Physiology week3,4,5 Flashcards
Name the 2 types of simple diffusion
Simple and facilitated
Name and describe the 2 types of diffusion
Simple diffusion : Where molecules move through the membrane openings or spaces without interactions with carrier proteins .
Facilitated diffusion : Where carrier proteins help transport molecules by binding with them and moving them through the membrane
NAME the 2 pathways of simple diffusion
Through the lipid bilayer and
Through protein channels
Explain the 2 pathways of simple diffusion
1.Through the lipid bilayer
- Where lipid soluble substances like oxygen, nitrogen, carbon dioxide and alcohols dissolve in the lipid bilayer and diffuse easily .
2. Through protein channels
Where water and small insoluble molecules pass through the channels in protein molecules embedded in the membrane .
How is water diffused?
Through aqaporins
Explain the structure of protein pores
They are integral membrane proteins that form open tubes that allow substantances to move by simple diffusion from one side to another
Name 2 features of a protein pore and what they provide and give an example of what they cause
The diameter of a pore and its electrical charges provide selectivity that allows only certain molecules to pass through .
E.gAquaporins which have a narrow pore that allow water molecules to diffuse through the membrane but the pores is too narrow for hydrated ions
Name 2 features of a protein pore and what they provide and give an example of what they cause
The diameter of a pore and its electrical charges provide selectivity that allows only certain molecules to pass through .
E.gAquaporins which have a narrow pore that allow water molecules to diffuse through the membrane but the pores is too narrow for hydrated ions
Explain the potassium channel selectively-
- The potassium channels allow potassium ions to pass more easily than sodium ions due to a specific selectivity filter lined with carbonyl oxygen which intercats with the potassium ions and excludes Na ions.
Explain the sodium channel selectivity
- Na channels have a narrow selectivity filter lined with negatively charged amino acids that attract and allow sodium ions to pass while excluding other ions.
Why is the sodium channel selectivity important?
- It is crucial for cellular function as it ensures that Na ions can pass through the channels under normal conditions
What is the role of Gating of protein channel
They control ion permeability by opening or closing channles in response to stimuli
Name the types of gatings
- Voltage
- Chemical(Ligand) gating
Explain both types of gating without examples
VOLTAGE
- The gate responds to changes in electrical potential across the cell membrane
CHEMICAL(LIGAND)
-The gate opens when a chemical(ligand) binds to the protein, causing a confromational change
Give examples for both types of gating
Voltage
- A negative charge inside the membrane keeps the Na channels closed but when the membrane looses its negativity the Na channels open allowing the ions to pass
Chemical(ligand)
- The nerotransmitter acetylcholine binding to its receptors opening a channel for ion passage facilitating nerve signal transmission
What is the patch clamp method?
A technique used to measure ion current through single channels by creating a seal between a micropipette and a small membrane path
Name the factors affecting net rate of diffusion
- Concentration difference across the membrane
- The membrane electrical potential
- The pressure difference across the membrane
What is Osmosis?
- It refers to the net movement of water across a selectively permeable membrane from an area of high water concentration to an are of low water concentration
What is the role of the selectively permeable membrane in osmosis
Allows water to pass more easily than solutes like Na and Cl
Name the factors affecting osmotic pressure
- The number of osmotic particles
- the number of solute particles - Osmole
- If a substance dissociates the number of osmoles increases with the number of ions
What is Osmolality?
The concentration of osmotically active particles in osmoles
What is the osmotic pressure
The pressure required to stop osmosis. It is determined by the concentration of non-diffusible solute particles on one side of the membrane.
What is Active transport?
+ the substances they move
It moves substances across the cell membrane against their conentration gradient, requiring enrgy
substances include: Na, Cl, K, H, ca ions
and certain sugars and amino acids
Name and describe the types of Active Transport
- Primary AT
- Energy is dervied from the breakdown of ATP
Secondary ATP - Which uses energy stored in ionic concentration differences created by PAT
- What mechanism does Primary Active Trasnport use
- What is the function
- And its importance
Mechanism: Sodium-Potassium Pump
Function: It pumps Na ions out of the cell and K ions in.
It uses ATP to exchange 3 Na ions out of the cell and 2 K ions in the cell
Importance: -Mainatais cell volume . -Creates cells negative electrical potential, cruicial for nerve function
What is the Mechanism for the primary Active transport of Calcium ions and its function
Mechanism Calcium Pump
- It pumps calcium out of the cells or into organelles, maintaining low cytosolic calcium levels
What is the Mechanism for the primary active transport of hydrogens and where is it found
- Hydrogen Pump
It is found in the gastric glanels and kidney tubules
What 2 types of transport are in Secondary Active Transport
- co transport and counter transport
Describe the role and give examples of the 2 types of transport in Secondary Active Transport
-Co-Transport (Symport): Substances are transported in the same direction as sodium ions.
Examples: Glucose and amino acids are co-transported into cells with sodium.
-Counter-Transport (Antiport): Substances are transported in the opposite direction of sodium.
Examples: Sodium-calcium exchange and sodium-hydrogen exchange, important for calcium and pH regulation.
What is the definition of the Nerst potential
-It is the diffusion potential across a membrane that exactly counteracts the net diffusion of a particular ion
What is the Neest potential based on
The concentration gradient of the ions across the membrane
How is the magnitude of the nerst potential determined ?
- By the ratio of the concentrations of the specific ion on the two sides of the membrane
What does the formula for the Nerst potential assume
It assumes the potential in the ECF remains at zero potential
How is the membrane potential measured?
- By inserting a micropipette filled with electrolyte solution into a cell or nerve fibres
What is the role of the voltmeter
- It measures the potential difference between the inside and outside of the cell
What is the resting membrane potential?
- -70 mv
why is the resting membrane potenital negative?
- The sodium potassium pump actively transports Na ions out of the cell and K ions in the cell in the ratio of 3 Na + out for every 2 K + in.
- This creates a deficient + ions, resulting a negative potential inside the membrane
What happens in Potassium lekage?
- The potassium ions can leak out of the cell through potassium ‘leak’ channels, which are 100 times more permeable to potassium than sodium.
What is the definition of action potential
- A rapid change in membrane potential ., propagating along the nerve fibre, transmitting signals
What happens at the resting stage
-The memabrans is polarised at -70mv
What happens in depolarisation
- Membrane becomes permeable to Na ions, Na ion channel opens
- Allows the postively charged sodium ions o difffuse through the membrane
- Making it more postively charged
What happens in repolarisation
- The Na ion channels close
- K ion channels open
They excite the cell , restoring the negative resting potential
Explain activaton,in the voltage-gated sodium channels
When the membrane potential becomes less negative, rising from the -70mv to near -55mv, the activation gates open allwoing a large influx of sodium ion.
What happens in inactivation in the voltage gated sodium ion channels
- A slower process closes the inactivation gate after a brief time, stopping the sodium ions influx
What happens in resting in the voltage gated sodium channels
The sodium channels cannot open till the memrbane returns to its resting state
What happens in the resting state of the voltage gated potassium channels
- The gate is close, preventing k ions from exititng
What happens in activation in the voltage gated potassium ion
The activayion gate opens when the membrane potential rises towards 0 allowing potassium ions to flow out
Explain the timing stage in the voltage gated potassium channels
The potassium channels open as the sodium channels inactivate, speeding up repolarisation
What is the nerst equation used to calculate
The equillibirum potential for an ion at a given concentration difference acroos a membrane
What is the goldman equation
Used to calculate the diffusion potential when the membrane is permeabke to several differentions
What is the refractory period?
- When another Action potential cannot be generated in an excitable cell
what happens in the propogation of an action potential
An action potential excites the adjacent regions of the membrane, sending signals along the membrane
Explain the mechanism of propogation of Action potential
- The sodium influx in depolarised areas generate postive charges which spread along the axon
- These positive charges deoplarise the adjcant regions, opening the sodium channels and propogating the action potential further
What is the direction of propgation
An action potential travles in all directions from the stimulus point convering the enitre excitable membrane
What is the All or nothing principle
- One an action potential is triggered at a point at point on the membrane, it propogates across the enitre membrane if the conditions are favourable
If the condiitons are not favourable action potentil does not propogate
What are the key features of the All or nothing principle
For propogation to occur the acion potential must reach a certain voltage, to stimulate adjacent membrane areas
Explain the mylinated nerve fibres.
- Large with thick mylein sheath that surrounds the axon
What is myelin sheath formed by ?
Schwaan cells that create layers rich in sphingomylein
what is Saltory conduction
- Action potentials only occur at the node of ranvier
- impulses jump from node to node through extracelluler fluid
What are the advantages of Salatory conduction?
- Increased speed
- Energy efficient
