Nervous system Flashcards
What does a typical neuron have
some, one axon, one or more dendrites
what does the soma contatin
nucleus, er, golgi and ribosomes
what is the axon hillock
part of axon, typically where integration of the input is completed and the action potential is generated
how does the axon conduct information away from the soma
action potential
what is at the end of the axon branch
presynaptic terminals
what are the function of a neuron
input, integration, conduction, out, maintenance
Input
incoming synapses. can come into any part of neuron
integration
accomplished in dendrites and soma
-resulting info reaches axon hillock, decision about what info to conduct down axon is completed
conduction
information must be carried from the soma to the presynaptic terminals
output
usually in form of chemical synapse
-could also be paracrine, endocrine, or electrical synapse
maintenance
membranes and proteins used to process info must be replaced with new ones
kinesin
motor protein that drags vesicle of new membrane down the axon in an anterograde direction
dynein
motor protein that drags vesicle of old membrane down the axon in a retrograde direction
calculating equilibrium potentials
E-ion=60mV/(ion charge)log*(ion out)/(ion in)
what is equilibrium potential
when flow of ion out of cell due to concentration equals the flow into cell because of voltage
potassium voltage
flows out of cell because of concentration, flows back in because that makes the voltage in the cell negative and it attracts the positively charged K+
how the closing of channels determines flow of ions and membrane potential change
- if channels open, membrane potential goes towards the equilibrium potential for that ion
- if channels close, membrane potential goes away from the equilibrium potential for that ion
what determines the membrane potential of the cell
the concentration gradients and permeabilities of each ion
what is the membrane potential closest to at any given time
closest to equilibrium potential of the ion with the greatest permeability
what is the cell at when resting
K+ channels open, so the cell is near Ek, some negative membrane potential
-average is -70mV
hyperpolarization
changes that make the membrane potential more negative
depolarization
changes that make the membrane potential more positive
graded potentials
caused by inputs to the neuron
- can be on any amplitude
- spread across the membrane and decrease in strength the further from origin they are
action potentials
triggered by graded potentials
- all or nothing
- happen fast
- conduct down an axon
- have a refractory period
- time after one spike when another one either cannot occur (absolute) or has a higher than normal threshold (relative)
two different kinds of voltage gated channels that influence action potentials
voltage gated Na+
voltage gated K+
voltage gated Na+ channels
- active when they are depolarized because the gate is positively charged, and is pushed outwards as the inside of the cell becomes positive
- very fast
- causes positive feedback loop, continues depolarization
- Na+ gradient makes Na+ flow inwards
- inactivation occurs when the inactive gate closes as a result of depolarization
- slower gate, happens after active gate
Voltage-gated K+ channels
- active when the are depolarized because the voltage gate is positively charged, and it is pushed outwards as the inside of the cell becomes positive
- activate slowly
- K+ gradient makes K+ diffuse outward, so repolarizes/hyperpolarizes cell
- do not inactivate, cause hyperpolarization, close when membrane potential is below threshold
what is an action potential in terms of channels
sequential opening and closing of ion channels
- membrane potential will be closest to the equilibrium potential of the ion with the most open channels
- opening a channel causes Vm to move towards Eion and closinga channel causes Vm to move away from Eion
what happens at the peak of an action potential
greatest number of open Na+ channels, Vm close to Ena
what impacts how far current will travel in an axon
the larger the axons diameter, the more current will flow and the easier it will flow
- larger conduction velocity
- if membrane resistance is high (more difficult for the current to leave the axon). that’s why there’s myelination
nodes of ranvier
myelinated axon spaces where voltage gated Na+ and K+ channels are located. Action potential “jumps” from node to node
chemical synapse
an AP in axon depolarizes presynaptic terminal
- voltage gated Ca++ channels open near active zones
- increased cytoplasmic Ca++ causes exocytosis of neurotransmitter
- neurotransmitter diffuses across synaptic cleft
- NT receptors in postsynaptic cell respond
what does Ca++ do in the presynaptic terminal
the ca++ binding proteins in synaptic vesicle membrane cause membrane fusion in response to Ca++ (no calmodulin)
quantum
the entire content of each synaptic vesicle being released during exocytosis
how is ca++ removed
ca++-atpase pumps
where are the receptors for NT located
in the subsynaptic (post) membrane because NT is water soluble, not lipid soluble
things that affect the response of target cell
- number of receptors
- affinity of receptor
- concentration of neurotransmitter
- type of receptor present
EPSP
- voltage change in post-synaptic cell that causes the cell to be more likely to fire action potentials or causes it to release more neurotransmitter
- excitatory post-synaptic potential
IPSP
- inhibitory post-synaptic potential
- voltage change in post-synaptic cell that causes the cell to be less likely to fire action potentials or release neurotransmitter
the 8 h2o soluble neurotransmitters
- amino acids: glutamate, glycine, GABA
- monoamines
- -catecholamines (made from tyrosine): dopamine, epinephrine, norepinephrine
- made from tryptophan: seratonin
- made from histidine: histamine
- acetylcholine (monoamine)
type of synapse for acetylcholine
cholinergic
type of synapse for nor/epinephrine
adrenergic
temporal summation
summation of PSP that arrive at different times
-quick firings from one synapse to reach AP
spatial summation
summation of PSP that arrive at different synapses
amplitude coding
level of excitation in the soma is encoded by amplitude of the graded potentials
-represents summation of various PSP
frequency coding
translation of amplitude coding
- coding of action potentials at axon hillock
- frequency of action potentials increases as the amplitude of the graded potential increases
what do somatic motor nerves use as a neurotransmitter
acetylcholine
-called a cholinergic synapse
what are preganglionic and postganglionic synapses called in parasympathetic
cholinergic-use acetylcholine
what are postganglionic synapses called in the sympathetic system
adrenergic because they use norepinephrine
-preganglionic fibers are cholinergic
varicosities of axons
release neurotransmitter into tissue of organ, resemble paracrine secretion
