EEG: Electro Encephalo Graphy: Recording & the study of electrical activity of brain By electrodes : summation of neural depolarization in the brain due to stimuli from five senses and thought process Surface of skull : 10 mV Propagation through skull bone : 1 to 100 µV Frequency : 0.5 to 3000 Hz

EEG

Origin of EEG: Originate within the dendrite potential (acetylcholine)

The Cell Membrane: Na+ Cl- K+ A- Outside of Cell Inside of Cell Cell Membrane at rest Na+ Cl- K+ A- Outside of Cell Inside of Cell Potassium (K+) can pass through to equalize its concentration Sodium and Chlorine cannot pass through Result - inside is negative relative to outside - 70 mv Key words: Cell membrane; semi-permeable; K+; Na+; Cl- The cell membrane is semi-permeable. That is, when the neuron is at rest, the cell membrane allows some ions (K+) to pass freely through the cell membrane, whereas other ions (such as Na+ and Cl-) cannot. Hit enter once and K+ ions will slowly pass through the cell membrane. After K+ animation is finished, hit enter again and animation showing that Na+ and l- ions cannot pass through the membrane will occur.

Brain spatially represented:

Two ways Tremendous numbers of nerve fibres can discharge in synchronous with each other Large number of neurons can partially discharge, though not emit action potential

Action potential: Disturbances in resting potential along the nerve fibre: transfers the message When the action potential reaches the cell, it fires and spike is produced IPSP (Inhibitory Post Synaptic Potential) Transmitter: Inhibitory Receptor : membrane potential increases in negative direction EPSP (Excitatory Post Synaptic Potential) Transmitter: Excitatory Receptor : membrane potential increases in positive direction

Evoked potential: Potentials developed in the brain as the responses to external stimuli like light, sound etc. Event related potential

Types of Electrode Placement 10-20 System Of Electrode Placement 10-10 System Of Electrode Placement

Normal Recorded Sample EEG

EEG Waves alpha (8 – 13Hz): awake, closed eyes Occupital region beta (13 – 30Hz): awake, alert Parietal & frontal regions gamma (> 30Hz): memory, active thought delta (0.5 – 4 Hz): deep sleep cortex region theta (4 – 8Hz): infants, sleeping adults (frustration, disappointment) parietal & temporal regions

Normal EEG Recorded in Man Eyes opened condition. Examples of different waves.

Placement of electrodes: Disc like surface electrodes Bipolar electrode (difference between 2 adjacent electrodes) Monopolar electrode (potential of each electrode with respect to reference electrode) Wilson technique (one of the electrode potential with respect to the central terminal)

Recording setup:

Modern EEG unit:

Contd.. The electrodes are attached to the channel selector in a group of eight : Mortage 50 Hz a.c. interference is reduced by employing differential amplifiers as preamplifiers with more than 80 db CMRR 50 Hz notch filter Room is covered with ferrous metal screen, avoids

Analysis of EEG: Level of consciousness: Brain tumors: Epilepsy: REM : rapid eye movement Anaesthesia: frequency decreases & amplitude ↑ Brain tumors: In cortex, electrical activity will be absent Epilepsy: Symptom of brain damage Synchronous discharge of large group of neurons Grandmal & Peritmal

EMG – ElectroMyoGraphy: is a science of recording & interpreting the electrical activity of muscle’s action potentials Recording peripheral nerve’s action potentials Action potentials: both positive & negative polarities of the electrode Contraction of the muscles

Recording set up:

Amplitude depends on: the type of electrode Placement of electrodes Degree of muscular exertions 0.1 mV to 0.5 mV 20 Hz to 10 kHz Reflex responses and muscular diseases

Determination of conduction velocities in motor nerves: Brain to sensory organs By stimulating the nerves with brief electric shock 0.2 ms to 0.5 ms Latency : elapsed time Conduction velocity, v = (l1-l2) / (t1-t2) = 50 m/s If v<40 m/s, disorder in nerve conduction

Determination of conduction velocities in motor nerves:

Electro Retino Graphy (ERG): Recording and interpreting the electrical activity of eye Retina is the extension of the cerebral cortex The cornea is about 20 mV positive relative to the fundus of the eye Change in illumination changes the potential Ag-Agcl electrode on a contact lens Reference electrode on cheek

Electro Ooculo Graphy (EOG): Recording the corneal – retina potential associated with eye movements More simpler than ERG

Electro Ooculo Graphy (EOG):

Electro Ooculo Graphy (EOG): The source of electrical energy in eye is the corneo-retinal potential or electrostatic field which rotated with respect to eye Applications: Effects of drugs State of semicircular canals Neurological disorders Level of anaesthesia

ERG Electrodes

ERG Electrodes

PHONOCARDIOGRAPHY Phonogram – graphic record of heart sounds – vibrations of cardiac structure Phonocatheter – catheter with microphone at the tip Heart sounds – short duration – transient – opening and closing of valves Murmur – longer duration – noisy – turbulent flow of blood in the heart – 1000 Hz

Heart sounds Valve closure sounds Ventricular filling sounds Valve opening sounds Extra cardiac sounds

Valve closure sounds First heart sound : beginning of systole – closure of mitral and tricuspid valves 0.1 to 0.2 s Second heart sound : beginning of diastole - closure of aortic and pulmonary valves 0.08 to 0.14 s

Ventricular filling sounds: Third heart sound : rapid filling of the ventricles 0.12 to 0.18 s Valve opening sounds: Opening of Atrio - Ventricular valves and semilunar valves Extra cardiac sounds: Mid or late systole or early diastole – thickened pericardium

Characteristics of sound Frequency – 10 to 1000 Hz Low range – 10 to 60 Hz – 3rd and 4th heart sound Medium range – 60 to 150 Hz – 1st and 2nd heart sounds High range – 150 to 1000 Hz – diastolic murmurs & pulmonary insufficiency Amplitude quality

Block diagram

Placement of microphone

Microphone Air coupled microphone Contact microphone

Amplifier

Filter

BP, Heart sounds and ECG

Analysis of heart sounds