Psychobiology part 2 unit 7

Question 1

What is a neuron, and why is it important?

Answer 1

Neurons are the basic functional units of the nervous system.
They form a vast network for processing and transmitting information, connecting up to 50,000 other neurons each.

Question 2

Name the key parts of a neuron and their functions.

Answer 2

Dendrites: Receive signals through synaptic receptors.
Cell body: Integrates incoming signals.
Axon: Transmits signals to other neurons, muscles, or organs.
Presynaptic terminal: Releases neurotransmitters to communicate with the next cell.

Question 3

What is the function of the cell membrane in a neuron?

Answer 3

The cell membrane controls what enters and exits the neuron, using protein channels to regulate the movement of substances like ions and water. This is essential for generating nerve impulses.

Question 4

Why do neural impulses lose strength over long distances?

Answer 4

Electrical signals weaken when traveling through the conductive organic material of the body, meaning signals from far body parts could arrive weaker than those from nearby.

Question 5

How does the nervous system ensure neural signals maintain their strength over long distances?

Answer 5

The nervous system regenerates the signal at each point along the axon, keeping the message strong regardless of the distance it travels.

Question 6

What are ions and what forces act on them?

Answer 6

Ions: Charged particles created when substances dissolve in water. Example: NaCl splits into Na⁺ and Cl⁻.
Forces on Ions:
Electrostatic Pressure: Opposite charges attract, similar charges repel.
Diffusion: Ions move from high to low concentration (like perfume spreading).
Gradients:
Electrical Gradient: Difference in charge between areas.
Concentration Gradient: Difference in ion concentration between areas.
Both gradients are crucial for transmitting neural impulses!

Question 7

What does the neuron’s cell membrane do?

Answer 7

The cell membrane acts as a barrier, controlling the movement of ions like Na⁺ and K⁺, which is crucial for generating nerve impulses.

Question 8

What is the resting potential of a neuron?

Answer 8

The resting potential is the difference in charge across the membrane at rest (~-70 mV).
Maintained by:
Sodium-potassium pumps (3 Na⁺ out, 2 K⁺ in).
Negatively charged proteins (A⁻) inside the cell.

Question 9

What does the sodium-potassium pump do?

Answer 9

It pumps 3 Na⁺ out and 2 K⁺ in to maintain the resting potential.

Question 10

Why is the resting potential important?

Answer 10

It keeps the neuron ready to fire, like a bowstring pulled tight.

Question 11

What causes an action potential?

Answer 11

The threshold of excitation is reached (around -55 mV).

Depolarization: Na⁺ rushes in, making the inside positive.

Repolarization: K⁺ exits, restoring negativity.

Hyperpolarization: The cell briefly becomes more negative than at rest.

Question 12

What is hyperpolarization?

Answer 12

When the membrane potential becomes more negative than the resting potential due to a negative charge being applied

Question 13

What is the threshold of excitation?

Answer 13

The specific membrane potential (around -55 mV) that triggers voltage-gated ion channels to open, leading to an action potential

Question 14

What happens when the threshold of excitation is reached?

Answer 14

Voltage-gated Na⁺ channels open, allowing Na⁺ to rush into the cell.
This causes a rapid depolarization (action potential)

Question 15

What happens during the action potential?

Answer 15

Na⁺ rushes in, reversing the membrane potential (inside becomes positive).
Sodium channels close at the peak of the action potential.

Question 16

What is repolarization?

Answer 16

The process of returning the membrane potential to its resting state (-70 mV) as K⁺ exits the cell through potassium channels.

Question 17

What restores the resting potential after hyperpolarization?

Answer 17

The sodium-potassium pump, which actively:

Pumps 3 Na⁺ out of the cell.
Pumps 2 K⁺ in to re-establish ion gradients

Question 18

Why is the sodium-potassium pump important?

Answer 18

It maintains the resting potential and prepares the neuron to fire again. This process consumes up to 40% of the neuron’s energy.

Question 19

Why does the neuron need hyperpolarization after an action potential?

Answer 19

It ensures the neuron cannot fire immediately, allowing it time to reset before the next signal.

Question 20

What is the peak of the action potential?

Answer 20

When the membrane potential reaches around +40 mV, and the inside of the cell becomes more positive than the outside.

Question 21

What are voltage-gated ion channels?

Answer 21

Special protein channels that open in response to specific voltage changes, allowing Na⁺ or K⁺ to move across the membrane

Question 22

What is saltatory conduction, and why is it efficient?

Answer 22

In myelinated axons, action potentials jump between nodes of Ranvier.
It speeds up conduction and conserves energy by limiting ion exchange to the nodes.

Question 23

What is the resting potential, and how is it maintained?

Answer 23

Resting potential is the charge difference across the membrane at rest (~ -70 mV).
Maintained by:
Sodium-potassium pumps (3 Na⁺ out, 2 K⁺ in).
Negatively charged proteins (A⁻) inside the cell.

Question 24

What triggers an action potential in a neuron?

Answer 24

When the membrane reaches the threshold of excitation (~-55 mV), Na⁺ channels open.
Na⁺ rushes in, causing depolarization and making the inside positive.

Question 25

Describe the key phases of an action potential.

Answer 25

Depolarization: Na⁺ enters, making the inside positive.
Repolarization: K⁺ exits, restoring the negative charge.
Hyperpolarization: The membrane temporarily becomes more negative than the resting potential.

Question 26

How does the action potential travel along the axon?

Answer 26

Continuous conduction: In unmyelinated axons, the impulse moves as a wave.
Saltatory conduction: In myelinated axons, it jumps between nodes of Ranvier, making it faster.

Question 27

What are the two types of refractory periods in a neuron?

Answer 27

Absolute refractory period: No action potential can occur.
Relative refractory period: A stronger stimulus can trigger an action potential.

Question 28

What is the role of voltage-gated ion channels in neural impulses?

Answer 28

Na⁺ channels: Open during depolarization to allow sodium ions to enter.
K⁺ channels: Open during repolarization to allow potassium ions to exit.
Both are critical for generating and propagating the action potential.

Question 29

What are nodes of Ranvier, and what is their role in neural impulses?

Answer 29

Nodes of Ranvier are gaps in the myelin sheath along myelinated axons.
They allow the action potential to be regenerated by exposing the axon membrane to the extracellular fluid.
This enables saltatory conduction, where the action potential jumps between nodes, making signal transmission faster and more efficient.

Question 30

What is the All-or-None Law in neural impulses?

Answer 30

The All-or-None Law states that a neuron either fires a full action potential or does not fire at all.
Once the threshold of excitation (~-55 mV) is reached, the action potential is generated with the same strength and speed regardless of the stimulus size.
A stronger stimulus does not produce a stronger action potential, but it may increase the frequency of firing.

Question 31

What role does K⁺ play in repolarisation?

Answer 31

K⁺ channels open, and potassium ions leave the cell, taking positive charges with them.
This movement makes the inside of the neuron more negative, restoring the resting potential.

Question 32

Why does hyperpolarisation occur after repolarisation?

Answer 32

Hyperpolarisation happens because too much K⁺ exits the cell, making the membrane potential temporarily more negative than the resting potential.
This overshoot ensures proper resetting of the neuron.

Question 33

What is the refractory period, and why is it important?

Answer 33

The refractory period is the time after an action potential when the neuron cannot fire another signal.
There are two types:
Absolute refractory period: No action potential can occur.
Relative refractory period: A stronger stimulus can trigger an action potential.
It ensures signals move in one direction and prevents overfiring.

Question 34

How does Cl⁻ contribute to hyperpolarisation?

Answer 34

Chloride ions (Cl⁻) enter the cell when the inside is highly positive.
This increases the negative charge inside the cell, contributing to hyperpolarisation and resetting the neuron for its next signal.

Question 35

What are voltage-gated ion channels, and why are they important?

Answer 35

Voltage-gated ion channels open or close depending on the membrane potential.
Two key channels:
Na⁺ channels: Open during depolarisation to let sodium ions in.
K⁺ channels: Open during repolarisation to let potassium ions out.
These channels are essential for generating and propagating action potentials.

Question 36

How does the sodium-potassium pump help reset the neuron after an action potential?

Answer 36

The sodium-potassium pump restores the ion gradient by actively:
Pumping 3 Na⁺ out.
Pumping 2 K⁺ in.
This process restores the resting potential (~-70 mV) and prepares the neuron for the next action potential.

Question 37

Why is the action potential considered an all-or-none event?

Answer 37

If the stimulus reaches the threshold of excitation (~-55 mV), the neuron fires a full action potential.
If the threshold is not reached, no action potential occurs.
The strength of the stimulus does not affect the size or speed of the action potential.

Question 38

How does continuous conduction differ from saltatory conduction?

Answer 38

Continuous conduction:
Occurs in unmyelinated axons.
The action potential travels as a continuous wave along the axon.
Saltatory conduction:
Occurs in myelinated axons.
The action potential jumps between nodes of Ranvier, making it faster.

Question 39

What is depolarisation, and what triggers it?

Answer 39

Depolarisation occurs when the neuron becomes less negative (more positive) inside.
Triggered by the opening of voltage-gated Na⁺ channels, allowing Na⁺ to flow into the cell.

Question 40

What is propagation, and how does it occur?

Answer 40

Propagation is the movement of the action potential along the axon.
In unmyelinated axons, the action potential travels as a continuous wave.
In myelinated axons, it jumps between nodes of Ranvier (saltatory conduction), making the process faster and more energy-efficient.

Question 41

What is Multiple Sclerosis, and how does it affect neural impulses?

Answer 41

Multiple Sclerosis (MS) is an autoimmune disease that damages the myelin sheath in the CNS.
This disrupts saltatory conduction, slowing or blocking action potential propagation along axons.
Symptoms include muscle weakness, coordination issues, and cognitive impairment.