T8 - Grey matter Flashcards
What are dendrites and axons
Dendrites carry impulses towards the cell body and axons carry impulses away from the cell body.
What is a Schwann cell
Schwann cells lay down myelin (a fatty, insulating later) around the axons of neurons.
Describe the differences in the structure of a sensory neurone and a motor neurone. (4)
- A sensory neurone has a long dendron, whilst a motor neurone has much shorter dendrites.
- A sensory neurone has myelinated dendrons, whilst a myelinated motor neurone has unmyelinated dendrites.
- A sensory neurone has a shorter axon than a motor neurone.
- The cell body (soma) of sensory neurone is located in the middle, whilst the cell body (soma) of a motor neurone is located at the post-synaptic end.
What is a reflex
A reflex is an automatic reaction that happens very quickly in order to prevent or minimise harm to the body.
Step in a reflex arc
- stimulus
- receptor
- sensory neuron (to CNS)
- relay neuron (spinal cord)
- motor neuron (to effector)
- effector (muscle or gland)
- response
How do eyes respond to bright light
- radial muscles relax
- circular muscles contract
- pupil constricts
How do eyes respond to dim light
- radial muscles contract
- circular muscles relax
- pupils dilate
What does the sodium-potassium pump do in the axon
- It pumps sodium ions OUT of the axon, higher concentration of sodium ions OUTSIDE.
- It pumps potassium ions INTO the axon, higher concentration of potassium ions INSIDE.
What is the resting membrane potential
-70 mV, more negative inside axon
Why is the resting membrane potential -70 mV
Potassium ion leak channels are more permeable to potassium than sodium leak channels are permeable to sodium ions. So more potassium leaves than sodium.
What causes depolarisation
The influx of sodium ions through voltage gated sodium channels which open at -55 mV, the threshold.
What is the membrane potential at the end of depolarisation
+30 mV
What is repolarisation
The change in membrane potential from +30 mV towards a -70 mV again.
What causes repolarisation
The influx of potassium ions through voltage gated potassium channels which open at +30 mV.
What is the membrane potential at the end of repolarisation
A little more than -70 mV leading to hyperpolarisation. This is called the refractory period.
What is an excitatory neurotansmitter
e.g. acetylcholine generates an action potential by binding to receptors on the post-synaptic membrane causing gated sodium ion channels to open.
What is an inhibitory neurotransmitter
e.g. GABA generates hyperpolarisation by binding to receptors on the post-synaptic membrane causing gated potassium ion channels to open.
What is spatial summation
!Excitatory potentials from many neurons trigger threshold point.
What is temporal summation
Many excitatory potentials from one neurone triggers threshold point.
Steps in synaptic transmission
- An action potential reaches the presynaptic membrane.
- The presynaptic membrane undergoes depolarisation.
- Calcium ion channels open.
- Calcium ions enter the neurone.
- The calcium ion concentration increases.
- The synaptic vesicles fuse with the presynaptic membrane.
- The neurotransmitter is released into the synaptic cleft (exocytosis).
- The neurotransmitter diffuses across the synaptic cleft.
- The neurotransmitter binds to the postsynaptic receptor.
- Associated sodium ion channels open.
- Sodium ions enter the neurone.
- An action potential is initiated.
- The neurotransmitter diffuses away and degrades. OR The neurotransmitter is taken back up by the presynaptic membrane (endocytosis).
What is habituation
Habituation is the process of responding LESS strongly over time in response to repeated stimuli. Ca2+ channels in the presynaptic membrane become less responsive.
What does genome sequencing allow in the future
- Identification of mutations
- More bespoke targeted therapy and treatment for the individual.
ethical issues raised by the Human Genome Project and genetic screening
- People may be put under undue pressure to not have children or terminate pregnancies.
- Increases pressure for germ line therapy to prevent children inheriting genetic conditions
- Embryo has no choice/say in the matter.
- May lead to designer babies
How to transfer genes from humans to bacteria
- Isolate the human gene to be transferred using a restriction enzymes (endonuclease) to cut out the gene. This creates sticky ends to the gene that allows it to be inserted into another DNA molecule.
- Use PCR to amplify the gene using DNA polymerase.
- Use a restriction enzyme (endonuclease) to cut open a bacterial plasmid and create sticky ends. Add the human gene to the plasmid.
- Use DNA ligase enzyme to join the sticky ends together to create phosphodiester bonds.
- Culture the recombinant bacterium (with the recombinant plasmid/DNA) to produce the human protein, e.g. insulin. Purify the human protein for use as a drug therapy.
Ways to transfer genes from humans to plants
- Coat the gene in gold then bombard the plant cell.
- Use bacteria that infects plants
- Use viruses that infect plants
What happens to rod cells in the light
- Light energy converts Cis retinal into Trans retinal. (in the outer segment of rod cells)
- Trans retinal cannot bind to Opsin so Rhodopsin is not made, the retina has been ‘bleached’.
- The presence of Opsin causes the cation channels in the outer segment (in rod cells) to close.
- So no Na+ ions can enter.
- But Na+ ions are still pumped out of the inner segment, so hyperpolarisation occurs. (inside is only negative).
- Because of hyperpolarisation the rod cells do not release Glutamate into the synapse with bipolar neurone.
- Without the inhibitory effect of glutamate, the bipolar neurone depolarises and an action potential is generated.
What happens to rod cells in the light
- In the dark (once ATP has converted Trans retinal back into Cis retinal) Cis retinal binds with Opsin to make Rhodopsin (pink).
- No free Opsin means the cation channels remain open.
- So Na+ ions can enter the outer segment.
- The influx of sodium ions leads to depolarisation.
- Depolarisation causes glutamate to be released from the rod cell into the synapse with associated bipolar neurone.
- Glutamate inhibits the bipolar neurone from depolarising and no action potential is generated.
Why does the inner segment require lots of mitochondria?
For actively pumping sodium ions out of the cell in the inner segment, leading to a more hyperpolarised rod cell.
This prevents depolarisation and the release of glutamate.
How does auxin lead to cell elongation
- Auxin activates transcription factors that leads to genes being activated that leads to proteins being made.
- Enzymes cause acidification the breaks the cross-links (H-bonds) that hold cellulose together in the cell wall.
- The vacuole can then increase in size.
How do plants know when to flower
- Using phytochrome red
- Which turns into phytochrome far-red in the presence of light
- Phytochrome far-red turns back into phytochrome red at night (no light)
- Plants can determine the duration of light + season and therefore when to flower
Why do plants flower in the summer
- For long day plants that flower in the summer
- Because when the days are long, the nights are short
- So there is less time for Pfr to turn back into Pr
- So Pfr is above the threshold causing flowering
Why do plants flower in the winter
- For short day plants that flower in winter
- Because the days are short, the nights are long
- So there is more time for Pfr to turn back into Pr
- So Pfr is below the threshold causing flowering
What causes depression
Low serotonin activity
What are the 2 ways depression can be treated
- SSRIs - prevents serotonin being taken up again by transporter proteins remaining in the synaptic cleft for longer.
- Monoamine oxidase inhibitor - inhibits monoamine oxidase enzyme that degrades serotonin.
Wha causes low serotonin leading to depression
- MDMA usage
- Anger control problems
- OCD
What causes Parkinson’s disease
Low dopamine level
What are the 4 ways Parkinson’s disease be treated?
- L-Dopa - gets converted into dopamine in the brain.
- Monoamine oxidase inhibitors - inhibits monoamine oxidase enzyme that degrades dopamine.
- Agonists - structurally similar to dopamine.
- Deep Brain Stimulation - electrodes stimulate the production of dopamine.
What causes schizophrenia
High dopamine levels
How could a drug used to treat schizophrenia exert its effect at a synapse
- The drug needs to be able to pass the blood-brain barrier and bind to post-synaptic, blocking the binding of dopamine.
- The dopamine is unable to bind and stops Na+ ions from entering.
- The reduced influx of Na+ ions causes reduced depolarisation and, therefore, reduced action potentials.
What side effects might a person taking a drug for schizophrenia experience?
Dopamine levels become too low leading to Parkinson’s disease symptoms.
3 advantages of CAT scans
- A 3D image can be created by the computer
- Able to detect tumours
- Relative to other scanning technology, it is cheaper
2 disadvantages of CAT scans
- Unable to determine detail
- X-rays are harmful, so can only use with limited frequency
3 advantages of MRI scans
- High resolution images created (much better than CT scans) so detail can be seen
- No x-rays, so safer and can be used more often to determine disease progression or treatment effectiveness
- Forms 3D images, tumours can be detected
2 disadvantages of MRI scans
- Only able to take an image from one moment in time
- Unable to determine function of different brain regions
3 advantages of PET scans
- Like fMRI, the function of different brain areas can be determined
- Numerous brain disorders can be diagnosed
- Forms 3D images
2 disadvantages of PET scans
- Potential hazards involved as radioactive material is injected into the body
- It is expensive
What is the cerebrum responsible for
Advanced mental activity and controlling voluntary activities. e.g. language, memory.
What is the hypothalamus responsible for
Controls homeostasis and thermoregulation.
What is the cerebellum responsible for
For coordinating muscle movements and balance.
What is the medulla oblongata responsible for
Controls body processes like breathing, heart rate and blood pressure.
