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Biology > 5.1.3 - Neuronal communication > Flashcards

5.1.3 - Neuronal communication Flashcards

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1
Q

What is a stimulus ?

A

Changes in the internal and external environment

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2
Q

What does the body need to do once a stimulus is detected ?

A

Needs to process the information and produce an appropriate response

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3
Q

What are neurones ?

A

Specialised nerve cells

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4
Q

What is the role of a neurone ?

A

To transmit electrical impulses rapidly around the body so that the organism can respond to changes in its internal and external environment

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5
Q

What do the neurones work together to do ?

A

Carry information detected by sensory receptors to the effector, which in turn carries out the appropriate response

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6
Q

What are the different neurones found in the body ?

A
  • Sensory
  • Relay
  • Motor
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7
Q

What is the structure of a neurone like ?

A
  • Cell body
  • Axons
  • Dendrons
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8
Q

What does the cell body contain ?

A

Nucleus surrounded by cytoplasm

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9
Q

What is found in the cytoplasm of the cell body ?

A
  • Large amounts of mitochondria and endoplasmic reticulum
  • They are involved in the production of neurotransmitters
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10
Q

What are neurotransmitters ?

A

These are chemicals which are used to pass signals from one neurone to the next

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11
Q

What are dendrons ?

A

These are short extensions which come from the cell body

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12
Q

What do dendrons divide into ?

A

They divide into smaller branches called dendrites

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13
Q

What is the role of dendrons ?

A

Responsible for transmitting electrical impulses towards the cell body

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14
Q

What are axons ?

A

These are singular, elongated nerve fibres that transmit impulses away from the cell body

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15
Q

What is the structure of an axon like ?

A

Cylindrical in shape consisting of a very narrow region of cytoplasm surrounded by a plasma membrane

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16
Q

What is the role of a sensory neurone ?

A

They transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain

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17
Q

What is the role of a sensory neurone ?

A

What is the structure of the sensory neurone like ?They transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain

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18
Q

What is the structure of the sensory neurone like ?

A
  • They have one dendron, carries the impulse to the cell body
  • They have one axon, carries the impulse away from the cell body
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19
Q

What is the role of a relay neurone ?

A

They transmit impulses between neurones

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20
Q

What is the structure of the relay neurone like ?

A

They have many short axons and dendrons

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21
Q

What is the role of a motor neurone ?

A

They transmit impulses from a relay or sensory neurone to an effector

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22
Q

What is the structure of the motor neurone like ?

A

They have one long axon and many short dendrites

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23
Q

What is the normal nervous response pathway ?

A

Receptor → sensory neurone → relay neurone → motor neurone → effector cell

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24
Q

What covers the axon of some neurones ?

A

Myelin sheath

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25
Q

What is the myelin sheath made of ?

A

Plasma membrane layers

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26
Q

What are schwann cells ?

A
  • They produce the layers of membrane making up the myelin sheath
  • They do this by growing around the axon
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27
Q

What happens when each schwann cell grows ?

A

It lays down a double layer of phospholipid bilayer

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28
Q

What does the myelin sheath act as ?

A

It acts as an insulating layer and allows these myelinated neurones to conduct the electrical impulse at a much faster speed than non myelinated neurones

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29
Q

How quickly can myelinated neurones conduct an electrical impulse ?

A

100 times faster than non myelinated neurones

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30
Q

What is present in between each schwann cell ?

A

Node of ranvier

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31
Q

What do the nodes of ranvier create ?

A

They create gaps in the myelin sheath

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32
Q

What does the node of ranvier allow for the impulse ?

A
  • It allows for the impulse to jump from one node to the next as it travels along the neurone
  • This allows the impulse to be transmitted much faster
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33
Q

How does the impulse travel in non myelinated neurones ?

A
  • The impulse does not jump
  • It transmits continuously along the nerve fibre
  • This is much slower
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34
Q

What is the role of the sensory receptors ?

A

Detect changes in the environment

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35
Q

Where are the sensory receptors located ?

A

Sense organs e.g. ear and eye

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36
Q

What do sensory receptors do ?

A

They convert the stimulus they detect into a nerve impulse

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37
Q

Where do nerve impulses travel to ?

A

Passed through the nervous system and on into the CNS - normally to the brain

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38
Q

What does the brain do with information from a nerve impulse ?

A
  • Coordinates the response and sends an impulse to an effector
  • The effector results in the desired response
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39
Q

What are the two main features of sensory receptors ?

A
  • Specific to a single type of stimulus
  • Act as transducers
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40
Q

How do sensory receptors act as transducers ?

A

They convert a stimulus into a nerve impulse

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41
Q

What are the four main types of sensory receptors ?

A
  • Mechanoreceptor
  • Chemoreceptor
  • Thermoreceptor
  • Photoreceptor
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42
Q

What is the stimulus for a mechanoreceptor ?

A

Pressure and movement

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43
Q

What is the stimulus for a chemoreceptor ?

A

Chemicals

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44
Q

What is the stimulus for a thermoreceptor ?

A

Heat

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45
Q

What is the stimulus for a photoreceptor ?

A

Light

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46
Q

What is a generator potential ?

A

It is the nervous impulse that is formed by the receptor converting the stimulus

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47
Q

What is a Pacinan Corpuscle ?

A

They are specific sensory receptors that detect mechanical pressure

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48
Q

Where are Pacinian Corpuscle’s located ?

A
  • Deep within your skin
  • Most abundant in the fingers and the soles of the feet
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49
Q

What is found in the centre of the Pacinian Corpuscle ?

A

The end of the sensory neurone

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50
Q

What is the neurone surrounded by in the Pacinian Corpuscle ?

A

Layers of connective tissue

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51
Q

What separates each layer of tissue in the Pacinian Corpuscle ?

A

A layer of gel

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52
Q

What is present in the membrane of the neurone ?

A

Sodium ion channels

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53
Q

What are the sodium ion channels responsible for ?

A

Transporting sodium ions across the membrane

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54
Q

What type of sodium ion channel is present in the neurone ending in a Pacinian Corpuscle ?

A

Stretch-mediated sodium channels

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55
Q

What happens to stretch-mediated sodium channels when they change shape ?

A

Their permeability to sodium changes

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56
Q

What are the stretch-mediated sodium ion channels like at rest ?

A

They are too narrow to allow sodium ions to pass through them

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57
Q

What is the neurone of the Pacinian Corpuscle said to have at rest ?

A

A resting potential

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58
Q

What happens when pressure is applied to the Pacinian Corpuscle ?

A
  • The corpuscle changes shape
  • The membranes surrounding the neurone stretch
59
Q

What happens when the membrane in the Pacinian Corpuscle stretches ?

A
  • The sodium ion channels present widen
  • Sodium ions can now diffuse into the neurone
60
Q

What does an influx of sodium ions cause in the membrane of the Pacinian Corpuscle ?

A

The membrane becomes depolarised

61
Q

What does the depolarisation of the membrane in the Pacinian Corpuscle result in ?

A

Results in a generator potential

62
Q

What does the generator potential create ?

A

An action potential

63
Q

What happens to the action potential once it has arisen ?

A

It is transmitted along neurones to the CNS

64
Q

What are the two potentials that the axon membrane can go between ?

A
  • Resting potential
  • Action potential
65
Q

When does a neurone have a resting potential ?

A

When the neurone is not transmitting an impulse

66
Q

What is the charge like when the neurone is at its resting potential ?

A
  • The outside of the membrane is more positively charged than the inside of the axon
  • Membrane is said to be polarised
67
Q

What is the potential difference of the membrane when it is resting (polarised) ?

A
  • 70 mv
68
Q

Why does the resting potential occur ?

A

It occurs as a result of the movement of the sodium and potassium ions moving across the axon membrane

69
Q

What acts as a barrier to Na+ and K+ ions crossing into the membrane ?

A

The phospholipid bilayer

70
Q

What are the two types of protein channels in the axon ?

A
  • Voltage gated channel proteins
  • Channel proteins that remain open
71
Q

Where are sodium ions transported to ?

A

Out of the axon

72
Q

Where are potassium ions transported to ?

A

Into the axon

73
Q

What transports sodium and potassium ions ?

A

Na+/K+ pump

74
Q

What is the movement of ions like (Na+/K+ pump) ?

A
  • Movement is not equal
  • 3 sodium out and 2 potassium in
75
Q

What does the action of the Na+/K+ pump lead to ?

A

More sodium ions outside the membrane and more potassium ions in the membrane

76
Q

What does more sodium ions outside of the axon lead to ?

A

Sodium ions diffusing back into the axon

77
Q

What gradient do the sodium ions use to move back into the axon ?

A

Electrochemical gradient

78
Q

What are most of the gated sodium ion channels like ?

A

They are closed and therefore prevent the movement of sodium ions

79
Q

Why is there a large movement of potassium ions out of the axon ?

A

Because there are more potassium ion channels that are open

80
Q

What does the outflow of potassium ions from the axon lead to ?

A
  • Leads to a more positive charge outside the axon
  • This creates the resting potential across the membrane of -70 mV
81
Q

What happens to the charge on the membrane when a stimulus is detected ?

A

The charge is temporarily reversed

82
Q

What happens to the potential difference across the membrane when the charge is reversed?

A
  • The potential difference across the membrane changes and becomes positively charged
  • It is now +40 mV
83
Q

What is depolarisation ?

A

A change in potential difference from negative to positive

84
Q

What is repolarisation ?

A

A change in potential difference from positive to negative

85
Q

When does an action potential occur ?

A

When protein channels ion the axon membrane change shape as a result of the change of voltage across its membrane

86
Q

Which channels open and close as a result of a change in action potential ?

A

Voltage gated ion channels

87
Q

What is the activity of the proteins like when the neurone has a resting potential ?

A

Some potassium channels are open but sodium voltage gated ion channels are closed

88
Q

What does the energy of a stimulus trigger in a neurone ?

A

Triggers some sodium voltage gated ion channels to open, making the membrane more permeable to sodium ions

89
Q

What happens when the membrane becomes more permeable to sodium ions ?

A
  • Sodium ions diffuse into the axon down their electrochemical gradient
  • This makes the inside of the neurone less negative
90
Q

What does a change in charge across the membrane lead to ?

A

It causes more sodium ion channels to open, allowing more sodium ions to diffuse into the axon

91
Q

What happens when the potential difference reaches approximately +40 mV ?

A
  • The voltage gated sodium ion channels close and voltage gated potassium ion channels open
  • Sodium ions can no longer enter the axon but the membrane is more permeable to potassium ions
92
Q

How is the charge reduced when the pd is +40 mv ?

A

Potassium ions diffuse out of the axon down their electrochemical gradient

93
Q

What does potassium ions moving out of the axon lead to ?

A

Reduces the charge, resulting in the inside of the axon becoming more negative than the outside

94
Q

What is hyperpolarisation ?

A

When the axon becomes more negative (relative to the outside) than in its normal resting state

95
Q

What causes hyperpolarisation ?

A

Potassium ions diffusing out of the axon

96
Q

What happens once the membrane is hyperpolarised ?

A
  • Voltage gated potassium ion channels close
  • Sodium potassium pump causes sodium ions to move out and potassium ions to move in
  • Resting potential reinstated
97
Q

How does a nerve impulse move along a neurone ?

A

It is propagated along the axon from one end of the neurone to the other

98
Q

What does the depolarisation of the first region of the axon act as ?

A
  • It acts as a stimulus for the depolarisation of the next region of the membrane
  • The process continues along the length of the axon, forming a wave of depolarisation
99
Q

What happens once sodium ions are inside the axon ?

A

They are attracted by the negative charge ahead and the concentration gradient to diffuse further along the axon

100
Q

What does the movement of sodium ions along the membrane cause ?

A

They trigger the depolarisation of the next section

101
Q

What is the refractory period ?

A

A short period of time when the axon cannot be excited again

102
Q

What happens during the refractory period ?

A

The voltage gated sodium ion channels remain closed, preventing the movement of sodium ions into the axon

103
Q

Why is the refractory period important ?

A

It prevents the propagation of an action potential backwards along the axon as well as forwards

104
Q

What does the refractory period ensure ?

A
  • It ensures the action potentials do not overlap
  • It makes sure action potentials are unidirectional
105
Q

Why are myelinated axons faster than non myelinated axons at transferring electrical impulses ?

A

This is because depolarisation of the axon membrane can only occur at the nodes of ranvier where no myelin is present

106
Q

What happens at the node of ranvier ?

A

The sodium ions can pass through the protein channels in the membrane

107
Q

What does the action potential do between nodes ?

A

It jumps from one node to another

108
Q

What is saltatory conduction ?

A

The action potential jumping from one node to another

109
Q

Is saltatory conduction more efficient than repolarisation ?

A

Yes it is more efficient than repolarisation

110
Q

Why is saltatory conduction more efficient than repolarisation ?

A

Repolarisation uses ATP, so by reducing the amount of repolarisation needed, saltatory conduction makes the conduction of impulses more efficient

111
Q

What are the two factors that affect the speed at which an action potential travels ?

A
  • Temperature
  • Axon diameter
112
Q

How does axon diameter change the speed at which an action potential travels ?

A
  • The bigger the axon diameter, the faster the impulse is transmitted
  • This is because there is less resistance to the flow of ions in the cytoplasm
113
Q

How does the temperature change the speed at which an action potential travels ?

A
  • The higher the temperature, the faster the nerve impulse
  • This is because ions diffuse faster at higher temperatures
114
Q

What does a stimulus have to reach for an action potential to be triggered ?

A

A certain threshold value that will trigger a response

115
Q

What happens if the threshold is not reached ?

A

No action potential will be triggered

116
Q

What does the size of the stimulus affect ?

A

Affects the number of action potentials that are generated in a given time

117
Q

What happens as the stimulus gets larger ?

A

Action potentials are generated more frequently

118
Q

What is a synapse ?

A

The junction between two neurones

119
Q

What is a neurotransmitter ?

A

Chemicals that transmit impulses across the synapse

120
Q

What is the synaptic cleft ?

A

The gap which separates the axon of one neurone from the dendrite of the next neurone

121
Q

What is the presynaptic neurone ?

A

Neurone along which the impulse has arrived

122
Q

What is the postsynaptic neurone ?

A

Neurone that receives the neurotransmitter

123
Q

What is the synaptic knob ?

A
  • The swollen end of the presynaptic neurone
  • It contains many mitochondria and large amounts of ER to enable it to manufacture neurotransmitters
124
Q

What are synaptic vesicles ?

A
  • Vesicles containing neurotransmitters
  • The vesicles fuse with the presynaptic membrane and release their contents into the synaptic cleft
125
Q

What are neurotransmitter receptors ?

A

Receptor molecules which the neurotransmitter binds to in the postsynaptic membrane

126
Q

What are the two types of neurotransmitters ?

A
  • Excitatory
  • Inhibitory
127
Q

What is an excitatory neurotransmitter ?

A
  • These neurotransmitters result in the depolarisation of the postsynaptic neurone
  • If the threshold is reached in the postsynaptic membrane, an action potential is triggered
128
Q

Give an example of an excitatory neurotransmitter

A

Acetylcholine

129
Q

What is an inhibitory neurotransmitter ?

A
  • These neurotransmitters result in the hyperpolarisation of the postsynaptic membrane
  • This prevents an action potential being triggered
130
Q

Give an example of an inhibitory neurotransmitter

A

GABA, found in some synapses in the brain

131
Q

How does synaptic transmission occur ?

A
  • The action potential reaches the end of the presynaptic neurone
  • Depolarisation of the presynaptic membrane causes calcium ion channels to open
  • Calcium ions diffuse into the presynaptic knob
  • This causes synaptic vesicles containing the neurotransmitters to fuse with the presynaptic membrane
  • Neurotransmitter is released into the synaptic cleft by exocytosis
  • Neurotransmitter diffuses across the synaptic cleft and binds with its specific receptor molecule on the postsynaptic membrane
  • This causes sodium ion channels to open
  • Sodium ions diffuse into the postsynaptic neurone
  • This triggers an action potential and the impulse is propagated along the postsynaptic neurone
132
Q

Why do action potentials have to be removed from a postsynaptic neurone ?

A
  • So the stimulus is not maintained
  • So another stimulus can arrive and affect the synapse
133
Q

What happens to neurotransmitters left in the cleft ?

A

They are removed

134
Q

What happens to the breakdown products of the neurotransmitter ?

A
  • They are taken back into the presynaptic knob
  • This acts as a way of recycling
135
Q

Which neurotransmitter do cholinergic synapses use ?

A

Acetylcholine

136
Q

Where are cholinergic synapses usually found ?

A

In the CNS of vertebrates and at neuromuscular junctions

137
Q

What is a neuromuscular junction ?

A

Where a motor neurone and a muscle cell (effector) meet

138
Q

Describe the mechanism of transmission across a cholinergic synapse

A
  • Arrival of an action potential at the end of the presynaptic neurone causes calcium ion channels to open and calcium to enter the synaptic knob
  • The influx of calcium ions into the presynaptic neurone causes synaptic vesicles to fuse with the presynaptic membrane, and so releases acetylcholine into the synaptic cleft
  • Acetylcholine molecules fuse with receptor sites on the sodium ion channel in the membrane of the postsynaptic neurone
  • This causes the sodium ion channels to open allowing sodium ions to diffuse in
  • The influx of sodium ions generates a new action potential in the postsynaptic neurone
  • Acetylcholinesterase hydrolyses acetylcholine into choline and acetyl, which diffuse into the presynaptic neurone
  • ATP released by mitochondria is used to recombine choline and acetyl into acetylcholine.
  • This is stored in the synaptic vesicle for future use
139
Q

What are the main roles of synapses ?

A
  • Ensure impulses are unidirectional
  • Allow an impulse from one neurone to be transmitted to a number of neurones at multiple synapses
  • Alternatively, a number of neurones may feed into the same synapse with a single postsynaptic neurone
140
Q

How do synapses ensure impulses are unidirectional ?

A

As the neurotransmitter receptors are only present on the postsynaptic membrane, impulses can only travel from the presynaptic neurone to the postsynaptic neurone

141
Q

What does each stimulus from a presynaptic neurone cause ?

A
  • Causes the release of the same amount of neurotransmitter into the synapse, sufficient neurotransmitter impulse will generate an action potential
  • However, in some synapses the amount of neurotransmitter from a single impulse is not enough to trigger an action potential
142
Q

What is summation ?

A

The triggering of an action potential if there is enough build up of neurotransmitter

143
Q

What is spacial summation ?

A
  • This occurs when a number of presynaptic neurones connect to one postsynaptic neurone
  • Each releases neurotransmitters which build up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone
144
Q

What is temporal summation ?

A
  • This occurs when a single presynaptic neurone releases neurotransmitters as a result of an action potential several times over a short period
  • This builds up in the synapse until the quantity is sufficient to trigger an action potential

Biology (30 decks)

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