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Neuroscience > Ch 2- Physical and Electrical Properties of Cells in Nervous System > Flashcards

Ch 2- Physical and Electrical Properties of Cells in Nervous System Flashcards

1
Q

What are neurons (nerve cells)?

A

Specialized cells that conduct messages in the form of electrical impulses throughout the body

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2
Q

What does the Cell Body (soma) do?

A

Synthesizes proteins used as neurotransmitters

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3
Q

What are the types of neuron processes?

A

Multiple dendrites

a single axon with axon-terminal branches (Telodendria)

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4
Q

What structures are usually found within neurons?

A
  • Cell body
  • Neuron process
  • Nucleus
  • Cytoplasm
  • Mitochondria
  • Nissl bodies
  • Smooth ER
  • Cytoskeleton
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5
Q

What are nissl bodies?

A

Clusters of RER - Synthesize proteins

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6
Q

What structures are found within the cytoskeleton?

A

Microtubules (Neurotubules): Help to transport substances between the cell body and axon terminals

Microfilaments

Neurofibrils: bundles of intermediate filaments (neurofilaments) that provide structural support

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7
Q

Describe neuron processes

A

Arm-like processes that extend from the cell body

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8
Q

What are the dendrites of a neuron?

A

The main receptive regions

Usually have branches called dendritic spines

Convey incoming messages toward the cell body

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9
Q

What is found on the plasma membranes of dendrites?

A

Contain numerous receptor sites for binding neurotransmitters from other cells

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10
Q

What is a neuronal axon?

A

A long, thin process

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11
Q

What is an axon hillock of a neuron?

A

A cone-shaped region where the axon joins the cell body

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12
Q

What is the Initial Segment of a neuron?

A

The part of the axon that joins the axon hillock

Has lots of voltage gated channels

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13
Q

What is the axoplasm of a neuron?

A

The cytoplasm of the axon

Contains various organelles

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14
Q

What is the axolemma of a neuron?

A

The plasma membrane of the axon

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15
Q

What are the branches along the length of an axon called?

A

axon collaterals

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16
Q

How do the axon and its axon collaterals end?

A

by dividing into many fine processes called terminal branches (telodendria)

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17
Q

What are axon terminals?

A

Aka synaptic terminals or synaptic knobs

Knob-like distal ends of the terminal branches

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18
Q

What is a neuronal synapse?

A

A specialized site where a neuron communicates with another neuron or effector cell

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19
Q

What 2 cells are involved in a neuronal synapse?

A

Presynaptic Cell: the neuron conducting the electrical signal toward the synapse

Postsynaptic Cell: the cell which receives the signal

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20
Q

What is a Neuromuscular Junction?

A

A synapse between a neuron and a muscle cell

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21
Q

What is a Neuroglandular Junction?

A

A synapse between a neuron and a gland

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22
Q

What is a neuronal synaptic cleft (gap)?

A

A narrow space

Separates the Presynaptic Cell and Postsynaptic Cell

Filled with interstitial fluid

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23
Q

What is Axoplasmic Transport?

A

The transport of materials between the cell body and axon terminals

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24
Q

In which direction along neurotubules within the axon does axoplasmic transport occur?

A

In both directions

Anterograde: Movement of materials from the cell body to the synaptic knob

Retrograde: Movement of materials from the synaptic knob to the cell body

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25
Q

What powers axoplasmic transport?

A

Powered by mitochondria, kinesin, and dynein

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26
Q

How are neurons parts organized?

A

The organization of the parts of a neuron varies with the type of neuron

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27
Q

What are 3 common types of neurons based on structure?

A

Bipolar Neurons

Pseudounipolar Neurons (Unipolar Neurons)

Multipolar Neurons

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28
Q

How many processes do bipolar neurons have?

A

2 primary processes that extend from the cell body

  • A Dendritic Process
  • An Axon

The cell body is between the 2 processes

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29
Q

Where are bipolar neurons found?

A

in special sensory organs (sight, smell, hearing)

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30
Q

How many processes do Pseudounipolar Neurons (Unipolar Neurons) have?

A

One process extends from the cell body and divides T-like into 2 axons

The 2 axons form 1 continuous process

No true dendrites

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31
Q

Where are Pseudounipolar Neurons (Unipolar Neurons) found?

A

Found in sensory neurons of PNS

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32
Q

How many processes do Multipolar Neurons have?

A

Multiple processes extend from the cell body

2 or more dendrites and 1 axon

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33
Q

Where are Multipolar Neurons found?

A

All motor neurons that control skeletal muscles are Multipolar Neurons

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34
Q

What are the most common type of neurons in the CNS?

A

Multipolar Neurons

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35
Q

Where are Purkinje Cells (Neurons) found?

A

In the cerebellum, Multipolar Neurons are called Purkinje Cells

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36
Q

What do the apical dendrites of Purkinje Cells form?

A

a large fan of finely branched processes

that enables them to receive input from a large number of neurons

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37
Q

What are the 3 Functional Classification of Neurons?

A

Sensory (Afferent) Neurons

Motor (Efferent) Neurons

Interneurons

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38
Q

Describe the function of sensory neurons?

A

Afferent neurons of the PNS

Deliver impulses from sensory receptors to the CNS

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39
Q

Where are the cell bodies of sensory neurons located?

A

in peripheral sensory ganglia

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40
Q

What are the 2 types of sensory neurons?

A

Somatic Sensory Neurons: monitor the external environment- Body position and movement

Visceral Sensory Neurons: monitor internal conditions- status of organs

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41
Q

Describe the function of motor neurons?

A

Efferent neurons of the PNS

Deliver impulses from CNS to peripheral effectors

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42
Q

What do Somatic Motor Neurons innervate and where are their cell bodies?

A

Innervate: Skeletal Muscles

Cell Bodies: Are located in the CNS

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43
Q

What do Visceral Motor Neurons innervate?

A

Smooth Muscle

Cardiac Muscle

Glands

Adipose Tissue

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44
Q

What kind of system is the Visceral Motor system?

A

A 2-neuron system:

  • Preganglionic Neuron: Cell body located in the CNS
  • Postganglionic Neuron: Cell body is located in peripheral autonomic ganglia
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45
Q

What is the location of interneurons (Internuncial Neurons)?

A

Located between neurons

Example: can process incoming sensory information from sensory neurons and stimulate a motor response by activating appropriate motor neurons

Only found in the CNS

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46
Q

Are interneurons sensory or motor?

A

neithersensoryor motor

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47
Q

What are the most common neuron in the body?

A

Interneurons make up over 99% of the neurons in the body

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48
Q

What is convergence in term of interactions between neurons?

A

Several neurons synapse on a single postsynaptic neuron

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49
Q

What does diverging mean in terms of interactions between neurons?

A

One neuron spreads stimulation to many neurons or neuronal pools in the CNS

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50
Q

What are glial cells?

A

Cells of the nervous system

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51
Q

Do glial cells generate or propagate action potentials?

A

No

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52
Q

How much of the volume of the CNS do glial cells make up?

A

Make up about half of the volume of the CNS

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53
Q

What is the function of glial cells?

A

Support neuronal survival and activities

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54
Q

What are the 4 types of Neuroglia in CNS?

A

Ependymal

Astrocytes

Oligodendrocytes

Microglia

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55
Q

What are the 2 types pf Neuroglia in PNS?

A

Satellite Cells

Schwann Cells

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56
Q

What are ependymal cells?

A

Cilia (or microvilli) lined cells that form an epithelial membrane (ependyma)

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57
Q

What do ependymal cells line?

A

Central canal of the spinal cord

Ventricles of the brain

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58
Q

What is the function of ependymal cells?

A

Produce, monitor and circulate CSF

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59
Q

Do ependymal cells have a basement membrane?

A

No basement membrane

Basal ends of ependymal cells are elongated and extend into underlying gray mater

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60
Q

What are Astrocytes?

A

The most abundant glial cells

Contain a numerous radiating processes

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61
Q

What are the functions of Astrocytes?

A
  • Maintaining the Blood-Brain-Barrier: radiating processes with expanded perivascular feet wrap around capillary endothelial cells; Secrete chemicals that control the permeability of the capillary endothelial cells
  • Provide a structural framework for CNS neurons
  • Repair damaged neural tissue
  • Guide neuron development in the embryonic brain
  • Help adjust composition of interstitial fluid in the brain
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62
Q

What are Micoglia?

A

Immune system cells act as phagocytes

Macrophages of the CNS

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63
Q

When do Microglia exist?

A

if the Resting state as Ramified Microglia

if the Active state as Reactive Microglia

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64
Q

What are ramified microglia?

A

aka “resting microglia”

Monitor CNS environment: explore CNS tissue via fine processes that continuously extend and retract

If they detect damage, disease or infection, they are activated and become Reactive Microgli

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65
Q

What activate Reactive Microglia?

A

Injury
Infection
Disease (e.g., MS, Parkinson Disease, Alzheimer Disease)

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66
Q

What are the functions of Reactive Microglia?

A

Engulf and destroy

  • Pathogens
  • Foreign material
  • Necrotic tissue
  • Cellular debris and waste products

Signal other immune cells for assistance

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67
Q

What are oligodendrocytes?

A

Cells with processes that extend out and coil around axons of CNS

The processes produce and maintain myelin sheaths around segments of multiple axons of CNS

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68
Q

How does CSF form in ependymal cells?

A

forms as filtrate containing glucose, oxygen, vitamins, and ions (Na+, Cl-, Mg2+, etc)

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69
Q

What is the function of satellite cells?

A

Surround neuron cell bodies in ganglia of PNS

Regulate the exchange of materials between the neuronal cell bodies and interstitial fluid

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70
Q

What do schwann cells do?

A

Encircle a segment of an axon

Can then either

  • Coil around the axon forming myelin sheath around a segment of a single axon (myelinated internode); Several Schwann Cells are needed to enclose an axon along its entire length
  • Not coil around the axon
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71
Q

What are myelin sheaths composed of?

A

lipid and protein

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72
Q

What are Myelinated Internodes?

A

Areas of the axon wrapped in myelin that:

  • Insulate axons
  • Increase speed of nerve impulse conduction
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73
Q

What are Nodes of Ranvier?

A

The gaps between adjacent myelinated internodes

Present on neurons with:

  • Myelinating Schwann Cells
  • Oligodendrocytes
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74
Q

What is Neurilemma?

A

The outer nucleated cytoplasmic layer of the Schwann Cell

Lies outside of the Myelin Sheath

Encloses the myelin sheath

Helps in the regeneration of an injured axon

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75
Q

What is include in Neurilemma?

A

A thin cell membrane forming the outer layer

Cytoplasm

Nucleus of the Schwann Cell

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76
Q

Where are Neurilemma found?

A

Only present around axons of the PNS

Oligodendrocytes dont have a neurilemma b/c their cell body and nucleus dont envelop the axon so, they generally dont regenerate after an injury

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77
Q

What are Nonmyelinating Schwann Cells?

A

Schwann Cells that surround axons of neurons in the PNS but coiling process doesnt occur

Neurons associated are said to be unmyelinated

Support and physically separate unmyelinated axons

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78
Q

Do Nonmyelinating Oligodendrocytes exist?

A

yes, but Few in number and Function is unknown

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79
Q

What are the steps in schwann cell myelination?

A
  1. schwann cell starts to wrap around a portion of an axon
  2. schwann cell cytoplasm and plasma membrane begin to form consecutive layers around axon
  3. the overlapping inner layers of the schwann cell plasma membrane form the myelin sheath
  4. eventually, schwann cell cytplasm and nucleus are pushed to periphery of the cell as the myelin sheath is formed
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80
Q

What are the steps in unmyelinated schwann cell axon formation?

A
  1. schwann cell starts to envelop multiple axons

2. the unmyelinated axona are enveloped by the schwann cell, but there are no myelin sheath wraps around each axon

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81
Q

What are he functions of Transmembrane Channels?

A

Serve as openings through the cell membrane

Control the movement of ions across the membrane

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82
Q

What are the 2 Main Types of Membrane Channels?

A

Leak Channels (passive)

Gated Channels (active)

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83
Q

Describe Leak (passive) membrane channels

A

Always open

Allow for diffusion of a small number of ions through the cell membrane

The plasma membrane has many more K+ leak channels than Na+ leak channels

Help maintain a stable resting membrane potential

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84
Q

How are K+ leak channels in comparison to Na+ leak channels/

A

K+ are “leakier” than Na+ leak channels

So, its easier for K+ to leak out than for Na+ to enter

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85
Q

Describe Gated (active) membrane channels?

A

Open in response to a specific stimulus

Close when the stimulus is removed

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86
Q

What are the 3 gated channels?

A

Modality (Mechanically)-Gated Ion Channels

Ligand (Chemically)-Gated Ion Channels

Voltage-Gated Ion Channels

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87
Q

Describe Modality (Mechanically)-Gated Ion Channels

A

Are specific to sensory neurons

Open in response to

  • Mechanical Forces
  • Stretch
  • Touch
  • Pressure
  • Temperature Changes

The force distorts the channel, causing the gate to open

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88
Q

Describe Ligand (Chemically)-Gated Ion Channels

A

A ligand is a chemical substance that binds to specific receptor

Open in response to the binding of a ligand (e.g., chemical)-examples:

  • Neurotransmitters
  • Hormones
  • Specific Ions

Are most abundant on dendrites and cell body of a neuron

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89
Q

Describe Voltage-Gated Channels

A

Open and close in response to changes in membrane potential (voltage)

Participate in generation and conduction of APs

Located in Axolemma of axons and Plasma
membranes of muscle fibers

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90
Q

When open, what do membrane channels allow flow of?

A

Allows flow of ions between the extracellular and intracellular environments

This results in a change in membrane potential

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91
Q

How is gradient defined?

A

The degree of inclination

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92
Q

How do ions, molecules and particles move in a gradient?

A

Tend to move down a gradient (from high concentration to low) until the concentration gradient is removed - dynamic equilibrium (uniform concentration)

The steeper the gradient, the faster the rate of movement

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93
Q

What are 3 examples of gradients?

A

Concentration Gradients

Electrical Gradients

Pressure Gradients

94
Q

How do molecules move in the state of dynamic equilibrium?

A

Molecules will still move around (and cross a membrane) but there will be no net movement of the number of molecules from one area to another

95
Q

What is a concentration gradient?

A

A state in which a substance is found indifferent concentrations eitherover a region of space or on opposite sides of a membrane

A difference in ions, molecules, or particles
between 2 regions

96
Q

How do substances move in a concentration gradient?

A

substance will move from an area of high concentration to an area of low concentration (down its concentration gradient)

97
Q

What is an electrical gradient?

A

A difference in electrical charges between 2 regions

The plasma membrane creates a difference in the distribution of positively charged ions (cations) and
negatively charged ions (anions) between the 2 sides of plasma membrane

98
Q

Electrical Gradient example: if there is a higher concentration of Na+ in the ECF compared to the ICF where does Na+ move?

A

Na+ is favored to diffuse into a cell because of the concentration gradient (chemical gradient and electrical gradient)

This combination is referred to as the Electrochemical Gradient

99
Q

Define Transmembrane Potential (Membrane Potential)

A

difference in electrical charge across plasma membrane due to differences in concentrations of ions inside and outside cell

100
Q

What is Transmembrane Potential (Membrane Potential) important for?

A

Transmission of nerve signals

Muscle contraction

Glandular secretions

The function of various other activities of the body

101
Q

What is Resting Membrane Potential?

A

The transmembrane potential in an undisturbed cell

There is no net flow of ions across the membrane

102
Q

What are the charges of the inner surface and outer surface of the plasma membrane compared to each other?

A

Inner surface more negatively charged

Outer surface more positively charged

103
Q

What is the charge range of the Resting Membrane Potential?

A

from -10 mV to -100 mV

Depending on cell type

104
Q

What channels are open with Resting Membrane Potential?

A

Only leakage channels are open

All gated Na+ and K+ channels are closed

105
Q

What is the average resting membrane potential?

A

varies by cell type, but averages -70 mV

106
Q

How is Resting Membrane Potential maintained?

A

Unequal distribution of ions in the ECF and cytosol

Inability of most ions to leave the cell

Leak channels

Na+/K+ Pumps

107
Q

What does Extracellular Fluid contain a high concentration of?

A

Na+ and Cl-

108
Q

What does Cytosol contain a high concentration of?

A

K+ and negatively charged proteins

109
Q

Are K+ leak channels or Na+ leak channels more abundant in the plasma membrane?

A

more K+ leak channels

110
Q

What does a higher abundance of K+ leak channels as compared to Na+ leak channels lead to?

A

more K+ can diffuse down their concentration gradient and out of the cell than the amount of Na+ that can diffuse down their concentration gradient into the cell

Result in:

  • Cytoplasmic surface of the plasma membrane is more negative
  • ECF surface is more positive
111
Q

What are most anions inside the cell attached to?

A

Non-diffusible molecules or Large proteins

most cannot leave

112
Q

What is the function of Na+/K+ Pumps?

A

Help maintain Resting Membrane Potential by:

  • Pumping out 3 Na+
  • Pumping in 2 K+

Requires ATP

113
Q

Define depolarization

A

Any shift from the Resting Membrane Potential toward a more positive potential

114
Q

In what situation does depolarization occur?

A

Occurs when the resting membrane is exposed to a stimulus that opens the Chemical-Gated Na+ Channels

Na+ enters the cell and creates a voltage change

The positive charge of Na+ shifts the Transmembrane Potential toward 0 mV

115
Q

What is the maximum change in Transmembrane Potential proportional to?

A

the size of the stimulus

116
Q

What does a greater Transmembrane Potential stimulus lead to?

A

greater the number of chemical channels to open

more Na+ that enters the cell

greater the membrane area affected

greater the degree of depolarization

117
Q

Define Hyperpolarization

A

A change in the Transmembrane Potential toward a more negative value than the Resting Membrane Potential (it “over shoots”)

118
Q

Hyperpolarization example: If the RMP is -70 mV, how would hyperpolarization occur?

A

Hyperpolarization would occur if the membrane potential becomes more negative than its RMP, say to -80 mV

119
Q

What can cause hyperpolarization?

A

Opening of voltage-gated K+ channels: Allows K+ to flow out of the cell

Opening of voltage-gated Cl- channels: Allows Cl- to flow into the cell

120
Q

When Transmembrane Potential changes in the membrane potential what are the 2 types of signals can be produced?

A

Graded Potentials

Action Potentials

121
Q

Describe graded potentials

A

Also called local potentials

Are a short-lived localized change in the resting membrane potential

122
Q

How do graded potentials spread?

A

Can not spread far (1 – 2 mm) from the site of stimulation

These changes cause current flows that decrease in magnitude with distance

123
Q

How does the magnitude of graded potentials vary?

A

Varies with strength of stimulus

The greater the stimulus, the greater voltage change and the farther the current will flow

124
Q

What will any stimulus that opens a Chemical-Gated Ion Channel produce?

A

a graded potential

125
Q

How are localized current (graded potentials) established?

A

A stimulus causes Chemically-Gated Ion Channels to open at site of stimulation

A small amount of a specific ion crosses the plasma membrane

A localized change in the resting membrane occurs

A localized current is established as the ions move along the cytoplasmic side of the plasma membrane

The flow of current dies out

126
Q

Why does the flow of current die out in a localized current (graded potentials)?

A

The ions entering the cell experience resistance to movement by contents of the cell

The ions leak out through leakage channels

127
Q

Where can graded potentials be generated?

A

sensory neurons

motor neurons

interneurons

128
Q

Describe graded potentials in sensory neurons

A

At peripheral sensory receptors, sensory receptors have Modality-Gated Ion Channels

When stimulated, these ion channels open allowing an influx of ions, generating a graded potential

129
Q

Describe graded potentials at Motor Neurons and Interneurons

A

On postsynaptic membrane
graded potentials are generated in motor neurons and interneurons when they’re stimulated by input from other neurons

Presynaptic neuron releases neurotransmitter

Binding of neurotransmitter to receptor on postsynaptic membrane opens Ligand-Gated Ion Channels

This causes a change in the Resting Membrane Potential of postsynaptic cell

Action of neurotransmitter on membrane channel
determines whether synaptic potential will be depolarizing (excitatory) or hyperpolarizing (inhibitory)

130
Q

What does a single nerve impulse produce?

A

a small local graded depolarization that cant induce an action potential

131
Q

Define summation

A

The process of combining the electrical impulses

132
Q

What does summation greatly increases the probability of?

A

that a postsynaptic membrane will reach threshold depolarization and result in an action potential

133
Q

What are the 2 forms of summation?

A

Temporal Summation

Spatial Summation

134
Q

What is temporal summation?

A

The combined effect of a series of small potential changes that occur within milliseconds of each other

Occurs when nerve impulses are received in rapid succession at a single synapse

Effects of the 2nd (excitatory) stimulus are added to those of the 1st (excitatory) stimulus

135
Q

In temporal summation, what does the first impulse produce?

A

A small local graded potential

Before it dissipates, successive impulses trigger more small graded potentials

These impulses summate and produce a much greater depolarization of the postsynaptic membrane than would result from a single impulse

136
Q

What happens in temporal summation if the postsynaptic membrane reaches threshold depolarization?

A

An action potential can occur

137
Q

When does spatial summation occur?

A

When simultaneous stimuli at different locations have a cumulative effect on the transmembrane potential

Involves multiple synapses that are active simultaneously

138
Q

What does the activity of one synapse produce in spatial summation?

A

a graded potential with localized effects

139
Q

What happens if more than one synapse is active at the same time in spatial summation?

A

All will “pour“ Na+ across the postsynaptic membrane

140
Q

What happens at each active synapse in spatial summation?

A

The Na+ that produce the EPSP spread out along the inner surface of the membrane and mingle with those entering at other synapses

The effects on the membrane are cumulative

141
Q

What determines the degree of depolarization in spatial summation?

A

How many synapses are active at any moment

Their distance from the initial segment

142
Q

When does an action potential occur in spatial summation?

A

When the transmembrane potential at the initial segment reaches threshold

143
Q

What actions occur with no summation in temporal summation?

A

2 stimuli separated in time cause EPSPs that do not add together

144
Q

What is spatial summation of EPSPs and IPSPs?

A

changes in membrane potential can cancel each other out

145
Q

What are the steps in a summation action potential generation?

A

neurotransmitter release

receptor binding

ion channels open or close

conductance change causes current flow

postsynaptic potential changes

postsynaptic cells excite or inhibit

summation determines whether or not an AP occurs

146
Q

What is an action potential?

A

A brief reversal of the membrane potential

Consists of propagated changes in the transmembrane potential that, once initiated, affect the entire excitable membrane

It is an electrical impulse that travels along the cell membrane and does not diminish as it moves away from its source

147
Q

What must happen in terms of depolarization for an action potential to occur?

A

Depolarization has to be great enough to reach the membrane threshold causing the voltage-gated channels to open

148
Q

What is threshold in terms of action potential?

A

The minimum voltage to stimulate an action potential

Varies, but average is about -55 mV in many neurons

149
Q

What are the cells with excitable membranes that can generate action potentials?

A

Neurons

Muscle Cells

150
Q

What is the principle way neurons communicate?

A

action potentials

151
Q

What is the All-or-None principle?

A

A stimulus either triggers an action potential or does not produce one at all

You can not have a partial action potential

152
Q

When the threshold is reached what occurs with the impulse?

A

The impulse generated will travel the entire length of the membrane

153
Q

What kind of actions potentials are produced by strong stimuli as compared to minimally sufficient stimuli?

A

Strong stimuli produce action potentials of the same voltage and duration as are produced by minimally sufficient stimuli

154
Q

What depolarization is sufficient to trigger and action potential?

A

15 mV depolarization (from -70 mV to -55 mV)

155
Q

What is the trigger zone (Spike Initiation Zone)?

A

In most neurons, where action potentials are generated at the junction of the axon hillock and initial segment as a result of a graded potential that occurred in the cell body or dendrites

156
Q

What does the trigger zone have a high concentration of?

A

voltage-gated Na+ channels

157
Q

What type of summation occurs with synaptic potentials initiated in the cell body and dendrites in the trigger zone?

A

spatially and temporally summated

158
Q

What happens if the influx of Na+ reaches the Trigger Zone and is sufficient to depolarize the Trigger Zone to threshold?

A

The voltage-gated Na+ channels will open and an action potential will be propagated

159
Q

What are the steps in an action potential at the trigger zone?

A
  1. a graded potential above threshold reaches the trigger zone
  2. voltage-gated Na+ channels open, and Na+ enters the axon
  3. positive charge flows into adjacent sections of the axon by local current flow
  4. local current flow from the active region causes new sections of the membrane to depolarize
  5. refractory period prevents backward conduction. loss of K+ from the cytoplasm repolarizes the membrane.
160
Q

What are the 3 steps in generation of an action potential?

A

Depolarization
Repolarization
Hyperpolarization

161
Q

What is involved in the depolarization step of an action potential?

A

A stimulus opens the chemical-gated Na+ channels

Opening of the voltage-gated Na+ channels occurs at the transmembrane potential known as threshold (–60 to –55 mV)

When the voltage-gated Na+ channels open plasma membrane becomes much more permeable to Na+

Due to their electrochemical gradient Na+ rushes in and rapid depolarization occurs

162
Q

What happens with the transmembrane potential in depolarization?

A

The transmembrane potential changes from – 70 mV to a positive value

163
Q

After depolarization what kind of ions are found on the cytoplasmic side of the plasma membrane like?

A

cytoplasmic side of the plasma membrane now contains more + ions than – ions

164
Q

Do all depolarizations lead to action potentials?

A

No, the stimulus must be significant enough to cause the membrane potential to reach the threshold

The stimulus must cause a depolarization large enough to open voltage-gated Na+ channels to initiate an action potential

165
Q

What happens as transmembrane potential approaches +30mV?

A

Repolarization begins

Voltaged-gated Na+ channels close and Voltaged-gated K+ channels open

K+ exit the cell and flows out, down its electrochemical gradient

Transmembrane potential shifts back towards its resting level

166
Q

What is repolarization in an action potential?

A

The process of returning the transmembrane potential to normal resting levels

167
Q

What occurs on the cytoplasmic side of the plasma membrane during repolarization?

A

Starts to move away from a positive value and towards its resting potential as a result of ion movement through the membrane channels

More positive ions are exiting the cell than entering

168
Q

After repolarization how long do the voltage-gated Na+ channels remain inactivated?

A

Until the membrane has repolarized to near threshold levels

At that level they remain closed but capable of opening

169
Q

After repolarization when do voltaged-gated K+ channels begin closing?

A

as the membrane reaches the normal resting potential (– 70 mV)

Until all of the K+ channels close K+ continue to exit the cell (until about – 90 mV) which causes a brief hyperpolarization

170
Q

At what point does the repolarization phase end?`

A

when the membrane potential reaches its resting state (e.g., – 70 mV) but K+ will continue to exit until all K+ channels close

171
Q

What is hyperpolarization of an action potential?

A

The phase during which the membrane potential temporarily becomes more negative than the resting potential

172
Q

When are the K+ voltage channels finally closed?

A

at about – 90 mV

AP has ended

173
Q

How is resting potential restored after repolarization?

A

K+ leaks into the cell to restore normal resting electrical potential

Na+/K+ pump restores normal resting ionic conditions

174
Q

What is the absolute refractory period?

A

Period from opening (activation) of the voltage-gated Na+ channels until voltage-gated Na+ channels reset to original resting state

During this time, the plasma membrane cannot respond to further stimulation because the voltage-gated Na+ channels either are Already open or Inactivated

175
Q

What is the relative refractory period?

A

Begins when voltage-gated Na+ channels have returned to resting state with some voltage-gated K+ channels still open and repolarizing occurring

Ends when the membrane has returned to resting potential

During this time, axon’s threshold for AP generation is substantially elevated and a stimulus that would normally have generated an AP is not sufficient

A very strong stimulus is needed to re-open the voltage-gated Na+ channels that have already returned to resting state and allow another AP to generate

176
Q

What are the Sequence of Events that Transmit Sensory Information along an Axon?

A
  1. Deformation of a peripheral receptor
  2. Change in local membrane potential of the sensory ending
  3. Development of an action potential in the sensory axon
  4. Release of neurotransmitter from the sensory neuron presynaptic terminal
  5. Binding of neurotransmitter to the ligand-gated channel on the postsynaptic cell membrane
  6. Activation of postsynaptic membrane potential
177
Q

What is the refractory period?

A

The period from the time an action potential begins until the normal resting potential has stabilized

The membrane will not respond normally to additional depolarizing stimuli

178
Q

What are the 2 parts of the refractory period?

A

Absolute Refractory Period

Relative Refractory Period

179
Q

What does the Absolute Refractory Period prevent?

A

Prevents the neuron from generating a second action potential

Ensures that each action potential is a separate “all or none” event and one-way transmission

180
Q

What is the speed of nerve impulse transmission is affected by?

A

Myelin

Diameter of Axon
-The larger the diameter, the lower the resistance and the faster the propagation speed (b/c cytosol offers less resistance than the plasma membrane)

181
Q

What are the 2 ways an AP travel along an axon?

A

Continuous Propagation (unmyelinated axons)

Saltatory Propagation (myelinated axons)

182
Q

What is Continuous Propagation (unmyeliated axons)?

A

The AP moves along the axon membrane in segments, starts at initial segment of axon

The initial segment has an abundance of voltage-gated Na+ channels

The local current spreads in all directions

183
Q

Why cant an axon cell body respond to an AP in continuous propogation?

A

Because it lacks voltage-gated Na+ channels

184
Q

In continuous propagation what happens to the previous segment as the next segment depolarizes?

A

an AP is generated and the previous segment enters Refractory period

so, APs only move in one direction (forward)

185
Q

In continuous propagation, how does an AP move?

A

across the surface of the membrane in a series of tiny steps

186
Q

What is Saltatory Propagation (myelinated axons)?

A

Myelin increases the resistance to the flow of ions across the membrane

Voltage-gated Na+ channels are concentrated at the nodes so only the nodes respond to depolarization

Ions can only cross the plasma membrane at the Nodes of Ranvier

The action potential “jumps” from node to node

187
Q

Are nerve impulses carried along an axon faster in continuous propagation or saltatory propagation?

A

Saltatory Propagation

188
Q

What are the three steps of Saltatory Propagation?

A
  1. local potentials: local potentials usually generated in the neuron’s dendrites accumulate and reach the trigger zone of the axon
  2. action potentials: trigger zone depolarizes to threshold and generates an action (AP)
  3. action potential propagation: the action potential is propagated down the axon to the axon terminals
189
Q

What is Neuroinflammation?

A

The response of the CNS to Infection, Disease, and Injury

190
Q

What is the Neuroinflammation response mediated by?

A

Reactive Microglia

Astrocytes

191
Q

When are reactive microglia beneficial?

A

Engulf and destroy: Pathogens, Foreign material, Necrotic tissue, Cellular debris and waste products

Signal other immune cells for assistance

Produce neurotrophic factors (proteins) that support axonal regeneration and remyelination

Mobilize astrocytes to: Reseal the blood-brain barrier and Provide nutritional support

192
Q

What kind of harmful effects can Neuroinflammation cause?

A

Death of neurons and oligodendrocytes

Inhibit neural regeneration

193
Q

In what conditions can a correlation between abnormal glial activity and neural damage be seen?

A

Stroke

Alzheimer’s Disease

Parkinson’s Disease

MS

194
Q

What kind of harmful correlation can reactive glial cells cause?

A

correlation between abnormal glial activity and neural damage

195
Q

When Microglia and Astrocytes become excessively activated this can cause them to what?

A

Lose their physiologic buffering function

Release harmful substances such as: Inflammatory Cytokines and Proteinases

Contribute to neuronal damage

196
Q

What is the reason for the dual role of a delicate balance between the protective roles and destructive roles of microglia?

A

not fully known

197
Q

For what function is myelin a critical component?

A

conduction of information in the nervous system

198
Q

What happens to an AP as it travels along an axon from a myelinated region to an area where myelin has been damaged?

A

Resistance to the electrical signal increases as Na+ leaks out

Propagation of the electrical current slows and eventually may stop before it reaches the next site of conduction

199
Q

Cell implantation advances have been made to enhance neuronal regeneration where/when?

A

In demyelinating disease

and

Following nerve trauma

200
Q

In animals, what does Schwann cell implants result in?

A

significant regeneration of axons across a spinal cord transection

201
Q

What is the significance of regeneration of axons across a spinal cord transection in animals?

A

It’s often associated with improved motor function

It has great potential as a medical intervention for individuals with spinal cord injury

202
Q

Following trauma to the spinal cord what is the migration path of Schwann cells and why?

A

From periphery into spinal cord injury site, where they participate in endogenous repair processes

B/c of Schwann cell’s intrinsic characteristics including the ability to secrete a variety of neurotrophic factors that help in the repair process

203
Q

What are the capabilities of Transplanted Schwann Cells?

A

Myelinating Regenerating Axons

Remyelinating Demyelinated Axons

204
Q

What does the transplantation of Schwann Cells result in?

A

significant regeneration of axons across a spinal cord

205
Q

What do axons remyelinated by transplanted Schwann cells exhibit?

A

restoration of conduction through the lesion with reestablishment of normal conduction velocity

206
Q

How do demyelinating diseases affect conduction?

A

Reduce or block conduction when current leaks out of previously insulated regions between the nodes

207
Q

What is Guillain-Barré Syndrome?

A

A life-threatening group of autoimmune disorders that attack the PNS?

208
Q

What are the subtypes of Guillain-Barré Syndrome?

A

Acute Inflammatory Demyelinating Polyneuropathy

Acute Axonal Neuropathy

209
Q

What is the onset and cause of Guillain-Barré Syndrome?

A

Onset: rapid and often preceded by a Viral Infection or Bacterial Infection

Cause: Unknown

210
Q

What is the suspected pathogenesis of Guillain-Barré Syndrome?

A

Depends on subtype

Autoantibodies may attack the: Myelin causing demyelination of the axon OR
Axon causing axonal degeneration

211
Q

What are the motor clinical manifestations of Guillain-Barré Syndrome?

A

Rapidly progressive ascending muscle weakness of the limb

Starts in the legs

Spreads upward to the arms and face

Can lead to flaccid paralysis

212
Q

What are the sensory clinical manifestations of Guillain-Barré Syndrome?

A

Paresthesia

Numbness

Neuropathic Pain

213
Q

What are the ANS clinical manifestations of Guillain-Barré Syndrome?

A

Hypotension

Arrhythmias

Abnormalities in sweating

214
Q

Why is Guillain-Barré Syndrome usually a medical emergency?

A

Because it may involve respiratory muscles in which rapid respiratory failure can occur requiring use of a ventilator

215
Q

What population does Guillain-Barré Syndrome affect?

A

anyone at any age, male/female

216
Q

When are peak symptoms seen in Guillain-Barré Syndrome?

A

Often within 10 - 14 days

217
Q

What methods are used to diagnose Guillain-Barré Syndrome?

A

Examination

Signs/Symptoms

Loss of Deep Tendon Reflexes

Nerve Conduction Studies, EMG

Analysis of CSF: High levels of protein

218
Q

What is plasmapheresis?

A

A process that filters blood, separating plasma from the blood cells

Blood cells are returned to the person

Plasma, which contains the antibodies is removed

Plasma is replaced with: Donated plasma or A plasma substitute

219
Q

What treatment methods are used for Guillain-Barré Syndrome?

A

High-dose Immunoglobulin Therapy

Plasmapheresis

220
Q

Do people with Guillain-Barré Syndrome ever recover?

A

80% - 90% of persons achieve a full and spontaneous recovery within 6 - 12 months

221
Q

Explain the physiological issue that occurs with Guillain-Barré Syndrome?

A

Autoantibodies bind to and attack myelin

Macrophages subsequently invade myelin

Autoantibodies bind to the axolemma at the Nodes of Ranvier and damage the axon

222
Q

What is OT for Guillain-Barré Syndrome? directed at?

A

Activities of daily living, including self-care

Stretching and range of motion exercises

Return of functional mobility

223
Q

If voluntary movement is present in a person with Guillain-Barré Syndrome why should exercise be gentle?

A

To avoid causing damage in partially denervated muscles

Because exercise of partially denervated muscles can interfere with axonal regrowth

224
Q

What is the most common demyelinating disorder?

A

Multiple Sclerosis

225
Q

What is Multiple Sclerosis?

A

A chronic inflammatory autoimmune demyelinating disease of the CNS

Characterized by: Inflammation and Selective destruction of CNS myelin

226
Q

How does Multiple Sclerosis affect the PNS?

A

it doesnt

227
Q

Multiple sclerosis is the leading cause of what in early adulthood?

A

neurologic disability

228
Q

What is the age of onset for Multiple Sclerosis?

A

20 – 40 years of age

229
Q

Does MS affect men or women more?

A

Women affected twice as frequently as men

230
Q

What is the cause of MS?

A

Unknown but possibly related to:

  • Genetic Mutation: A group of genes that affect many immune functions
  • Environmental Factors like Exposure to the Epstein-Barr Virus, Smoking and Low levels of Vitamin D
231
Q

How can low levels of vitamin D cause MS?

A

Vitamin D activates receptors on immune regulatory cells

Once activated, these cells decrease immune activity, potentially decreasing the likelihood of developing an autoimmune disease like MS

232
Q

When is MS more likely to occur?

A

If there is a family history of MS: 15% of individuals with MS have a first-degree relative with MS

In individuals who live in a region where MS is more common - regions farther away from the equator

Neuroscience (3 decks)

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