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ELECTROPHYSIOLOGY

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Title: ELECTROPHYSIOLOGY


1
ELECTROPHYSIOLOGY
  • Single Neuron Recording
  • Patch Clamp Recording
  • ECG
  • EEG- Brain activity Recording
  • PET, MRI, fMRI ,CAT

2
Single-unit recording
  • It is the use of an electrode to record the
    electrophysiological activity (action potentials)
    from a single neuron.

3
  • An electrode introduced into the brain of a
    living animal will detect electrical activity
    that is generated by the neurons adjacent to the
    electrode tip. If the electrode is a
    microelectrode, with a tip size of 3 to 10
    micrometers, the electrode will often isolate the
    activity of a single neuron.

4
  • The activity consists of the voltages generated
    in the extra cellular matrix by the current
    fields outside the cell when it generates an
    action potential. Recording in this way is
    generally called "single-unit" recording.

5
  • The recorded action potentials look very much
    like the action potentials that are recorded
    intracellularly, but the signals are very much
    smaller (typically about 0.1 mV).

6
  • Recordings of single neurons in living animals
    have provided important insights into how the
    brain processes information, following the
    hypothesis put forth by Edgar Adrian that unitary
    action potential events are the fundamental means
    of communication in the brain.

7
  • Microelectrodes used for extra cellular
    single-unit recordings are usually very fine
    wires made from tungsten or platinum-iridium
    alloys that are insulated except at their extreme
    tip and are less often glass micropipettes filled
    with a weak electrolyte solution similar in
    composition to extra cellular fluid.

8
  • Hubel and Wiesel were awarded the Nobel Prize in
    Physiology or Medicine in 1981.

9
The patch clamp technique
  • It is a laboratory technique in electrophysiology
    that allows the study of single or multiple ion
    channels in cells.

10
  • The technique can be applied to a wide variety of
    cells, but is especially useful in the study of
    excitable cells such as neurons, cardiomyocytes,
    muscle fibers and pancreatic beta cells. It can
    also be applied to the study of bacterial ion
    channels in specially prepared giant
    spheroplasts.

11
  • It is a laboratory technique in electrophysiology
    that allows the study of single or multiple ion
    channels in cells

12
  • Erwin Neher and Bert Sakmann developed the patch
    clamp in the late 1970s and early 1980s.
  • This discovery made it possible to record the
    currents of single ion channels for the first
    time, proving their involvement in fundamental
    cell processes such as action potential
    conduction.

13
  • Neher and Sakmann received the Nobel Prize in
    Physiology or Medicine in 1991 for this work.

14
  • Patch clamp recording uses, as an electrode, a
    glass micropipette that has an open tip diameter
    of about one micrometer, a size enclosing a
    membrane surface area or "patch" that often
    contains just one or a few ion channel molecules

15
  • In some experiments, the micropipette tip is
    heated in a microforge to produce a smooth
    surface that assists in forming a high resistance
    seal with the cell membrane.
  • The interior of the pipette is filled with a
    solution matching the ionic composition of the
    bath solution, as in the case of cell-attached
    recording, or the cytoplasm for whole-cell
    recording

16
  • Unlike traditional two-electrode voltage clamp
    recordings, patch clamp recording uses a single
    electrode to record currents.

17
  • ELECTROCARDIOGRAPH

18
  • As cardiac impulses pass through the heart,
    electrical currents spread into the tissues
    surrounding the heart, and a small portion of
    these currents spread throughout the surface of
    the body.

19
  • If electrodes are placed on the skin on opposite
    sides of the heart, electrical potential
    generated by these currents can be recorded.

20
  • Electrocardiograph is an instrument which records
    the electrical activity of the heart during a
    cardiac cycle.

21
  • A record of the minute electrical pulses
    generated by the heart used to determine the
    condition of the patients heart is the
    ElectroCardioGram.

22
  • Electrodes are placed on the chest and limbs, and
    the impulses which they detect are amplified by
    the electrograph to which the electrodes are
    connected.

23
  • The ECG was developed by William Einthoven of
    Leiden University, England between 1903 and 1910

24
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25
  • Electrical impulses in the heart originate in the
    sinoatrial node and travel through the heart
    muscle where they impart electrical initiation of
    systole or contraction of the heart.
  • The electrical waves can be measured at
    selectively placed electrodes (electrical
    contacts) on the skin.

26
  • Electrodes on different sides of the heart
    measure the activity of different parts of the
    heart muscle.
  • An ECG displays the voltage between pairs of
    these electrodes, and the muscle activity that
    they measure, from different directions, also
    understood as vectors.

27
  • This display indicates the overall rhythm of the
    heart and weaknesses in different parts of the
    heart muscle.
  • It is the best way to measure and diagnose
    abnormal rhythms of the heart, particularly
    abnormal rhythms caused by damage to the
    conductive tissue that carries electrical
    signals, or abnormal rhythms caused by levels of
    dissolved salts (electrolytes), such as
    potassium, that are too high or low. In
    myocardial infarction (MI), the ECG can identify
    damaged heart muscle

28
  • The ECG cannot reliably measure the pumping
    ability of the heart for which ultrasound-based
    (echocardiography) or nuclear medicine tests are
    used.

29
  • A typical electrocardiograph runs at a paper
    speed of 25 mm/s, although faster paper speeds
    are occasionally used. Each small block of ECG
    paper is 1 mm².
  • At a paper speed of 25 mm/s, one small block of
    ECG paper translates into 0.04 s (or 40 ms).
  • Five small blocks make up 1 large block, which
    translates into 0.20 s (or 200 ms).
  • Hence, there are 5 large blocks per second.

30
  • A standard signal of 1 mV must move the stylus
    vertically 1 cm, that is two large squares on ECG
    paper.

31
Leads used in ECG
  • Limb Leads
  • Leads I, II and III are the so-called limb leads
  • Lead I is a dipole with the negative (white)
    electrode on the right arm and the positive
    (black) electrode on the left arm.
  • Lead II is a dipole with the negative (white)
    electrode on the right arm and the positive (red)
    electrode on the left leg.
  • Lead III is a dipole with the negative (black)
    electrode on the left arm and the positive (red)
    electrode on the left leg.

32
Augmented limb
  • Leads aVR, aVL, and aVF are 'augmented limb
    leads'. They are derived from the same three
    electrodes as leads I, II, and III. However, they
    view the heart from different angles
  • Lead aVR or "augmented vector right" has the
    positive electrode (white) on the right arm. The
    negative electrode is a combination of the left
    arm (black) electrode and the left leg (red)
    electrode, which "augments" the signal strength
    of the positive electrode on the right arm.

33
  • Lead aVL or "augmented vector left" has the
    positive (black) electrode on the left arm. The
    negative electrode is a combination of the right
    arm (white) electrode and the left leg (red)
    electrode, which "augments" the signal strength
    of the positive electrode on the left arm.
  • Lead aVF or "augmented vector foot" has the
    positive (red) electrode on the left leg. The
    negative electrode is a combination of the right
    arm (white) electrode and the left arm (black)
    electrode, which "augments" the signal of the
    positive electrode on the left leg

34
Precordial
  • The precordial leads V1, V2, V3, V4, V5, and V6
    are placed directly on the chest. Because of
    their close proximity to the heart, they do not
    require augmentation

35
Waves and intervals
  • A typical ECG tracing of a normal heartbeat (or
    cardiac cycle) consists of a P wave, a QRS
    complex and a T wave.
  • A small U wave is normally visible in 50 to 75
    of ECGs. The baseline voltage of the
    electrocardiogram is known as the isoelectric
    line.
  • Typically the isoelectric line is measured as the
    portion of the tracing following the T wave and
    preceding the next P wave.

36
Schematic representation of normal ECG
37
P wave
  • During normal atrial depolarization, the main
    electrical vector is directed from the SA node
    towards the AV node, and spreads from the right
    atrium to the left atrium.
  • This turns into the P wave on the ECG, which is
    upright in II, III, and aVF and inverted in aVR
    . A P wave must be upright in leads II and aVF
    and inverted in lead aVR to designate a cardiac
    rhythm as Sinus Rhythm.

38
  • The relationship between P waves and QRS
    complexes helps distinguish various cardiac
    arrhythmias.
  • The shape and duration of the P waves may
    indicate atrial enlargement

39
QRS complex
  • The QRS complex is a structure on the ECG that
    corresponds to the depolarization of the
    ventricles.
  • Because the ventricles contain more muscle mass
    than the atria, the QRS complex is larger than
    the P wave.

40
  • In addition, because the His/Purkinje system
    coordinates the depolarization of the ventricles,
    the QRS complex tends to look "spiked" rather
    than rounded due to the increase in conduction
    velocity.
  • A normal QRS complex is 0.08 to 0.12 sec (80 to
    120 ms) in duration represented by three small
    squares or less, but any abnormality of
    conduction takes longer, and causes widened QRS
    complexes

41
PR/PQ interval
  • The PR interval is measured from the beginning of
    the P wave to the beginning of the QRS complex.
  • It is usually 120 to 200 ms long. On an ECG
    tracing, this corresponds to 3 to 5 small boxes.
    In case a Q wave was measured with a ECG the PR
    interval is also commonly named PQ interval
    instead.
  • A PR interval of over 200 ms may indicate a first
    degree heart block.

42
  • A short PR interval may indicate a pre-excitation
    syndrome via an accessory pathway that leads to
    early activation of the ventricles, such as seen
    in Wolff-Parkinson-White syndrome.
  • A variable PR interval may indicate other types
    of heart block.

43
  • The duration, amplitude, and morphology of the
    QRS complex is useful in diagnosing cardiac
    arrhythmias, conduction abnormalities,
    ventricular hypertrophy, myocardial infarction,
    electrolyte derangements, and other disease
    states.

44
  • "Buried" inside the QRS wave is the atrial
    repolarization wave, which resembles an inverse P
    wave.
  • It is far smaller in magnitude than the QRS and
    is therefore obscured by it.

45
ST segment
  • The ST segment connects the QRS complex and the T
    wave and has a duration of 0.08 to 0.12 sec (80
    to 120 ms).
  • It starts at the J point (junction between the
    QRS complex and ST segment) and ends at the
    beginning of the T wave.

46
  • The typical ST segment duration is usually around
    0.08 sec (80 ms).
  • The normal ST segment has a slight upward
    concavity.

47
T wave
  • The T wave represents the repolarization (or
    recovery) of the ventricles.
  • The interval from the beginning of the QRS
    complex to the apex of the T wave is referred to
    as the absolute refractory period.

48
  • The last half of the T wave is referred to as the
    relative refractory period (or vulnerable
    period). Tall or "tented" symmetrical T waves may
    indicate hyperkalemia.
  • Flat T waves may indicate coronary ischemia or
    hypokalemia.

49
QT interval
  • The QT interval is measured from the beginning of
    the QRS complex to the end of the T wave.
  • Normal values for the QT interval are between
    0.30 and 0.44 seconds.

50
  • The QT interval as well as the corrected QT
    interval are important in the diagnosis of long
    QT syndrome and short QT syndrome.
  • The QT interval varies based on the heart rate,
    and various correction factors have been
    developed to correct the QT interval for the
    heart rate.

51
  • The QT interval represents on an ECG the total
    time needed for the ventricles to depolarize and
    repolarize

52
U wave
  • The U wave is not always seen. It is typically
    small, and, by definition, follows the T wave. U
    waves are thought to represent repolarization of
    the papillary muscles or Purkinje fibers.
    Prominent
  • An inverted U wave may represent myocardial
    ischemia or left ventricular volume overload

53
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54
Computed Axial Tomography (CAT)
  • Computed tomography (CT) is a medical imaging
    method employing tomography.
  • Digital geometry processing is used to generate a
    three-dimensional image of the inside of an
    object from a large series of two-dimensional
    X-ray images taken around a single axis of
    rotation.

55
  • CT scan was invented by Sir Godfrey Hounsfield
  • He got Nobel prize in 1979 for the discovery

56
CT Scanner
57
CT Image of Brain
58
Brain Images
59
  • The word "tomography" is derived from the Greek
    tomos (slice) and graphein (to write).
  • Computed tomography was originally known as the
    "EMI scan" as it was developed at a research
    branch of EMI, a company best known today for its
    music and recording business.
  • It was later known as computed axial tomography
    (CAT or CT scan) and body section röntgenography.

60
Positron emission tomography (PET)
  • Positron emission tomography (PET) is a nuclear
    medicine imaging technique which produces a
    three-dimensional image or picture of functional
    processes in the body

61
  • The system detects pairs of gamma rays emitted
    indirectly by a positron-emitting radionuclide
    (tracer), which is introduced into the body on a
    biologically active molecule.

62
  • Images of tracer concentration in 3-dimensional
    space within the body are then reconstructed by
    computer analysis.
  • In modern scanners, this reconstruction is often
    accomplished with the aid of a CT X-ray scan
    performed on the patient during the same session,
    in the same machine.

63
  • If the biologically active molecule chosen for
    PET is FDG, an analogue of glucose, the
    concentrations of tracer imaged then give tissue
    metabolic activity, in terms of regional glucose
    uptake.

64
  • To conduct the scan, a short-lived radioactive
    tracer isotope, is injected into the living
    subject (usually into blood circulation).
  • The tracer is chemically incorporated into a
    biologically active molecule
  • The molecule most commonly used for this purpose
    is fluorodeoxyglucose (FDG), a sugar, for which
    the waiting period is typically an hour.

65
  • As the radioisotope undergoes positron emission
    decay (also known as positive beta decay), it
    emits a positron, a particle with the opposite
    charge of an electron.
  • After traveling up to a few millimeters the
    positron encounters and annihilates with an
    electron, producing a pair of annihilation
    (gamma) photons moving in opposite directions.

66
  • These are detected when they reach a scintillator
    in the scanning device, creating a burst of light
    which is detected by photomultiplier tubes or
    silicon avalanche photodiodes

67
PET
68
PET IMAGE
69
PET Image of Brain
70
PET Acquisition Process
71
Radioisotopes
  • Radionuclides used in PET scanning are typically
    isotopes with short half lives such as carbon-11
    (20 min), nitrogen-13 (10 min), oxygen-15 (2
    min), and fluorine-18 (110 min).

72
  • These radionuclides are incorporated either into
    compounds normally used by the body such as
    glucose (or glucose analogues), water or ammonia,
    or into molecules that bind to receptors or other
    sites of drug action. Such labelled compounds are
    known as radiotracers.

73
Applications
  • PET is both a medical and research tool
  • It is used heavily in clinical oncology (medical
    imaging of tumors and the search for metastases),
    and for clinical diagnosis of certain diffuse
    brain diseases such as those causing various
    types of dementias
  • PET is also an important research tool to map
    normal human brain and heart function.

74
Magnetic resonance imaging (MRI)
  • Magnetic resonance imaging (MRI), or nuclear
    magnetic resonance imaging (NMRI), is primarily a
    medical imaging technique most commonly used in
    radiology to visualize the structure and function
    of the body. It provides detailed images of the
    body in any plane.

75
MRI
76
  • NMR was discovered by Bloch and Purcell in 1952

77
MRI Image of Brain
78
  • MRI provides much greater contrast between the
    different soft tissues of the body than computed
    tomography (CT) does, making it especially useful
    in neurological (brain), musculoskeletal,
    cardiovascular, and oncological (cancer) imaging

79
  • Unlike CT, it uses no ionizing radiation, but
    uses a powerful magnetic field to align the
    nuclear magnetization of (usually) hydrogen atoms
    in water in the body.

80
  • Radiofrequency fields are used to systematically
    alter the alignment of this magnetization,
    causing the hydrogen nuclei to produce a rotating
    magnetic field detectable by the scanner.
  • This signal can be manipulated by additional
    magnetic fields to build up enough information to
    construct an image of the body.

81
  • The body is mainly composed of water molecules
    which each contain two hydrogen nuclei or
    protons.
  • When a person goes inside the powerful magnetic
    field of the scanner these protons align with the
    direction of the field.

82
  • A second radiofrequency electromagnetic field is
    then briefly turned on causing the protons to
    absorb some of its energy.
  • When this field is turned off the protons release
    this energy at a radiofrequency which can be
    detected by the scanner.

83
  • The position of protons in the body can be
    determined by applying additional magnetic fields
    during the scan which allows an image of the body
    to be built up. These are created by turning
    gradients coils on and off which creates the
    knocking sounds heard during an MR scan.

84
  • Diseased tissue, such as tumors, can be detected
    because the protons in different tissues return
    to their equilibrium state at different rates.

85
Applications
  • In clinical practice, MRI is used to distinguish
    pathologic tissue (such as a brain tumor) from
    normal tissue.
  • One advantage of an MRI scan is that it is
    harmless to the patient. It uses strong magnetic
    fields and non-ionizing radiation in the radio
    frequency range
  • Compare this to CT scans and traditional X-rays
    which involve doses of ionizing radiation and may
    increase the risk of malignancy, especially in a
    fetus.

86
MRI Signs
  • Safe Conditional Unsafe

87
Functional MRI (fMRI)
  • It is a type of specialized MRI scan. It measures
    the haemodynamic response related to neural
    activity in the brain or spinal cord of humans or
    other animals

88
  • It is one of the most recently developed forms of
    neuroimaging.
  • Since the early 1990s, fMRI has come to dominate
    the brain mapping field due to its low
    invasiveness, lack of radiation exposure, and
    relatively wide availability.

89
f MRI Image
90
Electroencephalography (EEG)
  • EEG is the recording of electrical activity along
    the scalp produced by the firing of neurons
    within the brain.

91
  • In clinical contexts, EEG refers to the recording
    of the brain's spontaneous electrical activity
    over a short period of time, usually 20-40
    minutes, as recorded from multiple electrodes
    placed on the scalp

92
  • EEG used to be a first-line method for the
    diagnosis of tumors, stroke and other focal brain
    disorders, but this use has decreased with the
    advent of anatomical imaging techniques such as
    MRI and CT.

93
  • EEG was discovered in 1929 by a German
    psychiatrist Hans Berger
  • In 1932 by a British electrophysiologist, Edgar
    Adrian won Nobel prize for the demonstration of
    electrical impulses from brain

94
EEG
95
1 Second EEG
96
  • It is generally accepted that the activity
    measured by EEG is electrical potentials created
    by the post-synaptic currents, rather than by
    action potentials.
  • More specifically, the scalp electrical
    potentials that produce EEG are due to the
    extracellular ionic currents caused by dendritic
    electrical activity (whereas the fields producing
    magnetoencephalographic signals are associated
    with intracellular ionic currents).

97
Wave patterns
  • delta waves.
  • Delta is the frequency range up to 3 Hz. It tends
    to be the highest in amplitude and the slowest
    waves. It is seen normally in adults in slow wave
    sleep. It is also seen normally in babies

98
Delta Wave
99
  • Theta is the frequency range from 4 Hz to 7 Hz.
    Theta is seen normally in young children. It may
    be seen in drowsiness or arousal in older
    children and adults it can also be seen in
    meditation

100
Theta Wave
101
  • Alpha is the frequency range from 8 Hz to 12 Hz.
    Hans Berger named the first rhythmic EEG activity
    he saw, the "alpha wave." This is activity in the
    8-12 Hz range seen in the posterior regions of
    the head on both sides, being higher in amplitude
    on the dominant side. It is brought out by
    closing the eyes and by relaxation.

102
Alpha Wave
103
  • Beta is the frequency range from 12 Hz to about
    30 Hz.
  • It is seen usually on both sides in symmetrical
    distribution and is most evident frontally.
  • Low amplitude beta with multiple and varying
    frequencies is often associated with active, busy
    or anxious thinking and active concentration.
    Rhythmic beta with a dominant set of frequencies
    is associated with various pathologies and drug
    effects, especially benzodiazepines.

104
Beta Wave
105
  • Gamma is the frequency range approximately 26100
    Hz.
  • Gamma rhythms are thought to represent binding
    of different populations of neurons together into
    a network for the purpose of carrying out a
    certain cognitive or motor function.

106
Gamma Wave
107
Medical Imaging Instruments
  • Barium X ray X ray
  • CT Scan X ray
  • Bronchography Optical
  • Endoscopy Optical
  • PET Nuclear
  • MET Nuclear
  • Echocardiograph Ultrasound

108
  • ECG Bioelectricity
  • Electromyograph EMG Bioelectricity
  • EEG Bioelectricity
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