nerve/synapse lectures 1-2 Flashcards
what parts of nervous system are part of cns and pns
cns = brain and spinal cord
pns = everything else
describe CNS
central nervous system
info processing system centered in brain but involves all parts
brain processes and outputs
describe brain
biggest and most complex part of nervous system
what are the 2 components of peripheral system
input and output
brings info
describe input of pns
all sensory systems convey info about world into cns - from outside to inside
other sensory system = monitor inside of you - critical for internal milieu (homeostasis)
describe output of pns
enable you to act - cns connected to skeletal muscles = makes you have voluntary movements
autonomic nervous system = internal (makes intestines contract, etc), part of pns
how many neurons in nervous system
100 billion
what are neurons
electrical cells
Specialized
electrical properties = very diverse and at highest level
describe how neurons talk to each other
communication takes place at special sites called synapses
how many synapses in nervous system
hundred of trillions
creates neural network of vast complexity
approx 1000 synapses per neuron - many on all neurons
what is fastest that impulses can be sent
100 impulses/second = fastest that info moves around ~100m/s
carries out many functions at once
are neurons all the same shape and size
NOOOO
come in a large range of shapes and sizes
morphologically diverse
describe some neurons morphologically
perkinje = found in cerebellum, involved in coordination, leaves through axon
pyramidal = found in cerebral cortex (outer coating of brain, consciousness/perception)
what happens when neurons have more dendrites
more branches = more input synapses and places to communicate with other neurons
what characteristic structures do neurons share
cell body (soma)
branching dendrites
single axon (can be a few milimeters or more than a meter long)
describe polarization of neuron
in through dendrites - receive info from other neurons
goes out through axons towards presynaptic terminals
input and output generates impulse
describe soma of neurons
cell body
nucleus, DNA, ribosomes, protein synthesis
keeps cell alive
if crush cell body = dead
describe axon
can be long or short
enables communication
propagates info from one part to another - signals and many functions
describe flow of information through neuron
moves in certain direction
dendrites receive input from other axons
adds info together and makes decision if to send to another neuron
chain of info
describe resting membrane potential
inside typical neuron = -60 to -70 mV compared to outside
resting membrane potential caused by small excess of negatively charged ions inside cell
what is resting membrane potential used as
source of potential energy gradient to send info from one part to another
what is voltage
measure of electrical potential energy
kinda like pressure
describe electrical potential energy across neurons
neurons are surrounded by plasma membrane
electric potential energy differs across membrane - but its very small, 0.7 volts
what are millivolts
1/1000 of a volt
why is the inside of a neuron more negative compared to the outside
both the inside and outside have dissolved ions (like NaCl - dissociates)
tiny imbalance of negative charges inside so more negative on inside but not balanced by positive charges
can only be measure electrically - creates voltage gradient - essentially all cells have this
what is resting membrane potential created by
concentration gradients for various physiological ions
selective permeability of the resting membrane to K+ ions
how is concentration gradient for various physiological ions created
not spontaneous
gradients created by ATP
pumps Na+ out and K+ in
describe concentrations of ions inside and outside cell - gen
Na+ high outside cell and low inside - wants to flow in
K+ low outside and high inside
Cl- high on outside and low inside
Anions (A-) high inside = lots of negatively charged atoms (amino acids) floating around
describe concentrations of ions inside and outside cell - numbers
outside =
Na+ = 145mM
K+ = 5mM
Cl- = 100mM
A- = 50mM
inside =
Na+ = 10mM
K+ = 140 mM
Cl- = 5mM
A- = 145mM
positives and negatives on inside and outside equal each other, but inside has very little more negatives floating around
describe selective permeability of the resting membrane to K+
when neuron at rest = skin on outside is almost completely impermeable to ions (like Na+) - sodium wants to flow in but cannot
also less permeable to Cl- and anions
BUT IS HIGHLY PERMEABLE TO K+ IONS
describe why resting neuronal membrane is highly permeable to K+
a cell has a bunch of pores that are gated and only allow K+ through, they all open at same time and K+ flows out to outside of cell since low concentration of K+
what happens when pores open in membrane (what happens to K+)
ions leak out of cell down concentration gradient
leaves behind negatively charged atoms and these cannot flow since membrane is impermeable to them
do many K+ ions leak out of cell
NOOOO
outward movement of K+ stops rapidly and hardly any K+ will leak out before process stops
why does barely any K+ leak out
the more K+ moves out it attracts negative ions
creates an electrical gradient that pulls K+ back into cell (opposite direction, since attracted to negatives inside cell)
when do the gradients stop
when system is at equilibrium
concentration gradient (pushing out K+) = electrical gradient (pulling K+ back in)
rates will be equal
the membrane potential at equilibrium can be describe by what
nernst equation
find when - specific concentrations
describe nernst equation
measures voltage when electrical force is equal to concentration force
E(ion) = (2.3RT/zF) log (ion out/ion in)
R = gas constant
T = temp in kelvin
F = faradays constant
z = charge on ion
log of concentration on outside and inside
what is main factor for determine the neuron resting membrane potential
equilibrium potential for K+ (Ek)
- 90mV
equilibrium state when inside of cell is -90mV compared to outside of cell
describe ion channels
membrane protein with hole in centre
makes a pore/channel for ions
separate channels per ion
many are gated
what is resting permeability to K+ caused by
leak chanells
describe leak channels
proteins that form K+ selective pores through membrane
open at resting membrane potential
surface of neuron have many of these proteins
leak channels are leaky - even when membrane is resting K+ will still flow
what would happen if the membrane of the resting neuron were exclusively permeable to K+
voltage difference across membrane would be Ek = -90mV
but irl its closer to -70mV
what does each ion have
equilibrium potential
what is equilibrium potential determined by
the ions charge
internal and external concentrations
state equilibrium potentials for sodium, potassium and chlorine
Na+= +70mV
K+ = -90mV - has large influence since membrane is permeable to it
Cl-=-80mV
why is resting membrane potential a bit more positive than equilibrium potential for K+
due to small inward leak of Na+
pushes membrane slightly towards Ena
Na+ leaks in and trys to get potential to +70mV - makes it a bit more positive but too much since membrane is more permeable to K+
what is membrane potential determined by
concentration gradients and relative permeabilities of membrane to different physiological ions
do concentration gradients change much
NOOOO
do permeabilities change much
yes they can change rapidly and dramatically
what makes greatest contribution to the membrane potential
dominant permeability
at rest = dominant permeability is to potassium and membrane potential close to Ek
what is dominant permeability when neuron is at rest and active
rest = K+
active = Na+
