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The Dynamic Cell > Neuronal communication > Flashcards

Neuronal communication Flashcards

1
Q

What is the somatic nervous system

A

motor nerves from CNS to skeletal muscles. Voluntary control.

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2
Q

What is the autonomic nervous system

A

nerves from CNS to internal organs e.g., heart

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3
Q

What is an excitatory synapse

A

electrical activity in presynaptic neuron to increase the excitability of postsynpatic neuron. (Inhibitory – decreases)

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4
Q

What is a chemical synapse

A

prevent direct electrical propagation of AP from pre – to post - synaptic neuron

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5
Q

What happens when an action potential reaches a synapse

A
  1. Pores in cell membrane open allowing influx of Ca2+ into pre-synaptic terminal
  2. Neurotransmitter is released into synaptic cleft
  3. Neurotransmitter diffuses across the synaptic cleft and interacts with receptors on the post-synaptic membrane
  4. the neurotransmitter causes a pore to open allowing an influx of ions into the post-synaptic terminal which is propagated along the dendrite towards the soma
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6
Q

How long is the synaptic delay

A

~0.5ms

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7
Q

How long is the sypase

A

20-30nm

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8
Q

What is removed and uptaken at the synapse

A

enzymes, reuptake by glial cells

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9
Q

Fusion of vesicle with presynaptic membrane - part 1

A
  1. Opening of Ca 2+ channels and actin.
  2. Fusion protein macromolecules (FPMs) separate to allow fusion.
  3. Vesicle membrane incorporated into presynaptic membrane.
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10
Q

Fusion of vesicle with pre-synaptic membrane - part 2

A
  1. Clathrin molecules assist inward movement of the vesicle membrane. Dynamic assists in FPM pairs and pinching the neck of the emerging vesicle.
  2. Vesicles are now free for recycling.
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11
Q

How are neurotransmitters removed from the synaptic cleft

A
  1. Enzymatic breakdown
  2. Active reuptake (rapid) - pumped back into pre-synaptic terminal
  3. Active uptake (rapid) - pumped into glial cells
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12
Q

How does novichok poison you

A

inhibits acetylcholinesterase

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13
Q

Symptoms of novichok poisoning

A

Symptoms: Spasm, prevents relaxation of muscles (cardiac and respiratory). Cause of death asphyxiation or cardiac arrest

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14
Q

Features of novichok poisoning

A

Fast acting. Remain poisonous for a long time period

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15
Q

Features of an excitatory post-synaptic potential (EPSP)

A

fast rise time, slower decay time - depolarising

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16
Q

What causes EPSP

A

Usually caused by ligand gated channels once neurotransmitter has binded, Na enters to depolarise. G protein couples receptors can also cause this, (neurotransmitters bind)

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17
Q

What are EPSPs and IPSPs

A

‘mini action potentials’ which cause transient a small transient change in membrane potential of a cell (either aid or hinder action potential formation. They can summate (an opposed to Aps).

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18
Q

Excitatory neurotransmitters

A

Glutamic acid (most common) and acetylcholine are excitary neurotransmitters and cause influx of Na (EPSP)

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19
Q

Inhibitory neurotransmitters

A

Glycine and GABA, produce an increase in negative potential (away from action potential threshold). Chloride entering cell of Potassium leaving the cell cause this.

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20
Q

What is convergence of neuronal communication

A

integrating information from a number of inputs

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21
Q

What is divergence of neuronal communication

A

response to be felt from a number of effectors

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22
Q

What happens if Ex1 fires twice with sufficient time between the 2

A

the post synaptic potential has decayed so there is no summation of inputs and no action potential, firing.

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23
Q

When does temporal summation occur

A

EX1 fires twice in a short time, so can summate sufficient to cause an action potential.

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24
Q

What happens when EX1 and EX2 are fired at the same time

A

EPSPS can summate and cause an action potential

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25
Q

What can prveent an action potential firing

A

An inhibitory presynaptic input

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26
Q

Wat do inhibitory neurotransmitters cause

A

IPSPs which can prevent action potentials firing

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27
Q

Why are action potentials required

A

for correction functioning of the brain, heart and skeletal muscles.

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28
Q

What is a nerve fibre

A

the axon of a single neuron

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29
Q

What is a nerve

A

a bundle of nerve fibres

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30
Q

What is intracellular recording

A

recording electrical activity across a membrane of one single cell (one electrode is inside the cell and one (earth) is outside).

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31
Q

What is extracellular recording

A

recording electrical activity from a population of cells (both electrodes are outside of the cell).

32
Q

Extracellular recording technique

A

metal, hollow, saline-filled glass or silicon electrodes

33
Q

Extracellular recording technique

A

metal, hollow, saline-filled glass or silicon electrodes

34
Q

Intracellular recording technique

A

with an electrolyte-filled hollow glass ‘spear’ (<0.1um tip)

35
Q

Patch recording (with a clean ~ 1 +um tip diameter glass pipette):

A

Record from slices of brain tissue, kept alive in solution that mimics extracellular fluid (cerebrospinal fluid, CSF) or record from cultured, dissociated cells. Measure voltage or current in the cell. Record action potentials/synaptic communication using electrodes. Ca2+ imaging using a dye.

36
Q

What is electrophysiology

A

recording the signals in excitable cells

37
Q

Patch recordings: Giga seal

A

Ensures negligible current leaks out under rim of pipette
Reduces the noise
Enables the detection of very small current (picoamps 10^-12 A, pA) flowing through single channels
Brings small electrode onto the cell, positive pressure applied to electrode so there is a clean passage through solution of brain, positive pressure removed and gentle suction pulls cell membrane up to the pipette, further suction rips a whole in cell gaining electrical access to the cell.

38
Q

Intracellular sharp electrode recordings

A

In Vivo (intact animals, via skull ‘window’). Measure electrically during behavior. Can introduce fluorescent dyes to help visulaise individual cells dendritic trees

39
Q

How does a lipid membrane have capacitance

A

the lipid membrane separates (stores) opposite electric charges and voltage (potential) is produced across the membrane between separated opposite charges, by electrostatic attraction

40
Q

charge formula

A

current x time

41
Q

What is voltage

A

the electrical driving force for a current

42
Q

Voltage formula

A

charge stored/capcaitance

43
Q

What is capacitance

A

ability of the membrane to store charge

44
Q

Positive feed back cycle of action potential

A

triggering event -> depolarization -> opening of voltage gated Na+ channels -> Influx of Na+

45
Q

How does tetrodoxtin effect the nervous system

A

Selectively blocks Na+ channels (prevents action potentials)

Binds to extracellular side

High affinity (blocks at nM concentrations)

46
Q

Where is tetrodoxtin found

A

naturally in puffer fish

47
Q

What does tetraethylammonium (TEA+) affect

A

TEA+ blocks K+ channels from wither side

Causes paralysis of the skeletal muscles and marked drowsiness

Effects the falling phase – becomes longer and slower falling as K+ efflux is prevented

48
Q

What is the most widely distributed ion channel

A

K+ channel

49
Q

What do voltage sensors do

A

(detect depolarisation) cause voltage gated ion channels to open allowing Na+ to enter

50
Q

What causes inactivation of Na+

A

Hinged lid and allosteric blocking mechanism - cytoplasmic gate is closed more slowly by depolaristaion

51
Q

What is permeability of the membrane proportional to

A

number of channels open or total conductance of that channel type.

52
Q

Max firing rate

A

Pyramidal neurons (excitary) ~ 300 spikes vs AP duration ~ 1.5ms

53
Q

What is the conduction velocity

A

the speed at which propagation of the action potential occurs. Measured in m/s, can range from 1-100 m/s

54
Q

What is current to produce a given change in voltage proportional to

A

1/thickness

55
Q

Is more or less current required with myelinated fibres

A

less

56
Q

What is current to produce a given voltage change inversely proportional to

A

membrane thickness

57
Q

What does the current flow occur between

A

the active and adjacent inactive areas

58
Q

What do nodes of ranvier have

A

a high Na+ concentration

59
Q

How do myelinated fibres transmit an action potential

A

saltatory conduction - current jumps between nodes (increases conduction velocity)

60
Q

What does myelin prevent

A

charge through ion channels

61
Q

What factors effect conduction velocity

A
  1. Myelination of the axon (good insulator, increases resistance, decreases conductance?)
  2. Diameter of the axon (internal resistance)
62
Q

Pros of myelination

A

+Speed:20 m/s unmyelinated squid giant axon vs up to 120m/s in myelinated
+Economy: squid giant axon consumes 5000 times more energy than same speed myelinated axon
+Space

63
Q

Cons of myelination

A

Metabolic and developmental costs of setting up vulnerable to demyelinating diseases e.g. Multiple Sclerois (CNS). Guillain-Barre syndrome (peripheral nerves)

64
Q

What do demyelinating conditions do

A

decrease conduction velocity in affected axons. Can eventually result in block of conduction. Will cause axonal death in the long term

65
Q

What is multiple sclerosis

A

disruption in myelin sheath in CNS neurons

66
Q

Symptoms of multiple sclerosis

A

numbness and tingling. Progressive muscle weakness. Mobility problems.

67
Q

What is the cause of multiple sclerosis

A

genetics, gender and some viral infections

68
Q

Causes of Guillain Barre syndrome

A

campylobacter, influenza virus, cytomegalovirus, epstein-barr virus

69
Q

What happens in Guillain Barre syndrome

A

Disruption of myelin sheath in PNS neurons

70
Q

Symptoms of Guillain Barre Syndrome

A

pins and needles in the hands and feet, limb weakness and uncoordinated movement

71
Q

Extracellular recordings of action potentials:

A

From population of neurons. Measure voltage difference between 2 electrodes relative to one another. Stimulate whole nerve. Biphasic compound action potential -

72
Q

When are action potentials graded

A

Compound AP recorded from whole nerve is NOT “all or none” they are graded. Graded dependent on size of the stimulus

73
Q

What is a small stimulus

A

few fibres – small potential

74
Q

What is a larger stimulus

A

more fibres – larger potential

75
Q

What is a maximum stimulus

A

all fibers – max potential

76
Q

What causes a lower action potential threshold

A

thicker fibers - easier to stimulate an action potential

The Dynamic Cell (8 decks)

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