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A Biology A Level > Topic 8 > Flashcards

Topic 8 Flashcards

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1
Q

What is a nerve?

A
  • Bundle of neurones surrounded by protective coating
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2
Q

What is a neurone?

A
  • A single cell responsible for detection of a stimulus, relay of an impulse and stimulation of a response
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3
Q

What are the different types of neurones?

A
  • Sensory neurone
  • Relay neurone
  • Motor neurone
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4
Q

What is a sensory neurone?

A
  • Transmit impulses from receptor cells to relay neurones in CNS
  • Consist of long myelinated dendron (impulse from receptor to body cell)
  • Consist of short myelinated axon (impulse from body cell to relay neurone)
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5
Q

What is a relay neurone?

A
  • Located in CNS and transmits impulses between sensory and motor neurones.
  • Many short dendrites which send impulses along myelinated neurone
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6
Q

What is a motor neurone?

A
  • Transmit from CNS to effector cells.
  • Long myelinated axon which transmits impulses from cell body to motor end plates
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7
Q

What are dendrites?

A
  • Form synaptic connections with other neurones
    allowing an impulse to be received from other neurones.
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8
Q

What are dendrons?

A
  • Long nerve fibre extensions that conduct an impulse towards cell body
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9
Q

What is an axon?

A
  • Long nerve fibre extension that conduct an impulse towards the cell body
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10
Q

What is the myelin sheath?

A
  • Glycolipid layer wrapped around the axon
  • Electrical insulator made of schwann cells and its role in saltatory conduction.
  • Nodes of ranvier is where sodium ions are concentrated
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11
Q

What is the reflex arc?

A
  • Responsible for coordinating reflexes, which are rapid, involuntary responses to stimuli
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12
Q

What is the process of the reflex arc?

A
  • Receptor cells detect a stimulus and generate an impulse.
  • Sensory neurones transmit impulse from receptor cells to relay neurones in the CNS (brain or spinal cord.)
  • CNS processes the information and coordinates a response.
  • Relay neurones in the CNS transmit impulses between sensory neurones and motor neurones.
  • Motor neurones transmit impulses from the CNS to effector cells, such as muscles and glands.
  • Effector cells produce a response
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13
Q

What happens when there is bright light?

A
  • Photoreceptors in the retina detect bright light and generate an impulse.
  • Sensory neurones transmit impulse through bipolar neurones and the
    optic nerve from photoreceptors to relay neurones in the CNS
  • The CNS processes the information and coordinates a response.
  • Relay neurones in the CNS transmit impulses
    between sensory neurones and motor neurones.
  • Motor neurones transmit impulses from the CNS
    to effector cells, such as muscles and glands.
  • Muscles work antagonistically - Circular muscles contract and radial
    muscles relax. This constricts the pupil and decreases the quantity of light able to enter the eye.
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14
Q

What happens if there’s dim light?

A
  • Photoreceptors in the retina detect dim light and generate an impulse.
  • Sensory neurones transmit impulse through bipolar neurones and the
    optic nerve from photoreceptors to relay neurones in the CNS
  • The CNS processes the information and coordinates a response.
  • Relay neurones in the CNS (brain or spinal cord) transmit impulses
    between sensory neurones and motor neurones.
  • Motor neurones transmit impulses from the CNS
    to effector cells, such as muscles and glands.
  • Muscles work antagonistically - Radial muscles contract and circular
    muscles relax. This dilates the pupil and increases the quantity of light able
    to enter the eye.
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15
Q

Why is a neurone’s cell membrane polarised at rest?

A
  • Potential difference equal to -70mV
  • This means that inside of the neurone it’s negatively charged and outside is positively charged
  • This is
    because sodium-potassium pumps and potassium ion channels maintain the resting potential of -70mV.
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16
Q

Why is the resting potential -70 mV?

A
  • Active transport with ATP moves three Na+ ions out of the neurone for every two K+ ions that move into the neurone.
  • This creates an electrochemical gradient and a concentration gradient as there are more Na + ions outside of the neurone.
  • Sodium-potassium pumps move K + ions into the neurone; however, the membrane is permeable to K + ions, so they diffuse
    back out of the neurone through potassium ion channels.
  • The inside of the neurone is negatively charged, and the outside of
    the membrane is positively charged.
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17
Q

How is an action potential generated?

A
  • Action potential arrives at the cell membrane, causing it to depolarise as sodium ion channel opens so influx of Na+ ions.
  • If the threshold potential equal to -55mV is reached, more sodium ion channels will open.
  • Continues to depolarise so action potential is generated.
  • Once a potential difference of +30mV is reached, voltage gated sodium ion channels will close and voltage gated potassium ion channels will open.
  • Neurone repolarises as K+ ions move out
  • Potassium ion channels are too slow to close causing hyperpolarisation of the membrane as too many K+ diffuse out the membrane.
  • Resting potential until depolarised by another action potential
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18
Q

What is the refractory period?

A
  • Delay between action potentials as voltage-gated ion channels are recovering so can’t be opened.
  • Makes sure action potentials don’t overlap are are discrete
  • Impulse can only travel in one direction
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19
Q

What is the wave of depolarisation (action potential transmitted)?

A
  • In unmyelinated neurones where an action potential causes Na+ ions to diffuse into next section of axon triggering a new action potential.
  • Repeats the length of the axon (wave)
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20
Q

What is saltatory conduction?

A
  • In myelinated neurones where there are patches of bare membrane between Schwann cells called nodes of Ranvier where sodium ion channels are concentrated.
  • Depolarisation occurs meaning action potentials are generated
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21
Q

What are features found in all neurones?

A
  • Long fibres called axons
  • Cell body containing nucleus and cellular structures
  • End of axon (axon terminal)
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22
Q

What is a synapse?

A
  • Found at the axon terminal and is the cleft between adjacent neurones which allow an impulse to be transmitted
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23
Q

What is the synaptic knob?

A
  • Contains synaptic vesicles containing neurotransmitters (acetylcholine)
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24
Q

What is the synaptic vesicles?

A
  • Contain neurotransmitters
  • When an action potential reaches the axon terminal, synaptic vesicles fuse with the presynaptic membrane and release their contents into the synaptic cleft via exocytosis.
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25
Q

What are receptor proteins?

A
  • Found in the postsynaptic membrane which are complementary to specific
    neurotransmitters.
  • When neurotransmitters bind to these receptor proteins, they may generate an action potential.
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26
Q

What enzymes are in the synapse?

A
  • Found in the synaptic cleft and are responsible for breaking down neurotransmitters, so the response doesn’t keep happening.
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27
Q

How do neurotransmitters transmit nerve impulses across the synapse?

A

-

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28
Q

How do synapses allow impulses to be amplified?

A
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29
Q

How do synapses allow impulses to be dispersed?

A
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30
Q

What happens when there is a weak stimulus?

A

-

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31
Q

What happens when there is a strong stimulus?

A

-

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32
Q

What is the conjunctiva in the eye?

A
  • Thin mucous membrane covering the front of the eye which protects the cornea
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33
Q

What is the sclera?

A
  • Tough connective tissue layer responsible for protecting the eye and maintaining its shape
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34
Q

What is the cornea?

A
  • Thick transparent layer responsible for focusing light rays onto the retina
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35
Q

What is the iris?

A
  • Pigmented layer containing circular and radial muscles that constrict and dilate the pupil to control the amount of light
36
Q

What is the lens?

A
  • Stacks of long narrow transparent cells responsible for focussing light onto retina
37
Q

What is the ciliary body?

A
  • Ciliary muscles and suspensory ligaments that contract and relax in order to control shape of lens
38
Q

What is the vitreous humous?

A
  • Transparent fluid which gives eye its shape
39
Q

What is the retina?

A
  • Contains photoreceptors (rods and cones) which absorb light and generate an impulse which travel to brain through bipolar and optic nerve
40
Q

What are photoreceptors?

A
  • Contain light-sensitive pigment called rhodopsin (joined by opsin and retinal)
  • Responsible for absorbing light energy and generating an impulse which travels to the brain through bipolar neurones and the optic nerve.
41
Q

What are the two types of photoreceptors?

A
  • Cone cells - found in the fovea and are responsible for trichromatic (colour) vision
  • Rod cells - found in peripheral parts of retina and are responsible for monochromatic (black + white) vision
42
Q

What is the fovea?

A
  • Part of retina containing a high concentration of cone cell photoreceptors
  • Increases resolution of vision
43
Q

What is the choroid?

A
  • Black vascular layer found behind retina which prevents internal reflection of light in the eye
44
Q

How does rod cells in retina respond to bright light?

A
  • Bleaching occurs where rhodopsin breaks down opsin and retinal
  • The opsin then binds to the rod cell membrane and cis retinal converts to trans retinal
  • This causes voltage-dependent sodium cation channels to close
  • So rod cells hyperpolarise
  • Prevents release of neurotransmitter glutamate meaning bipolar neurone is no longer inhibited
  • Bipolar neurone depolarises and generates an action potential that travels to the brain through the optic nerve.
45
Q

How does rod cells in retina respond to darkness?

A
  • Dark adaptation occurs whereby opsin uncouples from the rod cell membrane and trans retinal converts to cis retinal
  • This allows rhodopsin to be reformed from opsin and retinal with ATP
  • Causes voltage-dependent sodium channel to open
  • Rod cell depolarise
  • Trigger release of neurotransmitter glutamate which diffuses across the synaptic cleft and binds to the bipolar neurone.
  • This inhibits the bipolar neurone, meaning it can no longer depolarise and generate an action potential.
46
Q

What is phytochromes?

A
  • Found in plants and consists of light absorbing pigments attached to a protein molecule
  • Coordinates plants responses
47
Q

What is Pr phytochrome?

A
  • Inactive so responsible for absorbing red light (660nm)
  • More Pr converted into Pfr in daylight (more red light)
48
Q

What is Pfr phytochrome?

A
  • Active so responsible for absorbing far-red light (730nm)
  • More Pfr converted to Pr in darkness (more far-red light)
49
Q

How do levels of phytochrome change throughout the day?

A
  • During the day, levels of PFR rises as there is conversion of PR to PFR
  • During the night, levels of PR rise as PFR slowly converts back to PR
50
Q

How do phytochromes co-ordinate plant responses?

A

-

51
Q

What is tropism?

A
  • The growth of a plant in response to a directional stimulus
52
Q

What is phototropism?

A
  • Plants grow in response to the direction of light
  • Plant shoots are positively phototrophic so grow in direction of light
53
Q

What is gravitropism?

A
  • Plants grow in response to direction of gravity
  • Plant roots are positively gravitropic meaning they grow in direction of gravity
54
Q

How does phototropism occur?

A

-

55
Q

What is a gland?

A
  • Group of cells specialised to secrete substances (hormones) when they receive a stimulus
56
Q

What is a hormone?

A
  • Chemical messenger released from glands
  • Alter cell activity with complementary receptor proteins
57
Q

What is the nervous control?

A
  • Receptor detects a stimulus and generate an impulse
  • Sensory neurones transmit impulse from receptors to relay neurones
  • CNS coordinate a response
  • Relay neurones transmit impulses between sensory and motor neurones
  • Effector cells produce a response
58
Q

What is the hormonal control?

A
  • Receptor cells on organs detect a stimulus
  • Effector cells produce a hormone
  • Hormones transport in blood to where they are needed
  • Hormones produce a response
59
Q

How are nervous and hormonal control different?

A
  • Nervous uses impulses/Hormonal uses chemical messengers
  • Nervous is faster response/Hormonal slower as depends on blood flow
  • Nervous is short-term/Hormonal is long-term
60
Q

What 4 sections is the brain divided into?

A
  • Forebrain, midbrain, hindbrain and spinal cord
61
Q

What is the cerebrum?

A
  • In the forebrain
  • Two halves called the cerebral hemispheres and surrounded by the cerebral cortex
62
Q

What are the 4 sections of the cerebrum?

A
  • Frontal lobe (thinking + decision making)
  • Parietal lobe (sensation + calculation)
  • Temporal lobe (auditory info, memory + speech)
  • Occipital lobe (visual info + memory)
63
Q

What is the hypothalamus?

A
  • In midbrain
  • Thermoregulation and sleep
  • Acts as an endocrine gland
64
Q

What is the cerebellum?

A
  • In the hindbrain
  • Controls motor movement and coordination and memory and balance
65
Q

What is the medulla oblongata?

A
  • Above the spinal cord
  • Basic physiological function
66
Q

What is the process of CT scanning?

A
67
Q

What is the process of MRI scanning?

A
68
Q

What is the process of fMRI scanning?

A
69
Q

What is the process of PET scanning?

A
70
Q

What is the critical period?

A
  • Important period of postnatal visual cortex development
71
Q

What happens to the visual cortex in the critical period?

A
  • ## Visual cortex is in the occipital lobe in the forebrain.
72
Q

How is brain development investigated using Hubel and Wiesel?

A
  • They conducted monocular deprivation experiments on monkeys and cats.
  • The eye of a baby mammal was stitched shut for several months
  • When the eyes were unstitched, it was discovered that the visually deprived eyes were blind.
  • The ocular dominance columns in the open eyes had expanded to take over the other columns that weren’t being stimulated, which is an example of switched dominance in the neurones in the visual cortex.
  • The experience was then conducted on adult mammals.
  • When the eyes were unstitched, it was discovered that the visually deprived eyes weren’t blind, and vision fully recovered. It was also discovered that the size of the ocular dominance columns in the open eyes were unchanged.
73
Q

What was Hubel and Wiesel concluded?

A
  • Period of postnatal visual cortex development is vital in baby mammals so it is important that they receive postnatal stimulation in order to form connections with the visual cortex.
74
Q

What are the advantages of animal medical research?

A
  • Physiologically similar
  • Only used when necessary
  • Greater right to life
75
Q

What are the disadvantages of animal medical research?

A
  • Animals are slightly physiologically different to humans so inaccurate results.
  • Can cause pain and distress
  • Unnecessary because there are alternatives
  • Animals have a right to life
76
Q

What is habituation?

A
  • Change in response to a stimulus as a result of repeated exposure over time
77
Q

How does habituation occur in animals?

A
  • Repeated exposure to a stimulus reduced the number of voltage-dependent calcium ion channels in the presynaptic neurone that opens in response to action potential.
  • Smaller influx of calcium ions into synaptic knob causes less synaptic vesicles to fuse with presynaptic membrane
  • Less neurotransmitters diffuse across the synaptic cleft and bind to complementary receptor proteins on the postsynaptic membrane.
  • Likelihood of depolarisation of postsynaptic neurones have decreased so less action potentials being generated.
78
Q

What is the cause of Parkinson’s?

A
  • Less dopamine neurotransmitters will be released from the presynaptic neurone into the synaptic cleft
  • No action potentials generated.
  • Dopamine neurotransmitter deficit
79
Q

What are the symptoms of Parkinson’s?

A
  • Stiffness of muscles
  • Tremors
  • Slowness
  • Issues with balance
80
Q

What is the treatment of Parkinson’s?

A
  • L-dopa
  • MOA inhibitors and dopamine agonists
  • Gene therapy and deep brain stimulation
81
Q

What is the cause of depression?

A
  • Serotonin neurotransmitter deficit in the brain
  • Less serotonin released from presynaptic cleft
  • Less depolarisation in postsynaptic neurone which won’t exceed threshold potential so less action potentials will be generated
82
Q

What is the symptoms of depression?

A
  • Anxiety, restlessness, sadness, loss of interest
83
Q

What is the treatment of depression?

A
  • Selective serotonin reuptake inhibitors
  • MAOI inhibitors
  • Antidepressants
84
Q

What is L-dopa?

A
  • Used to treat Parkinson’s which causes dopamine neurotransmitter deficit in the brain
  • Used because dopamine cannot cross the blood-brain barrier
85
Q

How does L-dopa affect synaptic transmission?

A
  • Crosses the blood-brain barrier and is converted into dopamine so increase conc in synaptic cleft
  • Increases likelihood of depolarisation of postsynaptic neurones which therefore increases action potentials generated
  • Increases transmissions of impulses across synapses in part of brain which controls movement.
86
Q

How does MDMA affect synaptic transmission?

A
  • MDMA binds to serotonin re-uptake proteins on presynaptic membrane so inhibits re-uptake of serotonin into presynaptic neurone
  • Increase depolarisation of postsynaptic neurone which increases action potentials being generated
  • Impulses across synapses in part of brain that controls mood so elevating mood.
87
Q

How does MDMA lead to depression?

A
  • Causes a loss of serotonin receptors on postsynaptic membrane so less responsive to serotonin
  • Serotonin neurotransmitter deficit in the brain

A Biology A Level (8 decks)

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