Lecture 8 & 9 Questions Flashcards
(30 cards)
List the functional components of the nervous system
- 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
How are neurons specialized to carry electrical signals
specialized to carry electrical signals & communicate with other cells due to:
- unique morphology
- axons, dendrites, etc
- can communicate with distant targets - high density of ion channels
- special transport mechanisms to move materials from one end to the other
- depend on cytoskeleton - secrete signaling molecules (neurotransmitters & neurohormones)
Draw & label a neuron
slide 8 in notes from lec 8-9
How is myelin in the CNS different from myelin in the PNS?
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
What do glia & cinnamon rolls have in common?
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)
What is the role of astrocytes?
- make up the blood brain barrier
- trophic factors
- take up excess water & K+
- neural stem cells
- pass lactate to neurons
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”
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. ??
Describe how resting membrane potential is established using the follow terms: ATPase, Na+, K+, Cl-, gradients, relative permeability, selectively permeable membrane, Goldman equation
d
What happens to membrane potential when the permeability of Na+ is increased?
depolarize?
List 4 ways ion channels can be gated?
- Na+ channels (VG along axon, any type of gating on dendrites)
- VG K+ channels along axon
- VG Ca2+ channels in axon terminal
- Chemically gated Cl- channels
Is an ion channel an integral protein, a peripheral protein, explain
d
Differentiate b/t an action potential & a graded potential
Graded Potentials:
1. Signals communicated from one neuron to the next are graded potentials: POSTSYNAPTIC POTENTIALS
- Small, “SUBTHRESHOLD” changes in membrane potential
- Can be DEpolarizing or HYPERpolarizing
- PASSIVE (do NOT regenerate)
- Gradually DISSIPATE as they travel through a cell
- Proportional to the SIZE of the stimulus
- Caused by the FLOW OF IONS through a few ion channels
- Can be SUMMED
- Can be LONG-LASTING
Action Potentials:
- Wave of depolarization that ACTIVELY PROPAGATES across neuronal membrane (=REGENERATIVE, NOT PASSIVE)
- ALL or NONE
- FAST! Lasts only a few milliseconds
- Often called a SPIKE, or abbreviated AP
- LARGE AMPLITUDE, about 100 mV (from RMP to peak)
- ALWAYS DEpolarizing
- Requires the membrane be depolarized PAST a THRESHOLD
- There is a REFRACTORY PERIOD
- CANNOT be summed
- In neurons, SITE of AP generation is the AXON HILLOCK
Why do graded potentials degrade?
(nothing to regenerate
- Electrical resistance in the cytoplasm
- not a perfect conductor/wire - The cell membrane is leaky to ions
- so b/c ions can leak in & out depending on what leakage changes are there
What is meant by regenerative?
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
Can two action potentials be summed? Why or why not?
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.
What direction (hyperpolarizing or depolarizing) does a graded potential go? What about an AP?
Graded Potentials can be DEpolarizing or HYPERpolarizing
Action Potentials are ALWAYS DEpolarizing
Describe the basis of the action potential, using the follow words, RMP, threshold, Na+ channels, K+ channels, activation, inactivation, rising phase, falling phase, afterhyperpolarization
d
What is lidocaine? How does it work? (google lidocaine)
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
What does TTX kill you? Is TTX an organic molecule? Is it good for you?
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
What would you expect the result of a drug that antagonizes K+ channels?
d
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
c?
Describe how an AP is propagated along an unmyelinated axon. How is this different from conduction on a myelinated axon?
Unmyelinated axon:
- a graded potential above threshold reaches the trigger zone
- voltage-gated Na+ channels open, & Na+ enters the axons
- Positive charge flows into adjacent sections of the axon by local current flow
- 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!)
Which conducts faster?
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)
Why aren’t all of our axons giant, unmyelinated axons?
b/c then they wouldn’t be able to speed up velocity of AP along an axon (which myelinated axons can do) ?
