Physiology of the Neurons

Question 1

what comprises the neuron?

Answer 1

cell body, dendrites, axon

Question 2

what is the difference between unmyelinated and demyelinated axons?

Answer 2

unmyelinated means no myelin is covering the axon and demyelinated is the loss of the myelin sheath resulting in loss of communication, i.e. - multiple sclerosis

Question 3

what are myelinated axons called in the CNS?

Answer 3

oligodendrocytes and myelin sheaths on multiple axons

Question 4

what are the myelinated axons called in the PNS?

Answer 4

schwann cells 1:1 for axon and myelin

Question 5

describe the axon

Answer 5

it projects from the cell body at the site of the axon hillock

carries impulse away from the cell body

myelinated or unmyelinated

contains numerous Na+ channels

Question 6

what is the disadvantage of an unmyelinated axon?

Answer 6

it loses strength the further away it moves from the initiation site

Question 7

what is wallerian degeneration? is there a cure if this happens in the CNS? PNS?

Answer 7

so we know that neurons are in a way connected to one another via communication stemming from a primary neuron due to signaling, if we have neurons communicating and there is a break in the axon of the middle neuron, the neurons retro and antero of it will also be affected, the distal neuron can no longer communicate and it degenerates

loss of axonal action distal to the lesion leading to degeneration of the synaptic terminal, proximal to the lesion, problems also occur; ER also degenerates

No

Yes; proximal part of the degeneration we will see axon sprouting to attempt communication to the distal portion past the area of degeneration to regain function

Question 8

recall the steps used in the axonal degeneration and regeneration

Answer 8

Step 1: Degeneration of synaptic terminal distal to lesion

Step 2: Wallerian degeneration

Step 3: Myelin degeneration

Step 4: Scavenging of debris

Step 5: Chromatolysis

Step 6: Retrorade transneuronal degeneration

Step 7: Anterograde transneuronal degeneration

Question 9

what are the two major microtubules in the neuronal cytoskeleton?

Answer 9

kinesin(moves to positive end) and dynein(moves toward the negative end, the cell body)

Question 10

which protein is responsible for fast anterograde?

Answer 10

kinesin and material transported being mitochondria and vesicles

Question 11

which protein is responsible for fat retrograde?

Answer 11

dynein and the material transported being degraded vesicular membrane, absorbed exogenous material

Question 12

The mechanisms by which polio virus enters the central nervous system (CNS) are poorly understood. Mainly two theories have been suggested to explain its entry. One theory is that virus passes directly from the blood into the CNS by crossing the blood brain barrier. A second hypothesis suggests that the virus is transported from the muscle to the spinal cord through nerve pathways by retrograde axonal transport. Which of the following molecules plays an important role in retrograde axonal transport?

Kinesin 8 family
Kinesin 13 family
Dynein.
Microglia

Answer 12

dynein

Question 13

An 88-year-old man has been bothered by continuing outbreaks of painful lesions on the skin of his right chest for the past year. On physical examination, there is a vesicular eruption over a 1 x 7 cm area over the right seventh rib. He is treated with acyclovir, and the skin lesions resolved, but the pain persisted for the next 3 months. Which of the following is the most likely cause for his findings?

Aging
Multiple sclerosis
Varicella-zoster virus infection.
Vitamin-B12 deficiency

Answer 13

Varicella-zoster virus infection

Question 14

what happens in the presynaptic terminal when the signal is received?

Answer 14

nt molecules are packaged into membraneous vesicles, which are concentrated and docked at the presynaptic terminal

presynaptic membrane depolarizes, usually as the result of the action potential

the depolarization causes the voltage dependent Ca2+ channels to open and allow Ca2+ ions to flow into the terminal

the resulting increase of intracellular calcium triggers fusion of vesicles with the presynaptic membrane

transmitter is released into the extracellular space in quantized amounts and diffuses passively across synaptic cleft

some of the transmitter molecules bind to receptors in the postsynaptic membrane and the activated receptors trigger some postsynaptic event usually the opening of an ion channel or the activation of a G protein coupled signal cascade

transmitter molecules diffuse away from the postsynaptic receptors and are eventually cleared away by continued diffusion, enzymatic degradation, or active uptake into cells

Question 15

what is depolarization?

Answer 15

excitatory input to a neuron that usually generates a flow of positive charge across the dendritic membrane and because the interior of a resting neuron is polarized negatively the inward current depolarizes, make the membrane voltage more positive, the cell and a threshold potential is initiated activating an action potential

Question 16

why is hyperpolarization important for inducing patients before surgery?

Answer 16

patients need to be asleep, hyper polarize pain sensing neurons so they are far below the threshold level that even the most painful stimulus could not reach the threshold, hence a graded potential that would not reach threshold

Question 17

what is the change in membrane potential caused by a nt at the postsynaptic membrane?

Answer 17

postsynaptic potential (PSP)

Question 18

if the nt is excitatory, what is produced?

Answer 18

Excitatory PSP (EPSP)

Question 19

if the nt is inhibitory, what is produced?

Answer 19

a hyper polarizing inhibitory PSP (IPSP)

Question 20

what constitutes as an excitatory postsynaptic potential?

Answer 20

postsynaptic increase in sodium or calcium conductance

postsynaptic decrease in potassium conductance

both increase the positive charge in the cell

Question 21

what constitutes as an inhibitory postsynaptic potential?

Answer 21

increased potassium efflux or chloride influx

both decrease the positive charge in the cell

Question 22

spatial summation is the adding together of EPSPs or IPSPs over _____?

Answer 22

space

Question 23

temporal summation is the adding together of EPSPs or IPSPs over _____?

Answer 23

time

Question 24

what is the advantage of having a thicker and shorter dendrite?

Answer 24

the more likely is a dendritic EPSP to trigger an action potential at the axon hillock

Question 25

what do we mean when we say that most dendrites are low pass filters?

Answer 25

decrease high frequency/rapidly changing signals more than low frequency/steady signals

Question 26

what is the all or none principle in terms of the action potential?

Answer 26

A neuron fires with the same potency each time

Frequency for firing can vary

It either fires or not; it cannot partially fire

Question 27

what are the advantages of action potentials for signaling?

Answer 27

reliable
-Voltage threshold for triggering-Once triggered, it is self-shaping

can travel very long distance
-Self-propagating-Passive spread of electrical signal ~1mm

rapid
-Propagate up to 120 m/s

specific
-Carries a signal from one point to another

Question 28

what is the effect on conduction velocity when the myelinated axon increases linearly with diameter?

Answer 28

conduction velocity of a myelinated axon increase

Question 29

what are thicker myelinated axons used for?

Answer 29

proprioceptors of skeletal muscle

Question 30

what are the unmyelinated axons used for?

Answer 30

temperature, pain, itch

Question 31

how do demyelinated axons conduct action potentials?

Answer 31

slowly, unreliably, or not at all

Question 32

what are demyelinating disease of the CNS?

Answer 32

Multiple sclerosis (most common),
progressive multifocal leukoencephalopathy,
central pontine myelinolysis

Question 33

what are the demyelinating disease of the PNS?

Answer 33

Landry-Guillain-Barre syndrome

Question 34

what is central pontine myelinolysis?

Answer 34

pons affected, physician error. So, often seen in chronic alcoholics, diet is bad, sugar obtained from alcohol, glucose levels are skewed so they need to be corrected and glucose given, also thiamine. Note that sodium is low and if give them sodium, this can make the pons worse affecting their neuro condition

Question 35

what is the most common demyelinating disease of the CNS?

Answer 35

multiple sclerosis

Question 36

what does MS affect?

Answer 36

so its an autoimmune disease directed against the myelin or oligodendrocytes

Question 37

is MS more common in men or women?

Answer 37

women

Question 38

what are the characteristics of MS?

Answer 38

remission and relapses

Question 39

what is MS relapse?

Answer 39

An exacerbation is due to the occurrence of active inflammation of a white matter tract in the CNS.

Question 40

what is MS remission?

Answer 40

A remission occurs when the inflammation subsides and the demyelinated axons recover some of their function, and are able to conduct action potentials through the area of myelin damage.

Question 41

wha is the most common demyelinating disease of the PNS?

Answer 41

Landry-Guillain-Barre Syndrome

Question 42

what is Landry-Guillain-Barre Syndrome?

Answer 42

Following a respiratory or other viral infection, an ascending neurologic syndrome develops

Starts with weakness, leads to paralysis of the legs&raquo_space; subsequent involvement of the hands and arms

It may involve the paralysis of the nerves feeding the brain stem&raquo_space; requires mechanical ventilation

Initial stage reaches a plateau, then gradually resolves

Pathology: segmental demyelination in PNS

Question 43

A 22 year old female college student comes to your office complaining of problems with vision. She also brought an MRI showing a small white lesion in the periventricular area and the levels of IgG in the CSF are very high. Her muscle stretch reflexes are slightly hyperactive in the left lower limb, but normal in the right lower limb and when she walks her gait is unsteady. She states that she had similar symptoms a few months earlier, but they went away. Which of the following is the most likely diagnosis?

amyotrophic lateral sclerosis
Guillain Barre syndrome
multiple sclerosis.
poliomyelitis

Answer 43

multiple sclerosis.

Question 44

A 70-year-old man has had increasing difficulty with movement, starting with his feet and ascending to involve legs, trunk, and now arms, over the past 10 days. On physical examination there are variable sensory changes noted. He is afebrile. He does not lose consciousness and remains mentally alert. He becomes ventilator dependent a week after the onset of this illness. He gradually recovers over the ensuing 4 weeks. Which of the following conditions most likely preceded the onset of this man’s illness?

Recent viral infection
Severe hypotension
Bacterial septicemia
Radiation therapy

Answer 44

Recent viral infection

Question 45

for axonal transport, how fast is fast anterograde; what mechanism; material transported?

Answer 45

400; kinesin; mitochondria, vesicles

Question 46

for axonal transport, how fast is fast retrograde; what mechanism; material transported?

Answer 46

200-300; dynein; degraded vesicular membrane and absorbed exogenous material

Question 47

for axonal transport, how fast is slow anterograde; what mechanism; material transported?

Answer 47

1-5; unknown; cytoskeleton elements, soluble proteins