Practicals Flashcards
What is low/high pass filtering?
Low pass: low frequency components allowed to pass
High pass: high frequency components allowed to pass through
Filtering generally removes noice from data
What is aliasing
When the sample rate is too low to accuractly capture changes in the sample
Ideally sampling rate should be twice the frequency of the original signal
What is the resolution of the powerlab?
The number of ‘steps’ in between the minimum and maximum voltage. Basically how clean the data will look.
Define systolic and diastolic pressure
Peak pressure reached during the cardiac cycle (after ventricular contraction)
Diastolic is the the lowest measurement for arterial blood pressure.
What side of the artifical cell do we change the concentration of KCl in?
The reference side
How is potential difference across an artifical membrnae reported from the power lab?
Test side relative to reference
+20mV means the test side is 20mV more positive than the reference
Nernst equation
Eion = 58/z log(10) ([ref]/[test])
Eion = equilibrum potential at 20 degrees in mV
Relate voltage charge and capacitance
V = Q/C (= IR)
- the larger the capacitance, the more charge that can be stored at a given voltage
- capacitance of a capacitor can be increased by having a larger surface area or the plates being close together
Some capacitance things to remember
Current only flows through the capacitor when it is charging
Voltage increases at a capacitor while it is charging till it reaches a maximum (Q/C)
Time constant definition
Resistance*Capacitance.
Time taken for voltage to reach 63% original value after capacitor is attached.
Equation for voltage across a charging capacitor?
V(t) = Vt(1-e^(-t/T))
T = time constant
What does the finger pulse transducer measure?
Change in force not a measure of the actual force applied
Can convert change in force to force by intergrating with respect to time.
What is the dicrotic notch?
As the heart relaxes, aortic pressure exceeds that in left ventricle and the backflow of blood as the aortic valve closes creates a small notch.
What graph should we plot for values for voltage against reference concentration?
Semi log plot
y-axis: voltage
x-axis: log([K+]ref)
To give a straight line
Why might measured membrane potentials be different to those predicted by the nernst equation?
Membrane is partially permeable to chloride as well as to potassium.
Why do membranes have such a high capacitance?
Because the phospholipid bilayer is thin and very close together
Some key features of the earthworm and their location
Prostomium at the anterior end
Clitellum on dorsal side: glandular structure that produces coocoon for eggs to be deposited into
Gonopore: male openings on the body surface
What makes up the ventral nerve cord of earthworms?
1000 neurones
Median giant fibre (myleinated - unusal in inverebrates) and two lateral giant fibres
Each giant fibre behaves as though it were a singal axon
Role of median and lateral fibres
Median: action potentials from anterior to posterior
Lateral: action potentials from posterior to anterior
Role of stimulating electrodess
Produce an electrical current that depolarises the nerve fibres
Specifically the cathode (as it reduces the potential difference between the inside and outside of the axon)
Role of the earth electrode
Reduce noice and the stimulating artifact
Stimulus artefact: due to teh stimulating current traveling directly to the recording electrodes rather than through stimulating the nerve fibres
Calculation for nerve conduction velocity
Difference method
(D2 - D1) / (LP2 - LP1)
Define latency period
Delay between point of stimulation and the action potential reaching the first recording electrode.
What may change the ampnitude of the action potential measured in the worm median giant fibre?
The distance between the recording electrodes and the actual nerve fibre
Furthur distance = more resistance = smaller recorded action potential.
Overall, the electrical resistance of the tissue will make a difference
Which earthworm fibres are stimulated at low stimulating voltages?
The median giant fibres are stimulated at low volatges
Lateral fibres respond at higher voltages due to recruitment (and they have a longer latency)
- possibly due to fewer sodium ion channels
Which of the earthworm fibres has a lower conduction velocity?
The lateral giant fibres (not myleinated)
Why does latency period increase with freezing the fibres?
Affects kinetic properties of channel opeing mechanism (slow the rate that they open)
Sodium channels also inactivate more slowly and potassium channels open more slowly, effecting repolarisation
How can we determine the scaling coefficent?
Plot a log log graph
The gradient of the graph is equal to the scaling coefficent
Use a statistical test to determine is scaling coefficent differs significantly from what was predicted
How to calculate volume O2 consumed by shrimp in the time frame? (a measure of metabolic rate)
VO2 = (V x C (PO - P1) x 60) / t
V = volume of water that the shrimp was in
C = concentration O2 at 100% saturation at experimental temperature
P0 = reading 1
P1 = reading 2
t = time in minutes between readings
Assumptions made when using oxygen concentration to measure metabolic rate?
Constant amount of energy produced for each litre of oxygen
(will actually differ depending on food consumed)
How would tibia length of a locus expect to scale with body mass?
length is proportional to mass^(1/3)
How is force expected to scale with body mass?
Force is proportional to cross sectional area of muscle
Area is proportional to mass^(2/3)
Therefore expect force to be proportional to mass^(2/3)
How is acceleration expected to scale with body mass?
Accleration = force/mass
accleration proportional to mass^(-1/3)
How does take off velocity scale with body size?
velocity = root(2 x acceleration x distance)
= m^0 = constant
Take of velocity expected to be independent of body mass
Why might the prediction that take off velocity is independent of mass not be met?
Drag disproportionally affects smaller animals
Also possible that small and large locusts are not isometric
How to estimate mean arterial blood pressure
diastolic + 1/3(pulse pressure)
Pulse pressure = systolic - diastolic
Where and how is human blood pressure usually measured?
Brachial artery using a sphygmomanometer
Pressure applied to artery to cut off blood flow. Gradually decrease pressure and when it becomes equal to systolic pressure, blood will start to flow again (korotkoff sound begins)
Pressure is lowered and sounds become louder until diastolic pressure is reached and the sounds stop as blood can flow as normal.
What may affect blood pressure readings?
Auscultatory gap: disappearence of sounds between systolic and diastolic pressures
Width of the cuff relative to the arm
Too narrow: pressure seems higher than actual (because artery is compressed at a higher pressure)
Too wide: pressure seems lower
Recommended that cuff is 40% the circumference of the midpoint of the arm
How to estimate diastolic and systolic blood pressure?
Estimate systolic by palpitation first (raise pressure until no radial pulse)
Then take pressure of cuff to 30mmHg above estimated and slowly deflated. Hold stethescope over bracial artery and determine when korokoff sounds appear and disappear
What to the ECG components represent?
P wave: atrial depolarisation
PR: delay at AV node
QRS: ventricular depolarisation
T wave: ventricular depolarisation
What does the PR interval represent?
Time from start of atrial depolarisation to ventricular depolarisation (delay at the AVN)
What effect does standing up rapidly have on blood pressure and why?
Venous pooling may occur in the lower limbs, which means that venous return is impaired and so cardiac output falls (and so blood pressure falls)
This drop in pressure is recognised by receptors in the carotid sinus, which initate a baroreflex
What is electrical systole in an ECG?
Period of time between the QRS beginning and end of the T wave
What is electrical diastole
Any remaining time in teh ECG cycle outside of sytole (which is start of QRS to end of T)
Converting partial pressure of gases when water pressure is involved?
Partial pressure of gas = (A - 47) * (%gas (dry)/100)
Useful because the gas anazlyser measures dry percentages
Equation for calculating exercise efficentcy from work rate and energy expendature?
100 x work rate / total energy expenditure
Absorbance definition (in terms of light entering and leaving the sample)
A = log(light before sample/light leaving sample)
Function of subsidory cells in stomata
Buffer changes in tugor pressure of guard cells
Commelina communiais and Zea mays both have sunsidory cells
What is standard error of the mean used for?
Indicates confidence in the position of the population mean relative to sample mean
Why does systolic pressure increase with exercise but diastolic pressure does not?
Stroke volume rises with exercise so more blood is forced into the aorta per peat = increase in systolic pressure
Metabolic vasodilatation reduces TPR means the arterial pressure drops more rapidly following systole, which offsets the difference
Equation for alveolar ventilation rate? Relationship between ventilation rate and CO2 partial pressure
Va (l/min) = rate CO2 production/partial pressure CO2
Inversley proportional relationship (so greater ventilation rate lowers pCO2)
Where are peripheral chemoreceptors?
Carotid and aortic bodies
How to estimated alveolar partial pressures of carbon dioxide and oxygen?
Use end-expiratory sample (assume to be in equilbrum with the blood around the alveoli)
What is standard conditions (for STPD)
760mmHg
293K
How does pulse oximeter work?
Measures colour of blood to determine haemoglobin O2 saturation
Equation for max pulse rate
208 - (0.7 x age)
What would we expect to happen to ventilation rate as work rate increases
Increase linearlly with work rate
Might see disproportionally large increase at high work rates as acidosis takes place when anaerobic exercise is occuring
Effect of exercise on %spO2? (and pCO2 / pO2)
No change - blood gas partial pressures do not change significantly becuase they are not controlled only through negative feedback
A rise in pCO2 and a fall in pO2 are not observed during normal exercise. Due to feed forward mechanisms ventilation rate increases as soon as exercise begins and not in response to changes in blood gas partial pressures.
How to reduce insesible water loss?
Water lost across the skin other than for sweating
Includes respiratory water loss (water loss at respiratory tracts)
What is SVP and how does it change with temperature?
Saturated water vapour pressure (47 mmHg at 37 degrees)
Decreases with decreasing temperature (because it condenses)
Difference between external work rate and total work rate
Exernal work rate: that measured by the bike (work done against the resistance of the bike)
Total work rate: bodys metabolic rate
- only 25% of energy produced from total work rate can be converted to useful work rate, the rest must be lost as heat
Why is nose breathing good for heat and water loss loss?
Nasal passage way cooled as you breath in
As you breath out, warm moist air passes over the cold passageway and some of the water vapour consenses and is reasbsorbed into the blood
Because temperature of exhaled air is lower, loss from water vapour is less
Temporal countercurrent mechanism
Work, force and distance equation
Work = force (N) x distance (m)
Power = force x velocity (work done per unit time)
What is mesentery?
Thin web of tissue that surrounts the gut
What happens if a smaller current is applied from the power lab (when testing force of muscle contraction)
Fewer axons in the ulnar nerve are depolarisaed sufficently to generate action potentials
Fewer motor units stimulated
Smaller muscle contraction
What does the Cafar rehab X2 do that is different to previous experiment
Stimulates muscles of the hand (abductor muscles) directly (rather than stimulating motor neurones in the ulnar nerve)
Main advantage: can produce stimuli in the pattern we want (eg. high frequency)
What is hysteresis?
The nature of a physiological event depends on its past history
(eg. contraction ampnitude measured by force transducer are different when stimulation is increasing than when it is decreasing)
Reasons for hysteresis in muscle contraction: muscles were fatigued
What is a motor unit
Group of muscle fibres all innerverated by the same motor neurone
Electromyography?
Measures muscle response to nerve stimulation
Represented by an electromyogram
The EMG is not an all or none event becuase it measures a compound action potential
Why does force of muscle contraction increased as current produced by Cefar rehab X2 increase?
More muscle fibres are recruited with a larger stimulus
Why does frequency summation take place?
greater contraction ampnitude in the second/third contraction becuase calcium remains in the sarcoplasmic reticulm
As frequency increases, less time for calcium to be pumped back and can get a continous contraction (tetany)
How is smooth contraction obtained in vivo?
Asyncrousnous stimulation of motor units
In this experiment though, all motor units are stimulated at once.
What nerves did we look at in histology
Sciatic: motor fibres to leg muscles (larger than ulnar)
Ulnar: motor fibres to forearm muscles
Splanchnic: sympatheic fibres to the gut
What is observeable on a nerve tissue slide?
Circular structures are myelinated axons
Small intestine layers (inside -> out)
Muscosa
Submuscosa
Circular smooth muscle (thicker)
Longitudinal smooth muscle (thinner)
Serosa - thin layer of connective tissue
More permeable membrane to an ion - closer or furthur from E?
Closer to predicited value from nernst equation
Why is ampnitude from lateral giant fibres larger?
A compound action potential as there are two fibres
What do PR proteins do in plants
Accumlate with minutes of plant defence indiction
Regulated by SA
They are useful markers for plant defence induction
When is nitrate reductase induced?
When nitrate is avalible
Converts nitrate to nitrite (which then goes on to be reduced into ammonium)
What are two controls needed for nitrate reductase practical?
Negative: no enzyme present
Positive: with enzyme
Ideal gas law
P1V1/T1 = P2V2/T2
Aim of positive/negative control
P: Check that the assay works and can produce a response
N: Check for contamination of buffers or chemicals
Why does high potassium concentration in the bathing medium decrease guard cell sensitivity to light?
At any given membrane potential, a much higher internal concentration of potassium accumlates passivley
Equation for turgor pressure
Turgor pressure = gas constant x solute concentration (M) x temperature
How much space does a mole of gas occupy at SVP?
22.4 litres
Voltage, current resistance calculation?
V = IR
When might you use a high pass filter?
If we want to examine the high frequency part of the recording
eg. vibrations of the ear in response to a high frequency sound
