Topic 8 - Grey Matter Flashcards
1
Q
What is the nervous system divided into?
A
The central nervous system and the peripheral nervous system
2
Q
What does the central nervous system consist of?
A
- The brain
- The spinal cord
3
Q
What does the peripheral nervous system consist of?
A
- Sensory nerves which carry sensory information from the receptors to the central nervous system
- Motor nerves carrying the motor commands from the CNS to the effectors
4
Q
What is the peripheral nervous system subdivided into?
A
- The autonomic nervous system
- The somatic nervous system
5
Q
What are the characteristics of the autonomic nervous system?
A
- It is involuntary
- It stimulates smooth-muscle, cardiac muscle and glands
6
Q
What are the characteristics of the somatic nervous system?
A
- Voluntary
- Stimulates skeletal muscle
7
Q
What is the autonomic nervous system subdivided into?
A
- The sympathetic nervous system
- The parasympathetic nervous system
8
Q
What is the function of the sympathetic nervous system?
A
It prepares the body for fight or flight response (e.g. Speeds up heart rate)
9
Q
What is the function of the parasympathetic nervous system?
A
Prepared body for rest and digest
10
Q
What is the difference between a neurone and a nerve?
A
A neurone is a single cell whereas the nerve is a more complex structure containing a bundle of axons of many neurones surrounded by protective covering.
11
Q
What is the cell body of a neurone?
A
It contains the nucleus and cell organelles within the cytoplasm.
12
Q
What are the two types of thin extensions from the cell body of a neurone and describe their function?
A
- Dendrites - conduct impulses towards the cell body (very thin)
- The axon - A single long process, transmits impulses away from the cell body
13
Q
List the three types of neurones
A
- Motor neurones
- Sensory neurones
- Relay neurones
14
Q
What are motor neurones and what is the function?
A
These conduct impulses from the CNS to the effector (muscles or glands). The cell body is always situated within the central nervous system and the axon extends out. The axons of some motor neurones can be extremely long such as those that run the full length of the leg.
15
Q
What is the function of sensory neurones?
A
These carry impulses from sensory cells to the CNS.
16
Q
What is the function of relay neurones?
A
These are found mostly within the CNS. They can have a large number of connections with other nerve cells. Relay neurones are also known as connector neurones and as interneurones.
17
Q
What are motor neurones also known as?
A
Motor neurones are also known as effector neurones.
18
Q
What is the myelin sheath?
A
Fatty material which forms a layer round the axons in many
mammal neurones. It acts as an insulator.
19
Q
What is the importance of the myelin sheath in ensuring that nerve impulses pass quickly along the axon?
A
Myelin sheath only allows the electric currents which are set up by an action potential to flow at the gaps where no myelin is present. Nerve impulses therefore travel along myelinated axons in a series of jumps. This allows them to transmit impulses much faster than non-myelinated neurones.
20
Q
What is the myelin sheath made up of?
A
Schwann cells
21
Q
What are Schwann cells?
A
A cell that produces myelin, the fatty material that surrounds many axons in mammalian nerve cells. Each Schwann cell wraps round and round the axon forming a layer of myelin.
22
Q
What are simple nerve pathways known as?
A
Reflex arcs
23
Q
Define reflexes
A
Rapid, in voluntary responses to stimuli
24
Q
Describes a reflex arc including all the different receptors and neurones that are used
A
1) Stimulus- a change in the environment (usually outside body)
2) Receptor - Detects stimulus + generates an impulse
3) Sensory neurone - Carries impulse to the CNS along a Sensory Pathway.
4) Sensory neurone forms a synapse with a relay neurone.
5) Relay neurone - Carries impulse through the CNS. Connects Sensory neurone to motor neurone . Relay neurone forms a synapse with a motor neurone.
6) Motor neurone - Carries impulse away from CNS
7) Effector - Muscle or gland which produce a response
8) Response - Movement or releases hormone
25
What are the advantages of a reflex arc?
- Fast
- Reflex arcs do not require conscious thought
- They are protective responses to threat
- Minimum number of neurons to minimise the number of synapses
26
What are synapses?
A small gap between two neurones. A nerve impulse travels along the presynaptic neurone. When it arrives at the synapse, it causes small amounts of a chemical neurotransmitter to be released. The neurotransmitter diffuses across the synapse and produces a nerve impulse in the postsynaptic neurone. Synapses of the slowest parts of the nervous system as they rely on diffusion not electrical impulses.
27
What controls the size of the pupil?
The muscles of the iris.
28
What are the two types of muscles in the iris?
- Circular muscles
| - Radial muscles
29
How do the muscles of the iris respond to light?
The size of the pupil is controlled by the autonomic nervous system. The radial muscles are controlled by the sympathetic reflex which means when they contract and the circular muscles relax that the pupil dilates allowing increased light to be taken in. The circular muscles are controlled by the parasympathetic reflex and they contract while the radial muscles relax to decrease the amount of light coming into the eye.
30
What are photoreceptors?
A receptor cell which is stimulated by light and enables us to detects changes in our environment. In the human eye photoreceptors are contained in the retina. There are two distinct types, rods and cones.
31
What happens when high light levels strike the photoreceptors in the retina regarding the pupil size? Describe how the pupil size changes because of this.
High light levels striking the photoreceptors in the retina cause nerve impulses to pass along the optic nerve to a number of different sites within the CNS, including a group of coordinating cells in the midbrain. Impulses from the cells are sent along parasympathetic motor neurones to the circular muscles of the iris, causing them to contract. At the same time, the radial muscles relax. This constricts the pupil, reducing the amount of light entering the eye.
32
What is the resting potential?
The difference in electrical charge across the membrane of a resting neurone. When the inside of the axon is more negative than outside; the membrane is said to be polarised. The potential difference across the membrane is about –70 mV and this is known as the resting potential. This is due to the difference in permeability of the cell surface membrane to different ions which results in their uneven distribution.
33
Describe how a resting potential is formed and maintained.
1) The action of Na+/K+ pumps creates concentration gradients across the membrane. The pumps generate a high concentration of K+ (potassium ions) inside the cell and a high concentration of an Na+ (sodium ions)outside the cell.
2) Protein channels allow K+ ions to cross the membrane but not the Na+. K+ leaves the cell by facilitated diffusion, moving from a high concentration inside the cell to a low concentration through the protein channels outside the cell.
3) As the K+ leaves, the inside of the cell becomes more negatively charged due to the loss of positively charged ions relative to the outside.
4) The more potassium ions that the diffuse out of the cell, the larger the potential difference across the membrane. The increased negative charge created inside the cell as a consequence attracts potassium ions back across the membrane into the cell down an electrical gradient.
5) When the potential difference across the membrane is around -70mV, the electrical gradient exactly balances the chemical gradient. There is no net movement of potassium ions and hence a steady state exists maintaining the potential difference and -70mV.
34
Why is the axon resting potential - 70mV?
- The concentration gradient generated by the Na+/K+ pump
| - The electrical gradient due to the difference in charge for the two sides of the membrane resulting from K+ diffusion
35
What is the electrochemical equilibrium regarding the resting potential of an axon?
When the potential difference across the membrane of the axon is around -70 mV, the electrical gradient exactly balances the chemical gradient. There is no net movement of K+ and hence a steady state exists.
36
The sodium potassium pumps of the axon pump against the concentration gradient of the two ions. How is the energy supplied?
By the hydrolysis of ATP
37
Define depolarisation
When the potential difference across the neurone is reversed, making the inside of the axon more positive than the negative outside.
38
Define repolarisation
The return of the resting potential of -70mV.
39
Define action potential
A large change in the voltage across the membrane.
40
What are the three stages of an action potential?
1) depolarisation
2) Repolarisation
3) hyperpolarisation and the restoring of the resting potential
41
What occurs before the depolarisation phase of an action potential?
A stimulus
42
Explain the function of a stimulus for an action potential
A stimulus excites the neurone cell membrane. This causes sodium ion channels to open and therefore the membrane becomes more permeable to sodium. Sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This makes the inside of the neuron less negative.
43
Describe what happens during the depolarisation phase of an action potential.
As the sodium continues to move by facilitated diffusion more voltage dependent sodium channels open causing more sodium ions to diffuse into the neurone. Depolarisation increases at a threshold of around -55 mV. There is a higher concentration of sodium ions outside the axon, so sodium ions flow rapidly inwards through the voltage-dependent Na+ channels, causing a buildup of positive charge inside. The potential difference across the membrane reaches +40mV.
44
Describe what happens during the repolarisation phase of an action potential.
At a potential difference of around +30/40mV voltage dependent sodium channels close and the voltage dependent potassium ion channels open. As a result, the potassium ions move out of the axon down the electrochemical gradient. As potassium ions flow out of the cell, the inside of the cell once again becomes more negative than the outside.
45
Describe what happens during the hyperpolarisation and restoring of the resting potential phase of an action potential.
Voltage dependent potassium ion channels are slow to close, so there is a slight overshoot with too many potassium ions diffuse out of the neurone. The potential difference becomes more negative than the resting potential. Therefore the resting potential is re-established by the closing of the voltage-dependent potassium ion channels and potassium ions diffuse into the axon, through K+ channels.
46
What is the refractory period?
Following an action potential, the neurone cell can't be excited again straight away. This is because the ion channels are recovering and they can't be made to open.
47
Explain how the impulse passed along an axon (wave of depolarisation -> non-myelinated)?
1) At resting potential there is a positive charge on the outside of the membrane and negative charge on the inside.
2) When stimulated, voltage-dependent sodium ion channels open, and sodium ions flow into the axon, depolarising the membrane. Localised electric currents are generated in the membrane. Sodium ions move to the adjacent polarised (resting) region causing a change in the electrical charge (potential difference) across this part of the membrane.
3) The change in the potential difference in the membrane adjacent to the first action potential initiates a second action potential. At the site of the first action potential the voltage dependent sodium channels close and voltage dependent potassium ion channels open. Potassium ions leave the axon, repolarising membrane. The membrane becomes hyperpolarised.
4) The third action potential is initiated by the second. In this way local electric currents cause the nerve impulse to move along the axon. At the site of the first action potential, potassium ions diffused back into the axon, restoring the resting potential.
48
What is all or nothing ?
An expression used to describe an action potential. When an action potential is produced in a nerve cell, it is always the same size. It does not matter how big the initial stimulus, the action potential will always involve the same change in potential difference across the cell surface membrane. Because of this, the only way that
information about the strength of a stimulus can be carried is by varying the number of nerve impulses in a given time.
49
How long is the refractory period?
About 5 milliseconds
50
Are impulses different sizes?
The same size action potential is generated by stimuli of different sizes and so impulses are the same size. A stimulus must be above a threshold to generate an impulse. The all or nothing law states that the size of a stimulus, assuming it is above the threshold has no effect on the size of the action potential.
51
What are the different mechanisms that are used to communicate the intensity of a stimulus?
- The frequency of impulses
| - The number of neurones in a nerve that are conducting impulses
52
What are the characteristics of the strongest stimuli?
High firing frequency + Many neurones used
53
What are the two main factors that determine the speed of the conduction of impulses?
- The diameter of the axon
| - Presence or absence of a myelin sheath
54
How does the diameter of the axon impact the speed of conduction?
Wider the diameter = faster the impulse travels
55
How does the presence of a myelin sheath increase the speed of the conduction of impulses?
Axons that are myelinated have a faster impulses.
- Myelin sheath acts as an electrical insulator, which prevents any flow of ions across the membrane.
- Myelin sheath is made of Schwann cells and between Schwann cells are tiny patches of bare membrane called the nodes of ranvier where the sodium ion channels are concentrated. Depolarisation occurs here. As ions flow across the membrane at one node during depolarisation, a circuit is set up which reduces the potential difference of the membrane at the next node, triggering an action potential. This is much faster than a wave of depolarisation along the whole membrane and means a myelinated axon has a higher impulse velocity than an unmyelinated axon. This is known as saltatory conduction which is very fast.
56
What is saltatory conduction?
The way in which a nerve impulse travels along a myelinated axon in a series of jumps. Myelin is fatty material which forms a layer round the axons in many mammal neurones. It acts as an insulator and only allows the electric currents which are set up by an action potential to flow at the gaps where no myelin is present. This allows myelinated axons to transmit impulses much faster than non-myelinated ones.
57
What is the synaptic cleft?
The gap between a synaptic knob and post-synaptic membrane at a synapse. When a nerve impulse arrives at synapse, it causes small amounts of a chemical neurotransmitter to be
released. The neurotransmitter diffuses across the synaptic cleft and produces a nerve impulse in the second neurone.
58
What the presynaptic cell?
A cell or membrane which comes before a synapse is described as presynaptic.
59
What is the postsynaptic cell?
A cell or membrane which comes after a synapse is described as postsynaptic.
60
What are synaptic vessels?
A small membrane-surrounded sac in the presynaptic neurone containing neurotransmitter.
61
What are neurotransmitters?
Chemical that is responsible for carrying a nerve impulse across a synapse.
62
Explain how the synapse transmits an impulse?
1) An action potential arrives at the presynaptic membrane.
2) The membrane depolarises. Calcium ion channels open. Calcium ions enter the neurone.
3) Calcium ions cause synaptic vessels containing neurotransmitter to fuse with the presynaptic membrane.
4) Neurotransmitter is released into the synaptic cleft.
5) Neurotransmitter binds with receptors of the post synaptic membrane. Cation channels open. Sodium ions flow through the channels.
6) The membrane depolarises and initiate an action potential.
7) When released from the receptor the neurotransmitter will be taken up across the presynaptic membrane (hole or after being broken down), or it can diffuse away and be broken down.
63
What are the three stages leading to the nerve impulse passing along the postsynaptic neurone?
- Neurotransmitter release
- Stimulation of the postsynaptic membrane
- Inactivation of the neurotransmitter
64
Why is the calcium important in the transmission of an impulse across the synapse?
When the presynaptic membrane is depolarised by an action potential, channels in the membrane open and increase the permeability of the membrane to calcium ions. These calcium ions are in greater concentration outside the cell, so they diffuse across the membrane and into the cytoplasm. The increased calcium concentration causes synaptic vessels containing acetylcholine to fuse with the presynaptic membrane and release their contents into the synaptic cleft by exocytosis.
65
Explain how the shape of cation channels changes to allow the flow of sodium ions into the postsynaptic membrane.
Embedded in the postsynaptic membrane are specific receptor proteins that have a binding site with a complimentary shape to part of the acetylcholine molecule. The acetylcholine molecule binds to the receptor, changing the shape of the protein, opening cation channels and making the membrane permeable to sodium ions.
66
What does the extent of the depolarisation of the postsynaptic membrane depend on?
The amount of the acetylcholine reaching the postsynaptic membrane. This will depend on the frequency of impulses reaching the presynaptic membrane. The number of functioning receptors in the postsynaptic membrane will also influence the degree of depolarisation.
67
What can happen to the neurotransmitter once it has been used?
- Some neurotransmitters are actively taken up by the presynaptic membrane and the molecules are used again.
- Some neurotransmitters rapidly diffuse away from the synaptic cleft or are taken up by other cells of the nervous system.
- Some neurotransmitters are broken down, for example in the case of the acetylcholine a specific enzyme (acetylcholinesterase) at the postsynaptic membrane breaks it down so that it can no longer bind to receptors.
68
What are the two roles of synapses?
- Control of nerve pathways, allowing flexibility of response
- Integration of information from different neurones, allowing a coordinated response.
69
What are the two main factors that affect the likelihood that the postsynaptic membrane will depolarise?
- The type of synapse
| - The number of impulses received
70
What are the two types of synapses?
- Excitatory
| - Inhibitory
71
What are excitatory synapses?
Neurotransmitters released from an excitatory synapse make the postsynaptic membrane more permeable to sodium ions, increasing the likelihood that an action potential will be triggered in the postsynaptic neurone. Several excitatory impulses added together produce sufficient depolarisation to produce an action
potential in the postsynaptic cell.
72
What is summation?
When several impulses added together produce an action potential in the postsynaptic cell.
73
What are the two types of summation?
- Spatial
| - Temporal
74
What is spatial summation?
Here the impulses are from different synapses, usually from different neurones.
75
What is temporal summation?
When several impulses arrive along a single neurone.
76
What are inhibitory synapses?
A synapse which will make it less likely that an action potential will occur in the postsynaptic nerve cell.
77
How do inhibitory synapses work?
Neurotransmitters from these synapses open channels for chloride ions and potassium ions. Chloride ions move into the cell carrying a negative charge and potassium ions will move out of the cell carrying a positive charge. Hyperpolarisation occurs as it inside becomes more negative than usual and this makes depolarisation harder.
78
What are the two types of photoreceptors?
- Rods
| - Cones
79
What are rods?
A receptor cell, found in the retina of the eye, which is sensitive to light. Rod cells contain a light-sensitive pigment called rhodopsin. When light falls on rhodopsin, it breaks down into retinal and opsin. This reaction leads to the generation of an action potential in a neurone in the optic nerve. Rod cells only give black and white vision but are able to work in dim light conditions.
80
What are cones?
A receptor cell, found in the retina of the eye, which is sensitive to light. Cone cells contain pigments which are sensitive to light of different wavelengths. Because of this, cones allow colour vision.
81
What are bipolar neurone cells?
A type of nerve cell which has a cell body with two long, thin branches. One of these is a dendrite which brings impulses to the cell body. The other is an axon which transmits impulses away from the cell body to other neurones. Bipolar cells in the retina of the eye are important in vision.
82
What are ganglion neurones?
A particular type of neurone found in the eye. The rods and cones are located in the retina and they are the photoreceptors. They form synapses with bipolar cells which, in turn, synapse with ganglion neurones. The axons of these ganglion neurones make up the optic nerve, which leads to the brain.
83
What is rhodopsin?
A light-sensitive pigment found in rod cells in the retina of the eye. When light falls on rhodopsin, it breaks down into retinal and opsin. This reaction leads to the generation of an action potential in a neurone in the optic nerve.
84
What are the cerebral hemispheres?
The forebrain is divided into a right and a left cerebral hemisphere. Each cerebral hemisphere consist of four lobes: the frontal, parietal, occipital and temporal lobes, which are responsible for interpreting different sensory inputs. The cerebral hemispheres are linked to each other by band of nerve cells axons called the corpus callosum.
85
What is grey matter?
Grey matter describes an area of the central nervous system that consists mainly of nerve cell bodies, synapses and dendrites. The outer layer of the brain is known as the grey matter.
86
When you look at the brain from the top down what do you see?
The cortex
87
What is white matter?
White matter describes any area of the central nervous system which consists mainly of axons. The myelin sheath surrounding many axons gives tissues containing the structure its characteristic white colour.
88
What are the four lobes of the cerebral hemispheres?
- Frontal lobe
- Parietal lobe
- Occipital lobe
- Temporal lobe
89
What is the frontal lobe and what is its function?
The frontal lobe is one of the four regions into which the cerebral hemispheres of the brain are divided. The frontal lobe is concerned with processes such as decision-making, reasoning and planning. It is concerned with forming associations and with ideas. It includes the primary motor cortex which has neurones that connect directly to the spinal cord and brain stem and from there to the muscles. It sends information to the body via the motor neurones to carry out movements. The motor cortex also stores information about how to carry out different movements.
90
What is the parietal lobe and what is its function?
It is one of the four regions into which the cerebral hemispheres of the brain are divided. The parietal lobe is concerned with orientation, movement, sensation, calculation as well as some types of recognition and memory.
91
What is the occipital lobe and what is its function?
It is one of the four regions into which the cerebral hemispheres of the brain are divided. The occipital lobe is concerned with processing information from the eyes which includes vision, colour, shape recognition and perspective.
92
What is the temporal lobe and what is its function?
It is one of the four regions into which the cerebral hemispheres of the brain are divided. The temporal lobe is concerned with processing auditory information. This is the information about hearing, sound recognition and speech. The temporal lobe is also involved with memory.
93
What side of the temporary lobe is concerned with speech?
The left temporal lobe
94
What is the thalamus and what is its function?
The thalamus is responsible for routing all the incoming sensory information to the correct parts of the brain, via the axons of the white matter.
95
What is the hypothalamus and what is its function?
A part of the brain responsible for monitoring and helping to regulate a number of physiological states including temperature, sleep, thirst and hunger. It contains the Thermo regulatory centre which monitors core body temperature and skin temperature and initiates the corrective action to restore the body temperature to its optimum. The hypothalamus also acts as an endocrine gland, secreting hormones.
96
What is the hippocampus and what is this function?
A region of the brain involved in laying down long-term memory.
97
What are the basal ganglia what is the function?
A group of neurones within each cerebral hemisphere of the brain responsible for selecting and initiating stored programs for movement.
98
What is the medulla oblongata?
Part of the hindbrain of a brainstem which is responsible for controlling body processes which we do not consciously have to control. These include heart rate, breathing and blood pressure.
99
What is the corpus callosum?
White-matter composed mainly of axons, whose white myelin sheaths give it its characteristic appearance. It provides connections between the cortex and the brain structures below. It also forms connections between the two hemispheres of the cortex.
100
What is the cerebellum and what is its function?
Part of the hindbrain which is responsible for posture and balance. It also coordinates movement as it is been carried out receiving information from the primary motor cortex, muscles and joints. The cerebellum constantly checks whether the motor program being used is the correct one.
101
What is the function of the midbrain?
Release information to the cerebral hemispheres including auditory information to the temporal lobe and visual information to the occipital lobe.
102
How do CT scans work?
CAT scans use large numbers of narrow beam x-rays which are rotated around the patient to pass through tissue at different angles. Each beam is reduced in strength according to the density of the tissue through which it passes. . The X-rays are then detected and used to produce an image of the tissue on a computer screen.
103
How are CT scans used to investigate brain structure and function?
- Skull is shown by white rim around the brain representing the skull.
- Provide frozen moment pictures.
- Shows major structures in the brain rather than function.
- If a CT scan shows a diseased or damaged brain structure and the patient has lost some function, the function of that part can be worked out.
104
Describe what happens to photoreceptors in the dark
1) Sodium ions flow into the outer segment through non-specific cation channels.
2) Sodium ions move down the concentration gradient into the inner segment where pumps continuously transport them back out of the cell.
3) The influx of Na+ produces a slight depolarisation of the cell. The potential difference across the membrane is about -40mV.
4) This slight depolarisation triggers the release of a neurotransmitter called glutamate, from the rod cells.
5) The neurotransmitter binds to the bipolar cell, stopping it from depolarising.
105
Describe what happens to photoreceptors in the light
1) When light falls on the rhodopsin molecule, it breaks down into retinal (non-protein) and opsin (protein).
2) The opsin activates a series of membrane bound reactions, ending in the hydrolysis of a cyclic nucleotide molecule attached to the cation channel in the outer segment. The breakdown of this molecule results in the closing of cation channels.
3) The influx of Na+ into the rod decreases, while the inner segment continues to pump Na+ out.
4) The inside of the cell becomes more negative and therefore hyperpolarised.
5) The release of the neurotransmitter, glutamate stops. There is no inhibition so cation channels in the bipolar cell open and the membrane becomes depolarised, generating an action potential which is transmitted to the neurone of the optic nerve.
106
What does a lack of glutamate result in? Is the bipolar depolarised?
Lack of glutamate results in the depolarisation of the bipolar cell. The neurones that make up the optic nerve are also depolarised and respond by producing an action potential.
107
What is the dark adaptation?
Reforming of rhodopsin in dark conditions.
108
Plants detect the quantity, direction and wavelength of light using what?
Photoreceptors
109
Why do plants have slow responses?
All messages in plants are chemical
110
What are phytochromes?
A plant photoreceptor molecule that consists of a protein component bonded to a non-protein light absorbing pigment molecule which absorb red and far-red light.
111
The non-protein component of phytochrome exist in two forms. What are the 2 isomers of phytochrome?
- Pr - Phytochrome red; absorbs red light (660mm).
| - Pfr - Phytochrome far-red; absorbs far-red light (730mm).
112
The 2 isomers of phytochrome are described as being ...
photoreversible
113
Absorption of red light converts ... to ...
Pr to Pfr
114
Absorption of far red light converts ... to ...
Pfr to Pr
115
During sunlight both isomers are converted but which isomer is converted the most?
Pr is converted into Pfr as more red light is absorbed.
116
During the day which isomer accumulates?
Pfr
117
During dark which isomer is converted?
Pfr is slowly converted into Pr.
118
What stimulates the response causing seeds to germinate?
Seeds germinate when they are exposed to red light causing Pr to be converted in Pfr. A higher ration of Pfr to Pr indicates to the plant that there is light, or that the days are longer than nights. Appearance of Pfr triggers germination.
119
Why do seeds not germinate when it is dark?
When seeds are kept in the dark, no Pr is converted to Pfr and therefore the seeds do not germinate because it is the appearance of Pfr that triggers germination.
120
What is the photoperiod?
The light period during a day. In temperate regions the amount of daylight varies throughout the year. In the winter, it is light for a relatively short part of the day. In the summer, it is light for much longer. Photoperiod affects many living organisms. It controls when birds migrate, when plants flower, and when some marine worms lay their eggs.
121
What are long-day plants?
Only flower when a day length exceeds a critical value. These flower when the period of uninterrupted darkness is less than (typically) 12 hours; they need Pfr to stimulate flowering.
122
What are short-day plants?
Tend to flower in spring or autumn when the period of uninterrupted darkness is greater than 12 hours. They require long hours of darkness in order to convert all Pfr present back to Pr.
123
What is greening?
Once a shoot has broken through soil into sunlight, the plant undergoes profound changes in both its form and biochemistry known as greening.
124
Once a shoot is in light what do phytochrome cause?
Phytochromes promote the development of primary leaves, leaf unrolling and the production of pigments.
125
How do phytochromes switch processes on or off?
1) Exposure to light causes phytochrome molecules to change from one to another, bringing about a change in shape.
2) Each activated phytochrome interacts with other proteins. The phytochromes may bind to the protein or disrupt the binding of a protein complex.
3) These signal proteins may act as transcription factors or activate transcription factors that bind to DNA to allow the transcription of light-regulated genes.
126
Other than light what other environmental cues are detected by plants?
- Gravity
| - Touch and mechanical stress
127
How do plants respond to gravity?
Before light can be a cue as the shoot in under the soil. The stimulus ensures that developing shoots reach the light while roots grow into the soil.
128
How do plants respond to touch and mechanical stress?
Mechanical stimulus activate signal molecules whose end result is the activation of genes that control growth. E.g. when a leaf of a particular species of plant is touched, it folds rapidly and then collapses.
129
How are CT scans used for medical diagnosis's?
- Show damaged or diseased areas of the brain.
- Blood has a different density from brain tissue, so it shows up as a lighter colour on a CT scan.
- A scan will show the extent of bleeding and its location in the brain. From this you can work out which blood vessels have been damaged and what brain functions are likely to be affected by the bleeding.
130
How do MRIs work?
They are a method of imaging soft tissues using a magnetic field and radio waves. The technique produces an image of thin slices through a tissue from which a computer can produce a three-dimensional image.
131
How are MRI scans used to investigate brain structure and function?
- Uses a magnetic field and radio waves to detect soft tissue.
- MRIs allow you to clearly see the difference between normal and abnormal (diseased or damaged) brain tissue.
- Same as CT scans, brain function can only be determined by looking at damaged areas.
132
How are MRI scans used for medical diagnosis's?
- Tumour cells respond differently to a magnetic field than healthy cells, so they show up lighter on an MRI.
- A scan will show the exact size of a tumour and its location in the brain which is then used to determine the most effective treatment.
133
How do fMRIs work?
They are a method of obtaining information about brain activity. It depends on using radio waves to determine oxygen uptake by distinguishing between haemoglobin and oxyhaemoglobin. This enables active areas of the brain to be identified and associated with the performance of particular tasks such as those involving memory, language and emotion.
134
How are fMRI scans used to investigate brain structure and function?
- Detailed, high resolution picture of the brain’s structure.
- If a function is carried out whilst a person is in the scanner, the part of the brain that’s involved with that function will be more active.
135
How are fMRI scans used for medical diagnosis's?
- Allows you to study conditions that don’t have obvious structural causes.
- Seizures – fMRI scan can be taken before and during a seizure to pinpoint which part of the brain is not working properly.
136
How does Positron Emission Tomography (PET) investigate brain structure and function?
- Very detailed
| - Investigate both structure and function of the brain in real time
137
How are PET scans used for medical diagnosis's?
- Show if areas of the brain are usually active or inactive
| - Study disorders that change the brain’s activity -> Alzheimer’s
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Where is the visual cortex?
Area of the cerebral cortex at the back of your brain.
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What is the role of the visual cortex?
Role of the visual cortex is to receive and process visual information.
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Neurones in the visual cortex receive information from ...
Either your right or left eye
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Neurones are grouped together in columns called ?
Ocular dominance columns
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How are the ocular dominance columns arranged?
Columns are arranged in an alternating pattern -> left, right, left, right.
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What is the critical window/critical period?
A period of time during development when the nervous system must obtain specific experiences to develop properly, for example, exposure to light stimulation for full visual development; the stimulation is required to create correct patterns of synapses within the brain.
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Have columns in the visual cortex formed before the critical period?
Yes
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What are animal models?
Animals used by scientists to learn about humans are known as animal models.
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What is monocular deprivation?
An experimental procedure in which light is prevented from entering one of the eyes of certain animals, e.g. monkeys.
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What is required for the refinement of the columns and so for full development of the visual cortex.
Visual stimulation
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Describe how an eye that does not receive visual stimulation during the critical window is affected?
1) There is a lack of visual stimulation in one eye.
2) Axons from the visually deprived eye do not pass impulses to cells in the visual cortex.
3) Axons from the non-deprived eye pass impulses to cells in the visual cortex.
4) Synapses made by active axons are strengthened.
5) Inactive synapses are eliminated.
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How do axons compete for target cells in the visual cortex?
Every time a neurone fires onto a target cell, the synapses of the other neurone sharing the target cell are weakened and they release less neurotransmitter. If this happens repeatedly, the synapses that are not firing will be cut back. When one eye is deprived of light, the axons from that eye will not be stimulated.
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What was Hubel and Wiesel experiment on Monkeys?
Monkeys were raised from birth to 6 months in which they were deprived of light in one eye (monocular deprivation). Monkeys became blind the light deprived eye. Deprivation in adult monkeys had no effect.
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What are the methods used to investigate the contributions of nature and nurture to brain development?
- Animal experiments
- Twin studies
- Cross-cultural studies
- Newborn studies
- Brain damage studies
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Describe how scientists study animals to investigate the contributions of nature to nurture
Scientists study the effects of different environments on brain development of animals of the same species. Individuals of the same species are genetically similar, so any differences in their brain development are more likely due to nurture rather than nature.
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Describe how scientists study identical twins to investigate the contributions of nature to nurture
* Identical twins are genetically identical.
| * Identical twins can be raised separately to see the impact of nurture.
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Describe how scientists use cross-cultural studies to investigate the contributions of nature to nurture
Children brought up in different cultures have different environmental influences, e.g. beliefs and education. Scientists can study the effects of a different upbringing on brain development by comparing large groups of children who are the same age from different cultures. Scientists look for major differences in characteristics. Any differences in brain development are more likely to be as a result of nurture.
155
What is the carpentered world hypothesis?
According to the carpentered world hypothesis, people who live in a world dominated by straight lines and right angles (i.e. a world in which carpenters work) tend to interpret images with acute and obtuse angles as having right angles.
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Describe how scientists study newborn babies to investigate the contributions of nature to nurture
* Brain of a newborn baby hasn’t really been affected by the environment.
* Scientists study the brains of newborn babies to see what functions they’re born with and how developed different parts of the brain are.
* Demonstrates natures influence.
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Describe how scientists use brain damaged studies to investigate the contributions of nature to nurture
* If a child’s brain is damaged, it can repair itself as it is still developing.
* Scientists can compare the development of a chosen function in children with and without brain damage.
* If the characteristic still develops in children who have brain damage, then brain development is more likely to be nurture than nature for that characteristic.
* If it doesn’t help in children who have brain damage, then brain development is more likely to be due to nature than nurture for that characteristic.
158
Where is memory stored in the brain?
Memory is not localised in one part of the brain. It is distributed throughout the cortex with different sites for short-term and long-term memory.
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What are the 2 ways in which memories can be created?
Through altering:
• The pattern of connections
• The strength of synapses
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What is habituation?
In this form of learning an animal responds less and less to a repeated stimulus.
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How is the habituation achieved?
1) With repeated stimulation, Ca2+ channels become less responsive so less Ca2+ crosses the presynaptic membrane.
2) Less neurotransmitter is released.
3) There is less depolarisation of the postsynaptic membrane, so no action potential is triggered in the motor neurone.
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What is sensitisation?
When an animal develops an enhanced response to a stimulus (opposite of habituation).
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What are animal rights?
If you believe in animal rights you believe that there are things that should not be done to certain animals (especially those capable of feeling pain) whatever the benefits.
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What are the 4 main ethics of using animals in medical research?
- Importance of consent
- Animal welfare rather than animal rights
- Animal suffering and experience of pleasure
- A utilitarian approach to the use of animals
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How is informed consent applied to using animals in medical research?
Accepting that animals have rights would mean that we could only use them if they give consent to participate in medical experiments. However, animals cannot give consent and so we must make the decision.
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What does the ethic of animal welfare involve?
European law states that no country in the European Union is allowed to use vertebrae in medical experiments if there are non-animal alternatives. If there are not, animals can be used provided the research warrants it and strict guidelines are followed.
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What is the ethic issue regarding animal suffering and experience of pleasure?
No one knows whether organisms such as fish and insects feel pain and suffering.
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What is the utilitarian approach to the use of animals?
The belief that the right course of action is the one that maximises the amount of overall happiness or pleasure in the world. A utilitarian framework allows certain animals to be used in medical experiments provided the overall expected benefits are greater than the overall expected harms.
169
What is animal welfare?
An animal’s welfare is a measure of how it feels. Animals that are capable of suffering, such as birds and mammals, may have a low level of welfare if, for example, they are hungry, thirsty, overcrowded, diseased or prevented from exhibiting normal behaviours such as moving around or nest building.
170
What is dopamine?
A neurotransmitter secreted by neurones including many which are located in the midbrain.
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What is the cause of Parkinson's disease?
Parkinson’s disease involves the death of some of the neurones of the midbrain and a reduction in the amount of dopamine produced in the brain -> dopamine-secreting neurones in the basal ganglia die.
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What is the impact of dopamine-secreting neurones in the basal ganglia dying?
These neurones usually release dopamine in the motor cortex. Therefore motor cortexes in people with Parkinson’s disease receive little dopamine.
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What are the main symptoms of Parkinson's disease?
- Stiffness of muscles
- Tremor of the muscles
- Slowness of movement
- Poor balance
- Walking problems
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What are the treatments for Parkinson's disease?
- MAO inhibitor (e.g. selegiline) -> Inhibit monoamine oxidase which is the enzyme responsible for breaking down dopamine in the brain. This increases the availability of dopamine. 2 types: MAOA + MAOB (MOAB is used to treat Parkinson’s and Alzheimer’s.
- L-dopa (a precursor in the manufacturing of dopamine) -> Once L-dopa is in the brain it is converted into dopamine, increasing the concentration of dopamine and controlling the symptoms of the disease (main therapy used for Parkinson’s).
- Dopamine agonists -> Drugs that activate the dopamine receptor directly and often more than one is given in the form of a combined pill. These drugs mimic the role of dopamine in the brain, binding to dopamine receptors at synapses and triggering action potentials.
- Gene therapy -> Genes for proteins that increase dopamine production, and that promote the growth and survival of nerve cells are inserted into the brain.
- Deep Brain Stimulation (DBS) -> Type of surgery used to treat the symptoms of the disease.
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What is an agonist?
A substance which mimics the action of a neurotransmitter at a synapse. The molecules of an agonist have a similar shape to the molecules of a particular neurotransmitter. As a result, they also fit into the receptor molecules in the postsynaptic membrane of the synapse. Neurotransmitters only exert their effects for a short time because they are rapidly broken down. Agonists on the other hand are not broken down so readily and can continue to stimulate the postsynaptic nerve cell.
176
What does excess dopamine cause?
Schizophrenia
177
What is serotonin?
A neurotransmitter released by neurones situated in the brain stem which targets a large area of the brain (axons extend into the cortex, cerebellum and spinal cord).
178
What is the cause of depression?
Serotonin plays an important part in determining a person’s mood -> serotonin transmits nerve impulses across synapses in the parts of the brain that controls mood. Depression is linked to a lack of serotonin. Depression is a multifactorial condition -> caused by genes and the environment. When people are depressed, fewer nerve impulses than normal are transmitted around the brain, which may be related to low levels of neurotransmitters being produced.
179
What are the treatments for depression?
- Monoamine oxidase inhibitors (MAOIs) -> first type of drug used to treat symptoms of depression. They break down neurotransmitters, including serotonin.
- Selective Serotonin Reuptake Inhibitors (SSRI) -> These inhibit the uptake of serotonin from the synaptic cleft (e.g. Prozac).
180
What is MDMA?
The drug that is in Ecstasy.
181
What are the short and long-term impacts of MDMA?
Both short and long-term effects include; changes in behaviour and brain chemistry.
182
What is ecstasy?
An illegal recreational drug that affects thinking, mood and memory in both the short and long term.
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How does MDMA in ecstasy affect synapses?
MDMA increases the concentration of serotonin in the synaptic cleft. It does this by binding to molecules in the presynaptic membrane that are responsible for transporting the serotonin back into the cytoplasm, therefore preventing the removal of serotonin from the synaptic cleft. Usually, serotonin is taken back into a presynaptic neurone after triggering an action potential, to be used again.
184
What are the positive effects of using MDMA?
- Feeling of euphoria
| - Enhanced senses
185
What are the negative effects of using MDMA?
- Clouded thinking, agitation and disturbed behaviour
- Sweating
- Dry mouth
- Increased heart rate
- Fatigue
- Muscle spasms
- Hyperthermia
186
What is the human genome project?
An international research effort to sequence and map all of the genes (genome) of members of our species, Homo sapiens.
187
How has the human genome project helped to develop personalised medicine?
* The HGP has also highlighted common genetic variations between people -> depending on the 1.4 million SNPs a person possesses.
* It’s known that some of these variations make some drugs less effective.
* Drug companies can use this knowledge to design new drugs that are tailored to people with these variations.
* Doctors can also personalise a patient’s treatment by using their genetic information to predict how well they will respond to different drugs and only prescribe the ones that will be most effective.
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What are the Social, Moral and Ethical Issues of the human genome project?
* Creating drugs for specific genetic variations will increase research costs for drug companies. These new drugs will be more expensive, which could lead to a two-tier healthcare system – with only wealthier people being able to afford these drugs.
* Some people might be refused an expensive drug because their genetic makeup indicates it won’t be effective for them.
* Information held within a person’s genome could be used by others -> e.g. employers or insurance companies to unfairly discriminate against them.
* Keeping records of individual genotypes raises issues of confidentiality.
189
What is genetic modification?
A term used to describe organisms when new genes have been inserted into them.
190
What is a transgenic organism?
A transgenic organism is one which has been genetically modified. It is used to describe organisms in which new genes have been inserted.
191
What is artificial selection?
Selects alleles for characteristics that are agriculturally viable.
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What are the vectors used for genetically modifying plants?
* A bacterium that infects many species of plant, such as a soil-inhabiting bacterium. When the bacteria invade plant cells, genes from plasmid DNA become incorporated into the chromosome of the plant cells.
* Minute pellets that are covered with DNA carrying the desired gene are shot into plant cells using a particle gun.
* Viruses -> infect cells by inserting their DNA or RNA which can be used to transfer the new genes into the cell.
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What is a marker gene?
When organisms are genetically modified, new genes are introduced into their cells. To label cells that contain a new gene, a marker gene is also inserted. The marker gene may produce resistance to an antibiotic. Incubating the cells with the antibiotic kills cells which have not taken up the resistance gene along with the other new gene. The use of marker genes is an effective way of finding those cells that have taken up the new gene.
194
What is micropropagation?
The production of new plants from individual cells or small pieces of tissue. By using this technique large numbers of genetically modified plants can be produced very rapidly from a single cell or callus. All the tiny plantlets formed will be genetically identical.
195
How do you genetically modify animals?
1) The gene for the protein (drug) is injected into the nucleus of a fertilised animal egg.
2) The egg cell is then implanted into an adult animal – it grows into a whole animal that contains a copy of the gene in every cell.
3) The protein produced from the gene is normally purified from the milk of the animal.
196
What are the health issues associated with genetic modification?
* Transfer of antibiotic-resistance genes to microbes
* Formation of harmful products by new genes
* Transfer of viruses from animals to humans
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How is the antibiotic resistance of Genetically modified organisms a health risk?
GM plants contain a marker gene which are often antibiotic resistant. When eaten the gene could potentially be transferred to pathogenic microbes in the gut, which could build up resistance to certain antibiotics used in medical treatments.
198
How is the formation of harmful products from new genes a health risk?
The biochemical changes to oils, proteins and other substances might conceivably result in toxic compounds or new allergens.
199
What are the environmental issues associated with genetic modification?
* Transfer of genes to non-target species
* Possible breeding of ‘superweeds’
* Possibility that GM crops will lead to increased use of other chemicals in agriculture
200
How is the transfer of genes to non-target species an environmental issue?
- Cross pollination
- GM crops can cross with conventional crops of the same species growing in nearby fields. This means genes introduced into a GM crop will almost inevitably spread to conventional crops. This is an environmental issue as through genetic modification of one species of plant it will lead to others becoming genetically modified indirectly.
201
How is the possible breeding of ‘superweeds’ an environmental issue?
If herbicide-resistant crops interbreed with wild plants, it could produce ‘superweeds'. This would make them harder to be killed and affect agricultural productivity.
202
What are the benefits of genetically modifying organisms?
- Higher crop yields
- Crops with pest resistance
- Some disorders can now be treated with human proteins from GMO in large quantities for less money
- Vaccines produced in plant tissues don’t need to be vaccinated
- Producing drugs from animals and plants is cheaper -> once the organisms have been genetically modified they can be reproduced using conventional farming methods.
- Enzymes used in industry can be produced from GMO in large quantities for less money.
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What are the risks of genetically modifying organisms?
- Health risks -> Antibiotic resistance, harmful products from new genes and the transfer of viruses.
- Unknown long-term impacts
- Ethically wrong to genetically modify animals for our benefit.
- Environmental issues -> Transfer of genes to non-target species, possible breeding of ‘superweeds’ and possibility that GM crops will lead to increased use of other chemicals in agriculture.
