MIDTERM 1 Flashcards
What is physiology
Study of the normal functioning of a living organism and its component parts.
How does a humans components / parts function, how do they do it?
What are the 4 key themes that are important in understanding physiology?
- Structure and Function
- Biological energy
- Information flow
- Homeostasis
For the levels of organization of an organism - start from most in to out
- Chemical - atoms, molecules, Na/K pump
- Cellular - neuron, lymphocyte
- Tissue - collection of cells (eg. connective)
- Organ - structural unit made of tissues (eg heart)
- Organ System - integrated group of organs
- Organism - individual form of life
What are current researchers of physiology focused on.
We already know the answers to questions on the organ level - function of the heart for ex.
Thus research is focused on the cellular and molecular level - we want to deepen our understanding by focusing on cells and how they influence neighboring cells, tissues, organs, and organ systems.
what do cells in the body assemble into?
tissue
what are cells held together by?
cell junctions
name 3 types of cell junctions
anchoring junctions, gap junctions, tight junctions.
Name the 3 types of anchoring junctions and their funcion
desmosomes and adherens - support between two cells
hemidesmosomes - anchor to the bottom (basal lamina) keeping it in place
describe tight junctions
keeping cells close and tight, this is important because you want regulation and control of nutrients entering cells. - this will in turn effect function of cells
describe gap junctions
allows direct cell-to-cell communication .
What is in between cells? and how is it created
Extracellular matrix - synthesized and secreted by cells in the tissue
what are the 4 primary tissue types in the human body
epithelial, connective, muscle, and neural.
Explain epithelial tissue
- Epithelial protect the internal environment of the individual.
- This tissue regulates the exchange of material between the external and internal environment. … any material that moves between these two environments must cross an epithelium
- Epithelia consist of one or more layers of cells connected to one another and to a basal lamina
List the 5 types of epithelia
- Exchange - rapid exchange of material (eg. gas exchange)
- Cilliated - hair-like projections, sweeping (eg. line airways and female reproductive tract)
- Secretory - sythesizes and release products into the external environment / blood (eg. mucous membranes)
- Transporting - selective transport of material (eg. bigger molecules than gas)
- Protective - found on surface of the body
what does stratified mean
laying on top of each other
what are the three shapes of cells + location
squamous - gas exchange in respiratory tract
cuboidal - ducts and glands
columnar - digestive tract
describe connective tissue
This is the material between cells - keeping things in place. Provides structural support and barriers, and has an extensive extracellular matrix that contain proteoglycans, collagen, elastin, and fibronectin
list the 5 types of connective tissue
- Loose - elastic tissue (eg. underlying the skin)
- Dense - strength is the primary function (eg. tendons)
- Adipose - contains adipocytes (eg white and brown fat)
- Blood - watery matrix lacking insoluble protein fibers
- Supporting - dense substances (eg. cartilage and bones)
describe muscle tissue
purpose is to contract and generate force and movement
List the three types of muscle
- Skeletal… responsible for gross body movement (major muscles)
- Smooth… responsible for influencing the movement of substances into/ our of/within the body (eg. organs)
- Cardiac… found only in the heart. contraction moves blood through body,
Describe neural tissue
carry information for one part of the body to another. There is very little ECM in neural tissue
what are the two types of cells in neural tissue
- neurons - carry info as electrical or chemical signals
- glial cells - supporting cells for neurons
what are the 10 main organ systems in the human body
nervous system
musculoskeletal system
circulatory system
respiratory system
immune system
endocrine system
reproductive system
digestive system
urinary system
integumentary system
T/F: Function and mechanism are two interrelated concepts in physiology
true
define function
the function of a system is the “why”
- why does this system exist
define mechanism
the process of a system is the “how”
- how does this system work?
How do people interrelate function and mechanism
Physiologist study MECHANISM (how) to understand FUNCTION (why).
What is homeostasis
it is the maintainance of a relatively stable internal environment.
your body is always changing slightly, thats why its relatively stable- its not static but rather always trying to regulate levels within a set point.
what is homeostasis a result of and how what does this lead to?
Homeostasis is acheived through the effect of different organ systems working together. This leads to the maintenance of similar conditions for all cells of the body.
Also the result of homeostatic control is oscullation around a set point - but this set point can change with time.
Define acclimatization
environmentally induced change in physiological function with NO genetic change.
it is acheieved through repeated exposure. - usually a short term change…
– what this means is youre not changing your genetics, youre chaging your set points … this is adaptation.
Explain whats happening to your body as you go to a hot place.
Your body will acclimatize to the weather. If you go to a hot place, your body will change to better adapt the environmental stress… failure to do this will disrupt the functioning of your body.
rather than your body always working to warm you up, it will adapt to try and naturally cool you down more.
what are the four basic mechansism of cell-to-cell communication
gap junctions, contact-dependent signal, local communication, long-distance communication
explain gap junctions
- Also known as direct cell-to-cell communication, this is where communication occurs between cells right next to each other connected by protein channels (connexons).
- What ever cell A is producing will flow into cell B but this can be regulated as gap junctions are capable of closing and opening.
They are also found in many cell types.
Explain contact-dependent signals
This type of communication is from the interaction between membrane molecules on two cells… its a physical binding to another cell because the ligand of one connects to the receptor of another.
eg. in immune cells
describe local communication
This is also known as communication with neighbouring cells as it occurs via paracrine and autocrine signals.
Paracrine: chemicals secreted by cells which act on neighbouring cells - act on immediate vicinity. eg histamine
Autocrines: chemicals that act on the cell that produce them.
explain long-distance communication
uses nervous and endocrine systems.
Nervous system uses a combination of chemical and electrical signals via neurohormone and neurotransmitters.
Endocrine system uses chemical signals - these signals are known as hormones. Signalling through blood - can send to cells on the other side of the body … long ways!
why do some cells respond to a chemical signal and others do not?
- Target cells have various receptor proteins
- Only the cell with the specific receptor will respond to the signal
This specificity is integral for regulation and control aka to maintain homeostasis
describe receptors
these are usually trans-membrane but can also be INTRAcellular (cytosolic or nuclear)
Describe intracellular signals
they are lipo-philic meaning they love lipids which is integral as the mem is made our of lipids and it has to get inside.
What are the three domains of trans-membrane receptors
- extracellular domain - involved in binding the ligand
- transmembrane domain - hydrophobic
- intracellular domain - involved in activating the cellular response which is triggered by a conformational change
T/F: it is just the signal that determines that type of response
FALSE! it is the receptor not just the signal that determines the type of response.
ANY molecule that can bind with the receptor and induce activity will elicit the response.
what are the three types of receptors
- receptor channel; ligan binding opens or closes a channel
- g protein coupled receptors; ligand binds to a gpcr open a ion channel or alters enzyme activity
- catalytic receptors
what are antagonist’s
these ligands do not allow a response from the binding, this can BLOCK receptors.., and is useful in drugs
what are agonist ligands
these are molecules that can bind to the receptor to signal the same response as the primary ligand.
eg. a signal can be endo, para, auto – it might be a primary ligand for a para signal BUT it can then go through the blood and be an agonist signal through endocrine signaling.
For diseases, if your body is not producing enough of a primary ligand what can you do?
a scientist can create a drug with an agonist signal to help you maintain normal function
List the steps to responses to chemical signals
- signalling molecule binds to receptor
- activated receptor interacts with molecules inside the cell to start a signal
- signal is carried to appropriate places inside the cell - signal transduction
- response occurs
T/F: Homeostasis is only controlled by long distance pathways
FALSE! Homeostasis may be maintained by local and long distance pathways.
What is local control
- This means that local change will initiate local response.
- The effects are exerted on neighbouring cells.
eg. paracrine control of blood vessel diameter in response to low o2
what is reflex control?
This refers to the reaction in one or more organs controlled from elsewhere in the body
This is initated by any long distance path of the nervous and/or endocrine system
What are some points to remember on homeostatic control systems?
- stability is a result of balance between input and output (oscilations)
- negative feedback returns variable to original condition
- homeostatic systems maintain similarity NOT consistency
- set points can be reset (NOT PERMANENT)
- Some variables are controlled more closely than others
- Most control systems require communication between cells
What are response loops a result of
Reflex control
What controls response loops
feedback pathways
What do response loops start / result in
start with a stimulus and result in a response
Explain NEGATIVE FEEDBACK LOOPS
-Negative feedback results in a change that OPPOSES or REMOVES the signal, thus RETURNING the variable to its original value
- It allows for homeostatic control, and keeps a system near or at set-point
- Because of this, it results in oscilation around the set point … eg blood pressure.
Give the 5 stages to a feedback loop
stimulus, sensor, control, effector, response
Give an example of negative feedback loop using body temp regulation
Stimulus: body temp exceeds 37 degrees ferenhite
Sensor: nerve cells in skin and brain
Control: temperature regulatory center in brain
Effector: sweat glands throughout the body
Response: increased heat loss
Explain a POSITIVE feedback loop
- in this feedback loop, the response sends a signal that REINFORCES the stimulus. This sends the variable even FURTHER from the set point until an EXTERNAL SIGNAL turns OFF the response
- this is NOT homeostatic, as the response reinforces the stimulus
- this type of loop sends the system temporarily out of control.
eg. labour, the babyd head pushing down on the cervix causes a pos feedback loop of oxytocin to be released and DELIVERY of the baby stops this loop.
What is feedforward control?
This is anticipatory control meaning your body is predicting that change is about to hapens so the response loop starts.
- this is done to PREVENT change.
eg. sight, smell or though of food - your body starts to salivate as its anticipating eating it.
Explain positive feedback when explaining a furnace.
House gets hotter , furnance does not turn off – YOU have to turn it off to stop the response… needs an external factor to turn it off
What are the two key control structures?
nervous system and endocrine system
What is the function of the nervous system
- Receive information: using sensory neurons (receptors) to receive from external environment
eg. in our eyes - we are receiving info, or our fingertips feeling the wood - Integrate information: organizes the info and brings it together with already stored info
- stimulus travels to the integration center where it deduces information. - Transduces information: sends appropriate signals to he appropriate target (mostly muscles or glands)
When does the integrate center go to? Where does the effect or response go?
- Afferent pathway
- Efferent pathways
What are the two main parts of the nervous system? What are they made up of?
- Central nervous system
- brain and spinal cord - Peripheral nervous system
- everything outside the brain and spinal cord
- consists of sensory (afferent) and motor (efferent) neurons
Where does the afferent pathways send signals to?
The brain
Where do signals sent from the efferent pathway go to?
Muscles, glands, outwards bc they are the response.
What are the two basic types of cells found in the nervous system
- Neurons
- Glial cells
What are the function of neurons
generate and transmit electrical impulses often over long distances
What are the 4 main parts of a neuron?
- soma (cell body)
- dendrites
- axon
- axon terminal
Explain the function of the soma
This contains the nucleus and all biosynthetic machinery. Thus it is the center of the chemical processes - keeping the cell functioning and alive.
What is the specific terminology for clusters of cell bodies in the nervous system?
clusters of soma in the CNS = nuclei
clusters of soma in the PNS = ganglia
What is a nuclei?
cluster of cell bodies in the CNS
what is a ganglia
cluster of cell bodies in the PNS
What are dendrites
slender processes that receive information
- then transmits electrical signal TOWARDS soma
What is the function of axon
this is the cytoplasmic extension that sends out information
- transmits electrical signals AWAY from soma
What is the terminology to describe a bundle of axons in the nervous system
bundle of axons in CNS forming a pathway = tracts
bundle of axons in PNS forming a pathways = nerves
What are tracts
a bundle of axons in the CNS
What are nerves
a bundle of axons in the PNS
What is the function of axon terminals
These are the ends of axons that build the connection between neuron and other cells.
They also participate as part of the synapse
Describe the structure and purpose of a pseudounipolar neuron.
These are somatic sensory neurons that detect touch, pain, and temperature.
The structure is the axon and dendrites fuse during development into a single process.
Describe the purpose and structure of bipolar neurons
These neurons are vital for smell/vision sensory neurons. They contain a single axon, and a single dendrite. Each extend outwards on opposite sides of the soma.
What are the purpose and structure of multipolar neurons.
These are the most common neurons, yet are apart of the CNS and efferent pathway.
They have a single axon and two or more dendrites.
(aka the typical way you think of a neuron)
Describe the function of afferent (sensory) neurons
- receive info from the receptor cells
- then they send sensory info TO the CNS
- cell bodies are located outside the CNS
- Long cytoplasmic extensions transmit info to cell within the CNS (interneurons)
Describe interneurons and their function
They are neurons located inside the CNS and make up 90% of all neurons.
These neurons transmit information signals WITHIN the CNS - either laterally with other interneurons or vertically to the brain.
The function of these neurons is to integrate (make sense of) information received from the afferent neurons and send these signals to efferent neurons.
Describe the function and location of efferent (motor) neurons
These neurons receive information from interneurons.
The cell bodies of these neurons are located within the CNS, and the cytoplasmic extentions transmit information to the effectors.
- the effectors carry out the message so they are typically muscles, glands, ect.
Using the classification of neuron function, describe the pathway from stimulus to response.
A stimulus is picked up by the afferent sensory neurons which are the sensors. These neurons then transmit the signal to the interneurons which are located within the CNS. The information sent from the signal is then integrated and understood (integrate center). Once the correct response from the brain has been decided, a signal is sent from the interneurons to the efferent sensory neurons. The efferent neurons will then send the signal to the effector - which would be muscles or glands that will illicit a response from the body.
Explain glial cells
These cells are associated with neurons… and while they do not actually carry electrical signals (info) over long distances- they instead communicate with each other and with neurons using electrical and chemical signals.
How do glial cells contribute to the function of neurons
- aid it nerve impulse conduction
- maintain the microenvironment around neurons
so while they serve no purpose in sending info, they may help in how its collected.
What are the PNS glial cells
Schwann cells and satellite cells
What are schwann cells
these are special glial cells that are wrapped around axons, this forms myelin which is layers of membrane.
Myelin acts as an electrical insulator.
And there are lots of schwann cells on an axon.
What is myelin
this is layer of membrane that can act as an electrical insulator.
What are satellite cells
These are non-myelinating schwann cells … meaning they do not wrap around anything but instead provide support for soma.
Support includes, maintaining environment, giving nutrients, or being the blood - tissue barrier.
what are the glial cells of the CNS
Oligodendria, astroglia, microglia, ependymal cells.
what do oligodendria (oligodendrocytes) do?
They are the CNS version of schwann cells, they wrap themselves around axons which forms myelin to insulate CNS axon.
What are astroglia (astrocytes)?
These are like satellite cells of the CNS.
They connect blood vessels and neurons, and maintain neuron microenvironment- which helps maintain homeostasis in ECF around neurons.
what are microglia ‘s
these are very small specialized immune cells (macrophage-like). Thus they function to remove damaged or foreign invaders.
what are ependymal cells
these are epithelial cells that produce cerebral spinal fluid. they also create blood - brain barrier.
The pns is broken down into what parts?
sensory – motor
-
somatic , autonomic
-
sympathetic - fight or flight
parasympathetic - rest or digest
how do neurons transmit electrical impluses
via energy stored as electrochemical gradient
T/F: The human body is electrically neutral
True - the law of conservation of electrical charge states the amount of electrical charge produced in a process is zero.
what does the cell membrane do to charge?
it is an electrical insulator so it allows for the separation of charge
What is the net charge of the ICF and ECF
ICF is neg and ECF is pos, this difference in charge creates an electrochemical gradient,
what is membrane potential
its the difference of the electrical potential between the inside and outside of the cell . (# cations to # anions)
what are excitable tissue- and what do they do
They are specificially nervous and muscle cells that use rapid changes of membrane potential when they are excited .. this allows neurons to conduct an electrical signal and muscle cells to contract.
T/F: All cells have mem potential and are thus all excitable.
FALSE! All cells have mem potential- but NOT are all excitable .
What are two factors that determine membrane electrical properties
- unequal distribution of key ions between ICF and ECF
- eg Na, Ca, Cl are higher in ECF and K is higher in ICF
- anions (large neg proteins) higher in ICF - Selective movement of these ions across the membrane
- bc of their size, anions do not move across the mem
- [ ] of Na & K maintained by a ATP using pump to drive them against their gradient.
- ions can move through highly specific protein channels (passive or gated)
T/F: Na has an easier time moving passively due to the large number of passive channels of Na compared to K
FALLLLSEEE!!! Its easier for K to move passively due to the large number of passive channels for K compared to Na.
- K is always leaking out while Na are slowly moving in.
What is another name for membrane potential
equilibrium potential
What is equilibrium potential
this is the membrane potential that exactly opposes the concentration of an ion… therefore, the electrical and chemical forces are acting equal and opp on an ion.
T/F: you need a lot of ions to change the charge of the cell
NOOO FALSE! You do not need a lot of ions to change the charge of the cell, in fact its so little that the concentration grad is not disturbed at all.
explain equilibrium potential using the flow of Na into the cell.
As Na channels open, the [ ] grad and electric grad is causing the ions to flow in. But only a small # of ions is rqu to change the charge of the cell - SO NOW the electrical grad wants the ions out and the [ ] wants the ions in.
The two potentials are opposing each other
What is the equation to calc the electrical potential of the ONE ION that the cell needs to generate an equilibrium state.
Nernst equation - you need to know the [ ] grad
Why is the nernest equation not the greatest
it looks at what membrane pot would be if permeable to only one ions - but this is unrealistic to living systems where there are multiple ions that contribute to mem pot.
If the equilibirm pot for K in a typically neuron is approx. -90mV or +60mV, what does this mean?
This indicate the charge of the cell at equilibirum.
-/+ does not mean direction, it indicates charge
What is the equil pot for Na
+60 mV
What is the equil pot of K
-90 mV
What is the charge diff between the ICF and ECF at rest called?
Resting membrane potential
T/F: Only excitable cells have resting mem potentials
FALSE, diff types of cells have diff resting potentials…. however only excitable cells have the ability to change their RMP.
What happens if you change the environment of the body - such as increase K+ efflux?
The resting mem potentials will change … it will be more neg.
For a typical neuron what is the resting mem potential?
-70mV
Why is it called resting mem potential
Resting - bc mem potential is at a steady state… not changing
Membrane potential - the elect and chem gradients caused by ion distribution is a source of potential energy.
What happens if the membrane pot is disturbed
this is when a signal is sent / activity is happening
What sets the resting mem pot?
The concentrations of each of the ions and their relative permeability
- the more easily it can cross the mem, the more important it will be for the resting mem potential (eg. K)
- if the molecule cannot move across the mem, it does not contribute to RMP (eg Ca)
what equation would you use to predict mem pot using multiple ions
Goldman-Hodgkin-Katz
- this considers the mem permeability of each ion.
T/F: in the goldman-hodgkins-katz equation if a ion is not permeable to the mem you still consider it in the equation.
FALSE you Do NOt consider it in the equation
If you eat so sososo many bananas, what would happen on a cellular level?
The concentration of K would increase in the ECF, because of this, the leaking of the K from inside the cell would be slower (as [] is lower) – and the RMP would slowly become depolarized
On a cellular level, what would happen if you ate a lot of salty chips?
The concentration of Na would be higher on the outside of the cell, because of this, Na will really want to get into the cell. There may be more passive movement of the ions causing it to be more depolarized.
What happens if there is a change in the permeability of the cell to a given ion…
Then the ions will flow down its electrochemical gradient
WHat is trying to offset the passive movement of Na & K at rest?
Na / K pump
What is depolarization?
A decrease in the mem potential difference..
aka the cell mem potential becomes LESS neg (more pos).
eg. We see this as ion channels open for Na to come in, the cell as a result becomes depolarized.
What is hyperpolarization
This is an increase to the mem pot difference … the cell becomes MORE neg.
eg. Large potassium efflux causes hyperpolarization in the cell
How can the movement of ions be regulated
gated ion channels as they can open or close by stimuli
Describe mechanically gated channels
These are found in sensory neurons and open in response to physical forces (e.g stretch, tapping on a desk)
Describe ligand-gated channels
these have specificity of certain ligands onto receptors - that will elicit signals for a response.
(eg. ligand such as neurotransmitters attaching to specific receptor)
Describe voltage-gated channels
these respond to changes of voltage… and are thus important in initiation and conduction of electrical signals along the axon.
(eg. Cell is resting (-70mV) a signal comes and changes the mem pot (depolarization or hyp) a channel will open to try to get back to resting — eg of negative feedback aka trying to get it back to homeostasis)
There are 4 major types of selective ion channels in the neuron:
- Na channels - entry causing depolarization
- K channels - exit causing hyperpolarization
- Cl channels - entry causing hyperpolarization
- Ca channels - entry causing depolarization
what are the two types of signals generated by neurons
short distance signals — graded potentials
long distance signals – action potentials
T/F: Graded potentials can be depolarizing OR hyperpolarizing
True!
Where do graded potentials occur?
they occur in dendrites or cell body of neurons.
why are they called “graded” potentials?
because the size of the potential is equal to the strength of the triggering event
eg. light tapping = less channels = shorter signal strength
vs
hard tapping = more channels = stronger pot
How do graded potentials lose strength?
a) current leak - some pos charges leak back into ECF with the depolarization
b) cytoplasmic resistence - cytoplasm restricts flow of the current
what causes the ions to enter the cell?
initiated by neurotransmitters binding to mem receptors and opening ion channels
Why dont graded potentials ALONE ever have enough effect to create a response.
The graded potential signal diminishes in strength as distance increases
What are depolarizing graded potentials
They depolarize the cell mem, and bring it closer to the threshold potential.
These depolarizing graded potentials are called Ecitatory Post Synaptic Potentials (EPSP)… this is bc they INCREASE the chance of an action potential
What is threshold potential?
-55mV
what are hyperpolarizing graded potential?
They hyperpolarize the cell membrane potentials, and this takes the membrane potential FARTHER away from the threshold potential.
These hyperpolarizing graded potentials are called Inhibitory Post Synaptic Potentials (IPSP), this is bs they DECREASE the chances of an action potential.
T/F: signals can fight for how the neuron behaves
TRUE!
Neuron A can fire an excitatory and neuron B can fire inhibitory, they will fight for the neurons to behave a certain way. Depending on how strong the signal is the more hyper/de polarizing it is.
– if its very hyperpolarizing youre gonna need a lot of excitatory for the neuron to fire.
graded potentials travel only short distances, so how can a neuron carry a signal over long distances in the body?
ACTION POTENTIALS!!!
what are two different ways in which action potentials differ from graded potentials
- action potentials are identical, meaning no matter how strong the stimulus is - they will fire with the same strength everytime
- action potentials do not diminish in strength as they travel long distances through the neuron — signal is strong all the way!
Where do action potentials start?
At the trigger zone - also known as the integrating center of the neuron.
It has to be –55 AT the triggering zone, which is where the inhibiory or excitory come into play – they could cancel each other out which would not cause firing
Where is the trigger zone in afferent (sensory) neurons
they are adjacent to the receptors
in efferent neurons and interneurons, where is the triggering zone?
the axon hillock
T/F: While graded potentials dont have the strength for long communication, they can sum together at the trigger zone to trigger an action potential
TRUE
Graded potentials can sum over:
- Space: adjacent channels all getting the signal at the same time … the the waves combine together to get bigger signal
- Time: one receptor is receiving signal after sigal.. building that wave to the hillock
What are the phases of the action potential?
- resting membrane potential (-70mV)
- Depolarizing stimulus
- membrane depolarizes to threshold (-55mV), voltage-gated Na and K channels begin to open.
- Rising depolarization phase -due to rapid Na entry. goes to max of +30mV.
- Na channels close and slower K channels open - its at peak AP
- Repolarization phase - K exits quicker results in mem potential traveling towards RMP
- Hyperpolarization phase (undershoot) becaise K channels remain open.
- Voltage gated K channels close, less K leaks out
- Membrane returns to resting permeability - retention of K and leak of Na into the axon brings membrane potential back to -70mV
Describe the structure of voltage-gated channels .. use Na as an example
Voltage gated channels have two gates to regulate the ion movement during an action potential.
- Activation gate, this is cloased at resting membrane potential to prevent Na influx
- Inactive gate, this is a ball and chain of amino acids on the cytoplasmic side of the mem and is open at RMP
What are the sequence of event impacting the voltage-gated Na channel
- RMP
- Depolarizing stimulus to -55mV stimulates the entire channel
- activation gate opens and Na enters the cell, causing further depolarization
- this causes more voltage gated channels to open
– this is a pos feedback loop bc if nothing occured, then gate would not close and Na would diffuse into the cell until no more driving force. - This is where the inactivation gate closes, the gate will swing and plug the whole… rmb reaching threshold triggers the whole channel but theres a delay on the movement of the inactive gate.
… this ends pos feedback and is at peach of action potential.
How does the membrane potential return to the resting level?
K ions leave the cell - which is the falling phase of action potentials
T/F: K channels open faster than Na channels
FALSE! They open slower than Na channels even though the threshold also trigers them at the same time.
They fully open (gating potential) around+30 mV - compared to fully open Na channels at -55mV
