Physical and Electrical Properties of Cells in the NS Flashcards
what is the main job of the neuron?
to transmit info
what are the 4 basic functions of a neuron?
receive, integrate, transmit, and transfer info
what is the soma and what does it do?
the cell body that integrates info
what are dendrites and what do they do?
projections from the soma that receive info
what is the axon hillock?
the connection b/w the soma and axon
what is the axon and what does it do?
long projection out of the soma that transmits info via the electric voltage potential that runs down the axon to the terminal
what is the axon terminal?
the end of the axon that forms a synapse with another neuron’s dendrites
what is myelin?
fatty and protein sheath that wraps around the axon
prevents current flow across axonal membrane
what maintains the shape of the neuron?
cytoskeleton proteins such as microtubules, neurofilaments, and microfilaments
what is axoplasmic transport?
old and new proteins transported up and down the axon
what is anterograde transport
new materials brought from the soma to the axon
what is retrograde transmission
old materials brought from the axon up to the soma
what is a unipolar neuron?
one projection from the soma
what is a bipolar neuron?
2 projections from the soma (dendrite and axon)
what is a pseudounipolar neuron?
a single projection from the soma that divides into two branches (one is dendrite, other is axon)
most sensory neurons (cell body in DRG, dendrite in organs, axons synapse in dorsal horn SC)
what is a multipolar neuron?
more than 2 projections from the soma (multiple dendrites and 1 axon
Purkinje cells
how are membrane channels classified?
the mechanism that opens them and the ions they conduct
leak channels
open and close at random
considered to be open all the time
contribute to the resting membrane potential
what are the 3 types of gated channels?
voltage-gated channels
ligand-gated channels
modality-gated channels
voltage-gated channels
opened by a change in the voltage
sodium, calcium, and chlorine move in
potassium moves out
what ions are concentrated outside the membrane?
sodium, calcium, and chlorine
what ions are concentrated inside the membrane?
potassium
ligand-gated channels
a molecule binds to the receptor and opens it
NT receptor can allow more than 1 ion through at a time
can be opened by a molecule inside or outside the cell
modality-gated channels
opens/closes in response to mechanical forces (stretch, acidity, chemical, etc)
electric potentials
difference in electrical charge on each side of the membrane with the inside being more negative than the outside
rapid changes in the electrical charge transmits info along the axon
resting, local, and action
resting membrane potential
no net flow of ions (neuron not in excited state)
about -70 mV (-90 to -60 mV)
maintained by the electrochemical gradient
what is the electrochemical gradient?
the ion concentration (chemical) gradient and electrical gradient determine the ion concentration across the membrane
what is the ion concentration (chemical) gradient and what does it do?
unequal distribution of ions with more ions concentrated inside the cell
more potassium inside, more calcium, sodium, and chloride outside
what is the electrical gradient and what does it do?
inside cell is more negative than outside the cell
organic anions (neg ions) trapped inside the cell
chemical and electrical gradients are equal and opposite forces at resting membrane potential
what 3 factors maintain the resting membrane potential?
chemical gradient, electrical gradient, and passive diffusion of ions
what is the flow of ions in and out of the cell using leak channels (passive diffusion)?
sodium leaks in and potassium leaks out because there is more sodium outside and more potassium inside and ions will flow from more to less
is energy expended to maintain the resting membrane potential?
yes, ATP is used to reverse the pattern of leak channels (sodium potassium pump pushes sodium out and potassium in against their concentration gradients)
3 sodium out, 2 potassium in
what are local potentials?
environment acts on neuron or neuron acts on neuron creating a local signal
depolarization or repolarization, no hyperpolarization
receptor and synaptic
what are receptor potentials?
outside environment is producing a signal on the neuron from peripheral receptors
outside signal stimulates receptor, membrane potential goes up, sodium channels open to make it more positive inside (depolarization).
what are synaptic potentials?
one neuron to another
what is a passive electrical signal?
higher stimulus=higher response
has a direct relationship b/w stim strength and stim response
local potentials
don’t last long and don’t produce APs
what is an active electrical signal?
more stimulus=more APs
threshold exceeded
stim strength affects # of APs
travel more reliably
what is temporal summation of local potentials?
1 neuron constantly sending synaptic potentials
a series of consecutive potentials sent onto a neuron summates to get past the threshold and fire APs
what is spacial summation of local potentials?
many neurons connected to 1 neuron send signals to that 1 neuron
gets past threshold to fire APs
need more than 1 source of input
action potentials
transient changes in membrane permeability
rapid and brief Na+ permeability
(sodium influx and depolarization)
- can react to slight changes in membrane potential
delayed and prolonged K+ permeability (K+ leaves the cell and repolarization occurs then as it keeps leaving the cell hyperpolarization occurs)
- needs a larger change in voltage than sodium
upstroke
opening
downstroke
closing
what is a refractory period?
period occurring during and after APs are fired
lasts a few milliseconds
limits max frequency of APs (longer period=lower frequency)
what is the difference b/w absolute and relative refractory periods?
during absolute refractory periods, no AP is possible due to the voltage inactivation of Na+ channels
during relative refractory period, an AP is possible with a greater than normal stimulus
properties of APs
all or none events
threshold (around 15 mV positive to resting) exceeded
constant amplitude
increased strength=increased frequency
how are axon potentials rejuvenated along unmyelinated axons?
Na2+ influx, K+ efflux=AP
Na2+ and K+ channels are all along the axon
current spreads back and forward
refractory period doesn’t allow the axon length behind the current fire AP
how do currents flow along myelinated axons?
Na2+ and K+ channels are only concentrated where there’s no myelination (nodes of Ranvier)
what are nodes of Ranvier?
areas of no myelination on myelinated axons
only place on myelinated axons that can produce APs
is myelinated or unmyelinated propogation faster and why?
myelinated propogation is faster bc it skips segments allowing the current to flow faster
myelin sheaths ____ conduction and ____ resistance
decrease; increase
how does axon diameter affect speed of AP transmission?
larger diameter axons increase conduction velocity of APs bc larger axons have more room for ions to flow without hitting the exoskeleton
what axons have the fastest transmission speed?
large diameter myelinated axons
afferent neurons
towards the CNS (from periphery (DRG) to CNS (dorsal horn))
peripheral sensory neurons
pseudounipolar and some bipolar neurons
efferent neurons
away from CNS (AP from ventral horn of SC to muscle at NMJ)
interneurons
connect afferents and efferents as well as among themselves
projection neurons
most abundant neurons
multipolar neurons
what is orthodromic conduction?
an AP flows from the soma to the axon
natural propagation of APs
same direction as anterograde
what is antidromic conduction?
an AP flows from the axon to the soma
E stim
same direction as retrograde
what is the antidromic conduction flow of sensory neurons?
dorsal horn to the DRG (CNS to periphery)
what is convergence of neurons?
one neuron getting lots of info from multiple neurons
can help identify what an object is
somatosensory cortex in the brain
what is divergence of neurons?
one neuron synapsing on different neurons
one stimulation can result in multiple responses
painful stimulus
what is the role of glia?
support and signaling, but not directly involved in conduction
what are the different types of macroglia?
astrocytes, oligodendrocytes, satellite cells, Schwann cells, and ependymal cells
astrocytes
CNS
neurotrophic factors, signaling among themselves, and act as phagocytes taking up ions outside the neuron
oligodendrocytes
form myelin sheath in CNS
satellite cells
PNS
cover the soma
nutrients
Schwann cells
forms myelin sheath in PNS
secrete neurotrophic factors, especially when injury is present
ependymal cells
CNS
secretes CSF
microglia
known to be essential in normal healing in the CNS
CNS demyelination
MS
PNS demyelination
peripheral neuropathy and Guillan Barre
positive neuroinflammation
reorganization, increased plasticity, tissue repair, and neuroprotective
immune surveillance, memory, learning, development, and injury induced remodeling
negative neuroinflammation
collateral damage, depression, anxiety, cognitive impairment, reduced plasticity, and neural damage
CNS injury, repeated social deficit stress, aging, TBI, neurodegenerative disease.
