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Neuroscience Exam 1 > Neuronal Signaling > Flashcards

Neuronal Signaling Flashcards

1
Q

What are excitable cells and how do they differ from other cells?

A

Excitable cells include nerve cells and muscle cells. they differ from other cells in that their resting (cell) membrane potential can be significantly and quickly altered. This change can serve as a signaling mechanism.

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2
Q

Cell Membrane: Structure

Lipid Bilayer

A

The lipid bilayer of the cell membranes is composed of phospholipids with hydrophilic heads oriented outward and hydrophobic tails oriented toward the center of the membrane.

It is NOT PERMEABLE to ions, which establishes CONCENTRATION gradients.

It is able to store charges of opposite sign that are attracted to each other but unable to cross the membrane and thereby establish ELECTRICAL gradients.

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3
Q

Cell Membrane: Structure

Proteins - how are they integrated into the cell membrane?

A

Proteins in the cell membrane can either be associated with the outer or inner layer of the lipid bilayer, or can be incorporated within and spanning both layers of the lipid bilayer.

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4
Q

Cell Membrane: Structure

Transporter Proteins - Carriers

A

These proteins actively move ions into or out o cells AGAINST their concentration gradients. Specific to a certain ion.

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5
Q

Cell Membrane: Structure

Transporter Proteins - Ion Channels

A

These are proteins that allow only certain kinds of ions to cross the cell membrane in the direction of their concentration gradients.

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6
Q

Cell Membrane: Structure

Transporter Proteins - What other types are there?

A

Voltage-gated, ligand-gated, thermally gated, mechanically gated (stretch).

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7
Q

Cell Membrane: Structure

What other proteins that are NOT transporters are in the cell membrane?

A

Receptors, structural proteins, enzymes, adhesion proteins (helps proteins adhere to something in the environment)

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8
Q

Cell Membrane: Structure

Glycocalyx

A

External surface of the cell membrane composed of carbohydrates

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9
Q

Cell Membrane: Function

A

Acts as a selective barrier separating the intracellular and extracellular compartments

Intercellular communication - cell recognition and attachment to other cells and extracellular molecules

Transduction of signals from the cell’s exterior to the cel’s interior.

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10
Q

Resting Membrane Potential: Why are electrical potentials generated across neuronal cell membranes?

A

Because there are differences in the concentration of specific ions across cell membranes, and the membranes are selectively permeable to some of these ions.

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11
Q

Resting membrane potential: what components contribute to the IONIC basis of the resting membrane potential?

A

The sodium potassium pump (which is a type of CARRIER protein in the cell membrane), actively keeps the sodium ion concentration in the cell low and keeps the potassium content in the cell high. it works against the concentration gradients of both ions, making this a process that requires energy.

The cell membrane is selectively permeable to potassium due to the presence of open potassium ion channels. Therefore, potassium ions tend to leak out of the cell along their concentration gradient

The above 2 factors create an excessive positive outside the cell and an excessive negative charge inside the cell.

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12
Q

Resting membrane potential: properties

A

The resting membrane potential is approximately -65mV (ranges from -40 to -90 mV)

The resting membrane potential is uniform throughout the cell.

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13
Q

Resting membrane potentials: alterations

Depolarization - what is it and how does it happen?

A

Depolarization is a reduction in the resting membrane potential (the number becomes more positive)

It happens with there is an increase in SODIUM permeability (sodium channels open) and there is an influx sodium (travels along its concentration gradient.

The influx of sodium is excitatory, meaning that it increases the ability of a neuron to generate an action potential.

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14
Q

Resting membrane potentials: alterations

Hyperpolarization - what is it and how does it happen?

A

Hyperpolarization is an increase in the resting membrane potential (the potential becomes more negative)

Cl- permeability increases because Cl- ion channels open and there is an influx of Cl- ions

Hyperpolarization is generally INHIBITORY, meaning that it decreases the ability of a neuron to generate an action potential.

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15
Q

Signals within Neurons - Electrochemical basis of nerve function

How do neurons produce behaviors?

A

To produce a behavior, each participating neuron sequentially generates 4 different signals within the cell: input, trigger, conducting, and output.

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16
Q

Signals within Neurons - Electrochemical basis of nerve function

What are the 4 functional components of neurons and what do they do?

A

There are 4 functional components or regions that generate the 4 different signals. They are:

Receptive - local input component
Trigger - summing or integrative component
Signaling - long-range conducting component
Secretory - output component

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17
Q

Signals within Neurons - Input component

Function

A

Produces graded, local signals (the signal acts on a specific area and can be either small or large)

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18
Q

Signals within Neurons - Input component

Regions: Where is the input component in sensory neurons?

A

The input component is in the sensory receptors that respond to sensory stimuli.

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19
Q

Signals within Neurons - Input component

Regions: Where is the input component in motor and inter-neurons?

A

The input component is the postsynaptic (receiving side) membrane receptors that respond to communication from other cells.

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20
Q

Signals within Neurons - Input component

What are the signals at the sensory input and motor/interneuron inputs called respectively?

A

Sensory input signals = receptor potentials

Motor and interneuron input signals = Synaptic potentials (aka postsynaptic potentials or end plate potentials.

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21
Q

Signals within Neurons - Input component

Signals: What is the ionic basis of the signal?

A

There is a brief change in the resting membrane potential due to the alteration of the membrane permeability to ions.

The change in the resting membrane potential can either be excitatory and cause depolarization, or be inhibitory and cause depolarization.

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22
Q

Signals within Neurons - Input component

Signals: What are the properties of these input signals?

A

The input signals are graded in amplitude and duration, proportional to the amplitude and duration of the input stimulus.

Propagation is passive, therefore the signal decreases in amplitude with distance from the input component.

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23
Q

Signals within Neurons - Trigger component

Function

A

The trigger component makes the decision to generate an action potential.

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24
Q

Signals within Neurons - Trigger component

Where is the trigger component located and what is its main feature?

A

The trigger component is located adjacent to the input component (has to be since the input component signal is local).

This is the part of the cell that has the highest concentration of voltage gated sodium channels, which is important for the initiation of the AP.

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25
Q

Signals within Neurons - Trigger component

Regions: Where is the trigger component in sensory neurons?

A

It is the myelinated axon’s first node of Ranvier

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26
Q

Signals within Neurons - Trigger component

Regions: Where is the trigger component in motor and Intern-neurons?

A

It is the axon hillock.

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27
Q

Signals within Neurons - Trigger component

Signals: What signal is generated at the trigger component of the cell and how?

A

The signal that is generated is the action potential.

The activity of all receptor (or synaptic) potentials is summed at the trigger component of the cell. If the size of the input signal reaches a threshold (a critical value of membrane potential or depolarization at which the AP is initiated), the the neuron will fire an action potential.

28
Q

Signals within Neurons - Trigger component

Signals: What is the ionic basis of the action potential? What are the steps?

A

1) Upstroke - Rapid depolarization
Voltage gated sodium channels open, increasing sodium ion permeability. this is followed by a rapid influx of sodium.

2) Overshoot - reversal of membrane potential
The sodium ion levels within the cell become so high that the membrane potential goes into the positive range

3) Repolarization
There is a decrease in sodium permeability (sodium channels are inactivated and then closed) and an increase in potassium permeability (voltage gated potassium ion channels open) followed by an efflux of potassium ions

4) Hyperpolarization
Potassium ion permeability remains increased for a long period of time allowing the efflux of potassium to continue until the membrane potential is more negative than the resting membrane potential.

29
Q

Signals within Neurons - Trigger component

Signals: What are the properties of the signal at the trigger component (AP)?

A

It is NOT a graded signal - it is all or none. All stimuli above the threshold will initiate the same signal (same amplitude, same duration)

The amplitude and duration of the input signal influence the frequency and number of action potentials (this is how we can tell if a stimulus is stronger or is happening over time).

There is an absolute refractory period after the AP during which the stimulus CANNOT elicit a second AP. (allows for unidirectional flow)

There is a relative refractory period after an AP during which only a suprathreshold stimulus can initiate a second AP

30
Q

Signals within Neurons: Conducting Component

Function

A

Propagates the Action Potential

31
Q

Signals within Neurons: Conducting Component

Region

A

Axon

32
Q

Signals within Neurons: Conducting Component

Signal: What signal is conducted?

A

The Action Potential

33
Q

Signals within Neurons: Conducting Component

Signal: What the ionic basis of the AP in the conducting components

A

Same as the ionic basis of the AP in the trigger component.

34
Q

Signals within Neurons: Conducting Component

Signal: What are the properties of the signal (AP) that the axon conducts?

A

Propagation is ACTIVE (unlike input signal); does not reduce in amplitude with distance because it is periodically regenerated.

It is unidirectional because once the AP passes, the sodium channels left behind are in the inactivated state and are refractory to any further stimulation.

The conduction velocity (the rate at which the AP travels) depends on the axon diameter and myelination status (signals will travel faster down wider, myelinated axons)

35
Q

Signals within Neurons: Output component

Function

A

The output component releases neurotransmitter.

36
Q

Signals within Neurons: Output component

Region

A

Active zones of the presynaptic terminal

37
Q

Signals within Neurons: Output component

Signal: What is the signal generated at the output component of the neuron?

A

The signal is a release of a chemical neurotransmitter at a synapse with a second neuron or effector cell.

38
Q

Signals within Neurons: Output component

Signal: What is the ionic basis of the output signal?

A

1) The action potential reaches the presynaptic terminal
2) Voltage gated Ca++ channels open
3) Ca++ influx causes the synaptic vesicles to migrate to and fuse with the presynaptic membrane
4) Synaptic vesicles release neurotransmitters via exocytosis

39
Q

Signals within Neurons: Output component

Signal: What are the properties of the output signal?

A

Neurotransmitters are released in discrete units called QUANTA

The total amount of neurotransmitter released is determined by the amount of Ca++ that enters the presynaptic terminal, which is dependent on the frequency and number of the action potentials that reach the presynaptic terminal (higher frequency of APs or longer duration of APs will increase the amount of neurotransmitter that is released)–> more transmitter released, greater chance of more receptor potentials on the next neuron.

The total amount of neurotransmitter that is released can me regulated from outside the cell.

40
Q

Signals Between Neurons - Chemical Basis of Neuronal Communication

Where do these signals occur?

A

They occur between part of one neuron and a part of a second neuron (or effector cell) via synapses.

the occur between one neuron’s axon and another neuron’s dendrite (axodendritic connection), cell body (axosomatic),

Communication with skeletal muscle cells happens at specialized chemical synapses between neuron axons and skeletal muscles. these regions are called NEUROMUSCULAR JUNCTIONS.

41
Q

Signals Between Neurons

Synapses - Definition

A

Synapses are the functional contact between cells. the average neuron forms about 1000 synaptic contacts, and receives about 10,000 connections.

42
Q

Signals Between Neurons

Synapses - How is information carried to the synapse?

A

Information is carried by action potentials to the synapse.

**the message of the action potential is determined by the neural pathway that carries it.

43
Q

Signals Between Neurons: Electrical Synapses

What is the function of an electrical synapse?

A

To create electrical continuity between cells.

44
Q

Signals Between Neurons: Electrical Synapses

What is the structure of an electrical synapse?

A

Structure = gap junctions

These are specialized membrane channels with pores that connect pre and post synaptic cell membranes.

45
Q

Signals Between Neurons: Electrical Synapses

What is the function of an electrical synapse?

A

It acts as a mechanism of signal transmission that allows:

1) Ions (and other molecules) to diffuse directly from the pre into the post synaptic cell
2) Rapid communication
3) No threshold is needed to signal transduction
4) Can allow both a uni-directional and a bi-directional flow of information.

46
Q

Signals Between Neurons: Electrical Synapses

Why are gap junctions useful?

A

They synchronize the electrical activity among populations of neurons. For example, brainstem neurons that generate rhythmic activity underlying breathing are signaled via gap junctions. (This activity is rhythmic and therefore requires a constant, rhythmic electrical signal)

47
Q

Chemical Synapses: Structure

Presynaptic terminal

A

Contains synaptic vesicles filled with neurotransmitter that are concentrated in active zones along the presynaptic membrane.

48
Q

Chemical Synapses: Structure

Synaptic Cleft

A

Space between the pre and post synaptic membrane.

49
Q

Chemical Synapses: Structure

Postsynaptic Membrane

A

Contains receptors (proteins). these target molecules exhibit an affinity for individual neurotransmitters.

50
Q

Chemical Synapses: Function

A

Chemical synapses are a mechanism of signal transduction.

51
Q

Chemical Synapses: Function

What is are the steps in chemical signal transduction?

A

1) Ionic basis of the output component (influx of Ca++)
2) Neurotransmitter that has been released into the synaptic cleft binds with receptors on the postsynaptic membrane.
3) Postsynaptic ion channels open or close (depending on the type of receptor and the neurotransmitter.
3) receptors cause changes to the postsynaptic cell membrane’ permeability to ions
4) An excitatory or inhibitory synaptic potential is induced

52
Q

Comparison of electrical vs. chemical synapse

A

1) Synaptic delay
Electrical synapse is very rapid, whereas there is a delay at chemical synapses

2) Threshold for synaptic Transduction
In a chemical synapse, if the input component threshold is not reached there will be no signal whereas no threshold exists for electrical synapses

3) Uni-directional flow of information - chemical synapses have only unidirectional flow while electrical synapses can also have bi-directional flow.

53
Q

Neurotransmitters: Definition

A

Neurotransmitters are chemicals localized and released from a presynaptic terminal that bind to receptors in the postsynaptic membrane, resulting in an effector function within the target cell.

There are over 100 different agents that can act as neurotransmitters, and many types of neurons synthesize and release two or more neurotransmitters.

54
Q

Neurotransmitters: Small molecule neurotransmitters

A

In general, small molecule neurotransmitters tend to mediate RAPID synaptic transmission

55
Q

Neurotransmitters: Neuropeptides

A

In general, these tend to mediate SLOW synaptic transmission.

56
Q

Neurotransmitters: How is the activity of neurotransmitter limited?

A

Activity is limited by diffusion away from the post-synaptic membrane, enzymatic degradation of neurotransmitters in the synaptic cleft, and re-uptake of neurotransmitters across cell membranes and surrounding glial cells

57
Q

Neurotransmitters: what are the effects of neurotransmitters?

A

The effects of neurotransmitters (whether excitatory or inhibitory) are determined by the receptors. Because there are multiple types of receptors for most neurotransmitters, most neurotransmitters can have more than one effect.

58
Q

Receptors: Definition and Function

A

Receptors are glycoproteins located within the cell membrane (most commonly) in intracellularly in the cytoplasm or nucleus.

They transduce a chemical signal from a neurotransmitter into an intracellular event.

59
Q

Receptors: Ionotropic Receptos

A

These receptors are linked directly to ion channels.

They mediate fast synaptic transmission, and are therefore receptors for small molecule neurotransmitters

60
Q

Receptors: Ionotropic Receptors

How do they work?

A

1) Small molecule neurotransmitter is released into the synaptic cleft
2) It binds to a receptor site on an ionotropic receptor
3) Binding of neurotransmitter causes a conformational change in the ion channel that allows it to open
4) Once the channel is open, ions can enter the cell.

61
Q

Receptors: Metabotoropic

A

Aka G-Protein coupled

These receptors can modulate ion channels either directly or indirectly

When ion channels are modulated indirectly, it is done through intracellular enzymes that alter the level of intracellular second messengers

Changes in the level of second messengers can open ion channels

Second messenger levels can also affect intracellular Ca++ levels, activity of enzymes, and expression of specific genes

These receptors are bound by NEUROPEPTIDES, and mediate SLOW synaptic transmission

62
Q

Effects of Neurotransmitters: Agonists

A

Agonists are endogenous (neurotransmitters) or exogenous (drugs) agents that ACTIVATE a receptor. They bind to a receptor and initiate a change

When the agent binds, the postsynaptic cell generates either an excitatory or inhibitory post synaptic potential.

The type of postsynaptic potential will be dependent on the type of RECEPTOR, not the type of neurotransmitter

63
Q

Effects of Neurotransmitters: Antagonists

A

Endogenous and exogenous agents that bind to a receptor and do NOT initiate a response

Essentially, these are binding in order to PREVENT a postsynaptic potential

Example: Beta Blockers

64
Q

Receptor Regulation - What is it?

A

Post synaptic receptors are not static, meaning that the number of receptors can change in response to changes in the synaptic environment such as over stimulation and understimulation

65
Q

Receptor Regulation: Response to overstimulation

A

Cells can become desensitized to a stimulus. This is a fairly brief and transient decrease in responsiveness.

If desensitization is prolonged because of overstimulation, downregulation can occur, meaning that there can be a decrease in the actual number of receptors in the postsynaptic membrane. This is a slower and more prolonged process.

66
Q

Receptor Regulation: Response to decreased stimulation

A

Supersensitivity - the cell will become supersensitive to the stimulus by a slower and more prolonged process in which the number of post synaptic receptors is increased

67
Q

What effect can drugs have on synaptic function?

A

Drugs can alter virtually every level of neuronal and synaptic function such as neurotransmitter sythesis, vesicular uptake and storage, depolarization and induced exocytosis, neurotransmitter receptor binding, and termination of neurotransmitter action

Neuroscience Exam 1 (10 decks)

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