practical 6: EMG, ulnar nerve conduction velocity & reflexes

how to calculate conduction velocity

1. calculate difference between 2 latency periods

2. given distance (mm)/latency difference

   • units mm/sec

   • from mm/sec to m/sec = divide by 100

units for amplidtude

mV

what is the latency period (how do you se it on a graph)

time delay between stimulus & muscles electrical response (flat line before first increase after stimulus)

2 factors that increases nerve conduction ability

• large diameter

• myelinated

what does having more motor units in a muscle result in

less finely controlled movements

where are the black and white leads placed in EMG

bicep

where are the red & brown leads placed in EMG

tricep

where is the green lead placed in EMG

wrist

what nerve supplies the abductor digiti minimi muscle

ulnar

where is the ulnar nerve found

down forearm from the elbow & enters hand at the wrist on the same side as the pinky

where + how many are electrodes are placed on a muscle during EMG

• midway along it’s length

• a pair of electrodes (2)

3 reasons why shouldn’t electrodes be placed across the muscle during EMG

• muscle fibers generate action potentials that are parallel to the length of the fibers

• perpendicular placement = more likely for electrical signals of other muscles to be picked up

• depolarisation across the muscle fibre can’t be detected

3 reasons why the subject be seated in a relaxed position & their arm at 90 degrees during EMG

• relaxation avoids unnecessary muscle activation eg: muscle spindles twitching

• 90 degrees standardises muscle length effect

• secondary muscles in the arm aren’t activated

why is the stimulating electrode bathed in saline prior to applying electrical stimulation

to improve conduction between the electrode and the skin

how are the contractions represented on the EMG trace

spikes on the trace (peaks)

relationship between contraction & wave amplitude

larger contraction = higher amplitude

x% w/v meaning

theres that many g of substance in 100mL of water

how to caluculate xmL solution of x% w/v

1. divide mL volume by 100

2. multiply % by mL

what type of graph would you plot to represent changes in total electrical activity in males & females

scatter

what statistical test would you use to see if theres a difference in changes in total electrical activity in males & females

2 sample unpaired t-test

what muscle, levels & nerve is involved in the knee jerk (patellar) reflex

• quadriceps femoris

• levels: L2, L3, L4

• nerve: femoral

what muscle, levels & nerve is involved in the bicep jerk

• biceps

• levels: C5, C6

• nerve: musculocutaneous

what muscle, levels & nerve is involved in the tendon reflex of the tricep muscle

• tricep

• levels: C6, C7, C8

• nerve: radial

what muscle, levels & nerve is involved in the ankle jerk

• gastrocnemius muscle

• levels: L5, S1, S2

• nerve: tibial

what muscle, levels & nerve is involved in the plantar reflex (toes)

• toe flexors

• levels: L5, S1, S2

• nerve: tibial

what other muscles in the hand are innervated by the ulnar nerve

• Flexor Digiti Minimi Brevis

• Opponens Digiti Minimi

3 ways excitation-contraction coupling differs between skeletal muscle and cardiac muscle

1. depolarisation trigger: skeletal muscle = motor neuron, cardiac muscle = pacemaker cells (SA node)

2. Ca release mechanism: skeletal muscle = no influx of calcium needed, cardiac muscle = influx of calcium needed

3. contraction type: skeletal muscle = voluntary, cardiac muscle = involuntary