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Biology A2 > 3.8 nervous system > Flashcards

3.8 nervous system Flashcards

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1
Q

3 functions of a nervous system?

A

deflecting change or stimuli inside the body + the environment
process + stores information
initiates response

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2
Q

Stimulus?

A

detectable change in the internal or external environment of an organism that produces a response in the organism

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3
Q

Sensory receptors?

A

Senses
taste
smell
touch
eyesight
hearing

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4
Q

Specialised sensory cells?

A

pressure sensors in the skin

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5
Q

Sensory receptors?

A

transducers because they detect energy in one form and convert it to electrical energy

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6
Q

Electrical impulse?

A

travel along neurones and initiate a response in an effector ( muscle or gland)

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7
Q

Central nervous system?

A

brain and spinal cord
processes information from a stimulus
brain + spinal cord are surrounded by a tough protective membrane called meninges
white matter only contains nerve fibres surrounded by myelin
Grey matter has nerve fibrous of relay neurones but the colour is provided by cell bodies of motor neurones

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8
Q

Myelin?

A

fatty + tissue which is white in colour

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9
Q

Peripheral nervous system?

A

split into 2 parts
somatic nervous system
autonomic nervous system

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10
Q

Somatic nervous system?

A

pairs of nerves that originate from the brain or the spinal cord + branch outwards
nerves contain sensory neurones which carry impulses to the CNA
motor neurones carry impulses from the CNS to the effectors

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11
Q

Autonomic Nervous system?

A

provides unconscious control for the functioning of internal organs such as heartbeat or digestion

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12
Q

Structure of sensory neurone?

A

Dendrites
Schwann cell
Myelin sheath
Axon
Nodes of ranvier
Cell Body
Synaptic bulb
direction of impulse = towards cell body

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13
Q

Motor neurone?

A

Cell body
dendrites
schwann cell
nodes of ranvier ( no myelin sheath)
Schwann cell (nucleus)
axon
synaptic bulb

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14
Q

Spinal cord?

A

Sensory neurone
cell body in dorsal root ganglion
central canal
grey matter
dorsal root gangolion
dorsal root
spinal nerves
ventral root
motor neurone

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15
Q

Reflex arc?

A

stimulus ( hot objects)
Receptors
Sensory neurone
Relay neurone
Coordinators ( Brain/spinal cord)
Motor neurone
Effector - Muscle/gland
Response

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16
Q

What is a reflex arc?

A

rapid automatic response, resulting from a nerve impulse initiated by a stimulus
The decision making area of the brain is not involved
so action = involuntary
usually protective functions

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17
Q

Withdrawal reflex?

A

stimulus = heat
sensory receptor = located in dermis of skin
responds to pain + temp

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18
Q

Sensory neurone?

A

sends the impulse up the arm of the spinal cord
CNS relays the impulse from the sensory neurone to the motor neurone
the motor neurone sends the impulse to the effector which would be muscle in arm.

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19
Q

Response?

A

the arm muscle contracts, hand = removed from heat source

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20
Q

Pupil reflex?

A

stimulus = light
sensory receptor= photo sensitive cells in the retina
sensory neurone = the optic nerve
CNS= brain
motor neurone carries impulses to the muscle pf the iris
circular - contraction
dilation - radial

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21
Q

Response?

A

iris muscle contracts, altering diameter of pupil

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22
Q

Nerve nets?

A

Phylum ponfera (sponge)
has no nervous system
Phylum Chdaria ( jellyfish)
Radial symmetry
nerve net
( nervous system)
Phylum chordata
( humans)
Bilaterally symmetrical
CNS

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23
Q

Hydra(cnidaria)?

A

nerve net= diffuse network of cells
Grouped into ganglia
(swelling of nerves )
but no brain = formed

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24
Q

2 types of cells in a nerve net?

A

Ganglian - provides connections in all directions
Sensory cells - detect light, sound, touch, temp

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25
Q

About Hydra?

A

studied as they have the simplest nervous system
Can regenerate rapidly e.g if they lost a tentacle
Hydra’s nets are in its ectoderm ( outer layer of the 2 layers of the body wall. sensitive to light, physical contact + chemicals)
In response, it can contract, perform locomotion, hunt and feed
has no brain but has complex movements + behaviour

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26
Q

Comparison of Human + Hydra?

A

Hydra
nerve net
2 cell types
rapid regeneration
no myelin sheath
conduction speed = 5ms-1
Human
CNS
numerous cell types
very slow regeneration
myelin sheath on all axons
conduct speed - 120 ms-1

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27
Q

Sensory neurone?

A

carries impulses from the sense receptors to the CNS

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28
Q

Motor neurone?

A

carries impulse from the CNS to the effectors
( muscles or glands )

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29
Q

Relay neurone?

A

receives impulses from sensory neurone and transmit to motor neurone

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30
Q

structure and function of neurone?

A
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31
Q

cell body - function - contains a nucleus + granular cytoplasm

A

function - contains a nucleus + granular cytoplasm

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32
Q

cytoplasm?

A

contains ribosome for protein synthesis

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33
Q

Granules?

A

made of ribosomes grouped on rough ER

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34
Q

Dendrite?

A

thin fibre carrying impulses towards a cell body

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35
Q

Axon?

A

thin fibre carrying impulses away from cell body

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36
Q

Schwann cell?

A

wrap around the axon, many times + withdraw their cytoplasm, leaving a multi layered phospholipid myelin sheath

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37
Q

Myelin sheath?

A

an electrical insulator which speeds up the transmission of an impulse

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38
Q

Nodes of ranvier?

A

1 nanometre in the myelin sheath where adjacent schwann cells meet and the membrane is exposed at these points, the membrane is exposed at these points, the impulse can leave the axon and jump to the next node - known as saltatory conduction

39
Q

What does saltatory conduction do?

A

speeds up the rate of conduction

40
Q

synaptic bulb?

A

a swelling at the end of an axon, where a neurotransmitter is synthesised

41
Q

axon terminal?

A

secretes a neurotransmitter onto the synaptic cleft, so a nerve impulse can be transmitted to an adjacent neurone

42
Q

Nerve impulse?

A

a neurone is an excitable cell which means it can change its resting potential
( potential difference)

43
Q

Resting potential?

A

the potential difference across the membrane of the cell when no nerve impulse is being conducted

44
Q

Potential difference across the membrane?

A

usually 70 mV
membrane = more negative inside so resting potential = -70 mv
as there is pd, membrane is described as polarised
(difference in charge)

45
Q

why is resting potential?

A

due to negative ions of large proteins or organic acids such as pyruvate in the cytoplasm

46
Q

The process of K + and Na+

A

Inside of a cell has a high concentration of K+ ions but low concentration of Sodium ions than outside
K+ ions tend to diffuse out and Na+ diffuse in
Specific channels which allow K+ ions to diffuse out while the channels for Na+ ions are closed
Makes the axon 100 x more permeable to k+ ions which diffuse out faster than sodium diffuses in
Sodium Potassium pumps pump k+ ions back into the cell and Na+ ions back out

47
Q

How is it moved along by active transport?

A

These transmembrane proteins are fuelled by ATP
and the enzyme ATP synthetase which allows K+ and Na+ to be moved along the concentration gradient by active transport.

48
Q

Action potential?

A

the rapid rise and fall of the electrical potential across a nerve cell membrane as a nerve impulse passes

49
Q

Nerve impulse?

A

the transmission of a change in potential along a nerve fibre due to the movement of sodium ions
At the site of an action potential, sodium ions diffuse into the axon because the Na+ channels are open
K + ions diffuse out through the channels which remain open
Na+ ions have faster than K+ ions, so there is a reversal of the potential difference between the inside and outside of the membrane.
Known as depolarisation

50
Q

What happens to the depolarisation?

A

opens, the voltage gated sodium channels, so even more Na+ ions flood in
Na+ ions diffuse further down the axon, creating a wave of depolarisation
Known as the absolute refractory period

51
Q

What is the absolute refractory period?

A

period when no new action potential can be intiated and lasts 1 millisecond

52
Q

Why is there an absolute refractory period?

A

it ensures the action potential = not propagated back in the direction from which it came and the nerve impulse will only travel in 1 direction

53
Q

What is hyper polarisation?

A

fora period of 5-10 milliseconds, if the impulse is strong enough, a new action potential may be generated
Known as the absolute refractory period + occurs when the sodium and potassium pumps try to restore the resting potential

54
Q

What is repolarization?

A

Restoring the original charge to the membrane, positive on the outside and negative on the inside
The potassium channels open + K+ ions diffuse out down a concentration gradient
The cell becomes + inside asm more ions diffuse out, known as repolarization
The Na+ and K+ pump, pump K+ ions back in and Na+ back out, restoring resting potential

55
Q

Depolarization?

A

the temporary reversal of the potential across the membrane of a neurone such that the inside becomes less negative than the outside as an action potential is transmitted

56
Q

Action refractory potential?

A

period at which no new action potential can be intiated

57
Q

When an action potential is generated?

A

Na+ ions diffuse into the axon
This created localised circuits as Na+ move laterally along the axon
The Na+ ions depolarise the adjacent section of the membrane
the voltage gated sodium channels open and Na+ flood in, depolarising the axon
This creates a self perpetuating ( goes on) wave of depolarisation along the axon
At the site of the initial action potential, Na+ channels cannot open until a resting potential = established known as the absolute refractory period, lasting 1 millisecond

58
Q

What’s the purpose?

A

to ensure that the wave is not propagated in the wrong direction
for the next 5-10 milliseconds, Hyper polarisation occurs + if it the impulse, strong enough, it will pass and is known as the relative refractory period

59
Q

when does the relative refractory period occur?

A

when the K+ and Na+ pumps restoring the potential

60
Q

The all or nothing law?

A

a nerve impulse is either initiated or not + is always the same size

61
Q

Purpose of the all or nothing law?

A

allows the action potential to act as a filter to prevent the brain being overloaded with information

62
Q

Graph of a very weak stimulus?

A

flat

63
Q

Graph of a weak stimulus?

A

up then down

64
Q

Graph of a strong stimulus?

A

3 x up then down

65
Q

Very strong stimulus?

A

5 x up then down

66
Q

As stimulus increases?

A

frequency also increases
all action have a max pd of + 40 mv

67
Q

Factors affecting speed of conduction?

A

Temperature
The diameter of the axon
Myelination

68
Q

Temperature?

A

the ions move faster at higher temp, so have more kinetic energy, so birds + mammals are warm blooded, so transmit nerve impulses faster

69
Q

Diameter of the axon?

A

the wider the diameter, the greater the volume, so more Na+ ions flow through so impulse is faster
Humans have none myelinated axons of 0.2 - 1.5 nanometres
this allows slow transmission of an impulse.
Marine invertebrates live in water close to 0 degrees such as squids, which have giant axons of 1 mm
Earthworms have evolved giant axons up to 700 nanometres for rapid response

70
Q

Myelination?

A

speeds up the rate of transmission of the impulse as there is faps in the myelin called nodes of ranvier

71
Q

Nodes of ranvier?

A

at the nodes, na+ can enter, creating a change in voltage which allow the action potential to jump between the nodes , known as saltatory conduction, making transmission more rapid.
nodes of ranvier = 1 mm apart
myelinated nerve fibres have a transmission rate of 120m/s. whereas non myelinated = 0.5m/s

72
Q

Neurotransmitter?

A

a chemical secreted in response to an action potential which carries a chemical signal across a synapse from 1 neurone to the next, allowing an action potential to be initiated

73
Q

What are neurones separated by?

A

a synapse which allows nerve impulses to pass in only 1 direction

74
Q

2 types of synapse?

A

electrical synapse
chemical synapse

75
Q

electrical synapse?

A

3 nanometre junction which is small enough for an electrical impulse to jump from 1 neurone to the next

76
Q

chemical synapse?

A

20 nanometre junction which is too large for the nerve impulse to jump, so neurotransmitter is secreted and diffuses across the synaptic cleft from the presynaptic membrane to the presynaptic membrane

77
Q

Diagram?

A

Mitochondria
Post synaptic membrane
Receptor sites
Myelin sheath
Axon
Vesicles containing neurotransmitter
Receptor sites
Postsynaptic membrane
Synaptic cleft
Action potential
( nerve impulse) moves to the right

78
Q

Process?

A

arrival of an impulse at a synaptic bulb alters the membrane permeability
The voltage gated calcium channels open and ca2+ ions diffuse into the bulb.
( down a concentration gradient)
The Ca2+ ions cause the vesicles to fuse with a
presynaptic membrane
The vesicles release the neurotransmitter acetylcholine into the cleft by exocytosis
Acetylcholine attaches to the intrinsic proteins / receptor cyles on the postsynaptic membrane
The receptor proteins change shape, opening Na+ channels in the post synaptic membrane
Na+ ions flood to the post synaptic membrane, causing depolarisation
when the depolarisation is strong enough, the action potential can be transmitted between the neurones

79
Q

Removing acetylcholine from the cleft?

A

Active transport of Ca2+ ions out of the bulb prevents exocytosis of Acetylcholine
AcetylCholine is hydrolysed by the enzyme acetyl cholinesterase
The products of hydrolysis = choline + ethanoic acid
These diffuse back into the presynaptic neurone + reform acetylcholine using acetyl coenzyme A
this is an energy requiring process, so requires mitochondria

80
Q

Properties of a synapse?

A

Transmit information between neurones
Pass impulses in 1 direction
act as a junction
Protect the nervous system from over stimulation
They filter out low level stimuli and an action potential - only generated when the depolarisation reaches a threshold value of -55 milivolts

81
Q

Temporal summation?

A

depolarisation which builds up over to reach a threshold at which an action potential is generated

82
Q

Spatial summation?

A

several presynaptic neurones contribute to the depolarization which generate an action potential

83
Q

Drug?

A

a molecule that has physiological effects on the body when ingested, inhaled, absorbed or infection

84
Q

What do drugs act as?

A

synapses and disrupt the functioning of neurotransmitters

85
Q

4 Main Neurotransmitters?

A

Acetyl Choline
ABA
Monomaines
( dopamine + serotonin)
Neuropeptide (endorphins)

86
Q

Sedatives?

A

creates a fewer action potentials in the postsynaptic neurone

87
Q

Stimulant?

A

allows more action potentials to reach the postsynaptic neurone
e.g
amphetamines

88
Q

Drug action?

A

drugs mimic the action of neurotransmitters
have the same shape + bind to post synaptic neurone, increasing frequency of action potentials

89
Q

Nicotine?

A

increases the frequency of impulses but unlike acetylcholine, it is not hydrolysed, so continues to initiate impulses
body becomes habituated by nicotine and will only function its presence
to achieve desired effects, more nicotine must be taken in

90
Q

If excess nicotine is taken in?

A

person experiences withdrawal

91
Q

Organo phosphates?

A

found in insecticides, herbicides, nerve gas
These drugs prevent the breakdown of neurotransmitters
by cohibiting the enzyme Acetylcholinesterase
AcetylCholine is not hydrolysed and remains in the cleft
this causes repeated firing of the action potential
This can be inhaled, absorbed or ingested, causing long term health problems
nerve gas inhibits acetylcholinesterase, causing uncontrollable
muscle contractions which are strong enough to break bones

92
Q

Psychoactive drugs?

A

act on the CNA to outer brain function
Alters perception, mood, consciousness + your behaviour
Therapeutic drugs such as Ritalin ( ADHD)
Prozac(depression)and Paxil (anxiety)
recreational drugs
(nicotine, alcohol, cannabis,cocaine,
heroin,
amphetamine,
ecstasy)

93
Q

what does these cause?

A

these cause euphoria and increased alertdnes

94
Q

Negatives?

A

dependency and impaired health

Biology A2 (9 decks)

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