Neurophysiology

Question 1

Neuron

Answer 1

The basic element of all rapid signal processing within the body. A neuron consists of a cell body (soma), dendrites, and the axon (nerve fiber).

Question 2

Afferent neurons

Answer 2

Transmit impulses from peripheral receptors to the CNS

Question 3

Efferent neurons

Answer 3

Transmit impulses from the CNS to the periphery

Question 4

Afferent neuron classifications

Answer 4

A, B, and C by fiber diameter and velocity of conduction of nerve impulses.

Question 5

A-alpha fibers

Answer 5

Myelinated
Diameter 12-20 (largest of afferent neurons)
Conductions velocity 70-120 (fastest conduction velocity)
Fxn: innervation of skeletal muscles & proprioception

Question 6

A-beta fibers

Answer 6

Myelinated
Diameter 5-12
Velocity 30-70
Fxn: touch and pressure

Question 7

A-gamma fibers

Answer 7

Myelinated
Diameter: 3-6
Velocity: 15-30
Fxn: skeletal muscle tone

Question 8

A-delta fibers

Answer 8

Myelinated
Diameter: 2-5
Velocity: 12-30
Fxn: Fast pain, touch, temperature

Question 9

Beta fibers

Answer 9

Myelinated
Diameter: 3
Conduction Velocity: 3-15
Fxn: preganglionic autonomic fibers

Question 10

C-fibers

Answer 10

Unmyelinated!
Diameter: 0.4-1.2 (SMALL!)
Velocity: 0.5-2 (slow due to a small diameter and lack of myelin)
Fxn: chronic, slow pain; postganglionic sympathetic fibers; touch and temp

Question 11

Myelin

Answer 11

Surrounds A and B fibers
Acts as an insulator to prevent the flow of ions across nerve membranes.
Type C fibers are unmyelinated.

Question 12

Nodes of Ranvier

Answer 12

Allow for saltatory conduction (jumping of conduction). This allows for a 10-fold increase in the velocity of nerve transmission.

Question 13

Resting membrane potential

Answer 13

The resulting voltage differences across the cell membrane. The cytoplasm is electrically negative (-60 to -80mV) relative to the extracellular fluid.

Question 14

Action potential

Answer 14

A rapid change in transmembrane potential due to the opening of Na+ channels (depolarization) and rapid influx of Na+ ions down the concentration gradient, reversing the net negative charge within the cell. The membrane resting potential is restored by the closing of Na+ channels and the opening of K+ channels (repolarization) after the action potential has passed.

Question 15

Tetany

Answer 15

A deficiency of calcium ions in the extracellular fluid (hypocalcemia) prevents the Na+ channels from closing between action potentials (tetany).

Question 16

Low K+ effects on action potentials

Answer 16

Low K+ concentration in extracellular fluid increase the negativity of the resting membrane potential, resulting in hyperpolarization, and decrease cell membrane excitability.

Question 17

Local anesthetics effect on action potentials

Answer 17

Local anesthetics decrease the permeability of nerve cell membranes to sodium ions, preventing achievement of a threshold potential that is necessary for the generation of an action potential.

Question 18

Neurotransmitters

Answer 18

Chemical mediators that are released in the synaptic cleft in response to the arrival of an action potential at the nerve ending. Neurotransmitter release is voltage dependent and requires the influx of Ca++ ions into the presynaptic terminal. Mg2+ counteract this.
NTs may be excitatory or inhibitory.

Question 19

Glutamate vs. GABA

Answer 19

Glutamate is the major excitatory NT in the CNS vs. GABA is the major inhibitory NT.

Question 20

NTs that play a role in the sleep pathway

Answer 20

ACh, Dopamine, histamine, and NE are widely distributed in the CNS and play an important role in the sleep pathways that are impacted by GA

Question 21

Ga proteins

Answer 21

Can either by stimulatory, promoting a specific enzymatic reaction within the cell, or inhibitory, depressing a specific enzymatic reaction.

Question 22

Gas proteins vs. Gai proteins

Answer 22

B-adrenergic receptors couple with stimulatory Gas proteins and increase the activity of adenylyl cyclase. Opioid receptors are associated with inhibitory Gai proteins that decrease the activity of adenylyl cyclase. By regulating the level of activity of AC, the B-adrenergic and opioid receptors modulate the internal level of cAMP, which functions as an intracellular second messenger.

Question 23

Dopamine

Answer 23

High concentrations in basal ganglia. Can either be stimulatory or inhibitory, depending on the specific dopaminergic receptor it activates. It plays an essential role in the reward center of the brain and addiction.

Question 24

NE

Answer 24

Norepinephrine is present in large amounts in the RAS and hypothalamus and plays an essential role in natural sleep and analgesia. It is released the lowest during sleep, rises during wakefulness, and reaches much higher levels during situations of stress or danger, in the so-called fight-or-flight response.
In the brain, norepinephrine increases arousal and alertness, promotes vigilance, enhances the formation and retrieval of memory, and focuses attention; it also increases restlessness and anxiety. In the rest of the body, norepinephrine increases heart rate and blood pressure, triggers the release of glucose from energy stores, increases blood flow to skeletal muscle, reduces blood flow to the gastrointestinal system, and inhibits voiding of the bladder and gastrointestinal motility.

Question 25

Substance P

Answer 25

Excitatory neurotransmitter

Co-released by terminals of pain fibers that synapse on the substantial gelatinosa of the spinal cord.

Question 26

Endorphins

Answer 26

Endogenous opioid peptide agonists (act through the mu receptor, the same receptor responsible for the effects of administered opioids.

Question 27

Ion channel types

Answer 27

1. Ligand-gated ion channel (excitatory and inhibitory)
2. Voltage-gated ion channels
3. Ion channels that respond to other types of gating

Question 28

Excitatory ligand-gated ion channels

Answer 28

Cause the inside of the cell to become less negative typically by facilitating the influx of cations into the cell (ACh, glutamate, 5HT)

Question 29

Inhibitory ligand-gated ion channels

Answer 29

Cause the inside of the cell to become more negative, typically by facilitating the flux of Cl- (GABA and glycine)

Question 30

CNS components

Answer 30

Brain, brainstem, and spinal cord constitute the CNS

Question 31

Cerebral cortex

Answer 31

It is made up of two cerebral hemispheres. Constitutes the largest division of the human brain. Made up of the frontal, temporal, parietal and occipital anatomical regions.

Question 32

Somesthetic cortex

Answer 32

It is known as the somatosensory cortex. Lies on the parietal lobe, dorsal to the central sulcus. It is where the peripheral sensory signals are projected from the thalamus (SENSORY HAL).

Question 33

Motor cortex

Answer 33

The primary motor cortex lies on the frontal lobe, ventral to the central sulcus (MOTOR HAL). It is involved with the voluntary control of skeletal muscles. There is a prefrontal cortex that lies even more ventral, that is responsible for the planning of movements

Question 34

Corpus callosum

Answer 34

Connects the two cerebral hemispheres of the brain (across longitudinal fissure) and forms the roof of the lateral ventricles. It is the largest of the commissural fibers (tracts in the white matter).

Question 35

Memory storage

Answer 35

Their cerebral cortex, especially the temporal lobes, serve as the storage site for information that is often characterized as memory. There is both short term and long term memory.

Question 36

Short term memory

Answer 36

lasts seconds to hours

Question 37

Long term memory

Answer 37

lasts hours to months/lifetime (long-lasting)

Question 38

Awareness

Answer 38

Conscious memory of events during anesthesia. Has been a recurrent problem since the introduction of NMB agents and inadequate anesthetic.

Question 39

Brainstem

Answer 39

Homeostatic life-sustaining processes are controlled subconsciously in the brainstem (control of systemic blood pressure and breathing in the medulla).

Question 40

Limbic system

Answer 40

Located in the basal regions of the brain, the limbic system functions to provoke behaviors associated with emotions.