Topic 8

Question 1

what does the CNS consist of

Answer 1

brain and spinal cord

Question 2

what is the peripheral nervous system made up of

Answer 2

• sensory neurones
• motor neurones

Question 3

what is the peripheral nervous system split into

Answer 3

the automatic nervous system
the somatic nervous system

Question 4

what is the automatic nervous system

Answer 4

• involuntary
• stimulates smooth muscle, cardiac muscles and glands

Question 5

what is the somatic nervous system

Answer 5

• voluntary
• stimulates skeletal muscle

Question 6

what is the automatic nervous system subdivided into

Answer 6

sympathetic and parasympathetic

Question 7

what does the sympathetic nervous system do

Answer 7

• prepares body for fight or flight responses
• e.g speed up heart rate
• norepinephrine
• epinephrine

Question 8

what does the parasympathetic nervous system do

Answer 8

• prepares body for rest and digest
• oxytocin

Question 9

recall the 3 different types of neurones

Answer 9

relay
motor
sensory

Question 10

draw and describe the structure of the sensory neurone

Answer 10

• cell body seperate

Question 11

where is the axon and dendron on a neurone

Answer 11

where the axon and dendron is depends on direction of impulse
impulse going left to right → dendron before cell body (on the left hand side) , axon after cell body (on the right hand side)
vice versa if the impulse is going from right to left

Question 12

what does the sensory neurone do

Answer 12

carries information from receptors to CNS

Question 13

what do motor neurones do

Answer 13

carry motor commands from the CNS to effectors

Question 14

draw the structure of the relay neurone

Answer 14

Question 15

draw the structure of motor neurones

Answer 15

Question 16

what is the differences between axons and dendrites

Answer 16

axons:

• unbrached
• myelinated
• only one per cell
• take information away from the cell body
• branch further from cell body

dendrites:

• accept neurotransmitters whereas axons dont
• no myelin sheath
• branched
• multiple dendrite

Question 17

recall the pathway of the reflex arc

Answer 17

1. receptors detect a stimulus and generate a nerve impulse
2. sensory neurones conduct a nerve impulse to the CNS along a sensory pathway
3. sensory neurones enter the spinal cord through the dorsal route
4. sensory neurone form a synapse with a relay neurone
   cell body of sensory neurone found in dorsal route ganglion of the reflex arc
5. relay neurone forms a synapse with a motor neurone that leaves the spinal cord through the ventral route
6. motor neurone carries impulses to an effector which produces a response

Question 18

what is the antagonistic pair in the eye

Answer 18

antagonistic pair → radial muscle and circular muscles
circular muscles contract and radial muscles relax to constrict and vice versa

Question 19

which nervous system controls the radial and circular muscles in the eye

Answer 19

• radial muscles are controlled by sympathetic reflex
• circular muscles are controlled by parasympathetic reflex

Question 20

what is the process of the pupils constricting

Answer 20

high levels of light hits photoreceptors in retina
causes a nerve impulse
the nerve impulse is passed along the optic nerve
one of the sites it passes is a set of coordinating cells in the midbrain
impulses from these cells are sent through parasympathetic motor neurones
the impulse is sent to the circular muscle in the iris
circular muscles will contract, radial will relax
pupil constricts

Question 21

what is the process of the pupils dilating

Answer 21

low levels of light hits photoreceptors in retina
causes a nerve impulse
the nerve impulse is passed along the optic nerve
one of the sites it passes is a set of coordinating cells in the midbrain
impulses from these cells are sent through the sympathetic motor neurones
the impulse is sent to the radial muscle in the iris
the radial muscle with contract and the circular muscle will relax
pupil dilates

Question 22

why does the pupil appear black

Answer 22

the pupil appears black because the cones and rods at the back of the retina ‘’absorb all the light, so none is reflected back

Question 23

what is a stimulus

Answer 23

any change in the internal and external environment

Question 24

what are receptors

Answer 24

• receptors detect stimuli
  
  • they can be cells or proteins on cell surface membranes
    receptors only detect one particular stimulus

Question 25

what are effectors

Answer 25

• effectors are cells that bring about a response to a stimulus
  
  • this includes muscle cells and cells found in glands

Question 26

how do receptors communicate with the effectors

Answer 26

receptors communicate with effectors via the nervous or hormonal system

Question 27

what do the relay neurones do

Answer 27

relay neurones transmit electrical impulses between sensory neurones and motor neurones

Question 28

what happens when a stimulus is detected

Answer 28

• a stimulus is detected by receptor cells and an electrical impulse is sent along a sensory neurone
• when an impulse reaches the end of a neurone neurotransmitters take the information across to the next neurone which then sends an electrical impulse
• the CNS processes the info and sends impulses along motor neurones to effectors

Question 29

what is the hormonal system made up of

Answer 29

made up of glands and hormones

Question 30

what is a gland

Answer 30

a gland is a group of cells that are specialised to secrete hormones

Question 31

what are hormones

Answer 31

• hormones are secreted when a gland is stimulated
  
  • glands can be stimulated by a change in conc. of a specific substance (sometimes another hormone
  • can also be stimulated by electrical impulses

Question 32

how are hormones transported and what do they do

Answer 32

• hormones diffuse directly into the blood and then taken around the body by the circulatory system
• they then diffuse out of the blood all over the blood but only bind to specific receptors on the membranes of target cells
• the hormones trigger a response in the target cells (which are effectors)

Question 33

how does the hormonal system increase the concentration of glucose in the blood when the concentration is low

Answer 33

receptors in the pancreas detect the low blood glucose conc
the pancreas releases the hormone glucagon into the blood
target cells in the liver detect glucagon and convert glycogen into glucose
glucose is released into the blood so blood glucose conc increases

Question 34

what are the characteristics of the nervous system

Answer 34

• uses electrical impulses
• faster response → electrical impulses travel fast
• localised response → neurones carry electrical impulses to specific cells
• short-lived response→ neurotransmitters are removed quickly
• electrical transmission by nerve impulses and chemical transmission at synapses

Question 35

what are the characteristics of the hormonal response

Answer 35

• uses chemicals
• slower response→ hormones travel at the ‘speed of blood’
• widespread response→ targets cell can be all over the body
• long-lived response → hormones arent broken down very quickly

Question 36

what happens when the nervous system is in resting state

Answer 36

• (not being stimulated)
  there’s a difference in charge between the inside and outside of the cell
  
  • this means there’s a voltage across the membrane
  • membrane is polarised
  • voltage across the membrane is called potential difference

Question 37

what happens when a stimulus is detected in a nerve cell

Answer 37

• when a stimulus is detected → permeability of the cell membrane to ions changes
  if the change in potential difference is big enough → will trigger action potential

Question 38

what is an action potential

Answer 38

• an action potential is an electrical impulse along a neurone
  
  • is only triggered if the potential difference reaches a certain level called the threshold level

Question 39

how is the amount of light that is entering the eye controlled

Answer 39

controlled by muscles of the iris

Question 40

where does light enter the eye

Answer 40

light enters the eye through the pupil

Question 41

what does the lens do

Answer 41

the lens focuses light rays onto the retina which lines the inside of the eye

Question 42

what does the retina contain

Answer 42

the retina contains photoreceptors which detects light

Question 43

what is the fovea

Answer 43

an area of the retina where there are lots of photoreceptors

Question 44

how are nerve impulses carried in the eye

Answer 44

nerve impulses from photoreceptor cells are carried from the retina to the brain by the optic nerve which is a bundle of neurones

Question 45

what is the blind spot in the eye

Answer 45

• where the optic nerve leaves the eye is called the blind spot
  
  • there arent any photoreceptor cells so its not sensitive to light

Question 46

describe the process that occurs when light hits the eye

Answer 46

• light enters the eye, hit photoreceptors and is absorbed by light-sensitive pigments
• light bleaches the pigments which causes a chemical change
• this triggers a nerve impulse along a bipolar neurone
  bipolar neurones connect photoreceptors to the optic nerve which takes impulses to the brain

Question 47

what are the two types of receptors in the human eye

Answer 47

human eye has two types of photoreceptor→ rods and cones

Question 48

where are rods found

Answer 48

rods are mainly found in the peripheral parts of the retina
over the remainder of the retina, rods outnumber cones by a factor of about 20 to 1
high abundance

Question 49

draw a diagram of the eye and label the different parts

Answer 49

Question 50

what do cones do

Answer 50

cones allow colour vision in bright light
low abundance
high spacial acuity (gives detailed images)

Question 51

what do rods do

Answer 51

rods only give black and white vision and work in dim light aswell as in bright light
low spacial visual acuity (gives less detailed images)

Question 52

where are cones found and why

Answer 52

• in the centre of the retina there’s only cones
  
  • this area allows us to pinpoint the source and detail of what were looking at

Question 53

what does the rods and cones synapse with ?
what does the bipolar neurone synapse with?

Answer 53

• the rods and cones synapse with bipolar neurone cells
• bipolar neurone cells synapse with the ganglion neurones whose axons together make up the optic nerve
• light hitting the retina through the layers of neurones before reaching the rods and cones

Question 54

what is the name of the photochemical pigment which absorbs the light resulting in a chemical change

Answer 54

in the rods the molecule is a purplish pigment called rhodopsin

Question 55

what is the structure of a rod cell?
where are rhodopsin molecules found?

Answer 55

• in the rods, the molecule is a purplish pigment called rhodopsin
• the rod cell has an outer and inner segment
• the outer segment contains many layers of flattened vesicles
• the rhodopsin molecules are located in the membranes of the vesicles

Question 56

describe the process that occurs in the dark in rod cells

Answer 56

• Na+ flow into the outer segment through non-specific cation channels
• Ca2+ can also pass through these channels but it is largely sodium involved
• the sodium ions move down the concentration gradient into the inner segment where pumps continuously transport them back out of the cell
• the influx of Na+ produces a slight depolarisation of the cell
• the potential difference across the membrane is about -40mV compared with the -70m resting potential of a cell
• this slight depolarisation triggers the release of the neurotransmitter glutamate from the rod cells
• in the dark rods release this neurotransmitter continuously
• the neurotransmitter binds to the bipolar cell, stopping it depolarising

Question 57

describe the process that occurs in the light in rod cells

Answer 57

• when light falls on the rhodopsin molecule, it breaks down into the retinal (non protein component) and opsin (protein component)
• the opsin activates a series of membrane-bound reactions, ending in hydrolysis nucleotide molecule attached to the cation channels
• the influx of Na+ into the rod decreases while the inner segment continues to pump Na+ out
• this makes the inside of the cell more negative
• it becomes hyperpolarised and the release of the glutamate neurotransmitter stops
• the lack of glutamate results in depolarisation of the bipolar cell with which the rod synapses
• the neurones that make up the optic nerve are also depolarised and respond by producing an action potential

Question 58

What happens after rhodopsin has been broken down

Answer 58

once the rhodopsin has been broken it is essential that its rapidly converted back to its original form so that subsequent stimuli can be perceived
each individual rhodopsin molecule takes a few minutes to do this process

Question 59

what happens to rhodopsin when theres a higher light intensity

Answer 59

the higher the light intensity the more rhodopsin molecules are broken down and the longer it can take for all the rhodopsin to reform up to a maximum of 50 mins

Question 60

what is dark adaptation

Answer 60

this reforming of rhodopsin is called dark adaptation

Question 61

what do dendrites and dendrons do

Answer 61

they carry nerve impulses towards the cell body

Question 62

what do axons do

Answer 62

carry nerve impulses away from the cell body

Question 63

describe the structure of motor neurones

Answer 63

• many short dendrites
  
  • carry nerve impulses from the CNS to the cell body
• one long axon carriers nerve impulses from the cell body to effector cells

Question 64

describe the structure of sensory neurones

Answer 64

• one long dendron carries nerve impulses from receptor cells to the cell body
• cell body located which is located in the middle of the neurone
• one short axon carries nerve impulses from the cell body to the CNS

Question 65

describe the structure of relay neurones

Answer 65

• many short dendrites carry nerve impulses from the sensory neurones to the cell body
• an axon carries nerve impulses from the cell body to motor neurones

Question 66

what is the myelin sheath and what is it made of

Answer 66

the myelin sheath is an electrical insulator
- myelin sheath is made of Schwann cell

Question 67

what are the nodes of ranvier

Answer 67

• between Schwann cells there are tiny patches of bare membrane which is called the nodes of Ranvier
• sodium ion channels are concentrated at the nodes
  in a myelinated neurone, depolarisation only happens at the node of ranvier

Question 68

what is saltatory conduction

Answer 68

• the cytoplasm of the neurone conducts enough electricity charge to depolarise the next node, so the impulse jumps from node to node
• this is called saltatory conduction and its really fast

Question 69

what happens in a non myelinated neurone

Answer 69

in a non-myelinated neurone, the impulse travels as a wave along the whole length of the axon membrane
this is slower than saltatory conduction

Question 70

what is conduction velocity

Answer 70

• the speed at which an impulse moves along a neurone is known as conduction velocity
  
  • a high conduction velocity means that the impulse is travelling quickly

Question 71

describe an experiment design to measure the potential difference across the membrane of an axon

Answer 71

• with both electrodes in the bathing solution there’s no potential difference
• if one electrode is pushed inside the axon then the oscilloscope shows a potential difference of around -70mV (millivolts)
• inside of axon is more negative than outside → the membrane is said to be polarised
• value of -70mV is known as resting potential

Question 72

what does the sodium/potassium pumps in the cell surface membrane of the axon do

Answer 72

• these carry Na+ out of the cell and K+ into the cell
  
  • these pumps act against the concentration gradients of these 2 ions and are driven by energy supplied by hydrolysis of ATP

Question 73

what are the two forces involved in the movement of potassium ions which keeps the axon at resting potential

Answer 73

• the concentration gradient generated by Na+/K+ pump
• the electrical gradient due to the difference in charge on the two sides of the membrane resulting fro K+ diffusion

Question 74

describe how resting potential is brought about

Answer 74

• the Na+/K+ pump creates concentration gradients across the membrane
  
  • inside the cell → high K+, low Na+ conc.
  • outside the cell → low K+, high Na+ conc.
  • 3Na+ leaves the axon for every 2K+ that enters the axon using active transport
  • once Na+ leaves the axon during resting state, it doesn’t come back in
  • membrane is x100 more permeable to K+ than Na+
• K+ diffuse out of the cell down the K+ concentration gradient, making the outside of the membrane positive and the inside negative → creates a potential difference
• the potential difference/ concentration gradient will put K+ back into the cell
  
  • amount that leaves = amount that comes back in → to reach an equilibrium
  • causes outside to be more positive than the inside
  • inside the axon → overall negative charge due to presence of organic anions that cant cross the membrane
• at -70mV potential difference, the two gradients counteract and each other and there is no net movement of K+

Question 75

what causes an action potential

Answer 75

• once threshold stimulation occurs, an action potential is caused by the change in the permeability of the cell surface membrane to Na+ and K+ → due to the opening and closing of voltage-dependent Na+ and K+ channels
• threshold is -55mV
  once this threshold is reached it causes the voltage gated channels to open

Question 76

what are the three stages of the generation of an action potential

Answer 76

depolarisation
repolarisation
hyperpolarisation/ restoring resting potential

Question 77

what happens in the depolarisation stage of an action potential

Answer 77

• when neurone is stimulated some depolarisation occurs
• change in potential difference across the membrane causes a change in the shape of Na+ gate → opens some of the voltage-dependent sodium ion channels
• as sodium ions flow in depolarisation increases → triggers more gates to open once a potential difference threshold is reached
• opening of more gates increases depolarisation further → an example of positive feedback
• influx of sodium ions into the cell
  -voltage reaches +40mV

Question 78

what happens in the repolarisation stage of an action potential

Answer 78

• after 0.5ms, the voltage-dependent Na+ channels spontaneously close and Na+
• permeability of membrane to Na+ returns to usual (very low level)
• voltage-dependent K+ channels open due to the depolarisation of the membrane so potassium ions move out of the axon, down the electrochemical gradient (are attracted by the negative charge outside the membrane)
• inside of the cell becomes more negative than the outside again

Question 79

what happens in the restoring resting potential stage of an action potential

Answer 79

• membrane is now highly permeable to potassium ions
• more ions move out than occurs at resting potential
• makes potential difference more negative than the normal resting potential
  
  • known as hyperpolarisation
• resting potential is re-established by closing of the voltage-dependent K+ channels and potassium ions diffuse into the axon

Question 80

how is the impulse generated along an axn

Answer 80

• action potential triggers a sequence of action potentials along the length of the axon
• as part of the membrane becomes depolarised due to an influx of sodium ions at the site of the action potential → a local electrical current is created as the charged sodium ions flow between the depolarised part of the membrane and the adjacent resting region
• the depolarisation spreads to the adjacent region and the nearby Na+ gates will respond to this by opening → triggering another action potential
  
  • this is repeated along the membrane
  • as a result a wave of depolarisation will pass along the membrane → this is the nerve impulse
• at the site of the first action potential -> resting potential is restored

Question 81

what is the refractory period and how long does it last for

Answer 81

• a new action potential can’t be generated in the same section of the membrane for about 5ms→ refractory period
• it lasts until all the voltage-dependent sodium and potassium ion channels have returned to their normal resting state (closed) and the resting potential is restored

Question 82

what is the role of the refractory period

Answer 82

refractory period ensures that impulses only travel in one direction

Question 83

what is the all or nothing effect for action potentials

Answer 83

all or nothing effect for action potential means that the size of the stimulus (if its above the threshold) has no effect on the size of the action potential

Question 84

what does the size of the stimulus affect

Answer 84

• the frequency of impulses/ number of impulses
• the number of neurones in a nerve that are conducting impulses

Question 85

what is associated with a strong stimulus

Answer 85

a high frequency of firing and the firing of many neurones are associated with a strong stimulus

• this is because there’s only a certain amount of sodium ions

Question 86

what is the speed of nervous conduction determined by

Answer 86

• speed of nervous conduction is partly determined by the diameter of the axon
• wider diameter= impulse travels faster

Question 87

why does a nerve with an axon with a small diameter make it more difficult for an action potential to propogate

Answer 87

• smaller diameter has a larger surface area to volume ratio than axons with a larger diameter
• this causes a larger amount of ions to leak out of the axon → makes it more difficult for an action potential to propagate

Question 88

why are the nerve axons of mammals narrower than other species

Answer 88

nerve axons of mammals are narrower than other species yet the impulse travels quicker → this can be explained by the presence of the myelin sheath around the mammalian nerve axons

Question 89

what are the factors that affect speed of conduction

Answer 89

• temperature → increases rate of diffusion
• myelin sheath
• diameter of the axon

Question 90

what is the role of the myelin sheath

Answer 90

myelin sheath acts as an electrical insulator, preventing any flow of ions across the membrane
nodes of Ranvier occur in the myelin sheath at regular intervals → these are the only places where depolarisation can occur

Question 91

why does a myelinated axon have a higher impulse velocity than an unmyelinated axon

Answer 91

• nodes of Ranvier occur in the myelin sheath at regular intervals → these are the only places where depolarisation can occur
• as ions flow across the membrane at one node during depolarisation → a circuit is set up which reduces the potential difference of the membrane at the next node → triggering an action potential
  
  • through this, the impulse jumps from one node to the next
  • this is faster than a wave of depolarisation along the whole membrane

Question 92

describe the first stage of saltatory conduction

Answer 92

• at resting potential there is positive charge on the outside of the membrane and negative charge on the inside
• high sodium ion conc. on the outside and high potassium ion conc. inside

Question 93

describe the second stage of saltatory conduction

Answer 93

• when stimulated, voltage dependent sodium ion channels open and sodium ions flow into the axon, depolarising the membrane
• localised electric currents are generated in the membrane
• sodium ions move to the adjacent polarised (resting) region → causes a change in the electrical charge (potential difference) across this part of the membrane

Question 94

what is the third stage of saltatory conduction

Answer 94

• a third action potential is initiated by the second
• in this way local electric currents cause the the nerve impulse to move along the axon
• at the site of the first action potential, potassium ions diffuse back into the axon → restores the resting potential

Question 95

why is saltatory conduction beneficial

Answer 95

• saves energy as the whole membrane doesn’t have to be polarised
• also because the sodium/ potassium pumps uses ATP as they pump the ions via active transport
• more energy efficient

Question 96

what is a synapse

Answer 96

when two neurones meet, small gap

Question 97

draw the structure of the synapse

Answer 97

Question 98

what is the synaptic cleft

Answer 98

synaptic cleft that separates the presynaptic membrane of the stimulating neurone from the post synaptic membrane of the other cell
gap is 20-50mm → nerve impulse cant jump across it

Question 99

how does the synapse transmit an impulse

Answer 99

• the arrival of an action potential at the presynaptic membrane causes the release of the neurotransmitter into the synaptic cleft
• neurotransmitter diffuses across the gap → results in events which cause depolarisation of the postsynaptic membrane and then the impulse goes along the cell
• the presynaptic cells uses energy to produce the neurotransmitter and package it into vesicles ready for transport out of the cell

Question 100

what was the first neurotransmitter to be discovered

Answer 100

acetylcholine was the first neurotransmitter to be discovered

Question 101

what is the process of the nerve impulse passing from the pre synaptic neurone to the post synaptic neurone

Answer 101

1. action potential arrives
2. the membrane depolarises. calcium ion channels open and enter the neurone
3. calcium ions cause synaptic vesicles containing neurotransmitter to fuse with the presynaptic membrane
4. neurotransmitter is released into synaptic cleft
5. neurotransmitter binds with the receptors on postsynaptic membrane. cation channels open and sodium ions flow through the channels
   
   1. receptors have specific binding site which are complementary to the shape of the neurotransmitter
   2. transmitter changes shape of the protein, causing cation channels to open
6. membrane depolarises and initiates an action potential (rest of the process for the generation of an action potential occurs → depolarisation, repolarisation, hyperpolarisation, resting state)

Question 102

what does the extent of depolarisation depend on

Answer 102

extent of depolarisation depends on the amount of transmitter reaching the postsynaptic membrane
- this will depend on the frequency of the impulse reaching the postsynaptic membrane
- several impulses required to depolarise the postsynaptic membrane as a single impulse isnt enough
- the number of functioning receptors in the post-synaptic membrane will also influence the degree of depolarising

Question 103

how are neurotransmitters inactivated

Answer 103

• some neurotransmitters taken up by the presynaptic membrane are used up again
• others rapidly diffuse away from the synaptic cleft or is taken up by other cells of the nervous system

Question 104

what happens to acetyl choline after its used

Answer 104

acetylcholinesterase breaks down acetylcholine into ethanoic acid and choline so that it can no longer bind to receptors
some breakdown products are then reabsorbed by the presynaptic membrane and reused

Question 105

what are the 2 roles of synapses in nerve pathways

Answer 105

• control of nerve pathways, allowing flexibility of a response
• integration of information from different neurones allowing a coordinated response

Question 106

what are the two main factors that affect the likelihood that the postsynaptic membrane will depolarise

Answer 106

• type of synapse
• number of impulses received

Question 107

what do inhibitory synapses do

Answer 107

others are inhibitory and make it less likely that the post synaptic membrane will depolarise
- a post synaptic cell can have many inhibitory and excitatory synapses
- whether an action potential results depends on the balance of excitatory and inhibitory synapses acting at a given time

Question 108

what are the two types of synapses

Answer 108

excitatory synapse
inhibitory synapse

Question 109

what does the excitatory synapse do

Answer 109

• makes the postsynaptic membrane more permeable to sodium ions
• a single excitatory synapse typically does not depolarise the membrane enough to produce an action potential

Question 110

what is needed to produce sufficient depolarisation

Answer 110

several impulses arriving within a short time produce sufficient depolarisation via the release of neurotransmitters to produce an action potential in the postsynaptic cell

Question 111

what is summation

Answer 111

the fact that each impulse adds to the effect of the others

Question 112

what are the two types of summation

Answer 112

spatial summation
temporal summation

Question 113

what is spacial summation

Answer 113

impulses from several different neurones produce an action potential in the post synaptic neurone

Question 114

what is temporal summation

Answer 114

several impulses along one neurone produce an action potential in the post synaptic neurone

Question 115

how does the inhibitory synapse work

Answer 115

• the neurotransmitter from these synapses opens channels for chloride ions and potassium ions in the postsynaptic membrane
• these ions will then move through the channels down their diffusion gradients
• chloride ions will move into the cell carrying a negative charge and potassium ions will move out carrying a positive charge
• the result will be a greater potential difference across the membrane as the inside becomes more negative than usual (about -90mV) → hyperpolarisation
• this makes subsequent depolarisation less likely
• more excitatory synapses will be required to depolarise the membrane

Question 116

what is the structure of the bipolar neurone

Answer 116

Question 117

how do plants coordinate growth and development

Answer 117

plants lack a nervous system so they se chemicals to coordinate growth, development and responses to the environment

Question 118

which chemicals are used in plants to bring about a response

Answer 118

plant hormones, plants regulator/ plant growth substances are chemicals that are produced in the plant in low concentrations and transported to where they cause a response
produced in growing regions of the plant

Question 119

what are the different types of plant growth factors and what do they do

Answer 119

• gibberellins stimulate flowering and seed germination
• cytokinins stimulate cell division and cell differentiation
• ethene stimulates fruit ripening and flowering
• abscisic acid (ABA) involved in leaf fall

Question 120

what is positive tropism

Answer 120

growth towards the stimulus

Question 121

what is negative tropism

Answer 121

growth away from the stimulus

Question 122

what is phototropism

Answer 122

the growth of a plant in response to light

Question 123

how do shoots response to light

Answer 123

shoots are positively phototropic → grow towards the light

Question 124

how do roots of plants respond to light

Answer 124

roots are negatively phototrophic and grow away from the light

Question 125

how do shoots respond to gravity

Answer 125

shoots are negatively geotropic and grow upwards

Question 126

how do roots respond to gravity

Answer 126

roots are positively geotropic and grow downwards

Question 127

what did darwins experiment on phototropism show

Answer 127

• the experiments showed an oat coleoptile with its tip cut off stops bending towards the light
• replacing the tip starts growth towards the light again

Question 128

what was darwins conclusion from his experiment on phototropism

Answer 128

some influence was transmitted from the shoot tip to the lower part of the seedlings, causing them to bend

Question 129

how did the conclusion of a chemical being made in the tip that is passed down the plant come about

Answer 129

this was demonstrated by removing the tip and placing it on a small block of agar and putting the agar on top of the cut end of the coleoptile
the coleoptile started to grow again → a chemical produced by the tip had diffused down through the agar jelly

Question 130

what investigation did Went carry out to provide further evidence that chemicals are produced in plant shoot

Answer 130

by placing the agar blocks on one side of the cut coleoptile tip in the dark → this caused it to curve away from the side receiving the chemical messenger from the agar
the chemical was eventually identified as the auxin, indoleacetic acid (IAA)

Question 131

what is the function of auixns

Answer 131

• one of its major functions is to stimulate growth
• growth response is a result of cell elongation
  high concentrations of auxins inhibit growth in roots

Question 132

what did Went discover about the amount of auxin in shoots

Answer 132

he found that the total amount produced didnt change compared with a shoot illuminated from all sides
- instead more auxin had been passed down the shaded side
- the increased conc. of auxin on the shaded side increased cell elongation
the reduced concentrated on the illuminated side inhibited cell elongation
as a result the shoot grew towards the light stimulus

Question 133

what happens if theres equal concentrations of auxin in the shoot

Answer 133

there wil be vertical growth
cell elongation will occur on both sides

Question 134

what is the cholodny-went model

Answer 134

explains growth curvature as a result of unequal distribution of auxin due to lateral transport of auxin

Question 135

why was the cholodny-went model critisised

Answer 135

criticised due to the small sample sizes and difficulty of measuring the very small concentrations involved

Question 136

what new techniques are being used to study tropisms

Answer 136

the use of genetically modified plants which produce fluorescent proteins in the presence of auxin → makes it possible to visualise the location of the auxin

Question 137

how do auxins work in phototropism

Answer 137

• IAA moves to more shaded parts of the shoots and roots so theres uneven growth
• auxins move to the side where there’s no light / move away from the light
  wherever IAA goes to shoot → elongation occurs
  wherever IAA goes in the root → growth in inhibited

Question 138

why does IAA affect growth

Answer 138

because IAA regulates the transcription of genes related to cell elongation and growth

Question 139

how does IAA work in geotropism

Answer 139

IAA moves to the underside of shoots and roots so theres uneven growth

Question 140

where is IAA synthesised

Answer 140

in actively growing root and shoot tips (meristems) and in developing leaves, seeds and fruits

Question 141

how is IAA transported

Answer 141

they are transported long distances in the phloem and shorter distances between cells via specific carrier proteins in the membrane
results in different parts of the plant having different amounts of IAA

Question 142

how do auxins bring about changes in plants

Answer 142

the auxins bind to protein receptors in the target cells
- this activates intracellular second messenger signal molecules which activate transcription factors
- these control the transcription of auxin-regulated genes
- the proteins produced bring about metabolic changes which result in a range of responses such as changes in cell expansion, division and differentiation

Question 143

how does cell expansion occur

Answer 143

to bring about cell expansion → required loosening of the cell wall
auxin causes the acidification of the cell wall by stimulating activity of proton pumps that move H+ ions out of the cytoplasm and into the cell wall
the low pH activates proteins called expansins which disrupt the bonds that hold cellulose microfibrils and hemicelluloses together→ loosens the wall so it can take up more water by osmosis
there is slippage of the polysaccharides relative to each other, bonds reform in new locations allowing expansion of the cell
- the acidification of the cell wall increases the potential difference across the membrane
- this enhances the uptake of ions into the cell
- the presence of these ions causes water uptake by osmosis → causes cell the swell resulting in cell elongation
- this process happens where the auxins are

Question 144

what does plant growth involve

Answer 144

• plant growth involves cell division and enlargement
• in the meristem cells are actively dividing and most of these cells enlarge, forming a region of elongation adjacent to the meristem
• these cells go on to mature and differentiate

Question 145

what is the cortex of the brain

Answer 145

outer layer that lies ontop of the cerebrum of the brain
- grey
- highly folded
- composed mainly of nerve cell bodies, synapses and dendrites
- this is known as grey matter

Question 146

where is the cortex

Answer 146

• cortex accounts for two-thirds of the brains mass → largest region of the brain
  
  • positioned over and around most other brain regions
  • divided into left and right cerebral hemispheres

Question 147

what is each hemisphere of the brain composed of

Answer 147

• composed of four other regions called lobes
  
  • frontal lobe
  • parietal lobe
  • occipital lobe
  • temporal lobe

Question 148

what is white mater

Answer 148

• composed of axons, lies below the grey matter
• composed of millions of nerve axons that connect neurones in different parts of the brain
  white colour due to the axons myelin sheath

Question 149

how are the two cerebral hemispheres connected

Answer 149

• the two cerebral hemispheres are connected by a broad band of white matter called the corpus callosum
  
  • allows communication between the two hemispheres

Question 150

what is the thalamus

Answer 150

responsible for routing all the incoming sensory information to the cortex part of the brain via the axons of the white matter

Question 151

what is the role of the frontal lobe

Answer 151

controls higher brain functions such as decision making, reasoning, planning and consciousness of emotion
also concerned with forming associations by combining information from the rest of the cortex and with ideas
it includes the primary motor cortex

Question 152

what is the primary motor cortex

Answer 152

has neurones which directly connect to the spinal cord and brain stem and from there to the muscles
- sends info to the body via motor neurones to carry out movements
stores information about how to carry out different movements

Question 153

what does the parietal lobe do

Answer 153

concerned with orientation, movement, sensation, calculation, some types of recognition and memory

Question 154

what does the occipital lobe do

Answer 154

(visual cortex)→ concerned with processing information from the eyes including vision, colour, shape recognition and perception

Question 155

what does the temporal lobe do

Answer 155

concerned with processing auditory information (hearing, sound recognition and speech (left temporal lobe). also involved in memory

Question 156

where are the different lobes on a diagram of the brain

Answer 156

Question 157

what is the hypothalamus and what does it do

Answer 157

• contains the thermoregulatory centre
• monitors core body temp, skin temp and initiates corrective action to restore the body to optimum temp
  other centres are located in the hypothalamus that control sleep, thirst and hunger
  secretes hormones
  connects directly to the pituitary gland which secretes other hormones

Question 158

what does the hippocampus do

Answer 158

involved in laying down long term memory

Question 159

what is the basal ganglia

Answer 159

a collection of neurones that lie deep within each hemisphere and are responsible for selecting and initiating stored programmed for movement

Question 160

what is the brain stem

Answer 160

• brain stem → oldest part of the brain
  
  • lies at the top of the spinal column
  • brain stem extends from the midbrain to the medulla oblongata

Question 161

label this diagram of the brain

Answer 161

Question 162

what environmental cues do plants respond to

Answer 162

light is the most important environmental cue for plants and influences growth and development
- plants detect quantity, direction and wavelength of light using photoreceptors
- they respond to changes in light conditions

Question 163

what are phytochromes

Answer 163

• plants contain a photoreceptor called phytochromes
• these absorb red and far-red light

Question 164

what is a phytochrome molecule made up of

Answer 164

consists of a protein component bonded to a non protein light-absorbing pigment molecule

Question 165

what are the two isomers of the non protein component of phytochrome

Answer 165

Pr -> absorbs red light
Pfr -> absorbs far red light

• these two isomers are photoreversible
• plants synthesise phytochromes in the Pr form
• absorption of red light converts Pr into Pfr

Question 166

what happens to the two phytochromes in sunlight

Answer 166

in sunlight, Pr is converted into Pfr| and Pfr is converted into Pr
this reaction dominates in sunlight because more red than far-red light is absorbed
so Pfr accumulates in the light

Question 167

what happens to the phytochromes in the dark

Answer 167

in the dark, any Pfr present is slowly converted to Pr

Question 168

what is the role of phytochromtes

Answer 168

trigger germination

Question 169

how were phytochromes discovered

Answer 169

experiments with lettuce indicate that a flash of red light will trigger germination but if followed by a flash of far-red light, germination is inhibited
- a further flash of red light will promote germination while a second flash of far red inhibits germination
- suggests that the effects of red and far red light are reversible
- the final flash of light determines whether or not gemination occurs

Question 170

how does red and far red light affect germination

Answer 170

• red light → triggers germination as Pr is converted into Pfr whch triggers germination
• far-red - inhibits germination as Pfr is converted back to Pr which inhibits germination

Question 171

what happens when lettuce seeds are exposed to red light

Answer 171

Pr is converted into Pfr → germination

Question 172

what happens when lettuce seeds are in the dark

Answer 172

Pr not converted into Pfr → no germination because the appearance of Pfr triggers germination

Question 173

what happens when lettuce seeds are exposed to far-red light

Answer 173

when exposed to far-red light Pfr is converted back into Pfr → inhibits germination

Question 174

what factors determine the time of flowering

Answer 174

the photoperiod, the relative of day and night
the ratio of Pr to Pfr in a plant enables it to determine the length of day and night

Question 175

what happens to phytochromes during long winter night

Answer 175

give a lot of time for Pfr to covert to Pr so that by sunrise all phytochrome will be Pr

Question 176

what happens to phytochromes during the summer

Answer 176

summer nights may not be long enough to do so, so some Pfr may still be present in the morning

Question 177

what affects whether a long day plant flowers

Answer 177

only flower when the period of uninterrupted darkness if less then 12 hours → they need Pfr to stimulate flowering

Question 178

what affects whether a short day plant flowers

Answer 178

• short day plants tend to flower in the spring or autumn when the period of uninterrupted darkness is greater than 12 hours
  
  • they need long hours of darkness in order to convert all Pfr present at sundown back to Pr

Question 179

what does Pfr do in terms of flowering in short day plants

Answer 179

• Pfr inhibits flowering in short-day plants
• in most short-day plants a flash of red light in the middle of the dark period negates the effect of the dark period as it causes for some of the converted Pr to convert back to Pfr
  Pr needed for flowering

Question 180

what is greening in plants

Answer 180

once a shoot has broken down through oil into sunlight → the plant undergoes profound changes in both its biochemistry

Question 181

how do phytochromes cause greening

Answer 181

• once in the light, phytochromes promote the development of primary leaves, leaf unrolling and the production of pigments
• they can also inhibit certain processes such as elongation of internodes

Question 182

how do phytochromes switch processes on or off

Answer 182

exposure to light causes phytochrome molecules to change from one form to another → brings about a change in shape
phytochrome may bind to the protein or disrupt the binding of a protein complex
these signal proteins may act as transcription factors or activate transcription factors that bind to DNA → allow transcription of light-regulated genes
the transcription and translation of proteins result in the plants response to light
e.g in seedlings, synthesis of the enzymes that control chlorophyll production will result in greening of the shoot

Question 183

what other environmental cues affect the growth of plants

Answer 183

gravity
touch and mechanical stress

Question 184

how does gravity act as an environmental cue for plants

Answer 184

• stimulus for a shoot to grow upwards and root to grow downwards after a short distance under the soil is gravity and not light
• response ensures that developing shoots reach the light while the root grows in the soil

Question 185

how does touch and mechanical stress act as an environmental cue

Answer 185

• some plants are sensitive to touch and mechanical stress
• rubbing plant stems can result in shorter stems than in controls
• mechanical stimulus activates signal molecules whose end result is the activation of genes that control growth
• some plants have leaves that move rapidly in response to mechanical stimulation

Question 186

what is the mechanism that occurs when a plant is touched

Answer 186

• mechanism when its touched → specialised cells lose K+ ions
• water follows by osmosis and the cells become flaccid → no longer supports the leaf and keep it upright
• the movement of the leaves is thought to be an adaptation and helps prevent grazing by herbivores

Question 187

how can scientists determine the function of different regions of the brain

Answer 187

by studying the consequences of accidental brain damage → can determine the functions of certain regions of the brain
researchers have studied the consequences of injuring or destroying neurones to produce lesions

Question 188

what are lesions

Answer 188

lesions are areas of tissue destruction in non-human animal models and the consequences of removal of brain tissue

Question 189

describe the case of phineas gage

Answer 189

• a dynamite explosion propelled a long iron bar through his head
• he didn’t die and although most of the left hand side of his brain was destroyed he could still walk and talk
• however after the accident his personality changed
• highly likely that the accident severed connections between his midbrain and frontal lobes
  
  • gages reduced ability to control his emotional behaviour after the accident was related to the damage here

Question 190

how can strokes affect the brain

Answer 190

brain damage caused by a stroke can cause problems with speaking, understanding speech and writing
paul broca concluded that the lesions in a small cortical area in the left frontal lobe were responsible for deficits in language production which is why some patients cant speak after a stroke

Question 191

what is neural plasticity

Answer 191

some patients can recover some abilities after a stroke which shows the potential of neurones to change in structure and function
- structure of the brain remains flexible even later in life and can respond to changes in the environment
- brain structure and function is affected by both nature and nurture

Question 192

how do CT scans work

Answer 192

• CT scans are thousands of narrow beam X-says rotated around the patient to pass through the tissue from different angles
• each narrow beam is reduced in strength according to the density of the tissue in its path
• the X rays are detected and are used to produce an image of a think slice of the brain on a computer screen in which the different soft tissues within the brain can be distinguished

Question 193

what are the limitations of CT scans

Answer 193

they only have limited resolution so small structures of the brain cant be distinguished
- CT scans can only give frozen-moment pictures
- they look at structures in the brain rather than function
cant be used for imaging soft tissue -> can only be absorbed by denser material such as bone

Question 194

what can CT scans be used for

Answer 194

are used to detect brain disease and to monitor the tissues of the brain over the course of an illness

Question 195

what are the advantages of magnetic resonance imaging

Answer 195

• don’t rely on harmful X-rays
• can be used more frequently
• uses a magnetic field and radio waves to detect soft tissue- higher resolution images produced

Question 196

how do MRIs work

Answer 196

• when placed in a magnetic field, the nuclei of atoms line up with the direction of the magnetic field in the way that compass needles aligns itself to the earths magnetic field
• hydrogen atoms in water are monitored in MRI as there is a high water content in tissues under investigation and hydrogen has a strong tendency to line up with the magnetic field
• exposed to radiowaves
• the combined fields cause the direction and frequency of spin of the hydrogen nuclei to change, taking in energy from radiowaves to do so
• when the radio waves are the hydrogen nuclei returns to their original alignment and release the energy they absorbed
• this energy is detected and a signal is sent to a computer which analyses it to produce an image on the screen

Question 197

how does an MRI produce an image

Answer 197

• different tissues respond differently to the magnetic field from the radio waves and so produce contrasting signals and distinct regions in the image
• MRI examines tissues in small sections/ thin slices which when put together give 3D images

Question 198

what are MRIs used for

Answer 198

• MRI is widely used in the diagnosis of tumours, strokes, brain injuries and infections of the brain and spine
• MRI can be used to produce finely detailed images of the brain structures such as soft tissues, vessels, sinuses, tumours with better resolution than CT scans for the brain stem and spinal cord

Question 199

how does fMRI’s work

Answer 199

look at functions of different areas of the brain by following the uptake of oxygen in the active brain areas
deoxyhaemoglobin absorbs the radio wave signal, whereas oxyhaemoglobin doesnt (oxyhaemoglobin present when brain is active)
more deoxyhaemoglobin= more radiowaves absorbed
inc activity-> inc bloodflow to that area
the less radio signals absorbed the higher the level of activity in a particular area → so different areas of the brain will light up according to when they are active
imaged are collected continually while the subject alternates between resting and carrying out a task

Question 200

what are the limitations of MRIs

Answer 200

expensive
noisy
cant be used if you have a pacemaker

Question 201

what is the disadv of using fMRI

Answer 201

poor temporal resolution

Question 202

what are the uses of PET scans

Answer 202

• used to produce detailed images that allow the structure and functioning of tissues and organs to be evaluated
• used to help diagnose cancers, heart disease and brain disorders
• also used to help plan heart surgery, monitor the spread of cancers and observe the effect of treatment
  useful in the diagnosis and monitoring of Alzheimers disease

Question 203

how do PET scans work

Answer 203

uses isotopes with short half lives such as carbon-11, nitrogen-13 or oxygen-15 that are incorporated into compounds such as glucose or water or into molecules that bind to receptors- radiotracers
- the patient is first injected with the radiotracer
- as the radiotracer decays, it emits positrons
- when a tissue or organ is active, there will be increased energy use in that area
- an increase in blood flow will show up on a PET image as more radiotracer atoms will be present in that area
- in the tissue when a positron collides with an electron, 2 gamma rays are emitted and these can be picked up by detectors → converted into a signal and then displayed as an image by the computer
- bright spots on the image indicate high levels of neurone activity
- dark spots → low levels of neurone activity
- by running a video sequence of PET images, changes in activity can be followed

Question 204

what are the limitations of PET scans

Answer 204

• however PET scans can only be done once or twice a year due to safety
• they’re also expensive and so arent used for routine screening

Question 205

what are the symptoms of Alzheimer’s

Answer 205

• memory loss, problems with thinking, problem solving or language
• symptoms occur when the brain experiences neurone loss

Question 206

how can PET scans be used to detect alzheimers

Answer 206

• as neurones die, pieces of beta-amyloid protein found in the myelin sheath clump together to form clusters of sticky plaque which can block signalling at synapses
• plaques can also activate immune cells which trigger an inflammatory response
• the accumulation of beta-amyloid in the brain is an early sign of alzheimers disease and patients can undergo a PET scan with an amyloid tracer to visualise fibres of beta-amyloid in the brain
• as the condition progress more beta-amyloid plaques accumulate, and synapses and acetylcholine receptors are destroyed in the brain
• PET thus allow the monitoring of the disease’s clinical progression

Question 207

what is the pathway of an impulse from the eye to the brain

Answer 207

• the axon of the ganglion cells that make up the optic nerve pass out of the eye and extend to several areas of the brain, including a part of the thalamus
• the impulses are then sent to the primary visual cortex where the information is processed further
• before reaching the thalamus, some of the neurones in each optic nerve branch off to the midbrain, where they connect to motor neurones involved in controlling the pupil reflex and movement of the eye

Question 208

how does the nervous system develop at conception

Answer 208

• human nervous system begins to develop soon after conception
• by the 21st day, a neural tube has formed
• the front part of the neural tube goes onto develop into the brain, while the rest of the neural tube develops into the spinal cord

Question 209

what factors affect postnatal increase in brain size

Answer 209

• the elongation of axons
• myelination
• the development of synapses

Question 210

what happens when neurones stop dividing in the brain

Answer 210

• once the neurones have stopped dividing the immature neurones migrate to their final position and start to wire themselves
• axons lengthen and synapse with the cell bodies of other neurones
• neurones must make the correct connections in order for a function such as vision to work properly

Question 211

how do axons of neurones from the retina grow

Answer 211

axons of the neurones from the retina grow to the thalamus where they form synapses with neurones in the thalamus in a very ordered arrangement

Question 212

how do axons from thalamus neurones grow

Answer 212

axons from these thalamus neurones grow towards the visual cortex in the occipital lobe

Question 213

how is the brain able to create a 3D image of what the eyes see

Answer 213

• one column of the cells receives stimuli from the left eye, the next column from the right eye in an alternating pattern
• the information from the same area of the retina in the right eye and left eye synapse next to each other
• this gives the brain the ability to create one 3D image of what the eyes see

Question 214

when was it thought that the column of cells in the visual cortex were formed

Answer 214

it used to be thought that these columns of cells in the visual cortex were formed during a critical period for visual development after birth → this is now known to not be the case

Question 215

when is the column of cells in the visual cortex formed and how was this shown

Answer 215

Crowley and Katz showed by injecting labelled tracers that the column in the visual cortex are formed before the critical period for the development of vision

Question 216

what is the formation of columns determined by

Answer 216

the formation of columns is genetically determined and not the result of environmental stimulus

Question 217

what is the critical period for the development of vision

Answer 217

• There is a window of time during which the brain is particularly sensitive to certain types of stimuli.
• If these stimuli are not received during this time, normal development may be disrupted

Question 218

what medical observations are there that is evidence for a critical period in visual development

Answer 218

• a young Italian boy has a minor eye infection as a baby
• as part of his treatment his eyes were bandaged for 2 weeks
• when the bandage was removed he was left with permanently impaired vision

Question 219

how can studies of people born with cataracts contribute to the understanding in critical periods in develpment

Answer 219

• cataracts is the clouding of the lens of the eye which affects the amount of light getting to the retina
• if cataracts arent removed before the child is 10 they can result in permanent impairment of the persons ability to perceive shape or form, including difficulties in face recognition

Question 220

what study on new born animals has been carried out to provide evidence for the critical period

Answer 220

• a group of newborn monkeys were raised in the dark for the first 3-6 months of their lives and another was exposed to light but not to patterns
• when the monkeys were returned to the normal visual world, researchers found that both groups led difficulty with objects discrimination and pattern recognition

Question 221

what is the molecular deprivation investigation

Answer 221

• Hubel and Wiesel raised monkeys from birth to 6 months, depriving them of any light stimulus in one eye
• after 6 months the eye was exposed to light
• on exposure to light it was clear that the monkey was blind in the light-deprived eye
  retinal cells in the deprived eye did respond to light stimulus, but the cells of the visual cortex didn’t respond to any input from the formerly deprived eye

Question 222

what conclusions were made from the studies on new born animals on finding evidence for the critical period in visual development

Answer 222

• deprivation for only a single week during a certain period after birth produce the same result, with the deprived eyes visual cortex cells failing to respond to light
• deprivation in adult monkeys had no effect
• a visual deprivation of both eyes during this critical period has much less effect than when just one eye is deprived

Question 223

what is the difference between the structures of the visual cortex in new born monkeys and adult monkeys

Answer 223

• at birth in monkeys there is a great deal of overlap between the territories of different axons
• in adults there is less overlap even though the mass of the brain is greater with more dendrites and synapses

Question 224

what occurs when theres light deprivation in one eye and what does this suggest

Answer 224

• after light deprivation in one eye, columns with axons from the light-deprived eye are narrower than those for the eye receiving light stimulation
• dendrites and synapses from the light-stimulated eye take up more territory in the visual cortex
• this suggests that visual stimulation is required for the refinement of the columns and so for full development of the visual cortex

Question 225

how do axons compete for target cells in the visual cortex

Answer 225

• axons compete for target cells in the visual cortex
• every time a neurone fires onto a target cell, the synapses of another neurone sharing the target cell are weakened and they release less neurotransmitter
  
  • if this happens repeatedly the synapses that arent firing will be cut back

Question 226

what happens to the synapses in a light deprived eye

Answer 226

• when one eye is deprived of light, the axons from that eye will not be stimulated
• in the area of the visual cortex, where neurones from both eyes overlap, only the synapses on axons receiving light stimulation will fire
• the synapses from the light-deprived eye will be weakened and eventually lost

Question 227

what happens if the synapses are made and maintained during the critical period

Answer 227

• if synapses are made and maintained during the critical period, neurones in the visual cortex are able to respond to the information from the retina
• individual neurones in the columns of cells within the visual cortex respond in different ways to the information from the retina and to different characteristics of the object being viewed

Question 228

what are simple cell neurones

Answer 228

respond to bars of light

Question 229

what are complex neurone cells

Answer 229

respond to edges, slits or bars of light that move
other neurones respond to the angle of the edge, and others to contours, movement or orientation

Question 230

what does visual perception involve

Answer 230

it involves knowledge and experience as the brain interprets the sensory information received from the retina to create our visual experience of the world

Question 231

what is depth perception

Answer 231

• when we look at an object we can make a judgement about how far away the object is
• the brain does this in different ways for close and distant objects

Question 232

what happens in the visual cortex for close objects which are less than 30m away

Answer 232

• depend on the presence of cells in the visual cortex that obtain information from both eyes at once
• the visual field is seen from two different angles
  
  • cells in the visual cortex let us compare the view from one eye with that from the other
  • this is called stereoscopic vision and allows the relative positions of objects to be perceived

Question 233

what happens in the visual cortex for distant objects which are more than 30m away

Answer 233

• the images on our two retinas are very similar so visual cues and past experiences are used when interpreting the images
• image converges → gives impression of distance

Question 234

what can help determine depth of an image

Answer 234

• smaller image = further away as you know the rough size of the object from experience
• overlaps of images and changes in colour also help in judging depth
• even if an object becomes smaller on the retina, we perceive is as moving further away

Question 235

what were cross cultural studies used for

Answer 235

can help to answer the question of whether depth perception is innate or learned by studying how different people respond to optical illusions

Question 236

why may kenge have not been able to recognise buffalos from far away

Answer 236

• kenge was unable to recognise buffalo from a distance, but could recognise them from up close
• he may not have developed depth perception over long distances because he has no experience of seeing long distances on an open plain, having always lived in the enclosed forest

Question 237

what is the carpentered word hyothesis

Answer 237

those of us who live in a world dominated by straight lines and right angles tend to perceive depth cues very different from those who live in a ‘circular culture’

Question 238

how do people who live in a carpentered world interpret images

Answer 238

in the carpentered world we are surrounded by building with right-angle corners so unconsciously from an early age we tend to interpret images with acute and obtuse angles (as long as they don’t differ too much from 90 degree) as right angles

Question 239

how do people who live in a circular culture interpret images

Answer 239

• people who live in a ‘circular culture’ with few straight lines or right angle corners (such as those with circular houses and no roads) have little experience of interpreting acute and obtuse angles on the retina as representations of right angles
  
  • studies have shows they are rarely fooled by visual illusions such as the Muller-Lyer illusion

Question 240

what is the muller-lyer illusion

Answer 240

• in the Muller-Lyer illusion, the angles between the line and the arrowheads are interpreted as right angles, providing depth clues to the image
• we unconsciously perceive X to be shorter because depth clues make us think its further away and Y is closer to us

Question 241

what do some researchers think the lack of susceptibility to the muller-lyer illusion may be due to

Answer 241

suggest its not the result of different experience, but due to genetic differences in pigmentation between individuals
- they suggest that individuals who find it harder to detect contours are less susceptible to the Muller-Lyer illusions
- they link poor contour detection to high retinal pigmentation
- in light coloured people, with low retinal pigmentation, contour detection is good so are more easily caught out by the illusion (According to the argument)

Question 242

how were depth cues in pictures investigated

Answer 242

• in another cross cultural study, individuals from a number of different cultures were shown pictures wth depth cues such as object size, overlap of objects and linear perspective
• it was found that all young children had difficulty perceiving the pictures as 3D
  they wouldve said that the man is pointing to the elephant
  by the age of 11 almost all of the children interpreted the pictures in 3D
• non literate adults didnt interpret the image as 3D
• they had less experience of depth cues in pictures

Question 243

what conclusion can be made from the study of depth cues in pictures

Answer 243

• therefore depth cues in pictures arent innate and they have to be learnt
• this suggests that visual perception is partly learnt

Question 244

what do studies with new born babies show

Answer 244

the fact that babies are born with a range of characteristic behaviours suggest that they are determined by genes e.g crying, walking movements and grasping
these types of inborn capacities exhibited by a new born baby are used as evidence for the role of genes in determining the hard wiring of the brain before birth

Question 245

what is the visual cliff study with new born babies

Answer 245

• in a classic experiment, babies are encouraged to crawl across a table made of glass or Perspex, below which is a visual cliff
• patterns placed below the glass create the appearance of a steep drop

Question 246

how does the viual cliff study with new born babies determine whether depth perception is innate or learnt and what was the result

Answer 246

• if the perception of depth is innate, then babies should be aware of the drop even if they havent previously experienced the stimulus themselves
• the - the experiment is only possible with babies who have learned to crawl
• its likely that a six-month old baby may have already learned depth perception
• therefore the experiment was repeated with animal that can walk as soon as theyre born, such as chicks, kids and lambs
• they too refused to cross the cliff

Question 247

what forms the bases of learning and memory

Answer 247

• memory stores vast amounts of information from sights and sounds to emptions and skills
• changes to synapses, changes in the network of neurones also forms the basis of learning and memory
  is any relatively permanent change in behaviour or knowledge that comes from experience

Question 248

where are memories stored

Answer 248

• memory is not localised in one part of the brain
• its distributed throughout the cortex with different sites for short and long-term memory
• different types of memory are controlled by different parts of the brain
• this is clearly demonstrated by looking at cases where people lost the use of different parts of their brain

Question 249

explain the study of the patient HM

Answer 249

• HM who suffered from severe epilepsy
• areas of the brain that was thought to be causing the problem was removed → immediately caused amnesia
• HMs long term memory from before the operation were unaffected but he could no longer for new long term memories
• his memories for how to do everyday things was still intact
• this case shows that making memories is an active process

Question 250

how are memories stored

Answer 250

• in the brain, neurones connect with many other neurones to make up a complex network

memories can be created by:

• the pattern of connections
• the strength of synapses

Question 251

why are sea slugs used to study habituation

Answer 251

• neurobiology of a sea slug is simpler than that of a human
• sea slugs have large accessible neurones → so those involved in behaviours can be identified

Question 252

what is a siphon on a sea slug

Answer 252

• giant sea slug breathes through a gill located in a cavity on the upper side of its body
• water is expelled through a siphon tube at one end of the cavity
• if the siphon is touched the gill is withdrawn into the cavity
  
  • this is a protective reflex action similar to the removal of a hand from a hot plate

Question 253

how is habituation achieved

Answer 253

• with repeated stimulation, Ca2+ channels become less responsive so less Ca2+ crosses the presynaptic membrane
• less neurotransmitter released
• less depolarisation of the postsynaptic membrane → no action potential is triggered in the motor neurone

Question 254

why have sea slugs become habituated to waves

Answer 254

since the slugs live in the sea and their gills are hit by a wave they’ve learnt not to withdraw their gill every time a wave hits them → have become habituated to waves

Question 255

what is habituation

Answer 255

• habituation is a type of learning
  
  • gives animals the ability to ignore the unimportant repetitive stimuli so that limited sensory, attention, memory resources can be concentrated on more threatening or rewarding stimuli

Question 256

what is sensitisation

Answer 256

happens when an animal develops an enhanced response to a stimulus

e.g notice smaller noises more after hearing a loud noise when home alone

Question 257

how is sensitisation achieved in a sea slug to enhance gill withdrawal response

Answer 257

• impulse due to electric shock to tail
• serotonin released
• gradual calcium ion uptake
• impulse passes along sensory neurone due to the water jet stimulating the siphon
• more neurotransmitter released
• greater depolarisation
• higher frequency of action potentials
• enhanced gill withdrawal response

Question 258

what does long term memory storage involve

Answer 258

• long term memory storage involves an increase in the number of synaptic connections
  
  • repeated use of a synapse leads to the creation of additional synapses between the neurones

Question 259

what does it mean if you accept t hat animals have rights

Answer 259

• accepting that animals have rights means that you can only use animals which have consented to participate in medical experiments
• this would bring an end to the use of animals in medical research

Question 260

what is the animal welfare approach for ethics of using animals is research

Answer 260

• cant use vertebrates in medical experiments if there are non animal alternatives in the EU
• strict guidelines followed if there’s no non animal alternatives for animals being used in research → as long as its necessary

Question 261

what is the animal suffering and experiencing pleasure argument for ethics of using animals in research

Answer 261

• animal rights and welfare approach assumes the animals can suffer and experience pleasure
• most experts reckon fish, spiders, insects cant suffer

Question 262

what is the utilitarianism approach to the use of animals

Answer 262

• utilitarianism - the belief that the right course of action is the one that maximises the amount of overall happiness or pleasure in the world
• this allows certain animals to be used in medical experiments as long as the overall expected benefits are greater than the overall expected harms
  e.g finding a cure for cancer using 250 000 mice but only 50 000 suffer for half of their life

Question 263

what is the blood brain barrier

Answer 263

• the endothelial cells forming the capillary cells in the brain are more tightly joined together than those in capillaries elsewhere in the body
  
  • they form a barrier to control the movement of substances into the brain
  • protect the brain from the effects of changes in blood ionic composition
  • protect brain from toxic molecules

Question 264

when can drugs cause issues

Answer 264

can cause issues when they cross the blood-brain barrier
imbalances in naturally occurring brain chemicals can cause issues

Question 265

what is dopamine

Answer 265

• dopamine is a neurotransmitter secreted by neurones in the midbrain especially
• the axons of the neurones in this mid brain extend throughout the frontal cortex, brain stem and spinal cord

Question 266

what happens in people with parkinsons disease

Answer 266

• in people with parkinsons, dopamine secreting neurones in the basal ganglia die
  
  • these neurones normally release dopamine in the motor cortex
• the motor cortex in people with parkinsons disease receive little dopamine → and theres a loss of control of muscular movement

Question 267

what are the main symptoms of parkinsons

Answer 267

• stiffness of muscles
• tremour of muscles
• slowness of movement
• poor balance
• walking problems
• depression and difficulties with speech and breathing may also arise

Question 268

name examples of treatments used for parkinsons

Answer 268

selegiline
L-dopa
dopamine agonists
genes for proteins that increase dopamine production being inserted into the brain (being trialled)
deep brain stimulation

Question 269

how does selegiline work to treat parkinsons

Answer 269

• slows the loss of dopamine from the brain
  
  • this drug is an MAO inhibitor
  • it inhibits monoamine (MAO) oxidase which is the enzyme responsible for breaking down dopamine in the brain
  • increases availability of dopamine
  • two types of monoamine oxidase: MAOB and MAOA
  • MOAB is used in parkinsons treatment

Question 270

why cant dopamine itself be used to treat parkinsons

Answer 270

it cant cross into the brain from the blood stream

Question 271

how can L-dopa be used to treat parkinsons

Answer 271

• precursor in the manufacture of dopamine
  
  • once in the brain L-dopa coverts into dopamine
  • increases conc. of dopamine and controls the symptoms of the disease

Question 272

how can dopamine agonists be used to treat parkinsons

Answer 272

• dopamine agonists → drugs that activate the dopamine receptor directly
  
  • the rug mimics the role of dopamine in the brain
  • it binds to dopamine receptors at synapses and triggers action potentials
  • can be useful in treating parkinsons as they avoid higher than normal levels of dopamine in the brain

Question 273

how can deep brain stimulation be use to treat parkisnons

Answer 273

• a type of surgery used to treat the symptoms of the disease
  
  • person can reduce their medication and therefore reduce side effects

Question 274

what happens if theres excess dopamine in the brain

Answer 274

believes to be major cause of schizophrenia

Question 275

how can excess dopamine in the brain be treated

Answer 275

• excess dopamine in the brain can be treated with drugs that block the binding of dopamine to its post synaptic receptor sites
• these drugs are simular to dopamine in structure but unable to stimulate the receptors

Question 276

what are the side effects of the drug used to treat excess dopamine in the brain

Answer 276

side effect of the patients taking this drug is that it can induce the symptoms of parkinsons

Question 277

what is serotonin

Answer 277

• seratonin → important neurotransmitter in determining a persons mood
• neurones that secrete serotonin are found in the brains tem
• their axons extend into the cortex, cerebellum, spinal cord → targets a large area of the brain

Question 278

what is a lack of serotonin linked to

Answer 278

• lack of serotonin linked to depression
  dopamine and noradrenaline also has a role
  its not fully understood whether the lack of serotonin is a cause of depression or a result of it
• depression→ persistently feeling safe for weeks or months and those feeling interfere with everyday life
  
  • associated with feelings of sadness, anxiety and hopelessness, loss of interest in pleasurable activities and reduced energy levels, insomnia, restlessness and thoughts of death

Question 279

what is thought to be the cause of depression

Answer 279

• causes of depression not completely understood
• there may be a genetic element
• it may be a multifactorial condition → several genes may be involved in being susceptible to depression
  
  • environmental factors also contribute

Question 280

what gene is known to influence the susceptibility of depression and what does it do

Answer 280

gene 5-Htt
it codes for transporter protein that controls serotonin reuptake into presynaptic neurones
people with the short version of 5-HTT gene are more likely to develop depression after a stressful life event
two people who inherit the same susceptibility genes may not both develop depression →it will depend on environmental factors acting as triggers to bring about the symptoms of the disease

Question 281

what happens in someone who is depressed in terms of impulses

Answer 281

• when someones depressed fewer nerve impulses are transmitted around the brain → may be related to low levels of neurotransmitters being produced
• people with depression have pathways with a number of abnormalities
• molecules needed for serotonin synthesis are often present in low concentrations but the serotonin binding sites are more numerous than normal → may be to compensate for the low level of the molecule

Question 282

how can twin studies help determine whether a disease or trait has a genetic cause

Answer 282

identical twins are produced by the division of the same egg → are almost genetically identical
- if a trait identified in one twin is caused by a gene then its likely to be present in the other twin
- when environment has a greater effect similarity between identical twins fall

Question 283

what do twin studies suggest in terms of depression

Answer 283

twin studies suggest that there may be a specific gene that causes clinical depression to develop in certain families but they also indicate that there’s a number of other genetic factors that determine the vulnerability to depression

Question 284

what was the first drug used to treat depression and why arent they used anymore

Answer 284

monoamine oxidase inhibitors
- break down neurotransmitters including serotonin
- they’re rarely used nowadays as they have a lot of side effects

Question 285

give an example of an effective drug which is used to treat depression nowadays and what does it do

Answer 285

• one of the most effective types of drugs inhibits the reuptake of serotonin from the synaptic cleft
• e.g Prozac → maintains higher levels of serotonin and increase the rate of nerve impulse in serotonin pathways
  
  • reduced some symptoms of depression

Question 286

how can drugs affect synapse transmission

Answer 286

may prevent the release of a neurotransmitter, block or open ion channels
may inhibit the a breakdown enzyme which breaks down the neurotransmitter
a chemical with a similar molecular structure to a particular neurotransmitter is likely to bind to the same receptors and stimulate the post synaptic neurone

Question 287

what is MDMA and what does it do

Answer 287

• the drug MDMA is in ecstasy
• it affects thinking mood and memory
• it can cause anxiety and altered perception (similar to hallucination
• most desirable effect of ecstasy → provides feelings of emotional warmth and empathy

Question 288

what are the short and long term effects of MDMA

Answer 288

• short term effects of MDMA → changes in behaviour and brain chemistry
• long term effects → changes in behaviour and brain structure, insomnia, depression

Question 289

how does MDMA in ecstasy affect synapses

Answer 289

• MDMA increases the conc of serotonin in the synaptic cleft by binding to molecules in the presynaptic membrane that are responsible for transporting serotonin back into the cytoplasm
• prevents removal of serotonin from synaptic cleft
• the drug may also cause further increasing amount of serotonin outside the cell
• these higher levels of serotonin bring about the mood changes seen in a user of ecstasy
• may be possible that MDMA has a similar effect on molecules that transport dopamine

Question 290

what are the effects of using MDMA

Answer 290

• users report feelings of euphoria, wellbeing and enhanced senses
  
  • these are side effects and unpredictable consequences of using the drug
• some experience clouded thinking, agitation and disturbed behaviour
• can also cause sweating, dry mouth, increased heart rate, fatigue, muscle spasms and hyperthermia
  
  • as MDMA an disrupt the ability of the brain to regulate body temp

Question 291

what can a single high dose or repeated doses of MDMA cause

Answer 291

repeated doses or a single high dose of MDMA can cause hyperthermia, high BP, irregular heartbeat, muscle breakdown and kidney failure → can be fatal

Question 292

why cay MDMA have an effect on normal brain activity even when the drug isnt being taken

Answer 292

this is because the drug has stimulated so much serotonin release that cells cant synthesise enough to meet demand when its gone → results in the feeling of depression

Question 293

what can the human genome project be used to do

Answer 293

• human genome project helping us to gain a better understanding of the way genes control phenotype
• this is leading to major advances in understanding of diseases which are genetic and help improve treatments
• hoped that it will also help put us in a better position to avoid risk factors to out own genetic make up
  can be used to make personalisaed medicien

Question 294

what is the genome

Answer 294

• genome → all of the DNA of an organism
  
  • includes the genes that carry all the info for making proteins needed by the organism

Question 295

how can the sequence of bases in DNA be found

Answer 295

• DNA is used as a template to replicate a set of DNA fragments each differing in length by one base
• the fragments are separated according to size using gel electrophoresis → the base at the end of each fragment is identified
• this allows the sequence of bases in the whole DNA chain to be determined

Question 296

what can DNA base sequencing be used for

Answer 296

from this it became possible to work out the entire sequence of bases in the human genome and determine the location of all our genes
using the sequence biologists are gaining a better understanding of the genome itself, identifying new genes, working out how theyre controlled and discovering what they code for
- plays a major part in research into the role of genes in disease and the development of new diagnostic techniques and treatments
- can be used to find genetic variants that are shared by atleast 1% of the populations studied

Question 297

how many genes does the human genome have roughly

Answer 297

• estimated that our genome has 20 000 to 25 000 genes → gives rise to complex proteins
• average gene consists of 3000 bases

Question 298

what has the role of non coding regions of DNA thought to be

Answer 298

• comparative genomics studies suggest that some of this non coding DNA has been conserved for a long time
• this suggests that they confer a selective advantage in preserving useful biological traits or minimising traits that arent useful

Question 299

what are SNPs

Answer 299

single nucleotide polymorphism (SNP)→ DNA sequence variation that occurs when a single nucleotide in the genome sequence is altered in at least 1% of the population, with one base substituted for another

Question 300

what may SNPs do

Answer 300

• SNPs may alter the protein formed or may have no effect on cell function
• scientists believe that possession of particular SNPs could predispose people to a disease or influence their response to a drug

Question 301

how can genes be identified aswell as their function

Answer 301

• its now possible to locate a candidate gene (this is a gene which may cause a particular disease) on our DNA and then screen the gene for mutations in affected individuals
• analysing DNA sequence patterns in humans side by side with those in well studied model organisms e.g yeast has become a good strategy in identifying human genes and interpreting their function

Question 302

which genes have been identified for parkinsons

Answer 302

several genes associated with Parkinson’s have been identified including parkin, DJ1 and PINK1

Question 303

what kind of disease is alzheimers and what is its symptoms

Answer 303

• alzheimers is a multifactorial disease → age, genes, environment are all factors which can inc risk

symptoms:

• confusion
• progressive severe memory loss

Question 304

what is a drug target

Answer 304

a drug target is a specific molecule that a drug interacts with to bring about its effect

Question 305

how can new target drugs be found

Answer 305

identification of disease genes and their products allowed biologsits to find new target drugs

Question 306

how can sequencing a persons genome be used to produce personalised medicine

Answer 306

• differences in response to a drug may be due to slight variations in the genome, depending on the SNPs they have
• prescribing the best drug for a patient is usually trial and error
• info about a persons genome is hoped to enable doctors to prescribe the right drug and correct dose
• some SNPs have been associated with differences in target drugs and the effects of drugs
  if a person knew they carried mutations associated with a particular disease they may make changes to their lifestyle to reduce the risk of the disease or opt for preventative treatment

Question 307

what can advances in genome sequencing be used to do

Answer 307

• advances in genome sequencing allow accurate, quick and inexpensive DNA sequencing → improve diagnosis, treatment and preventions of diseases with gene based personalised medicine
• pharmacogenomics→ sequencing a patients DNA to determine if they possess a specific SNP which is associated with a severe side effect to a particular drug enables it to be modified to suit the individual

Question 308

what ethical implications are there involved with the human genome sequencing

Answer 308

• who should decide about the use of genetic predisposition tests and when they should be used
• confidentiality problems with making and keeping record of an individuals genotype
• personalised medicine is expensive so theres restricted availability → problem with deciding who is eligible for such treatments
• individuals identified for possesing genes associated with inherited diseases may face discrimination in employment or when applying for insurance→ may not be able to get certain types of cover
  
  • possession of gene doesnt mean the person will develop the disease

Question 309

how can modifying organisms be used to produce drugs

Answer 309

• plasmid cut using restriction enzymes
• using the same restriction enzyme cut a piece of DNA from another species
• DNA from the other species can be inserted/spliced into the plasmid → theyll have the same sticky ends as same restriction enzyme used
• plasmid inserted back into bacteria
• bacteria allowed to multiply in fermenter
• protein produced extracted from the culture
• can be used to produce vaccines, insulin etc

Question 310

how can genetically modofied plants be produced

Answer 310

• artificial selection
  foreign genes being inserted into plants

Question 311

what is artificial selectio

Answer 311

• artificial selection - choosing alleles for characteristics that are valuable
• in this way crops have steadily improved
• plant breeding is a slow process
• when genetic engineers introduce new genes with alleles for desired characteristics into a plants DNA → genetically modified plants can be produced quicker

Question 312

what can genetically modified crops be used for

Answer 312

can be used to mass produce medicines or other chemicals cheaply and efficiently

Question 313

what are the different ways foreign genes be inserted into plants to produce GMOs

Answer 313

• in each case a length of DNA that carries the gene to be used is known as a vector:
• a bacterium which infects many species of plant can be used
  
  • when the bacteria invades plant cells, genes from the plasmid DNA become incorporated into the chromosomes of plant cell
  • insert gene into plasmid and carries the genes into plant DNA
• minute pellets covered in DNA carrying the desired genes are shot into plant cells using a particle gun
• viruses → infect cells by inserting their DNA or RNA → can be used to transfer new genes into cell

Question 314

how can gene insertion be screened to ensure its successful

Answer 314

• this is done by incorporating a gene for antibiotic resistance, called a marker gene along with the new desired gene
• the antibiotic is toxic to plant cells at a high conc
• the plant cells are incubated with the antibiotic → kills off any cells that havent been taken up by the new genes
• the only cells that survive are the ones that have successfully incorporated the new genes and are resistant
• the GM plant cells can be cultured in agar with nutrients and plant growth substance to produce new plants
• this micropropagation can multiple a single cell to form a callus which then differentiates to form plantlets and then novel plants

Question 315

how can genetically modified animals be produced

Answer 315

• inject DNA into nucleus of fertilised egg
• egg implanted into surrogate
• DNA is only successfully incorportated into genome of 1% of treated embryos
• retrovirus also been used to introduce new genes into fertilised egg→ virus incorporates its DNA into host

Question 316

recall the issues with genetic modification

Answer 316

health issues
antibiotic resistance
harmful products from new genes
environmental
who owns these new organisms

Question 317

why may health issues arise from genetic modification

Answer 317

• transfer of antibiotic resistance genes to microbes
• formation of harmful products by new genes
• transfer of viruses from animals to humans

Question 318

why may antibiotic resistance occur as from genetic modification

Answer 318

• • GM contains marker gene as well as gene with codes for desired protein
• the gene could be passed onto pathogenic microbes in the gut when the plant is eaten
• the microbes could build up antibiotic resistance
• however → no evidence that dietary DNA can be integrated into genome of a gut bacterium of into the genome of an animal

Question 319

why may environmental issues occur from genetic modification

Answer 319

• GM has increased crop production and prevented use of pesticide issues such as the following still remain:
  
  • transfer of genes to non target species
  • the possible breeding of superweeds
  • GM could lead to inc use of chemicals in agriculture
  • cross pollination can occur over long distances and some crops grown are related to wind plants and can cross with them → so genes used in GM crops may spread to conventional crops or to wild plants

Question 320

how can environmental issues from genetic modification be evaluated

Answer 320

• most of our crops cant survive in the wild
• wild species would overrun our crops without the use of pesticide, fertilisers etc
• therefore any escaped transgenic crop may disappear quickly
• however if this gene makes any plant its transferred to fitter then it could produce super weeds which could have an advantage over others in the wind
• invasive species → superweeds

Question 321

what solution is there to GM superweeds

Answer 321

• one solution to GM superweeds would be to ensure that outcrosses (crosses between GM and other plants of a different variety) arent fertile
• or development of tech to ensure pollen deosnt contain the modified gene so it cant spread

Question 322

what is the ownership issue when it comes to GMOs

Answer 322

• many farmers may keep GM seeds to save money so they dont have to buy more
• however these seeds may not be as good as the original
• biotech companies now have patents on new tech used in GM
• developing countries unlikely to be able to afford expensive licences to new tech to grow GM crops and they may need them more as they may find it difficult to compete with GM crops in affluent countries → these farmers may become poorer
• difficult to predict social consequences of scientific development

Question 323

how do you carry out a spearmans rank test

Answer 323

ranks all of the values from lowest to highest
calculate the difference between ranks-> d
then square the d values
sum of d squared values
insert values into the formula
n= number of the amount of data collected

Question 324

why is it difficult to treat parksinsons

Answer 324

dopamine cant cross blood brain barrier
excess dopamine could lead to schizophrenia