Grey matter Flashcards
describe the function of a motor neuron
- transmitting electrical signals from CNS to effectors - glands and muscles.
Describe the structure and function of a sensory neuron
Cell body in the middle of the cell
transmits impulses from receptors to CNS
describe the structure and function of a relay neuron.
- located within the CNS, and transmit electrical impulses from sensory to motor neurons.
- lots of short dendrites and a long axon, with the cell body at the end of the neuron.
Describe the function of myelin sheath
- increases the speed of impulses by acting as an electrical insulator, allowing travel by saltatory conduction.
What factors affect transmission of an impulse?
- thickness of the neuron.
Describe the process in an axon that allows nerve impulses to be detected.
- potential difference across the axon changes from -70 to +40mV.
- voltage gated sodium channels open.
- causing sodium ions to move into axon.
- this causes potassium channels to open
- this causes repolarisation as potassium ions move out of the axon.
Describe the role of dendrites in a neuron.
- forms connection with other neurons
- receives impulses from other neurons
- initiate an action potential to the cell body/axon.
Describe the process of synaptic transmission
- on the arriving of action potential, the presynaptic neuron depolarises, and causes Ca2+ channels to open, and allow flow of Ca2+ ions into the neuron.
- This causes the fusion of synaptic vesicles filled with a certain neurotransmitter to the presynaptic neuron membrane into the synaptic cleft (the gap between)
- the neurotransmitter binds to receptors on the postsynaptic membrane, which stimulates Na+ ions to move in, causing another action potential (due to depolarisation)
- following the breakdown of the neurotransmitter, its taken up by the pre synaptic membrane and reused - this (presence of receptors on only one side) and the refractory period allows for travel in only one direction.
Name 3 processes Schwann cells are involved in.
- Phagocytosis
- electrical insulation
- nerve regeneration
Describe the role of the dendrites in a neurone.
- connect neurons to each other
- allow for receiving impulses from other neurons
- involved in summation
Describe the sequence of events that leads to the formation of an image.
- Light (stimulus) is received by the photoreceptor cells in the retina
- this causes impulses to travel up the CNS via the optic nerve
- info is passed on to the brain via a relay neuron
- info is processed
- Impulses sent down relay neuron to motor neuron
- Motor neuron impulses received by effector which carries out response (radial muscles and circular muscles)
Describe what happens to the radial and circular muscles when there is very little light
- pupil dialates
- because circular muscles relax
- radial muscles contract
Describe what happens to the radial and circular muscles when there is a lot of light
- pupil contracts
- circular muscles contract
- radial muscles relax.
describe saltatory conduction
- the idea of impulses ‘jumping’ from one node of Ranvier to another- which reduces the potential difference of the next node, causing the impulse to jump - initiating another action potential.
Excitatory neurons
- neurons that make the membrane more permeable to Na+ ions
- making it more likely that the threshold potential will be reached
- and more likely that the neuron will depolarise.
Inhibitory neurons
- make membrane more permeable to Cl- ions
- so less likely that the threshold potential will be reached
- so less likely the neuron will depolarise
Spatial summation
- when simultaneous impulses from multiple different neurons come along a pre-synaptic neuron to a post synaptic neuron
- number of these impulses coming determines response.
Temporal summation
- multiple impulses coming one after another in a short amount of time on one pre-synaptic neuron
- the time interval has to be short - only then can they summate and initiate an action potential.
what causes plant cells to elongate?
- auxins
Where are auxins released
- the darkest part of the shoot
what is a tropism
- growth in response to a stimulus
What are shoots in a seed showing?
- negatively gravitropic
Describe the role of photoreceptors
- name 2 types of photoreceptors in the eye.
- to detect light
- rods and cone
What do the rods and cones synapse with?
- bipolar neurons
What do bipolar neurons synapse with?
- ganglion neurons
Describe light reception in rod cells in the dark in terms of synaptic transmission
- Na+ ions diffuse into the rod cell, moving down the conc gradient in the cell, and is then actively pumped out. This creates a state of constant depolarisation.
- This results in synaptic vesicles of the rod cell constantly fusing with the synaptic membrane of the rod cell, releasing glutamate into the synaptic cleft.
- Glutamate binds to bipolar cell, stopping it from depolarising.
- this prevents an action potential from occurring in the Ganglion neuron, which prevents impulse reach optic neuron - no image is seen.
Describe light reception in rod cells in terms of synaptic transmission and action potential when its light.
- rhodopsin broken down into opsin and retinal
- the presence of opsin closes the ion channel, resulting in no Na+ ions diffusing into the rod cell, but still being actively pumped out.
- thus, this causes no action potential in the rod cell, meaning no glutamate can be diffused across the synaptic cleft to the bipolar neuron.
- this allows the bipolar neuron to depolarise, allowing the flow of Na+ ions into the bipolar neuron
- Thus, an action potential can be initiated in the optic nerve, allowing for the formation of the image.
Define dark adaptation
the reforming of rhodopsin after its breakdown from exposure to light.
What is a phytochrome
consists of a protein component bonded to a non protein component, and acts as photoreceptors in plants
What will happen if Pr is exposed to red light
it will be converted to Pfr
What will happen if Pfr is exposed to far-red light
- it will be converted to Pr
What happens to Pfr in the dark
Its converted (reverted) back to Pr
What triggers and inhibits germination?
red light: triggers
far red light: inhibits
Define what is meant by a photoperiod
The relative length of day and light that determines time of flowering - allows for determining the ratio of Pr: Pfr
Give 3 characteristics of long day plants
- flower when day length exceeds a critical value
- flower when period of uninterrupted darkness is less than 12 hours
- need Pfr to stimulate flowering \
Give 3 characteristics if short day plants
- tend to flower when periods of uninterrupted darkness exceeds 12 hours
- need long hrs of darkness to convert all their Pfr to Pr for flowering
- a flash of red light in the middle of the dark period may negate the effect of the dark period.
Describe what is meant by greening
- when a shoot has broken through soil into sunlight and goes through profound changes in both its form and biochemistry.
How do phytochromes switch processes on or off?
- exposure to light means that they may change shape
- the phytochrome may also bind to other proteins and act as transcription factors, or activate transcription factors
- these transcription factors can bind to DNA that allows transcription that result in the plants response to light
- thus translation can take place, allowing for the amino acid chain to be formed, and thus the protein.
Name the 4 lobes of the brain
- frontal
- temporal
- parietal
- occipital
Function of the frontal lobe
- higher brain functions- eg decision making, reasoning, planning, consciousness of emotion, associations
Function of parietal lobe
- orientation
- movement
- sensation
- calculation
- recognition + memory
Function of temporal lobe
- auditory information, hearing sound
- speech recognition
- memory
Function of thalamus
- responsible for routing sensory information to the correct part of the brain via axons of the white matter
function + location of the hypothalamus
- underneath the thalamus
- contains thermoregulatory centres, to maintain body temp.
- sleep, thirst and hunger control centres.
- acts as an endocrine gland, eg releasing ADH
Function of hippocampus
- involved in laying down long term memory
Function of midbrain
- relays info to the cerebral hemispheres, including auditory info to the temporal lobe, and visual info to the occipital lobe.
Explain how PET scans work.
- use radioactive markers
- detect position of gamma rays
- provides 3d image.
Explain how fMRI can be used to identify the part of the brain involved in interpreting
information from the visual cortex.
- detects oxygen in the brain.
- increased activity results in more blood flowing to that area, carrying oxygen
- oxyhaemoglobin absorbs fewer radio waves, and fMRI detects this signal which helps produce an image with an area of the brain ‘highlighted’
Describe CT scans
- narrow beamed X-ryas fired
- each narrow beam is reduced in strength on its path depending on the density of the tissue it passes through
- this is detected and an image is produced.
Describe how MRI works
- magnetic field created
- radio waves fired which generates an image
Name 4 uses of genetic modification
- produce medicines which are scarce
- remove impact of diseases
- improve characteristics of an organism
- speed up production of foods.
Describe the process of genetic modification in microorganisms such as bacteria.
- Isolate the gene of interest from organism
- Use bacterial plasmid as a vector
- cut the human DNA and plasmid using the same restriction enzyme
- splice the gene together using ligase
- put the modified plasmids into bacterial cells
- allow bacterial cells to divide in a fermenter.
- purify and extract protein of interest.
Define micropropagation
- propagation of plantlets through tissue culturing them, then planting them.
What are the main arguments FOR GMOs? (3)
- to make them more resistant to diseases
- To produce enzymes/vaccines
- To improve nutritional value of foods
define innate
- something that is natural and not learned
describe the route of neurons in the brain to form an image.
- optic nerve goes to the thalamus
- neurons from the thalamus go to alternative columns of cells in the visual cortex in the.
define depth perception
ability to determine dimensions, including size and how far a certain stimulus is.
Define stereoscopic vision
- the sense of depth derived by both eyes for images less than 30m
Define the critical period
- the period of time early in the life of animals in which exposure to visual stimuli is vital to ensure proper development of the visual cortex.
Describe what happens to neurons of the visual cortex during visual development
- synapses that do not receive visual stimuli during the critical period are destroyed.
- the rest are retained and synapse with the visual columns in the visual cortex.
- This is because neurons compete for space on the visual columns.
Describe the procedure, findings and conclusions of Hubel and Wiesel’s experiments to study development of the visual cortex of young kittens
- conducted on young kittens.
- one eye was stitched shut, and kept like this for several months.
- on unstitching the eye, they found that the eye was blind.
- repeated the experiment with monkeys, and found the same results.
- concluded that ocular dominance columns remain normal in both eyes if stimulated early in life.
Arguments AGAINST GMOs? (3)
- often patented and seeds expensive - disadvantage to farmers in developing countries
- GM plants cross-pollinating other species, potentially creating superweeds that are resistant to herbicides.
- long term impact of GMOs cannot be predicted.
Arguments FOR the use of animal studies? (2)
- unethical to carry out on humans, so animals still allow to test effects on a whole organism without risking human lives.
- animals and humans are similar so we can apply results to humans.
Arguments against the use of animal research?
- unethical to cause pain or suffering to a living being
- alternatives to using animals - cell cultures
- animal studies not necessarily applicable to humans.
Define habituation
- repeated exposure to stimuli which causes the individual to ignore the stimuli.
Why is habituation important?
-so that limited attention and memory resources can be concentrated on on more threatening or rewarding stimuli.
Describe how habituation takes place.
- fewer calcium ions move into the presynaptic neurone when its depolarised
- leading to fewer neurotransmitter molecules are released.
Describe the role of dopamine
- neurotransmitter that makes you feel satisfied, motivated.
Which neurons secrete dopamine into the motor cortex
- neurons in the basal ganglia
Describe 3 symptoms of low dopamine levels
- poor balance
- walking trouble
- stiffness/tremors
Describe the mechanism of Parkinson’s disease.
- Parkinson’s disease causes low dopamine levels
- thus, less dopamine available to bind with post-synaptic neuron
- so fewer sodium channels open, firing less action potentials
Describe the mechanism of L-Dopa in the treatment of Parkinson’s disease.
- it is a precursor to dopamine(it gets converted to dopamine itself)
- drug is converted to dopamine by dopa-carboxylase in the brain
- thus more dopamine is available to bind to post-synaptic neuron, making it more likely for sodium channels to open and for an action potential to fire.
Describe the mechanism of MDMA for the treatment of depression
- It increases the level of serotonin in brain by inhibiting the reuptake of serotonin by presynaptic neurons as it blocks the reuptake proteins.
- This means serotonin level remain high in synapse, which results in more action
potential across synapses that control mood.
Define the term genome
all the DNA, including inter-organelle DNA inside of an organism.
Name 2 outcomes of the Human Genome project
- can identify genes that relate to disease, or increase susceptibility to a disease.
- personalised medicine, as genetic variation can determine how people respond to drugs.
Outline 3 ethical issues for the outcomes of the Human Genome project.
- higher research costs may mean that only wealthier people have access to personalised medicine.
- insurance companies unfairly discriminating against people who may have a genetic vulnerability to a disease.
- distress caused to the patient and their families knowing that the only available meds might not work.
Explain how genome sequencing could be used to identify genes related to a certain disease.
- sequence the genome of people without the disease.
- sequence the genome of people with the disease.
- compare the base sequences, and identify mutations only present in people with the condition.
