Origin of Biopotential Signals

Question 1

What are the 5 different bioeletric signals

Answer 1

1. Electrocardiogram (ECG)
2. Electroencephalogram (EEG)
   - typically look at size and speed of response
3. Electroneurogram (ENG)
4. Electromyogram (EMG)
5. Electroretinogram (ERG)

Question 2

Describe the pathway from bioelectric signal input to output

Answer 2

1. Input
   - bioelectric signals on / in body
2. collection
   - via surface / needle electrodes
3. processing
   - amplifier, noise removal, filter
4. output
   - signal waveform for recording / display

Question 3

What types of electrodes are used for EMG measurements (3)

Answer 3

1. Ring electrode
   - used for listening
2. Surface electrode
   - used to ground the signals
3. Needle electrodes
   - used to send signals

Question 4

Describe the pathway of the reflex arc

Answer 4

1. Sensory organ
   ex. Muscle spindle
2. sensory nerve
3. transducer (cell body of sensory nerve fiber)
4. motor nerve
5. effector organ
   ex. biceps

Question 5

What do you measure using an ENG (3)

Answer 5

1. Motor-nerve conduction velocity

v = D / (L1 - L2)
D –> distance between 2 sensors
L1/2 –> distance between signal 1/2 input and actioni potential

2. Field potentials of sensory nerves
   sensory nerves–> simulation of index finger w/ ring electrode
   (stimulating signal is short but strong: 100V w/ duration of 100 us)

closer activation = stronger impulse

3. Reflexly-evoked field potentials
   - latency of consequtive responses
   (sensory nerves have large diameters –> excite at lower stimuli)
   - only measure max response of nerves from both m-wave and h-wave

a) H-wave (only sensory)
- simulation is sensed by sensory nerve cell and sent to spine

b) M-wave (only motor)
- direct stimulation of muscle (faster than H-wave)

c) F-wave (both)
- direct simulation of muscle AND shocks spinal cord (causes another muscle stimulation)

Question 6

Electromyogram (EMG)

Answer 6

• measures the motor unit action potential during muscle contraction

Single motor unit:
- 1 motor nerve and bundle of muscle fiber it excites
- fibers mix –> distributed bio electric source

Question 7

Describe the resting potential and active state of excitable cells

Answer 7

Resting potential:
(-40 to -90 mV internal relative to external)
- membrane is slightly permeable to Na+ but freely to K+ and Cl-

Flow of ion:
- diffusion gradients
- electric field (pos to neg)
- membrane structrue porosity
- active transport of ions via channels

Permeability:
- depends on voltage and time

Active state:
- requires adeqate stimulus (all-or-nothing)

Question 8

Describe the series of steps for excitiation of cells

Answer 8

1. Depolarization
   - Na+ enters cell s
   - increases permeability to Na+
2. Action potential
   - stimulates adj cell s
   - K+ leave cell
   - increases permeability to K+
3. Repolarization
   - voltage returns to rest potential
4. Hyperpolarization
   - undershoot + recovery of ATP pump