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MD4001 > Neurophysiology Revision > Flashcards

Neurophysiology Revision Flashcards

1
Q

What is the resting potential of a neuron?

A

-64mV

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2
Q

What are the resting intracellular values for sodium and potassium in a neuron

A

Sodium: 15mM
Potassium: 140mM

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3
Q

What are the resting extracellular values for sodium and potassium?

A

Sodium: 150mM
Potassium: 5mM

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4
Q

Describe the 3 principles of transmission of an action potential

A

1) Self propagates
2) Travels in one direction
3) No volume control, just on or off

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5
Q

Describe the evolution of an action potential

A
  • The neuron reaches the threshold level of excitation (depolarisation) and voltage gated sodium channels open and Na+ enters
  • K+ channels open and K+ begins to leave the cell
  • Na+ channels become refractory, no more Na+ enters the cell
  • K+ continues to leave the cell, causing the membrane potential to return to resting level
  • K+ channels close and Na+ channels reset
  • Extra K+ outside the cell diffuses away
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6
Q

Describe the mechanisms of voltage dependent sodium channels

A
  • At resting potential, Na+ channels are closed, their activation gate is closed
  • Depolarisation opens the activation gate and Na+ flows into the cell along its electrochemical gradient
  • A delayed component of voltage dependent activation is the blocking of the channel by the inactivation gate (after about 0.5ms)
  • Repolarisation of the cell re sets the two gates to their equilibrium positions
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7
Q

Why can the cell not be stimulated to its threshold potential in the refractory period?

A

All of the Na channels are closed (although a stronger than normal stimulus could induce an action potential - some Na+ ready but more K+ channels are open than usual)

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8
Q

How can you increase the speed of transmission in a neuron?

A
  • Increase the diameter

* Myelination

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9
Q

What cells are responsible for myelination?

A
  • In the PNS, the Schwann cells

* In the CNS, oligodendrocytes

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10
Q

Describe saltatory conduction

A
  • With a myelin sheath, local currents can be extended further as current leakage is reduced by the myelin sheath
  • Conduction of the impulse flows rapidly along the inside of the axon to the node where it slows and the ionic depolarisation takes place (only a few ions needed so is energy saving)
  • Then, fast conduction inside of the axon resumes (action potential only exists at the nodes of ranvier)
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11
Q

What is normal conduction velocity?

A

50-60 meters/second

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12
Q

What is the conduction speed of the fastest neurones and what are they?

A
  • 120m/s

* Alpha motor neurons

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13
Q

What is the terminal swelling of a presynaptic cell called?

A

Bouton

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14
Q

What is the size of the synaptic gap?

A

Approx 20nm (twice the size of a membrane)

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15
Q

How do vesicles and presynaptic membranes recognise each other?

A

• V-SNARE on the vesicle complex pairs with T-SNARE at the presynaptic membrane

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16
Q

Describe synaptic docking and fusion

A
  • SNARE complex folds and strongly draws the membrane close
  • Vesicle becomes docked on the membrane
  • Action potential triggers calcium influx at the end bulb, inducing synaptotagmin to displace complexin and exocytosis proceeds
17
Q

What is the effect of the Botulinum toxin?

A

The botulinum toxin targets the SNARE membrane, inactivating acetylcholine related processes causing paralysis

18
Q

How are neurotransmitters inactivated?

A
  • Diffusion
  • Re-uptake
  • Enzymal inactivation
19
Q

What are the different types of receptors that recognise neurotransmitters?

A
  • Ionotropic receptors (directly gate ion flow)

* Metabotropic (indirectly gate ion flow or activate other pathways) e.g. activate a G protein

20
Q

What type of receptor is the acetylcholine receptor?

A

Ionotropic

21
Q

What is an EPSP?

A
  • Excitatory post synaptic potential
  • Net flow of positive ions into the cell depolarises the membrane bringing it closer to the threshold
  • Influx of Na+
22
Q

What is the typical amplitude of an EPSP?

A

1-5mV

23
Q

What is an IPSP?

A
  • Inhibitory post synaptic potential
  • Causes a hyper polarisation, making the neuron more resistant to an action potential
  • Influx of Cl- ions
24
Q

What is spatial summation?

A
  • Multiple EPSPs
  • Can reach the threshold so an action potential can be generated
  • EPSPs arrive at the same time but at different locations on the axon
25
Q

What is Temporal summation?

A
  • Multiple EPSPs
  • Can reach the threshold so an action potential can be generated
  • EPSPs arrive in succession at the same point
26
Q

What ions are SNARES dependent on?

A

Calcium ions

27
Q

How are action potentials generated in a sensory neuron?

A
  • Most receptors will code duration and magnitude of the external signals as a generator potential
  • A stronger external signal will result in a higher frequency of Action Potentials in the axon
  • Sensory receptors can adapt to a stimulus with time (not all adapt in the same way)
28
Q

How can we measure nerve conduction?

A

Clinically we don’t measure individual action potentials, we measure the sum of all action potentials in a nerve or the resulting stimulus inside a target such as a skeletal muscle
• Electrodes at two points

29
Q

In a nerve conduction study, what would a reduced amplitude mean?

A

Less axons

30
Q

In a nerve conduction study, what would a slowed conduction velocity mean?

A

Reduced myelin

31
Q

What is a SNAP?

A

Sensory nerve action potential

32
Q

What is a CMAP?

A

Compound muscle action potential

33
Q

What happens in carpal tunnel syndrome?

A
  • The median nerve is compressed at the wrist resulting in numbness/pain.
  • Entrapped by the transverse carpal ligament
34
Q

What are the types of inherited channelopathies?

A
  • Neurological

* Cardiac

35
Q

What are the autoimmune channelopathies?

A
  • Myasthenia gravis
  • Lambert-Eaton myasthenia syndrome (associated with small cell lung cancer)
  • Limbic encephalitis (memory loss; with an underlying neoplasm)
36
Q

What is Myasthenia Gravis?

A
  • Involved acetylcholine receptors
  • Prevents the muscles from contracting e.g. weakness in eye muscles, weakness in arms, legs etc.
  • Sometimes in cases of severe weakness, may cause respiratory failure
37
Q

Describe the involvement of muscle spindles in muscle contraction

A

Mediate stretch reflexes to enable muscle fibres to oppose forces that elongate them.

MD4001 (28 decks)

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