Nervous Tissue Lecture 3

Question 1

What are the two factors essential for the ability to send electrical signals in neurons?

Answer 1

• Very negative resting membrane potential
• Specific ion channels in the cell membrane

Question 2

Define resting membrane potential.

Answer 2

the electrical potential difference (voltage) across the cell membrane when the neuron is at rest.

Question 3

What causes the buildup of membrane potential?

Answer 3

The buildup of positive ions outside of the cell membrane and negative ions on the inside creates the membrane potential.

Question 4

What are the two main reasons for the resting membrane potential?

Answer 4

• Unequal distribution of ions between the extracellular fluid (ECF) and the cytosol (ICF)
• Inability of most anions to leave the cell

Question 5

Describe the unequal distribution of ions between the extracellular fluid (ECF) and the cytosol (ICF).

Answer 5

ECF has high concentrations of sodium ions (Na+) and chloride ions (Cl–), while cytosol has high concentrations of potassium ions (K+) and negatively charged proteins (Pr–).

Question 6

Explain the role of the sodium/potassium (Na+/K+) pump in establishing the resting membrane potential.

Answer 6

The Na+/K+ pump actively transports ions against their electrochemical gradients, pumping 3 Na+ out for every 2 K+ in, making the inside of the cell more negative.

Question 7

What are leak channels, and how do they contribute to the resting membrane potential?

Answer 7

Leak channels are passive membrane channels that are always open, allowing ions to flow down their concentration gradients, contributing to the membrane potential.

Question 8

Why can’t most anions leave the cell, and how does it affect the membrane potential?

Answer 8

Most anions can’t leave the cell due to being attached to large molecules or lacking appropriate channels, resulting in a more negative internal environment.

Question 9

How do neurons send signals through ion channels?

Answer 9

Neurons send signals by allowing ions to either enter or leave the cell through ion channels.

Question 10

What are the three types of ion channels relied upon for sending signals through neurons?

Answer 10

mechanically gated channels, ligand-gated channels, and voltage-gated channels.

Question 11

Describe mechanically gated channels and their function.

Answer 11

Open in response to physical distortion of the membrane surface and are important in sensory receptors responding to stretch, pressure, or vibration, particularly found in dendrites.

Question 12

What are ligand-gated ion channels and where are they most abundant?

Answer 12

They open when they bind specific chemicals. They are most abundant on dendrites and the cell body of a neuron, where most synaptic communication occurs.

Question 13

Explain voltage-gated ion channels and their characteristic.

Answer 13

Voltage-gated ion channels open or close in response to changes in membrane potential and are characteristic of excitable membranes, which can generate and/or spread action potentials.

Question 14

What are the examples of ions channels that are voltage-gated?

Answer 14

Examples of voltage-gated ion channels include Na+, K+, and Ca2+ channels.

Question 15

How do sodium channels differ from potassium channels in terms of gates?

Answer 15

Sodium channels have two independent gates: activation gate opens on stimulation to let sodium in, while the inactivation gate closes to block entry of sodium ions. In contrast, potassium channels typically only have one gate.

Question 16

Where are chemically gated channels predominantly found on a neuron?

Answer 16

Chemically gated channels are predominantly found in the neuron cell body and dendrites.

Question 17

What are the two types of electrical signals neurons use to communicate?

Answer 17

Neurons communicate using graded potentials (GPs) and action potentials (APs).

Question 18

Where does the initial stimulation of a neuron causing graded potentials (GPs) occur?

Answer 18

The initial stimulation causing graded potentials (GPs) occurs in the dendrites and cell body of neurons.

Question 19

What are the three possible outcomes when a GP is generated in response to stimulation?

Answer 19

When a GP is generated, it can either result in firing an action potential (AP), not firing an AP, or inhibiting the neuron.

Question 20

What are graded potentials (GPs) and what types of channels are involved in their generation?

Answer 20

Graded potentials (GPs) are small deviations from the membrane potential involving ligand-gated or mechanically-gated channels.

Question 21

Describe the amplitude variation of graded potentials (GPs) and its dependence on stimulus strength.

Answer 21

Depends on the strength of the stimulus: stronger stimuli lead to larger amplitude GPs.

Question 22

Differentiate between excitatory post-synaptic potentials (EPSPs) and inhibitory post-synaptic potentials (IPSPs).

Answer 22

EPSPs make the cell more positive (depolarize), bringing it closer to an AP, while IPSPs make the cell more negative (hyperpolarize), inhibiting AP generation.

Question 23

What is the process of summation of graded potentials (GPs)?

Answer 23

Summation of graded potentials (GPs) is the process by which GPs add together to influence the likelihood of an AP.

Question 24

Explain the concept of spatial summation and temporal summation in graded potentials (GPs).

Answer 24

• Spatial summation occurs when GPs from different locations on the neuron’s membrane combine,
• Temporal summation occurs when GPs from the same location fire repeatedly in quick succession

Question 25

What is an action potential (AP) and what triggers its occurrence?

Answer 25

An action potential (AP) is an all-or-none electrical impulse triggered by a sufficiently large depolarization of the membrane potential, typically at the axon hillock.

Question 26

Describe the all-or-none principle in the generation of action potentials (APs).

Answer 26

The all-or-none principle states that once the depolarizing stimulus reaches the threshold, the action potential is generated with a consistent size and amplitude.

Question 27

What are the three phases of an action potential (AP)?

Answer 27

The three phases of an action potential (AP) are **depolarization**, **repolarization**, and **hyperpolarization**.

Question 28

What happens during the depolarization phase of an action potential (AP)?

Answer 28

During depolarization, voltage-gated sodium channels open, allowing sodium ions to rush into the cell, making the inside more positive.

Question 29

Explain the repolarization phase of an action potential (AP).

Answer 29

Repolarization involves the return of the membrane potential to its resting state as potassium ions rush out of the cell.

Question 30

What occurs during the hyperpolarization phase of an action potential (AP)?

Answer 30

Hyperpolarization occurs when the membrane potential becomes more negative than the resting state due to delayed closing of potassium channels.

Question 31

Outline the events involved in the generation of an action potential (AP)

Answer 31

The generation of an action potential involves depolarization to threshold, activation of sodium channels, inactivation of sodium channels, activation of potassium channels, and closure of potassium channels.

Question 32

At what membrane potential do voltage-gated sodium and potassium channels typically close during the action potential (AP) process?

Answer 32

Voltage-gated sodium and potassium channels typically close when the membrane potential returns close to the normal resting potential of -70 mV.

Question 33

Define refractory period in the context of action potentials (APs).

Answer 33

The refractory period is the period following an action potential (AP) during which no other AP can be generated.

Question 34

What is the relative refractory period?

Answer 34

The relative refractory period is a phase within the refractory period where a stronger-than-normal stimulus is required to generate a second AP.

Question 35

Describe the physiological changes during the relative refractory period.

Answer 35

During the relative refractory period, potassium channels are still open, and positive charges are leaving the cell, making it more difficult to generate another AP.

Question 36

Explain action potential propagation.

Answer 36

Action potential propagation refers to the transmission of action potentials along the axon.

Question 37

What are the two types of propagation?

Answer 37

The two types of propagation are continuous propagation and saltatory propagation.

Question 38

How does continuous propagation occur?

Answer 38

Continuous propagation occurs in unmyelinated axons and involves the step-by-step movement of the action potential along the entire axon.

Question 39

What characterizes saltatory propagation?

Answer 39

Saltatory propagation occurs in myelinated axons and involves the depolarization only at the nodes of Ranvier, skipping the internodes.

Question 40

Why is saltatory propagation faster than continuous propagation?

Answer 40

Saltatory propagation is faster than continuous propagation because it skips internodes where ions can't cross the membrane, reducing resistance and allowing for faster propagation.