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Alevel Biology > 5.3 > Flashcards

5.3 Flashcards

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1
Q

What are sensory receptors

A

Specialised cells that can detect changes in our surroundings, most are energy transducers that convert 1 form of energy to another, each type of transducer adapted to detect changes in a certain energy form, may be change in light level or chemicals present

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2
Q

What is a stimulus

A

Change in environment, change in every level or new chemical present

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3
Q

How do sensory receptors respond to stimulus

A

Create signal in form of electrical energy called nerve impulse

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4
Q

What sensory receptor and energy change involved with stimulus change in light intensity

A

Light sensitive cells in retina (rods and cones), light to electrical

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5
Q

What sensory receptor and energy change involved with stimulus change in temp

A

Temp receptors in skin and hypothalamus, heat to electrical

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6
Q

What sensory receptor and energy change involved with stimulus change in pressure on skin

A

Pacinian corpuscles in skin, movement to electrical

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7
Q

What sensory receptor and energy change involved with stimulus change in sound

A

Vibration receptors in ear, movement to electrical

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8
Q

What sensory receptor and energy change involved with stimulus change in movement

A

Hair cells in inner ear and movement to electrical

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9
Q

What sensory receptor and energy change involved with stimulus change in muscle length

A

Muscle spindles in skeletal muscles, movement to electrical

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10
Q

What sensory receptor and energy change involved with stimulus change in chemicals in air

A

Olfactory cells in nose epithelial lining, chemical to electrical

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11
Q

What sensory receptor and energy change involved with stimulus change in chemicals in food

A

Chemical receptors on tongue taste buds, chemical to electrical

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12
Q

What is the pacinian corpuscle

A

Pressure sensor that detects changes in pressure on skin

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13
Q

What is the pacinian corpuscle structure

A

Corpuscle is an oval shape structure consisting of series of concentric rings of connective tissue wrapped round end of nerve cell

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14
Q

How does pacinian corpuscle work

A

When pressure on skin changes it deforms rings of connective tissue pushing against nerve endings, corpuscle only sensitive to changes in pressure that deform rings of connective tissues so when pressure constant they stop responding

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15
Q

What is embedded in a plasma membrane

A

Cell surface membranes contain proteins, some are channels that allow movement of ions across membrane by facilitated diffusion, others transport proteins actively move ions across membrane against concentration gradient, requires use of energy in form of ATP

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16
Q

What happens if Channel proteins always open

A

If channel proteins always open then ions can diffuse across membrane until in equilibrium, if channels can be closed action of active pumps create concentration gradient across membrane

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17
Q

What specialised channel proteins do cells associated with nervous system have

A

Sodium ion channels and potassium ion channels and gates to open and close these channels

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18
Q

What are sodium ion channels sensitive to and what does this mean

A

Small movements of membrane, so when membrane deformed by changing pressure sodium channels open allowing sodium ions to diffuse into cell producing generator potentials

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19
Q

What do membranes contain in nerve associated cells and what does this mean

A

Contain sodium potassium pump that actively pump 3 sodium ions out of cell and 2 potassium ions into cells, when channel proteins closed pump makes concentration gradient

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20
Q

What does the sodium potassium pump in a nerve cell cause

A

Concentration of sodium ions outside cell increase while concentration of potassium ions inside cell increase, so membrane has more permeability to potassium ions, some leak out of cell and membrane less permeable to sodium ions so don’t leak into the cell

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21
Q

What is the result of the ionic movements of a sodium potassium pump in nerve related cell membranes

A

Result of ionic movements is potential gradient across cell membrane, cell negatively charged inside compared with outside, negative potential enhanced by presence of negatively charged anion inside cell

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22
Q

When is cell membrane polarised

A

When cell inactive, negatively charged inside to outside

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23
Q

How is nerve impulse created

A

By altering permeability of nerve cell membrane to sodium ions, achieved by opening sodium ion channels as channels open, membrane permeability increased and sodium ions move across membrane down concentration gradient into cell and this movement of ions creates charge across membrane

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24
Q

What is depolarisation

A

Inside cell becomes less negative that usual

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25
Q

What is generator potential

A

Change in potential across receptor membrane

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26
Q

What happens if small stimulus detected

A

Only few sodium ion channels open

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27
Q

What happens the larger the stimulus detected

A

More gated channels will open, if enough gates opened and enough sodium ions enter cell, potential difference across cell membrane changes significantly and initiates impulse/action potential

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28
Q

What happens when stimulus detected

A

Energy converted to depolarisation of receptor cell membrane, and impulse transmitted to other parts of the body

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29
Q

How are impulses transmitted

A

Along neurones as action potentials

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30
Q

How are action potentials carried

A

As a rapid depolarisation of membrane caused by influx of sodium ions

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31
Q

What are the 3 different types of neurones and function

A

Motor neurone carries action potential from central nervous system to an effector like muscle or gland, sensory neurones carry action potentials from sensory receptor to CNS, relay neurone connects sensory and motor neurone

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32
Q

Do neurones have similar or different basic structure

A

Similar all enabling transmission of action potentials

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33
Q

What are neurone cells specialised features

A

They’re very long to transmit action potentials over long distance, plasma membrane has gated ion channels, sodium potassium pump use ATP to actively transport sodium ions out and potassium ions in, neurones maintain potential difference across plasma membrane

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34
Q

What are neurone cells further specialised features

A

Cell body contains nucleus, mitochondria and ribosomes, dendrites connect to other neurones and carry impulse to cell body, axon carries impulse away from from body, neurones surrounded by fatty layer that insulates cell from electrical activity in other nerve cells, fatty layer composed of Schwann cells closely associated with neurone

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35
Q

How are motor neurones different from other neurones

A

Have cell body in CNS and have long axon that carries action potential out of effector

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36
Q

How are sensory neurones different from other neurones

A

Long dendrons carrying action potential from sensory receptor to cell body which is positioned outside CNS, have short axon carrying action potential to CNS

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37
Q

How are relay neurones different from other neurones

A

Connect sensory and motor neurone, have short dendrites and axon, number of divisions of axon is variable, conduct impulse in coordinated pathways

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38
Q

What is a myelinated neurone

A

Insulated by myelin sheath

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39
Q

What are associated with Schwann cells

A

Sensory and motor neurones associated with Schwann cells make up fatty myelin sheath

40
Q

What is structure of a myelin sheath

A

Schwann cells wrapped tightly round neurone so sheath consists of layers of membrane and thin cytoplasm from Schwann cells

41
Q

What are in gaps of myelin sheath

A

Nodes of ranvier (very short)

42
Q

What does it mean that myelin sheath is tightly wrapped around neurone

A

Prevents movement of ions across membrane so movement of ions across membrane only occurs at nodes of ranvier (so action potential jumps from one node to next making more rapid conduction)

43
Q

What are non-myelinated neurones

A

Associated with Schwann cells but several neurones may be hid in 1 loosely wrapped cell meaning action potential moves along neurone in wave instead of jumping node to node

44
Q

What is main advantage of myelinated neurones

A

Transmit action potential quicker than non-myelinated neurone

45
Q

What do myelinated neurones carry

A

Action potentials from sensory receptor to CNS and from CNS to effectors, carrying over long distances but increased spread of myelinated neurone means rapid response to stimulus

46
Q

Why and when are non myelinated neurones used

A

Shorter and carry action potentials shorter distances so used in coordinating body functions like breathing and action of digestive system, so increased speed of transmission less important

47
Q

When is a neurone at rest

A

When not transmitting action potential

48
Q

At rest what is a neurone doing

A

Pumping ions across plasma membrane, as with sensory receptors sodium/potassium pumps use ATP to pump 3Na+ out of cell of 2K+ pumped in

49
Q

What are gated sodium and gated potassium ion channels doing at rest

A

Na ion channels kept closed but some K+ left open so plasma membrane more permeable to K+ than Na+, k+ ions tend to diffuse out of cell

50
Q

What does neurone cell cytoplasm contain and what does this mean

A

Contains large organic anions, so interior of cell maintained at negative potential compared with outside (cell membrane polarised)

51
Q

When does ion exchange occur on myelinated neurones

A

Nodes of ranvier

52
Q

At rest what do neurones maintain and what causes depolarisation

A

Concentration of Na+ across plasma membrane, if some Na+ channels open, Na+ diffuses down concentration gradient into cell from tissue fluid causing depolarisation

53
Q

What occurs at generator region of neurone

A

Gated channels are opened by action of synapse, when a few gated channels open it allows a few Na+ into cell producing small depolarisation (generator potential), this may go no further but if more channels open generator potentials sum produces larger depolarisation, if threshold net action potential occurs

54
Q

What are most Na+ channels in neurones opened by

A

Potential difference across membrane

55
Q

What happens when enough generator potentials to reach threshold potential

A

Voltage gated channels open

56
Q

How is opening of voltage gated channel positive feedback

A

Small depolarisation of membrane causes change to increase depolarisation further

57
Q

What does opening of voltage gated Na+ channels allow

A

Large influx of Na+ and depolarisation reaches +40mV on inside of cell, once value reached action potentials transmitted by neurone

58
Q

Why is action potential all or nothing response

A

It’s self perpetuating (once it starts at 1 point of neurone continues to end of neurone)

59
Q

What are the first 3 stages of an action potential

A

1.membrane starts in resting state, polarised and inside cell (-70mV), higher concentration of Na+ outside than inside cell and higher K+ inside cell 2.Na+ channels open and some Na+ diffuses into cell, 3.membrane depolarises meeting threshold (-50mV)

60
Q

What are the middle 3 stages of an action potential

A

4.positive feedback causes near sodium ion gated channels to open and Na+ floods in, as more Na+ enters cell becomes more positively charged than outside 5.potential difference across membrane reaches +40mV, inside cell positive v outside 6.Na+ channels close and K+ channels open

61
Q

What are the last 3 stages of an action potential

A

7.K+ diffuses out of cell brining potential difference back to negative inside v outside (repolarisation) 8.potential difference overshoots slightly making cell hyperpolarised 9.original potential difference restored so cell returns to resting state

62
Q

What happens after action potential

A

Na+ and K+ in wrong place, concentration of ions inside v outside must be restored by action of sodium/potassium pumps, for short time after each action potential impossible to stimulate cell membrane to reach another action potential (called refractory period)

63
Q

What does refractory period allow

A

Cells to recover after action potential and ensures action potentials only transmitted in 1 direction

64
Q

What is a synapse

A

Junction between 2 or more neurones where 1 neurone can communicate with another neurone (synaptic cleft in between both)

65
Q

How do action potentials travel and what can’t they travel through

A

Travel along neurones as series of ionic movements across neurones membrane, but can’t bridge gap between 2 neurones, so action potential in pre-synaptic terminal releases neurotransmitters that diffuse across synaptic cleft and generates new action potential in post-synaptic terminal

66
Q

What are synapses that use acetylcholine called

A

Cholinergic synapses

67
Q

What is the pre-synaptic bulb

A

Swelling at the end of pre synaptic neurone containing specialised features

68
Q

What specialised features do pre-synaptic bulb contain

A

Many mitochondria as active processes need ATP, large amount of smooth endoplasmic reticulum to packages neurotransmitters into vesicles, many vesicles with acetylcholine to diffuses across synaptic cleft, many voltage gated calcium ion channels on cell surface membrane

69
Q

What does the post synaptic membrane contain

A

Specialised sodium ion channels that can respond to neurotransmitters, these channels have 5 polypeptide molecules, 2 of which have acetylcholine receptors

70
Q

What occurs in post synaptic membrane when acetylcholine present

A

Receptor sites complementary to acetylcholine, when acetylcholine present in synaptic cleft it binds to receptor site and causes sodium ion channels to open

71
Q

What are the first 4 steps for transmission across synapse

A

1.action potential arrives at synaptic bulb 2.voltage gated calcium ion channels open 3.calcium ions diffuse into synaptic bulb 4.calcium ions cause synaptic vesicles to move and fuse with pre-synaptic membrane

72
Q

What are the middle 4 steps for transmission across synapse

A

5.acetylcholine released by exocytosis 6.acetylcholine diffuses across synaptic cleft 7.acetylcholine molecules bind to receptor site on sodium ion channels in post synaptic membrane 8.sodium ion channel opens

73
Q

What are the last 4 steps for transmission across synapse

A

9.sodium ions diffuse across post synaptic membrane into post synaptic neurone 10.excitatory post synaptic potential created 11.if sufficient generator potential then threshold reached 12.new action potential created in post synaptic neurone

74
Q

What happens if acetylcholine left in synaptic clef

A

Continues to open sodium ion channels in post synaptic membrane and continues to cause action potential

75
Q

What does acetylcholinerase enzyme in post synaptic cleft do

A

Hydrolyses acetylcholine to acetic acid and choline to stop signal transmission so synapse doesn’t continue to produce action potentials in post synaptic neurone

76
Q

What happens to acetic acid and choline once acetylcholinerase hydrolyses acetylcholine

A

It’s recycled and they re enter synaptic bulb by diffusion and recombine to acetylcholine using ATP from respiration in mitochondria, recycled acetylcholine stored in synaptic vesicles for further use

77
Q

How is action potential all or nothing response

A

Once action potential starts it’s conducted along whole length of neurone and doesn’t vary in size or intensity

78
Q

What is an example of cell signalling in transmission across neurones

A

Pre synaptic membrane releases neurotransmitter into synaptic clef and post synaptic neurone responds

79
Q

How does cell signalling across synapse work in cholinergic synapses

A

Signal sent to next neurone consists of acetylcholine molecules, more intense stimulus transmitted as more frequent action potentials

80
Q

What is main role of synapse

A

To connect 2 neurones so signal can pass

81
Q

How can nerve junctions be more complex than than simple connection between 2 neurones

A

Nerve junctions often involve a few neurones (either from different places converging on 1 neurone or 1 neurones sensing signals to several neurones that diverge to different effectors)

82
Q

What happens when 1 action potential passes down axon to synapse

A

It causes a few vesicles to move to and fuse with pre synaptic membrane, relatively small number of acetylcholine molecules diffusing across synaptic cleft produces small depolarisation which is an EPSP and on its own won’t cause an action potential (may take several EPSP to reach threshold and cause action potential)

83
Q

What is summation

A

Effect of several EPSPs combine together to increase membrane depolarisation until threshold reached

84
Q

What is temporal summation

A

Results from several action potentials in same pre synaptic neurone

85
Q

What is spatial summation

A

From action potentials arriving from several different pre-synaptic neurones

86
Q

What is Inhibitory post synaptic potentials

A

Can be produced at some pre synaptic neurones, these reduce effect of summation and prevent action potential in post synaptic neurone

87
Q

What does nerve junctions having serval neurones enable

A

Synapses to control communication passed along nervous system

88
Q

What does several pre synaptic neurones converging on 1 post synaptic neurone allow

A

Allows action potentials from different parts of nervous system to contribute to generating action potential in 1 post synaptic neurone creating a certain response (spatial summation) useful when stimulus warning us of danger

89
Q

What could the combination of several EPSPs be prevented by

A

Prevented by production of action potential by 1 IPSP

90
Q

What does 1 pre synaptic neurone diverging into several post synaptic neurones allow

A

1 action potential to be transmitted to several parts of nervous system, useful in reflex arc, 1 post synaptic neurone elicits response and another informs brain

91
Q

What do synapses ensue

A

Action potentials transmitted in right direction (only pre synaptic bulb has acetylcholine vesicles) so if action potential started half way along neurone and ends at post synaptic membrane, won’t cause response in next cell

92
Q

What can synapses filter out

A

Unwanted low level signals, if low level stimulus creates action potential in pre synaptic neurone it’s unlikely to pass across synapse to next neurone as several acetylcholine vesicles must be released to create action potential in post synaptic neurone

93
Q

How can low level action potentials be amplified

A

By summation, if low level stimulus persists it will generate several successive action potentials in pre synaptic neurone, release of acetylcholine vesicles over short period enables post synaptic EPSPs to combine together and produce action potential

94
Q

What may happen to synapse after repeated stimulation

A

A synapse may run out of vesicles with neurotransmitter, synapse is fatigued to nervous system doesn’t respond to stimulus, explains why we get used to smells and background noises and avoid over stimulation of effector which could cause damage

95
Q

What is creation and strengthening of specific pathways in nervous system is thought to be

A

Basis of conscious thought and memory, synaptic membranes adaptable especially post synaptic membrane can be made more sensitive to acetylcholine by addition of more receptors meaning post synaptic neurone more likely to fire an action potential creating specific pathway in response to stimulus

Alevel Biology (25 decks)

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