Topic 6: Communication Along and Between Neurons

The permeabilities of the ions can change in a fraction of a millisecond, as a result of activation of _______ ion channels.

ligand-gated

In contrast action potentials have a _____ amplitude and time course.

fixed

A sensory receptor receives energy from a ______ stimulus which will cause a change in the membrane potential in a specialized receptor region of the sensory neuron cell membrane.

physical

The receptor potential is _______ in proportion to the strength of the stimulus.

graded

The receptor potential will progressively decay with _______ from the site of initiation (i.e.; the site where the stimulus was received).

distance

Decremental Transmission or Passive Electrotonic Transmission is a type of ______ potential.

graded

Since the graded potential cannot travel the length of the neuron without decrement the signal will be converted into what?

action potential

The next exchange of information occurs where the axon terminals of the sensory neuron synapse with the dendrites of the next is called?

Postsynaptic Neuron

Most synapses are chemical synapses where the electrical message of the ________ neuron is converted to a chemical message that will then become an electrical message in the postsynaptic neuron.

presynaptic

Most synapses are chemical synapses where the electrical message of the presynaptic neuron is converted to a chemical message that will then become an electrical message in the _______ neuron.

postsynaptic

The chemicals that allow for the exchange of information across the synapse are called what?

Neurotransmitters

The neurotransmitter must cause a change in the membrane potential of the _______ neuron to cause the signal to be generated.

postsynaptic

The amount of neurotransmitter released will be due to the number and frequency of action potentials traveling in the ______ neuron.

presynaptic

Passive Electrotonic Transmission is also called what?

Decremental Transmission

Electrotonic Transmission is the ______ spread of the electrical signal through the neuron.

passive

Active, or Regenerative, Conduction of the signal through the use of _____ Potentials.

Action

What requires the presence and activity of biological molecules, such as voltage-gated channels, to allow for the movement of ions across the neuron cell membrane.

Active or Regenerative conduction

Electrotonic potential is a nonpropagated local potential, resulting from a local change in ionic _______.

conductance

Neurons that are small and have short processes have only ________ potentials.

electrotonic

Neurons that are small and have short processes are incapable of producing an _______ potential.

action

To allow a signal to travel along an axon without decrement action potentials must be ________ sequentially.

regenerated

The action potential generated at the spike-initiating zone propagates as a wave along the ______.

axon

The greater the ________ of the neuron the further the local portion of the impulse can flow before it becomes too weak to reach the threshold potential and propagate itself.

Length Constant

The length constant (λ) is a mathematical constant used to quantify the distance that a graded electrical potential will travel along a neuron via _______ electrical conduction.

passive

The _______ the value of the length constant, the further the potential will travel.

greater

Over evolutionary time the ______ of the impulse has increased.

velocity

Myelination is seen in _________.

vertebrates

What is made up by different supporting cell types, and varies in chemical composition and configuration but performs the same insulating function.

Myelin

_______ axons are white in appearance, hence the "white matter" of the brain.

Myelinated

Myelin is made by ________ in the PNS and by Oligodendrocytes in the CNS.

Schwann cells

Myelin is made by Schwann cells in the PNS and by _______ in the CNS.

Oligodendrocytes

Myelin helps to _______ the axons from electrically charged atoms and molecules.

insulate

Myelin will _______ the effective transmembrane resistance and ______ the effective membrane capacitance.

increase, decrease

The resistance between the cytoplasm and extracellular fluid _______ with the number of myelin layers wrapped around the axon.

increases

The capacitance decreases because the ensheathing myelin is _____.

thick

myelinated axons the axon will have gaps in the myelin sheath called what?

Nodes of Ranvier

Nodes of Ranvier size?

10 um of axon

The myelinated portions of the axon, between the nodes of Ranvier, are called what?

internodes

In the internodal regions the myelin is very ______ wrapped around the axon.

closely

internodal regions lack voltage-gated ____ and voltage-gated ___ channels.

Na+, K+

The impulse is jumping over the internodes and action potential propagation is occurring only at the nodes of Ranvier. This is called what?

Saltatory Conduction

Instead of having to propagate action potentials along the entire length of the axon action potential must only be propagated at the nodes of Ranvier. This is what type of conduction?

Saltatory

The ______ of axons' myelinated segments is important to the success of saltatory conduction.

length

The _______ is a gap between the two neurons.

Synaptic Cleft

Type of synapse where cells are not separated by a synaptic cleft.

Electrical Synapses

The typical gap junction in an electrical synapsis is ____ nm.

3.5

Electrical synapses are _____ in the transmission of information than are chemical synapses.

faster

True or False: Electrical synapses are often found in neural systems that require the fastest possible response, such as defensive reflexes.

True

Unlike chemical synapses, electrical synapses are usually ________.

bidirectional

unidirectional electrical junctions are called?

Rectifying synapses.

In vertebrates gap junction channels are composed of two hemi-channels called what?

Connexons

Connexons are formed by six 7.5 nm long membrane-spanning protein subunits called what?

Connexins

Connexons are formed by six ____ nm long membrane-spanning protein subunits called Connexins.

7.5

The relative speed of electrical synapses also allows for many neurons to fire ________.

synchronously

At a chemical synapse, the presynaptic neuron releases ________ molecules into the synaptic cleft between it and the postsynaptic cell.

neurotransmitter

The neurotransmitters are kept within small organelles called what?

Synaptic Vesicles

The neurotransmitters are released into the synaptic cleft by what?

exocytosis

The presynaptic ________ (or axonal bouton, end bulb) is a specialized area within the axon of the presynaptic cell that contains the synaptic vesicles.

terminal

Synaptic vesicles are docked at regions of the presynaptic cell membrane called what?

Active Zones

On the postsynaptic cell membrane immediately opposite of the synaptic cleft is a specialized region containing a network of neurotransmitter receptor proteins and other membrane proteins called what?

The Postsynaptic Density (PSD).

In the typical axon-dendrite synapse the receptors and PSDs are often found in specialized protrusions from the main dendritic shaft called what?

Dendritic Spines

Fast chemical synaptic transmissions is a _______ mode of synaptic transmission found in the neuromuscular junction and at many CNS synapses.

common

Slow chemical synaptic transmissions are much _____ common than are fast.

less

The neurotransmitters used in a slow chemical synaptic transmission are ______ molecules.

large

Whether fast or slow chemical synaptic transmissions the neurotransmitters will modify the current traveling across the postsynaptic membrane. This will cause what?

the synaptic potential

The primary function of the synaptic transmission is to control the excitability of the postsynaptic cell. When neurotransmitters diffuse across a synapse they generate what?

Postsynaptic Potential

If the postsynaptic potential depolarizes the cell membrane it is?

Excitatory

________ is an increase in the probability that a cell will generate an impulse or, if the neuron is already generating impulses, it is the probability that the frequency of impulse generation will increase.

Excitation

The depolarizations are graded, each with a brief rising phase and a decaying phase (~10-20 ms), and are termed what?

Excitatory Postsynaptic Potentials (EPSPs)

If the postsynaptic potential hyperpolarizes the cell membrane it is _______.

Inhibitory

_________ is a decrease in the probability of an impulse being generated or a decrease in impulse frequency.

Inhibition

The neurotransmitter __________ is predominantly known to trigger IPSPs.

GABA (gamma-aminobutyric acid)

Fast chemical synapses were first studied in the __________ and that is still the model that is used today to explain the fast chemical synapse.

Neuromuscular Junction (NMJ)

What is a motor neuron and all of the myofibers that it is directly innervating.

A Motor Unit

Basically the NMJ functions as a?

relay synapse

The postsynaptic neurotransmitter receptor in a fast chemical synapse is an _________ Receptor.

Ionotropic

Ionotropic receptors produce their effects ______.

directly

Calcium is the only essential element in the synaptic transmission.

Fast Chemical Synapse Using the NMJ

The increased calcium ion concentration causes synaptic vesicles to fuse with special sites on the presynaptic membrane called __________ and release neurotransmitter

Active Zones

In the case of the NMJ the neurotransmitter is what?

Acetylcholine

In the case of the NMJ the postsynaptic cell membrane is arranged into folds at the site of synapsis. These folds are called what?

Junctional Folds

These acetylcholine receptors are _______ channels that are opened by the binding of neurotransmitters to them.

ligand-gated

In the vertebrate CNS the neurotransmitter is ________ instead of acetylcholine.

Glutamate

Slow chemical synapses were discovered decades _____ fast chemical synapses.

after

Slow Chemical Synapses use what?

Metabotropic Receptors

The receptors involved in a slow chemical synapse are linked to what?

G Proteins

G proteins, also known as ______ nucleotide-binding proteins, are a family of proteins involved in transmitting signals from a variety of different stimuli outside a cell into the inside of the cell.

guanosine

When G proteins bind to ____, they are 'on', and, when they bind to _____, they are 'off'.

GTP, GDP

G proteins belong to the larger group of enzymes called what?

GTPases

G proteins located within the cell are activated by ___________ that span the cell membrane. They are transmembrane proteins.

G protein coupled receptors (GPCRs)

Neurotransmitter molecules are released from the presynaptic ______ by presynaptic impulses.

terminal

Acetylcholine is synthesized in the _______ of the axon terminal from acetyl coenzyme A and choline through the use of the enzyme choline acetyltransferase.

cytoplasm

Acetylcholine is synthesized in the cytoplasm of the axon terminal from __________ through the use of the enzyme choline acetyltransferase.

acetyl coenzyme A and choline

Choline acetyltransferase is synthesized in the ________ and must be transported down the axon to the axon terminal.

perikaryon

The limiting factor in ACh synthesis is the availability of what?

choline

Under normal circumstances the release of neurotransmitter requires both _________ and an influx of Ca+2.

presynaptic depolarization

Under normal circumstances the release of neurotransmitter requires both presynaptic depolarization and an influx of ______.

Ca+2