Practicals (michaelmas) Flashcards
What is a low pass filter?
Filter that only allows frequencies below a certain limit to pass through. 50Hz low pass means everything above 50Hz is filtered out.
What is a high pass filter?
Filter that only allows frequencies above a certain limit to pass through. 50Hz high pass means everything below 50Hz is filtered out.
How is the minimum sampling rate determined?
Minimum sampling rate = 2 x Hightest prequency in data
What is responsible for the incisura that occurs during the finger pulse?
Slight backflow of blood from the aorta into the heart just before the aortic valves close during ventricular relaxation.
What causes decrease in finger pulse amplitude when hand immersed in cold water?
Thermoregulatory vasoconstriction.
What causes increase in finger pulse amplitude when hand immersed in warm water?
- Thermoregulatory vasodilation.
- Metabolic vasodilation as a result of increased metabolic rates in warm water.
Why was the measured equilibrium potential for K+ ions smaller (closer to 0) than was predicted by the Nernst equation?
The membrane was also slightly permeable to Cl- ions as well as K+ ions.
Why did EK deviate away from the predicted value at lower [K]test?
The lower [K]test, the smaller the K+ current across the membrane. This meant that the Cl- current had a bigger influence on VE, and so it deviated away from EK.
What is the capacitance equation?
C = Q/V
Capacitance = Charge/Voltage
What is the time constant equation?
τ = RiC
What is the mains frequency in the UK?
50Hz
What is the set up of electrodes for the earth worm experiment?
From anterior to posterior:
- Stim. andoe
- Stim. cathode
- Earth
- Recording 1
- Recording 2
What produces the stimulus artifact in earth worm experiment?
Current travelling directly from the point of stimulation to the recording electrodes through the body and surface liquid of the worm.
What is the purpose of the earth electrode in the eart worm experiment?
To attenuate any stimulus artifacts and noise in experiement
Why is a second action potential always smaller than the first if stimulated just after refractory period?
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.
What are the terms used to describe directions of conduction in nerves?
Orthodromic: AP travels in same direction as normal.
Antidromic: AP travels in opposite direction as normal.
Why did the worm warm up quicker than it cooled down when ice was applied?
- 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.
Why does cooling decrease conduction velocity?
Cooling increases the amount of time taken for voltage-gated Na+ channels to open upon depolarisation.
How can a monophasic AP be produced during the earth worm experiment?
Nerve could be crushed between A and B, preventing AP from reacting B.
What are some problems with measuring AP conduction velocity with just one latency period?
- There may have been a delay in the time of stimulation compared to the time of AP generation.
- AP may have been recorded after it had initially arrived at the recording electrodes.
- Conduction velocities are generally lower than normal when measured this way.
What is the equation for measuring conduction velocity by differences?
V = (D2 - D1)/(LP2 - LP1)
What is the latency period between point of stimulation and contraction of a muscle dependent on?
- Time taken for stimulus to generate AP.
- Speed of conduction of AP in nerve.
- Time of transmission at NMJ.
- Time taken for AP to be generated by EPP in muscle itself.
What is responsible for the dishing effect seen in muscle contraction experiment after filtering?
Artifact
What us hysteresis?
Nature of physiological event depends on previous events that have occured.
What is responsible for hysteresis shown in muscle experiment?
- 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.
Why can smooth contractions be achieved at lower stimulus frequencies in vivo?
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.
What are ECG leads measuring?
Instantaneous mean vector component of cardiac depolarisation parallel to the line of action of the leads.
What do the different parts of an ECG represent?
- P-wave: Atrial depolarisation
- QRS complex: Ventricular depolarisation
- T-wave: Ventricular repolarisation
What causes variability between ECGs?
- Heart shape
- Heart size
- Heart orientation
- Position of ECG leads.
Note: Strength of cardiac contractions do not affect the amplitude of ECGs
What causes systole to shorten when heart rate is high?
- 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.
What events occur during respiratory sinus arrhythmias?
- Heart rate increases during inspiration.
- Heart rate decreases during expiration.
What causes changes in ECG amplitudes duing respiration?
- 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.
What are the principles behinf sphygnomonometry?
- Cuff inflated to beyond systolic blood pressure, causing permanent collapse of blood vessels in arm.
- As cuff deflated, it will become equal to systolic pressure. During systole, blood pressre just enough to open collapsed vessels and cause Korotkoff sounds.
- When cuff deflated below diastolic pressure, Korotkoff sounds disappear.
What are the results of systolic/diastolic pressure measurments from class data?
- 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.
What might be a possible explanation for men having higher average systolic pressure than women?
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.
