Topic 8A - Responding to the Environment Flashcards
EQ. Explain the electrical changes in an axon that allow nerve impulses to be detected. (4 marks)
- the potential difference of the axon changes
- as sodium channel open
- sodium ions enter the axon membrane
- this is depolarisation
- as sodium channels close and potassium channels open
- potassium leaves the cell membrane during repolarisation
How does a sensory neurone structurally differ from motor and relay neurones
In a sensory neurone the cell body is in the middle of the axon
EQ. Explain why there is a difference in the conduction velocity of a myelinated neurone and a unmyelinated neurone. (5 marks)
- schwann cells wrap around the axon to create a myelin sheath
- this is an insulator as its impenetrable to Na+ and K+ ions
- depolarisation occurs at the nodes of ranvier
- electrical impulse jumps from node to node
- this is called saltatory conduction
During depolarisation, are the K+ channels open or closed?
closed
During depolarisation, are the Na+ channels open or closed?
open
During repolarisation, are the Na+ channels open or closed?
closed
During repolarisation, are the K+ channels open or closed?
open
Describe the resting potential of the axon membrane
At rest, the inside of the axon membrane is more negatively charged than the outside
At what potential difference is an action potential produced
+30mV
At what potential difference is the threshold for depolarisation
-55mV
At what potential difference is the resting potential at?
-70mV
During hyperpolarisation, does the potential difference become more or less negative than the resting potential
more
State 3 factors that affect the speed of nerve transmission
- myelination increases speed cuz of saltatory conduction
- higher temperature increases speed
- larger surface area
Describe saltatory conduction
When action potentials jump from node to node (node of Ranvier). This is because the axon is myelinated and wrapped in Schwann cells, making it impenetrable to Na+ and K+ ions.
What causes flowering in plants
phytochromes
Describe Pfr
Pfr is the active form and absorbs far red light
Describe Pr
Pr is the inactive form and absorbs red light
What does a high proportion of Pfr represent
a longer day, shorter night
What does a high proportion of Pr represent
a shorter day, longer night
If Pr absorbs red lights what does it convert into
Pfr
In short day plants, what effect will Pfr have on flowering
It will inhibit flowering
In long day plants, what effect will Pr have on flowering
It will inhibit flowering
In shoots, does IAA promote or inhibit growth?
promote
In roots, does IAA promote or inhibit growth?
inhibit
Describe the process of phototropism in shoots
Shoots are positively phototropic. So IAA is transported to the more shady parts, promoting growth and causing it to elongate towards the light.
Describe the process of phototropism in roots
Roots are negatively phototropic. So IAA is transported to the more shady parts, inhibiting growth causing it to grow away from the light
EQ. Explain how the structure of the cell surface membrane of a motor neurone is related to the conduction of a nerve impulse along its axon. (6 marks)
- the membrane is made out of a phospholipid bilayer
- with the hydrophobic tails facing inwards to inhibit the movement of charged particles across the membrane
- there are protein channels like Na+ channels
- to allow Na+ to diffuse during depolarisation
- and K+ channels
- to allow K+ to diffuse during repolarisation
- theres a sodium-potassium pump
- to export Na+ and take in K+
- in saltatory conduction only the nodes of Ranvier will be used since the action potential jumps from node to node
EQ. Suggest an explanation for how eugenol affects the movement of calcium ions and reduces pain. (6 marks)
- because less Ca2+ channels will be open
- less Ca2+ ions will diffuse into the pre-synaptic membrane
- less vesicles carrying neurotransmitters will fuse with the pre-synaptic membrane
- so less neurotransmitters will be released into the synaptic cleft
- less neurotransmitter will bind to the receptors on the post-synaptic membrane
- pain will not be sensed as the impulse will be stopped before leaving the senory neurone
EQ. Explain how myelination increases the speed of transmission of nerve impulses in a sensory neurone. (5 marks)
- when myelinated, sensory neurones are covered in schwann cells
- this acts as an electrical insulator making it impenetrable to Na+ and K+ ions so no depolarisation can occur
- however at the nodes of Ranvier theres no myelination -so depolarisation can occur at the nodes
- the impulse jumps from node to node
- this is called saltatory conduction
Name one hormone and state its function.
Testosterone, stimulates sperm production
EQ. Describe and explain the sequence of events that occurs at the synapse, after a neurotransmitter has been released. (5 marks)
- neurotransmitters diffuse across the synaptic gap
- they bind to receptors on the post-synaptic membrane
- Na+ channels open, allowing Na+ ions to diffuse into the post-synaptic membrane
- causing depolarisation
- and therefore a action potential is produced
- neurotransmitters are broken down by enzymes
- and reabsorbed through the pre-synaptic membrane
EQ. Explain why L-Dopa is used to treat people with Parkinson’s disease. (2 marks)
- can convert to dopamine in the brain
- and increase dopamine levels in the brain
- can reduce symptoms of parkinson’s disease because they have low dopamine levels
EQ. Explain how MDMA could affect levels of serotonin in the brain. (3 marks)
- inhibits the reabsorbtion of seratonin into the pre-synaptic membrane from the synapse
- increasing levels of seratonin
EQ. In trials of this treatment, marmosets (small monkeys) were given a drug to reduce dopamine production. Suggest a reason why the marmosets were treated with a drug to reduce dopamine production. (1 mark)
to mimic parkinson’s disease
EQ. Describe the steps that would need to be taken before a similar treatment could be used in humans. (3 marks)
- test a small sample of healthy individuals for safety
- test a large sample of patients for effectiveness
- can use a double blind trial
- where neither doctor or patient know whose been giving a drug or a placebo
What is the non-protein part of the light-absorbing pigment in the rod cells of the retina called?
retinal
What is the protein part of the light-absorbing pigment in the rod cells of the retina called?
opsin
Name the part of the brain involved in interpreting the info processed in the visual cortex
cerebellum
EQ. Describe the role of visual stimulation on the development of the visual cortex during the critical period. (3 marks)
- ocular dominance columns develop in the visual cortex
- neurones form synapses with these columns
- stimuli is required to strengthen connections with the columns of ocular dominance in the visual cortex in the critical period
EQ. What is the role of dendrites. (3 marks)
- dendrites receive electrical impulses from other neurones
- dendrites interconnect multiple neurones allowing them to send electrical impulses
- it initiates an action potential to the axon
What is tropical
The response of a plant to a directional stimulus
Why do plants and animals need to responde to stimulus
To increase their chances of survival