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BILD 2 - Multicellular Life > Nervous System II > Flashcards

Nervous System II Flashcards

0
Q

I. Electrical signaling -overview (parts)

A

A. Types of electrical signals

B. Types of Connections

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1
Q

Nervous System II

A 
I. Electrical signaling
II. Resting Potential
III. Nernst Equation
IV. Action Potentials (AP)
V. Action Potentials Features
VI. Action Potentials Propagation
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2
Q

I. Electrical signaling

A. Types of Electrical Signals

A
  1. Action potentials
  2. Postsynaptic potentials
  3. Generator potentials (GPs)
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3
Q

Action Potentials (APs)

A

Conduct signals over long distances

e.g. always axon

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4
Q

Postsynaptic potentials (PsPs)

A

Localized signal at synapses

-in postsynaptic cell

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5
Q

Generator Potentials (GPs)

A

Localized signals in sensory neuron; transducer physical stimulus to electrical

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6
Q

I. Electrical signaling

B. Types of connections

A
  1. Cell type
  2. Purpose
  3. Signal _> 10^5 interneurons / motor neurons

(Flow Chart)

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7
Q

Sensory neurons

Purpose?

A

Detect sensation

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8
Q

Sensory neurons

Signal?

A

GP➡️AP

Generator potentials ➡️ action potentials

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9
Q

Inter neurons

Purpose?

A

Process information

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10
Q

Inter neurons

Signal?

A

PsPs ➡️ AP

Postsynaptic potentials ➡️ action potentials

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11
Q

Motor neurons

Purpose?

A

Issue commands

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12
Q

Motor neurons

Signal?

A

PSP ➡️ AP

Postsynaptic potentials? ➡️ action potentials

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13
Q 
Effector cells (muscle, glands)
Purpose?
A

Carry out commands

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14
Q 
Effector cells (muscle, glands)
Signal?
A

PsPs ➡️AP➡️Effect

Postsynaptic potentials ➡️ action potentials ➡️ effector cells?

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15
Q

Cell types order (flow chart top line)

A

[sensory neurons] ➡️ [interneurons] ➡️ [motor neurons] ➡️ [effector cells ]

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16
Q

II. Resting Potentials (RP) (parts)

A

A. Potentials
B. Magnitude of RP
C. Ionic bases of RP
D. Ionic Bases -schematic

17
Q

II. Resting Potentials

A. Potentials

A

Arise from charge separation
(Note: potential = voltage)
e.g. Na+ + Cl- separated in solution
➡️high voltage: force of attraction

18
Q

II. Resting Potentials

B. Magnitude of RP

A

About 60-70 mV

Drawing: gland, amplifier, oscilloscope
Figure 37.8 research method: intercellular recording
Drawing chart

19
Q

II. Resting Potentials

C. Ionic Bases of Resting Potentials (RP)

A
  1. ion concentration GRADIENTS across membrane at rest
    (produced by ion pumps driven by ATP) / due to pumps: Na+, K+, and
    ATPase
  2. SELECTIVE permeability of membrane to certain ions at rest
    ➡️ charge separation (permeable ions diffusing down their
    concentration gradients) ➡️ Resting Potential (RP)
20
Q

II. Resting Potentials

D. Ionic Bases - schematic

A
  • selective permeability to K+
  • K+ leaves cell (down its concentration gradient)
  • leaves behind net negative charge ➡️ produces RP

Figure: 37.6 the basis of the membrane potential (RP) & drawing

21
Q

III. Nernst Equation - definition

A

How much K+ leaves cell?

How negative will RP be?

22
Q

III. Nernst Equation - parts

A

A. At equilibrium

B. Nernst Equation

23
Q

III. Nernst Equation

A. At Equilibrium

A

equal and opposite forces on an ion.

Diffusional Force OUT (for K+) = Electrical Force IN (for K+)
(down concentration gradient) (charge attraction)
Fick’s Law Coulomb’s Law

24
Q

III. Nernst Equation

B. Nernst Equation

A

at equilibrium the following occurs:

Vm = 2.3 [RT/zF] log[(X)out/(X)in]

for monovalent cations (eg.K+) at room temperature:
Vm = 58 log [(X)out/(X)in] = Ex = Equilibrium Potential for ion “X”

25
Q

Given the normal ion gradients at rest:

A

E(K) = about - 90mV
proof: 62mV log(5M/140mM) = -90mV

E(Na) = about + 62 mV
proof: 62mV log(150mM/15mM) = +62

26
Q

at rest the cell is mostly permeable to

A

K+ ➡ ️E(K)

butsome permeability to Na+ ➡ small contribution E(Na)

27
Q

RP is more

A

positive than E(K)

E(K) about = to -90mV
RP about= to -70
E(Na) about= to 62 mV

28
Q

Note: very little K+

A

leaves cell to RP

➡-70 mV

29
Q

what maintains the concentration gradient?

A

Na+, K+, ATPase

30
Q

IV. Action Potentials (AP)

parts

A

A. Electrical events
B. Initiation of AP
C. Termination of AP

31
Q

IV. Action Potentials

A. Electrical Event

A 
drawing of Vm Vs. Time
rising phase (depolarization)
overshoot
falling phase (repolarization)
undershoot
32
Q

IV. Action Potentials

B. Initiation of AP

A
  1. Input of neuron (PSP or electrical stimulus)
    - small depolarization
    - P Vm
  2. The
33
Q

IV. Action Potentials

C. Termination of AP

A
  1. Time- dependent inactivation of VGNaCs at high Vm.

2. Voltage gated K+ channels (VGNaCs)

34
Q

Time- dependent inactivation of VGNaCs at high Vm

A

diagram
circle

open -> inactivated -> closed -> open

35
Q

Voltage gated K+ channels (VGKCs)

A
  • open when Vm ⬆️ selective for K+
  • slow to open initially
  • do not inactivate

-open, therefore as VGNaCs drive the Vm to E(Na) (peak of AP), VGNaC’s INACTIVE while VGKCs open –> drive Vm back down to RP. In fact, Vm goes below RP briefly “undershoot”

  1. NEED VGNCs to inactivate so they don’t work against VGKC
  2. need VGKCs to be SLOWER than VGNaCs or else AP would never
    get going

diagram
Figure 37.10 graded potentials and action potential in a neuron
Figure37.11 role of voltage-gated ion channels in the AP

36
Q

V. Action Potential Features

parts

A

A. Threshold for AP
B. All-or-none APs (non-additive)
C. Normal Activation

37
Q

V. Action Potential Features

A. Threshold for AP

A

Push Vm > threshold ➡️ generate full AP
Push Vm < threshold ➡️ nothing

at “threshold” enough VGNaCs open to further depolarize Vm

[at “threshold, Vm opens enough VGNaCs to let enough Na+influx to ope more (faster than they close & faster than the depolarization can dissipate) - hence the positive feedback]

38
Q

V. Action Potential Features

B. All-or-none APs (non-additive)

A

(limited only by E(Na))

trigger an AP - get the full AP. limited only by E(Na)
e.g. can’t exceed E(Na)

39
Q

V. Action Potential Features

C. Normal Activation

A
  1. APs triggered by electrical signals: PSPs & GPS
  2. Alternative: use electrode to drive current into the cell, producing a depolarization to reach threshold for eliciting an AP
40
Q

VI. Action Potential Propagation

define

A
  • active, regenerative, process
  • serial induction of AP along axons

(no reduction in amplitude = active regeneration)

diagram
Figure 37.12: conduction of an action potential

BILD 2 - Multicellular Life (8 decks)

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