Membrane Physiology (Resting Membrane Potential) Flashcards
1
Q
What does the cell membrane do?
A
- Defines boundaries of the cell
- Encloses the cell’s organelles
- Enables the cell to create an internal environment that promotes the normal functions of the cell
- Creates an internal environment that is different from that outside of the cell
2
Q
What is the structure of the cell membrane?
A
- Cell membranes are composed of closely apposed 2 layers of phospholipids
- Each unit of the phospholipid layer has a:
- Head that is hydrophilic
- Tail that is hydrophobic
- Layers of phospholipid units of the membrane arrange themselves such that
- Hydrophobic tails align deep within layers of the membrane
- Hydrophilic heads form outer surfaces of the membrane
- Arrangement allows the cell membrane to be impermeable to any particles that are hydrophilic
3
Q
What does the cell membrane create?
A
- A perfect seal
- Two distinct environments
- Can influence the contents of the internal
4
Q
How does the cell membrane establish a resting potential?
A
- Concentration difference of species of charge-carrying ions between intra-& extra-cellular compartments
- Standing electro-chemical gradient between intra-& extra-cellular compartments of the cell
- Electro-chemical gradient is known formally as the ‘resting membrane potential’
5
Q
Resting membrane potential of nerve cells
A
- In nerve cells at rest, the inside of the cell is relatively negatively charged with respect to outside the cell
- The resting membrane potential of nerve cells is around -65mV to -70 mV with respect to the outside of the cell
- RMP will vary between cell types
6
Q
A defining characteristic of electrically excitable tissues
A
they are able to momentarily discharge the standing electrical potential between the intracellular and extracellular compartments
7
Q
How do nerve cells communicate?
A
- In nervous tissues, the process of discharging the standing electrical potential is also a mechanism of electrical communication between cells
- Upon discharging the standing potential between the intracellular and extracellular compartments, the cell membrane works to restore the resting membrane potential
8
Q
Factors that define whether or not particles cross the cell membrane
A
- Size of the particles
- Electrical charge on the particles
- Whether particles are recognised by specialised transport systems that cross the cell membrane or not
- Solubility of molecules in water
9
Q
What specialised proteins allow movement across membranes?
A
Ion channels, and ion pumps
10
Q
Properties of ion channels
A
- Protein assemblies that are lodged within the substance of the cell membrane
- These protein assemblies span the full thickness of the cell membrane
- Also known as trans-membrane spanning proteins
- They have a water-filled central pore that passes from inside to the outside of the cell (or vice-versa)
- They facilitate passive movement of ions across the cell membrane
- From inside to outside
- From outside to inside•
- Some ion channels are selective as to which ions they conduct through their pores
- Other ion channels are less selective in terms of which ions they will conduct
11
Q
How do ion channels differ?
A
- which species of ions they conduct
- how their conductance of ions is governed
- gating mechanisms of the ion channels
12
Q
Different types of ion channel
A
- Voltage-gated ion channels
- Voltage-gated sodium channels
- Voltage-gated potassium channels
- Ligand-gated ion channels
- Most common ligands are neurotransmitters e.g. Acetylcholine
- Mechanically-gated ion channels
- Non-gated ion channels
- Leak channels
13
Q
What are ion pumps?
A
- They are also found lodged within the cell membrane
- Their main function is to maintain the resting membrane potential
- They do not set-up the RMP
- They require energy in the form of ATP to maintain the RMP
