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Undeleted > Chapter 3 > Flashcards

Chapter 3 Flashcards

Neurons & Glia Resting Membrane Potential Action Potentials The Synapse

1
Q

The Neuron Theory Battle

A

Golgi’s Reticularist Doctrine
versus
Cajal’s Neuron Doctrine (wins)

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2
Q

Neurons

A

–Functional unit of the nervous system

–Specialized for the reception, conduction and transmission of electro-chemical signals

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3
Q

Dendrite

A

Collect incoming information at synapses from target neurons

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4
Q

Axon

A

Transmits information at the synapse to dendrites of other neurons or to an effector cell
Conducts action potentials (Conduction zone)
Branches to form axon collaterals
Axon diameter varies substantially across species
Diameter related to speed of signaling

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5
Q

Cell Body (Soma)

A

Integrates information and generates outgoing signals

–Provides metabolic (energy) and synthetic (protein) support
–Acts to “gate” information flow to and from other neurons
–Integrates signals from many sources of input (Integration zone)

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6
Q

Cytoplasm

A

Consists of the the cell’s cytosol and organelles.

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7
Q

Nucleus

A

Contained in nuclear envelope

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8
Q

Gene Expression

A

23,000 human genes

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9
Q

Transcription

A

mRNA assembly

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10
Q

Translation

A

Assembly of proteins from 20 amino acids

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11
Q

Neuronal Cytoskeleton

A

Structural support for maintenance of neuronal shape

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12
Q

Microtubles

A

responsible for moving material around cell

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13
Q

Neurofilaments

A

provide structural support to axon

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14
Q

Microfilaments

A

may assist in reorganization of neuronal branches

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15
Q

Cell Membrane

A 
•Defines boundary of cell
•Intracellular/Extracellular environments are different
•Double layer of lipid (fat) molecules
•Contains protein molecules
–Receptors
–Channels
–Transporters
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16
Q

The two basic cellular processes:

A

1) Protein Synthesis

2) Energy Production

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17
Q

Dendritic Tree

A
  • Collection of dendrites from single neuron
  • Receives input from other neurons (Input zone)
  • Inputs may number in the thousands
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18
Q

Dendritic Spines

A
  • Contact point between axon and dendrite.
  • Sensitive to the type and amount of synaptic activity.
  • Dynamic: synaptogenesis can occur on rapid time scale.
  • External and internal factors influence spine morphology and density.
  • In an Enriched environment, the dendritic spines are more numerous and thicker than those seen in individuals living in a less stimulating environment.
  • Estrous cycle: Peak density of dendritic spines occurs during ovulation
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19
Q

Axon Hillock

A

where axon merges with the cell body

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20
Q

Myelin

A

Provides insulation, allowing for faster signaling and for smaller diameter axons.
-No need for ion channels under myelin sheath—reduces work done by sodium-potassium pumps.
-Fewer ions move through axon membrane in myelinated than unmyelinated axons.
Myelin is fatty and white-collored.

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21
Q

Nodes of Ranvier

A

Bare space of a myelinated axon’s membrane.

Ions move through channels only at nodes.

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22
Q

Axon Length

A

Axons vary in length

  • Local circuit neurons: short axons
  • Projection neurons: very long axons
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23
Q

Collaterals

A

branches that arise from axon

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24
Q

Terminal

A

swelling at end of axon collateral

Terminal contains mitochondria (provide energy) and synaptic vesicles containing neurotransmitter

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25
Q

Synapse

A

point of contact between the axon terminal and the somatic or dendritic membrane (spine) of another neuron.

Information passed directionally from presynaptic to postsynaptic cell.

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26
Q

The 3 principal components of a Synapse

A

presynaptic membrane, postsynaptic membrane, synaptic cleft

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27
Q

Classification of Neurons

A

Length of axons
−Local circuit: short axons
−Projection: long axons

Shape (Structure)
−Monopolar
−Bipolar
−Multipolar

Function
−Motor
−Sensory
−Interneuron

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28
Q

Sensory Neurons

A

Carry info from body to brain and spinal cord (Afferent)

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29
Q

Motor Neuron

A

Carries info from brain and spinal cord to muscles and organs (Efferent)

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30
Q

Interneuron

A

Connects one neuron to another in brain or spinal cord

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31
Q

Glia

A

−Non-neural
−9X more numerous than neurons
−Provide physical and functional support to neurons
−May have many important clinical implications

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32
Q

Schwann Cell

A

Myelinates axons in the Peripheral Nervous system.
One cell contributes to only one axon.
Schwann cells help guide the regrowth of damaged axons.

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33
Q

Oligodendrocyte

A

Myelinates axons in the Central Nervous system.

One cell contributes to several axons.

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34
Q

Microglia

A

Cleans up debris in the Central Nervous system.
Sense molecules associated with cellular damage and digest the debris.
Microglia release substances that can lead to neuroinflammation, possibly contributing to multiple neurodegenerative diseases, including Alzheimer’s disease and multiple sclerosis.

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35
Q

Astrocyte

A

Found in the Central Nervous system.

Provides Structural and nutritional support for neurons
Isolates the synapse
Cleans up debris
Play a role in the blood brain barrier (don’t allow highly charged, too large. or fat-insoluble substances)
May play a role in signaling and synaptogenesis

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36
Q

Astrocyte

A

Found in the Central Nervous system.

Provides Structural and nutritional support for neurons
Isolates the synapse
Cleans up debris
Play a role in the blood brain barrier
May play a role in signaling and synaptogenesis

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37
Q

Ingredients of Intracellular and

Extracellular Fluid

A

• Water
– H2O

• Ions
– Charged particles
Potassium – K+
Sodium – Na+
Calcium – Ca2+
Chloride – Cl-
Protein anions – A-
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38
Q

Ion Concentrations

A

Because of the distribution of ions and other charged particles the inside of the neuron, neurons are negatively charged relative to the outside

39
Q

Relative Ion Concentrations

A

Higher Inside the Cell:
Protein anions
Potassium

Higher Outside the Cell:
Sodium
Chloride
Calcium

40
Q

Resting Membrane Potential

A

The difference in charge between the inside and outside of the membrane of a neuron at rest.

At rest, the inside of the cell is about –70 mV lower than outside of cell

41
Q

Potential =

A

Voltage

42
Q

Diffusion

A

Molecules will move from areas of high concentration to areas of low concentration.

Diffusion pressure moves molecules along a Concentration Gradient.

43
Q

Electrical Force

A

Charged molecules or ions will be attracted to areas of opposite charge and repelled by areas of like charge.

Like charges repel each other.

Opposite charges attract each other.

44
Q

Selective Permeability

A

Different channels and receptors “gate” specific ions (i.e., they are selectively permeable).

45
Q

Resting Membrane Potential

A

•Resting membrane potential is about -70mV
•Resting membrane potential due to:
−Selective permeability of membrane
−Uneven distribution of ions on the inside vs. outside of the cell

The neuron is polarized in it’s resting state

46
Q

Depolarization

A

membrane potential becomes less negative

47
Q

Hyperpolarization

A

membrane potential becomes more negative

48
Q

Action Potentials

A

method by which neurons communicate

–When the axon hillock region becomes more positive, to about -65 mV from -70, an AP is generated

49
Q

Action Potential properties, once threshold reached

A

–Rising phase
•Na+ enters neuron
•Depolarization

–Overshoot
•Neuron positive inside
relative to outside

–Falling phase
•K+ exits neuron
•Hyperpolarization

50
Q

Properties of Action Potentials

A

−All or None
−AP amplitude & speed is constant
−Each AP followed by refractory period

51
Q

Voltage-Gated Channels

A
  • Voltage-gated Na+ and K+ channels open and close as a function of the neuronal membrane potential
  • They are located along axon hillock, axon membrane and terminals
  • Their rapid opening and closing is responsible for AP initiation and propagation
52
Q

Absolute Refractory Period:

A

–Neuron can NOT fire again
–Limits how frequently a neuron can fire
–Accounts for unidirectional nature of action potential
–Na+ channel can only open again once membrane potential hyperpolarizes

53
Q

Neural information code

A

Pattern (temporal code)

Frequency (rate code)

54
Q

Relative Refractory Period

A

–Membrane potential becomes more negative than resting membrane potential
–Neuron can fire again, but only with strong stimulus
–Plays a role in intensity coding, i.e. stimulus intensity coded by firing rate

55
Q

Action Potential Propagation

A

Remember, once a voltage-gated Na+ channel opens and closes, it can only be opened again once the membrane potential has hyperpolarized. In this way, the AP cannot flow backwards.

56
Q

The Speed of an Action Potential depends on

A

−Myelination: myelinated is faster than unmyelinated
−Axon diameter: large is faster than small

Invertebrate axon: 11 mph
Human axon: 268 mph

57
Q

Axon Terminal

A

AP invades axon terminal; the signal changes from electrical to chemical

58
Q

Ion Movement During an Action Potential

A

During an action potential, positive ions first flow into the axon. There is little to no net change in distribution of the negative ions.

When the inside of the axon accumulates maximal levels of positive charge, positive ions begin to flow out of the axon.

When the action potential reaches the axon terminal, it triggers the release of neurotransmitters.

59
Q

Charles Sherrington

A

coined term Synapse (1897)

60
Q

Soups vs. Sparks

A
  • Physical nature of synaptic transmission
  • Chemical vs. Electrical transmission

Soup vs Spark Controversy: Is synaptic transmission generally chemical or electrical?

Controversy lasted from 1936-1950’s
    J.C. Eccles (one of Sherrington’s last students)
        •1st an electrical impulse passed directly from the presynaptic axon to postsynaptic cell
       • then a more prolonged action of Neurotransmitter 

Experiments by B. Katz and many colleagues particularly S. Kuffler refuted direct electrical transmission at NMJ
        irreducible synaptic delay => not electrical
        endplate and synaptic potentials precede the AP
        subthreshold stimulation led to a graded postsynaptic response rather than the all or none response like AP presynaptically

Eccles conceded NMJ chemical and later also showed CNS inhibition involved the same properties, therefore also chemical.

61
Q

Soup vs Spark Controversy

A

The ‘soup vs. spark’ debate (1930s): the origin of modern psychiatric & neuropharmacology

Neurons communicate via synapses, which depend on a chemical substance called a neurotransmitter to pass along the messages. This theory was first established by Henry Dale and Otto Loewi; it was called ‘soup’ camp, for there was a chemical molecule involved.

John Eccles theorized that the message transmission between neurons had to be an electrical phenomenon, thus called ‘spark’ camp.

Bernard Katz fled Hitler’s Germany to England and witnessed a ‘stand-up fight’ between John Eccles and Henry Dale and the chairman (at University College at London) “acting as a most uncomfortable and reluctant referee.” The sparkers were in the wrong.

The experimental results were the same in both camps; it was the different interpretation and theory that led to the radically different conclusions.

John Eccles later discovered synaptic inhibition in the spinal cord. GABA is the main inhibitory transmitter in brain. Many tranquilizers and general anesthetics bind to GABA receptors, producing a calming effect by enhancing the receptors’ inhibitory function. The drug-made equanimity should be credited to John Eccles, who was once so wrong in the soup vs. spark debate. He went on to receive a Nobel in 1963, nearly 30 years after Henry Dale and Otto Loewi (the soupers) got theirs.

62
Q

Neurotransmitters regulate information transfer: Vagusstoff

A

Vagusstoff (German for “Vagus Substance”) refers to the substance released by stimulation of the vagus nerve which causes a reduction in the heart rate (slowed heart beat).
Discovered in 1921 by physiologist Otto Loewi, vagusstoff was the first confirmation of chemical synaptic transmission and the first neurotransmitter ever discovered.
It was later confirmed to be acetylcholine, which was first identified by Sir Henry Dale. In 1936 Loewi was awarded the Nobel Prize in Physiology or Medicine, which he shared with Dale.

63
Q

axoaxonic synapse

A

one between the axon of one neuron and the axon of another neuron.

64
Q

axodendritic synapse

A

one between the axon of one neuron and the dendrites of another.

65
Q

axodendrosomatic synapse

A

one between the axon of one neuron and the dendrites and body of another.

66
Q

dendrodendritic synapse

A

one from a dendrite of one cell to a dendrite of another.

67
Q

electrotonic synapse

A

a special type of gap junction found in tissue such as the myocardium.

68
Q

Steps in Synaptic Transmission

A

?

69
Q

Calcium and the Synapse

A
  • Voltage-gated calcium channels open in response to AP

- Calcium must be cleared prior to arrival of next AP

70
Q

Vesicular Release

A

Exocytosis: Entering calcium releases vesicles from protein anchors and stimulates fusion with membrane.
Endocytosis: Excess membrane pinches off to form new vesicle.

71
Q

Neurotransmitters

A

endogenous chemicals that transmit signals from a neuron to a target cell across a synapse.

72
Q

Types of Neurotransmitters

A

–Small molecules: serotonin, norepinehprine, epinephrine, dopamine, acetylcholine
–Amino acids: GABA, glutamate
–Neuropeptides: secretin, oxytocin
–Soluble gases: nitric oxide, carbon monoxide

73
Q

Activation of Receptor Sites

A

Neurotransmitter molecules diffuse into and throughout the synaptic cleft
Neurotransmitters bind to specific receptors in a lock and key fashion
–Post-synaptic receptors
–Pre-synaptic receptors (autoreceptors)

74
Q

Autoreceptors

A

An autoreceptor is a receptor located in presynaptic nerve cell membranes which serves as a part of a negative feedback loop in signal transduction.

NT synthesis and release regulated (usually inhibited) by presynaptic autoreceptors

75
Q

Terminal autoreceptor:

A

reduce NT synthesis and release

76
Q

Somatodendritic autoreceptor

A

hyperpolarizes neuron, reducing AP spiking rate

77
Q

Terminating NT Signal Can occur by which 3 Methods?

A
  1. Diffusion
  2. Deactivation Enzymes
  3. Reuptake
78
Q

Describe the Two Receptor Types

A

Voltage-gated Receptors: activated based on changes in the membrane potential

Ligand-gated Receptors: activated by the binding of specific molecule or neurotransmitter

79
Q

Postsynaptic Receptors

A

Ionotropic or Metabotropic

80
Q

Ionotropic Receptor

A
  • Opens channels directory
  • Relatively fast
  • Relatively short
  • Effects are localized
81
Q

Metabotropic

A
  • Opens channels indirectly
  • Uses chemicals called second messengers
  • Relatively slow acting
  • Relatively long-lasting effects
  • Effects are more widespread and varied
82
Q

Local Effects of Receptor Activation

A

•Excitatory Postsynaptic Potential (EPSP):
–Opens sodium channels
–Depolarizes dendrites and cell body
–Facilitates likelihood of Action Potential

•Inhibitory Postsynaptic Potential (IPSP):
–Opens potassium or chloride channels
–Hyperpolarizes dendrites and cell body
–Decreases likelihood of Action Potential

83
Q

Inhibitory Postsynaptic Potential (IPSP):

A

–Opens potassium or chloride channels
–Hyperpolarizes dendrites and cell body
–Decreases likelihood of Action Potential

84
Q

Excitatory Postsynaptic Potential (EPSP):

A

–Opens sodium channels
–Depolarizes dendrites and cell body
–Facilitates likelihood of Action Potential

85
Q

Neural Integration

A

Combining a number of individual signals into one overall signal

Two ways:
•Over time (temporal summation)
•Over space (spatial summation)

Effect:
•Summation of EPSPs: action potential is more likely
•Summation of IPSPs: action potential is less likely

86
Q

Temporal Summation

A

An action potential lasts ~1ms

A graded potential lasts ~5-10ms

Thus, APs that occur very rapidly can build on one another

87
Q

Graded Potentials

A

Local Potentials……

88
Q

Spatial Summation

A

Combines all EPSPs and IPSPs occurring at different locations on the dendrite and cell body

89
Q

EPSP/IPSP integration:

A

analogue signal is summed over time and space

Action Potentials are Binary signal

90
Q

Neuromodulation

A

Presynaptic Facilitation: Increases amount of neurotransmitter released by the postsynaptic terminal button

Presynaptic Inhibition: Reduces amount of neurotransmitter released by the postsynaptic terminal button

91
Q

Electrical Synapses

A

AKA gap junctions
Fast transmission
Bi-directional
Do not typically occur at axon terminals

92
Q

Negative Feedback

A

Occurs when the result of a process influences the operation of the process itself in such a way as to reduce changes. Negative feedback tends to make a system self-regulating; it can produce stability and reduce the effect of fluctuations. Negative feedback loops in which just the right amount of correction is applied in the most timely manner can be very stable, accurate, and responsive.

93
Q

Steps in Synaptic Transmission

A

Action Potential reaches the axon terminal

Calcium ion channels open, calcium flows into cell.

Calcium, causes vesicle to release from microtubules

Synaptic vesicles fuse with axon membrane at release sites

Vesicles open, releasing neurotransmitters into the synaptic gap

Vesicle material is recycled

Vesicles either return to neuron cell body via retrograde transport or are refilled at the axon terminal

94
Q

Graded potentials

A

Graded potentials are changes in membrane potential that vary in size, as opposed to being all-or-none. They arise from the summation of the individual actions of ligand-gated ion channel proteins, and decrease over time and space. They do not typically involve voltage-gated sodium and potassium channels.

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