C2.2: Neural Signalling Flashcards
1
Q
State the function of the following neuron cell part: Axon
A
Axon: An elongated fibre that transmits electrical signals to terminal regions for communication with other neurons or
effectors
2
Q
State the function of the following neuron cell parts: cell body/soma.
A
Cell Body/Soma: A cell body containing the nucleus and organelles, where essential metabolic processes occur to maintain cell survival
3
Q
State the function of the following neuron cell parts: dendrites
A
Dendrites: Short-branched fibres that convert chemical information from other neurons or receptor cells into electrical signals
4
Q
Define propagation
A
- The passage of the nerve impulse through the axon
5
Q
Identify the cell body, axon and dendrites in diagrams of typical sensory and motor neurons.
A
- long squigly thing on the giant body = dendrites
- axon is the thing connected the sausage buns (myelin sheath)
- Soma / cell body is the area outside the nucleus (like the cytoplasm in a cell) which is enclosed in an oval
6
Q
Define membrane potential.
A
A membrane potential is the difference in charge across the membrane
7
Q
Define resting potential.
A
A resting potential is the difference in charge across the membrane when a neuron is not firing
8
Q
Outline three mechanisms that together create the resting potential in a neuron.
A
- Neuron Depolarising: Na/K pumps transfer Na+ ions out of the neuron and at the same time transfer K+ ions in using energy in the form of ATP.
- Neuron Repolarising: Leakage of K+ ions is caused which increases the difference between Na+ and K+ concentration gradients
- Resting potential being maintained by continual operation of the Na/K pump
9
Q
State the voltage of the resting potential.
A
-70mV
10
Q
Outline the six steps of sodium-potassium pump action.
A
- 3 Na+ ions attach to binding sites of Na/K pump
- ATPase catalyses the hydrolysis of ATP to ADP and Phosphate which results in Na/K pump undergoing a conformational change
- The conformational change translocates the Na+ ions to the outside of the axon and the pump closes
- Immediately after, the pump opens to reveal 2 K+ ions that bind to the pump thus, the Phosphate group detaches from the pump
- This causes the pump to go back to its original conformation
- Na/K pump translocates the K+ ions to the interior of the axon and closes
11
Q
Define nerve impulse.
A
Nerve impulses are action potentials that move along the length of an axon as a wave of depolarisation
12
Q
Define action potential.
A
The depolarisation and repolarisation of a neuron due to the movement of positive ions
13
Q
State the 3 stages of action potential
A
- Depolarisation
- Repolarisation
- Refractory period
14
Q
Outline the correlation between conduction speed of nerve impulses and axon diameter.
A
- Larger the diameter of axons, the faster the propagation of action potentials
15
Q
State 3 factors affecting the speed of transmissions
A
- Amount of myelination
- Diameter of the axon
- Temperature
16
Q
Explain the difference in nerve impulse speed for myelinated and unmyelinated fibers.
A
Nerve impulse speed for myelinated fibers:
- Presence of myelin sheath speeds up transmission signals by causing nerve impulses to jump from one node of ranvier to another (120m/s)
Nerve impulse speed for unmyelinated fibers:
- Slows down transmission signals (1-3m/s)
- This is because depolarisation has to take place throughout the length of the axon and the action potential has to travel the entire length which takes up more time
17
Q
State the correlation between conduction speed of nerve impulses and animal size.
A
- Giant squids, an example of great animal size, conduct impulses extremely fast compared to smaller sized animals due to their larger sized diameter of axons
- Animals dont have the space for many giant axons thus, they can can only use them to coordinate actions where speed is vital (like rapid responses to danger)
18
Q
Define synapse, synaptic cleft and effector.
A
- Synapse: A junction between 2 cells in the nervous system
- Synaptic cleft: The space between the presynaptic and postsynaptic neurones
- Effector: Muscles that carry out a response to a stimulus
19
Q
List examples of effector cells.
A
- Glands
- Muscle cells
20
Q
How does a signal typically pass across a synapse?
A
A signal can only pass in one direction across a typical synapse.
21
Q
State the role of neurotransmitters.
A
Neurotransmitters are released from neurons and function to transmit signals across the synaptic cleft
22
Q
What properties of neurotransmitters influence their role in neural communication?
A
Neurotransmitters can either be:
- excitatory (encourages receiving neuron to fire a signal)
- inhibitory (tells receiving neuron to not fire a signal)
23
Q
How does calcium serve as a key component in the process of neurotransmitter release from a presynaptic neuron?
A
Calcium functions as a chemical signal which triggers exocytosis of neurotransmitters from a presynaptic cell.
24
Q
Outline the mechanism of synaptic transmission occurring at a presynaptic cell, including the role of depolarization, calcium ions, exocytosis and diffusion.
A
- Action potential arrives at the axon terminal
- V-G Ca2+ Channels open
- Ca2+ enters the presynaptic neuron; Depolarisation occurs
- Ca2+ signals to neurotransmitter vesicles
- Vesicles move to the membrane and docking protein
- Neurotransmitters get released via exocytosis and diffuse to receptors
- Neurotransmitters bind to receptors on postsynaptic neuron
- Signal is initiated in postsynaptic cell (either excitatory or inhibitory)
25
Outline the mechanism of synaptic transmission occurring at a post-synaptic cell, including the role of neurotransmitters, diffusion, receptors, gated ion channels, threshold potential and action potential.
- Neurotransmitters diffuse into postsynaptic celft from high to low conc
- Receptors on postsynaptic membrane receive the neurotransmitters
- This binding allows V-G Na+ channels to open
- Na+ enters the postsynaptic neuron
- This causes depolarisation due to imbalance of charge
- If depolarisation reaches a threshold potential, it triggers an action potential and results in the generation of an excitatory postsynaptic potential which transmit the signal further
26
what is one of the most common neurotransmitters in both invertebrates and vertebrates and is used as the neurotransmitter in many synapses including between neurons and muscle fibers.
The acetylcholine neurotransmitter
27
Outline the digestion of acetylcholine by acetylcholinesterase.
- Acetylcholine diffuses into the synaptic cleft
- Acetylcholine binds to its receptors in the postsynaptic membrane at the cholinergic synapse
- Only 1 action potential is initiated in the postsynaptic neuron
- This is because acetylcholinesterase is present in the synaptic cleft and rapidly breaks down acetylcholine into choline and acetate
- Choline gets reabsorbed into the presynaptic neuron where its converted back into acetylcholine
28
How is an action potential initiated?
An action potential is only initiated if the threshold potential is reached.
29
Define depolarization.
Depolarisation refers to a sudden change in membrane potential – usually from a negative to positive internal charge
30
Outline the mechanism of depolarization during an action potential using voltage gated sodium channels.
- Action potential arrives at neuron and this triggers opening of V-G Na+ Channels thus,
- There is an influx of Na+ ions into the axon therefore, resulting in depolarisation of the axon until threshold potential is reached then, another action potential is generated
31
Define repolarization.
Repolarisation refers to the restoration of a membrane potential following depolarisation (i.e. restoring a negative internal charge)
32
Outline the mechanism of repolarization during an action potential using voltage gated potassium channels.
- Depolarisation results in the V-G K+ channels to open, almost immediately, for a short amount of time
- There is an efflux of K+ ions out of the axon therefore, resulting in repolarisation of the axon
- Membrane potential returns to normal
33
Describe the movement of sodium ions in a local current.
Na+ ions diffuse from the polarised part back to the part that has just depolarised - This influx of Na+ ions generates a local current
- The local current depolarises the adjacent region of the axon membrane because the local current causes threshold potential to be reached
34
How do local currents contribute to the propagation of an action potential along an axon?
The local currents generated by the influx of Na+ ions in 1 region of the axon trigger the opening of V-G Na+ channels in the next region therefore, propagating the action potential forward
35
Explain how the movement of sodium ions propagates an action potential along an axon.
- V-G Na+ channels open due to depolarisation
- Na+ ions flow into the axon due to the open channels which generates a local current and the adjecent region of the axon is depolarised by this current which also allows the threshold potential to be reached
- V-G Na+ channels open in domino-like effect of depolarisation
- Due to the refractory period, the previously depolarised segments repolarise hence, they can't generate another action potential ensuring the action potential moves in a single direction along axon
36
Outline the cause and consequence of the refractory period after depolarization.
Cause:
- Depolarised regions undergo repolarisation and enter a refractory period
Consequence:
- The axons are unable to generate another action potential
- Ensures that the action potential moves in a single direction along the axon
37
Explain the changes in electrical charge on the inner side of the plasma membrane during the transmission of a nerve impulse through a nerve fibre
- First, a negative charge during the polarised phase (at resting potential)
- Then, when the stimulus reaches the plasma membrane, it becomes positively charged and enters into the depolarised phase
- When the impulse moves away again and passes through membrane, it becomes negatively charged just like the first resting potential phase
38
Outline the use of oscilloscopes in measuring membrane potential.
- Oscilloscopes can record and display the voltage changes occurring during neuronal activity
- Electrodes are placed on either side of the axon membrane and an oscilloscope trace is recorded
39
Explain the 4 different stages of an oscilloscope trace
1. Stimulus must be more than the threshold potential for an action potential to be triggered
2. Depolarisation causes Na+ channels to open causing an influx of Na+ ions into the axon
3. K+ channels open to allow efflux of K+ ions out of the cells to reach resting potential again
4. Resting potential is reached at -70mV
40
Annotate an oscilloscope trace to show the resting potential, action potential (depolarization and repolarization), threshold potential and refractory period.
- x axis is time in milliseconds
- y axis is membrane potential in millivolts
- resting potential is the horizontal line that stays constant
- action potential is the narrow peak seen
(rising phase shows depolarisation, falling phase shows repolarisation)
- threshold potential is the horizontal line above the resting potential
- refractory period is the area of the curve of on the opposite side after the action potential peak
41
Deduce the number of nerve impulses per second from an oscilloscope trace.
- Determine the action potential (peak)
- Determine time interval (to determine the time interval between successive action potential peaks)
- Calculate frequency of the action potential (f=1/time interval between peaks)
- Convert frequency to impulses per second (same value as frequency but instead of SI unit being Hertz, it is action potentials per second
42
Describe the structure of a myelinated nerve fibre.
- Myelins are cylindrical in shape
- Nodes of Ranvier are in between each Myelin
- Diameter is about 1um although some nerve fibres are wider than this
- Myelin Sheath consists of myelins + node of ranviers
- Allows for saltatory conduction to be present which increases the transmission of the signal
43
Functions of the myelin sheath
- To insulate the axon
- to increase rate at which impulses propagate themselves
- to prevent depolarisation
44
State what the nodes of Ranvier are
The gaps between the myelin sheath
45
Requirements of Saltatory Conduction and State what does saltatory conduction actually do
- Requires myelinated neurons
- Serves as a means of increasing the rate of propagation of an action potential
- Results in an increased speed of impulse transmission thus, conserving energy for the axon
46
Outline how the myelination of neurons allows for saltatory conduction, in which the differences in the distribution of electrically charged ions across the membrane can effectively jump from node of Ranvier to node of Ranvier.
- The myelin sheath prevents ion movements so action potentials only occur at nodes of Ranvier thus, conserving energy for the axon
- Depolarisation at one node of Ranvier generate local currents that quickly depolarise the next node (called a saltatory conduction)
- Thus, there's less movement of ions
- Therefore, aiding in the rapid propagation of the action potential as Na+ and K+ concentration differences are re-established
47
How does the distribution of ion channels at the nodes of Ranvier in myelinated neurons contribute to efficient nerve impulse transmission?
In myelinated neurons, the ion channels are clustered down at nodes of Ranvier.
48
Define exogenous chemicals.
Exogenous chemicals are chemicals that enter the body of an organism from an outside source and some affect synapatic transmission
49
Outline the effects of neonicotinoids on synaptic transmission.
- Neonicotinoids bind to the acetylcholine receptor in cholinergic synapses in CNS of insects. Acetylcholinesterase doesn't break down neonicorinoids thus, the binding is irreversible.
- This results in acetylcholine receptors on postsynaptic neuron to be blocked causing acetylcholine to be unable to bind and therefore, synaptic transmission is prevented leading to death and paralysis of insects
50
Outline where neonicotinoids are commonly used
- Pesticides; Specifically, Imidacloprid is widely used as insecticide as it is effective in killing insects affecting crops
- However, concerns include effects on non-pest species leading to controversy about the actual effectiveness in harm to the insects
51
Outline the effects of cocaine on synaptic transmission.
- Cocaine acts at the synapses that use dopamine as a neurotransmitter
- Cocaine binds to the dopamine reuptake transporters on the presynaptic neuron
- Thus, this results in dopamine building up in the synaptic cleft and the postsynaptic neuron is continuously excited
- Therefore, Cocaine is an excitatory drug having similar effects as dopamine which is the rewarding feeling
52
Define hyperpolarisation
When neurotransmitters bind to the postsynaptic membrane and the membrane potential becomes more negative thus, making it difficult for the postsynaptic neuron to reach threshold potential
53
Compare inhibitory and excitatory neurotransmitters.
Inhibitory neurotransmitters:
- Bind to receptors causing hyperpolairsation of the postsynaptic neuron due to a more negative membrane potential
Excitatory neurotransmitters:
- Bind to receptors causing influx of positively charged ions to postsynaptic neuron leading to depolarisation
54
Outline the inhibitory mechanism of the neurotransmitter GABA.
- GABA binds to its receptors and chloride channels open causing hyperpolarisation (becomes more negative) at the postsynaptic knob due to the influx of chloride ions
55
Outline the consequence of hyperpolarization by inhibitory neurotransmitters.
Hyperpolarisation by inhibitory neurotransmitters is a making the neuron's membrane potential more negative thus, making it less likely to generate an action potential
56
Describe the effects of excitatory and inhibitory neurotransmitters on the ability of a postsynaptic cell to reach its threshold potential.
Effects of excitatory neurotransmitters:
- Increases likelihood of the postsynaptic cell to generate an action potential by depolarising the cell
Effects of inhibitory neurotransmitters:
- Decreases the likelihood of the postsynaptic cell to generate an action potential by hyperpolarising the cell
57
Define summation.
Summation is the combined effect of the excitatory and inhibitory stimuli received form from more than one presynaptic neuron and transmitted to the axon of the postsynaptic neuron
58
Interpret graphical representations of the summation of combinations of excitatory and inhibitory neurotransmitters.
- The peak just below the action potential peak is the excitatory postsynaptic potential
- Line mirroring the peak of the excitatory postsynaptic potential along the x-axis is the inhibitory postsynaptic potential
59
Where are sensory receptors located in the skin
- Dermis region (middle of: epidermis - top and hypodermis - bottom)
60
Describe the mechanism by which environmental stimuli are able to activate nerve endings in the skin, including the role of receptor proteins, ions channels, and threshold potential.
- Stimulus detected
- Receptors at the end of sensory neurons convey impulses to the CNS
- Ion channels on nerve endings open after a stimulus is triggered
- Influx of positive charged ions into the neuron
- threshold potential is reached and nerve impulses are generated and pass through sensory neuron to the spinal cord
- Impulses propagate along nerve fibres at the spinal cord to the brain
- Brain signals effectors to reduce exposure to the stimulus by, e.g: contracting muscles to move hand away
61
List stimuli which can trigger a pain response.
- puncturing of the skin
- High temperature
- Acid
- Chemicals like capsaicin
62
Outline the flow of information during the pain response.
- Stimulus detected
- Nerve impulses generated
- Nerve impulses propagated along sensory neuron to the spinal cord
- Nerve impulses propagated to other neurons at spinal cord
- Nerve impulses transmitted to the brain to process the signals
- Response occurs (i.e. withdrawal reflexes, emotional response, physiological responses etc)
63
Define emergent property.
A characteristic of something that emerges only when the parts interact in wider whole
64
What occurs at each level of biological organization
New properties emerge at each level of biological organization.
65
Define Consciousness and how does it emerge?
- Consciousness is the state of being aware and awake
- It emerges from the collective interactions of neurons in a brain
66
State what part of the brain is responsible for our consciousness
- Cerebrum
67
Outline consciousness as an emergent property.
Neurons interact to create the property of consciousness that isn't present in the individual neurons that make it up
68
Outline the 2 leading hypotheses that explain a clear neural pathway that produces consciousness
Global Workspace Theory
- Specialised molecules send messages into a network where they compete for dominance and the winner is broadcasted globally therefore entering consciousness
Integrated Information Theory:
- Phi is high (a measure of consciousness) and it is high in systems with many interconnected molecules
69
What types of cells make up the Myelin Sheath
Schwann cells
70
How to calculate number of action potentials per minute
- Convert second to m/s (x1000)
- divide by the time taken for neuron charge returns to resting potential
71
What type of response does acetylcholine or epinephrine (adrenaline) trigger
Triggers excitatory neurotransmitters
72
What is the Myelin Sheath made of (disregarding the cells it is made of)
Propteins and Lipids
73
At what voltage to voltage-gated sodium channels open
-50mV
74
At what voltage is the aciton potential occured
-55mV
75
What side of the neuron is more negative, the inside or outside
Inside is more negative
76
Explain why is a resting potential negative (3 marks)
- Na+/K+ Pump moves 3 Na+ ions out and 2 K+ in the cell
- Membrane is more permeable to K+ Ions thus, K+ ions leak out
- There are more anions inside the cell than outside
77
Explain how the structure of a neuron is adapted to its function (5 marks)
- Axon fibre is long to carry electrical impulses over long distances in body
- Many branched dendrites to send electrical impulses
- Myelination provide insulation to ensure electrical impulses are conducted faster
- Saltatory conduction occurs
- Neurons have a variety of voltage gated channels that regulate the movement of ions
- Postsynaptic membrane of neurone contain receptors that bind to neurotransmitters
78
Explain why myelination is essential for the rapid transmission of impulses (4 marks)
- Myelin acts as an insulator
- Myelin sheath is composed of proteins and lipids
- There are nodes of ranvier between the Schwann cells thus,
- Allowing impulses to jump from node to node (saltatory conduction)
- V-G Na+ channels and V-G K+ channels are concentrated at the nodes
79
Explain how neonicotinoids work on insects (4 marks)
- Neonicotinoids bind to acetylcholine receptors
- In the postsynaptic membrane
- at the cholinergic synapses
- They bind irreversibly meaning acetylcholinesterase can't break neonicotinoids down thus,
- Acetylcholine cannot bind and synaptic transmission is blocked
80
What would occur if gardeners used pesticides that were broken down by acetylcholinesterase (1 mark)
- Synaptic transmission would occur
81
Explain why neonicotinoids containing pesticides are less toxic to mammals than insects (1 mark)
- Insects contain more cholinergic synapses than mammals
82
State 2 things that happen to neurotransmitters once they reach the postsynaptic membrane (2 marks)
1. Bind to receptors
2. They are broken down
83
Predict what would happen if neurotransmitters didn't not bind to receptors and get broken down at the postsynaptic membrane (2 marks)
- Nerve impulse would not be generated
- There would be disruptions in the flow of information
84
Explain why a nerve impulse can only be conducted in one direction across the synaptic cleft (2 marks)
- Vesicles of neurotransmitters are only found in presynaptic knob
- Receptors for neurotransmitters are only found on postsynaptic knob
85
What is necessary in the creation of a resting potential across a neuron
- Active transport of ions
- ATP from respiration
- Concentration gradients of Na+ and K+ ions
86
Outline the use of ATP in the resting potential and action potential
- Resting potential and action potential both use ATP
87
Explain the role in the functioning of a synaptic vesicle
- release of neurotransmitters via exocytosis into synaptic cleft
- Vesicles move towards the presynaptic membrane
88
Explain how the threshold potential in the heat receptor in the skin is involved in the withdrawal response of the forearm to touching a hot object
- Once threshold potential is reached
- Action potential is generated
89
Explain how summation in the dendrites of the sensory neurones are involved in the withdrawal response of the forearm to touching a hot object
- Many dendrites interact with one post-synaptic membrane
- The impulse travels through the sensory neuron to the CNS
90
Explain how saltatory conduction is involved in the withdrawal response of the forearm to touching a hot object
- Allows for faster transmission of signal
- Depolarisation of a node causes depolarisation of the next node
