Ch 9 Flashcards
Discuss the unique structures of the neuronal membrane
-double layer of lipids in which proteins are embedded
Discuss the functions of the neuronal membrane
-separates the intracellular and extracellular fluid
-each have their own ionic composition
extra
-outside
intra
-inside
hydro
-water
philic
-loves
phobic
-fears/dislikes
lipid component: structure
-double layer of phospholipids which have 2 ends
(polar & non-polar)
polar head
-hydrophilic
-loves fluids
-goes towards the intra and extracellular fluid
non-polar head
-hydrophobic
-fears/dislikes fluid
-away from fluid
tails
-face each other in the center of the membrane
lipid component: function
-this bilayer isolates the cytoplasm of the neuron from the extracellular fluid; it is not permeable to ions (diffusion barrier)
lipid component: function pt 2
-this layer also serves as a capacitor in that it is able to
store charges of opposite sign that are attracted to each other but unable to cross the membrane
protein component: structure
-some proteins are exposed on the outer or inner surface & some span the membrane
protein component: function
-regulate the movement of ions across the membrane
protein component: function (actively)
-pumping ions across the membrane
-occurs through proteins called ion pumps
-uses energy
protein component: function (passively)
-allows ions to flow down the concentration or electrical gradients
-occurs through ion channels
-does not require energy
ion channels can have:
-multiple states: open or closed
gating
-a mechanism by which ion channels switch states (open & closed)
voltage gated
-gate open/closes based on the changes in electrical membrane potential
ligand gated
-gate open/closes based on binding of neurotransmitters or hormones like ligand
thermally
-gate opens/closes based on
temperature of neuron
mechanically
-gate opens/closes based on
movement
selectivity
-ion channel’s ability to allow only certain ions through
resting membrane potentials
inside of a neuron
-more negative at rest
resting membrane potentials
outside of a neuron
-more positive at rest
resting membrane potential
- (-65 mV)
because of the imbalance at rest, the neuron is said to be ______ & ready to fire at any second
-polarized
the difference in electrical potential on either side of the neuronal membrane is due to
-differences in ion concentration
ion pumps
-aka other protein in the neuronal membrane
intracellular fluid contains many fixed ______ and this helps maintain a negative electrical charge inside the cell
-anions
additionally, membrane proteins called ion_____ use a process called ________ ________ to maintain intracellular negativity
-pumps
-active transport
active transport
-energy needed to move ions across cell membrane
this pump pumps ____ Na+ from the intracellular space to the extracellular space and pumps ___ K+ from the
extracellular space to the intracellular space
-out
-in
to do this, the pump uses energy in the form of adenosine triphosphate (____)
–ATP
for every __ Na+ that go out of the cell; only ___ K+ come into the cell, thus contributing to maintaining the negative charge on the inside of the cell
-3
-2
temporal summation
-the adding up of postsynaptic potentials generated in
the same neuron at slightly different times
spatial summation
-the adding up of postsynaptic potentials generated at
spatially separate sites on a neuron
first step of the action potential
-neuronal membrane begins at resting membrane potential (-65 mV)
second step of the action potential
-local excitatory state
first part of the local excitatory state
-neuron receives an excitatory input and cell membrane depolarizes
second part of the local excitatory state
-this change in voltage inside the cell causes voltage-gated Na+ ion channels to open so Na+ starts to flow into cell
second part of the local excitatory state pt 2
-concentration gradients move ions from areas of high concentration to low concentration
-electrical gradients move ions from areas of positive charge to negative & vice versa
third part of the local excitatory
-this changes the electrical gradient of the neuron since more positive ions
are coming to the cell
third step of the action potential
-threshold
threshold definition
-level of depolarization that results in an action potential 50% of the time OR “the point of no return
threshold
-sufficient depolarization occurs at -55 mV and leads to mass opening of voltage-gated Na+ channels
Na+ rushes in
fourth step of the action potential
-rising phase
-Na+ channels in open state
-mass increase in Na+ permeability: Na+ flows in rapidly
fifth step of the action potential
-spike peak: approximately +35 mV
-Na+ channels close
-K+ channels open
sixth step of the action potential
-falling phase
-K+ begins to flow out of the neuron down its concentration and electrical
gradient
seventh step of the action potential
-Hyperpolarization
-outward flow of K+ causes the membrane potential to dip below (and be
even more negative than) resting membrane potential
eighth step of the action potential
-resting membrane potential
-action potentials happen rapidly in an all-or-none fashion
characteristic of action potentials
-action potentials propagate with full amplitude
-they propagate with constant velocity
action potentials propagating with full amplitude
-passive spread of + voltage to adjacent areas of the axon
-this passive spread results in voltage-gated Na+ channel opening and another AP occurs in this
adjacent area
action potentials propagate with constant
-the specific velocity depends on features of
the axon
larger diameter axons have…
-increased velocity (less resistance)
myelinated axons have…
-increased velocity (more insulation)
saltatory conduction
-the nodes of Ranvier, which are exposed areas of myelinated axons, are home to a large number of voltage-gated Na+ channels
-voltage passively travels through myelinated axon sections until it reaches a node
-Na+ channels open at the node, producing another AP. As this keeps happening, velocity tends to “jump” forward to every node.
first step in conventional chemical synaptic transmission
-the neuron itself synthesizes/makes neurotransmitters
second step in conventional chemical synaptic transmission
-nts are concentrated and packaged in synaptic vesicles which are found in the presynaptic element or travel there by anterograde axonal transport
third step in conventional chemical synaptic transmission
-nts are released into synaptic cleft
-ap traveling down axon depolarizes the presynaptic nerve terminal
third step in conventional chemical synaptic transmission pt 2
-voltage-gated Ca2+ channels located in presynaptic terminal open
-Ca2+ enter
-influx of Ca2+ causes NT-filled vesicles to bind to active zones on neuronal membrane
-exocytosis occurs
exocytosis occurs
-nts are released into synaptic cleft
fourth step in conventional chemical synaptic transmission
-nts bind to ion channels in postsynaptic membrane
a. Ligand-gated ion channels either open or close, thus changing the permeability of the postsynaptic cell membrane
b. This is called postsynaptic potential and is an example of a graded, local
electrical potential
last step in conventional chemical synaptic transmission
-nt action is terminated in several ways:
a. NTs in synaptic cleft can diffuse away
b. NTs can be reabsorbed by presynaptic ending or by glial cells
c. NTs can be degraded by enzymes in the synaptic cleft
excitatory postsynaptic potential (EPSP)
-nts bind to ion channel on postsynaptic membrane
-ion channels open causing an influx of positively charged ions
-membrane is depolarized (becomes less negative), the EPSP
inhibitory postsynaptic potential
(IPSP)
-nts bind to ion channel on postsynaptic membrane
-ion channels open causing an influx of negatively charged ions or an efflux of positively charged ions
-membrane is hyperpolarized (becomes more negative), the IPSP
-inhibits generation of an AP by postsynaptic cell
myasthenia gravis
-an autoimmune condition where the body makes antibodies that attach to motor end plate ion channels and block acetylcholine from connecting to these receptors
-muscle weakness follows, usually in the face and limbs.
