What gives a neuron its electrical properties?
The neural membrane (very thin, has lipids & proteins, communication abilities)
What is the function of the lipid bilayer?
Surrounds the cell and separates the cytoplasm from extracellular fluid
What do hydrophilic heads & hydrophobic tails do?
Hydrophilic heads attract water; hydrophobic tails repel water
What is the function of intrinsic proteins?
Serve as receptors and ion channels, aid in neuronal signaling
What type of membrane does the neuron have?
Selectively permeable
What can pass through freely?
Water & gases
What is polarization?
Difference in electrical charge between the interior and exterior of the cell
What is potential in a neuron?
Any change in a membrane’s voltage
What does polarization result from?
Membrane’s selective permeability
What force allows ions to flow from high to low concentration?
Diffusion force
What is the term for high to low concentration?
Concentration gradient
What causes ions to flow towards oppositely charged areas?
Electrostatic pressure
What type of gradient is created by electrostatic pressure?
Electrical gradient
What is the resting membrane potential (RMP)?
Difference in charge between the inside & outside of a neuronal membrane at rest
What causes the RMP?
Unequal ion distribution across the membrane
What is the typical value of a neuron’s RMP?
-65 mV
Why is the RMP negative?
More negative charges on the inside
What is the charge of the outside of the neuron?
Positive
Are neuron membranes permeable to large anions?
No
Which ion can enter and leave neurons freely?
K+
What direction do K+ ions move at rest?
They move into the negative interior due to electrostatic pressure
As K+ ions build up, which direction do they move?
They diffuse out along their concentration gradient
When is equilibrium reached?
When ion movement out is balanced by ion movement in
What are proteins that allow ions to pass in/out?
Ion channels
When are leak channels open?
All the time
What do gated channels respond to?
Voltage changes, molecules binding, or mechanical action
What are ion pumps?
Membrane-spanning proteins that require energy to move ions
Which ions are mostly outside the neuron?
Sodium (Na+), Chloride (Cl-), Calcium (Ca+2)
Which ions are mostly inside the neuron?
Potassium (K+) and organic anions
How permeable is the membrane to sodium ions?
Slightly permeable; they slowly leak in
What is the purpose of the sodium-potassium pump?
To maintain the RMP
How many sodium ions does the pump move out in one cycle?
3 sodium out
How many potassium ions does the pump move in during one cycle?
2 potassium in
What molecule blocks voltage-gated sodium channels in pufferfish?
Tetrodotoxin (TTX)
What is a graded potential?
Local potential that can be inhibitory or excitatory
Where does summation of graded potentials occur?
Axon hillock
When does an action potential occur?
When graded potentials exceed threshold
What happens to the inside of the cell during an action potential?
It becomes briefly positive
What is the all-or-none property?
An action potential fires only if threshold is reached
What happens to action potentials with increased stimulus strength?
They increase in frequency
What happens before threshold with excitatory graded potentials?
Voltage-gated Na+ channels open in response to depolarization
What happens as Na+ begins to enter?
More VG channels open, leading to increased sodium influx
What happens at threshold?
All VG sodium channels open and sodium rushes in
What occurs at the peak of the action potential?
VG Na+ channels inactivate
What happens when VG K+ channels open?
Potassium moves out, restoring RMP.
What is the term for when membrane potential dips below RMP?
Hyperpolarization
What is the absolute refractory phase?
No more APs can be produced due to inactivated Na+ channels.
What is the relative refractory phase?
Only strong stimulation can produce an AP due to continued outward K+ diffusion.
What is myelin's purpose?
Insulates axons, covering Na+ channels except for Nodes of Ranvier.
What are the gaps between myelin segments called?
Nodes of Ranvier
What is the term for potential jumping node to node?
Saltatory conduction
Do unmyelinated PNS axons receive support?
Yes, from Schwann cells.
Why do APs travel in one direction?
The refractory state of the membrane post-depolarization.
What is special about the Nodes of Ranvier?
VG Na+ channels are clustered here for recharging the AP.
What is the mechanism of injury in Multiple Sclerosis?
Oligodendrocyte injury from autoimmune attack.
What is the pathway for reactive gliosis?
Disease/injury leads to microglial/astrocytic activation, inflammation, necrosis.
What are the components of a synaptic cleft?
Presynaptic neuron, postsynaptic neuron, synapse.
Which ion do VG channels open for at axon terminals?
Calcium (Ca+2)
What happens when calcium enters the cell?
Synaptic vesicles fuse with presynaptic membrane and release neurotransmitter.
What are the two types of postsynaptic potentials?
EPSP (excitatory) and IPSP (inhibitory).
What does EPSP do?
Causes small local depolarization, moving closer to threshold.
What does IPSP do?
Causes small local hyperpolarization, moving away from threshold.
What kind of potentials are EPSP and IPSP?
Graded potentials.
How does a neuron decide to fire?
EPSPs and IPSPs are summed at the axon hillock; if threshold is reached, AP occurs.
What binds to decrease presynaptic release?
Autoreceptors.
What are the mechanisms for NT inactivation?
Degradation, reuptake, recycling.
What is an example of NT degradation?
Acetylcholinesterase (AChE) breaks down acetylcholine (ACh).
Which glial cell is associated with NT recycling?
Astrocytes.
What is the chemical pathway for glutamate recycling?
Glutamate is recycled into glutamine and returned to presynaptic terminal.
What are electrical synapses?
A synapse in which IONS FLOW DIRECTLY through large channels into adjacent neurons--> faster, allows for synchronization, & saves energy
What is the most widespread inhibitory NT?
GABA
What is the most widespread excitatory NT?
GLUTAMATE
Oxytocin and vasopressin are what type of NTs?
Peptide
What are some of the amine NTs?
ACh, Dopamine, Serotonin, (Nor)Epinephrine
Which type of receptor directly opens an ion channel upon NT binding?
IONOTROPIC
What is another name for an Ionotropic receptor
LIGAND-GATED ION CHANNEL
Which type of receptor indirectly opens an ion channel upon NT binding via use of G proteins and activation of 2nd messengers?
METABOTROPIC
What are seizures?
They are a wave of abnormally synchronous electrical activity in the brain
What is channelopathy?
A genetic abnormality of ion channel(s)
Which test is a recording of brain potentials?
Electroencephalogram (EEG)
What is characteristic of tonic-clonic seizures?
Slow & rhythmic/spastic contractions -->followed by confusion/sleep
What are absence attacks/seizures characterized by?
Generalized activity for a few seconds but 100s of times/day-->people usually stop and stare-->events not remembered post-seizure
What is the rarest type of seizure?
SIMPLE PARTIAL
What is the most common type of seizure in kids/teens?
COMPLEX PARTIAL (awareness impaired but abnormal activity localized
What does simple vs. complex mean?
What does simple vs. complex mean? Simple normal awareness; Complex awareness impaired
What gives a neuron its electrical properties?
The neural membrane (very thin, has lipids & proteins, communication abilities)
What is the function of the lipid bilayer?
Surrounds the cell and separates the cytoplasm from extracellular fluid
What do hydrophilic heads & hydrophobic tails do?
Hydrophilic heads attract water; hydrophobic tails repel water
What is the function of intrinsic proteins?
Serve as receptors and ion channels, aid in neuronal signaling
What is the resting membrane potential (RMP)?
Difference in charge between the inside & outside of a neuronal membrane at rest
What direction do K+ ions move at rest?
They move into the negative interior due to electrostatic pressure
As K+ ions build up, which direction do they move?
They diffuse out along their concentration gradient
What happens before threshold with excitatory graded potentials?
Voltage-gated Na+ channels open in response to depolarization
What is the relative refractory phase?
Only strong stimulation can produce an AP due to continued outward K+ diffusion.
What is special about the Nodes of Ranvier?
VG Na+ channels are clustered here for recharging the AP.
What is the mechanism of injury in Multiple Sclerosis?
Oligodendrocyte injury from autoimmune attack.
What is the pathway for reactive gliosis?
Disease/injury leads to microglial/astrocytic activation, inflammation, necrosis.
What happens when calcium enters the cell?
Synaptic vesicles fuse with presynaptic membrane and release neurotransmitter.
How does a neuron decide to fire?
EPSPs and IPSPs are summed at the axon hillock; if threshold is reached, AP occurs.
What is the chemical pathway for glutamate recycling?
Glutamate is recycled into glutamine and returned to presynaptic terminal.
What are electrical synapses?
A synapse in which IONS FLOW DIRECTLY through large channels into adjacent neurons--> faster, allows for synchronization, & saves energy
Which type of receptor indirectly opens an ion channel upon NT binding via use of G proteins and activation of 2nd messengers?
METABOTROPIC
What is characteristic of tonic-clonic seizures?
Slow & rhythmic/spastic contractions -->followed by confusion/sleep
What are absence attacks/seizures characterized by?
Generalized activity for a few seconds but 100s of times/day-->people usually stop and stare-->events not remembered post-seizure
What is the most common type of seizure in kids/teens?
COMPLEX PARTIAL (awareness impaired but abnormal activity localized
What does simple vs. complex mean?
What does simple vs. complex mean? Simple normal awareness; Complex awareness impaired
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