6.5 Neurons and synapses

Question 1

What do neurons transmit?

Answer 1

Electrical impulses.

Question 2

What allows for saltatory conduction of nerve impulses?

Answer 2

The myelination of nerve fibres.

Question 3

How do neurons generate a resting potential?

Answer 3

By pumping sodium and potassium ions across their membranes.

Question 4

What does an action potential consist of in a neuron?

Answer 4

Depolarisation and repolarisation.

Question 5

What are the stages indicated on an oscilloscope trace of a neuron’s activity?

Answer 5

Resting potential, action potential (depolarisation and repolarisation), threshold potential, and refractory period.

Question 6

What initiates a nerve impulse?

Answer 6

Reaching the threshold potential.

Question 7

How are nerve impulses propagated along neurons?

Answer 7

Through action potentials propagated along the axons.

Question 8

Describe how the propagation of nerve impulses occurs.

Answer 8

It’s the result of local currents that cause each successive part of the axon to reach the threshold potential.

Question 9

What are synapses?

Answer 9

Junctions between neurons, and between neurons and receptor or effector cells.

Question 10

How does depolarisation of presynaptic neurons affect synapses?

Answer 10

They release a neurotransmitter into the synapse.

Question 11

What is involved in the secretion and reabsorption of acetylcholine at synapses?

Answer 11

Neurons release acetylcholine into the synapse, which is then broken down and reabsorbed.

Question 12

How do neonicotinoid pesticides affect synaptic transmission at cholinergic synapses in insects?

Answer 12

By binding to acetylcholine receptors, blocking synaptic transmission.

Question 13

How does the myelination of nerve fibres enhance the speed of nerve impulse conduction?

Answer 13

Myelination provides an insulating layer around nerve fibres, allowing electrical impulses to jump from one node of Ranvier to the next, speeding up nerve impulse conduction through saltatory conduction.

Question 14

What mechanism is responsible for generating a neuron’s resting potential?

Answer 14

The resting potential is generated by the differential distribution of ions, primarily sodium and potassium, across the neuron’s membrane, facilitated by the Na+/K+ pump and ion channels.

Question 15

Describe the sequence of events in an action potential.

Answer 15

An action potential begins with depolarisation, where sodium channels open and sodium ions rush in, followed by repolarisation, where potassium channels open and potassium ions exit the cell. This sequence restores the original ion distribution.

Question 16

How can an oscilloscope trace be used to analyze neuronal activity?

Answer 16

An oscilloscope trace can display the changes in membrane potential over time, showing phases like resting potential, threshold potential, depolarisation, repolarisation, and the refractory period, enabling analysis of nerve impulses.

Question 17

What signifies the threshold potential on an oscilloscope trace?

Answer 17

The threshold potential is indicated by a sudden rise in membrane potential from resting level towards positive values, marking the initiation of an action potential.

Question 18

Explain the local current flow during nerve impulse propagation.

Answer 18

Local currents are movements of ions in and out of the neuron’s membrane adjacent to the active site. These currents depolarise the next segment of the membrane to the threshold potential, propagating the nerve impulse along the axon.

Question 19

What role do synapses play in neural circuits?

Answer 19

Synapses allow neurons to form circuits, providing sites where signals can be transmitted between neurons or from neurons to other cells, like muscle or gland cells, through the release and reception of neurotransmitters.

Question 20

Detail the process by which neurotransmitters are released into the synaptic cleft.

Answer 20

Upon arrival of an action potential at the presynaptic terminal, voltage-gated calcium channels open, causing an influx of calcium ions, which triggers vesicles containing neurotransmitters to fuse with the presynaptic membrane and release their contents into the synaptic cleft.

Question 21

How is acetylcholine removed from the synaptic cleft?

Answer 21

Acetylcholine is broken down into choline and acetate by the enzyme acetylcholinesterase. Choline is then reabsorbed by the presynaptic neuron for reuse, while acetate diffuses away.

Question 22

How do neonicotinoid pesticides specifically affect insect neurons at synapses?

Answer 22

Neonicotinoids irreversibly bind to acetylcholine receptors on postsynaptic neurons, blocking these receptors and preventing acetylcholine from triggering a response, which can disrupt neural signaling, leading to paralysis or death in insects.