nerves 2 Flashcards
what is the major ion that contributes to the RMP/resting membrane potential?
K / potassium( as there are more open K channels
According to Nernst’s equation of K+, the RMP for neurons should be approx -90mV, but that isn’t the case in reality.
Why is that?
it is -70mv due to the different membrane permeability to the ions
what happens when a action potential reaches it thresehold?
- causes opening on Na+ voltage gated channels
- Na+ goes in , causes depolarisation
-then Na+ channels close
what is the mv for when the threshold is reached ?
-55mV
describe the process of repolarization
-K+ voltage gated channels open
-K+ moves OUT
-causes repolarisation
how does hyperpolarization occur ?
due to K+ voltage gated channels being open longer than needed to
which potentials have a threshold , is it action potential or graded potential?
action potential , graded potential has no threshold- it tries to reach a thresold with EPSPs
what does the Nernest equation describe?
if the membrane was permeable to only one ion
what happens as graded potentials increase in their strength/ amplitude?
trigger more action potentials and therefore releasing more neurotransmitters
At the start of an action potential propagation the excitability of the cell is high, but once the action potential fires it drops to zero, and no action potential can be generated this is called the what?
absolute refactory period
Once the action potential passes through a location, it goes through a phase where the excitability of the cell slowly rises and the Na+ gated channels slowly recover and open, this is called the
relative refactory period
why are IPSPs and EPSPs fast?
as they use ion channels
what receptors do fast IPSPs and EPSPs use ?
ionotropic receptor
why are IPSPs and EPSPs slow ?
use G-protein-coupled receptors
what receptors do slow IPSPs and EPSPs use ?
metabotropic receptors
In the neuromuscular junction (NMJ) what does the presynaptic terminal contain within it?
contains aceytlcholine
where are the pacemaker potentials located?
in the heart
in the brain and spinal cord where is the grey and white matter located ?
brain-white matter on the inside and grey matter on the outside
spinal cord - white matter on the outside and grey matter on the inside
what distance do graded and action potentials travel?
graded potentials - short distance
action potential - long distance
How does the Na+ / K+ pump contribute to the resting membrane potential?
5mV contribution
makes inside more negative (2k+ pumped inside )
how is a compound action potential generated ?
axons based on their conduction velocity & degree of myelination
give 2 examples of demyelinating diseases and where they occur in the nervous system
multiple sclerosis in the CNS & gullian syndrome in the PNS
action potential encode stimulus intensity in their amplitude or frequency?
in their frequency
they encode a stronger stimulus by firing more action potentials
do action potential travel slowly on their own?
yes 1 m/s
what does the word decremental mean when referring to graded potentials
they diminish over time (like throwing a pebble into water)
compare the endplate graded potential in the NMJ and the graded potential in the CNS synpase
yes , it is always BIG enough to reach threshold and fire action potential
CNS synapse is synpatic integration therefore it may or may not reach threshold
what does the Goldman-Hodgkin-Katz (GHK) calculate
calculates all the ions that can cross the membrane
what is the neuromuscular junction synpase between?
motor neuron and skeletal muscle
what are the 2 ways to speed up an action potential ?
- large axons: allows Na+ channels to be wider spread along the membrane
- myelination: increases membrane resistance and decreases membrane capacitance so less current wasted
What are the consequences of demyelination?
decrease of membrane resistance and increase of membrane capacitance
Why does the cell permeability to Na+ increase more than usual as voltage gated Na+ channels open?
Because there is a positive feedback mechanism
Entry of Na+ leads to depolarization, which causes more voltage gated Na+ channels to open, increasing the cell permeability to Na+ even more.
describe the steps of a neuromuscular action potential formation
- Ca+ voltage gated channels open which causes the fusion of vesicles (Ca+ dependent exocytosis)
-Ach is released into the synpatic cleft & binds to its receptor :nicotinic receptor
-binding opens ligand gated channels , and causes Na+ voltage gated channels to open making Na+ enter the cell causing depolarisation and therefore action potential
-leading to the muscle contracting
(remember the endplate in NMJ is not synpatic integration so an action potential is always gonna happen)
in skeletal muscle where is Ca+ (calcium) stored?
stored in the sarcoplasmic reticulum
when is a Resting membrane potential generated ?
when there is a difference in charge on both sides of membrane - a leaky K+ channels causes this !!
what process are the neurotransmitters in the CNS released in?
Ca+ dependent exocytosis
can nitric oxide diffuse through the membrane ?
yes (its lipophilic)
where are the neurotramsitters GABA , Glutamate and Glycine located and are they excitatory or inhibitory ?
GABA is inhibitory neurotransmitter in the brain
glutamate excitatory in the CNS
glycine ihibitatory in spinal cord
describe convergent pathways
many presynaptic neurons influence a smaller number of postsynaptic neurons
describe divergent pathways
one presynaptic neuron influence a larger number of postsynaptic neurons
the 4 types of synaptic connections in the CNS are axo-denditic , axo-somatic and axo-axonal ,are they excitiatory or inhibitory ?
axo-dendritic - usually excitatory
axo-somatic -inhibitory
axo-axonal- can be ecitatory or inhibitory
