Lecture 8 & 9 Questions

Question 1

List the functional components of the nervous system

Answer 1

• the NS can be divided into 2 parts: the CNS consists of the brain & the spinal cord & the PNS consists of sensory (afferent) neurons & efferent neurons
• the PNS subdivides into the sensory division of the PNS (afferent division) & the efferent division of the PNS
• efferent neurons are subdivided into the somatic motor division & the autonomic division
• automatic neurons are further divided into sympathetic & parasympathetic branches
• a 3rd division of the NS is the enteric NS

Question 2

How are neurons specialized to carry electrical signals

Answer 2

specialized to carry electrical signals & communicate with other cells due to:

1. unique morphology
   - axons, dendrites, etc
   - can communicate with distant targets
2. high density of ion channels
3. special transport mechanisms to move materials from one end to the other
   - depend on cytoskeleton
4. secrete signaling molecules (neurotransmitters & neurohormones)

Question 3

Draw & label a neuron

Answer 3

slide 8 in notes from lec 8-9

Question 4

How is myelin in the CNS different from myelin in the PNS?

Answer 4

oligodendrocytes are the type of glia in the CNS that myelinate axons

schwann cells are the type of glia in the CNS that myelinate axons

Question 5

What do glia & cinnamon rolls have in common?

Answer 5

Schwann cells in the PNS resemble cinnamon rolls
- each Schwann cell wraps around a length of the axon sort of like a cinnamon roll (just curls around & around & around making an insulating layer)

Question 6

What is the role of astrocytes?

Answer 6

• make up the blood brain barrier
• trophic factors
• take up excess water & K+
• neural stem cells
• pass lactate to neurons

Question 7

What do you think the result of selective loss of sensory neurons would mean to homeostasis?

Think beyond the simple answer of “loss of sensory information”

Answer 7

Sensory cues influence homeostasis by modulating hormone secretion. … In step 1, sensory cues change the activity of sensory neurons. In step 2, the sensory information is processed and transmitted, which leads to step 3, where neuro- or nonneuronal endocrine cells secrete hormones required in maintaining homeostasis. ??

Question 8

Describe how resting membrane potential is established using the follow terms: ATPase, Na+, K+, Cl-, gradients, relative permeability, selectively permeable membrane, Goldman equation

Answer 8

d

Question 9

What happens to membrane potential when the permeability of Na+ is increased?

Answer 9

depolarize?

Question 10

List 4 ways ion channels can be gated?

Answer 10

1. Na+ channels (VG along axon, any type of gating on dendrites)
2. VG K+ channels along axon
3. VG Ca2+ channels in axon terminal
4. Chemically gated Cl- channels

Question 11

Is an ion channel an integral protein, a peripheral protein, explain

Answer 11

d

Question 12

Differentiate b/t an action potential & a graded potential

Answer 12

Graded Potentials:
1. Signals communicated from one neuron to the next are graded potentials: POSTSYNAPTIC POTENTIALS

2. Small, “SUBTHRESHOLD” changes in membrane potential
3. Can be DEpolarizing or HYPERpolarizing
4. PASSIVE (do NOT regenerate)
5. Gradually DISSIPATE as they travel through a cell
6. Proportional to the SIZE of the stimulus
7. Caused by the FLOW OF IONS through a few ion channels
8. Can be SUMMED
9. Can be LONG-LASTING

Action Potentials:

1. Wave of depolarization that ACTIVELY PROPAGATES across neuronal membrane (=REGENERATIVE, NOT PASSIVE)
2. ALL or NONE
3. FAST! Lasts only a few milliseconds
4. Often called a SPIKE, or abbreviated AP
5. LARGE AMPLITUDE, about 100 mV (from RMP to peak)
6. ALWAYS DEpolarizing
7. Requires the membrane be depolarized PAST a THRESHOLD
8. There is a REFRACTORY PERIOD
9. CANNOT be summed
10. In neurons, SITE of AP generation is the AXON HILLOCK

Question 13

Why do graded potentials degrade?

Answer 13

(nothing to regenerate

1. Electrical resistance in the cytoplasm
   - not a perfect conductor/wire
2. The cell membrane is leaky to ions
   - so b/c ions can leak in & out depending on what leakage changes are there

Question 14

What is meant by regenerative?

Answer 14

wave of depolarization that ACTIVELY PROPAGATES across neuronal membrane (=REGENERATIVE, NOT PASSIVE) b/c there is a mechanism to keep it going
- in action potentials

Question 15

Can two action potentials be summed? Why or why not?

Answer 15

CANNOT be summed
- (due to the all-or-none nature, and the presence of refractory periods). Graded potentials travel by passive spread (electrotonic spread) to neighboring membrane regions.

Question 16

What direction (hyperpolarizing or depolarizing) does a graded potential go? What about an AP?

Answer 16

Graded Potentials can be DEpolarizing or HYPERpolarizing

Action Potentials are ALWAYS DEpolarizing

Question 17

Describe the basis of the action potential, using the follow words, RMP, threshold, Na+ channels, K+ channels, activation, inactivation, rising phase, falling phase, afterhyperpolarization

Answer 17

d

Question 18

What is lidocaine? How does it work? (google lidocaine)

Answer 18

is an (local) anesthetic. It causes loss of feeling in the skin and surrounding tissues. It is used to prevent and to treat pain from some procedures. This medicine is also used to treat minor burns, scrapes and insect bites.
- block VG Na+ channels

Question 19

What does TTX kill you? Is TTX an organic molecule? Is it good for you?

Answer 19

Fugu poision, or tetrodotoxin (TTX) comes from pufferfish & several other species of animals

Fugu is a very specific antagonist of voltage gated Na+ channels

• high affinity, high specificity
• high efficacy, high potency

prevents entry of Na+ into cells

prevents action potentials in neurons & muscle

lidocaine, benzocaine & other local anesthetics also block VG Na+ channels

synthetic organic compound

kills 30-100 people per year in Japan

Question 20

What would you expect the result of a drug that antagonizes K+ channels?

Answer 20

d

Question 21

If a neuron was experimentally stimulated at both ends simultaneously,

a. The action potentials would pass in the middle & travel to the opposite ends
b. The action potentials would meet in the middle & then be propagated back to their starting positions
c. The action potentials would stop as they met in the middle
d. The strongest action potential would override the weaker action potential
e. Summation would occur when the action potentials met in the middle, resulting in a larger action potential

Answer 21

c?

Question 22

Describe how an AP is propagated along an unmyelinated axon. How is this different from conduction on a myelinated axon?

Answer 22

Unmyelinated axon:

1. a graded potential above threshold reaches the trigger zone
2. voltage-gated Na+ channels open, & Na+ enters the axons
3. Positive charge flows into adjacent sections of the axon by local current flow
4. Local current flow from the active region causes new sections of the membrane to depolarize

myelinated axons:

• myelinated sheaths form insulating segments along axon (formed by concentric layers of glial cell membranes compacted together)
• separated by nodes of Ranvier
• Na+ channels found at very high density at nodes of Ranvier, K+ channels found nearby
• instead of traveling as a wave, the action jumps from node to node: Saltatory Conduction (b/c of this they travel much faster!)

Question 23

Which conducts faster?

Answer 23

Myelinated sheaths opposed to unmyelinated sheath (b/c of the saltatory conduction - instead of traveling as a wave, the action jumps from node to node)

Question 24

Why aren’t all of our axons giant, unmyelinated axons?

Answer 24

b/c then they wouldn’t be able to speed up velocity of AP along an axon (which myelinated axons can do) ?

Question 25

Why is a larger diameter axon faster?

Answer 25

larger diameter axons can really speed up axonal conduction of AP

• increases velocity b/c as the axon radius becomes larger, internal resistance decreases (inverse square relationship)
• for ex, larger pipe (less resistance) is able to push more “water” for ex through then a small pipe b/c less resistance

Question 26

Where are Schwann cells found? Oligodendrocytes?

Answer 26

Schwann cells: found in PNS (outside brain & spinal cord)

Oligodendrocytes: found in CNS (brain & spinal cord)

Question 27

Why does demyelination inhibit axonal AP conduction?

Answer 27

well MYELINATION speeds up velocity of AP along an axon

• increases velocity b/c insulated areas mean less leakage of Na+ & K+
• also means less ATP used
• myelinated allows axons to be smaller, so you can fit more into a space

so demyelination does the opposite of this

Question 28

Differentiate b/t multiple sclerosis & guillian barre syndrome using the following terms: acute, chronic, recurring, viral, genetic, autoimmune, flaccid

Answer 28

Multiple Sclerosis:

• autoimmune disease
• unknown cause: environment, virus, genetics, cerebral blood flow (the “Zamboni hypothesis”, scientific studies largely rejected this)
• demyelination of CNS axons
• multiple patterns of progression: relapsing-remitting & several progressive phases
• symptoms include loss of balance, loss of speech, loss of vision, abnormal pupil reflexes, numbness, pain (symptoms are highly variable)
• treatments include immunosuppressants, other drugs as indicated by symptoms

Guillain Barre Syndrome (also acute inflammatory demyelinating polyneuropathy, AIDM)

• autoimmune, days after a seemingly minor GI or lung infection
• may be also associated with chronic illness such as lupus, HIV
• 1976 flu vaccine (1 additional case per 100,000)
• demyelination of sensory, motor & autonomic axons (PNS)
• slowing &/or loss of AP conduction
• initial symptoms include tingling, weakness, pain in hands/feet
• symptoms may rapidly progress to inability to speak, paralysis, respiratory distress
• treatment may include plasmapheresis (to remove antibodies from blood) & immunoglobin G (IGG) to inactivate circulating antiobodies
• most people survive, recovery may take months to years

Question 29

If both ends of an axon are stimulated, causing action potentials to travel towards the middle, what happens when they meet?

Answer 29

d

Question 30

When you stub your toe, the sensory info is carried back to the CNS by several types of axons. One type carries the “pain information” another causes the sensory info regarding touch/pressure. Which is unmyelinated, & which is myelinated?

Answer 30

d