Kapitel 11 Flashcards
A large family of membrane transport proteins that use the energy of ATP hydrolysis to transfer peptides or small molecules across membranes. (Figure 11–16)
ABC transporters
Membrane protein that responds to binding of acetylcholine (ACh). The nicotinic AChR is a transmitter-gated ion channel that opens in response to ACh. The muscarinic AChR is not an ion channel - but a G-protein-coupled cell-surface receptor.
acetylcholine receptor (AChR)
Rapid - transient - self-propagating electrical excitation in the plasma membrane of a cell such as a neuron or muscle cell. Action potentials - or nerve impulses - make possible long-distance signaling in the nervous system. (Figure 11–31)
action potential
Movement of a molecule across a membrane or other barrier driven by energy other than that stored in the electrochemical or concentration gradient of the transported molecule.
active transport
Glutamate-gated ion channel in the mammalian central nervous system that carries most of the depolarizing current responsible for excitatory postsynaptic potentials.
AMPA receptor
Carrier protein that transports two different ions or small molecules across a membrane in opposite directions - either simultaneously or in sequence. (Figure 11–8)
antiporter
Channel protein embedded in the plasma membrane that greatly increases the cell’s permeability to water - allowing transport of water - but not ions - at a high rate across the membrane.
aquaporin (water channel)
Long nerve cell projection that can rapidly conduct nerve impulses over long distances so as to deliver signals to other cells.
axon
Transport protein in the membrane of sarcoplasmic reticulum of muscle cells (and elsewhere). Pumps Ca2+ out of the cytoplasm into the sarcoplasmic reticulum using the energy of ATP hydrolysis.
Ca2+ pump (calcium pump - Ca2+ ATPase)
Opens in response to the raised concentration of Ca2+ in nerve cells that occurs in response to an action potential. Increased K+ permeability makes the membrane harder to depolarize - increasing the delay between action potentials and decreasing the response of the cell to constant - prolonged stimulation (adaptation).
Ca2+-activated K+ channel
Transmembrane protein complex that allows inorganic ions or other small molecules to diffuse passively across the lipid bilayer. (Figure 11–3)
channel (membrane channel)
Photosensitive protein forming a cation channel across the membrane that opens in response to light.
channelrhodopsin
Neuronal voltage-gated K+ channel that opens following membrane depolarization but during the falling phase of an action potential due to slower activation kinetics than Na+ channels; opening permits K+ efflux - driving the membrane potential back toward its original negative value - ready to transmit a second impulse.
delayed K+ channel
Extension of a nerve cell - often elaborately branched - that receives stimuli from other nerve cells.
dendrite
Deviation in the electric potential across the plasma membrane towards a positive value. A depolarized cell has a potential that is positive outside and negative inside.
depolarization
Combined influence of a difference in the concentration of an ion on two sides of a membrane and the electrical charge difference across the membrane (membrane potential). Ions or charged molecules can move passively only down their electrochemical gradient.
electrochemical gradient
Neurotransmitter that opens cation channels in the postsynaptic membrane - causing an influx of Na+ - and in many cases Ca2+ - that depolarizes the postsynaptic membrane toward the threshold potential for firing an action potential.
excitatory neurotransmitter
A supporting non-neural cell of the nervous system. Includes oligodendrocytes and astrocytes in the vertebrate central nervous system and Schwann cells in the peripheral nervous system.
glial cell
Neurotransmitter that opens transmitter-gated Cl– or K+ channels in the postsynaptic membrane of a nerve or muscle cell and thus tends to inhibit the generation of an action potential.
inhibitory neurotransmitter
Specialized membrane region at the base of a nerve axon (adjacent to the cell body) that is rich in voltage-gated Na+ channels plus other classes of ion channels that all contribute to the encoding of membrane depolarization into action potential frequency.
initial segment
Transmembrane protein complex that forms a water-filled channel across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients. (Figure 11–22)
ion channel
K+-transporting ion channel in the plasma membrane of animal cells that remains open even in a “resting” cell.
K+ leak channel
A long-lasting (hours or more) decrease in the sensitivity of certain synapses in the brain triggered by NMDA receptor activation. As the opposing process to long-term potentiation - it is thought to be involved in learning and memory.
long-term depression (LTD)
Long-lasting increase (days to weeks) in the sensitivity of certain synapses in the brain - induced by a short burst of repetitive firing in the presynaptic neurons. (Figure 11–44)
long-term potentiation (LTP)
Transmembrane ion channels that open in response to a mechanical stress on the lipid bilayer in which they are embedded.
mechanosensitive channels
Voltage difference across a membrane due to a slight excess of positive ions on one side and of negative ions on the other. A typical membrane potential for an animal cell plasma membrane is –60 mV (inside negative relative to the surrounding fluid). (Figure 11–23)
membrane potential
Membrane protein that mediates the passage of ions or molecules across a membrane. The two main classes are transporters (also called carriers or permeases) and channels. (Figure 11–4)
membrane transport protein
Neurotransmitter receptors that regulate ion channels indirectly through the activation of second-messenger molecules.
metabotropic receptors
Type of ABC transporter protein that can pump hydrophobic drugs (such as some anticancer drugs) out of the cytoplasm of eukaryotic cells.
multidrug resistance (MDR) protein
Insulating layer of specialized cell membrane wrapped around vertebrate axons. Produced by oligodendrocytes in the central nervous system and by Schwann cells in the peripheral nervous system. (Figure 11–33)
myelin sheath
Transmembrane carrier protein found in the plasma membrane of most animal cells that pumps Na+ out of and K+ into the cell - using energy derived from ATP hydrolysis. (Figure 11–15)
Na+-K+ pump (Na+-K+ ATPase)
Equation that computes relates the electrical potential (voltage) generated by differences in ion concentrations across a membrane.
Nernst equation
Specialized chemical synapse between an axon terminal of a motor neuron and a skeletal muscle cell. (Figures 11–37 and 11–39)
neuromuscular junction
Impulse-conducting cell of the nervous system - with extensive processes specialized to receive - conduct - and transmit signals. (Figures 11–28 and 21–66)
neuron (nerve cell)
Small signal molecule secreted by the presynaptic nerve cell at a chemical synapse to relay the signal to the postsynaptic cell. Examples include acetylcholine - glutamate - GABA - glycine - and many neuropeptides.
neurotransmitter
Subclass of glutamate-gated ion channel in the mammalian central nervous system critical for long-term potentiation and long-term depression. NMDA-receptor channels are doubly gated - opening only when glutamate is bound to the receptor and - simultaneously - the membrane is strongly depolarized.
NMDA receptor
Glial cell in the vertebrate central nervous system that forms a myelin sheath around axons. Compare Schwann cell.
oligodendrocyte
Use of genetically engineered channelrhodopsin and other light-responsive ion channels and transporters to modulate neuron function and hence analyze the neurons and circuits underlying complex functions - including behaviors in whole animals. (Figure 11–32)
optogenetics
A class of ATP-driven pumps comprising structurally and functionally related multipass transmembrane proteins that phosphorylate themselves during the pumping cycle. The class includes many of the ion pumps responsible for setting up and maintaining gradients of Na+ - K+ - H+ - and Ca2+ across cell membranes. (Figure 11–12)
P-type pumps
Transport of a solute across a membrane down its concentration gradient or its electrochemical gradient - using only the energy stored in the gradient. (Figure 11–4)
passive transport (facilitated diffusion)
Electrophysiological technique in which a tiny electrode tip is sealed onto a patch of cell membrane - thereby making it possible to record the flow of current through individual ion channels in the patch. (Figure 11–34)
patch-clamp recording
Neuronal voltage-gated K+ channel - open when the membrane is depolarized - with a specific voltage sensitivity and kinetics of inactivation that induce a reduced rate of action potential firing at levels of stimulation only just above the threshold required - thereby resulting in a firing rate proportional to the strength of the depolarizing stimulus.
rapidly inactivating K+ channel
Electrical potential across the plasma membrane of a cell at rest - i.e. a cell that has not been stimulated to open additional ion channels than those that are normally open.
resting membrane potential
Glial cell responsible for forming myelin sheaths in the peripheral nervous system. Compare oligodendrocyte. (Figure 11–33)
Schwann cell
The part of an ion channel structure that determines which ions it can transport. (Figures 11–24 and 11–25)
selectivity filter
Carrier protein that transports two types of solute across the membrane in the same direction. (Figure 11–8)
symporter
Communicating cell–cell junction that allows signals to pass from a nerve cell to another cell. In a chemical synapse - the signal is carried by a diffusible neurotransmitter. (Figure 19–22) In an electrical synapse - a direct connection is made between the cytoplasms of the two cells via gap junctions. (Figure 11–34 and 19–23)
synapse
Changes in the strength with which a chemical synapse transmits a signal. It is thought to be important in memory formation - where concentrations of postsynaptic AMPA receptor are modulated in response to a synapse’s activity.
synaptic plasticity
Transport of solutes - such as nutrients - across an epithelium - by means of membrane transport proteins in the apical and basal faces of the epithelial cells. (Figure 11–11)
transcellular transport
Ion channel found at chemical synapses in the postsynaptic plasma membranes of nerve and muscle cells. Opens only in response to the binding of a specific extracellular neurotransmitter. The resulting inflow of ions leads to the generation of a local electrical signal in the postsynaptic cell. (Figures 11–36 and 15–6)
transmitter-gated ion channel (ion-channel-coupled receptor - ionotropic receptor)
Membrane transport protein that binds to a solute and transports it across the membrane by undergoing a series of conformational changes. Transporters can transport ions or molecules passively down an electrochemical gradient or can link the conformational changes to a source of metabolic energy such as ATP hydrolysis to drive active transport. Compare channel protein. (Figure 11–3)
transporter (carrier protein - permease)
Carrier protein that transports a single solute from one side of the membrane to the other. (Figure 11–8)
uniporter
Turbine-like protein machines constructed from multiple different subunits that use the energy of ATP hydrolysis to drive transport across a membrane. The V-type proton pump transfers H+ into organelles such as lysosomes to acidify their interior. (Figure 11–12)
V-type pumps
Type of ion channel found in the membranes of electrically excitable cells (such as nerve - endocrine - egg - and muscle cells). Opens in response to a shift in membrane potential past a threshold value.
voltage-gated cation channel
Ion channel in the membrane of nerve cells that opens in response to membrane depolarization - enabling K+ efflux and rapid restoration of the negative membrane potential.
voltage-gated K+ channel
Ion channel in the membrane of nerve and skeletal muscle cells that opens in response to a stimulus causing sufficient depolarization - allowing Na+ to enter the cell down its electrochemical gradient
voltage-gated Na+ channe
