Practicals (michaelmas)

Question 1

What is a low pass filter?

Answer 1

Filter that only allows frequencies below a certain limit to pass through. 50Hz low pass means everything above 50Hz is filtered out.

Question 2

What is a high pass filter?

Answer 2

Filter that only allows frequencies above a certain limit to pass through. 50Hz high pass means everything below 50Hz is filtered out.

Question 3

How is the minimum sampling rate determined?

Answer 3

Minimum sampling rate = 2 x Hightest prequency in data

Question 4

What is responsible for the incisura that occurs during the finger pulse?

Answer 4

Slight backflow of blood from the aorta into the heart just before the aortic valves close during ventricular relaxation.

Question 5

What causes decrease in finger pulse amplitude when hand immersed in cold water?

Answer 5

Thermoregulatory vasoconstriction.

Question 6

What causes increase in finger pulse amplitude when hand immersed in warm water?

Answer 6

1. Thermoregulatory vasodilation.
2. Metabolic vasodilation as a result of increased metabolic rates in warm water.

Question 7

Why was the measured equilibrium potential for K⁺ ions smaller (closer to 0) than was predicted by the Nernst equation?

Answer 7

The membrane was also slightly permeable to Cl^- ions as well as K⁺ ions.

Question 8

Why did E_K deviate away from the predicted value at lower [K]_test?

Answer 8

The lower [K]_test, the smaller the K⁺ current across the membrane. This meant that the Cl^- current had a bigger influence on V_E, and so it deviated away from E_K.

Question 9

What is the capacitance equation?

Answer 9

C = Q/V

Capacitance = Charge/Voltage

Question 10

What is the time constant equation?

Answer 10

τ = R_iC

Question 11

What is the mains frequency in the UK?

Answer 11

50Hz

Question 12

What is the set up of electrodes for the earth worm experiment?

Answer 12

From anterior to posterior:

1. Stim. andoe
2. Stim. cathode
3. Earth
4. Recording 1
5. Recording 2

Question 13

What produces the stimulus artifact in earth worm experiment?

Answer 13

Current travelling directly from the point of stimulation to the recording electrodes through the body and surface liquid of the worm.

Question 14

What is the purpose of the earth electrode in the eart worm experiment?

Answer 14

To attenuate any stimulus artifacts and noise in experiement

Question 15

Why is a second action potential always smaller than the first if stimulated just after refractory period?

Answer 15

Some voltage-gated Na⁺ channels are still inactive at this stage, meaning that there are fewer Na⁺ channels involved in producing AP. This results in a smaller inwards Na⁺ current and thus a smaller AP.

Question 16

What are the terms used to describe directions of conduction in nerves?

Answer 16

Orthodromic: AP travels in same direction as normal.

Antidromic: AP travels in opposite direction as normal.

Question 17

Why did the worm warm up quicker than it cooled down when ice was applied?

Answer 17

• Vasoconstriction reduced blood flow to areas of the worm convered in ice. This reduced the rate it cooled down.
• Vasodilation (in response to metabolite accumulation) increased blood flow to areas of the worm covered in ice when the ice was removed. This increased the rate it warmed up.

Question 18

Why does cooling decrease conduction velocity?

Answer 18

Cooling increases the amount of time taken for voltage-gated Na⁺ channels to open upon depolarisation.

Question 19

How can a monophasic AP be produced during the earth worm experiment?

Answer 19

Nerve could be crushed between A and B, preventing AP from reacting B.

Question 20

What are some problems with measuring AP conduction velocity with just one latency period?

Answer 20

1. There may have been a delay in the time of stimulation compared to the time of AP generation.
2. AP may have been recorded after it had initially arrived at the recording electrodes.
3. Conduction velocities are generally lower than normal when measured this way.

Question 21

What is the equation for measuring conduction velocity by differences?

Answer 21

V = (D₂ - D₁)/(LP₂ - LP₁)

Question 22

What is the latency period between point of stimulation and contraction of a muscle dependent on?

Answer 22

1. Time taken for stimulus to generate AP.
2. Speed of conduction of AP in nerve.
3. Time of transmission at NMJ.
4. Time taken for AP to be generated by EPP in muscle itself.

Question 23

What is responsible for the dishing effect seen in muscle contraction experiment after filtering?

Answer 23

Artifact

Question 24

What us hysteresis?

Answer 24

Nature of physiological event depends on previous events that have occured.

Question 25

What is responsible for hysteresis shown in muscle experiment?

Answer 25

• Amplitude of given contraction lower for the same stimulus if previous contraction was stronger.
• This may be a condequence of muscle fatigue due to previous stronger contraction.

Question 26

Why can smooth contractions be achieved at lower stimulus frequencies in vivo?

Answer 26

Alternating, asynchronous contraction of muscle units allow smooth contractions to be generated in the muscle as a whole even though muscle units themselves may not be contracting smoothly.

Question 27

What are ECG leads measuring?

Answer 27

Instantaneous mean vector component of cardiac depolarisation parallel to the line of action of the leads.

Question 28

What do the different parts of an ECG represent?

Answer 28

• P-wave: Atrial depolarisation
• QRS complex: Ventricular depolarisation
• T-wave: Ventricular repolarisation

Question 29

What causes variability between ECGs?

Answer 29

1. Heart shape
2. Heart size
3. Heart orientation
4. Position of ECG leads.

Note: Strength of cardiac contractions do not affect the amplitude of ECGs

Question 30

What causes systole to shorten when heart rate is high?

Answer 30

• Sympathetic β₁ adrenergic stimulation decreases duration of cardiac APs by increasing outward K⁺ current though voltage-gated K⁺ channels, decreasing duration of stimulation.
• Rate of relaxation is also decreased as SERCA activity is increased.

Question 31

What events occur during respiratory sinus arrhythmias?

Answer 31

• Heart rate increases during inspiration.
• Heart rate decreases during expiration.

Question 32

What causes changes in ECG amplitudes duing respiration?

Answer 32

• Changes in heart position.
• During inspiration, the heart becomes more vertical. This results in vertical component of ECG increasing in amplitude while the horizontal component decreases.

Question 33

What are the principles behinf sphygnomonometry?

Answer 33

1. Cuff inflated to beyond systolic blood pressure, causing permanent collapse of blood vessels in arm.
2. As cuff deflated, it will become equal to systolic pressure. During systole, blood pressre just enough to open collapsed vessels and cause Korotkoff sounds.
3. When cuff deflated below diastolic pressure, Korotkoff sounds disappear.

Question 34

What are the results of systolic/diastolic pressure measurments from class data?

Answer 34

• Diastolic pressure was not significantly different between males and females.
• Systolic pressure was significantly different, with the males having slightly higher average systolic blood pressure.

Question 35

What might be a possible explanation for men having higher average systolic pressure than women?

Answer 35

Androgens in males stimulate Na⁺ retention by the kidneys through the renin-angiotensin system. This results in greater TBV and thus greater MSFP, resulting in greater CO and greater pressure.