Basic Neurophysiology

Question 1

Resting membrane potential

Answer 1

Voltage-gated Na and K channels are closed in the resting state; typical value is -70 mV inside the cell

Question 2

Absolute refractory period

Answer 2

You are unable to elicit another action potential no matter how much depolarization or stimulation you apply, due to the inactivation of the voltage gated Na channels

Question 3

Relative refractory period

Answer 3

You are able to elicit another action potential as long as there is enough stimulation. At this point the voltage gated Na channels have gone from inactivated back to closed/in the resting position

Question 4

Orthodromic conduction

Answer 4

Propagation in the normal physiologic direction - sensory toward the brain, motor away from the brain

Question 5

Antiromic conduction

Answer 5

Propagation opposite to normal direction - sensory away from the brain, motor toward the brain

Question 6

Spatial summation

Answer 6

Multiple different sites of post-synaptic potentials combined together to cross threshold

Question 7

Temporal summation

Answer 7

Multiple potentials at the same location combined together to cross threshold

Question 8

NCV formula

Answer 8

Distance/Onset latency

Question 9

Neuropraxia

Answer 9

Conduction block is due to a localized region of demyelination or ischemia in the nerve axon - axon is still viable. These have a good prognosis for recovery

Question 10

Axonotmesis

Answer 10

Loss of continuity of the axon itself, but preservation of the endoneurium or other connective tissues.

Question 11

Wallerian degeneration

Answer 11

Distal degeneration of the axon

Question 12

Neurotmesis

Answer 12

Involves not only the loss of continuity of the axon, but also disruption of the epineurium and perineurium, or may involve complete trans-section of the nerve. Wallerian degeneration will take place

Question 13

Nerve regeneration

Answer 13

In cases where WD has taken place, the distal stump of the live nerve cell will attempt to grow. Tubules will form. If regeneration is successful, many small unmyelinated fibers that regrew will die off and be replaced by large myelinated fibers. They have a shorter inter nodal distance

Question 14

Excitatory Neurotransmitters

Answer 14

Acetylcholine, epinephrine, glutamate

Question 15

Inhibitory Neurotransmitters

Answer 15

GABA, glycine