topic 8 - grey matter Flashcards
neurone definition
specialised cells of the nervous system which carry electrical impulses around the body
nerve definition
bundle of neurons
what are the three types of neurones and what do they do
- sensory - carry impulses from receptors to the brain and spinal cord in the CNS
- relay - found entirely in the CNS and connect sensory and motor neurones
- motor - carry impulses from CNS to effector muscles or glands
motor neurone structure
- large cell body at one end that lies within the spinal cord or the brain
- many highly branched dendrites, providing many connections with axon terminals of other neurones
relay neurone structure
- short neurones with axons and highly branched dendrites
sensory neurone structure
- cell body that branches off in the middle of the axon and has no dendrites
- axon terminal is attached to a receptor cell
- section of neurone that links axon terminal with cell body is a dendron
- section of neurone that connects cell body with the CNS is the axon
explain the nervous system pathway
- receptor cells detect changes in the environment, or stimuli
- nerve impulses travel from the receptor cells along sensory neurones to the CNS
- the CNS acts as a coordinating centre for the impulses that arrive from the receptors, determining what part of the body needs to respond and sending out a new set of impulses along motor neurones
- motor neurones send impulses to the effectors to bring about a response. effectors are muscles or glands.
what does the human nervous system consist of?
the CNS and the PNS
what does it mean to say that neurones are myelinated
- their axon is insulated by a fatty layer known as the myelin sheath
- the myelin sheath is made up of Schwann cells which wrap themselves around the axon
- there are insulated gaps between the Schwann cells known as the nodes of Ranvier
- electrical impulses in myelinated cells do not travel the whole axon but jump one node to the next, speeding up transmission
- in unmyelinated neurones electrical impulses travel more slowly
what two factors establish and maintain resting potential
- the active transport of sodium and potassium ions
- difference in membrane permeability to sodium and potassium ions
explain pupil response in bright light
- photoreceptors detect change in environment
- radial muscles relax
- circular muscles contract
- pupil constricts
- less light enters the eye
(dim light is opposite)
what are the stages of nerve transmission
- resting potential
- action potential generated
- repolarisation
- transmission of action potential
explain synaptic transmission
- when an action potential arrives at the end of the axon of the presynaptic neurone, the membrane becomes depolarised, causing calcium ion channels to open
- calcium ions diffuse into the synaptic knob via calcium ion channels
- calcium ions cause vesicles in the synaptic knob to move towards the presynaptic membrane where they fuse with it and release neurotransmitters into the synaptic cleft via exocytosis
- neurotransmitters diffuse across synaptic cleft and bind with receptor molecules on the postsynaptic membrane
- this causes associated sodium ion channels on the postsynaptic membrane to open, allowing sodium ions to diffuse into postsynaptic cell
- if enough neurotransmitters bind with receptors on the postsynaptic membrane, then an action potential is generated
- neurotransmitters are then broken down to prevent continued stimulation of postsynaptic neurone
what are the additional roles of synapses
- unidirectionality of impulse transmission
- ensures the one way transmission of nerve impulses - divergence of nerve impulses
- one neurone can connect to several others at a synapse, allowing nerve signals to be sent in several directions from a single presynaptic neurone - amplification of nerve signals by summation
receptor definition
specialised cell that can generate a electrical impulse in a sensory neurone when stimulated by a particular stimulus
what are the 2 photoreceptors in the retina
rod cells
- located on the outer retina
- sensitive to light intensity so detects brightness and presence of light
- images generated are black and white
cone cells
- found in fovea
- sensitive to different wavelengths of visible light and so detect colour
iris function
controls the amount of light that enters the eye
how do photoreceptors generate nerve impulses
- photoreceptors in the eye generate action potentials when stimulated by light
- light sensitive pigments inside the photoreceptors are bleached when light falls on them e.g.
Rod cells contain a light-sensitive pigment called rhodopsin
When light hits rhodopsin it breaks apart into constituent parts retinal and opsin
The breaking apart of rhodopsin is known as bleaching - the bleaching of light sensitive pigments causes a chemical change in the photoreceptor which generates a nerve impulse
- nerve impulses travel along a bipolar neurone to the optic nerve
how do rod cells pass information to the optic nerve in the dark
- sodium ions are actively pumped out of rod cells, generating a conc gradient
-sodium ions diffuse back down this conc gradient into the rod cell via sodium channels - the cell is now depolarised
- the depolarised rod cell releases neurotransmitters which diffuse across a synapse to a bipolar neurone
- this neurotransmitter inhibits the generation of an action potential, preventing a nerve impulse from being sent to the optic nerve
how do rod cells pass information to the optic nerve in the light
- Light bleaches rhodopsin, causing it to break apart into retinal and opsin
- this causes sodium ion channels to close, , preventing sodium ions from diffusing back into the rod cell
- the rod cell becomes hyperpolarised
- The hyperpolarised rod cell stops releasing an inhibitory neurotransmitter
- action potential is generated, and sends impulse to optic nerve
cerebrum structure and function
function:
- conscious activites including vision, hearing, speech and memory
structure:
- divided into two halves known as the cerebral hemispheres, joined together by the corpus callosum
- has a thin outer layer called the cerebral cortex
- the cerebral cortex consists of neurones
- it is highly folded, which increases surface area allowing it to contain more neurones
- beneath the cerebral cortex is the ‘white matter’ which consists of myelinated axons of neurones
hypothalamus functions
- regulates body temp: monitors blood temperature and initiates homeostatic response
- osmoregulation: monitors water balance of blood and releases ADH hormone is blood is too concentrated
- regulating digestive activity: regulates hormones that control appetite and the secretion of digestive enzymes
- controls endocrine functions:
causes pituitary gland to release hormones
cerebellum function
coordinates movement
medulla oblongata function
contains co-ordination centres that control different functions eg heart rate
how do CT scans work
- a beam of x rays are aimed at a patient from all angles around the body
- digital x-ray detectors are used to pick up the x-ray as they exit the patients body
- denser tissue absorbs more of the x-ray radiation so shows up as a lighter region on a scan
who are CT scans not recommended for
pregnant patients or children
- due to risks of exposure to the x-ray radiation, which is given at a higher level than in a normal x-ray
MRI
- uses magnetic field and radio waves to generate images through the body
- soft tissues can be seen clearly
- images have a higher resolution compared to CT scans
- useful for identifying areas of abnormal or damaged tissue so especially useful for tumour diagnosis
problems with MRI
- more expensive than CT scans BUT do not carry the risk associated with x-rays
- magnetic field of MRI scanner can interfere with medical devices such as pacemakers
difference between MRI and fMRI
fMRI scans allow brain function to be studied in real time
- show the location of oxygenated blood in the brain, therefore indicating which brain regions are active at any one time
PET scans
- radioactive tracers which collect in areas where there is increased blood flow, metabolism, or neurotransmitter activity
- The scanner can detect emissions of positrons and so the movement of the tracer through the body and any accumulation of tracer in the brain can be seen
- The amount of radioactive tracer present in a brain region can indicate whether that region is active or inactive
- provides a 3d image
what is the visual cortex
the region of the cerebral cortex where visual information is processed
how did the visual cortex develop
- soon after birth, the neurones in the visual cortex begin to form synapses
- both eyes need to be visually stimulated for the neurones to be organised correctly during this period of development known as the critical period
- Synapses that pass on nerve impulses during this critical period are strengthened and become permanent parts of the structure of the visual cortex
- Synapses that do not receive nerve impulses during this critical period are lost and cannot be re-formed
why are animal models used in brain research
- some animals have similar brain structure to humans, so the findings can be applied to the human brain
- experimenting on animals is MORE ethically acceptable than on humans
pros and cons of using animals in research
pros:
- drugs need to be tested on the whole organism rather than just on groups of cells
- testing medications on humans before we know they are safe is unethical
- animal anatomy is similar to humans
cons:
- testing on cells and tissues provides an alternative option
- many believe that animals should have the same rights as humans in welfare and consent
- many animals suffer pain during research
- animal and human anatomy are not identical
habituation definition
where an organism becomes insensitive to repeated stimuli over time which does not threaten their survival or does not benefit them in any way
how does the process of habituation occur
- animals become habituated due to changes in the transmission of nerve impulses from one neurone to the next
- repeated stimulus decreases permeability of pre synaptic membrane
- fewer calcium ions enter the presynaptic neurone
- so fewer vesicles fuse with the presynaptic membrane
- therefore less neurotransmitter binds to receptors on the post synaptic membrane
- an action potential is less likely to be generated in the post synaptic membrane
- the nerve impulse therefore, does not reach the effector organ
neurotransmitters definition
chemicals that transmit nerve impulses across synapses
what is parkinsons disease
- what neurones are lost
- a brain disorder than affects the co-ordination of movement, caused by the loss of neurones in some parts of the brain
- the lost neurones normally produce the neurotransmitter dopamine (dopamine is involved in muscle control)
how does a loss of dopamine affect parkinsons disease
- less dopamine is released into the synaptic cleft meaning less is able to bind with receptors on the postsynaptic membrane
- fewer sodium channels on the membrane are opened so depolarisation does not occur
- thus, fewer action potentials are generated
what drugs can be used to treat parkinsons
- dopamine agonists: produce the same effect as dopamine by binding to and activating dopamine receptors on the postsynaptic membrane
- dopamine precursors: chemicals that can be converted into dopamine in the neurones
- enzyme inhibitors: MAOB inhibitors inhibit the activity of enzymes that would normally break down dopamine in the synaptic cleft
what are other treatments for parkinsons that are currently being investigated
- gene therapy: involves the addition of genes to the affected cells in the brain to either increase dopamine or prevent the destruction of dopamine producing cells
- stem cell therapy
what neurotransmitter is linked to depression
- serotonin
- low levels of serotonin have increased episodes of depression
- other chemicals have also been linked such as: noradrenaline and dopamine
which drugs can be used to treat depression
SSRI’s: prevent the uptake of serotonin at synapses
TCA: increase levels of both serotonin and noradrenaline
MOAB inhibitors: inhibit enzymes that would otherwise break down neurotransmitters in the synaptic clefts in the brain
how can drugs increase transmission of impulses at a synapse
- causing more neurotransmitter to be produced at the synaptic knob
- causing more neurotransmitter to be released at the presynaptic membrane
- Imitating the effect of a neurotransmitter by binding to and activating receptors on the postsynaptic membrane
- Preventing the breakdown of neurotransmitters by enzymes
- Preventing the reuptake of neurotransmitters by the presynaptic cell
how can drugs decrease transmission of impulses at a synapse
- Preventing production of neurotransmitter in the presynaptic knob
- Preventing the release of neurotransmitter at the presynaptic membrane
- Enabling neurotransmitter to gradually leak out of the presynaptic knob so there is little left when an action potential arrives
- The neurotransmitter that leaks out of the cell is destroyed by enzymes
- Binding to receptors on the postsynaptic membrane and so preventing neurotransmitters from binding
how does MDMA affect neurotransmitters in the brain
serotonin:
- inhibits the reuptake of serotonin into the presynaptic neurone by binding to the specific proteins that enable serotonin reuptake
- triggers the release of further serotonin from presynaptic neurones
how does L-dopa affect neurotransmitters in the brain
- has a similar structure to dopamine
- L-dopa is transported from the blood into the brain, where it is converted into dopamine in a reaction catalysed by the enzyme dopa-decarboxylase
- The effect is to increase levels of dopamine in the brain
- Increased levels of dopamine mean that more nerve impulses are transmitted in parts of the brain that control movement
personalised medicine definition
the development of targeted drugs to treat a variety of human diseases in individuals with different genotypes
how can the human genome project be used to develop genomic medicine
- the HPG involved the sequencing of the entire human genome
- the information gathered is stored in databases, within which genes that code for certain proteins can be found and analysed
- knowing the structure and sequence of proteins involved in disease allows the development of drugs that target specific proteins
By combining information about the genome with other clinical and diagnostic information, patterns can be identified that can help to determine an individual’s risk of developing disease
Doctors can also use an individual’s genome to work out how well they might respond to specific treatments, allowing treatments to be selected on the basis of an individual’s genotype
what are the ethical issues associated with personalised medicine
- increased research costs for drug companies could increase the price of new medicines and mean that only wealthier people have access to personalised medicine
- breaches in medical data
- some patients may be refused personalised medicine if it is not predicted to be that effective for them
what are the risks and benefits of genetic engineering
risks
1. concerns about the long-term impacts of genetically modified foods on human health
2. pests may develop resistance to the modified crop defences, increasing the use of pesticides
3. genetically modified crops are often grown in large fields, creating monocultures that are bad for biodiversity
4. there could be transmission of genetic material between genetically modified organisms and non-GM organisms
benefits:
1. crops can be modified to produce higher yield, reducing famine
2. crops can be modified to be resistant to pests and reduce pesticide use, which lowers production cost and environmental damage
3. genetically modified organisms guarantee a low cost supply of some human medications
tropism definition
directional growth response to a stimulus in plants
phototropism and geotropism and hydrotropism definitions
phototropism: growth response to light
geotropism: growth response to gravity
hydrotropism: response to water
difference between a positive and negative tropism
positive tropisms involve a growth TOWARDS a stimulus
negative involve growth AWAY from a stimulus
auxins definition
group of plant growth factors that influence many aspects of plant growth
what is IAA
a type of auxin
- IAA brings about plant responses such as phototropism by altering transcription of genes inside plant cells
- it is produced in the growing plants of a plant before being distributed to other plant tissues through diffusion and active transport.
- transport of IAA occurs in the phloem
effect of IAA in plant shoots
- Light affects the growth of plant shoots in a response known as phototropism
- the conc of IAA determines rate of cell elongation; higher conc causes increase in elongation
- When light shines on a stem from one side, IAA is transported from the illuminated side of a shoot to the shaded side via active transport
- IAA gradient is established, with more on shaded side and less of illuminated side
- The higher concentration of auxin on the shaded side of the shoot causes a faster rate of cell elongation, and the shoot grows towards the source of light
effect of IAA in roots
- roots respond to gravity via geotropism
- In roots, IAA concentration also affects cell elongation, but higher concentrations result in a lower rate of cell elongation
- IAA is transported towards the lower side of plant roots via active transport
- the resulting high concentration of auxin at the lower side of the root inhibits cell elongation
- the lower side grows at a slower rate than the upper side of the root, causing the root to bend downwards
what is flowering in plants controlled by
night length
- when nights reach a certain length, genes that control flowering may be switched on or off, leading to activation or inhibition of flowering
- switched on genes are expressed, leading to the production of polypeptides for which they code
-length of night can be detected by a plant because it determines the quantities of different forms of a pigment called phytochrome in the leaf
two forms of the phytochrome pigment
Pr - inactive form, absorbs light from the red part of the spectrum
Pfr - is the active form of phytochrome, it absorbs light from the far red part of the spectrum
how do levels of Pr and Pfr change during the day and night
During the day levels of PFR rise
Sunlight contains more wavelengths at 660 nm than 730 so the conversion from PR to PFR occurs more rapidly in the daytime than the conversion from PFR to PR
During the night levels of PR rise
Red light wavelengths are not available in the darkness and PFR converts slowly back to PR
how are micro-organisms genetically modified
- Restriction enzymes are used to remove the gene coding for a desired protein from an organism’s genome
- Many copies of the gene are made using the polymerase chain reaction, or PCR
- These copies are inserted into small loops of DNA called plasmids, which then transfer the copies into micro-organisms - catalysed by DNA ligase
- The genetically modified micro-organisms are grown in large fermenters containing nutrients, enabling them to multiply and produce large quantities of the new protein
- The protein can be isolated and purified before being packaged and distributed
how are plant cells genetically modified
- After the gene is inserted into a plasmid and then transferred to a bacterial cell, the bacteria can be used to infect plant cells; the bacterium acts as a vector for introducing the gene into the plant DNA
- The gene is transferred from the bacterial cell into the plant cell nucleus, after which the plant cell is stimulated to multiply and grow into an adult plant
- The protein can now be purified from the plant tissues, or the plant can be eaten to deliver the drug
how can animals be genetically modified
- The gene that codes for the desired protein is injected into the nucleus of a zygote
- The zygote is implanted into the uterus of a surrogate animal where it develops into an adult animal
- The protein can be purified from e.g. the milk of the animal
brain development definition
the growth of the brain and the formation of connections between neurones
what factors can be measured to determine brain development
brain size
number of neurones
the level at which the brain is functioning
how can animal experiments be used to study nature and nurture
- the environment in which the animals live can be manipulated to allow the investigation of the impact of environment on brain development
- animals of the same species have similar genes, therefore it is more likely that differences in brain development would be due to environmental factors
- genetic modification can be used to switch off the function of a gene, raising genetically altered animals alongside unaltered animals in a similar environment allows the impact of genetic factors to be studied
how can twin studies be used to show the effect of nature vs nurture
- Identical twins are genetically identical to each other so if they are raised in different environments then any differences in brain development would be due to nurture, while similarities would be due to nature
-When identical twins are raised together their environments will be very similar, so it can be very difficult to distinguish between the impacts of nature and nurture - Scientists will often use non-identical twins raised in a similar environment as a control group when studying identical twins raised together in the same environment
- Non-identical twins are genetically different
This cancels out the effect of the environment
how do cross cultural studies show nature vs nurture
- Different cultures provide different environmental influences on the brain development of children
- Scientists can study the effect of this by comparing large groups of children of a similar age from different cultural backgrounds
- Any differences in brain development are more likely to be due to nurture, whereas any similarities will more likely be due to nature
how do newborn studies show nature vs nurture
- The environment outside the womb would not have impacted the brain development of a newborn baby
- The level of brain development that babies are born with are therefore more likely due to nature than nurture
how do brain damage studies show nature vs nurture
Scientists can choose a particular characteristic and then compare the development of that trait in children born with and without brain damage
- cant be used in adults as they are usually fully developed
compare and contrast between fmri and mri
- both use a combination of magnetic fields and radio waves to generate images
- Both can be used to identify areas of abnormal or damaged tissue
- fMRI scans show the location of oxygenated blood while MRI does not
- fMRI allows both the structure and function of the brain to be studied in real time WHILE MRI can only provide information on brain structure (static images)
explain the importance of the critical period in the development of the visual cortex
- the neurones in the visual cortex must be visually stimulated soon after birth to form synapses and transfer visual information through visual cortex
- in order for the neurones to be organised correctly in the visual cortex
state two arguments against animal research
- Animals are not able to give consent to being experimented on and many believe they should have the same rights as humans
- Many animals experience pain/distress or are killed during research
why is L-dopa an effective treatment parkinsons disease
It is transported from the blood to the brain where it is converted to dopamine by enzymes/dopa-decarboxylase;
Dopamine concentration in the synaptic cleft increases;
More (dopamine) binds to receptors on the postsynaptic membrane;
(This results in) more sodium channels on the membrane that opens;
The postsynaptic neurone is depolarised leading to more action potentials being generated / more nerve impulses are transmitted in parts of brain controlling movement;
The sufferer will have better control over their movement
how does transmission of nerve imuplses change during habituation
(When habituation takes place) fewer calcium ions move into the presynaptic neurone (when nerve impulse arrives)
Less neurotransmitter is released into the synaptic cleft;
(This results in) fewer molecules of neurotransmitter binding to receptors on the postsynaptic membrane;
Fewer sodium channels open and fewer sodium ions move into the axon;
The charge inside the axon remains negative;
The threshold potential is not reached
vector definition
- a carrier of DNA
- into another cell
give two advantages of using micro organisms in genetic engineering
- they are uniceullular so do not require much space
- They can reproduce quickly to produce large quantities of the new protein;
human genome definition
all the DNA present in a human
Describe the functions of the enzymes used to genetically modify bacteria.
- restriction enzyme used to cut plasmid
- forming sticky ends
- ligase enzymes used to add isolated gene to plasmid
- ligase forms phosphodiester bonds between nucleotides
- recombinant DNA produced
Explain how human genome sequencing can be used to identify mutations
- sequence the genome of the people with mutation
- sequence the genome of a number of people without the mutation
- compare the base sequences to identify mutations
genome definition
the complete set of genes or genetic material present in a cell or organism.
all of the introns and exons in an organism
why can tech be described as personalised medicine
- targets an individuals specific mutation
- the rna molecule used will be specific to each individual
The non-protein part of the light-absorbing pigment in the rod cells of the retina is called
retinal
Explain how fMRI can be used to identify parts of the brain
- fmri detects blood flow in the brain
- increased brain activity results in increased blood flow in the area of activity
- fmri detects areas where less signal is absorbed
how does IAA allow a plant to grow
- IAA diffuses from the tip
- so can be taken up by cells in zone of elongation
- which causes the cells to elongate
- therefore causing the plant to increase in height
what is phytochrome
a photosensitive pigment
what is the role of the dendrites in a neurone
- forms synapses with other neurones
- receives impulses from other neurones
- involved in summation
- initiates an action potential to the cell body
Compare and contrast the structure of a sensory neurone and a motor neurone
- both have a cell body containing a nucleus
- both have an axon
- both have dendrites at one end and terminal branches at the other end
- different location of the cell body
how does dopamine act as a neurotransmitter
released from presynaptic membrane into the synaptic cleft
binds to receptors on post synaptic membrane
opens sodium ion channels
initiating depolarisation and an action potential in the post synaptic neurone
explain how the use of MDMA could result in depression
MDMA use results in depletion of serotonin
pot synaptic membrane becomes less responsive to serotonin
State how an increase in calcium ion uptake by the neurone leads to the release of noradrenaline.
calcium ions cause vesicles to fuse with pre synaptic membrane
Describe the role of sodium ions in the functioning of a mammalian rod cell.
sodium ions are pumped out of the rod cell
in the light sodium ions do not move back into rod cell
in the dark sodium ions can move back into rod cell
Explain how an enzyme is involved in joining two different genes together
dna ligase joins the two genes
by forming phosphodiester bonds
by condensation reactions
phytochrome can be described as
a photosensitive pigment
Give one example of a growth response of a plant that is affected by phytochrome
flowering
Describe the role of visual stimulation on the development of the visual cortex during the critical period.
ocular dominance columns develop in visual cortex
neurones form synapses with these columns
action potentials along neurones required to strengthen connections
stimulation during critical period needed to form connection in visual cortex
It is safer to use MRI than computed tomography (CT) because
CT uses x rays that can cause mutations in the DNA of muscle fibres
nervous system and endocrine system differences
nervous:
electrical impulse
fast transmission
short effect
endocrine:
chemical
slower transmission
longer effect
why is conduction faster in myelinated neurones
schwann cells covering the axon
schwann cells provide insulation
action potential at nodes of ranvier
impulse jumps from node to node
local currents occur over a longer distance
Explain the advantages of using MRI scanning to identify tumours compared to
using CT scanning.
- mri gives better resolution
- therefore more detail can be seen
- no use of x rays
- therefore safer and can be used more often
