nerves Flashcards
What are the 3 layers of meninges?
Dura, arachnoid and pia matter.
What are the 3 main parts of the brain and what do they contain?
1) Forebrain (cerebrum and diencephalon), 2) midbrain (tectum and tegmentum), 3) hindbrain (cerebellum, pons and medulla)
What are the 3 types of membrane potentials?
Resting membrane, graded and action. Resting membrane keeps cells ready to respond, graded potentials decide when action potentials should be fired and action potentials transmit signals over long distances to allow something to happen.
Which ion moves out of the cell at rest?
K+ through leaky K+ channels. As it moves out it develops an electrical gradient.
What is the equilibrium potential?
The membrane potential at which the electrical potential is exactly equal and opposite to the concentration gradient.
Which equation can predict equilibrium potential?
Nernst for a single ion species.
What is the threat of bananas?
They contain a lot of K+. If there is a lot of extracellular K+ then this reduces the concentration gradient and increases the RMP. The cell depolarises and releases an AP. Hyperkalaemia causes ventricular fibrillation.
What is RMP in striated muscle and normal cells?
Striated muscle cells -90mV. Normal cells -70mV due to other leaky channels –> Na and Cl which are both at higher concentrations outside the cell.
When is RMP lost?
When K+ moves out of the cell down its concentration gradient. If extracellular K+ rises the concentration gradient is decreased.
When would a cell become hyperpolarised?
If K+ channels or Cl- channels are opened as this would make the cell more negative. Opening Ca2+ channels or Na+ channels makes the cell depolarise.
What happens if the Na/K pump is poisoned?
Little immediate effect as cell will only depolarise a few mV. Major contributor is K+.
When Na+ channels open, Na+ enters the cell because?
Electrical and concentration gradients push it in.
What makes a cell depolarise?
External stimuli acting on specific sets of ion channels. Threshold is -55mV.
What are EPSP’s and IPSP’s?
EPSP’s make a cell fire an AP. IPSP’s stop the cell reaching threshold.
What are the 4 main properties of graded potentials?
Decremental (only useful over short distances), electrotonic, non-propagated and local. They can also summate and are depolarising/hyperpolarising.
Give examples of graded potentials.
Generator potentials at sensory receptors. Post-synaptic potentials at synapses. End-plate potentials at NMJ. Pacemaker potentials at pacemaker tissues. These all determine whether an AP will be fired.
Does the strength of the stimulus have an effect on the graded potential?
Yes. Strength is encoded in amplitude. More neurotransmitter, for example, will make a bigger potential.
Give 2 examples of IPSP’s hyperpolarising a cell.
A neurotransmitter binds to the Cl- ion channel (ionatropic receptor). Cl- flows in and the cell becomes more negative. This is a fast IPSP. K+ is a metabotropic receptor. If more K+ channels are opened K+ flows out which makes the cell more negative. This is a slow IPSP.
Give 2 examples of EPSP’s depolarising a cell.
A fast EPSP is to open channels permeable to Na+ and K+. More Na+ gets in than K+ gets out. A slow EPSP is to block leaky K+ channels.
What is the difference between ligand-gated and voltage-gated ion channels?
Ligand-gated are when neurotransmitters bind to ion channels to open or close them. Voltage-gated are when the membrane potential depolarises and this opens ion channels like AP’s.
What is the difference between temporal and spatial summation?
Summation is when graded potentials add on to each other. Temporal is when one EPSP occurs and a second occurs shortly after. Spatial is the same effect but for more than 1 neuron. Temporal and spatial summation always occur together. This is synaptic integration and it decides whether or not a cell will fire an AP.
What happens when the cell reaches threshold (-55mV)?
There is a sudden massive depolarisation that shoots up to +30mV then rapid repolarisation beyond resting level. This is the action potential.
What is the ionic basis of the AP?
When a cell reaches threshold, voltage-dependent Na+ channels open and Na+ floods as there is a massive increase in permeability. Then repolarisation occurs when K+ permeability rises and K+ channels slowly begin to open. This causes hyperpolarisation. Eventually they shut and RMP returns to normal.
What is the refractory period?
The period immediately after an AP has been fired when no matter how much depolarisation occurs, another AP cannot be fired as ion channels need to rest.
