Chapter 13 Synapses

Muscarinic

Action of acetylcholine that is mimicked by muscarine, or receptors mediating the action. Contrast with nicotinic.

A cell has only two permeable ions: J + (EJ = -50 mV) and B+ (EB = +10 mV). 1,000 J+ channels are open, and 5,000 B+ channel are open. What should be the approximate membrane potential at equilibrium?

Between -20 and +10 mV

Inhibition

Decreasing the probability or frequency of action potentials.

Caffeine: (stimulant):

GABA antagonist

Metabotropic receptors

GPCR activation often results in activation of ion channels. Or a signaling cascade can lead to ion channel activation

A cell has only two permeable ions: J+ (EJ = - 50 mV) and B+ (EB = +10 mV). The resting membrane potential of the cell is -40 mV. Which ion has more leak channels?

J+

In a life or death situation, which of the following is not taking place?

Parasympathetic control of the heart rate

Induction of LTP:

The NMDA receptor allows Ca2+ flux when the post-synaptic cell is depolarized and it is bound to glutamate.

Chemical transmissions are terminated in many ways Uptake of neurotransmitter by nearby cell

(e.g. serotonin).

A neuron receives signals from five other neurons, A-E. Assuming local signal strength is equal, poisoning which synapse would result in the largest decrease of the neuron's likelihood of reaching threshold potential?

A

G protein-coupled receptor

A membrane receptor protein that, when it binds to its specific extracellular signal ligand, relays a signal into the cell by activating G proteins in the cell membrane.

Inositol trisphosphate (IP3)

A molecule derived from membrane phospholipids that acts as a second messenger in cell signaling

Diacylglycerol (DAG)

A molecule derived from membrane phospholipids that acts as a second messenger in cell signaling.

Habituation

A simple, non-associative form of learning characterized by a learned decrease in a behavioral response with repeated presentations of a nonthreatening stimulus.

Chemical synapse

A synapse that for signal transmission employs a chemical neurotransmitter that is released presynaptically and acts on postsynaptic neurotransmitter receptors

Excitatory postsynaptic potential (EPSP

A voltage change in a postsynaptic cell—normally a depolarization—that tends to excite the cell.

Synaptic facilitation

An increase in the amplitude of postsynaptic responses that occurs after repeated presynaptic action potentials.

Calmodulin (CaM)

An intracellular protein that binds calcium ions to form a Ca-CaM complex, which can then act as an intracellular messenger to affect other proteins.

Second messenger

An intracellular signaling molecule that is produced inside a cell in response to the binding of a chemically different extracellular signaling molecule to specific cell-membrane receptors.

Habituation:

Aplysia will initially withdraw its gills when they contact its own siphon. After this contact proceeds for many minutes, Aplysia will decrease this withdrawal behavior.

Unconditioned Aplysia withdraw their gills in response to electrical stimulation of their tails but not to tactile stimulation of their mantle.

By repeatedly presenting these two stimuli at the same time, scientists were able to condition Aplysia to withdraw their gills solely in response to tactile stimulation of their mantle. This response is mediated by longterm potentiation.

Synaptic plasticity

Change in properties of synapses or strength of synaptic interactions with time or circumstance. Changes of nervous system function during development or learning are thought to reflect synaptic plasticity.

Formation of long-term memories appears to be related to LTP as well as at least two other phenomena: (1) Gene expression:

Formation of long-term learning is prevented if, at the time an animal is being trained, neurons are presented with a protein synthesis inhibitor. Thus, protein synthesis appears to be required for formation of long-term memories.

A single EPSP from a sensory neuron is not sufficient to bring about an action potential in the postsynaptic cell. In addition, a nearby synapse causes an IPSP of relatively equivalent in strength to the EPSP. Which would most increase the odds of reaching an action potential?

If we trigger another EPSP quickly after the first

Neurotransmitter Release Step 2: Ca2+ triggers vesicle fusion and neurotransmitter release

Increased cytosolic Ca2+ activates vesicle fusion and exocytosis of synaptic vesicles.

Presynaptic inhibition (PSI)

Inhibition of a neuron by decreasing the amount of neurotransmitter released by an excitatory presynaptic neuron.

As you move your finger to touch your nose, specialized neurons called Purkinje cells in the cerebellum are receiving weak motor function signals from hundreds of thousands of other neurons. What aspect of Purkinje cells would you expect to be more extensively developed than other neurons?

More dendrites

Termination of neurotransmitter action:

Neurotransmitters are usually only active for a very short amount of time before they are terminated.

Excitation

Process tending to produce action potential

Scaffolding (or scaffold) proteins

Proteins that function to bring other proteins together in a relatively stable complex. Presynaptic terminals have scaffolding protein complexes involved in neurotransmitter release, and postsynaptic cells have scaffolding complexes mediating neurotransmitter receptor trafficking and action.

Multiple EPSPs can result in an action potential A single EPSP is not sufficient to bring the axon hillock to threshold

Temporal summation: If a single synapse is activated multiple times in a short span, these PSPs can also sum resulting in a more pronounced overall PSP.

Neurotransmitter Release Step 1: Arrival of action potential at terminal

The arrival of the AP terminal stimulates opening of voltage-gated Ca2+ channels, which results in and influx of Ca2+ into the cytosol.

Posttetanic potentiation

The augmentation of a postsynaptic potential following a period of rapidly repeated (tetanic) stimulation

Which of the following situations would interfere with the ability to discriminate whether a stimulus was light or touch?

The central nervous system can't tell which axon generated an action potential

Synaptic current

The current that flows through the postsynaptic membrane in synaptic transmission and produces a postsynaptic potential.

Prozac and Zoloft (anti-depressant):

block serotonin reuptake

Apamin (bees):

blocks Ca2+-activated K+ channels

α-Bungarotoxin (cobras):

blocks nicotinic ACh receptors

Dendrotoxin (mambas):

blocks presynaptic K+ channels

Brevetoxin (dinoflagellates):

blocks voltage-gated Na+ channels

Tetrodotoxin (puffer fish):

blocks voltage-gated Na+ channels

Unlike other stimulus receptors, those in the eye which have rhodopsin _____________.

cause hyperpolarization

Valium (anti-anxiety):

facilitates GABA binding

Neural control is __________ than endocrine control, and ____________.

faster, shorter-lasting

Argiotoxin (spiders):

glutamate antagonist

Monoamine oxidase inhibitors (MAOIs), e.g. Nardil (antidepressant):

inhibits enzymatic deactivation of monoamine neurotransmitters (e.g. serotonin, dopamine)

The equilibrium potential for Ca2+ (ECa) is +130 mV. When Ca2+ channels open in a resting neuron, Ca2+ should diffuse

into the cell

Electrical transmission: t

the cytoplasm of two neurons is connected via gap junctions, allowing the ions of the action potential to conduct directly into the effector neuron.

Where neurons and muscles meet The neuromuscular junction

the synapse between motor neurons and muscles, is the model system for fast synaptic transmission. For most skeletal muscles, each fiber is only innervated by one neuron. Acetylcholine is the neurotransmitter at the neuromuscular junction

β-Bungarotoxin (cobras):

permeabilizes axon terminal

Chemical transmission:

Unidirectional • Excitatory or inhibitory • Plastic

Resting membrane potential is -65 mV. ENa = +60 mV, EK = -90 mV, and ECl = -70 mV. Acetylcholine is considered an excitatory neurotransmitter. Which channel(s) might it activate?

Na+

Neuromuscular junction

The synaptic junction of a motor neuron and a muscle fiber.

Miniature EPSP (mEPSP

A small excitatory postsynaptic potential at a neuromuscular junction or postsynaptic neuron produced by presynaptic release of a single quantal packet of neurotransmitter.

Synapse

A specialized site of communication between two neurons, between a neuron and an effector, or between a non-neuronal sensory cell and a neuron.

Long-term potentiation (LTP)

A stable, long-lasting increase in the amplitude of the response of a neuron after it has been stimulated repeatedly by presynaptic input at a high frequency.

Electrical synapse

A synapse at which current spreads directly from cell to cell through a low-resistance gap junction.

Neurons transmit signals to each other

A synapse is the place where two neurons meet, which includes a small gap between the axon terminals of pre-synaptic membrane and the dendrites of the post-synaptic membrane (i.e. the synaptic cleft) and the post-synaptic membrane

Axodendritic synapse

A synapse of an axon onto the dendrite of another neuron.

Axosomatic synapse

A synapse of an axon onto the soma of another neuron.

Inhibitory postsynaptic potential (IPSP)

A voltage change in a postsynaptic cell—normally a hyperpolarization—that tends to inhibit the cell

Cotransmitter

In neurons that synthesize and release more than one kind of neurotransmitter molecule, the second kind of neurotransmitter.

Electrical transmission:

Faster • Bidirectional • Excitatory

Conotoxins

(marine cone snails): block Ca2+ channels, Na+ channels, nicotinic ACh receptors, and others?

ynapses change properties over time and with use Synaptic plasticity is the ability to change synaptic strength over time. This plasticity is believed to be an important mechanism in learning. Two basic examples:

1) Habituation: the decrease in intensity of a reflex response to a repeated stimulus 2) Sensitization: the prolonged enhancement of a reflex response to a stimulus, which results from a second stimulus that is novel or noxious.

Chemical transmissions are terminated in many ways Endocytic internalization

of the receptor.

Ionotropic receptors

Nicotinic ACh receptors allow both Na+ and K+ ion flow

Protein kinase

A regulatory enzyme that covalently bonds a phosphate group to a protein using ATP as the phosphate donor.

Cyclic adenosine monophosphate (cyclic AMP, cAMP)

A second messenger produced intracellularly in response to several neurotransmitters and hormones.

The neuromuscular junction vs neuron-neuron synapse

• The neuromuscular junction is larger. • EPSPs at the neuromuscular junction are also larger. • At the NMJ, a single action potential can produce an EPSP. • There is no IPSP at the NMJ in vertebrates.

Neurotransmitter Release Step 3: Neurotransmitter binds to post-synaptic receptor

3a: Fast chemical synaptic transmission: Binding to inonotropic receptors (ligand-gated ion channels) which increases membrane permeability of ions. 3b: Slow chemical synaptic transmission: Binding to metabotropic receptors (G-protein coupled receptors) which results in activation of a signaling cascade.

Chemical transmissions are terminated in many ways Ion channel inactivation:

: time-dependent change in conformation that causes desensitization to the neurotransmitter

Synaptic antifacilitation

A decrease in the amplitude of postsynaptic responses to repeated presynaptic action potentials. Also called synaptic depression.

Synaptic potential

A graded change in a postsynaptic cell's membrane potential produced by synaptic input. Also called a postsynaptic potential.

Antagonist:

A ligand that binds to the receptor for another molecule and exerts no effect Example: Opioids Endogenous: endorphins Agonists: morphine, codeine, heroin Antagonists: naloxone (e.g. Narcan®)

Agonist:

A ligand that binds to the receptor for another molecule and exerts an effect (positive or negative)

Motor neuron

A neuron that conveys motor signals from the central nervous system to the periphery to control an effector such as skeletal muscle.

Ionotropic receptor (in synaptic function)

A neurotransmitter receptor molecule that changes the membrane permeability of the postsynaptic cell to particular ions when it binds neurotransmitter molecules; usually a ligand-gated channel.

Metabotropic receptor (in synaptic function)

A neurotransmitter receptor that acts via signal transduction to alter a metabolic function of the postsynaptic cell, often by stimulating production of a second messenger.

G protein

A protein involved in signal transduction that is activated by binding with guanosine triphosphate (GTP). Some G proteins occur in cell membranes and are typically trimers; others occur intracellularly and are typically monomers.

Gap junction

A region where the cell membranes of adjacent cells are unusually close to each other and share channels (formed by adjoining connexons in vertebrates) that establish cytoplasmic continuity between the cells.

Postsynaptic Receptors for Fast Ionotropic Actions: Ligand-Gated Channels

ACh receptors are ligand-gated channels that function as ionotropic receptors Many, but not all, ligand-gated channel receptors have evolved from a common ancestor

Presynaptic Neurons Release Neurotransmitter Molecules in Quantal Packe

Acetylcholine is synthesized and stored in the presynaptic terminal Neurotransmitter release requires voltage-dependent Ca2+ influx Neurotransmitter release is quantal and vesicular Synaptic vesicles are cycled at nerve terminals in distinct steps Several proteins play roles in vesicular release and recycling

Nicotinic

Action of acetylcholine that is mimicked by nicotine, or receptors mediating the action. Contrast with muscarinic.

Postsynaptic density

An accumulation of dense material beneath the membrane of a postsynaptic cell, visible in electron micrographs. It corresponds to the accumulation of proteins associated with the concentration of neurotransmitter receptors.

Fast Chemical Synaptic Actions Are Exemplified by the Vertebrate Neuromuscular Junction

At the vertebrate skeletal neuromuscular junction, the neurotransmitter is acetylcholine. When stimulated, the presynaptic axon terminal releases acetylcholine, which diffuses to postsynaptic receptors. Acetylcholine binding to its receptors opens ion channels to increase permeability to both Na+ and K+ ions. The resulting Na+ and K+ currents drive the membrane toward a value (EEPSP) that is more depolarized than the threshold of the muscle fiber. At the neuromuscular junction, the amplitude of the EPSP is sufficient to exceed threshold and triggers a muscle fiber action potential. The EPSP itself is a nonregenerative, nonpropagated local response because the neurotransmitter-dependent permeability changes are not voltage-dependent. Fast excitatory synapses in CNSs work by mechanisms similar to those at neuromuscular junctions. Neurotransmitter-gated ion channels increase membrane permeability to Na+ and K+ ions to produce depolarizing EPSPs. Neuronal EPSPs are much smaller than neuromuscular EPSPs because at neural synapses the postsynaptic membrane encompasses a small area that has a small number of receptor molecules, and the presynaptic axon releases less neurotransmitter, activating fewer postsynaptic receptors. Fast synaptic inhibition results from the opening of ion channels to increase permeability to chloride. ECl is commonly at a hyperpolarized value relative to the resting potential, leading to a hyperpolarizing IPSP. CNS excitatory and inhibitory synapses often have characteristic differences in their appearance in electron micrographs of the vertebrate CNS.

Of chemical and electrical synapses, which statement is best?

Chemical synapses influence learning

Fast Chemical Synaptic Actions Are Exemplified by the Vertebrate Neuromuscular Junction

Chemical synapses work by releasing and responding to neurotransmitters Postsynaptic potentials result from permeability changes that are neurotransmitter-dependent and voltage-independent EPSPs between neurons resemble neuromuscular EPSPs but are smaller Fast IPSPs can result from an increase in permeability to chloride

Synaptic Transmission Is Usually Chemical but Can Be Electrical

Electrical synapses transmit signals instantaneously Chemical synapses can modify and amplify signals

Sensitization

Enhancement of a learned behavioral response to a harmless stimulus after exposure to a strong or harmful stimulus.

Formation of long-term memories appears to be related to LTP as well as at least two other phenomena:(2) Structural changes in the synapse itself:

Formation of LTPs often increases the size of the dendritic spines of the post-synaptic neuron.

For the majority of sensory receptors, how do they deliver information about the intensity of a stimulus?

Frequency of sensory action potentials varies

Postsynaptic Receptors for Slow, Metabotropic Actions: G Protein-Coupled Receptors

G protein-coupled receptors initiate signal transduction cascades Metabotropic receptors act via second messengers Other mechanisms of G protein-mediated activity G protein-coupled receptors mediate permeability-decrease synaptic potentials and presynaptic inhibition

Metabotropic synapses involve __________ receptors while ionotropic synapses involve __________ receptors.

G-protein coupled...ligand-gated

As in humans, young mice appear to be better learners than older mice. A strain of mice genetically engineered to express youthful levels of a subunit of the NMDA receptor in adulthood were better learners than wild-type mice

Likely because Doogie mice allow more Ca2+ to enter the cell during LTP formation as well as allowing NMDA receptors to respond to two stimuli that are not simultaneous

Postsynaptic Receptors for Slow, Metabotropic Actions: G Protein-Coupled Receptors

Many neurotransmitter receptors act via second messengers, triggering metabolic cascades in postsynaptic neurons. These metabotropic receptor effects are often slow and long-lasting. G protein-coupled receptors (GPCRs) are the major receptors of metabotropic synapses. All GPCRs have seven membrane-spanning segments, and all are evolutionarily related. GPCRs act via G proteins. A G protein has three subunits; normally the α subunit becomes activated when it dissociates from the regulatory β and γ subunits. An activated G protein activates an intracellular effector, usually to produce an intercellular second messenger. Second messengers of importance in metabotropic synapses include cyclic AMP, the membrane phospholipid derivatives DAG and IP3, and Ca2+ ions. Most second messengers activate protein kinases, which phosphorylate proteins such as ion channels and change their activity. G proteins can activate ion channels directly. Metabotropic receptors play roles in slow synaptic potentials in which permeability to ions decreases, and in presynaptic inhibition

Synaptic vesicles

Membrane-bound vesicles in a presynaptic terminal, into which neurotransmitter molecules are concentrated.

Synaptic Transmission Is Usually Chemical but Can Be Electrical

Most synapses are chemical; some are electrical. Electrical synapses are very fast and usually are bidirectional. Gap junctions are the anatomical basis of electrical synapses; they contain connexons that allow current to flow directly between the cells, electrically coupling them. Chemical synapses are unidirectional, with a presynaptic neuron that releases neurotransmitter when stimulated, and a postsynaptic neuron (or effector) that bears receptor molecules to which the neurotransmitter binds. Neurotransmitter receptors may directly open their own ion channels; or they may act indirectly through a signal transduction cascade that involves second messengers, to open, close, or change ion channels that are separate molecules. Electrical synapses mediate fast, synchronizing actions of neurons. Chemical synapses integrate neuronal functions, by fast (ionotropic) excitation and inhibition, or by slow (metabotropic) modulation of neuronal and synaptic properties.

Synaptic Potentials Control Neuronal Excitability

Most synapses in nervous systems are chemical synapses that mediate fast excitation and inhibition. Neurotransmitters act at receptors to open ion channels, to depolarize (EPSP) or hyperpolarize (IPSP) the postsynaptic neuron. EPSPs and IPSPs summate, so the membrane potential of the postsynaptic neuron is a moment-to-moment integral of synaptic input. Postsynaptic potentials are graded and spread passively to the axon initial segment (the site of action-potential initiation). Therefore more-distant synapses may have smaller effects on the neuron's output.

Resting membrane potential is -65 mV. ENa = +60 mV, EK = -90 mV, and ECl = -70 mV. Opening of which ion channel(s) should hyperpolarize the membrane?

Na+ and Cl-

A negatively charged ion is more abundant on the inside of the cell. It's equilibrium potential should be

Negative

Synaptic Plasticity: Synapses Change Properties with Time and Activity

Neuronal stimulation that increases the rate of neurotransmitter release also increases rates of neurotransmitter resynthesis. The homeostatic mechanisms of this regulation involve both substrate availability and more complex mechanisms. With a train of presynaptic action potentials, the amplitudes of the resultant postsynaptic potentials may increase (facilitation) or decrease (antifacilitation). Thus the synaptic transfer of information depends on its history. The synaptic bases of behavioral habituation, sensitization, and classical conditioning in Aplysia depend on second messenger-mediated control of the amount of neurotransmitter released at CNS synapses. Hippocampal long-term potentiation (LTP) is a long-lasting change in synaptic properties related to learning and memory. The induction of LTP depends on NMDA receptors that respond to both glutamate neurotransmitter and postsynaptic depolarization, to allow Ca2+ entry into the postsynaptic cell. LTP is maintained by means of Ca2+-dependent second-messenger pathways that make the postsynaptic cell more sensitive to glutamate neurotransmitter. Insertion of AMPA receptors into the postsynaptic membrane increases the amplitude of the postsynaptic response, and occurs along with expansion of the area of dendritic spines. Studies that manipulate the expression of critical genes in the LTP metabolic pathway significantly affect learning and memory in mice.

Neurotransmitters Are of Two General Kinds

Neurons have one or more characteristic neurotransmitters An agent is identified as a neurotransmitter if it meets several criteria Vertebrate neurotransmitters have several general modes of action Neurotransmitter systems have been conserved in evolution

Synaptic Plasticity: Synapses Change Properties with Time and Activity

Neurotransmitter metabolism is regulated homeostatically Learning and memory may be based on synaptic plasticity Habituation and sensitization in Aplysia Long-term potentiation in the hippocampus BOX 13.1 Synapse Formation: Competing Philosophies, Matthew S. Kayser Long-term potentiation is a necessary component of learning

Neurotransmitters Are of Two General Kinds

Neurotransmitters can be small molecules or peptides. Perhaps a dozen small-molecule neurotransmitters and several dozen peptide neurotransmitters have been identified. A neuron can be identified by its characteristic neurotransmitter, but a single neuron may produce and release more than one neurotransmitter. For any neurotransmitter there are several receptors. Different kinds of receptors for a transmitter may coexist in the same organism and the same neuron. Most fast synapses in CNSs employ glutamate for EPSPs and GABA or glycine for IPSPs. Many receptors for small-molecule neurotransmitters, and probably for all peptides, act metabotropically and mediate slow synaptic potentials and modulatory responses. Peptides are synthesized in the neuronal cell body and transported down the axon packed in vesicles, unlike small-molecule transmitters, which are synthesized locally in axon terminals. The synaptic action of small-molecule neurotransmitters is terminated by reuptake or by enzymatic destruction

Excitatory post-synaptic potential (EPSP) is a local depolarization of a membrane. Ion channels: Na+ or Ca2+

Neurotransmitters: Acetylcholine (Ach, muscles) and glutamate (neurons)

Inhibitory post-synaptic potential (IPSP) is a local hyperpolarization (or technically anything below the threshold potential). Ion channels: K+ or Cl

Neurotransmitters: Glycine and γ-aminobutyric acid (GABA). Note that Ach can also be inhibitory depending on the receptor.

"Neurons that fire together, wire together"

Normal synaptic transmission: Glutamate binds to ionotropic AMPA receptors, allowing flux of both Na+ and K+ .

Presynaptic Neurons Release Neurotransmitter Molecules in Quantal Packets

Small-molecule neurotransmitters are synthesized predominantly at axon terminals and are transported into synaptic vesicles. Neurotransmitters are released by presynaptic depolarization, which opens voltage-gated Ca2+ channels at active zones. Calcium ions trigger neurotransmitter release. Neurotransmitter is released in quantal packets, several thousand molecules at a time. Each quantum corresponds to a synaptic vesicle. Synaptic vesicles fuse with the presynaptic membrane to release their transmitter contents by exocytosis. Vesicular membranes are retrieved, refilled with neurotransmitter, and recycled. Specific proteins associated with synaptic vesicles play different roles in vesicular targeting, docking, fusion, and retrieval.

Chemical transmissions are terminated in many ways Enzymatic decay of neurotransmitter

Some neurotransmitters rapidly inactivated by enzymes (e.g. Acetylcholinesterase) in the synaptic cleft.

Multiple EPSPs can result in an action potential A single EPSP is not sufficient to bring the axon hillock to threshold.

Spatial summation: If a number of PSPs occur simultaneously at different locations of the post-synaptic membrane, their summed PSP at the axon hillock determines whether an action potential occurs.

Synaptic Potentials Control Neuronal Excitability

Synapses onto a spinal motor neuron exemplify functions of fast synaptic potentials Synapses excite or inhibit a neuron by depolarization or hyperpolarization at the site of impulse initiation

Reversal potential

The membrane potential at which the amplitude of a voltage response (such as a postsynaptic potential or receptor potential) is zero because there is no net driving force for ion flow. For example, EEPSP is the reversal potential of an EPSP.

Neuronal integration

The process by which a postsynaptic neuron sums the inputs from several presynaptic neurons to control its generation of action potentials.

Synaptic transmission

The process whereby one neuron influences the excitability of another neuron or effector. Synaptic transmission can be either chemical or electrical

Connexon

The protein channel of a gap junction at which cytoplasmic continuity is established between two adjacent cells. Two connexons, positioned respectively in the cell membranes of the two cells, form the channel. Channels of this sort electrically couple cells (permitting current flow between them) and permit small molecules to move between cells.

Postsynaptic Receptors for Fast Ionotropic Actions: Ligand-Gated Channels

The receptors that produce fast PSPs are ligand-gated channels. They are receptor-channels because the same molecule is both the receptor and the ion channel. The nicotinic acetylcholine receptor of the neuromuscular junction is the model ligand-gated channel. It contains five homologous subunits that surround a central ion channel that opens to allow Na+ and K+ ions to flow across the membrane. A ligand-gated channel opens briefly in response to binding two molecules of neurotransmitter, contributing to the synaptic current that produces a PSP.

Active zone

The region of a presynaptic ending where neurotransmitter molecules are released

Quantal release

The release of neurotransmitter molecules in multimolecular packets (quanta) corresponding to exocytosis of synaptic vesicles.

Spatial summation

The summation of postsynaptic potentials that result from presynaptic action potentials at different synapses onto a single postsynaptic cell.

Temporal summation

The summation of synaptic potentials in response to repeated presynaptic action potentials at the same synapse.

Sensitization:

Then once it receives a shock to the head, Aplysia will once again retract its gills in response to stimulation by the siphon.

After caffeine is allowed to bind to neuronal GABA receptors, these neurons are more likely to generate action potentials. Caffeine is likely

a GABA antagonist.

LSD, marijuana, PCP (hallucinogens):

alters serotonin activity

When the membrane potential crosses the threshold potential,

an action potential is produced.

Neurotransmitters

are chemicals released from one neuron to signal to another neuron and are usually either small-molecule neurotransmitters and neuroactive peptides. A single neuron usually releases only a singe neurotransmitter.

A presynaptic nerve terminal releases a neurotransmitter that activates K+ conductance in the postsynaptic membrane. If the postsynaptic cell body had an initial voltage of -65 mV and ENa = +70 mV, ECl = -70 mV and EK = -90 mV, the new postsynaptic voltage will be:

between -70 mV and -90 mV

Which area of the human brain is proportionally much larger than a fish or amphibian?

cerebrum

A snail initially only tucks into its shell when dropped. Physiologists repeatedly applied the dropping sensation neurotransmitter simultaneous with an unrelated neurotransmitter that normally is present during high temperature. Now the snail tucks in whenever its too warm even if it's not dropping. What happened?

long term potentiation

The nicotinic acetylcholine receptor is

metabotropic.

An ion is more abundant on the outside of the cell and has a positive equilibrium potential. It's valence should be

positive

You taste a fruit that tastes very sweet. Which of the following is most likely involved in this reception of flavor?

secondary messengers

Which of the following would contain mechanoreceptors?

semi-circular canals

Chemical transmission:

signals are sent between neurons via chemicals, called neurotransmitters, that bind to receptors on the post-synaptic membrane.

The simple circuit diagram above shows three sensory nerves A, B and C forming synapses on the dendrites of motor nerve D. Sensory nerves B and C are inhibitory, and sensory nerve A is excitatory. Assuming local synapse strength is equivalent, which of the following would be most likely to generate action potentials in motor nerve D?

simultaneous action potentials in nerves A and B

Dimethyltryptamine (DMT) (hallucinogen):

some kind of serotonin agonist

Which of the following does not involve metabotropic transduction?

tasting salt

Ex 1 and Ex 2 are EPSPs located at different locations on an axon, and In1 is an IPSP. In the above diagram, ____ would represent ____________.

temporal summation