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Brain and behaviour > Lecture 5 > Flashcards

Lecture 5 Flashcards

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1
Q

Loewi’s experiment

A
  • Vagus nerve of frog heart 1 is stimulated
  • Fluid is transferred from first to second container
  • Recording from frog heart 1 shows increased rate of beating after stimulation
  • As does the recording from frog heart 2 after the fluid transfer
  • Transmission of information between neurons happens chemically
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2
Q

What do synapses consist of? (3)

A
  1. Presynaptic terminal button
  2. Synaptic cleft
  3. Postsynaptic membrane
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3
Q

Presynaptic membrane

A

Contains protein molecules that transmit chemical messages

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4
Q

Synaptic cleft

A

Small space separating presynaptic terminal and postsynaptic dendritic spine

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5
Q

Postsynaptic membrane

A

Contains protein molecules that receive chemical messages

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6
Q

Action potential generated by the presynaptic neuron leads to…

A

Exocytosis of a neurotransmitter from the presynaptic terminal button and the synaptic cleft.

The transmitter binds to the postsynaptic membrane and causes a change in the resting potential of the postsynaptic neuron (EPSP or IPSP)

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7
Q

Synaptic transmission (4 steps)

A
  1. Synthesis and packaging
  2. Release
  3. Receptor action at postsynaptic membrane
  4. Inactivation
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8
Q

Synthesis and packaging

A

Building blocks of a transmitter substance are imported into the terminal.
Where the neurotransmitter is synthesised and packaged into vesicles.

  • Cell body (DNA, mRNA)
  • Axon terminal (precursor chemicals derived from food)
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9
Q

Release

A

In response to an action potential, the transmitter is released across the membrane by exocytosis

  • Calcium influx triggered by action potential.
  • Release into synaptic cleft (exocytosis)
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10
Q

Receptor action

A

The transmitter crosses the synaptic cleft and binds to a receptor

  • Depolarisation (excitation)
  • Hyperpolarisation (inhibition)
  • Modulation (inhibit or excite other chemical reactions)
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11
Q

Inactivation

A

The transmitter is either taken back into the terminal or inactivated in the synaptic cleft

  • Diffusion away from synaptic cleft
  • Degradation by enzymes
  • Re-uptake in presynaptic cell
  • Uptake by glial cells (astrocytes)
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12
Q

Neurotransmitter release (general)

A

When an action potential reaches the voltage-sensitive terminal, it opens calcium channels
Incoming calcium ions bind to calmodulin, forming a complex
This complex binds to vesicles, releasing some from filaments and inducing others to bind to the presynaptic membrane and to empty their contents to exocytosis.

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13
Q

Amount of neurotransmitter released depends on:

A
  1. Amount of calcium entering axon terminal
  2. Number of vesicles docked at the membrane
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14
Q

Varieties of synapses

A
  1. Axo-dendritic
  2. Axo-somatic
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15
Q

Axo-dendritic connection

A

From axon to dendrite

  • Axon terminal from one neuron synapses on dendritic spine of another
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16
Q

Axo-somatic connection

A

From axon to cell body

  • Axon terminal ends on cell body
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17
Q

Excitatory synapses (TYPE I)

A
  • At dendrites
  • Round vesicles
  • High density (both pre- and postsynaptical)
  • Wide synaptic cleft
  • Large active zone
  • Not determined by the neurotransmitter
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18
Q

Inhibitory synapses

A
  • At cell body
  • Flat vesicles
  • Low density (both pre- and postsynaptical)
  • Narrow synaptic cleft
  • Small active zone
  • Not determined by the neurotransmitter
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19
Q

‘Classical’ ways to identify criteria to determine whether a chemical substance is a neurotransmitter

A
  1. Synthesised or present in the neuron
  2. When released, must produce response in target cell
  3. Experimental placement must result in same response
  4. Mechanism of removal must exist

NB: many substances do not fulfill these criteria

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20
Q

More liberal explanation of what qualifies as a neurotransmitter

A

Chemicals that:

  • Change the structure of the synapse
  • Are transmitter from post- to presynaptic membrane
  • Only work in combination with other substances
  • Function as a neurotransmitter and as a hormone
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21
Q

Classification of neurotransmitters

A
  1. Small molecule transmitters
  2. Peptide transmitters
  3. Lipid transmitters
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22
Q

What are the most important small-molecule transmitters in the central nervous system?

A
  1. Acetycholine (Acth)
  2. Dopamine (DA)
  3. Norepinephrine (NE) = Noradrenaline
  4. Serotonin (SE)
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23
Q

Amines

A
  • Dopamine
  • Norepinephrine = noradrenaline
  • Epinephrine = adrenaline
  • Serotonin
24
Q

Amino acids

A
  • Glutamate
  • Gamma-aminobutyric acid
  • Glycine
  • Histamine
25
Q

Purines

A
  • Adenosine
  • Adenosine triphosphate
26
Q

Acetycholine (synthesised)

A

Synthesised from acetate (vinegar, lemon juice) and choline (egg yolk, avocado) by enzymes

27
Q

Serotonin (synthesised + regulation)

A

Is synthesised from L-trypophan (pork, milk)

  • It regulates mood and aggression, appetite and arousal, respiration and pain perception,
28
Q

GABA formation

A

Is formed by a simple modification of the glutamate molecule

  • In forebrain and cerebellum: glutamate main excitatory & GABA main inhibitory transmitter
  • In brain stem and spinal cord: Glycine more common inhibitory transmitter
29
Q

Dopamine, norepinephrine and epinephrine synthesised

A

All synthesised from the precursor chemical tyrosine

30
Q

Small-molecule transmitters and neuroactive drugs

A

Many neuroactive drugs are designed to reach the brain by the same route that small-molecule transmitters of their precursor chemicals follow: the digestive route.

31
Q

Rate limiting factor

A

Enzyme synthesising L-Dopa from Tyrosine is limited and thus restricts the pace at which other chemicals can be synthesised

  • L-Dopa can cross the blood-brain barrier
  • Dopamine cannot cross the blood-brain barrier
32
Q

How are neuropeptides often taken?

A

Digestive processes degrade neuropeptides so generally not taken orally as drugs but through other routes (e.g., intravenous)

33
Q

Peptide transmitters general

A
  • Short chains of amino acids
  • Synthesised through the transcription of DNA and translation of mRNA
  • Synthesis is slower compared to small molecule transmitters
  • Act as hormones
34
Q

2 types of peptide transmitters

A

Endogenous opioids

  • Beta-endorphin (strong analgesic, runners high)

Exogenous opioids

  • Opium, morphine, diamorphine (heroin)
35
Q

What is the main lipid transmitter?

A

Endocannabinoids

  • Generated by the body

Different from phytocannabinoids (THC, CBD)

36
Q

Lipid transmitters general

A
  • Synthesised at postsynaptic membrane to act on CB1 receptors at hte presynaptic membrane (retrograde neurotransmitters)
  • Affect appetite, pain, sleep. mood.
  • Lipophilic (fat-loving) and thus not stored in vesicles (synthesised on demand (slow)).
  • Act as neuromodulators
37
Q

Lipid transmitters - neuromodulators

A

Inhibit the release of Glutamate and GABA (dampen both neuronal excitation and inhibition)

38
Q

Excitatory neurotransmitters

A

DA, NE, EP
Glutamate

  • Activating
39
Q

Inhibitory transmitters

A

GABA

  • Dampening
40
Q

Post synaptic receptor classes

A
  1. Ionotropic receptors
  2. Metabotropic receptors
41
Q

Ionotropic receptors

A
  • Binding site for neurotransmitter + ion channel
  • Fast ~1ms
  • Direct effect, rapidly change membrane voltage
  • Usually excitatory - may trigger action potential
  • NB: structurally similar to voltage sensitive channels that propagate action potential
42
Q

Metabotropic receptors

A
  • Binding site only, no ion channel
  • Slow: some hundreds of ms
  • Indirect effect, change the condition of the cell via G-protein inside the cell membrane
  • Alpha subunit of G-protein may: activate nearby ion channel, which may lead to amplification cascade
43
Q

Neurotransmitter systems in the PNS

A
  • Somatic nervous system
  • Autonomic nervous system
44
Q

Somatic nervous system (neurotransmitter systems)

A
  • Acetycholine (ACh), nicotinic acetycholine receptor nAChr
45
Q

Autonomic nervous system (neurotransmitter systems)

A

Sympathetic divison

  • Preganglionic: Acetycholine (ACh)
  • Postganglionic: Norepinephrine (NE)

Parasympathetic division

  • Acetycholine
46
Q

Ach and NE heart rate & digestion

A
  • Ach decreases (inhibits) heart rate but increases (excites) digestion.
  • NE increases (excites) heart rate but decreases (inhibits) digestive functions
47
Q

Neurotransmitter systems in CNS

A
  • Cholinergic - acetycholine
  • Dopaminergic - dopamine
  • Noradrenergic - norepinephrine
  • Serotonergic - serotonin
48
Q

Cholinergic

A
  • Nucleus basalis of Meynert

Wakefulness, attention, memory

49
Q

Dopaminergic

A
  • Basal Ganglia
  • Nigrostriatal pathway - active in maintaining normal motor behaviour
  • Mesolimbic pathway - causes repetition of behaviours
50
Q

Noradrenergic

A
  • Locus coeruleus
  • Emotional tone
  • Lower levels may be related to depression
  • Higher levels may be related to mania
51
Q

Sertonergic

A
  • Raphe nuclei
  • Wakefulness during movement
  • High levels may be related to schizo & OCD
  • Lower levels are related to depression
52
Q

Chemical synapses

A
  • ~5 ms slower

Enabled neural plasticity because they can

  • Amplify or diminish signals
  • Change with experience to mediate learning
53
Q

Electrical synapses (gap junctions)

A
  • ~5 mc faster

Regulated gates (can either be open or closed)

  • Allow glial cells and neurons to exchange substances
  • Allows groups of neurons to synchronise their firing rhythmically.
  • NN: ions may flow in both directions
54
Q

Habituation - neural plasticity

A
  • Decreased neural response following repeated stimulation
  • Voltage-sensitive calcium channels become less sensitive to voltage changes
  • Decreases Ca2+ influx
  • EPSPs become smaller due to less neurotransmitter released in synaptic cleft causing less depolarisation of postsynaptic membrane
  • NB: habituation may eventually stop neurons from firing altogether
55
Q

Sensitisation - neural plasticity

A
  • Increased neural response to stimuli
  • Serotonin released by interneuron makes potassium channels less responsive
  • Reduced K+ efflux
  • Prolonged action potentials
  • Increase Ca2+ influx.
  • EPSPs become larger due to increased amount of neurotransmitter in synaptic clef causing greater depolarisation of postsynaptic membrane

Brain and behaviour (14 decks)

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