Module 2 Flashcards
How do neurons send messages?
Electrochemically
What gives charge to the cell?
Ions
How do we group ions?
Anions: negative
Cations: positive
How do ions move in or out of the cell?
Ion channels
Inside the cell
- Negative at rest
- Potassium (K+)
-Proteins (-)
Outside the cell
- Positive (+)
- Sodium (+)
- Chloride (-)
- Calcium (+)
Voltage
Difference between inside and outside of the cell
How do ions move?
Diffusion: Causes ions to spread towards a uniform concentration gradient
Electrostatic pressure: Causes ions to flow towards oppositely charged areas
The threshold
Minimum electrical charge needed to trigger an action potential
Depolarization
An increase in a neuron’s membrane potential, more positive
Hyperpolarization
A decrease in a neuron’s membrane potential, more negative
Gated
opens or closes in response to signals
Selective permeability
allows k but not na to enter and exit freely
Potassium leak channels
always open to k
Voltage-gated sodium channels and voltage gated potassium channels
gate is opened when neuron reaches a certain voltage
NA+/K+ Pump
Pumps out 3 NA+, brings in 2K+, repolarizing the membrane
Steps of the action potential
1) Resting potential
2) Sub-threshold depolarization
3) Depolarization
4) Absolute refractory/repolarization
5) Relative refractory/hyperpolarization
6) Return to rest
How do voltage-gated
sodium and voltage-gated
potassium channels
contribute to the different
phases of an action
potential? Be specific.
Depolarization Phase: Voltage-gated sodium channels open, allowing
Na+ ions to flow into the neuron, causing the membrane potential to
become more positive.
Repolarization Phase: Voltage-gated sodium channels close and
voltage-gated potassium channels open, allowing K+ ions to flow out
of the neuron, returning the membrane potential to a more negative
value.
Hyperpolarization Phase: Voltage-gated potassium channels remain
open slightly longer than necessary, causing an overshoot in the
membrane potential to more negative values before stabilizing at the
resting membrane potential.
Types of dendritic spines
Stubby: Very small, precursor to other spines
Mushroom: More stable and can last for months, the in between
Filopodia: More than 2 micrometers
Electrical synapses
Potential jumps directly to postsynaptic region without using chemicals
Neurotransmitters
Chemical messengers that are sent from the presynaptic neuron to the postsynaptic neuron.
Synaptic transmission events
1) Action potential arrives at the axon terminal
2) Voltage-gated calcium channels open and CA2+ ions enter
3) Synaptic vesicles fuse with the membrane and release transmitter into the cleft
4) Transmitter crosses the cleft and binds to postsynaptic receptors which opens the ion channels
5) Ion flow creates local EPSP or IPSP in the postsynaptic neuron
6) Transmitter is inactivated by enzymes
7) Transmitter may activate presynaptic auto receptors, decreasing its release
Exocytosis is mediated by specialized proteins
SNARES and synaptotagmin
Ligands
Fit into receptors binding sites to activate or block them
What do the postsynaptic transmitters determine?
The action of the transmitter
How do ligands bind ?
Endogenous ligands: Neurotransmitters and hormones produced by the body
Exogenous ligands: Drugs and toxins from outside the body
Agonists
Drug or toxin that mimics a neurotransmitter, elicits response
Antagonists
Drug or toxin that interferes with neurotransmitter, blocks response
Ionotropic receptors
Ligand-gated ion channel opens when bound by a transmitter
Metabotropic receptors
Activate G proteins when bound by a transmitter
EPSPs
Excitatory post-synaptic potentials caused by an influx of cations which depolarizes the membrane leading to an action potential.
IPSPs
Inhibitory post-synaptic potentials caused by an influx of anions which hyperpolarizes the membrane making it less likely to fire an action potential. (Results from chloride ions entering the cell, making it more negative).
End of synaptic transmission
Degradation—rapid breakdown by an enzyme, e.g., acetylcholinesterase
(AChE) breaks down ACh and recycles it.
Reuptake—transmitter is taken up by presynaptic receptors called
transporters.
Autoreceptors on presynaptic membrane bind transmitters; inform the
cell about transmitter concentration in the cleft, which can be adjusted.
