Neuronal signalling

Question 1

What is voltage?

Answer 1

voltage (ΔV) is the difference in electric potential energy per unit charge between two points. In physiology, most voltages are observed across a membrane.

Question 2

What is current?

Answer 2

Current (I) is the flow of electric charge through a medium or across a surface. It represents the movement of charged particles.

Question 3

What is resistance?

Answer 3

Resistance (R) is the opposition to the passage of an electric current. It represents how difficult it is for electricity to flow along a certain path.

Question 4

What is conductance?

Answer 4

Conductance (g) is the inverse quantity of resistance. It measures how easily electricity flows along a certain path or through a medium.

Question 5

What is the relationship between voltage, current, and resistance?

Answer 5

According to Ohm’s Law, the relationship between voltage (V), current (I), and resistance (R) is given by the equation V = I x R. It states that the voltage across a circuit is equal to the current flowing through it multiplied by the resistance.

Question 6

How is current related to conductance?

Answer 6

Current (I) is related to conductance (g) by the equation I = V x g. It states that the current flowing through a circuit is equal to the voltage applied across it multiplied by the conductance.

Question 7

What is a selectively permeable membrane?

Answer 7

A selectively permeable membrane refers to a membrane that allows the free movement of certain molecules while tightly controlling the movement of others. It acts as a selective filter.

Question 8

How do uncharged substances move across the cell membrane?

Answer 8

Uncharged substances, such as O2, CO2, urea, alcohol, and glucose, move across the cell membrane based on their concentration gradient. The membrane is permeable to these molecules, allowing them to move freely.

Question 9

How do charged substances cross the cell membrane?

Answer 9

Charged substances, such as K+, Na+, and Cl- ions, cannot easily diffuse through the hydrophobic cell membrane. They utilize specialized ion channels, which are water-filled pores, to cross the membrane.

Question 10

What are ion channels?

Answer 10

Ion channels are specialized proteins that form pores in the cell membrane, allowing the passage of specific ions. They are selective for particular ions.

Question 11

What factors induce the movement of ions through ion channels?

Answer 11

Concentration gradient: Ions move from areas of higher concentration to areas of lower concentration.
Electrical gradient: The electrical potential difference across the membrane attracts ions with opposite charges and repels ions with the same charge.
Electrochemical gradient: The combined influence of concentration and electrical gradients determines the net movement of ions.

Question 12

How does the concentration gradient influence the movement of potassium (K+) ions across the cellular membrane?

Answer 12

The intracellular concentration of potassium is higher than the extracellular concentration. As a result, potassium ions tend to move out of the cell following the concentration gradient.

Question 13

How does the electrical gradient influence the movement of potassium (K+) ions?

Answer 13

When positively charged potassium ions are released from the cell, the intracellular space becomes relatively negative. This negative charge attracts some potassium ions back towards the intracellular space, counteracting the concentration gradient.

Question 14

hat “streams” are created due to the combined influence of concentration and electrical gradients for potassium ions?

Answer 14

Two “streams” of potassium ions are created. One stream expels potassium ions according to the concentration gradient, moving them out of the cell. The other stream attracts potassium ions back towards the intracellular space due to the increasing negative electrical environment.

Question 15

What ions have the greatest impact on the resting membrane potential?

Answer 15

Sodium (Na+) and potassium (K+) ions have the greatest impact on the resting membrane potential as the cell membrane is most permeable to these ions.

Question 16

What is the resting membrane potential of neurons primarily determined by?

Answer 16

The resting membrane potential of neurons is primarily determined by the equilibrium potential for potassium ions (due to high permeability), with the slight influence of sodium ion influx making it slightly less negative.

Question 17

How can changes in ion permeability affect the membrane potential?

Answer 17

Changes in ion permeability caused by the opening or closing of ion channels can alter the membrane potential. This is how action potentials are generated.

Question 18

How is the resting membrane potential maintained?

Answer 18

The resting membrane potential is maintained by the sodium-potassium pump (Na+/K+ ATPase). This pump actively transports potassium ions into the cell and sodium ions out of the cell, against their electrochemical gradients. This helps maintain the ionic differences across the membrane and the resting membrane potential.

Question 19

How are concentration gradients maintained in neurons?

Answer 19

Concentration gradients in neurons are maintained by the action of the Na+/K+ ATPase through active transport. This helps in maintaining the membrane potential.

Question 20

What is the role of the Na+/K+ ATPase in maintaining the membrane potential?

Answer 20

The Na+/K+ ATPase actively transports potassium ions into the cell and sodium ions out of the cell, which helps in maintaining the ionic concentration gradients and the membrane potential.

Question 21

How does an action potential begin?

Answer 21

An action potential begins at the axon hillock as a result of depolarization. Voltage-gated sodium ion channels open due to an electrical stimulus, allowing sodium ions to rush into the cell and changing the potential inside the cell from negative to more positive.

Question 22

What is the threshold potential?

Answer 22

The threshold potential is the membrane potential that needs to be reached for an action potential to be produced. Action potentials occur only when the threshold is reached.

Question 23

How are action potentials described?

Answer 23

Action potentials are described as “all-or-nothing” because if the threshold is reached, an action potential of the same magnitude is always elicited, regardless of the strength of the stimulus.

Question 24

How do neurons use voltage as information for signaling?

Answer 24

Neurons use changes in membrane voltage, such as depolarization during an action potential, as information for signaling. These voltage changes are detected by other neurons or target cells and are crucial for the transmission of signals in the nervous system.

Question 25

What happens to the voltage-gated sodium ion channels during repolarization?

Answer 25

During repolarization, the voltage-gated sodium ion channels begin to close in response to the positive potential inside the cell. This prevents further entry of sodium ions into the cell.

Question 26

What happens to the voltage-gated potassium channels during repolarization?

Answer 26

During repolarization, the positive potential inside the cell causes voltage-gated potassium channels to open. This allows potassium ions to move out of the cell down their electrochemical gradient.

Question 27

What is hyperpolarization?

Answer 27

Hyperpolarization is the process during which the membrane potential becomes more negative than the resting potential following an action potential. It occurs as potassium ions continue to move out of the cell, causing the membrane potential to overshoot the resting potential.

Question 28

What is the role of the Na+/K+ ATPase during repolarization?

Answer 28

The Na+/K+ ATPase is not directly involved in the repolarization process following an action potential. Its primary role is to maintain the ionic concentration gradients across the membrane during the resting state.

Question 29

What is the refractory period?

Answer 29

The refractory period is a period following an action potential during which the neuron is less responsive to additional stimuli. It can be divided into the absolute refractory period and the relative refractory period.

Question 30

What happens during the absolute refractory period?

Answer 30

During the absolute refractory period, the sodium channels are in an inactive state and cannot be reopened, regardless of the membrane potential. This prevents the generation of another action potential.

Question 31

What happens during the relative refractory period?

Answer 31

During the relative refractory period, some sodium channels slowly recover from the inactivated state. The neuron can be excited with stimuli stronger than the one normally needed to initiate an action potential. The strength of the stimulus required gradually decreases throughout this period.

Question 32

How are action potentials propagated along axons?

Answer 32

Action potentials are propagated along axons via local currents. These currents induce depolarization of the adjacent axonal membrane, and if the depolarization reaches a threshold, further action potentials are generated.

Question 33

Why does the action potential only travel in one direction?

Answer 33

The action potential only travels in one direction because the areas of the membrane that have recently depolarized enter a refractory period and cannot depolarize again. This ensures that the action potential propagation is unidirectional.

Question 34

How do membrane capacitance and resistance affect the distance of action potential propagation?

Answer 34

Membrane capacitance: It refers to the ability of the membrane to store charge. A lower membrane capacitance results in a greater distance before the threshold for reaching an action potential is no longer reached.
Membrane resistance: It depends on the number of ion channels open. A lower number of channels open leads to higher membrane resistance. A higher membrane resistance results in a greater distance before the threshold for reaching an action potential is no longer reached.

Question 35

What is the function of the myelin sheath in neuronal axons?

Answer 35

The myelin sheath surrounds neuronal axons and serves as an insulating layer, allowing for rapid conduction of electrical signals and increasing energy efficiency.

Question 36

What are Nodes of Ranvier?

Answer 36

Nodes of Ranvier are periodic gaps along a myelinated axon where the axonal membrane is exposed. These nodes have a high density of ion channels and are the sites where action potentials occur.

Question 37

How does the myelin sheath affect conduction speed and efficiency?

Answer 37

The myelin sheath increases membrane resistance and reduces membrane capacitance along the axon. This speeds up conduction by allowing action potentials to jump from one node to the next (saltatory conduction), resulting in faster propagation along the neuron.

Question 38

What is saltatory conduction?

Answer 38

Saltatory conduction refers to the rapid conduction of action potentials along myelinated axons. The action potential “jumps” from one node of Ranvier to the next, where depolarization occurs. If the depolarization reaches the threshold, it initiates another action potential, allowing for efficient and fast signal transmission.

Question 39

What is the role of intracellular free calcium at the synapse?

Answer 39

Intracellular free calcium (Ca2+) plays a crucial role in synaptic transmission. It is involved in the release of neurotransmitters from the presynaptic neuron and the subsequent signaling between neurons at the synapse.

Question 40

How is intracellular free calcium increased at the synapse?

Answer 40

When an action potential depolarizes the synaptic terminal, voltage-gated calcium channels open, allowing an influx of calcium ions into the terminal. This increase in intracellular free calcium triggers various cellular processes, including the fusion of synaptic vesicles with the cell membrane (exocytosis) and the release of neurotransmitters into the synaptic cleft.

Question 41

What is the role of calcium in neurotransmitter release?

Answer 41

The increase in intracellular free calcium in the synaptic terminal triggers the fusion of synaptic vesicles containing neurotransmitters with the cell membrane. This fusion allows the release of neurotransmitters into the synaptic cleft, enabling their diffusion and subsequent binding to postsynaptic receptors.

Question 42

How are neurotransmitters synthesized and stored?

Answer 42

Neurotransmitters can be synthesized within the synaptic terminal of the axon or in the cell body. For example, acetylcholine (ACh) is synthesized in the axon terminal using precursors like choline and acetate. Other neurotransmitters, such as neuropeptides, are synthesized in the cell body and transported to the axon terminal for storage.

Question 43

How are neurotransmitters inactivated or removed from the synaptic cleft?

Answer 43

Neurotransmitters can be inactivated or removed from the synaptic cleft through several mechanisms:

Reuptake: Certain neurotransmitters, like serotonin, can be taken back into the presynaptic neuron by transporter proteins for recycling or degradation.
Breakdown: Neurotransmitters such as acetylcholine are broken down by specific enzymes, like acetylcholinesterase, in the synaptic cleft.
Diffusion: Some neurotransmitters can simply diffuse into the surrounding area, away from the synapse.

Question 44

What are the components of a synapse?

Answer 44

A synapse consists of three main components:

Axon terminal (presynaptic side): This is where information is transmitted from.
Synaptic cleft: The small gap between the presynaptic and postsynaptic neurons.
Dendrite (postsynaptic side): This is where the information is received.

Question 45

How do neurotransmitters transmit signals at synapses?

Answer 45

Neurotransmitters transmit signals across synapses in different locations, such as from one neuron to another target neuron, at the neuromuscular junction (NMJ) from a neuron to a muscle cell, or from a neuron to a gland. They bind to receptors on the postsynaptic neuron, resulting in either excitation or inhibition, depending on the neurotransmitter and receptor involved.

Question 46

What is the role of neuromodulatory neurotransmitters?

Answer 46

Some neurotransmitters have a neuromodulatory action, which involves larger-scale regulation of groups of neurons. These neurotransmitters can act on multiple neurons simultaneously and play a slower time-course role compared to excitatory and inhibitory neurotransmission.