73187
Description
Flashcards by reynoldslaura, updated more than 1 year ago
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Created by reynoldslaura
almost 11 years ago
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| Question | Answer |
| What is the 'receptive field' of a sensory neuron? | The region that when stimulated affects the discharge of that neuron |
| What is intensity coding? | It is the way of telling your brain how strong a stimulus is in an 'all or nothing' A.P. It can be done via increasing the freq. of an A.P or increasing the no. of sensory units activated |
| What is adaptation? | It is the decline in frequency of action potential discharge with time despite a maintained stimulus of constant strength (e.g. getting used to a smell) |
| What are phasic receptors and give an example? | They are receptors that are rapidly adapting e.g. pacinian corpuscles (if you sit down , your bum quickly forgets its being squished) |
| Give an example of a tonic receptor | A noicireceptor (pain receptor) - if you burn yourself it hurts for ages! |
| According to the Nerst equation, what is the K⁺ equilibrium potential? | -90mv |
| According to the Nerst equation, what is the equilibrium potential for Na⁺? | +70mv (however the membrane potential rarely reaches this- usually +30mv- as after 1ms a peak of depolarisation is reached and repolarisation takes over) |
| Is conductance faster in a wider or thinner axon and why? | Conductance is faster in a wider axon because they have less internal resistance |
| Where are nodes of ranvier found? | At intervals of 0.2-2mm along the nerve fibre |
| Define accomodation. | This is when a nerve or muscle is depolarised slowly or for a long period of time so that the threshold increases. This means that an action potential may fail to be produced |
| What is a 'compound action potential '? | It is the sum of the potential changes occurring as the action potentials propagate down a whole nerve |
| Where are action potentials generated from? | The axon hillock |
| What is the extracellular volume chlorine in mm/L | 114 |
| Why can an action potential never be generated in an absolute refractory period despite massively increasing the stimulus? | Because the majority of the sodium ion channels are in their 'inactive state' therefore they don't have the potential to reopen and cause depolarisation until they are in their 'closed state' |
| Can an action potential be created in the relative refractory period? | Yes, provided there is a larger than normal stimulus |
| How does tetrodoxin work as a poison? | It specifically blocks Na⁺ channels by binding to their extracellular side thus depolarisation cannot occur and action potentials cannot be generated - death! |
| What does tetraethylammonium (TEA⁺) do? | It blocks K⁺ ion channels by preventing them from opening therefore the repolarisation phase of the action potential takes much longer and there is no hyperpolarisation phase |
| What is an excitable cell? | A cell that can fire an action potential. It involves rapid alteration in the potential of a portion of the membrane from -70 to +30 mv |
| What are the three factors that affect membrane permeability? | 1. Binding of specific chemical messengers to receptors in the cell membrane 2. Distortion of the membrane 3. Changes in the membrane potential |
| What two things can affect the membrane potential? | The permeability of an ion across the membrane and the concentration difference of either side of the membrane of that ion |
| Define depolarisation. | When a cell becomes +ve inside with respect to the outside |
| Why does hyperpolarisation occur in a normal action potential? | Because the K⁺ channels are slow to close resulting in some of them still open despite going past the resting potential |
| What is the intracellular concentration of chlorine (mm/l) | 3 |
| What is the extracellular volume of sodium in mm/L? | 145 |
| What is the intracellular volume of potassium in mm/L | 150 |
| What is the extracellular volume of potassium in mm/L? | 4 |
| What is the intracellular volume of sodium in mm/L | 20 |
| What is the Nerst equation used for? | It is used to determine whether or not an ion is in equilibrium or not and if not it gives a prediction of the direction of net flow of the ion (only takes into account the presence of one ion) |
| What equation can we use to determine the resting potential of a cell? | The Goldman-Hodgkin-Katz equation. It takes into account concentrations of K⁺, Na⁺ and Cl¯ (should be -70mv) |
| In what three ways can neurotransmitters be removed from the synaptic cleft? | 1. broken down via an enzyme e.g. acetylcholinesterase 2. Active re uptake - neurotransmitter is pumped back into the pre-synaptic terminal 3. Active uptake by glial cells |
| What enzymes break down noradrenaline? | Mononamine oxidase and COMT (catechol-o-methyl transferase) |
| Name two excitatory post- synaptic neurotransmitters. | Acetylcholine and glutamic acid |
| Name two inhibitory post synaptic neurotransmitters | GABA and glycine |
| What happens with the generation of an inhibitory post-synaptic potential? | One of the inhibitory neurotransmitters glycine or GABA will bind causing chloride channels to open and chlorine release into the cell causing hyperpolarisation - no A.P can be fired |
| When can an action potential be fired with an inhibitory neurotransmitter? | When another neuron submits an excitatory neurotransmitter on the same neuron as the inhibitory one, in a greater quantity so the hyperpolarisation is overcome. |
| Describe spatial summation. | A number of different presynaptic neurones work together to release enough neurotransmitter to exceed the threshold value in the post synaptic neuron |
| Describe temporal summation. | A single presynaptic neurone releases neurotransmitter many times over a short period of time to increase the amount of neurotransmitter in the synaptic cleft- inc. threshold |
| What type of reflex is a stretch reflex? | A monosynaptic one |
| Give an example of a polysynaptic reflex? | A flexor crossed extensor reflex (occurs in response to treading on a painful stimulus) |
| Where does the inhibitory pathway of a neuron always occur? | In the spinal cord! |
| What happens in a stretch reflex? | The patella tendon is tapped→picked up via receptor in extensor→message sent via afferent neurone (1a)→spinal cord→ message sent via efferent neurone to extensor (contracts)→inhibitory message sent to flexor muscle (relaxes) |
| Skeletal muscle is under what neuronal control? | Somatic nervous system |
| Smooth muscle, cardiac muscle and glands are under what nervous control? | Autonomic nervous system |
| What receptors are found on the pre ganglionic nerve fibres in the parasympathetic division in the ANS? | Nicotinic (a ligand gated ion channel) |
| What receptors are found on the post ganglionic nerve fibres in the parasympathetic nervous system in the ANS? | Muscarinic (a G protein coupled receptor) |
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