paper 2 - response to stimuli and the nervous system Flashcards
1
Q
what is taxis
A
- directional movement to or away from a stimulus
- positive taxis - towards a stimulus
- negative taxis - away from a stimulus
2
Q
what is an example of taxis
A
- earthworms move away from light - negative phototaxis
- this is because there is more chance of survival as they move into the soil, as they are more likely to find food, more likely to avoid predators and less likely to dehydrate
3
Q
what is kinesis
A
simple response by an animal to a change in stimulus by changing in rate of movement ( increasing or decreasing activity or changing direction more or less frequently )
it is random and non directional
4
Q
example of kinesis
A
- low humidity results in more woodlice moving, so increased movement increased chance of leaving dry / unfavorable environment so reduce water loss via spiracles
5
Q
required practical 10 - investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze
A
- in the bottom half of the chamber they put a substance which absorbs water
- different concentrations of this substance produced different humilities in the air above the mesh
- record the number of woodlice not moving during the next 30 secs
6
Q
what is a reflex action
A
a reflex is a rapid involuntary response to stimuli it is automatic / not learnt so it does not involve the brain
7
Q
what is tropism
A
- the response of a plant to a directional stimulus. plants respond to these stimuli by regulating growth
-positive tropism - growth towards a stimulus - negative tropism - growth away from a stimulus
8
Q
examples of tropism
A
- plant shoots grow towards light - positive phototropism - increases chance of light falling on leaves and therefore increases rate of photoythesis
- plant roots grow away from light - negative phototropism -roots grow into soil, more likely to absorb water and mineral ions
9
Q
what is IAA and where does it move
A
- plant growth factor, one effect is to cause elongation of plant cells
- produced in tips of roots and shoots and moves to growing region
- then moves to more shaded parts of roots and shoots ( negative phototropism )
- also moves to underside of roots and shoots ( positive geotropism )
10
Q
what happens to IAA in the shoots
A
- IAA synthesised in shoot tips
- diffuses into growing region
- light causes movement of IAA from light to shaded side
- more IAA on shaded side
- IAA activates enzymes that increase cell wall plasticity resulting in cell elongation on shaded side
- causes shoot to bend towards the light
11
Q
what happens to IAA in roots
A
- IAA synthesised in root tips
- diffuses into growing region
- IAA moves towards underside / shaded side
- inhibits elongation, decreasing growth
12
Q
what is the cell body
A
- nucleus and cytoplasm
- produces protiens and neurotransmitters
13
Q
what are dendrites
A
- carry nerve impulses towards cell body
14
Q
what does the axon do
A
carries nerve impulses away from the cell body
15
Q
what do the schwann cells do
A
produce myelin
16
Q
what does the myelin sheath do
A
- myelin ( lipid) insulate axon increasing speed of transmission of nerve impulse
17
Q
what do the nodes of ranvier do
A
- gaps between shwann cells where myelin is absent
18
Q
what does the terminal end branch do
A
connect neurone to effector
19
Q
how does a neurone transmit electrical impulse
A
because there is a difference in electrical potential across the membrane
- the difference is a potential across the axon membrane and could be measured with a voltmeter
20
Q
what is resting potential
A
- potential difference of -70mv across the membrane
- membrane is polarised - it is maintaining a potential difference between 2 sides
21
Q
how is resting potential reached
A
- sodium ions are actively transported out of the cell and potassium ions are actively transported out of the cell and potasium ions actively transported into the cell by sodium potassium pump using ATP
- axon membrane is more permeable to potassium ions so potassium ions diffuse back out down their concentration gradient
- inside becomes more negative compared to outside
- electrochemical gradient is created, drawing some of the positive charged potassium ions in
- overall equilibrium between k+ diffusion out and electrochemical gradient back = -70mv
22
Q
synoptic points for sodium potassium pump
A
- sodium potassium pump is a carrier protein involved in active transport
- active transport requires energy in the form of ATP
- mitochondria are the site of aerobic respiration and are involved in the production of ATP, there will be many mitochondria in neurons
- channel proteins are involved in the facilitated diffusion o ions across the membrane
- protiens are specific
23
Q
what is electrical nerve impulse transmission
A
- changes in membrane permeability lead to depolarization and the generation of an action potential
- resulting potential is maintained until the membrane is disturbed or stimulated by a stimulus - an action potential is generated
24
Q
when does an action potential occur
A
when the membrane becomes depolarized
- an action potential is the reversal of the resting potential
- resting potential goes from -70mv to + 40mv in short period of time
25
what is depolarisation
- the stimulus causes the membrane to become more permeable to sodium ions ( the voltage gated sodium channels open if the threshold potential is reached )
- sodium ions rapidly diffuse into the axon
- the high concentration of positive ions inside the axon becoming positive in relation to the outside
26
what is repolarization
- as the volatge gated sodium gates close the voltage gated potassium gates open at + 40mv
- potassium ions diffuse out of the axon known as repolarisation
27
what is the all or nothing principle
- an action potential willl only occur when the membrane is stimulated so that all the sodium channels are open
- the minimum intensity of a stimulus is called a threshold
- below the threshold no action potential will occur
- above the threshold a full size action potential will occur
- regardless of the increase in the size of the stimulus
- this means that the impulse is always the same height - goes from -70mv to +40mv and the same width
- if the stimulus is bigger, the number of AP will increase
28
what is the refractory period
-after transmitting an electrical impulse an axon has to recover ( return to resting potential ) before it can transmit another impulse ( depolarise again )
- the period is inexcitability following the transmission of an impulse is the refractory period
- essential as it means that there are discrete impulses which pass along the axon and limits the frequency of impulse transmission
- potassium gates remain open for longer that needed to reach resting potential, making the inside of the axon even more negtive - hyperpolarisation
- the sodium potassium pump restores the membrane to resting potential
29
what is the impulse transmission along the axon
- nerve impulse is the movement of action potentials along the neuron
- action potentials act as a stimulus to adjacent polarized areas of the membrane and this causes the action potential to be passed along
30
how does impulse along the axon occur
- an impulse above threshold depolarizes the axon membrane
- sodium ions enter and the inside of the axon becomes positively charged
- this sets up loacalised electrical currents in the axon
- this depolarizes the next section of the axon membrane
- the first section of the axon membrane is in its refractory period as potassium ions diffuse out as it repolarizes
- this means the impulse cant pass back towards the cell body
- in this manner the impulse passes all the way along the synapse
31
what are the factors affecting speed of conductance
1) myelination
2) temp
3) axon diameter
32
how does myelination of neurones affect speed of conductance
- allows nerve impulses to travel by jumping from one node of ranvier to the next - known as saltatory conduction
- occurs because the lyelin sheath insulates the axon and depolarisation can only occur at the nodes
- the currents produced depolarise the next node and the impulse is passed along by jumping from node to node
33
how does temp affect speed of conductance
- higher temps increase rate of diffusion of ions due to higher kinetic energy, therefore increasing the rate of conductance
34
how does axon diameter affect speed of conductance
the larger the axon diameter the greater the surface area for ion movement so the greater the speed of conductance
35
why are synapses unidirectional
- vesicles containing neurotransmitters are found in presynaptic neuron only
- receptors for neurotransmitters are on post synaptic neuron only
36
what is acetylcholine
- neurotrasmitter in the parasympathetic branch of the ANS
- synapses where acytlcholin is found in called a cholinergic synapse
37
how does a synapse work
- impulse arrives at the end of presynaptic neurone causing calcium ion channels in the membrane to open
- calcium ions diffuse into the presynaptic neurone casuing vesicles containing neurotrasnmitter to move to and fuse with the presynaptic neurone membrane, releasing the neurotrasnmitter into the synaptic cleft
- neurotrasnmitters diffuse across the synapse and bind to specific complementary receptors on the post synaptic membrane
- this causes sodium ion channels to open allowing sodium ions to diffuse in and the membrane is depolarised
- if threshold potential is reached then an action potential occurs and spreads along the axon of the postsynaptic neurone
38
how does a cholinergic synapse work
- where neurotransmitter is acetylcholine the enzyme acetylcholinesterase hydrolyses acetyl choline into choline and ethanoic acid
- these then diffuse back across the synaptic cleft into the presynaptic neurone
- ATP released by mitochondria used to re synthesize acetylcholine which is then stored in vesicles
39
what is an excitatory synapse
cause an action potential in post synaptic neurone
40
what is an inhibitory synapse
neurotransmitters which affect different receptors on post synaptic neurone
the resting potential falls to a lower level and the postsynaptic membrane is therfore less likely to reach the thresholf value and generate an action potential
41
what is a neuromuscular junction
a synapse between a motor neurone and a muscle cell
so transmission needs to be fast
42
comparison of a cholingeric synapse and neuromuscular junction
c is between neurones whereas nj is between neurone
both are excitatory
both release acytlcholine
c post synaptic membrane is less folded whereas nj is more folded
c has less receptors whereas nj has more
c has acytl cholinesterase in synaptic cleft whereas nj has acytl cholinesterase in in its clefts in the folds of the post synaptic membrane
43
what is spatial summation
often synapses have different neurones converging so that impulses arrive from a number of neurones at the synapse
- this causes a release of enough neurotransmitters sufficient to reach threshold potential to cause an actiopn potential in the next neurone e.g. retina of the eye, allowing us to see in dim light conditions
44
what is temporal summation
- there is only one pre synaptic neurone but the impulses arrive in quick succession giving a cumulative effect which is sufficient to reach threshold potential, depolarising the post synaptic neurone
45
what 2 ways can drugs act on the synapse
1) they can stimulate the nervous system by creating more action potentials in the post synaptic neurone - excitatory effect
- drugs may have similar shape to neurotrasnmitters and bind to receptors on post syanptic membrane mimicking the effect of the neurotransmitter
- drug may cause an increase in the release of the neurotransmitter
- drug may inhibit enzyme that hydrolyse the neurotransmitter
2) they can create fewer action potentials in the post synaptic neurone and have an inhibitory effect
- drug may inhibit release of neurotrasnmitters
- block the receptors on the post synaptic membrane
