Neural Signalling

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Neurones: Function & Structure

The nervous system is divided into the central nervous system (CNS) (brain and spinal cord) and the peripheral nervous system (PNS) (all other nerves).
Information travels as electrical impulses along nerve cells called neurones; a bundle of neurones is a nerve.
Neurones have a long fibre called an axon, often insulated by Schwann cells that form the myelin sheath.
The cell body contains the nucleus and other cellular structures; dendrites are extensions that receive impulses from other neurones.
Sensory neurones carry impulses from receptors to the CNS; relay neurones connect sensory and motor neurones within the CNS; motor neurones carry impulses from the CNS to effectors (muscles or glands).
Motor neurones have a large cell body within the spinal cord or brain, with many highly branched dendrites.
Sensory neurones have a cell body that branches off in the middle, a single long dendron carrying impulses to the cell body, and a single long axon carrying impulses away.

Structure of a neurone

Resting Potential

In a resting neurone, the inside of the axon is negatively charged relative to the outside; this is the resting potential, about -70 mV.
The sodium-potassium pump uses ATP to actively transport 3 Na⁺ out for every 2 K⁺ in, creating concentration gradients.
The membrane is much less permeable to Na⁺ than to K⁺, so K⁺ diffuses out faster than Na⁺ diffuses in, contributing to the negative inside.
Negatively charged proteins inside the axon also contribute to the negative resting potential.
The membrane is said to be polarised at resting potential.

Action Potentials

A stimulus opens some sodium ion channels; if the membrane potential reaches the threshold potential (about -50 mV), voltage-gated sodium channels open.
A large influx of Na⁺ causes depolarisation, reversing the potential from -70 mV to about +40 mV; this is an action potential.
About 1 ms later, voltage-gated sodium channels close and voltage-gated potassium channels open, allowing K⁺ to diffuse out, causing repolarisation.
The membrane potential briefly becomes more negative than resting potential, a period called hyperpolarisation (the refractory period), during which a new action potential cannot be generated.
The all-or-nothing principle: an action potential is only generated if the threshold is reached; there is no small or large action potential.
A stronger stimulus increases the frequency of action potentials, not their size.
Propagation occurs via local currents: Na⁺ diffuses along the inside and outside of the axon, depolarising the next section to threshold.

Myelination and Saltatory Conduction

Schwann cells wrap around the axon to form the myelin sheath, which contains phospholipids and has high electrical resistance.
The myelin sheath acts as an electrical insulator, preventing impulses from passing through it.
Gaps between Schwann cells are nodes of Ranvier, where ion channels and pumps are clustered.
Action potentials jump from node to node, a process called saltatory conduction, which greatly speeds up transmission (up to 50 times faster).
Myelinated neurones conduct impulses much faster than unmyelinated ones.
A wider axon diameter also increases conduction velocity because it offers less resistance.

Synapses and Synaptic Transmission

A synapse is the junction between two neurones, separated by a small gap called the synaptic cleft.
When an impulse arrives at the presynaptic neurone, calcium ions enter and cause vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the cleft by exocytosis.
Neurotransmitters diffuse across the cleft and bind to receptors on the postsynaptic membrane, opening sodium channels and generating an action potential if threshold is reached.
Acetylcholine (ACh) is a common neurotransmitter; it is broken down by acetylcholinesterase into acetate and choline, which are recycled.
Synapses ensure unidirectional transmission because neurotransmitter is released on one side and receptors are on the other.
Inhibitory synapses open potassium channels, hyperpolarising the postsynaptic membrane and preventing an action potential.
Summation (temporal or spatial) allows multiple impulses to add together to reach threshold.

Interpreting Oscilloscope Traces

An oscilloscope displays membrane potential (mV) against time (ms).
A resting potential appears as a horizontal line at about -70 mV.
An action potential appears as a spike rising to between +30 and +40 mV.
The rising phase of the spike shows depolarisation; the falling phase shows repolarisation.
The trace often shows a short period of hyperpolarisation after repolarisation, when the potential is more negative than resting potential.

Nerve Conduction Velocity and Correlation

Conduction velocity is correlated with myelination and axon diameter.
Correlation is an association between variables; it does not necessarily imply causation.
The correlation coefficient (r) indicates the strength of a linear relationship; perfect correlation is 1 or -1, no correlation is 0.
Pearson's linear correlation tests for linear correlation between two quantitative variables with normal distribution.
The coefficient of determination (R²) is the square of r; a value closer to 1 (100%) indicates a strong correlation.

Effects of Exogenous Chemicals

Neonicotinoids are synthetic pesticides that bind irreversibly to acetylcholine receptors in insects, blocking synaptic transmission and causing paralysis and death.
They are less toxic to mammals because a smaller proportion of synapses are cholinergic and neonicotinoids bind more strongly to insect receptors.
Cocaine blocks reuptake of dopamine by binding to the dopamine transporter, leading to increased dopamine in the synapse and feelings of pleasure.
Cocaine also blocks reuptake of serotonin and norepinephrine, enhancing confidence and energy.
Regular cocaine use increases the number of dopamine receptors, leading to increased sensitivity and depression when drug levels fall.

Neurones in the Brain

Pain receptors (nociceptors) are sensory receptors with free nerve endings containing TRP channels that open in response to high temperature, acid, or chemicals like capsaicin.
Entry of positively charged ions triggers an action potential that travels to the CNS and then to the cerebral cortex, where pain is perceived.
The cerebrum is the largest part of the brain (about 80% of mass) and is responsible for conscious activities such as vision, hearing, speech, thinking, and memory.
The cerebral cortex (grey matter) consists of cell bodies of neurones and is highly folded, increasing surface area and allowing more neuronal connections.
More connections between neurones enable more complex behaviours, known as emergent properties.
Interactions between neurones in the cerebrum lead to consciousness, including qualitative perception and complex awareness of the environment.

Nerve cell (neuron)

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1.Between which structures do sensory neurones transmit electrical impulses?
Easy
- AFrom effectors to the central nervous system (CNS).
- BFrom effectors to receptors.
- CFrom receptors to effectors.
- DFrom receptors to the central nervous system (CNS).
2.Where would myelin be found?
Easy
- AWrapped around the axon of a neurone, forming an insulating sheath.
- BInside the synaptic cleft between two neurones.
- CIn the cell body, surrounding the nucleus.
- DAt the nodes of Ranvier, filling the gaps between Schwann cells.
3.Which event directly results in the production of an action potential?
Easy
- ADiffusion of neurotransmitter across the synaptic cleft.
- BFusion of vesicles with the presynaptic membrane.
- CMembrane potential reaches the resting potential.
- DMembrane potential reaches the threshold potential.
4.Neurotransmitters leave the presynaptic neurone and enter the synaptic cleft. After this, they travel across the cleft to a receptor on the postsynaptic neurone membrane. Which processes are required for this to occur? (select all that apply)
Medium
- AExocytosis of neurotransmitter from the presynaptic neurone
- BEndocytosis of neurotransmitter from the presynaptic neurone
- CDiffusion of neurotransmitter across the synaptic cleft
- DActive transport of neurotransmitter across the synaptic cleft
- EHydrolysis of neurotransmitter by acetylcholinesterase before it can bind
5.The following graph shows an action potential in a mouse neurone after stimulation with a pulse of current. What is the threshold potential needed to open voltage gated sodium channels in this neurone?
Medium
- A-70 mV
- B-50 mV
- C-30 mV
- D+50 mV
6.The opening of axon membrane voltage gated potassium channels are responsible for which part of the action potential?
Medium
- ARepolarisation of the membrane.
- BDepolarisation of the membrane.
- CHyperpolarisation of the membrane.
- DSignalling vesicular release of neurotransmitters.
7.It is thought that conditions such as schizophrenia are caused by an overabundance of the neurotransmitters serotonin and dopamine in some regions of the brain. Given this is the case, which drug mode of action could work in treating symptoms of schizophrenia?
Medium
- AIncreased permeability of the presynaptic neurone to calcium.
- BIncreased reuptake of serotonin and dopamine by pre synaptic neurones.
- CRelease of acetylcholinesterase into the presynaptic cleft.
- DBlockage of serotonin and dopamine receptors in postsynaptic neurones.
8.Which of the following statements about myelinated nerve fibres are correct? (select all that apply)
Medium
- ANodes of Ranvier facilitate saltatory conduction.
- BSchwann cells are responsible for forming the myelin sheath.
- CThe myelin sheath acts as an electrical conductor allowing electrical impulses to conduct at a more rapid rate.
- DThe myelin sheath prevents loss of nerve impulses along the axon.
- EMyelin increases the permeability of the axon membrane to sodium ions.

Soal lainnya

9.The diagram below shows the change in membrane potential during an action potential. Which of the following best describes the events indicated by the label X?
Medium
- ASodium channels open, potassium channels closed, membrane potential decreasing
- BSodium channels closed, potassium channels open, membrane potential increasing
- CSodium channels closed, potassium channels open, membrane potential decreasing
- DSodium channels open, potassium channels closed, membrane potential increasing
10.The diagram below shows a sensory neurone connected to its associated receptor cells. Which best describes the function of the structure labelled A?
Medium
- AContains most cellular structures
- BActs as an electrical insulator
- CTransmit impulses to the spinal cord
- DTransmit and receive impulses to other neurones
11.The diagram below shows a sodium-potassium pump within the axon membrane of a neurone. What is the role of active transport in the transmission of nerve impulses by neurones?
Medium
- AEstablishes the resting potential needed for impulse transmission by pumping sodium ions out of the axon and potassium ions into the axon.
- BDepolarisation of the axon by moving sodium ions across the membrane into neurone.
- CEstablishes the resting potential needed for impulse transmission by moving sodium ions into the axon and potassium ions out of the axon.
- DInitiates the action potential needed for the transmission of an impulse by pumping calcium ions into the axon.
12.Which line of the table represents a neurone at its resting potential?
Medium
- AConcentration of Na+ inside: high; K+ inside: low; membrane permeability to Na+: high; Na+/K+ pump: active
- BConcentration of Na+ inside: high; K+ inside: low; membrane permeability to Na+: low; Na+/K+ pump: inactive
- CConcentration of Na+ inside: low; K+ inside: high; membrane permeability to Na+: high; Na+/K+ pump: inactive
- DConcentration of Na+ inside: low; K+ inside: high; membrane permeability to Na+: low; Na+/K+ pump: active
13.Membrane channel proteins are essential for the normal functioning of nerves. Which process in nerves does not require a membrane protein?
Medium
- AActive transport of sodium.
- BDepolarisation during an action potential.
- CBinding of neurotransmitters.
- DDiffusion of neurotransmitters.
14.The use of pesticides is a cause of controversy due to its impact on pollinators such as bees. What effect do these pesticides have on the nervous system of insects?
Medium
- AThey prevent acetylcholinesterase from breaking down acetylcholine.
- BThey inhibit depolarisation in the presynaptic neurone which increases the level of acetylcholine.
- CThey block synaptic transmission by binding with postsynaptic acetylcholine receptors.
- DThey produce an inhibitor that promotes the binding of acetylcholine.
15.Neonicotinoids are synthetic compounds similar to nicotine that are commonly found in pesticides. Neonicotinoids are considered to be especially suitable as pesticides because they're not toxic to humans and other mammals. Which statements I - IV are the reasons for this? (select all that apply)
Hard
- AI. A larger proportion of synapses in insects are cholinergic compared to mammals.
- BII. Neonicotinoids are more effective at preventing acetylcholinesterase from breaking down acetylcholine in insects compared to mammals.
- CIII. Acetylcholinesterase in insects cannot break down neonicotinoids.
- DIV. Neonicotinoids bind more strongly to acetylcholine receptors in insects.
- EV. Mammals lack acetylcholine receptors entirely.
16.The diagram below shows the left to right transmission of an action potential in a myelinated axon by saltatory conduction. Which of the following rows correctly identifies I - IV?
Hard
- AI: Node at resting potential; II: Node at action potential; III: Node at refractory period; IV: Node becoming depolarised
- BI: Node at refractory period; II: Node at action potential; III: Node becoming depolarised; IV: Node at resting potential
- CI: Node at action potential; II: Node at refractory period; III: Node becoming depolarised; IV: Node at resting potential
- DI: Node at refractory period; II: Node becoming depolarised; III: Node at action potential; IV: Node at resting potential
17.A research group of geneticists found a fruit fly mutant that shakes vigorously when anaesthetized with ether. Their studies showed that the shaker mutant has K channels that do not function properly. An action potential of a normal fruit fly and a shaker mutant is shown below. Which of the following statements (I - IV) could be possible explanations for the differences between the action potentials? (select all that apply)
Hard
- AI. The faulty K channels don't open for as long so there is slower diffusion of K ions.
- BII. The faulty K channels may be opening early, preventing maximum depolarisation.
- CIII. The faulty K channels cause K ions to diffuse back into the axon more slowly, resulting in slower repolarisation.
- DIV. In wild-type drosophila, the functioning K channels allow for a faster rate of depolarisation.
- EV. The faulty K channels allow more sodium ions to enter during depolarisation.
18.Which of the following correctly describes the direction of impulse transmission in a motor neurone?
Easy
- AFrom receptors to the central nervous system
- BFrom the central nervous system to effectors
- CFrom effectors to the central nervous system
- DBetween sensory and motor neurones within the CNS
19.Which of the following is the correct description of the structure of a sensory neurone?
Easy
- AA cell body at one end within the spinal cord, with many highly branched dendrites
- BA cell body that branches off in the middle of the cell, with a single long dendron and a single long axon
- CShort, highly branched axons and dendrites, found entirely within the CNS
- DA large cell body at one end with a nucleus always in the axon terminal
20.The resting potential of a neurone is approximately -70 mV, meaning the inside of the axon is more negative than the outside.
Easy
True or false?
21.During depolarisation, voltage-gated potassium channels open and potassium ions diffuse into the axon.
Easy
True or false?
22.Match each type of neurone with its correct function.
Medium
- Sensory neurone
- Relay neurone
- Motor neurone
- Carries impulses from receptors to the CNS
- Connects sensory and motor neurones within the CNS
- Carries impulses from the CNS to effectors
23.Place the events of an action potential in the correct order, starting from the resting state.
Medium
- Resting potential at -70 mV
- Threshold potential reached at -50 mV
- Voltage-gated sodium channels open and sodium ions enter
- Membrane potential reaches +40 mV (depolarisation)
- Voltage-gated potassium channels open and potassium ions leave (repolarisation)
- Hyperpolarisation and refractory period
24.Which of the following statements about the nervous system are correct? (select all that apply)
Medium
- AThe CNS consists of the brain and spinal cord.
- BThe PNS consists of all of the nerves in the body.
- CInformation is sent through the nervous system in the form of electrical impulses.
- DA bundle of neurones is known as a nerve.
- EThe CNS sends impulses to receptors.
25.Which of the following are functions of dendrites? (select all that apply)
Hard
- AReceive impulses from other neurones.
- BTransmit impulses away from the cell body.
- CIncrease the surface area for connections with other neurones.
- DContain the nucleus.
- EForm the myelin sheath.
26.Which of the following contribute to the resting potential of a neurone? (select all that apply)
Hard
- AActive transport of sodium and potassium ions by the sodium-potassium pump.
- BDifference in rates of diffusion of sodium and potassium ions.
- CNegatively charged proteins inside the axon.
- DOpening of voltage-gated sodium channels.
- EInflux of calcium ions.
27.Which of the following statements about saltatory conduction are correct? (select all that apply)
Hard
- AAction potentials jump from one node of Ranvier to the next.
- BThe myelin sheath insulates the axon and prevents ion movement across the membrane.
- CSaltatory conduction is slower than conduction in unmyelinated axons.
- DNodes of Ranvier contain clusters of ion channels and pumps.
- ESaltatory conduction occurs in unmyelinated neurones.
28.Which of the following are effects of cocaine on synaptic transmission? (select all that apply)
Hard
- ABlocks reuptake of dopamine into the presynaptic knob.
- BBinds to the dopamine transporter protein.
- CIncreases breakdown of dopamine by acetylcholinesterase.
- DBlocks reuptake of serotonin and norepinephrine.
- EDecreases the number of dopamine receptors in the brain.
29.Match each stage of an action potential with the correct description.
Medium
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Resting potential
- Membrane potential becomes more negative than -70 mV
- Voltage-gated sodium channels open and sodium ions enter the axon
- Voltage-gated potassium channels open and potassium ions leave the axon
- Membrane potential is approximately -70 mV
30.Match each term with its correct description.
Hard
- Threshold potential
- Action potential
- Refractory period
- Summation
- The addition of multiple impulses to generate an action potential
- The potential difference at which voltage-gated sodium channels open
- A period during which a new action potential cannot be generated
- A rapid reversal of membrane potential from -70 mV to +40 mV
31.Place the events of synaptic transmission in the correct order.
Hard
- Action potential arrives at presynaptic membrane
- Calcium ions enter the presynaptic neurone
- Vesicles fuse with the presynaptic membrane
- Neurotransmitters are released into the synaptic cleft
- Neurotransmitters bind to receptors on the postsynaptic membrane
- Sodium ions enter the postsynaptic neurone
32.The sodium-potassium pump moves 3 sodium ions out of the axon and 2 potassium ions into the axon for each ATP used.
Easy
True or false?
33.During the refractory period, a new action potential can be generated if a strong enough stimulus is applied.
Medium
True or false?
34.In spatial summation, multiple impulses arrive simultaneously at different synaptic knobs on the same postsynaptic neurone.
Medium
True or false?
35.A student measures the conduction velocity of two axons of equal diameter: axon P is unmyelinated, and axon Q is myelinated. Which row correctly compares the conduction velocities?
Medium
- AAxon P conducts faster because the whole membrane can depolarise continuously.
- BAxon Q conducts faster because action potentials jump between nodes of Ranvier.
- CBoth axons conduct at the same speed because they have the same diameter.
- DAxon Q conducts faster because myelin conducts the electrical impulse like a wire.
36.A squid giant axon has a diameter of 1 mm and an unmyelinated conduction velocity of about 25 m/s. A mammalian myelinated axon has a diameter of 20 µm and a conduction velocity of about 100 m/s. Which conclusion is best supported by these data?
Medium
- AConduction velocity increases only with axon diameter.
- BMyelination can produce a higher conduction velocity despite a much smaller axon diameter.
- CA wider axon always conducts faster than a myelinated axon.
- DThe squid axon is faster because it is unmyelinated.
37.An oscilloscope trace of a neurone shows a resting potential of -70 mV. A stimulus is applied and the trace rises to -55 mV, then returns to -70 mV without a spike. Which statement best explains this result?
Medium
- AThe stimulus was above threshold, so an action potential was generated.
- BThe stimulus did not reach the threshold potential, so voltage-gated sodium channels did not open.
- CVoltage-gated potassium channels opened and caused repolarisation.
- DThe membrane was in the refractory period.
38.A neurone is treated with a drug that blocks voltage-gated potassium channels. Which effect on the action potential would be expected?
Medium
- ADepolarisation would be prevented because sodium ions could not enter.
- BRepolarisation would be slowed because potassium ions could not diffuse out.
- CThe resting potential would become more positive because the sodium-potassium pump would stop.
- DThe threshold potential would decrease, making an action potential easier to generate.
39.A graph shows the relationship between axon diameter and conduction velocity for unmyelinated axons. The data points lie close to a straight line with a positive correlation coefficient of r = 0.92. What does this indicate?
Medium
- AThere is a strong positive correlation between axon diameter and conduction velocity.
- BIncreasing axon diameter causes a decrease in conduction velocity.
- CThere is no relationship between axon diameter and conduction velocity.
- DThe correlation proves that diameter is the only factor affecting conduction velocity.
40.An experiment measures the conduction velocity of a myelinated axon before and after the myelin sheath is experimentally removed. Which result is most likely?
Hard
- AConduction velocity increases because the membrane is fully exposed to the extracellular fluid.
- BConduction velocity decreases because saltatory conduction can no longer occur.
- CConduction velocity stays the same because the axon diameter is unchanged.
- DConduction velocity increases because more sodium channels are available along the whole axon.
41.The oscilloscope trace shown below was taken using a digital oscilloscope. It shows an action potential in a hippocampal pyramidal neurone of a potoroo (a small marsupial species) that occurred when the neurone was stimulated with a current pulse. How many action potentials could be stimulated in this neurone every second?
Medium
42.Complete the sentence about the sodium-potassium pump using the correct terms.
Easy
The sodium-potassium pump actively transports ____ sodium ions out of the axon for every ____ potassium ions pumped in, using ____ as an energy source.
43.Complete the sentence about synaptic transmission by naming the correct neurotransmitter and enzyme.
Medium
The neurotransmitter released at a cholinergic synapse is ____, and it is broken down in the synaptic cleft by the enzyme ____.
44.What is the name of the gap between two neurones where neurotransmitters diffuse across?
Easy
45.What is the name of the process by which an action potential jumps from one node of Ranvier to the next in a myelinated neurone?
Medium
46.Complete the sentence about the resting potential using the correct terms.
Medium
The resting potential of a neurone is approximately ____ mV, and the inside of the axon is ____ charged compared to the outside.
47.An oscilloscope trace shows that one complete action potential takes 1.5 ms. Calculate the maximum number of action potentials that could be generated in one second, assuming no refractory period is limiting. Give your answer to the nearest whole number.
Medium
48.A neurone has a resting potential of -70 mV. During an action potential, the membrane potential reaches +40 mV. Calculate the change in membrane potential in mV.
Medium
49.Complete the sentence about the effect of myelination on conduction velocity.
Medium
In a myelinated axon, the action potential jumps between the ____ of Ranvier in a process called ____ conduction.
50.Complete the sentence about an experiment on axon diameter.
Medium
When the diameter of an unmyelinated axon increases, the resistance to the action potential ____ and the conduction velocity ____.
51.Name the statistical test used to determine whether there is a linear correlation between two variables such as axon diameter and conduction velocity.
Medium
52.What is the name of the value that indicates the strength of the relationship between two variables in a scatter graph?
Medium
53.Explain how the resting potential of approximately -70 mV is established and maintained in a neurone.
Hard
54.Explain how the myelin sheath and nodes of Ranvier increase the speed of nerve impulse transmission.
Hard
55.Explain how the structure of a myelinated axon increases the speed of nerve impulse transmission.
Hard
56.Explain why the use of neonicotinoid pesticides is considered suitable for killing insects but not toxic to humans and other mammals.
Medium
57.Explain how the all-or-nothing principle applies to the transmission of nerve impulses, and how stimulus intensity is detected by the brain.
Hard
58.The oscilloscope trace shown below was taken using a digital oscilloscope. It shows an action potential in a hippocampal pyramidal neurone of a potoroo (a small marsupial species) that occurred when the neurone was stimulated with a current pulse. How many action potentials could be stimulated in this neurone every second?
Medium
- A5 action potentials per second
- B6 action potentials per second
- C7 action potentials per second
- D8 action potentials per second
59.An oscilloscope trace shows that one complete action potential takes 1.5 ms. Calculate the maximum number of action potentials that could be generated in one second, assuming no refractory period is limiting. Give your answer to the nearest whole number.
Medium
- A801 action potentials per second
- B667 action potentials per second
- C600 action potentials per second
- D734 action potentials per second
60.A neurone has a resting potential of -70 mV. During an action potential, the membrane potential reaches +40 mV. Calculate the change in membrane potential in mV.
Medium
- A99 mV
- B132 mV
- C121 mV
- D110 mV

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