Physiology 2: Introducing Electrical Signalling in cells Flashcards
What is Membrane Potential (Vm)
A difference in voltage across the cell membrane arising due to small difference in the distribution of ions in the intracellular and extracellular solutions. Defined as intracellular voltage with respect to extracellular voltage.
What is resting membrane potential?
The membrane potential during a period when the cell is not active or being stimulated. Typically, a stable, steady-state condition of about −80 to −60 mV (because of 2 K+ in and 3 Na+ out)
What is the action potential?
A transient and rapid change in membrane potential, following a consistent trajectory. For instance, in many nerve and muscle cells Vm changes from about −70 mV up to about +20 mV before returning to −70 mV.`
What is depolarisation?
A change in the Vm in a positive direction. Typically increases the probability of a cell firing an action potential, hence typically excitatory.
What is hyperpolarization?
A change in the Vm in a negative direction. Typically decreases the probability of a cell firing an action potential, hence typically inhibitory.
What is repolarisation?
A return of the membrane potential to resting value following a large depolarization, such the hyperpolarisation phase of the action potential
What are excitable cells?
cells that can produce and respond to electrical signals (e.g. nerve cells, muscle cells, secretory cells)
All our sensory processes involve ________ being transmitted in our brain
action potentials
How do cells generate electrical signals?
By selective movement of ions across their cell membranes
Moving ions changes the __________ of the cell.A cation comes in, so the membrane potential becomes more positive (depolarization). For repolarization to occur, K+ is moved out of the cell by diffusion (through an ion selectively gated channel that only allows potassium through).
Membrane potential
What are the two ways a substance can move across a membrane?
Passive diffusion and Active Transport
What are the two types of passive diffusion?
- Simple diffusion
2. Facilitated diffusion
What is simple diffusion and what is the process (what can move in)?
Where substances move from high concentration to low concentration. Cell membrane is non-polar (in the layer of hydrophobic phospholipid tails), so only non-polar substances can move across the cell membrane by passive diffusion (e.g. gases like O2 or steroids). Ions and other substances (charged or polar) cannot dissolve in and move across the membrane by passive diffusion; they must be facilitated.
What is simple diffusion and what are the two processes?
a. Carrier mediated – substances (like neutrally charged glucose) are bound by proteins and released inside the cell
b. Ion channel mediated (facilitate ion transfer) – proteins make tiny channels (often filled with water) through the cell membrane through which hydrated ions can diffuse. Sometimes the holes are so small the water molecules are stripped off. They are selective. Ion channels are gated (with gates activated by voltage thresholds – voltage gated).
What is active transport (primary and secondary) and what are the basic processes involved?
- Primary transport - directly utilize energy to establish ion concentration gradients
• Sodium pump (Na+/K+/ATPase) – ATP hydrolysis drives uphill solute flux.
• 3 sodium ions are forced out of the cell for every 2 potassium ions forced in.
• This pump system establishes and maintains physiological [Na+] and [K+] and relevant concentration gradients (high sodium outside, high potassium inside)
• These concentration gradients can then be used to power other activities (such as the secondary transportation of glucose against its concentration gradient) - Secondary transport - movement of one ion species down its electrochemical gradient is coupled to uphill movement of other ion species or solutes against their electrochemical gradient.
