Week 1: Ion Channels, Resting Membrane & AP I Flashcards
What are the two main cell types in the nervous system?
Neurons and glial cells.
What are the primary functions of astrocytes?
Support neurons, anchor them to capillaries, regulate blood-brain barrier, mop up K+ and neurotransmitters.
What is the role of microglial cells?
Monitor neuronal health and transform into macrophages to remove debris.
What do ependymal cells do?
Line ventricles and help circulate cerebrospinal fluid.
Which glial cells form the myelin sheath in the CNS?
Oligodendrocytes.
Which glial cells form the myelin sheath in the PNS?
Schwann cells.
What is the function of satellite cells?
Provide support to neuronal cell bodies in the PNS, similar to astrocytes.
Define afferent neurons.
Neurons that carry sensory information to the CNS.
Define efferent neurons.
Neurons that carry motor commands from the CNS to muscles.
What are interneurons and their types?
CNS-only neurons; local (short distances) and projection (long distances).
What is the function of neuroendocrine cells?
Release hormones into the blood to affect distant organs.
What is the integration zone of a neuron?
Axon hillock, where action potentials are initiated.
What structures make up the neuronal cytoskeleton?
Microtubules (transport), neurofilaments and microfilaments (rigidity).
What are Nodes of Ranvier?
Gaps in myelin sheath that facilitate saltatory conduction.
What structures make up a typical neuron?
Dendrites, cell body, axon, and axon terminals.
What are the three main regions of ion channels?
Funnel-shaped entrance, central pore, and exit region.
What determines ion movement through a channel?
Whether the channel is open, the concentration gradient, and the electrical gradient.
What are non-gated ion channels?
Channels that are always open, allowing passive ion flow.
How do chemically-gated ion channels operate?
Open in response to binding of specific ligands like neurotransmitters.
Where are chemically-gated channels typically located?
At synapses between neurons.
How do voltage-gated channels work?
Open or close in response to changes in membrane potential.
What is a mechanically-gated ion channel?
Opens or closes in response to physical deformation like pressure.
What does it mean when a channel is refractory?
It is closed and cannot reopen until reset.
List one reason a channel may become refractory.
Voltage, binding of a chemical, or removal of an activating chemical.
What is ion selectivity in channels based on?
Charge and hydrated size of the ion.
Why can’t Na+ pass through K+ channels?
Hydrated Na+ is larger than hydrated K+.
Why are channels passive transporters?
Ions move along concentration and electrical gradients without energy.
What is the role of protein subunits in ion channels?
They form the structure and determine selectivity.
Which ion channel type is involved in sensory reception?
Mechanically-gated ion channels.
What is the significance of the axon hillock?
It is the primary site for action potential initiation.
What is the typical resting membrane potential (RMP) of a neuron?
-70 mV.
What causes the resting membrane potential?
Unequal ion distribution, mainly K+ and Na+.
What is depolarization?
Decrease in membrane potential (more positive).
What is hyperpolarization?
Increase in membrane potential (more negative).
What equation calculates ion equilibrium potential?
The Nernst equation.
What does the Nernst equation consider?
Concentration gradient of a single ion.
Why is the resting potential closer to K+ equilibrium?
Membrane is more permeable to K+ at rest.
What is the Goldman equation used for?
Calculating membrane potential considering multiple ions.
Why can’t Nernst fully explain RMP?
It only accounts for one ion at a time.
What is the role of Na+/K+ ATPase pump?
Maintains Na+ and K+ gradients using ATP.
What are leak channels?
Always-open channels that allow ions like K+ and Na+ to passively move.
Why is the interior of the neuron negative?
Due to K+ efflux and impermeable anions.
What is an equilibrium potential?
The voltage at which an ion’s net flow is zero.
How does ion movement affect membrane potential?
Ions move down gradients, altering charge difference.
What ions are mainly involved in RMP?
Potassium (K+) and sodium (Na+).
What initiates an action potential?
A stimulus strong enough to reach threshold (-55 mV).
What ion influx causes depolarization?
Sodium (Na+).
What happens during repolarization?
Potassium (K+) exits the cell.
What is the peak membrane potential during an action potential?
Approximately +30 mV.
What causes hyperpolarization after an action potential?
Delayed closure of K+ channels.
What is the refractory period?
Time when a neuron cannot fire another action potential.
How is the RMP restored after an action potential?
Na+/K+ pump restores ion distribution.
What is the axon hillock’s role in action potentials?
Acts as the trigger zone for AP initiation.
What determines the strength of a stimulus?
Whether it reaches threshold and triggers an AP.
Why don’t weak stimuli trigger APs?
They fail to depolarize the membrane to threshold.
How do graded potentials differ from action potentials?
Graded are local; action potentials travel long distances.
What channel state prevents back-to-back APs?
Refractory (inactive) state of Na+ channels.
Why does K+ movement lead to hyperpolarization?
K+ efflux continues briefly after threshold is restored.
What direction does Na+ move during an action potential?
Into the cell.
How does the action potential propagate?
Sequential opening of voltage-gated Na+ channels.
