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biology a level > 5.3 > Flashcards

5.3 Flashcards

1
Q

what are sensory receptors

A

specialised cells that detect changes and respond to a stimulus in the internal or external environment and can create action potentials. most are called transducers that convert energy from one into another

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2
Q

what are transducers

A

a cell that converts one form of energy into another- in this case to an electrical impulse

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3
Q

the stimulus is a change in light intensity;
1. what is the sensory receptor for this
2. what energy change is involved

A

1.sensory receptor= light sensitive cells (rods and cones) in the retina
2. energy change involved= light to electrical

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4
Q

the stimulus is a change in temperature;
1. what is the sensory receptor for this
2. what energy change is involved

A

1.sensory receptor= periphery temp receptors in the skin and hypothalamus- thermoreceptors ( detects temp of blood)
2. energy change involved= heat to electrical

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5
Q

the stimulus is a change in pressure on the skin;
1. what is the sensory receptor for this
2. what energy change is involved

A

1.sensory receptor= Pacinian corpuscles in the skin
2. energy change involved= movement to electrical

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6
Q

the stimulus is a change in sound;
1. what is the sensory receptor for this
2. what energy change is involved

A

1.sensory receptor= vibration receptors in the cochlea of the ear
2. energy change involved= movement to electrical

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7
Q

the stimulus is a change in movement;
1. what is the sensory receptor for this
2. what energy change is involved

A

1.sensory receptor= hair cells in inner ear
2. energy change involved= movement to electrical

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8
Q

the stimulus is a change in length of muscle;
1. what is the sensory receptor for this
2. what energy change is involved

A

1.sensory receptor= muscle spindles in skeletal muscle
2. energy change involved=movement to electrical

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9
Q

the stimulus is a change in chemicals in the air;
1. what is the sensory receptor for this
2. what energy change is involved

A

1.sensory receptor= olfactory cells in epithelium lining the nose
2. energy change involved= these receptors detect the presence of a chemical and create an electrical nerve impulse

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10
Q

the stimulus is a change in chemicals in food;
1. what is the sensory receptor for this
2. what energy change is involved

A

1.sensory receptor= chemical receptors in taste buds on tongue
2. energy change involved= these receptors detect the presence of a chemical and create an electrical nerve impulse

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11
Q

whats a Pacinian corpuscle

A

a Pacinian corpuscle is a pressure sensor that detects changes in pressure on the skin

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12
Q

describe the corpuscle

A

its an oval shaped structure consisting of a series of concentric rings of connective tissue wrapped around the end of a nerve cell.

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13
Q

what happens to the corpuscle when pressure is subjected to it

A

it deforms the rings of connective tissue, which push against the nerve endings

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14
Q

when pressure is constant on a corpuscle, do they continually respond

A

no, they stop responding as they are only sensitive to changes in pressure

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15
Q

what do fibroblasts in the corpuscle do

A

fibroblasts produce the connective tissue

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16
Q

are phospholipid bilayers permeable to charged ions?

A

no

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17
Q

the deformation of a Pacinian corpuscle causes what channel to open, what occurs next?

A

the deformation causes stretch mediated sodium ion channels to open. Sodium ions enter the cell which generates a generator potential, which would lead to an action potential.

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18
Q

what will happen if Channel Proteins are Permanently Open?

A

If channel proteins are permanently open then ions can diffuse across the membrane and will do so until their concentrations reach equilibrium.

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19
Q

what channels/ pumps are in the cells associated with the nervous system to generate a nerve impulse

A

-sodium/potassium pump
-sodium channels (can possess a gate (gated sodium channels)
-potassium channels (can possess a gate (gated potassium channels)

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20
Q

what are sodium and potassium channels

A

Cells associated with the nervous system have specialised channel proteins which are specific to Sodium (Na+) ions or Pottasium (K+) ions.

These channels have a gate that can open or close the channel.

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21
Q

what is unique/special about the Sodium (Na+) Channels?

A

the sodium channels are sensitive to small movements of the membrane, so when the membrane is deformed by changing pressure, the sodium channels open.
This allows sodium ions to diffuse into the cell, producing a generator potential.

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22
Q

what are sodium/potassium pumps?

A

-these actively pump sodium ions out of the cell and potassium ions into the cell.
-(to maintain resting potential), 3 sodium ions are pumped out for every two potassium ions pumped into the cell.
-when the channel proteins are closed, the sodium/potassium pump works to create a conc. grad.

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23
Q

due to the sodium/potassium pumps, what happens to the concentrations of sodium and potassium

A

-the conc of sodium ions outside the cell increases, while the conc of potassium ions inside the cell increases
-the membrane is more permeable to potassium ions so the conc. of potassium ions inside the cell increases
-the membrane is less permeable to sodium ions, so few of these are able to leak into the cell
-the inside of the cell becomes more neg

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24
Q

what is the resulting change between the membrane outside the cell and inside the cell.

A

-the result of these ionic movements is a pot grad across the cell membrane.
The cell is negatively charged inside compared with outside.
This negative potential is enhanced by the presence of negatively charged anions inside the cell.

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25
Q

what is the nerve cell like when its inactive

A

the cell membrane is said to be polarised. It is negatively charged inside the cell compared with the outside.

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26
Q

how is a nerve impulse created

A
  • A nerve impulse is created by altering the permeability of the nerve cell membrane to sodium ions
  • This is achieved by opening the sodium ion channels
    -As the sodium ion channels open, the membrane permeability is increased and sodium ions can move across the membrane down their conc grad into the cell.
    -the movement of ions across the membrane creates a change in potential difference (charge) across the membrane.
    -the inside of the cell becomes less negative (compared with the outside) than usual. This is called depolarisation.
    -The change in potential across a receptor membrane is called a generator potential.
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27
Q

what happens when a nerve cell only detects a small stimulus in terms of the plasma membrane

A

-only a few sodium ion channels will open

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28
Q

what happens when a nerve cell detects a large stimulus in terms of the plasma membrane

A

-the lager the stimulus, the more gated channels will open
-if enough gates are opened and enough sodium ions enter the cell, the potential difference across the cell membrane changes significantly and will initiate an impulse or action potential.

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29
Q

what is an action potential carried as and what is it caused by

A

the action potential is carried as a rapid depolarisation of the membrane caused by the influx of sodium ions

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30
Q

describe motor neurones

A

motor neurones carry nerve impulses from the CNS to the effector cells such as a muscle or gland/motor end plate.

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31
Q

where is the cell body of motor neurones

A

the cell body of a motor neurone is found in the spinal cord or the brain itself

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32
Q

describe sensory neurones

A

sensory neurones carry nerve impulses from receptor cells to CNS. They carry impulses via a dendron (long projection that carries a nerve impulse towards a cell body) from sense organs to the brain/spinal cord.

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33
Q

where is the cell body of sensory neurones

A

Their cell bodies are found just outside the spinal cord in structures called dorsal root ganglia

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34
Q

describe relay neurones

A

relay neurones carry nerve impulses between sensory and motor neurones. They are adapted to carrying nerve impulses from and to other neurones.

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35
Q

where is the cell body of relay neurones

A

relay neurones have cell bodies and cytoplasmic processes inside the brain or spinal cord

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36
Q

what structural features do neurones have in common with animal cells

A

-lots of mitochondria
-lots of ribosomes
-nucleus
-golgi
-R.E.R
-cell body

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37
Q

name the features that are specific to neurones

A

-axon hillock
-dendron
-node of Ranvier
-axon
-synaptic endings

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38
Q

what organelles do neurones have many numbers of and why

A

-many mitochondria (ATP for sodium potassium pump)
-many ribosomes and R.E.R (to make proteins on cell surface membrane and neurones need to make lots of neurotransmitters!!)

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39
Q

which features are specific to each type of neuron

A

motor & relay= multiple dendrons
motor & relay= cell body at one end of axon
sensory= cell body in the middle of dendron and axon
motor= longer axon (up to 1 m long)
sensory= myelin sheath
sensory & relay= short axon
relay= non-myelinated
sensory &motor= myelin sheath

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40
Q

what does an axon do

A

conducts inf away from the cell body

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41
Q

what does a dendron do

A

conducts info towards a cell body

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42
Q

once a stimulus has been detected, what is its energy converted to

A

its energy has been converted to a depolarisation of the receptor cell membrane

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43
Q

what is an action potential carried as

A

an action potential is carried as a rapid depolarisation of the membrane caused by the influx of sodium ions

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44
Q

neurones are specialised cells: talk about features based around their length

A

many are very long so that they can transmit the action potential over a long distance

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45
Q

neurones are specialised cells: talk about features based around their plasma membrane

A

the cell surface (plasma) membrane has many gated ion channels that control the entry and exit of sodium, potassium or calcium ions

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46
Q

neurones are specialised cells: talk about features based around the pumps that they have

A

their sodium/potassium pumps use ATP to actively transport sodium ions out of the cell and potassium ions into the cell

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47
Q

neurones are specialised cells: talk about features based around their cell body

A

the cell body contains the nucleus, many mitochondria and ribosomes

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48
Q

neurones are specialised cells: talk about features based around dendrites

A

numerous dendrites connect to other neurones. The dendrites carry impulses towards the cell body

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49
Q

neurones are specialised cells: talk about features based around their axon

A

an axon carries impulses away from the cell body

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50
Q

neurones are specialised cells: talk about features based around what they are surrounded by

A

neurones are surrounded by a fatty layer that insulates the cell from electrical activity in other nerve cells nearby. This fatty layer is composed of Schwann cells closely associated with the neurone

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51
Q

cell body present?
sensory neurone:
motor neurone:
intermediate/ relay neurone:

A

sensory neurone: yes
motor neurone: yes
intermediate/ relay neurone: yes

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52
Q

axon present?
sensory neurone:
motor neurone:
intermediate/ relay neurone:

A

sensory neurone: yes
motor neurone: yes
intermediate/ relay neurone: yes

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53
Q

dendron present?
sensory neurone:
motor neurone:
intermediate/ relay neurone:

A

sensory neurone: yes
motor neurone: yes
intermediate/ relay neurone: yes

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54
Q

cell body found in dorsal root ganglion?
sensory neurone:
motor neurone:
intermediate/ relay neurone:

A

sensory neurone: yes
motor neurone: no
intermediate/ relay neurone: no

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55
Q

cell body and axon found in CNS
sensory neurone:
motor neurone:
intermediate/ relay neurone:

A

sensory neurone: no
motor neurone: yes*
intermediate/ relay neurone: yes

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56
Q

what are the characteristics of motor neurones that make them different

A

-cell body in the CNS
- have a long axon

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57
Q

what are the characteristics of sensory neurones that make them different

A

-have a long dendron carrying the action potential from a sensory receptor to the cell body, which is positioned just outside the CNS
-a short axon carrying the action pot into the CNS

58
Q

what are the characteristics of relay neurones that make them different

A

-connect the sensory neurones and motor neurones
-many short dendrites and a short axon
-the number of dendrites and the number of divisions of the axon is variable

59
Q

how many peripheral neurones in vertebrates are myelinated?

A

around 1 third

60
Q

what are myelinated neurones surrounded by

A

an individual myelin sheath

61
Q

what neurones are mostly associated with schwann cells

A

motor neurones and sensory neurones

62
Q

what do Schwann cells make up

A

schwann cells make up a fatty sheath called the myelin sheath

63
Q

describe how Schwann cells wrap around neurones

A

schwann cells are wrapped tightly around the neurone so the sheath actually consists of several layers of membrane and thin cytoplasm from the schwann cell.

64
Q

what are the nodes of Ranvier

A

gaps in the myelin sheath along the neurone at intervals of 1-3mm are the nodes of Ranvier. Each node is very short (about 2-3um long)

65
Q

due to the myelin sheath being wrapped tightly around the neurone, what does this prevent

A

because the myelin sheath is wrapped tightly around the neurone it prevents the movement of ions across the neurone membrane and can only occur at the nodes of Ranvier.

66
Q

why does myelin make conduction more rapid

A

because the impulse or action potential jumps from one node to another ( the movement of ions can only occur at the nodes of Ranvier)

67
Q

are non-myelinated neurones also associated with Schwann cells

A

yes

68
Q

describe how non-myelinated neurones are associated with Schwann cells

A

several neurones may be enshrouded in one loosely wrapped Schwann cell

69
Q

how does the action potential move for non-myelinated neurones where they are enshrouded in a loosely wrapped Schwann cell

A

the action potential moved along the neuron in a wave rather than jumping from node to node as seen in myelinated neurones

70
Q

what are the advantages of myelinated neurones in terms of speed

A

myelinated neurones can transmit an action pot much more quickly than non-myelinated neurones. the typical speed transmission for M is 100-1200 ms^-1 while for NM its 2-20 ms^-1

71
Q

where do myelinated neurones carry action potentials to and from

A

-sensory receptors to CNS
-CNS to effectors

72
Q

in terms of myelinated neurones, how are they advantageous in terms of distance

A

they carry action pots over long distances- the longest neurone in a human is 1 m. the increased speed of transmission means the action pot reaches the end of the neurone more quickly, so faster response to a stimulus

73
Q

non-myelinated neurones are often shorter and carry action pots over a short distance, what does this mean they are used for (give examples)

A

often used in coordinating body functions such as breathing, and the action of the digestive system. Thus, the increased speed of transmission is not so important

74
Q

whats the function of the myelin sheath

A

-insulate the neurone
-increase speed at which nerve impulses are conducted

75
Q

does myelination make a difference when a neurone has a short axon

A

no (ref to relay)

76
Q

does a larger or smaller axon Diameter produce a greater speed of conduction

A

a larger diameter produces a greater speed

77
Q

why does an increase in temp lead to an increase in speed of conduction

A

more kinetic energy so ions diffuse more quickly into neurones

78
Q

as the temp increases, it reaches a point where conduction of the impulse ceases, why?

A

ion channels / pumps denature and phospholipid bilayer is disrupted

79
Q

what is the action potential said to be when a neurone is not transmitting information

A

its said to be at rest

80
Q

what is an action potential

A

the brief reversal of the potential across the membrane of a neurone causing a peak of +40mV compared to the resting potential of -60mV.

81
Q

whats the resting potential

A

the potential difference across the membrane while the neurone is at rest, the numerical value is -60mV

82
Q

whats depolarisation

A

when the inside of the cell becomes less negatively charged

83
Q

describe the ions and proteins when neurones are at rest

A

-sodium/potassium pumps pump three sodium ions out of the cell and 2 potassium ions into the cell
-gated sodium ion channels are kept closed *
-some potassium ion channels are kept open, thus the plasma membrane is more permeable to K+, K+ tends to diffuse out of the cell.
-the cell cytoplasm contains large organic anions, the cell membrane is polarised

84
Q

What is the initial stage in generating an action potential (at rest)

A

-the membrane starts in its resting state (-60mV) compared to the outside
-there is a higher conc. of sodium ions outside, and a higher conc. of potassium ions inside

85
Q

what happens after the initial resting stage (stimulus detected)

A
  • sodium ion channels open and some sodium ions diffuse into the cell
86
Q

what is a generator potential?

A

a generator potential is a small depolarisation of the membrane.
-generator potentials can be combined to produce larger depolarisation that may cause an action potential

87
Q

What happens after the initial wave of Sodium ions diffuses across the membrane via sodium channels opening/ voltage-gated sodium channels?

A

the membrane depolarises- it becomes less negative with respect to the outside and reaches the threshold value of -50 mV

88
Q

What happens when the potential reaches the -50 mV threshold?

A

positive feedback causes nearby voltage-gated sodium ion channels to open and many sodium ions to flood in.
As more sodium ions enter, the cell becomes more positively charged inside compared with the outside

89
Q

What happens as more and more Sodium ions diffuses across the membrane?

A

the potential difference across the plasma membrane reaches +40mV.
The inside of the cell is positive compared with the outside.

90
Q

What happens when the Potential difference reaches +40 mV?

A

the sodium ion channels close and the potassium ion channels open

91
Q

What happens after the sodium ion channels close and potassium channels open?

A

the potassium ions diffuse out of the cell bringing the potential difference back to negative inside compared with the outside. potassium channels rapidly close
in terms of charge, this is called repolarisation

92
Q

What happens after repolarisation?

A

The potential difference overshoots slightly, making the cell hyperpolarised.

93
Q

What happens after hyperpolarisation?

A

The original potential difference is restored so that the cell returns to its resting state.

94
Q

after the action potential, the sodium and potassium ions are in the wrong place, what restores the og resting potential

A

by the sodium/potassium ion pumps

95
Q

what is the refractory period

A

The short amount of time in which it is impossible to stimulate the cell membrane to reach another action potential. (allows the cell to recover after an action pot.)

96
Q

What is the ‘All-Or-Nothing’ principle?

A

Regardless of the strength of an impulse, all action potentials are of the same magnitude (+40 mV).

97
Q

what does the refractory period ensure (whats its role)

A

-the refractory period ensures that action potentials are transmitted in only one direction
-ensures that a cell can recover after an action potential

98
Q

What causes the Refractory Period?

A

After an action potential the neurone membrane becomes hyperpolarised - more negative inside than at rest.

The sodium ions and potassium ions need to be moved back to their original positions in order to reverse this hyperpolarisation.

99
Q

what causes local currents in the cytoplasm of the neurone

A

when sodium ions are allowed to flood into the neurone causing depolarisation

100
Q

when local currents are created and sodium ions move in, where do sodium ions move to

A

they move along the neurone to where concs are lower

101
Q

what type of feedback does local currents cause and why

A

positive feedback- the local currents cause a slight depolarisation of the membrane and causes sodium ion channels further along the membrane to open

102
Q

outline the 4 steps in the formation of local currents and the transmission of a nerve impulse

A
  1. when an action potential occurs, the sodium ion channels open at that point in a neurone
  2. sodium ion channels diffuse into the neurone, there is a localised increase in conc. of sodium ions is the action potential.
  3. sodium ions diffuse sideways along axon/dendron, away from the region of higher conc. This movement to charged particles is called a local current
  4. The local current causes a slight depolarisation further along the neurones, affecting voltage-gated sodium ion channels causing them to open. The open channels allow rapid influx of sodium ions causing a full depolarisation (action pot.) further along the neurone. Thus the action pot. has moved along the neurone
103
Q

why will the action potential not reverse in direction

A

because sodium ions behind the action poetntial is still high in concentration

104
Q

what is the myelin sheath

A

an insulating layer of fatty material, composed of Schwann cells wrapped tightly around the neurone

105
Q

where can ionic movements that cerate an action poetntial occur along a myelinated neurone

A

at the nodes of Ranvier (ions cant diffuse through myelin fatty layer)- action potentials can only occur at the gaps

106
Q

what happens to the local current in myelinate neurones

A

it appears elongated (sodium ions diffuse along the neurone from one node of Ranvier to the next)

107
Q

what is saltatory conduction

A

where the action potential appears to jump from one node to the next in myelinated neurones

108
Q

what are the advantages of saltatory conduction

A

this speeds up the transmission of an action potential.
myelinated neurones conduct action potentials more quickly (at 120ms^-1) than non myelinated neurones)

109
Q

describe the all or nothing rule

A

-all action potentials are the same intensity, each one produces a depolarisation at +40mV

110
Q

how does the sensory region of our brain know if one stimulus is larger than another

A

if the frequency of transmission is greater than the stimulus is larger. A higher frequency of action potentials means a more intense stimulus

111
Q

how do more frequent action potentials enter the CNS

A

-when a stimulus is at a higher intensity, more sodium channels are open in the sensory receptor. This produces more generator potentials so more enter the CNS

112
Q

what is a synapse

A

a synapse is a junction between two or more neurones, where one neurone can communicate with, or signal to, another neurone.

113
Q

what is the synaptic cleft

A

the small gap between the two neurones

114
Q

how does an action potential move across two neurones

A

the action potential in the pre-synaptic neurone causes the release of a chemical (the neurotransmitter) that diffuses across the synaptic cleft and generates a new action potential in the post-synaptic neurone.

115
Q

whats a cholinergic synapse

A

a synapse that uses acetylcholine as the neurotransmitter

116
Q

whats a neurotransmitter

A

a chemical used as a signalling molecule between two neurones in a synapse

117
Q

whats the pre-synaptic bulb

A

a swelling at the ending of a pre-synaptic neurone

118
Q

what are the 4 specialised features of the pre-synaptic bulb

A

-many mitochondria- indicating that an active process needing ATP is involved (fusing of vesicles via exocytosis)

-a large amount of SER, which packages the neurotransmitter into vesicles

-large numbers of vesicles containing molecules of a chemical called acetylcholine, the transmitter that will diffuse across the synaptic cleft

-a number of voltage gated calcium ion channels on the cell surface membrane

119
Q

what is specialised within the post-synaptic membrane

A

-there are specialised sodium ion channels that can respond to the neurotransmitter.

120
Q

describe the structure of the specialised sodium ion channels in the post-synaptic membrane

A

-these channels consist of 5 polypeptide molecules
-two of these polypeptides have a special receptor site that is specific to acetylcholine
-the receptor sites are complimentary to acetylcholine

121
Q

what occurs when acetylcholine is present in the synaptic cleft and comes in contact with the specialised sodium ion channels in the post-synaptic membrane

A

it binds to the two receptor sites and causes sodium ion channels to open

122
Q

state the sequence of events in the transmission of a signal across the synaptic cleft

A
  1. An action potential arrives at the synaptic bulb. The voltage-gates calcium ion channels then open, calcium ions diffuse into the synaptic bulb
  2. The calcium ions cause the synaptic vesicles (containing acetylcholine) to move to, and fuse with, the pre-synaptic membrane. Acetylcholine is released by exocytosis
  3. Acetylcholine molecules diffuse across the cleft. Acetylcholine molecules bind to the receptor sites on the sodium ion channels in the post-synaptic membrane.
  4. The sodium ion channels open. Then sodium ions diffuse across the post-synaptic membrane into the post-synaptic neurone
  5. A generator potential or excitatory post-synaptic potential (EPSP) is created.
  6. If sufficient generator potentials combine then the potential across the post-synaptic membrane reaches the threshold potential. this means a new action potential is created in the post-synaptic neurone and will carry on travelling down.
123
Q

what would happen if acetylcholine was left in the synaptic cleft

A

it would continue to open the sodium ion channels in the post-synaptic membrane and will continue to cause action potentials

124
Q

what happens to acetylcholine at the post-synaptic membrane

A

Acetylcholinesterase is a enzyme found in the Synaptic cleft.

It hydrolyses Acetylcholine into Ethanoic Acid and Choline. This is to stop the transmission of signals so action potentials don’t continually occur in post-synaptic neurone

The Ethanoic acid and Choline re-enter the synaptic bulb by diffusion and are recombined using ATP.

They (acetylcholine) are put back into vesicles for future use.

125
Q

why is it advantageous to have synapses instead of neurones

A

-synapses can lead to inhibition of an action*
-synapses allow for a wider range of responses
-synapses usually involve more than one neurone

126
Q

nerve junctions often involve several neurones, what are the two types of circuit

A

-converging circuit (several neurones to one neurone)
-diverging circuit ( one neurone to many neurones)

127
Q

whats the excitatory post-synaptic potential (EPSP)

A

-a small post-synaptic potential that makes the neurone more likely to fire an action potential
-the release of the transmitter substance will cause depolarisation on the post synaptic membrane

128
Q

how do EPSPs reach threshold

A

it may take several EPSPs to reach the threshold and cause an action potential. The effects of several EPSPs combine together to increase the membrane depolarisation until it reaches threshold, this is summation

129
Q

what is summation

A

occurs when the effects of several excitatory post-synaptic potentials (EPSPs) are added together. Can create an action poetntial

130
Q

what are two ways in which summation can occur

A

-via temporal summation ( several action potentials in the same pre-synaptic neurone)

-via spatial summation (action potentials arriving from several different pre-synaptic neurones)

131
Q

what is temporal summation

A

involves several action potentials arriving in the same pre-synaptic membrane in quick succession (high frequency of action potentials). Allows us to filter out unhelpful or unimportant stimuli. (e.g. background noise)

132
Q

what is spatial summation

A

involves action potentials arriving from several different pre-synaptic membranes. This contributes to producing a single action potential.

133
Q

along with EPSPs, what can some pre-synaptic neurones also produce

A

some pre-synaptic neurones can also produce inhibitory post-synaptic potentials (IPSPs).
These can reduce the effect of summation and prevent an action potential in the post-synaptic neurone.

134
Q

control of communication:
why is spatial summation important in terms of danger

A

-action potentials from different parts of the nervous system can contribute to generating an action pot. This is useful where several different stimuli are warning us of danger

135
Q

how could the combination of several EPSPs be prevented from producing an action potential

A

by one IPSP

136
Q

Why is diverging of action potentials important in action potentials

A

diverging to several post-synaptic neurones allows for one action potential to be transmitted to several parts of the nervous system. This is useful in a reflex arc because one post-synaptic neurone elicits the response while another informs the brain

137
Q

why are synapses important in direction of transmission

A

-synapses ensure that action pots are transmitted in the correct direction - only the presynaptic bulb contains vesicles of acetylcholine. Thus, if an action potential happens to start halfway along the neurone and ends at the post-synaptic membrane, it will not cause a response to the next cell

138
Q

why are synapses important in terms of low level signals

A

synapses can filter out low level signals. If a low-level stimulus creates an action pot in the pre synaptic neurone its unlikely to pass across the synapse to the next neurone cus several vesicles of acetylcholine must be released to create an action pot in the post-synaptic neurone

139
Q

how can low level action potentials produce an action potential

A

low-level action potentials cam ne amplified by summation. if a low level stimulus is persistent, it will generate several successive action potentials in the pre-synaptic neurone. The release of many vesicles of acetylcholine over a short period of time will enable the post synaptic EPSPs to combine together to create an action potential

140
Q

what does repeated stimulation of an action potential cause

A

after repeated stimulation, a synapse may run out of vesicles containing the neurotransmitter. the synapse is said to be fatigued. This means the nervous system no longer responds to the stimulus - we have become habituated to it. it explains why we soon get used to background noise or a smell. it may also avoid overstimulation of an effector, which could cause damage

141
Q

what leads to the basis of conscious thought and memory

A

the creation and strengthening of specific pathways within the nervous system

142
Q

how are synaptic membranes adaptable and what dos this mean

A

in particular , the post-synaptic membrane can be made more sensitive to acetylcholine by the addition of more receptors.

this means that a particular post-synaptic neurone is more likely to fire an action pot, creating a specific pathway in response to a stimulus.

biology a level (17 decks)

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