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Flashcards by Nicola Lines, updated more than 1 year ago
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| Question | Answer |
| Describe the nervous system | Uses nerve cells to pass electrical impulses; Secrete chemical (neurotransmitters) directly onto target cells; Rapid communication; Short lived effect; Restricted to localised regions |
| Describe the hormonal system | Produces chemical (hormones) that are transported in the blood to target cells; Slower communication; Long lasting effect; Widespread |
| What is a chemical mediator? | Chemical released by certain cells which have an effect on cells in their immediate vicinity |
| Give two examples of chemical mediators: | Histamine and Prostaglandins |
| Histamine a) Where is it stored? b) When is it released? c) What is its effect? | a) Stored in the white blood cells b) Released following injury or in a response to an allergen c) Causes dilation of arteries and arterioles and increased permeability of capillaries leading to swelling |
| Prostaglandins a) Where are they found b) When are the released? c) What effect do they have? | a) Found in the cell membranes b) Released following injury c) Cause dilation of arteries and capillaries, increasing the permeability of capillaries also affect blood pressure and neurotransmitters, in doing so affect pain sensation |
| What are plant growth factors and what do they respond to? | Plant hormones which respond to external stimuli; exerting their influence by effecting growth; made by cells throughout the plants; affecting the tissues which release them |
| How does the plant growth hormone IAA cause a shoot to bend towards the light? | Cells in tip produce IAA; transported down the shoot; IAA initially transported to all sides as it begins to move down the shoot; light causes the movement of IAA from light side to shaded side; IAA causes elongation of cells, so shaded side elongates the most; shaded side grows more/faster to shoot mends towards light |
| What are neurones? | Specialised cells adapted to rapidly carry electrochemical changes called nerve impulses |
| Describe the following structures, that make up a mammalian neurone: a) Cell body b) Dendrons | a) Contains a nucleus and endoplasmic reticulum; associated with protein and neurotransmitter production b) Small extentions of the cell body which extend into dendrites; carry nerve impulses towards the cells body |
| Describe the following structures, that make up a mammalian neurone: a) Axon b) Schwann cells | a) Single long fibre which carries impulses away from the cell body b) Cells which surround the axon, wrapping around it many times; provide protection and electrical insulation; carry out phagocytosis and nerve regeneration |
| Describe the following structures, that make up a mammalian neurone: a) Myelin sheath b) Nodes of Ranvier | a) Made up of schwann cell membranes, which are made of the lipid 'myelin' b) Gaps between adjacent Schwann cells where there is no myelin sheath |
| Describe the structure of a sensory neurone | One dendron which carries impulses to the cell body; one axon that carries impulses away from the cell body |
| What is the function of a sensory neurone? | Transmits nerve impulses from a receptor to an intermediate or motor neurone |
| Describe the structure of a motor neurone | One long axon with numerous short dendrites |
| What is the function of a motor neurone? | Transmits nerve impulses from an intermediate or sensory neurone to an effector |
| Describe the function of an intermediate neurone | Have numerous short processes; Transmit impulses between neurones, for example from a sensory neurone to a motor neurone |
| What is a nerve impulse? | A self propagating wave of electrical disturbance that travels along the surface of the axon membrane; Temporary reversal of the electrical potential difference across the axon membrane |
| Describe how sodium and potassium can be transported across the phospholipid cell membrane | The phospholipid bilayer prevents ion diffusion; Intrinsic 'gated' channel proteins Sodium/potassium active transport pumps |
| What is a resting potential? | When the axon is polarised, the inside of the axon is negatively charged relative to the outside of the axon; with a voltage of approximately 65mv |
| How is the resting potential maintained? | Na+ actively transported out of the axon and K+ actively transported into the axon by the Na+/K+ pump; Transport of Na+ is greater than that of the K+, 3Na+ out for every 2K+ in; More Na+ outside axon than K+ in the axons = chemical gradient; Na+ and K+ diffuse in/out of the axon, however membrane 100 times more permeable to K+ than Na+ so K+ diffuses back out faster further increasing potential difference; Outside the axon becomes more positive further outward movement of K+ is hard becomes difficult due to like charges opposing = electrical gradient; Equilibrium is established in which the chemical and electrical gradients are balanced = no net movement of ions |
| What is an action potential? | Temporary reversal of the charges of the axon membrane; Negative charge inside the membrane becomes a positive charge; Positive charge outside the membrane becomes negative |
| How does a stimulus cause an action potential? | Energy from the stimulus causes some Na+ gates to open; Na+ diffuses into the axon along its electrochemical gradients, triggering a reversal in the potential difference across the membrane; As Na+ diffuses into the axon more Na+ gates open resulting in further influx of Na+ ions; Once an action potential of +40mv has been established Na+ gates close and K+ gates open; When K+ gates open the electrical gradient is reversed, causing more K+ gates to open and so more K+ diffuses out out; Causing repolarisation of the axon; Outward diffusion of K+ causes temporary overshoot of the electrical gradient = hyperpolarisation; the inside is more (too) negative; K+ gates close and Na+/K+ pumps start again reestablishing resting potential |
| Generally describe the movement of an action potential down an unmyelinated axon | As one region of the axon produces an action potential and becomes depolarised it acts as a stimulus for the depolarisation of the next region of the axon, in the meantime the previous region is repolarised |
| How does a localised electric circuit propogate the depolarisation (caused by an action potential) down an unmyelinated neurone? | Stimulus causes sudden influx of Na+ ions and hence a reversal of charge on the axon membrane - this is the action potential and the membrane has been depolarised; The localised electic circuits established by the inglux of Na+ ions causes the opening of sodium channels further along the axon; Outward movement of K+ has continued to the extent that the axon membrane behind the action potential has returned to its original state = repolarised; Repolarisation of the axon allows sodium ions to be actively transported out, once again returning the axon to its resting potential in readiness for a new stimulus. |
| How does an action potential travel down a myelinated neurone? | Fatty sheath acts as an electrical insulator; Action potentials only occur at nodes of ranvier; Action potential 'jump' from node to node by saltatory conduction |
| What three factors affect the speed of the action potential? | Myelin sheath; Diameter of the axon Temperature |
| How does the myelin sheath increase the speed of a nerve impulse? | Acts as an electrical insulator; Action potential jumps from node of ranvier to node by saltatory conduction |
| How does the diameter of the axon increase the speed of the nerve impulse? | Greater the diameter the faster the speed of conductance; Less leakage of ions from a large axon (leakage mkaes the membrane potentials harder to maintain) |
| How does temperature affect the speed of a nerve impulse? | Affects the rate of diffusion of ions; Higher temperature faster nerve impulses; At very high temperatures enzymes needed for respiration are denatured so no ATP is produced for the K+/Na+ active transport pumps so no impulses are conducted at all |
| What is the refractory period? | Period after an action potential when inward movement of Na+ ions is prevented as the 'voltage gated' intrinsic channel proteins are closed |
| What three purposes does the refractory period serve? | Ensure propagation is in one direction only - AP can only pass from an active to a resting region; Produces discrete impulses - a new AP cannot be formed immediately behind the first one Limits the number of action potentials that can pass along a neurone at any one time |
| What is the all-or-nothing principle? | A certain level of stimulus, called the threshold value, is required to produce an action potential; Below the threshold value no AP is produced; Any stimulus above the threshold value will produce one AP |
| Describe the function of a synapse | To transmit impulses from one neurone to another |
| What is meant by the term 'unidirectionality'? | Impulses can only travel from the presynaptic neurone to the postsynaptic neurone ie. in one direction |
| Why is summation often necessary in order to produce an impulse in the postsynaptic neurone? | Low frequency action potentials often produce insufficient amounts of neurotransmitter to reach the threshold potential and hence trigger an impulse in the postsynaptic neurone |
| What are the two types of summation? | Spatial and Temporal |
| What is spatial summation? | Multiple neurones combine at a synapse, Only when both presynaptic neurones carry impulses and hence release neurotransmitter is an action potential in the postsynaptic neurone triggered |
| What is temporal summation? | One neurone transmits an impulse to another; High frequency action potentials are required to produce the high amount of neurotransmitter required to reach the threshold potential and so produce an action potential in the postsynaptic membrane |
| What is a cholinergic synapse? | Neurotransmitter = acetylcholine |
| What does the opening of calcium ion channels cause? | An action potential causes calcium (Ca2+) ion channels to open; Ca2+ ions enter the synaptic knob; Ca2+ causes synaptic vesicles to fuse with the presynaptic membrane - releasing acetylcholine into the synaptic cleft; Acetylcholine diffuses across the synaptic cleft; |
| How does the acetylcholine trigger an action potential in the postsynaptic neurone? | Fuses with receptor sites on the sodium ion channels on the postsynaptic membrane; Causing Na+ channels to open and Na+ to diffuse into the postsynaptic neurone along its concentration gradient; The influx of Na+ ions triggers an action potential |
| How is acetylcholine 'recycled' and what is the importance of this? | Enzyme acteylchoinesterase hydrolysis acteycholine into ethanoic acid (acety) and choline; Which diffuse across the synaptic cleft; Enter the presynaptic neurone; ATP used to put the ethanoic acid and the choline back together; In the absence of acetylcholine the Na+ channels close; Importance = prevent multiple or continuous action potentials being generates |
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