Topic 8 - Grey Matter

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The iris contains pairs of antagonistic muscles, that control the size of the iris. What are these muscles called?
Radial and Circular muscles.
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When the pupil is dilated, what is happening to the radial and circular muscles?
The radial muscles are contracting, whilct the circular muscles are relaxed.
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Define Photoperiodism and Phototrophism.
Photoperiodism: The germination of plants in response to chnges in day length. Phototrophism: Growth responses in plants where the direction of growth is determined by the direction of external stimuli.
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What is the name of the photoreceptor involved in photoperiodism? What forms can it take?
A blue-green pigment, known as phytochrome. An inactive form, Pr, and an active form, Pfr.
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Active Pfr is thought to trigger a range of photoperiodic responses, how can one form of the photoreceptor convert to the other?
When Pr recieves natural, or red, light, it is converted to Pfr. In the dark, Pfr is convrted back into Pr, as it is relatively unstable. Exposure to far red light may also trigger this conversion.
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What does the plant hormone, or growth substnce, Auxin do?
Causes cell elongation.
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Compare the speeds of the nervous system in mammals, the endocrine system in mammals and tropisms in plants.
The nervous system transmits electrical impulses, meaning it is rapid acting. By comparison, the two chemical systems are slower acting.
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What features do all neurones have in common?
All neurones, or nerve cells, have a cell body (which contains the nucleus and most of the cells organelles), dendrites, which conduct impulses towards the cell body and an axon, which does the opposite, conducting them away from the cell body.
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Most vertebrate neurones have a fatty insulating layer knwon as the myelin sheath. What benefit does this have?
The myelin sheath, which is wrapped around the axon, increases the speed of transmission of impulses, through a process known as saltatory conduction. In saltatory conduction, Action potentials jump between nodes of ranvier, or gaps in the sheath.
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Because in a resting neurone, there are more Sodium ions outside the cell and more Potassium ions inside it, the inside of the cell is more negatively charged than its outside. What is this difference in charge known as?
The potential difference, or resting potential. It is around -70mv.
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If the membrane of a neurone is stimulated, voltage dependent ion channels open, and Sodium ions from outside the cell flow in. What effect does this have?
The positive charge inside the cell increases, reversing the charge across the membrane. The potential difference of the membrane is now around +40mv and an action potential has been established.
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Straigh after an action potential has been formed, there is a short refractory period, in which a new action potential cannot be formed. How and why does this occur?
The Sodium ion channels cannot reopen. This ensures action potentials pass along as seperate signals and are unidirectional.
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What is the name given to the area at which two neurones meet?
A synapse, or synaptic cleft.
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Explain the process by which a signal is transmitted across a synapse, upto the release of neurotransmitter into the synaptic cleft. 1) An action potential arrives...
2) The presynaptic membrane depolarises. Calcium ion channels open and allow calcioum ions to enter. 3) These ions cause synaptic vesicles, which conatin neurotransmitter to fuse with the membrane. 4) Neurotransmitter is released into the cleft.
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What happens once neurotransmitter has been released into the cleft?
1) It binds with receptors on the postsynaptic membrane. Cation channels open, allowing sodium ions to flow in. The membrane depolarises and another action potential is triggered.
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What happens to the neurotransmitter?
Some is reabsorbed by the presynaptic membrane, the rest either diffuses away or is broken down.
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Define receptors.
Specialized cells able to detect stimuli.
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Human eyes have two types of photoreceptor cells, found in the retina on the back of the eye. What are they and wht do they do?
Rod and Cone cells. Cones allow clolur vision in bright light. Rod cells provide only black and white vision, but are more sensitive than cones and can work in darker conditions.
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There are five main areas of the brain, name them.
Frontal lobe, Parietal lobe, Occipital lobe, Cerebellum and Temporal lobe.
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What is the name of the area of the brain which controls heart rate, breathing and blood pressure?
Medulla Oblongata.
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What are critical windows? Periods of time where it is thought that the nervous system needs specific stimuli in order to develop properly?
Periods of time where it is thought that the nervous system needs specific stimuli in order to develop properly.
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What would happen if an eye were deprived of light during a critical window?
1) Axons would not pass nerve impulses to cells in the visual cortex. 2) Inactive synapses would be eliminated. 3) Eye has no working connection between itself and the visual cortex.
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What is habituation?
The loss of a response to a repeated stimulus, which fails to provide any form of reinforcement or reward.
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What is Parkinsons disease and how is it caused?
Parkinsons is a disease associated with the control of movement and emotional responses. It is caused by a shortage of dopamine, which is the rpoduct of a depleted supply of dopamine secreting neurones in the brain.
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Name three symptoms of Parkinsons.
Muscle tremors, stiffness of muscles, poor balance and walking problems, difficulties with speech and breathing and depression.
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Many drugs affect the nervous system by interfering with the normal functioning of synapses. For example ecstasy works by preventing the reuptake of serotonin. Describe how this may occur.
Some drugs, such as L-Dopa affect the synthesis or storage of neurotansmitter. Some drugs may affect the release of this neurotransmitter. Some drugs affect the interaction between neurotransmitters and the postsynaptic membrane.
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Several imaging techniques are useful in medical diagnosis and investigating brain structure and function. Name three of these processes.
MRI, fMRI and CT or CAT scanning.
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MRI uses a magnetic field and radio waves to make images of soft tissues like the brain. fMRI is an adaptation of this process. Explain how it works.
fMRI, or functional magnetic resonance imaging allows us to see the brain in action during live tasks by detecting the uptake of oxygen in active brain areas.
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Why are CT scan not as good as fMRI scans?
They can only capture standalone images, meaning they display on stractures and damage, rather than function. They have worse resolution and also use harmful X-Rays.
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What was the purpose of the human genome project?
To determine the base sequence of all the DNA of humans.
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What are some potential concerns of the use of GMOs or genetically modified organisms?
Genetic pollution - Transfer of their genes to natural, wild species. They may not produce fertile seed, meaning farmers must buy new seeds every time they plant a crop, which is very expensive. GM crops may become herbicide resistant super weeds.
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Other cards in this set

Card 2

Front

When the pupil is dilated, what is happening to the radial and circular muscles?

Back

The radial muscles are contracting, whilct the circular muscles are relaxed.

Card 3

Front

Define Photoperiodism and Phototrophism.

Back

Preview of the front of card 3

Card 4

Front

What is the name of the photoreceptor involved in photoperiodism? What forms can it take?

Back

Preview of the front of card 4

Card 5

Front

Active Pfr is thought to trigger a range of photoperiodic responses, how can one form of the photoreceptor convert to the other?

Back

Preview of the front of card 5
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