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2- cells electrochemical equilibrium is NOT possible (13 oct) (9-examples…
2- cells electrochemical equilibrium is
NOT possible (13 oct)
1-reason: membranes have multiple ion channels
so multiple ion gradients
we need to consider:
the relative permeability of each of these solutes and
their concentration gradient
membrane potential is the sum of conc. gra. and the permeability
for each of the ions tha memb. is permeable to
beca. any mov. of those ions will disrupt the eq. and memb. is not at eq.
we never have a situ. that any ion is at equi.
constantly ions are diffu. across mem. p
if memb. is much more permeable to K+ than Na+
K+ dominates the equ.
memb. potential will end up at a value close to the equ. for K+
if that changes and memb.
becomes more perm. to Na+
then the Na+ function dominates the overal equation and memb. potential switch and moves twards the equ.
but other ions are involved as well
comes down to relative perm. to that particular ion and what the con. gradient is.
this is goldman equation and more relevant to undestanding the memb. potential
what we have is steady state :star:
steady state: the memb. potential is not actually changing under normal condition>>>staying at constant value>>>
any movement of K+ into the cell is balanced by mov. of Na+ out of the cell and vise versa
2- memb. potential= -70 mV
Passive fluxes of Na+ into and K+ out of the cell
but memb. potential is constant
reason: Na-K pump takes the Na that diffused into the cell
and pumps it back out of the cell and pumps K+ back into the cell
so the situation is steady state situ.
3- Na - K pump
important to maintain steady state NOT electrochemical equi.
Na - K pump and memb. potential
maintenance of osmotic equilibrium
memb. pote.
creates very strong elec. field in the memb.
memb potential of -90mV over 10 nm memb.
scale that up to 1 m wide memb.
1 million volt memb.
any changes in memb. pot. can have a strong influence on electrical properties of ion channels and proteins and effect their function
5-generation of action potentials :star:
electrical signalling betw. nerve and muscle cells
resting memb. pot. is -60 or -70 mV
in nerve and muscle cells we can quickly
change the permeability of memb.
large and rapid change in mem. pot. which causes
action potentials
action potential
if you walk along and stub you toe
receptors in the toe
respond to that
generating action potential rapidly transmitted to cortex
travelling the whole length of the body in very small amount of time
that is enabled by fast transmission of action potentials
control the release of hormone from neuroendocrine
influence muscle contraction
encoding information through sensory sys.
6- we can inject the current in to the cell and manipulate the memb. potential artificially
we inject a positive charge or current into the cell
inside the cell becomes positive and then pasively comes back to the resting value
if we inject a large enough pasitively chaged ion or current into the cell>>> we reach critical treshhold value
we get a very large change in memb. potential
inside the cell becomes more positive than the outsode>>> quickly comes back to where it was before
rapid change in memb. potential=depolarisation
caused by the change in memb. potential>>>
causing a sudden change in the configuration of gated ion channes
suddenly changes the permeability of the membrane from K+ to being dominated by Na+
we get very rapid influx of positively charged ions
the region of the memb. where action potential is generated suddenly becomes more positive inside the cell compared to the ouside the cell.
quickly recovers back to its normal resting potential
7-ionic basis of action potential
sudden change of permeability from K+ to Na+ and back again to K+ bringing about the rapid change in memb. potentials
inject of current:
causes the influx of possitively charged ions in to the cell
ion channels adjacent to that and K+ channel are still close
but if we get a large enough change in membrane potentials
we reach the threshold value>>>>the electrical potential of that part of the membrane is large enough to activate or open the adjacent ion channels
wave of ion channels opening up
permeability to Na+ ion is much more than what it was before
very sudden change of relative permeability to Na
rapid mov. of ions down
their conc. grad. into the cell
inside of cell becomes positive
quickly Na gates become closed again
Na stops coming into the cell
delay in opening of voltage gated K channels
voltage gated K channels are activated by the same change in voltage that activated the Na channel but they are much slower- delayed in opening
1 more item...
read 2 slides about propagation of action potential
8-saltatory conduction :star:
we can speed up the process>>> huge number of ion channels that are opening and closing>>>> large changes in mov. of ions across the memb.
need a lot of pumping of Na-K pump in order to reestablish concentration gradients
energetically problematic
a way to make it much quicker and much metabolically efficient
with the presence of myelination :star:
myeln :star:
accessory cells that are wrapping around the out side of the axon- when we get depolarisation and we have a very high conc. of voltage gated Na channels >>> changes memb. potentials
spreads passively along the memb.
because of myeln layer that allows the PASSIVE DEPOLIRISATION to spred much larger distance
doesn't have to activate ion channels along this regions of membrane
it basically jumps down and causes the opening of ion channels in the next little junction between myeln sheets
in this situ. action potential propagates betw. ONE OF THESE REGIONS TO ANOTHER = NODES OF RANVIER :star:
speeds up the conduction of ion channels
improves the metabolic efficiency of the signalling process
9-examples of sensory receptors or sensitive cells and how they can transduce signalling energy from the environment into electrical signals
the basis of our sensory sys:
what these receptors are doing is transmitting or transducing some form of stimulus energy into electrical signalling in the form of action potentials
action potentials encode those sensory information
we have specialised ion channels on the memb. of the receptors
they respond to 4 different types of stimulus energy:
thermal sensitive receptors: respond in changes in temprature
photic: visual sys
chemical: chimo sensitive receptors gives us sense of taste and smell and other types of sensation
mechanical: give us perception of touch or mechanical gated ion chennels
all must have expression of specific types of ion channel sensitive or being gated by those mechanisms
pic: shows how sensory introduction processes work
we have specialised ion channel that some sort of stimulus (thermal, mechanical, photic, chemical) in some way imposes the opening of the ion channel
we have high conc. grad. for Na, usuallu Na or another +vely charged ion diffuses into the cell
causes a local change in membrane potential
if change is large enough
reaches a treshhold
large enough to causing a conformational change in the structure of ion channels
voltage gated Na channel will open up
1 more item...
so in this example we have 2 types of ion channel:
specialised ion channel that responds to stimulus energy
voltage gated Na+ channel
in the gustatory sys: sense of taste
specialised by little taste buds in our thong
expression of different ion channels in those taste buds that respond to different types of chemicals : chemo sensitive ion channels
Na cnc. in salty food activates ion channels
Na difuses through specialised selective ion channels
causes a change in membrane potentials : depolarises it
depolarisation causes the opening of voltage gated Ca Channels
Ca comes in and causes the release of the chemical signal : releasing the neurotransmitter
from this receptor cell>>> that bind to neuron in the form of action potentials
chemosensitive ion channels
expressed in taste receptors
photo: represents individual action potentials of that sensory nerve
by increasing the conc. of NaCl : stronger activation of receptor and higher frequency of action potentials
the more frequent the action potentials the stronger the stimulus or perception of the salty taste
photo sensitive receptors
receptors that respond to photic energy
different types:
Rod
gives us ability to see in low light condition
high sensitivity
cant distinguish colors
Cone
color distinguishing photo receptors
slower process but mediated by opening and closinfg of ion channels
compared to perception of taste
direct activation through a single ion channel
rhodupsin: photo sintetic pigment
absorbs the energy from light waves
that activates the G protein coupled pathway
GTP
activates the enzyme phosphodiesterase
couses the insactivation of cyclic GMP
cyclic GMP normally opens up the ligand gated Na channels
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detects photic energy
does so by transducing it into transsignal
does that by G protein couple pathway
mechanically gated channel
hair cells: perception of sound and perception of horizontal and linear acceleration
by spinning around activating these receptors
same types of receptors but give us different types of information
Hair cells are the basis of both auditory and
vestibular senses
receptor cells are similar
very different perceptions or sensory informations
different perc. becau. of diff. ways these being activated
left cartoon: location of hair cells in the chochlear
tip of those embeded in the tectorial membrane
sound comes through and get amplified through the choclear
1 more item...
embedded in different structures
in the vestibular system if we tilt our head or rotate our head
we get activation of hair cells again
little tip links that are embeded in glatino structure very dense crystall by bending head we get the bending of hair cells with respect to the base of the hair cells and mechanical coupling and stimulation of them
informs us about the orientation of head with respect to gravity
photo : hair receptors have angled projectors or cilia
in the cartoon we have cilia with different length>>> they are linked together by tip links
one ion channel in one cilia is mechanically
coupled to an ion channel on the adjacent cilia
mechanical stimulus that causes the deflection of those hair cells ; becau. thet are mechanically coupled it causes the opening of mechano sensitive ion channels
once they are open up we have the diffusion of the positively charged ion
K+ diffusing into the cell>>> brings about a change in receptor cells
causes release of the neuro transmitter >>> binds to a neuron and action potential is generated there
