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Lab work > Nerve Physiology > Flashcards

Nerve Physiology Flashcards

1
Q

What is the sciatic nerve made from?

A

The sciatic nerve of the frog consists of two or more spinal nerves which are normally distinguishable as separate bundles of fibres. Each of the bundles is a large collection of individual nerve fibres, both sensory (afferent) and motor (efferent), i.e. a mixed nerve

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2
Q

What is the difference between active/absolute and relative refractory period?

A

During an absolute/active period a new action potential cannot be elicited at all. During the relative period, a new partial action potential can be elicited if the circumstances are favourable, e.g. long enough refractory period, greater than normal stimulation.

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3
Q

What happens when a nerve is crushed?

A

The wave of depolarisation is prevented from reaching the second electrode. This results in a monophasic action potential.

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4
Q

What is the latency?

A

The time from the start of the stimulus arefact to the start of the CNAP

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5
Q

How could conduction velocity of the sciatic nerve be measured?

A

By measuring the time taken for the CNAP to be conducted over a cetain distance

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6
Q

What would be the effect of crushing or damaging the nerve between the 2 recording electrodes

A

The CNAP would increase. The depolarisation wave would not reach the second recording electrode so the deflection would not be seen, however the upwards deflection would still be present.

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7
Q

How does the amplifier gain the latency of a CNAP?

A

It does not. The amplifier only affects the amplitude

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8
Q

What is the isoelectric interval and what is its duration dependent on?

A

The isoelectric interval (ST segment) is based on the distance between the two recording electrodes, illustrating the region where there is no charge to create deflections on the trace

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9
Q

What effect would changing the polarity of the recording electrodes have on CNAP?

A

The trace would invert. Because the wave of depolarisation would reach the negative electrode first and cause a downward deflection and then an upwards deflection after crossing the positive electrode.

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10
Q

What would happen if you increased the distance between the 2 recording electrodes?

A

The isoelectric interval between the upward and downward deflections would increase

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11
Q

Define the stages of the biphasic CNAP on the oscilloscope:

A

As it passes the first electrode, the beam is deflected upwards then it returns to the isoelectric baseline as the depolarisation passes through the recording electrodes

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12
Q

How does a biphasic action potential occur?

A

This occurs when the recording system uses two surface electrodes of opposite polarity

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13
Q

Why is the nerve bath at room temperature with the lid on?

A

This ensures a humid atmosphere is maintained in the organ bath

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14
Q

What does the trigger lead do?

A

The trigger lead co-ordinates and stabilises the delivery of the stimulus to the muscle with the start of the trace moving across the oscilloscope screen. Without the lead, you would not be able to see the CNAP

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15
Q

How does the stimulus artefact arise?

A

When a small amount of current passes through the earth electrode to prevent too much current from reaching the recording

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16
Q

How does biphasic CNAP occur?

A

Nerve is electrically stimulated which gives rises to a CNAP. A wave of depolarisation is conducted to the recording electrodes and the signal is interpreted on the oscilloscope

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17
Q

What is the refractory period?

A

The period in time in which a neuron is unable to carry out an action potential. It refers to the amount of time it takes for an excitable membrane to be ready to respond to a second stimulus once it returns to its resting state

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18
Q

What is a supramaximal voltage?

A

A stimulus voltage which excedes that which will produces a CNAP of maximum amplituded. Supramaximal means greater than the maximal.

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19
Q

What is the axon diameter for humans?

A

Up to 100 µm (micrometres).

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20
Q

How would you measure the change of conduction velocity across a nerve?

A

Stimulate the nerve moving the positive recording electrode either closer or further away from the negative stimulating electrode. Then make multiple calculations on conduction velocity.

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21
Q

How does procaine affect the CNAP shape?

A

It decreases the amplitude of the CNAP i.e. the total number of fibres that are firing decreases

22
Q

How does the effect of procaine change over time?

A

The effects on both amplitude and conduction velocity increases over time

23
Q

How does procaine have an affect on fast vs slow conducting fibres?

A

The mean conduction velocity is decreased - fast conducting fibres are affected more than slow conducting ones. This makes the curve wider overall.

24
Q

How does procaine work?

A

It binds to sodium channels in the membrane which blocks the sodium currents and stops the propagation of an action potential in nerve fibres.

25
Q

Why does the effects of procaine increase over time?

A

It takes more time for procaine to penetrate to deeper fibres in the nerve bundle.

26
Q

What is procaine?

A

It is a lipid soluble, local anaesthetic. It stabilises membranes.

27
Q

How is the nerve laid down in the nerve bath?

A

Across the 5 electrodes, ringer solution if then poured into the bottom of the bath. The nerve is not immersed

28
Q

What is the purpose of the earth electrode?

A

Must be placed between both stimulator and recording electrodes. This prevents the stimulating current from being picked up by the recording electrodes.

29
Q

What are the electrodes used for?

A

2 of the electrodes are used for stimulating the preparation and must be connected to the 2 leads from stimulator. Inner lead must be negative. The other 2 record activity of nerve and should be connected to input that leads to the amplifier. The last electrode is the earth electrode, connected to earth lead.

30
Q

Describe the nerve bath:

A

A perspex lidded box with inserts for 5 electrodes. The electrodes are plastic coated wire enclosed in a perspex tubing and can be moved relative to each other

31
Q

Why do you use fluid?

A

It closely resembles the extracellular fluid of the frog

32
Q

Where is the sciatic nerve found in the spine?

A

It is associated with spinal segments L4 to S3

33
Q

What is important to maintain about the sciatic nerve during extraction?

A

Obtaining as long a stretch of uninjured nerve as possible

34
Q

How would you remove the lower half of the body?

A

Make a circular cut with a scissors around the belly to remove the trousers (lower skin)

35
Q

How would you destroy the brain and spinal cord?

A

Stun and pith it

36
Q

Why must care be taken when using metal dissection instruments?

A

Not to touch the nerve to damage it or to stretch the nerve unduly.

37
Q

Why is the preparation placed in frog Ringer solution?

A

To keep the nerve moist to maintain the integrity of the membrane which is vital for the function of the sciatic nerve

38
Q

What is the 5th step of removing the sciatic nerve from the frog?

A

A ligature is tied around the nerve at the knee end and the preparation is placed in a small beaker of frog Ringer solution.

39
Q

How is the nerve kept moist?

A

With the frog Ringer solution which closely resembles the extracellular fluid of the frog

40
Q

How do you keep integrity of the membrane of the nerve?

A

The nerve must be kept moist

41
Q

What does the functioning of the nerve depend on?

A

The integrity of the membrane

42
Q

What is the 4th step of removing the sciatic nerve from the frog?

A

The nerve is carefully dissected free from surrounding tissue down to the knee joint. The path of the nerve through the thigh may be exposed by parting the muscles of the thigh using the thumbnails.

43
Q

What is the 2nd step of removing the sciatic nerve from the frog?

A

A circular cut is made with scissors around the belly and the skin covering the lower half of the body removed (removing the “trousers”).

44
Q

What is the first step of removing the sciatic nerve from the frog?

A

The frog is stunned and pithed, a procedure which destroys the brain and the spinal cord.

45
Q

What is the 3rd step of removing the sciatic nerve from the frog?

A

Lay it on its dorsal surface, remove the urostyle by cutting through the muscle on both sides and finally cutting it away from the spinal column. The nerve is ligatured (attached to) where it leaves the spinal cord and cut anterior to the ligature.

46
Q

Where does the sciatic nerve arise form?

A

The sacral plexus

47
Q

Is the sciatic nerve the largest nerve in the body?

A

Yes

48
Q

What part of the body does the sciatic nerve control?

A

The lower musculature of the limbs such as the thigh, the posterior of the leg, the sole of the foot, the common peroneal.

49
Q

What is the sciatic nerve in humans made of?

A

Made from 2 nerves: the tibial and common peroneal, each of which have hundreds of individuals neurons.

50
Q

What nerve did you use?

A

frog sciatic nerve

51
Q

How can nerve fibres in a mixed nerve differ?

A

Diameter, degree of myelination, threshold of excitations and conduction velocity

52
Q

What is a compound action nerve potential?

A

An action potential which is recorded as a result of the combined activity of all the individual fibres releasing a single action potential.

Lab work (2 decks)

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