Chapter 5: Synaptic Transmission Flashcards by Apphia Trillo

the specialized junction where one part of a neuron contacts and communicates with another neuron or cell type; where information transfer occurs

synapses

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Direction of information flow in the nervous system is generally in one direction: ()

neuron to target cell

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Otto Loewi discovered (1), later known as (2)

Vagusstoff
acetylcholine

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Loewi studied action of the (1) in the frog heart system

vagus nerve

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allow transfer of ionic current from one cell to the next

electrical synapses

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the direct transfer of ionic current in electrical synapses occur at ()

gap junctions

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due to current transfer at electrical synapses, a small electrical () occurs in the second cell

postsynaptic potential

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gap junctions are composed of 2 () that meet and combine to form a continuous channel between 2 cells

connexons

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1 connexon in formed by six ()

connexins

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unlike most chemical synapses, electrical synapses are ()

bidirectional

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In invertebrate species, electrical synapses are found between sensory and motor neurons: ()

escape reflexes

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Bidirectional nature of electrical synapses allows () due to PSP from second cell

back current

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Several PSPs cause AP in ()

postsynaptic neurons

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(): several PSPs occurring simultaneously to excite a neuron (causes AP)

Synaptic integration

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Presence of gap junction allows () of APs

synchronization

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() – space between presynaptic terminal and postsynaptic dendrite

Synaptic cleft

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Receptors are concentrated on postsynaptic side of dendrite: ()

postsynaptic density

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() – site of neurotransmitter release

Active zone

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Presynaptic element (usually an axon terminal) contains dozens of small membrane-enclosed spheres, each about 50 nm in diameter: (1); and about 100 nm in diameter (2).

synaptic vesicles
secretory granules/dense-core vesicles

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CNS synapse type: axon to dendrite

axodendritic

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CNS synapse type: axon to dendritic spine

axospinous

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CNS synapse type: axon to cell body (soma)

axosomatic

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CNS synapse type: axon to axon

axoaxonic

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CNS synapse type: dendrite to dendrite

dendrodendritic

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Two Categories of CNS Synaptic Membrane Differentiations

1. Gray's type I: asymmetrical 2. Gray's type II: symmetrical

CNS synapses with Gray's type I membrane differentiations are usually ()

excitatory

CNS synapses with Gray's type II membrane differentiations are usually ()

inhibitory

() – large amount of synapses connecting muscle fibers and motor neurons

Motor end plate

Neurotransmitter Categories (based on molecular structure)

1. amino acids 2. amines 3. peptides

examples of amino acid neurotransmitters

glutamate, glycine, GABA

examples of amine neurotransmitters

dopamine, acetylcholine, histamine

examples of peptide neurotransmitters

dynorphin, enkephalins

because amines and amino acids are small organic molecules, they are stored in (1); on the other hand, peptide neurotransmitters are stored in (2)

1. vesicles 2. secretory granules

neurotransmitters stored in vesicles/secretory granules are released via ()

exocytosis

membrane proteins on vesicles and cell membrane; facilitate tight association between vesicle and target cell membrane

SNAREs

() binding to SNARE complex causes conformational change -> results in fusion of synaptic vesicle membrane and presynaptic terminal membrane

Ca2+

Vesicles are prepared by () mechanism

docking and priming

Vesicle components fused to cell membrane are recycled via ()

endocytosis

2 major kinds of NT receptors:

1. ligand-gated channels (transmitter-gated) 2. G protein-coupled receptors

summarize the mechanism of G protein-coupled receptors

G protein subunits (intracellular messengers) are activated by binding to receptor; these subunits activate other molecules/channels to induce changes in cell

transmitter-gated ion channels are not that selective for ()

specific ions

ACh-gated ion channel: permeable to both ()

Na+ and K+

The critical value of Vm at which the direction of current flow reverses (in I-V plot): ()

reversal potential

(): transient postsynaptic membrane depolarization caused by presynaptic release of neurotransmitter

EPSP (excitatory postsynaptic potential)

EPSPs usually occur at () ion channels

ACh and Glu-gated

(): transient hyperpolarization of postsynaptic membrane potential caused by presynaptic release of neurotransmitter

IPSP (inhibitory postsynaptic potential)

IPSPs usually occur at () ion channels

Glycin and GABA-gated (usually for Cl-)

If NTR is more permeable to negative ions, opening generates net (1) (influx of 2) -> membrane is (3) -> inhibitory PSP

1. outward current 2. negative ions 3. hyperpolarized

G protein-coupled receptors are often referred to as ()

metabotropic receptors

Activated G protein subunits activate ()

effector proteins

effect of ACh in heart

ACh activation of GPCR results in hyperpolarization -> reduces rate at which cardiac muscle cells fire acton potential

effect of ACh in skeletal muscle

ACh receptor on skeletal muscle is a transmitter-gated ion channel that when activated results in depolarization -> APs are fired

Presynaptic receptors sensitive to the neurotransmitter released by the presynaptic terminal called (), which are typically GPCRs

autoreceptors

common effect of autoreceptor activation is ()

inhibition of neurotransmitter release or synthesis

(1): Neurotransmitter re-enters presynaptic axon terminal and astrocytes through (2)

1. Reuptake 2. transporter proteins

Too high conc. of neurotransmitter often induce ()

desensitization

Receptor (): inhibitors of neurotransmitter receptors

antagonists

example of ACh receptor antagonist

curare

Receptor (): mimic actions of naturally occurring neurotransmitters

agonists

example of receptor agonist

nicotine

(): root cause of neurological and psychiatric disorders

Defective neurotransmission

(): neurotoxin protein preventing ACh release at the neuromuscular junction

Botulinum toxin

botox cleaves (), preventing exocytosis of vesicles containing ACh

SNARE proteins

Process by which multiple synaptic potentials combine within one postsynaptic neuron

synaptic integration

EPSP: reflect the number of (1) and the number of (2)

1. transmitter molecules in a single synaptic vesicle 2. postsynaptic receptors available at the synapse

minimal value of EPSP is caused by the release of ()

a single synaptic vesicle

Number of released vesicles determines () of EPSP

amplitude

Some vesicles are released even without AP stimulation; spontaneous response is regarded as release of ()

single synaptic vesicle

(): a method of comparing the amplitudes of miniature and evoked PSPs, can be used to determine how many vesicles release NT during normal synaptic transmission.

Quantal analysis

EPSPs generated simultaneously at different sites

spatial summation

EPSPs generated at same synapse in rapid succession

Temporal summation

Allows for neurons to perform sophisticated computations

EPSP summation

Integration of EPSPs: EPSPs added together to produce significant ()

postsynaptic depolarization

Length constant lambda is proportional to ()

Rm/Ri

large dendrite/axon diameter -> (large/small) Ri

small

Rm is (large/small) if membrane has a lot of leaky channels

small

These dendrites don’t generate APs, but they amplify PSPs; allows the effects of the AP to be delivered to longer distances

excitable dendrites

EPSP contributes to the AP based on

1. number of excitatory synapses 2. distance between synapses and spike initiation zones 3. properties of the dendritic membrane

examples of dendritic membrane properties that affect EPSP

number of channels, diameter, internal cystolic props, etc.

Action of ()—Take membrane potential away from action potential threshold; thus they exert powerful control over neuron output

inhibitory synapses

Synapse inhibits current flow from soma to axon hillock.

shunting inhibition

If the membrane potential was less negative than −65 mV (Ecl), activation of certain ion channels in inhibitory synapses cause (1) and (2)

1. Cl- influx 2. hyperpolarizing IPSP

No AP is generated bc effects of PSPs cancel each other out

EPSP-IPSP cancellation

() results from synaptic transmission that modifies effectiveness of EPSPs generated by other synapses with transmitter-gated ion channels

modulation

Chapter 5: Synaptic Transmission Flashcards

(84 cards)