Neurophysiology Review Flashcards
What are the divisions of the nervous system
CNS = brain and spinal cord
PNS = 12 pair of cranial nerves + 31 pair spinal nerves
What are CNS and PNS categorized into
Afferent = sensory
Efferent = motor
PNS is further divided into:
- somatic NS (voluntary)
- autonomic NS (involuntary)
- autonomic = sympathetic (fight/flight) and parasympathetic (rest/digest)
What are nuerons? Functions? Structure?
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)
What are nerves? What are the categories?
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
What is the structure of nerves
- Endoneurium = CT around axon
- Fascicle = group of axons
- Perineurium = CT around 1 fascicle
- Epineurium = CT around group of fascicles
What are the types of fibers
type A = largest, fasted, myelinated, afferent or efferent
Type B = slightly myelinated, efferent
Type C = smallest, unmyelinated, most numerous, efferent and afferent
What are type A fibers
Largest fibers = fastest impulse conduction
Myelinated
Afferent or efferent
4 subtypes: Aa, Ab, Agamma, Adelta
What are the subtypes of the A fibers
Typa Aalpha –> largest, fastest, efferent, muscle movement
Type Abeta –> afferent, proprioceptions, touch, pressure
Type Agamma –> efferent, muscle tone
Type Adelta –> afferent, pain, temp
What are type B fibers
Slightly myelinated, efferent
Preganglionic ANS; vascular smooth muscle
What are type C fibers
Smallest and unmyelinated (=slower)
Most numerous
Efferent and afferent
Post-ganglinic ANS, temperature and dull, achy, slow pain
What fibers are increased in oral cavity
Increased numbers of type A and type C in oral cavity
What fibers require more anesthetic volume
Type A (because they’re larger)
What are the functions of neurons
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
What are the nerve impulses
Action potentials - generated by all or none voltage change
(NO difference in strength of impulse, does not weaken as it travels)
What is RMP maintained by
sodium potassium pump
What happens when a neuron is resting
Membrane is POLARIZED (outside is positive, inside is negative)
- more Na+ outside cell (14:1 ratio)
- RMP = -70mV
What maintains RMP
sodium potassium pump
Closed K and closed Na channels
What happens during depolarization of a membrane?
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
What is released at synaptic cleft
Neurotransmitters
- can be:
Excitatory = triggers impulse, Ach/NE
Inhibitory = increase polarization, dopamine/serotonin
What occurs during repolarization of a membrane
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
What is the absolute refractory period
Interval when 2nd impulse can NOT be initiated
- due to inactivation of Na channels during repolarization
What is the relative refractory period
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
Steps of action potential
depolarization, repolarization, hyperpolarization
LA cause reversible anesthesia by:
- Preventing generation of impulses
- Preventing conduction of impulses
What type of block do LA cause
Chemical block between source of impulse and brain
(Impulse never reaches the brain)
What type of drugs are LA called
“Membrane stabilizing drugs” because they decrease the rate of depolarization
What do LA do
Bind to Na+ channels inside the cell = prevent Na+ from moving inside
- inhibit Na ion flux during depolarization
What does “state-dependent blockade” mean
This is what LA cause
Means it binds easier to NA+ channels that are firing (not the resting ones)
What size nerve fibers are more sensitive to LA
SMALL diameter = more sensitive (require less)
Large = require more volume of LA
What is the action of Local anesthetics
- Diffuse through neuron cell membrane
- Bind to Na+ channels (inside cell membrane)
- Prevent Na+ channels from opening
- Prevent conduction of nerve impulse (as long as LA is bound to receptor site)
- Prevent neuron from reaching firing potential (membrane remains polarized)
What are the 2 major routes of LA delivery? Which is more toxic?
- Topical - applied on mucosa, increased concentrations (needs to penetrate mucosa) = increased toxicity*
- Submucosal infection - more effective than topical, decreased concentrations needed (placed close to nerve trunk)
