Neurophysiology Review

Question 1

What are the divisions of the nervous system

Answer 1

CNS = brain and spinal cord
PNS = 12 pair of cranial nerves + 31 pair spinal nerves

Question 2

What are CNS and PNS categorized into

Answer 2

Afferent = sensory
Efferent = motor

PNS is further divided into:
- somatic NS (voluntary)
- autonomic NS (involuntary)
- autonomic = sympathetic (fight/flight) and parasympathetic (rest/digest)

Question 3

What are nuerons? Functions? Structure?

Answer 3

Nerve cells

3 functions: receive information, process information, send response

Structure: cell body, 1 axon (carries impulse away from cell body), 1 or more dendrites (carries impulse to cell body)

• also synaptic knob = terminal end of axon (allows impulse to travel to another neuron via NTs)

Question 4

What are nerves? What are the categories?

Answer 4

Many axons, an artery and a vein
- provides pathway for nerve impulses
- only found in PNS
- can be myelinated = fast conduction (via Nodes of Ranvier)

Categorized as: afferent, efferent or mixed

Question 5

What is the structure of nerves

Answer 5

1. Endoneurium = CT around axon
2. Fascicle = group of axons
3. Perineurium = CT around 1 fascicle
4. Epineurium = CT around group of fascicles

Question 6

What are the types of fibers

Answer 6

type A = largest, fasted, myelinated, afferent or efferent
Type B = slightly myelinated, efferent
Type C = smallest, unmyelinated, most numerous, efferent and afferent

Question 7

What are type A fibers

Answer 7

Largest fibers = fastest impulse conduction
Myelinated
Afferent or efferent

4 subtypes: Aa, Ab, Agamma, Adelta

Question 8

What are the subtypes of the A fibers

Answer 8

Typa Aalpha –> largest, fastest, efferent, muscle movement

Type Abeta –> afferent, proprioceptions, touch, pressure

Type Agamma –> efferent, muscle tone

Type Adelta –> afferent, pain, temp

Question 9

What are type B fibers

Answer 9

Slightly myelinated, efferent

Preganglionic ANS; vascular smooth muscle

Question 10

What are type C fibers

Answer 10

Smallest and unmyelinated (=slower)
Most numerous
Efferent and afferent

Post-ganglinic ANS, temperature and dull, achy, slow pain

Question 11

What fibers are increased in oral cavity

Answer 11

Increased numbers of type A and type C in oral cavity

Question 12

What fibers require more anesthetic volume

Answer 12

Type A (because they’re larger)

Question 13

What are the functions of neurons

Answer 13

1) Neurons are electrically excitable
2) Neurons have ion channels embedded in the membrane (Na, K, Cl, Ca)
3) Neurons maintain a concentration gradient
4) The voltage gradient of the resting membrane is maintained by the Na-K Pump
5) Nerve impulses are called Action Potentials - generated by “all or none” voltage change
6) Nerve impulses are triggered by a stimulus (chemical, thermal, mechanical, electrical)
7) Nerve impulse travels from 1 neuron to another by crossing a synapse
8) Nerve impulse passes through a neuron 7 milliseconds

Question 14

What are the nerve impulses

Answer 14

Action potentials - generated by all or none voltage change
(NO difference in strength of impulse, does not weaken as it travels)

Question 15

What is RMP maintained by

Answer 15

sodium potassium pump

Question 16

What happens when a neuron is resting

Answer 16

Membrane is POLARIZED (outside is positive, inside is negative)
- more Na+ outside cell (14:1 ratio)
- RMP = -70mV

Question 17

What maintains RMP

Answer 17

sodium potassium pump
Closed K and closed Na channels

Question 18

What happens during depolarization of a membrane?

Answer 18

Becomes positively charged* (positive ions move inside)
- stimulus must reach threshold at +15-20mV) (all or none)
- greater intensity does not mean stronger impulse but can make more impulses per second

K/Na Chanel’s open, Na flows inside = inside is positive
- action potential conduction as depolarization travels along membrane
- impulse crosses both electrical synapses (gaps between neurons) and chemical synapses (synaptic cleft at end of each axon)
- NT released at synaptic cleft - excitatory or inhibitory

Question 19

What is released at synaptic cleft

Answer 19

Neurotransmitters

• can be:
  Excitatory = triggers impulse, Ach/NE
  Inhibitory = increase polarization, dopamine/serotonin

Question 20

What occurs during repolarization of a membrane

Answer 20

After AP has peaked (+40 mV) —> membrane begins to move back to -70mV.
- beings with movement of K+ ions to outside
- Na/K pump moved Na outside to restore RMP

Question 21

What is the absolute refractory period

Answer 21

Interval when 2nd impulse can NOT be initiated
- due to inactivation of Na channels during repolarization

Question 22

What is the relative refractory period

Answer 22

Interval immediately after absolute refractory period when 2nd impulse is inhibited but possible if larger stimulus is applied
- due to hyper-polarization before RMP is established

Question 23

Steps of action potential

Answer 23

depolarization, repolarization, hyperpolarization

Question 24

LA cause reversible anesthesia by:

Answer 24

1. Preventing generation of impulses
2. Preventing conduction of impulses

Question 25

What type of block do LA cause

Answer 25

Chemical block between source of impulse and brain
(Impulse never reaches the brain)

Question 26

What type of drugs are LA called

Answer 26

“Membrane stabilizing drugs” because they decrease the rate of depolarization

Question 27

What do LA do

Answer 27

Bind to Na+ channels inside the cell = prevent Na+ from moving inside
- inhibit Na ion flux during depolarization

Question 28

What does “state-dependent blockade” mean

Answer 28

This is what LA cause

Means it binds easier to NA+ channels that are firing (not the resting ones)

Question 29

What size nerve fibers are more sensitive to LA

Answer 29

SMALL diameter = more sensitive (require less)
Large = require more volume of LA

Question 30

What is the action of Local anesthetics

Answer 30

1. Diffuse through neuron cell membrane
2. Bind to Na+ channels (inside cell membrane)
3. Prevent Na+ channels from opening
4. Prevent conduction of nerve impulse (as long as LA is bound to receptor site)
5. Prevent neuron from reaching firing potential (membrane remains polarized)

Question 31

What are the 2 major routes of LA delivery? Which is more toxic?

Answer 31

1. Topical - applied on mucosa, increased concentrations (needs to penetrate mucosa) = increased toxicity*
2. Submucosal infection - more effective than topical, decreased concentrations needed (placed close to nerve trunk)