Coordination

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  • Created by: r98
  • Created on: 22-03-16 16:34
What are the two main forms of communication in mammals?
The nervous system and the hormonal system.
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How does the nervous system stimulate their target cells?
By secreting neurotransmitters directly on to them.
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What are the responses produced from the nervous system like?
Short-lived and restricted to a localised region of the body.
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How does the hormonal system stimulate cells?
By producing chemicals (hormones) which are transported in the blood plasma to their target cells.
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How can the response produced by the hormonal system be described?
Long-lasting and widespread.
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What are chemical mediators?
Chemicals that are released from certain mammalian cells and have an effedt on cells in their immediate vicinity.
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What do plant growth factors do and how are they different to animal hormones?
They exert their influence by affecting growth. They differ to animal hormones because they're made by cells located throughout the plant rather than in a particular organ and some plant growth factors affect the tissues that release them.
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How does indoleacetic acid (IAA) affect plant cells?
Causes plant cells to elongate.
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What part of the plant produces IAA?
Cells in the tip of the shoot.
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Where is the IAA then transported to?
It's transported down the shoot.
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How does light affect the movement of IAA?
It causes the movement of IAA from the light side to the shaded side of the shoot.
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How does this build up of IAA on the shaded side affect the plant?
As IAA causes cells to elongate, the higher concentration on the shaded side means that these cells will elongate more. So, the shaded side of the shoot grows faster causing it to bend towards the light.
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What are neurones?
(Nerve cells) are specialised cells adapted to rapidly carrying electrochemical changes, nerve impulses, from one part of the body to another.
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What is a mammalian neurone made up of?
A cell body, dendrons, axon, Schwann cells, myelin sheath and nodes of Ranvier.
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What does the cell body of a neurone contain and what does it produce?
It contains a nucleus and large amounts of rough endoplasmic reticulum. It's associated with the production of proteins and neurotransmitters.
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What are dendrons and what do they do?
They're small extensions of the cell body, they subdivide into smaller branched fibres, dendrites, that carry nerve impulses towards the cell body.
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What is the axon and what does it do?
It's a single long fibre that carries nerve impulses away from the cell body.
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What's the role of the Schwann cells?
Surround the axon, protecting it and providing electrical insulation. They also carry out phagocytosis and play a part in nerve regeneration. They wrap themselves around the axon many times, which builds up the layers of their membranes.
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What is the myelin sheath and what's its role?
It's made up of the membranes of Schwann cells and contain a lot of the lipid myelin. It forms a covering to the axon.
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What ade neurones with a myelin sheath called?
Myelinated neurones.
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What are neurones without a myelin sheath called?
Unmyelinated neurones.
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Which transmit nerve impulses faster, myelinated or unmyelinated neurones?
Myelinated neurones transmit nerve impulses faster.
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What are nodes of Ranvier?
Gaps between adjacent Schwann cells where there is no myelin sheath. The gaps are 2-3um long.
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What are the 3 types of neurone?
Sensory, motor & intermediate.
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Which type of neurone has one dendron that carries the impulse towards the cell body and one axon that carries it away from the cell body?
Sensory neurone.
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What does a sensory neurone do?
Transmits nerve impulses from a receptor to an intermediate or motor neurone.
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What does a motor neurone do?
Transmits nerve impulses from an intermediate or sensory neurone to an effector.
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Which type of neurone has a long axon and many short dendrites?
Motor neurone.
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What does an intermediate neurone do?
Transmits impulses between neurones (e.g. sensory to motor neurones).
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What's the definition of a nerve impulse?
A self-propagating wave of electrical disturbance that travels along the surface of the axon membrane. It's a temporary reversal of the electrical potential difference across the axon membrane.
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Between what two states is the temporary reversal of electrical potential difference?
The resting potential and the action potential.
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How is the movement of sodium ions and potassium ions across the axon membrane controlled?
By the phospolipid bilayer, which prevents Na+ and K+ ions diffusing across it, and the use of intrinsic proteins.
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Where are intrinsic proteins found?
In the phospholipid bilayer.
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How do intrinsic proteins control the movement of Na+ and K+ ions?
They contain channels (ion channels), some of which have 'gates', these can be opened or closed. There are different 'gated' channels for Na+ and K+ ions. Some channels remain open all the time so these ions can diffuse through them unhindered.
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In what other way do intrinsic proteins control the movement of Na+ and K+ ions?
Some actively transport K+ ions into the axon and Na+ ions out of the axon. This process is called a sodium-potassium pump.
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How can you describe the inside of the axon, in terms of charge?
Negatively charged relative to the outside.
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What is the value of this negative charge and what is it know as?
It's known as the resting potential and ranges from -50 to -90 mV but is usually -65mV.
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What does mV stand for?
millivolts.
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When the axon is at ~65mV, how can the axon be described?
The axon is said to be polarised.
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What is the potential difference?
The difference in charge between the inside and the outside of the axon.
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During the establishment of the potential difference, what is the role of the sodium-potassium pumps?
The sodium-potassium pumps actively transport Na+ ions out of the axon & actively transport K+ ions into the axon.
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Which is greater, the active transport of sodium ions or potassium ions?
Na+ ions is greater. 3 sodium ions move out for every 2 potassium ions that move in.
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What is the distribution of sodium and potassium ions in the tissue fluid surrounding the axon and in the cytoplasm?
More Na+ ions in the tissue fluid than in the cytoplasm of axon. More K+ ions in the cytoplasm than in the tissue fluid.
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What does the distribution of Na+ and K+ ions create?
A chemical gradient.
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What starts to naturally happen, in relation to Na+ ions and K+ ions?
Na+ ions begin to diffuse back into the axon & K+ ions begin to diffuse back out of the axon.
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When the Na+ and K+ ions start to diffuse back in, through what do they travel?
Through sodium and potassium 'gates' that are permanently open. NOT through the phospholipid bilayer as this doesn't allow diffusion of these ions.
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Are the 'gates' open or closed during this time?
Most K+ ion 'gates' are opend while most 'gates' that allow Na+ ions to move through are closed.
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The axon membrane is 100 times more permeabl to K+ ions, what does this suggest about diffusion rates? How does this affect the potential difference?
K+ ions diffuse back out of the axon faster than Na+ ions diffuse back in. Potential difference between negative inside and positive outside of axon is further increased.
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Apart from a chemical gradient, what other type of gradient is there?
An electrical gradient
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How is the electrical gradient established?
As more K+ ions diffuse out of axon , the outside of axon becomes more and more positive. So further outward movement of potassium ions becomes difficult. They're attracted to the overall -ve state inside axon, so they move in.
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During the establishment of the electrical gradient, how does the tissue fluid affect the movement of K+ ions?
The tissue fluid is in a +ve state, so it repels the K+ ions which prevents them from moving out of the axon.
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What happens at the end of the establishment of the potential difference?
An equilibrium is established so chemical and electrical gradients are balanced & there's no net movement of ions.
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What happens to the charges on the axon membrane when a stimulus is received e.g by a receptor?
It's energy causes a temporary reversal of the charges on the axon membrane. So the charge of -65mV inside the membrane becomes +40mV.
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What is the temporary reversal of charges on the axon membrane known as? In this condition how can the axon membrane be described?
The action potential. The membrane is said to be depolarised.
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Why does depolarisation occur?
The channels in the axon membrane change shape, they open or close depending on the voltage across the membrane. They are therefore called voltage-gated channels,
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How does hyperpolarisation occur?
Temporary overshoot of electrical gradient due to outward diffusion of K+ ions. Inside of axon more negative (relative to outside) than usual.
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How does the axon become repolarised?
Gates on potassium ion channels close, sodium-potassium pumps, pump Na+ ions out and K+ ions in, resting potential (-65) is re-established.
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Does the size of the action potential change from one end of the axon to the other?
No, it remains the same.
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What does thw fatty sheath of myelin around the axon act as?
As an electrical insulator, preventing action potentials from forming.
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What are the 'breaks' in the myelin insulation called?
Nodes of Ranvier.
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Where can action potentials occur in a myelinated axon?
At the nodes of Ranvier.
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What is saltatory conduction?
The process of an action potential 'jumping' from node to node.
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What is the transmission of the action potential along the axon of a neurone known as?
The nerve impulse
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What factors affect the speed at which an action potential travels?
The myelin sheath, the diameter of the axon, temperature.
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How does the diameter of the axon affect the speed at which the action potential passes along the axon?
The bigger the diameter of the axon, the faster the speed of conductance. Due to less leakage of ions from a large axon.
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How does temperature affect the speed at which the action potential passes along the axon?
It affects rate of diffusion of ions, so higher the temperature the faster the nerve impulse. The energy for active transport comes from respiration, respiration (like the sodium-potassium) is controlled by enzymes, which work faster at higher temps.
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What happens to impulses if the temperature gets too high?
Enzymes and the plasma membrane proteins are denatured & impulses fail to be conducted.
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What is the refractory period?
The period after an action potential has been created, when inward movement of sodium ions is prevented due to the voltage-gated channels being closed. During this time it's impossible for another action potential to be generated.
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What are the purposes of the refractory period?
It ensures that an action potential is propagated in one direction only, it produces discrete impulses & it limits the number of action potentials.
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Why can nerve impulses be described as all-or-nothing responses?
There's a certain level of stimulus (threshold value) that must be exceeded to trigger an action potential. Any stimulus below the threshold value will fail to generate an action potential.
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How can an organism perceive the size of a stimulus?
By the number of impulses passing in a given time, larger stimulus = more impulses generated. By having different neurones with different threshold values.
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What's a synapse?
The point where an axon of one neurone connects to the dendrite of another or with an effector.
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What chemicals do synapses use to transmit impulses frok one neurone to another?
Neurotransmitters.
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What are neurones seperated by?
The synaptic cleft (a small gap) 20-30nm wide.
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What is the neurone that releases the neurotransmitter called?
The presynaptic neurone.
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What is the swollen portion of the end of the presynaptic neurone called?
The synaptic knob.
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What does the synaptic knob possess?
Many mitochondria and large amounts of endoplasmic reticulum.
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Why does the synaptic knob possess mitochondria and endoplasmic reticulum?
To manufacture the neurotransmitter.
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Where is the neurotransmitter stored?
In the synaptic vesicles.
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What does the postsynaptic neurone have to receive the neurotransmitter?
Receptor molecules on its membrane.
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By acting as a junction, the synapse can allow a single stimulus to create a number of simultaneous responses, how?
A single impulse along one neurone can be transmitted to a number of different neurones at a synapse.
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By acting as a junction, a synapse can allow stimuli from different receptors to interact in order to produce a single response, how?
A number of impulses can be combined at a synapse.
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When is the neurotransmitter released into the synapse?
When an action potential reaches the synaptic knob.
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How is a new action potential set up in the postsynaptic neurone?
The neurotransmitter binds with the receptor molecules.
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What are 3 features of a synapse?
Unidirectionality, summation & inhibition.
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With reference to synapses, what does unidirectionality mean?
Synapses can only pass impulses in one direction: from presynaptic neurone to postsynaptic neurone.
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With reference to synapses, what is summation?
The build-up of neurotransmitters in the synapse.
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What are the two methods of summation?
Spatial summation and temporal summation.
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What is spatial summation?
Many different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of postsynaptic neurone.
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What is temporal summation?
A single presynaptic neurone releases neurotransmitter many times over a short period. A new action potential is triggered if the total amount of neurotransmitter exceeds the threshold value of postsynaptic neurone.
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Why are some synapses called inhibitory synapses?
On the postsynaptic membrane of some synapses the protein channels carrying Cl- ions can be made to open, leading to an inward diffusion of chloride ions. This makes the inside of the postsynaptic membrane even more negative (hyperpolarisation).
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By being hyperpolarised, how do inhibitory synapses affect the probability of a new action potential being created?
Hyperpolarisation makes it less likely that a new action potential will be created.
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What is the name given to a synapse in which the neurotransmitter is acetylcholine?
Cholinergic synapse.
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What is acetylcholine made up of?
Acetyl (ethanoic acid) & choline.
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Where are cholinergic synapses common?
In vertebrates, occurring in the CNS and at neuromuscular junctions.
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What is the first of the main ways that drugs act on synapses?
They stimulate the nervous system by creating more action potentials in postsynaptic neurones.
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How does a drug create more action potentials in the postsynaptic neurone?
By mimicking a neurotransmitter, stimulating the release of more neurotransmitter or inhibiting the enzyme that breaks down the neurotransmitter. This enhances the body's responses to impulses passed along the postsynaptic neurone.
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What's an example of the first way a drug acts on synapses?
If the neurone transmits impulses from sound receptors, a person will perceive the sound as being louder.
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What is the second of the two main ways in which a drug acts on synapses?
They inhibit the nervous system by creating fewer action potentials in postsynaptic neurone.
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How does a drug create fewer action potentials in postsynaptic membrane?
By inhibiting the release of neurotransmitter or blocking receptors on sodium/potassium ion channels on postsynaptic neurone. This reduces the body's responses to impulses passed along the postsynaptic neurone.
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What's an example of the second way a drug acts on synapses?
If the neurone transmits impulses from sound receptors, a person will perceive the sound as being quieter.
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What are endorphins?
Neurotransmitters used by certain sensory nerve pathways, especially pain pathways.
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What do endorphins do?
Block the sensation of pain by binding to pain receptor sites.
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What's the effect of drugs, such as morphine & codeine, on the body?
They will reduce pain, as they act like endorphins, preventing action potentials being created in neurones of pain pathways.
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What is serotonin?
A neurotransmitter involved in the regulation of sleep and certain emotional states.
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What causes the synaptic vesicles to fuse with the presynaptic membrane in a cholinergic synapse?
The influx of calcium (Ca2+) ions.
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What do acetylcholine molecules fuse with?
Receptor sites on the sodium ion channels in the membrane of the postsynaptic neurone.
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What happens to acetylcholine after it has binded to the receptor sites?
It's hydrolysed, by acetylcholinesterase, back into choline and ethanoic acid (acetyl).
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What's used to recombine choline and ethanoic acid?
ATP released by mitochondria.
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What happens to sodium ion channels in the absence of acetylcholine in the receptor sites?
They close.
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Comments

Emilija

OMG SO GOOD I CANT EVEN

Ciara26

Omg thankyou r98! I used these to revise for my mocks and I got a D!! Two grades above my target grade! :D 

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