physiology uni 2.1

what is a chemical gradient? 1 pt

movement of particles from one side of a semi-permeable membrane depending on the concentration of the particles on both sides

what is the electrical gradient? 1 pt

movement of charged particles from one side of a semi-permeable membrane to the other depending on the balance of the electrical charges

what is the electrochemical gradient? 1 pt

movement of particles from one side of a semi-permeable membrane to another depending on the final balance of charges and concentration on each side

what are ion channels? 1 pt

membrane proteins that allow the passage of ions from one side of the membrane to the other

what are ligand gated channels? 1 pt

ion gate opens when the signalling molecule (ligand) signals the gate to open to allow the ions that are permeable to it in

what are voltage gated channels? 1 pt

each ion channel opens or closes at a certain membrane voltage

what are mechanically gated channels? 1 pt

ion channels that open in response to stretch, pressure, shear, and displacement of the membrane

what is membrane potential? 1 pt

the difference in electrical charge within the cell and outside the cell membrane

the interior ir negatively charged in comparison to the exterior

what is the resting membrane potential? 1 pt

-70mV

why is the inside of the cell more negatively charged than the outside of the cell? 3 pts

1. due to lots of negative charges inside the cell

2. a high permeability to K+ ions

3. Na/K+ pump takes out 3 positive ions and introduces 2 creating a negative net charge

what causes the movement of Na+ ions? 1 pt

the electrochemical gradient causes ions to move into the cell as most cells are impermeable to Na+

what causes the movement of K+ ions? 1 pt

the chemical gradient forces ions to move out of the cell however the electrical gradient opposes this

what is equilibrium potential? 1 pt

the membrane potential at which electrical and concentration gradient are balanced

at the equilibrium potential the net movement of that specific ion across the cell is 0 and membrane pontial tends to stay at the equilibrium potential

what does membrane potential depend on? 2 pt s

1. which ions the memrane is permeable

2. the concentration inside and outside the cell for each of these ions

what is the restin potential of most cells and why? 2 pts

1. resting membrane potential is -10mV

2. this is because of K+ that has the highest permeability in comparison to other ions and contributes the most to the resting membrane potential (K+ → -90mV)

what cells can modify their membrane potentials in response to stimuli? 3 pts

excitable cells which include:

1. neurons

2. muscle cells

3. sensory receptors

what sustains the resting potential? 1 pt

the Na+/K+ pump which uses 20% of our daily energy expenditure

what would happen if opened additional Na+ chances? 1 pt

Na+ has a strong tendency to enter the neuron down the gradient meaning multiple Na+ ions will be entering the cell and will make the potential more positive to be closer to Na+ equilibrium potential which is +65mV

what is depolarisation? 1 pt

voltage change that turns the potential more positive than -70mV

what is hyperpolarisation? 1 pt

voltage change that turns the potential more negative than -70mV

what is repolarisation? 1 pt

voltage change that returns potential to resting values -70mV

what are graded potentials? 1 pt

voltage changes of variable strength that travel over short distances and lose strength as they travel through the cell and their size depends on the strength of the stimulus

they can be inhibitory (hyperpolarization) or excitatory (depolarisation) and may lead to action potentials if strong enough

charactertistics of graded potentials? 2 pts

1. they can be inhibitory (hyperpolarization) or excitatory (depolarisation) and may lead to action potentials if strong enough

2. used for short distance communication in dendrites or the soma

3. occur at the dendrites or soma and several GPs can occur at once

what are action potentials? 1 pt

very brief large membrane depolarizations that travel for long distances through the aon of a neuron without losing strength

characteristics of action potentials?

1. constant intensity

2. used for long distance communication along the length of the axon

3. always excitatory (depolarization)

4. always has the same intensity

5. occurs around the axon and only one AP can be generated at a time

what threshold has to be reaches to trigger an action potential? 1 pt

-55mV

what are the two ion channels involved in action potentials? 2 pts

1. voltage gated Na+ channels (slower to close)

2. slow voltage gagted K+ channels (slower to open)

succession of events when generating an action potential? 7 pts

1. resting membrane potential- Na+ channel is closed by the activation gate

2. depolarizing stimulus arrives at the channel- if the graded depolarization reaches the -55 threshold the activation gate opens immediately

3. Na+ enters the cell massively- with the activation gate open Na+ further depolarizes the cell till it reaches +30mV (down the gradient)

4. the inactivation gate closes and Na+ entry stops- gate closes and depolarization stops

5. slow voltage gated K+ channels open- the inside of the cell is now positive and so K+ is pushed out of the cell down the electrochemical gradient bringing the potential down to -90mV hyperpolarizing the cell

6. the slow voltage gated K+ channels finally close- the neuron membrane goes back to its resting membrane potential and all variables are restored and the cycle begins

succession of events in 4 steps? 4 pts

1. resting state- voltage gated Na+ and K+ channels are both closed and the membrane is at -70mV

2. depolarization- the Na+ channels are open and Na+ influx through them depolarizes the membrane

3. depolarisation- K+ channels open and K+ leaves the cel making the potential negative again'; Na+ channels are closed by the inactivation gate

4. hyperpolarization- K+ efflux restores the potential and brings it down to -90mV, inactivation gates of the Ns+ channel open and voltage gateed K+ channels close; neuron returns to resting state

what is the absolute refractory period? 1 pt

voltage gated Na+ channels are closed and inactive meaning the potential can’t depolarize and a second AP cannot be triggered by the neuron

what is the relative refractory period? 1 pt

voltage gated Na+ channels are closed but can be opened if the depolarization stimulus is stronger the second time than it was the first time to reach the threshold

occurs due to continous outflow of K+ during hyperpolarization

what is the refractory period? 1 pt

when an area of the membrane is triggering an action potential becomes refractory and is unable to respond to a second stimulus, the minimum time period that prevents the generation of a second AP before the first has finished is the refractory period

what is the purpose of the refractory period? 1 pt

ensures the propagation of the APs is in one direction only (trigger zone to axon terminal)

where are action potentials generated? 1 pt

in the axon hillock where they travel down the aon

what is propagation/conduction? 1 pt

when the AP travels all the way down the axon

why does propagation occur? 1 pt

due to the entry of Na+ depolarizing the membrane and triggering the opening of the next voltage gated Na+ channels along the axon which carries the AP forward

propagation in unmyelinated axons? 1 pt

continous conduction- the AP has to regenerate in each part of the axon resulting in slower propagation

propagation in myelinated axons? 1 pt

saltatory conduction- APs are generated in the nodes of ranvier only where the voltage gated Na+ channels are concentrated; impulses travel faster are they “hop” from one node to another

what is propagation speed related to? 3 pts

1. axon diameter- bigger diameter = higher speed

2. myelination degree- myelin = faster propagation

3. distance between the nodes of ranvier (1-2mm) - longer distance = higher speed

4. temperature- higher temperature = higher speed

characteristics of APs? 5 pts

1. needs a stimulus over the threshold of -55mV

2. once threshold is reached the AP is always the same no matter what

3. stronger stimuli does not increase the amplitude but increases the triggering frequency

4. the amplitude does not diminish the distance of propagation through the axon

5. weaker stimulus = low frequency and little NT being released ; stronger stimulus = high frequency and more NT being released