Lecture Objectives for: Principles of Homeostasis and Membrane Potentials

Question 1

What is the definition of ‘Homeostasis’?

Answer 1

Homeostasis: the maintenance of a dynamic steady state (i.e. using control systems to regulate deviations to remain at/ close to a set point)

Question 2

What are the components of a Homeostatic system?

Answer 2

The sensor, integrator, effector(s), compensatory response

Question 3

What does the sensor do?

Answer 3

detects the deviation in the controlled variable and informs the integrator

Question 4

What does the integrator do?

Answer 4

computes this information and sends instructions to correct the deviation to an effector

Question 5

What does the effector(s) do?

Answer 5

the effector causes an appropriate compensatory response

Question 6

What is the compensatory response?

Answer 6

the response generated by the effector(s) that restores the controlled variable to normal

Question 7

What are the components of the homeostatic control system for blood pressure?

Answer 7

Baroreceptors (sensors), Cardiovascular Center of Brain Stem (the integrator), [Blood vessels, Kidney, Adrenal gland, and more] (the effectors), and vasoconstriction increases and more fluid retention is generated when bloop pressure drops (compensatory response)

Question 8

What’s the importance of negative feedback?

Answer 8

Negative feedback is important in a control system because it responds to deviations away from the set point by implementing a response that opposes the deviation, which drives the system back towards the set point, stopping the process that generated the deviation and aids homeostasis

Question 9

What are the parts of a neuron?

Answer 9

Cell body, dendrites, and axons

Question 10

What are the functional differences between neurons and glial cells?

Answer 10

• Neurons transmit signals between themselves from one part of the body to another; communicates with electrical signals
• Glial cells regulates homeostasis for the neurons, providing support and protection, and modulations for synaptic signals and signal transmission; communicates with chemical signals

Question 11

Similarities between facilitated diffusion, primary active transport, and secondary active transport

Answer 11

Transportation of ions across the plasma membrane using trans-membrane proteins

Question 12

Differences between facilitated diffusion, primary active transport, and secondary active transport

Answer 12

Facilitated diffusion is a passive form of transportation that relies on ion recognition and the concentration gradient; whereas active transport need energy for ions to move against the concentration- primary transport focuses only on generating energy for one concentration whereas secondary transport generates another gradient to move another ion across the membrane without using additional energy

Question 13

What are examples of ligand-gated channels?

Answer 13

ATP-gated channels and PIP2-gated channels

Question 14

What are examples of voltage-gated channels?

Answer 14

Voltage-gated sodium or potassium channels

Question 15

How does selectivity of ions lead to the development of the resting membrane potential?

Answer 15

The selective permeability causes a charge separation in which the inside of the cell is more positive than the outside because of the leakage of Potassium into the ECF while negatively charged ions cannot diffuse out. The Na/K pump maintains the imbalanced concentrations of Na and K in both the ICF and ECF so neither concentration is exhausted.

Question 16

Describe the role of Na/K-ATPase with respect to the resting membrane potential

Answer 16

Maintains concentrations of Na and K in the ECF and ICF so the resting membrane potential is not exhausted

Question 17

What is the Equilibrium Potential?

Answer 17

The equilibrium potential represents the voltage at which no net movement is seen in the ion concentration because the forces of the concentration and electrical gradient for a specific ion are equal

Question 18

What are the similarities between the Nernst equation and the GHK equation?

Answer 18

They both calculate the equilibrium potential using ionic concentration in the ICF and ECF

Question 19

What are the differences between the Nernst equation and the GHK equation?

Answer 19

The GHK uses permeability and all the monovalence concentrations, for simplicity of the calculations, and because the equilibrium potential is a sensitivity to the influence of selective permeability.

Question 20

Compare and contrast graded potentials and action potentials

Answer 20

Although they are both electrical signals, graded potential can be either depolarizing or repolarizing and are decremental, summutive withno refractory period, whereas action potentials are non-decremental (being all-or-nothing), longer in their duration, and only depolarizing

Question 21

What is meant by decremental conductance, seen in graded potentials, ijn terms of the length constant?

Answer 21

The length constant refers to the distance that a graded potential will travel before its strength diminishes to 0.

Question 22

How does changes in the membrane resistance and axial resistance effect the length constant?

Answer 22

R_m= 1/cell radius
R_a= 1/cell radius^2
and length constant is proportional to the sqrt(R_m/R_a). Because is under the sqrt, decreases in Resistance will cause for the length constant to increase.

Question 23

Describe the roles of voltage-gated Na+ and K+ ion channels during an action potential

Answer 23

During the action potential, the voltage-gated Na+ depolarize the cell by increasing the positive charge inside the cell. The voltage-gated K+ exit the cell, re-polarizing the cell as the positive charge decreases inside the cell and generates a negative charge inside the cell in comparison to the outside of the cell.

Question 24

Compare and contrast activation and inactivation gates in voltage-gated Na+ channels and describe the importance of inactivation gates to the refractory period

Answer 24

The activation gate is inside the transmembrane protein and inactivation is within the cell. The activation gate and inactivation rapidly opens in response to the voltage threshold. However, the inactivation gate has a delayed closing period which occurs at the action potential peak.

Question 25

Describe what is meant by the reversal potential and explain how it is determined in a voltage clamp experiment

Answer 25

Like the equilibrium potential, the reversal potential refers to the voltage at which the net ion influx is 0 (as the outward and inward rates of the ion are the same). Thus, by holding the membrane potential at a certain voltage and measuring the rate of the inward and outward current, the voltage clamp experiment can determine when the reversal potential has been met.