Chapter 4 - Excitable Cells Flashcards
Excitable Cells
cells that are able to send and receive electrical signals
Electrophysiology
study of excitability
Compartmentalization
having different homeostatic set points for a substance in two different regions of body or cell.
Gradient =
Gradient = [ion]out - [ion]in
Gating Mechanism
stimulus required to open or activate an ion channel
Voltage-gated ion channels
gated by changes in the relative distribution of changes in their local environment (senses positive and negative charges)
Ligand-gated ion channels
gated by a chemical messenger (a ligand) that binds to the channel on inside/outside of the cell
What kind of transport to ions do ion channels allow?
Passive
What is flux
flow of an ion between the 2 compartments
Which ions are more present INSIDE the cell?
Potassium (K+)
Which ions are more present OUTSIDE the cell?
Sodium (Na+), Chloride (Cl-), and Calcium (Ca+)
Membrane Potential
difference in charge between the two environments creating a form of potential energy
Nernst Equation
Eion = (61.5 mV/z)(log ([ion]out)/([ion]in))
Nissl bodies
sites of extensive protein synthesis
Anterograde transport
transportation of proteins and other materials from cell body to ends of both dendrites and axons
Retrograde Transport
From periphery back to the cell
Dendrites are filled with
cytoplasm and ribosomes
Dendritic spines
On dendrites and have a wide variety of ligand-gated and voltage-gated ion channels
Single axon arises from
axon hillock
Beginning of axon is termed:
initial segment/trigger zone (high density of voltage gated Na+ channels)
Axonal membrane is:
myelinated
Synapses
connections between neurons and target cells and stabilize
Three parts of synapse
presynaptic membrane (sends message), postsynaptic membrane (receives message), synaptic cleft (btwn the two; filled w/ interstitial fluid)
synaptic potential
a change in membrane potential produced on the post-synaptic membrane. Has ligand-gated ion channels (passive)
Graded potential
transient change from resting membrane potential that decreases in intensity over time and distance. Produced in dendrites and soma. Decremental
Action potentials
change from resting membrane potential that propagates over the excitable membrane and is maintained at constant intensity over time and distance. Produced in axon.
Most synapses are:
axodendritic synapses (formed btwn axon terminal of pre-synaptic cell and the dendrites of a post-synaptic cell)
Depolarization
EPSP; membrane potential increases, (+) sodium ions entering cell
Repolarization
membrane potential returning to normal level
Hyperpolarization
IPSP; membrane potential decreasing, (+) potassium ions leave cell
EPSP
excitatory post synaptic potential; a depolarizing synaptic potential
IPSP
inhibitory post synaptic potential; repolarizing synaptic potential
Temporal Summation
individual channel can be activated repeatedly over a short period of time, to cause greater change in postsynaptic potential.
Spatial Summation
Channels that are physically close together can be opened at the same time, to cause greater change in postsynaptic potential.
Subthreshold Potentials
synaptic potentials that do not depolarize membrane potential enough to reach threshold
Suprathreshold potentials
those that are strong enough to reach threshold
What kind of ion channels do axons have
Voltage-gated ions channels
Repolarization period is also known as
Relative Refractory Period
Inactivation period is also known as
Absolute Refractory Period. Action potential cannot be fired even w/ suprathreshold stimulus. Inactivation gate is open at resting potential.
Two major factors influence the speed of action potential propagation:
- axon diameter (wider = faster)
- Myelination (increased conduction velocity, schwann cells, oligodendrites, electrical insulator, internodes, nodes of Ranvier)
Internodes
myelinated axon segments
Nodes of Ranvier
gaps between internodes (action potential is recharged here)
Synapses can be either:
electrical or chemical
Agonists
chemicals that act like neurotransmitters at postsynaptic cell membrane and stimulate receptor
Antagonists
chemicals that block effects of neurotransmitters by inhibiting receptor
Neuromodulators
can alter the STRENGTH of signaling between neurons and can also affect cells a long distance away from sites of release.
Electrical synapses have:
Gap junctions that allow small molecules and ions to pass easily from cytosol of once cell directly into the cytosol of the next (both directions) cvbh
