate and choline by AChE - acetyl and choline are combined to ACh to be used in the vesicles again |
| What is summation? |
Created by:
Ziggyisweird