the action potential Flashcards
what is a neuron?
a specialized type cell that is electrically excital
what kind of signals do neurons send?
electrical and chemical signals that permit fast communication
explain reticulor theory
believed that the brain was a physically connected network
explain neuron doctrine
believed that the brain was composed of individual cells communicating
name and explain different parts of neuron
- soma
cell body: location of the nucleus and other organelles - dendrites:
sites for receiving chemical or sensory input - axon
electrical signals (action potentials) are sent down the axon. only one axon, but that axon can branch many times. - axon terminal:
end of axon, where the action potent triggers the release of neurotransmitters
describe the neuron anatomy
phospholipid bilaye: cell membrane
ions cannot move across
what’s inside?
- cytosol
salty water-like solution
filled with potassium (K+), chlorine (Cl-), and sodium (Na+)
what makes a cell specialized?
- all cells within an organism have the same DNA
- not all cells read the same sections of DNA
- a section of DNA (the gene) codes for a certain protein
- neurons are filled with proteins that determine the cell’s respiration
how does transcription happen?
dna:
- string of nucleic
- in the nucleus (where it’s safe)
- strings of DNA = gene
mRNA:
- string of nucleic acid
- moved out nucleus to cytosol
how does translation happen?
mRNA:
- read by ribosome to make strings of amino acids (proteins)
Protein:
- string of folded up amino acids
- made in cytosol
- a functional protein = folded up amino acid chains
give examples of proteins
channels, pumps, receptors, transporters, messengers, scaffolds
how do neurons communicate?
electrical:
relies on membrane potential (Vm; difference in charges between inside and outside of cell)
down the axon
chemical:
- relies on neurotransmitters
- release from axon terminal onto other neurons
- at the synapse
what are ions?
molecules carrying electrical charge
name the cations (4)
- sodium (Na+)
- potassium (K+) (more abundant inside cell)
- calcium (Ca2+)
- magnesium (Mg+)
anion (1)
chloride (Cl-)
name the ion channels that set the resting potential
sodium potassium pump
potassium leak channel
explain the sodium potassium pump
sets the concentration gradient (the gradual change in the concentration of solutes in a solution as a function of distance through a solution) sends Na+ out the cell and K+ into cell
explain the potassium leak channel
channel allows K+ to move freely in/out of cell; K+ leaking out sets negative Vm (membrane potential). if there is a greater concentration gradient of K+ outside the cell, K+ will travel into the cell using these channels
what starts an action potential?
- when different ions cross the neuron membrane
-we then have a negatively charged cell - positive ions want to come because of electrostatic pressure (the force on two ions with similar charge to repel each other and the force of two ions with opposite charge to attract to one another). - sodium also wants to come in to move down the concentration gradient
- some depolarizing stimulus:
eg; neurotransmitters released from another cell, sensory stimulus . receptor binding opens ion channels, allowing initial influx of Mv
name the ion channels during the action potential
voltage-gated sodium channel
voltage-gated potassium channel
explain the voltage-gated sodium channel
Opens when the cell is slightly depolarized
(~-40 mV); responsible for initiation of action potential
explain the voltage-gated potassium channel
Opens when the cell is very depolarized
(~+60 mV); responsible for return to baseline Vm
name the ion channel at axon terminal
voltage-gated calcium channel
explain the function of voltage-gated calcium channel
Ca2+ into the cell triggers neurotransmitter
release
how does the action potential travel down the axon?
The arrival of positive ions at this node depolarises this section of the axon as well, initiating another action potential. This process is repeated, allowing the action potential to propagate rapidly along the axon, effectively ‘jumping’ between nodes. This ‘jumping’ mechanism is known as saltatory conduction.
why doesn’t the action potential work backwards?
- an action potential involves an influx positive charge into the cell
- the influx of positive ions pushes other positive ions away (down the concentration gradient)
- previously active voltage-gated Na channels are in refractory period (a period of time during which a cell is incapable of repeating an action potential.) (ball clogging pore)
- influx of positive ions cannot reopen them
how do we make the propagation of action potential more efficient?
myelination: the production of the myelin membrane that wraps axons in the central and peripheral nervous systems.
describe the glia and its components
astrocytes:
janitors of the cell
break down and clean up waste
provides scaffolding for other cellular functions
microglia:
provide immune support
regulate cell development and response to injury
oligodendrocy:
create myelin , wrapped around nearby axon
can provide sheath for 50 axons
Schwann cells = equivalent in peripheral nervous system
explain the saltary conduction
- insulation means the ion inside myelinated axon segments are insensitive to charge differences outside
- positive charge quickly travels down axon and in repropagated a nodes of Ranvier *(unmyelinated segments of membrane at which the action potential is repropagated)
what happens at the axon terminal?
Voltage-Gated Calcium Channel – open following depolarization, permit
Ca2+ entry
name the two main types of receptors
I O N O T R O P I C
Ion channels
Direct, fast effect on cell
potential
Excitatory
EPSP
Na+ permeable
Inhibitory
IPSP
Cl- permeable
M E TA B O T R O P I C
G-protein coupled receptors
Can act indirectly on ion
channels
Slower modification of cell
excitability
name the two way neurotransmitters get removed
reuptake and enzymatic deactivation
explain reuptake
Reuptake proteins transport
neurotransmitter back across
the membrane of the
presynaptic cell
Neurotransmitter can then be
repackaged into a vesicle for
another round of release
explain enzymatic deactivation
Enzymes (proteins dedicated to
destruction) break down
neurotransmitter in the synapse
explain metabotropic receptors
Metabotropic receptors
have lots of different
effects on the cell –
depends on the receptor
and the signalling cascade
its activation causes
