Exam 1: Voltage Gated Channels and Synaptic Transmission (Lecture 2)

Voltage-Gated Ion Channels are __________________________ to each of the major physiological ions (Na+, K+, Ca++, Cl-).

selectively permeable

These channels are coded for by many ____________________ genes.

different

There is at least one voltage sensitive Na+ channel that doesn't _____________________, and give rise to action potentials of long duration. This channel is one of the targets for _________________________.

inactivate; local anaesthetics

Ligand-gated ion channels include those activated by the extracellular presence of _____________________________, such as ______________________.

neurotransmitters; glutamate

Other ligand-gated channels are activated by intracellular second messengers, such as ________ or the cyclic nucleotides ________ and __________.

Ca++; cAMP, cGMP

On the outside of the cell, Ca++ modulates ________________ because it effects the ___________________ for RMP. On the inside of the cell, Ca++ plays an important role as a ____________________________, but it also releases NTs from vesicles in the synapse.

excitability; electrical gradient; 2nd messenger

Voltage-gated Ca++ channels can give rise to _________________________ in much the same way as voltage sensitive Na+ channels. It can also conduct the ___________________ of the action potentials generated primarily by Na+ conductance changes.

action potentials; shape

Intracellular Ca++ concentrations are very _________, and affecting the activity of Ca++ channels regulates an enormous range of ________________________ processes within cells, particularly ________________________________ release.

low; biochemical; neurotransmitter

At least 16 genes have been identified to code for Ca++ channels, which have different _______________________ and _______________________ properties that allow for subtle variations in both electrical and chemical signaling processes mediated by Ca++.

activation; inactivation

Drugs that block voltage-gated Ca++ channels are very ________________________ in treating a variety of conditions ranging from heart disease to anxiety disorders

valuable

The largest and most diverse class of voltage-gated ion channels are ________ channels.

K+

Nearly ___________ different genes code for K+ channels, which differ substantially in their ___________________ properties.

100; gating

What do properties of voltage-gated K+ channels influence? This ultimately modulates axonal ________________ and __________________ transmission.

the duration and rate of action potential firing; conduction; synaptic

Most important function of K+ is to:

maintain resting membrane potential

Voltage-gated Cl- channels function to control _____________________, contribute to __________________________ and help regulate cell __________________.

excitability; RMP; volume

Voltage-gated channels are composed of several subunits that produce a central ____________ through the cell membrane to allow ions to travel passively down their _____________________________________.

pore; electrochemical gradient

Can similar sized and charged ions sometimes travel through voltage-gated ion channels?

yes

What are the 3 units of voltage-gated ion channels?

voltage sensor, pore, gate

_________, ___________, and __________ channels are composed of 4 transmembrane a-subunits and 2 regulatory B-subunits arranged around a central pore.

Na+, K+, and Ca++

Communication in the human brain is made possible by _______________.

synapses

What are synapses?

the functional contacts between neurons

What are the two general classes of synapses?

chemical and electrical

____________________________ permit direct, passive flow of electrical current from one neuron to another through ________________________, which are very _____________.

electrical synapses; gap junctions; rare

What are gap junctions?

specialized membrane channels that connect two cells

_____________________________ enable cell to cell communication via the secretion of ___________________________________.

chemical synapses; neurotransmitters

__________________________ are chemical agents released by the presynaptic neuron and produce secondary current flow in post synaptic neurons by activating specific receptors.

neurotransmitters

Neurotransmitter secretion is triggered by what? This gives rise to transient increase in Ca++ levels within the __________________ terminal.

influx of Ca++ through voltage gated channels; presynaptic

Increase in Ca++ causes _______________________________ to fuse with the presynaptic plasma membrane and release their content into the synapse by ________________________.

synaptic vesicles; exocytosis

Small molecule neurotransmitters in Class I include:

Acetylcholine

Small molecule neurotransmitters in Class II include:

EPI, NE, DA, Serotonin, Histamine (Biogenic amines)

Small molecule neurotransmitters in Class III include:

GABA, Glycine, Glutamate, Aspartate (AA neurotransmitters)

Small molecule neurotransmitters in Class IV include:

Nitrous Oxide

Neuropeptide transmitters include:

neuroactive peptides, pituitary peptides, peptides acting on the gut and brain, neuropeptides from other tissues

Chemical transmission was not understood until 1890 when Otto Loewi isolated frog hearts. It was discovered that nerves release __________________________, which acts to ____________ the heart.

acetylcholine; slow

The first step of chemical synaptic transmission is _______________________ of the ______________________ in the ____________________ nerve terminal.

synthesis; neurotransmitter; presynaptic

The second step of chemical synaptic transmission is ______________________ of the ___________________ in _________________________________.

storage; neurotransmitters; secretory vesicles

The third step of chemical synaptic transmission is regulated _____________________ of the __________________________ in the ________________ space between the pre- and post-synaptic neurons.

release; neurotransmitters; synaptic

The fourth step of chemical synaptic transmission is the presence of specific _________________ for the _________________________ on the _____________________________ membrane. This application to the synapse mimics the effect of nerve _________________________.

receptors; neurotransmitter; postsynaptic; stimulation

The fifth and final step of chemical synaptic transmission involves the _________________________ of the action of the released ______________________________. Why does this last step occur?

termination; neurotransmitter; would have too much stimulation

________________________ events during synaptic transmission are rapid, dynamic, and interconnected.

presynaptic

Is the time between Ca++ influx and exocytosis in nerve terminal a short or long process?

short

Voltage gated Ca++ channels open towards the _______________ of the action potential.

end

Short delays between Ca++ influx and exocytosis is important for __________________________________, which must already be at the ____________________ site.

synaptic vesicle fusion; release

A major fraction of the synaptic delay in chemical synaptic transmission is due to what?

the slow-opening, voltage-sensitive Ca++ channels

The supply of synaptic vesicles in the nerve terminal is ____________________.

limited

In neurotransmitter synthesis of small molecule transmitters, ______________ are synthesized in the nucleus by DNA. These are then transnported down the ______________ to the synaptic terminal where they are stored in ___________________.

enzymes; axons; vesicles

_______________________________ involves recycling vesicles and synthesizing NTs locally in the nerve terminal membrane.

fast synaptic transmission

In neurotransmitter synthesis of peptide transmitters, AKA _________________, large peptide NTs are synthesized in the _______________________ by DNA. They are packaged in vesicles in the ___________________. Small peptides are not packaged into vesicles until they reach the ___________________________.

neuropeptides; nucleus; cytoplasm; synaptic terminal

In peptide transmitter NT synthesis, to compensate for the amount of time it would take to replenish NTs, the molecules act on their receptors for a ____________ time and the vesicles (and some peptides) are ______________ so that constant resynthesis is not necessary.

long; recycled

Neuropeptides take longer to ________________ and require a __________________ concentration to elicit a greater effect.

inactivate; smaller

Action potential comes --> Ca++ _____________- --> vesicular fusion to __________________ and release of NTs --> NTs drift across the _____________________ to bind to receptors.

influx; membrane; synaptic cleft

NT activation of postsynaptic receptors results in a change in membrane potential. Does depolarization or hyperpolarization occur?

both

Postsynaptic potential are _______________ potential and __________________ and shouldn't be confused with action potentials which are all or none and travel down an axon.

graded; localized

NT are not inherently ______________________ or _____________________, different receptors for the same NT may function as either an _____________ or _____________.

excitatory; inhibitory; EPSP; IPSP

EPSP and IPSPs are transient changes in the _______________________________. Will a single EPSP trigger an action potential in the postsynaptic neuron?

membrane potential; no

Neurons receive hundreds to thousands of synaptic inputs, the _____________________ of all results in either the membrane reaching threshold or not.

summation

When does postsynaptic potential begin to terminate? When this occurs, ion channels will ____________ and the membrane is brought back to _______________________________.

when the NT is released from its receptor; close; RMP

______________________________ occurs when a constant stimulus is repeated, resulting in a gradual increase in intensity.

temporal summation

______________________________ occurs when multiple stimuli are applied simultaneously to different areas of a membrane, causing a cumulative effect.

spatial summation

T or F: It was once assumed that a single neuron synthesized and released only a single neurotransmitter.

true

It is understood today that many neurotransmitters _________________ in neurons and are released ___________________ during nerve firing.

coexist; together

Depending on the __________________ of nerve firing, certain types of NTs can be _______________________ released, meaning the quantity of NT release can be modulated.

frequency; preferentially

Low- frequency stimulation favors the release of ___________________ NTs.

small

High-frequency stimulation leads to the release of more Ca++, causing the release of ______________ small molecule NTs and larger neuropeptides

both