-
nerurons
- send and receive
- electrical impulses (nerve
- impulses)
-
oligodendrocytes
- cells form the insulating myelin sheath around neurons of the CNS and peripheral
- nerves respectively
-
schwann cells
- cells form the insulating myelin sheath around neurons of the CNS and peripheral
- nerves respectively
-
dentrites
form branches around the neuron that receives signals
-
cell body
the main part of the neuron where all of the organelles are stored
-
axon
the part of the neuron that sends sigals
-
axon hillock
the beginning part of the axon
-
synaptic bouton
the end of the terminal
-
myelin sheath
fatty acids that cover the axon
-
node of ranvier
the part that are not covered by myelin
-
What is membrane potential?
why isn't it zero?
- the voltage difference across a membrane due to accumulation of ions with
- unbalanced charges
a few of the positive ions cross the membrane from right to left, leave their negative counterions behind
-
What is the relative distribution of the following ions inside and outside of a squid axon or a typical mammilian neuron: na+,k+,Ca2+,Cl-.
-
When leak channels for Na+,K+, or Cl- open, what is the direction of net ion flow?
-
As a result of these net ion movements
, would the membrane potential become more
positive or negative?
negative
-
What anions are found inside the cell?
k+ and Na+
-
What is an electrochemical gradient?
it is the imbalance of electrons
-
How do voltage gradient and concentration
gradient affect movement of charged vs. uncharged solutes across the cell
membrane?
they dont require energy if they are moving down the gradient, movement increased?
-
What is resting membrane potential?
- •MP at steady-state
- •Of all of the ions associated with generating the RMP, the permeability of the
- membrane to K+ is
- the most important.
- •K+ leak channels plays a major role
- in generating the RESTING MP.
- •The RMP for the squid axon is - 60mV.
-
The permeability of which ion plays the most
important role in generating the RMP? Why this ion?
- •Of all of the ions associated with generating the RMP, the permeability of the
- membrane to K+ is
- the most important.
- •K+ leak channels plays a major role
- in generating the RESTING MP.
-
What is an action potential?
-
How long does each AP take?
6 msecs
-
What are the four phases (one of them is resting
state) of an AP?
resting phase, depolarizing, repolarizing, hyperpolarizing
-
For a squid axon, what are the resting membrane
potential and the threshold potential?
-60 mV, -40 mV
-
For a squid axon, to what voltage does the
membrane potential depolarize? What is responsible for depolarization?
+40 mV, The opening of the sodium channels
-
For a squid axon, to what voltage does the
membrane potential hyperpolarize? What is responsible for repolarization and
hyperpolarization?
-73 mV, Na+ channels close and K+ channels open.
-
What are the activation gate and the
inactivation gate of a voltage-gated Na+ channel?
-
When (at what membrane potential or voltage) do
these gates open or close in an action potential?
- •Depolarizing phase: opening of voltage-gated Na+ channels (Na+ in)
- •Repolarizing phase: closing of inactivation gate of Na+ channels; opening of voltage-gated K+ channels (K+ out)
- •Hyperpolarizing phase (undershoot): K+ channels remain open
- •Reset to RMP: outward K+ flow stops; Na + leak
- inward
-
What are absolute and relative refractory periods, what is
responsible for these periods?
- •Absolute refractory period
- –Inactivation gate of Na+ channels is closed
- –Impossible to trigger a new AP
- •Relative refractory period
- –Membrane potential is
- hyperpolarized
- –Possible but difficult to trigger
- an AP
-
What is a graded potential? How does it differ
from an action potential?
(passive spread of depolarization)
The strength of depolarization decreases over distance as it is spread across the cell body.
-
What is special about the axon hillock?
It is where AP is initiated most easily
-
What would happen when the neuron is stimulated
by a subthreshold or a suprathreshold stimulus?
-
How is action potential propagated down the axon?
What allows the propagation to occur only in one direction?
- 1. At the start the membrane is completely polarized.
- 2. When an action potential is initiated, a region of the membrane depolarized. As a result, the adjacent regions becomes depolarized.
- 3. When the adjacent region is depolarized to its threshold, an action potential starts there.
- 4. Repolarization occurs due to the outward flow of K+ ions. The depolarization spreads, triggering an action potential.
- 5. Depolarizion spreads forward, repeating the process.
- •Refractory periods allow AP to be propagated forward only.
- •Absolute refractory period
- –Inactivation gate of Na+ channels is closed
- –Impossible to trigger a new AP
- •Relative refractory period
- –Membrane potential is hyperpolarized
- –Possible but difficult to trigger an AP
-
What does it mean when it is stated that “all AP
are equal” or “APs are all or none”?
They are equal in amplitude and occur at maximum level
-
How do axon diameter and myelination affect the rate of electrical conduction?
Large axons offer less resistance to current flow and myelinated axons conduct action potentials as rapidly.
-
What is special about the node of Ranvier?
High concentration of voltage-gate Na+ channels.
-
What is salutatory conduction/propagation?
- propagation of AP along myelinated axons
-
What are electrical synapses and chemical
synapses? Which one involves gap junctions? Which one involves
neurotransmitters? What is a presynaptic or a postsynaptic cell?
- Chemical
- synapse: neurotransmitters
- from presynaptic neuron diffuse
- across the synaptic synaptic cleft to bind to
- receptors in the plasma membrane of the postsynaptic cell
- Electrical
- synapse: one neuron (presynaptic) is connected to a
- second neuron (postsynaptic) via gap junctions (ions move through the junctions
- between the cells)
-
What are ionotropic receptors and metabotropic
receptors?
- isonotropic receptor-Ligand-gated ion channels
- metabotropic-Receptors that exert their effects indirectly via a system of messengers
-
When AP reaches the synaptic bouton, what events
occur to lead to the release of neurotransmitters?
-
What will happen when an excitatory or an
inhibitory neurotransmitter binds to the receptor on the postsynaptic cell? (Would
it depolarize or hyperpolarize the membrane? Would it increase or decrease the
likelihood of firing an AP? Which ion channels may open?)
Excitatory neurotransmitters lead to EPSP while
inhibitory ones lead to IPSP.
- •Excitatory signals bind to receptor that
- –Open Na+ or Ca2+ channels
- –Lead to depolarizing graded
- potentials or EPSP
- (excitatory postsynaptic potential)
- •Inhibitory signals bind to receptors that
- –Open K+ or Cl- channels
- –Lead to hyperpolarizing graded
- potentials or IPSP
- (inhibitory postsynaptic potential)
-
How is the strength (strong vs. weak) of the
stimulus processed by the neuron? How does it relay that information to
the target cell it innervates?
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