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Biology 1 > Lecture 15- Neurons and nervous system > Flashcards

Lecture 15- Neurons and nervous system Flashcards

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1
Q

What are the two categories of cells that make up the nervous system?

A

Neurons and glia (also called glial cells)

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2
Q

What does it mean that neurons are ‘excitable’?

A

They can generate and propagate electrical signals

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3
Q

What is the name of the electrical signal that is generated and propagated by neurons?

A

Action potentials or nerve impulses

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4
Q

What is the function of glial cells with the nervous system?

A

To provide support and maintain the extracellular environment of the neurons physically, immunologically and metabolically.

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5
Q

What is a nerve?

A

A bundle of axons that come together from many different neurons

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6
Q

What is the purpose of long extensions on neurons?

A

Axons enable them to conduct action potential over long distances

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7
Q

How are nervous systems able to process information?

A

Their neurons are organised into networks of three functional categories.

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8
Q

Name the three functional categories of neuron cells.

A

Afferent neurons (information comes from sensory neurons)
Efferent neurons
Interneurons

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9
Q

What do afferent neurons do?

A

Carry sensory information into the nervous system from sensory neurons

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10
Q

What do sensory neurons do?

A

These transduce sensory information input into action potentials
(Afferent and sensory neurons are the same category)

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11
Q

What do efferent neurons do?

A

Carry commands to physiological and behavioral effectors such as muscles and glands

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12
Q

What do interneurons do?

A

Integrate and store information and facilitate communication between sensors and effectors

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13
Q

Simple animals such as cnidarians have simple networks of neurons that communicate directly between…

A

Sensory cells and effectors

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14
Q

Where is the cnidarian’s nerve net most developed?

A

Around the tentacles and oral openings to facilitate food detection or danger

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15
Q

Animals that move around for food and mates process and integrate larger amounts of information. How?

A

More neurons

Neurons organised into clusters called ganglia

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16
Q

How are ganglia distributed within different bodies?

A
  • Different purposes are distributed around the body, such as in earthworms and squid
  • Bilateral symmetry- ganglia come in pairs (1 per side)
  • Large animals have a large pair of ganglia- brain
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17
Q

In vertebrates, where are most cells of the nervous system found?

A

The brain and spinal cord

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18
Q

What are the brain and spinal cord together called?

A

The central nervous system

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19
Q

What are neurons that extend or reside outside of the brain or spinal cord called?

A

The peripheral nervous system

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20
Q

How many neurons does the human nervous system contain?

A

10^11

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21
Q

What are synapses?

A

Structures where neurons are in close proximity and pass on information

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22
Q

What is the name of the neuron sending the message?

A

The presynaptic neuron

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23
Q

What is the postsynaptic neuron?

A

The neuron that receives a message from the presynaptic neuron

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24
Q

How many synapses does the human brain contain and why?

A

10^14

Because each neuron can receive information from 1000+ synapses

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25
Q

What do specialized ganglia in squid do?

A

Serve more complex behaviors

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26
Q

How fast is transmission along a neuron?

A

100m per second or more

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27
Q

What are the 4 main regions of a neuron?

A

The cell body, dendrites, axon, axon terminals

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28
Q

What does the axon hillock do?

A

Integrates information collected by dendrites and initiates action potentials

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29
Q

What does the cell body contain?

A

The nucleus and most cell organelles

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30
Q

What is the function of dendrites?

A

Receive information from other neurons or sensory cells to the cell body

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31
Q

What is the function of the axon?

A

Conducts action potentials away from the cell body

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32
Q

What structures are at the end of the axon, away from the cell body?

A
  • Axon divides into a spray of fine nerve endings

- At the tip of these, there is an axon terminal that forms a synapse

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33
Q

What type of synapse is most abundant?

A

Chemical synapses

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34
Q

What distance separates the pre and post synaptic membranes?

A

25 nanometers

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35
Q

The arrival of an action potential at an axon terminal causes…

A

the release of chemical messenger molecules, neurotransmitters, from the axon terminal.

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36
Q

Nervous systems vary in size and complexity. Give an example of differences between the brains of vertebrate species.

A
  • Region that processes olfactory information is more developed in pigs than humans
  • Human brain has much of their brain given over to integration of complex behaviors, learning and memory
  • Shark brains deal primarily with sensory and motor information
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37
Q

What do brain stems serve?

A

Basic physiological functions

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38
Q

Are neurons or glial cells more abundant in the nervous system?

A

Glia

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39
Q

What are some roles of different glia?

A
  • Physical support and orientation of neurons during embryonic development
  • Supply neurons with nutrients, maintain extracellular environment
  • Insulation
  • Removal of debris/foreign matter
40
Q

What type of glial cells are seen in the CNS?

A

Glia called oligodendrocytes

41
Q

What type of glial cells are seen in the PNS?

A

Schwann cells

42
Q

What do oligodendrocytes and schwann cells do?

A

Wrap around axons of neurons and cover them with concentric layers of insulating plasma membrane, called myelin

43
Q

How does myelination effect axons?

A

Myelinated axons conduct action potentials faster than those not myelinated

44
Q

What is another type of glial cell?

A

Astrocytes

45
Q

What is the function of astrocytes?

A

Contribute to the blood-brain barrier

46
Q

What does the blood brain barrier do?

A

Protects the brain from toxic chemicals in the blood

47
Q

How do astrocytes protect the blood brain barrier?

A

They surround the smallest, most permeable blood vessels in the brain

48
Q

What does the blood-brain barrier consist of and is hence permeable to?

A

Plasma membranes- permeable to fat-soluble substances such as anesthetics and alcohol

49
Q

What is the charge of the inside of a neuron at rest compared to the outside?

A

Negative

50
Q

What is the membrane potential?

A

Any difference in the electric potential across the plasma membrane

51
Q

What is membrane potential measured in?

A

Milivolts

52
Q

What is resting potential?

A

The membrane potential when a neuron is resting and not firing action potentials.

53
Q

What does voltage cause?

A

Electric current as ions to move across cell membranes

54
Q

In solutions and across cell membranes, what carries electric current?

A

Ions

55
Q

What are the major ions that carry electric charges across the plasma membranes of neurons?

A

Na+, K+, Ca2+, Cl-

56
Q

What is voltage?

A

A force that causes electrically charged particles to move between 2 points

57
Q

How is membrane potential measured?

A

Electrodes
Made from a glass pipette and sharp tip filled with a conducting solution- one electrode inside the neuron and one outside- difference is measured.

58
Q

What is the resting potential of a typical axon?

A

-60 to -70 milivolts

59
Q

How does resting potential provide a means for neurons to respond to stimulus?

A

Chemical or physical processes that change the permeability of the plasma membrane to ions produce a change in the cell’s membrane potential

60
Q

What is an action potential?

A

A sudden and rapid reversal in the voltage across a portion of the plasma membrane.

61
Q

The plasma membrane is impermeable to ions. How do they cross the plasma membrane?

A

Ion pumps and channels

62
Q

How are ions moved against their concentration gradient?

A

Ion pumps which use energy

63
Q

What is a major ion pump in the plasma membranes of neurons?

A

Sodium-potassium pump (sodium-potassium ATPase)

64
Q

What does the sodium potassium pump do?

A

Actively expels Na+ from inside the cell and exchanges it for K+ outside the cell

65
Q

Ion channels are generally…

A

selective

66
Q

What is an electrochemical gradient?

A

The voltage difference and concentration difference across a plasma gradient that determines net movement of ions

67
Q

What channels are most commonly open in the plasma membranes of resting neurons?

A

Potassium channels

68
Q

Describe the movement of potassium ions in a resting neuron.

A

Potassium is pumped in
Concentration of potassium is lower outside of cell- potassium diffuses out
Charge inside the neuron becomes more negative
Potassium diffuses back in

69
Q

What is the membrane potential at which there is no net movement of potassium ions?

A

The potassium equilibrium potential

70
Q

How is the potassium equilibrium potential calculated?

A

Using the Nernst equation

71
Q

What is the Nernst equation?

A

Eion=2.3*RT/zF log([ion o]/[ion i])

72
Q

How can ion channels and their properties be studied?

A

Patch clamping

73
Q

Describe how patch clamping works.

A
  • Recording pipette filled with conducting solution is placed on the neurons membrane
  • Slight suction clamps the membrane to tip
  • Retracting pipette removes the membrane patch and ion channels
  • Record as electric currents
74
Q

What type of ion channel can open and close in response to voltage changes across the plasma membrane?

A

Voltage-gated channels

75
Q

What do chemically gated channels open or close in response to?

A

Presence of absence of specific molecules that bind to the channel protein or receptor that in turn alters the channel protein

76
Q

Other than chemical and voltage gated channels, what type of channel is there and what does it respond to?

A

Mechanically gated channels open or close in response to mechanical force applied to the plasma membrane

77
Q

What happens when sodium channels in the plasma membrane of a neuron open?

A

Na+ diffuses in

The plasma membrane is depolarised

78
Q

When does the membrane become hyperpolarised?

A

When gated K+ channels open and K+ leaves

79
Q

What does it mean when a membrane is hyperpolarised?

A

The cell becomes more negative inside

80
Q

What happens when a cell is depolarised?

A

Voltage gated Na+ channels open and Na+ rushes into the axon- influx of + ions causes more depolarization.

81
Q

When is a threshold reached?

A

5-10mV above resting potential, when influx of Na+ cannot be offset by outward movement of K+

82
Q

What happens when the threshold is reached?

A

Voltage-gated Na+ channels open- the membrane becomes positive and the action potential occurs

83
Q

What is the name given to the period of time when Na+ channels cannot open?

A

Refractory period

84
Q

What are the two Na+ channel gates?

A

Activation gate, inactivation gate

85
Q

When is a sodium channel activation gate open and closed?

A

Closed at rest, opens quickly at threshold

86
Q

When is an sodium channel inactivation gate open and closed?

A

Open at rest and closes at threshold but responds more slowly, the gate reopens 1-milliseconds later than the activation gate closes

87
Q

How do voltage gated K+ channels contribute to the refractory period?

A

By remaining open

88
Q

What does the movement of K+ ions back in to the neuron do?

A

Makes the membrane potential less negative than resting potential for a brief period- hyperpolarisation or undershoot

89
Q

What does hyperpolarisation (undershoot) do?

A

Prevents the action potential moving backwards along the axon

90
Q

Why can an action potential be described as an all-or-none event?

A

Voltage gated sodium channels have a positive feedback mechanism- ensures maximum value of action potential

91
Q

Why can an action potential be described as self-regenerating?

A

It spreads to adjacent membrane regions

92
Q

What effect does myelination by glial cells have?

A

Increases conduction velocity of axons

93
Q

What are nodes of Ranvier?

A

Regularly spaced gaps where the axon is not covered with myelin

94
Q

Where are action potentials generated?

A

At nodes- the positive current flows down the inside of the axon

95
Q

What happens when the action potential reaches the next node?

A

The membrane is depolarised and another axon potential is generated

96
Q

The movement of action potentials ‘jumping’ from node to node is called…

A

saltatory conduction

97
Q

What is the name of the neurotransmitter used by vertebrate motor neurons?

A

Acetylcholine

Biology 1 (16 decks)

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