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Neuro Physiology > Axonal Transmission > Flashcards

Axonal Transmission Flashcards

1
Q

What is the resting membrane potential? Give a value also.

A

When the inside of the cell is negatively charged with respect to outside.

Typically -70mV

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2
Q

How is the resting membrane potential maintained?

A

By the sodium-potassium pump. 3Na+ ions are pumped out of the membrane for every 2K+ ions pumped in.

Leaky K+ channels lead to K+ diffusing out of the axon, further increasing the negativity of the inside of the membrane.

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3
Q

Briefly outline the steps of an action potential.

A
  1. Neurotransmitter binds to specific ligand-gated ion channels causing influx of Na+
  2. Causes initial DEPOLARIZATION which stimulates opening of voltage gated Na+ channels resulting in further entry of Na+ ions
  3. When the threshold potential (-55mV) is reached, a positive feedback loop is created
  4. REPOLARIZATION occurs at +30mV. Na+ channels are inactivated. Sluggish voltage gated K+ channels open resulting in K+ diffusing out of the neurone and causing repolarization.
  5. As the voltage gated K+ channels are slow to close, K+ continues to diffuse out resulting in HYPERPOLARIZATION - -75mV
  6. Resting potential is restored. A second stimulus will not produce another action potential - the absolute refractory period.
  7. In the relative refractory period, a second action potential can be induced if the stimulus strength is great
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4
Q

How is conduction achieved?

A

Action potential generates local currents that depolarize adjacent membranes.

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5
Q

How does fibre diameter and myelination effect propagation speed?

A

The larger the fibre diameter, the faster the action potential (less resistance).
Myelination increases propagation speed.

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6
Q

What is saltatory conduction?

A

Myelinated neurones have nodes of Ranvier. Action potentials jump from one node to the next as they propagate along a myelinated fibre.

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7
Q

What is multiple sclerosis? Give symptoms as well.

A

Degeneration of myelin which blocks neurotransmission.

Symptoms: Uncontrolled eye movements, slurred speech, tremor.

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8
Q

What occurs at an excitatory synapse?

A

The membrane potential of a postsynaptic neurone is depolarised.

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9
Q

What occurs at an inhibitory synapse?

A

The membrane potential of a postsynaptic neurone is hyperpolarised or stabilised.

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10
Q

What are the two types of synapse?

A

Electrical and chemical (majority)

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11
Q

Give the features of an electrical synapse.

A
  1. Plasma membranes of the presynaptic and postsynaptic cells are joined by gap junctions
  2. Very rapid communication
  3. Synchronised transmission
  4. Found in brainstem and hypothalamus neurones
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12
Q

Give the features of a chemical synapse.

A
  1. Plasma membranes of presynaptic and postsynaptic neurones are joined by the synaptic cleft
  2. Presynaptic neurone ends as axon terminal which contains neurotransmitter molecules
  3. Covered by astrocytes which reuptake excess neurotransmitter
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13
Q

Outline the steps for neurotransmitter release.

A
  1. Action potential arrives at pre synaptic neurone and cause calcium ion channels to open
  2. Ca2+ ions cause vesicles containing neurotransmitter to fuse with the cell membrane
  3. Neurotransmitter is released by exocytosis and diffuses across synaptic cleft
  4. Neurotransmitter attaches to receptor sites on post synaptic membrane
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14
Q

What is temporal summation?

A

Signals arrive from the same presynaptic cell at different times. Potentials summate as there is a greater number of open ion channels.

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15
Q

What is spatial summation?

A

When two inputs occur at different locations in the postsynaptic neurone and combine.

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16
Q

Name 3 fast neurotransmitters (short lasting, rapid effect)

A

Acetylcholine
Glutamate
GABA

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17
Q

Name 3 neuromodulators (last longer, slow effect)

A

Dopamine
Noradrenalin
Serotonin

18
Q

Which molecules make acetylcholine?

A

Acetyl coenzyme A and choline

19
Q

Which enzyme breaks down acetylcholine? Which products are released?

A

Acetylcholinesterase. Produces choline and acetate.

20
Q

Name the two types of acetylcholine receptor.

A
  1. Nicotinic - found in neuromuscular junction. Respond to nicotine as well, and are found in reward pathways which explains why tobacco is so addictive.
  2. Muscarinic - couple with G proteins.
21
Q

What is noradrenaline affected by?

A

Antidepressants and stimulants. Imipramine and amphetamine blocks reuptake of noradrenaline.

22
Q

What is dopamine affected by?

A

Antipsychotic drugs e.g. chlorpromazine blocks receptor

Anti-parkisons drug e.g. L-DOPA increases dopamine production

23
Q

What is serotonin affected by?

A

Antidepressants. e.g. Prozac, increases serotonin

24
Q

Which is the main excitatory neurotransmitter?

A

Glutamate

25
Q

Which is the main inhibitory neurotransmitter?

A

GABA

26
Q

How do local anaesthetics work?

A

They block sodium channels in the membrane , preventing depolarisation so no action potential is developed. Results in pain relief as no pain is transmitted.

27
Q

Give the 4 parts of a neurone.

A

Dendrite
Cell body
Axon
Presynaptic terminal

28
Q

Which stain is used to see myelin?

A

Luxor fast blue

29
Q

What three functional types of neurone are there?

A

Afferent/sensory
Efferent/motor
Interneurons (CNS only)

30
Q

What is a nerve fibre and what is a nerve?

A

Nerve fibre = single axon

Nerve = bundle of axons

31
Q

Where are the peripheral and central processes of afferent neurones?

A

Cell body and axon is outside CNS. Part of the central process enters CNS.

32
Q

Where are the peripheral and central processes of efferent neurones?

A

Cell body and dendrites are within CNS. Axons extend out to the periphery.

33
Q

Which cells produce myelin in the CNS?

A

Oligodendrocytes

34
Q

Which cells produce myelin in the PNS?

A

Schwann cells

35
Q

What are glial cells?

A

Cells that surround the neurone and provide it with physical and metabolic support.

36
Q

Name the 5 types of glial cell

A 
Oligodendrocyte
Schwann cell
Astrocyte 
Microglia
Ependymal cells
37
Q

What is the role of astrocytes?

A

Regulates composition of extracellular fluid in the CNS by removing K+ ions & neurotransmitters.

38
Q

What is the role of microglia?

A

Phagocytic, migrate to sites of damage and phagocytose microbes.

39
Q

What is the role of ependymal cells?

A

Line ventricles and regulate production of CSF. Provides barrier between CSF and brain.

40
Q 
Are the following conditions diseases of the neurone, glia or both?
Epilepsy
Motor neurone disease
Depression
Alzheimers disease
MS
A 
Epilepsy: Neurone 
Motor neurone disease: Neurone & glia
Depression: Neurone & glia
Alzheimer's: Neurone & glia 
MS: Neurone & glia

Neuro Physiology (6 decks)

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