Nervous System II Flashcards
I. Electrical signaling -overview (parts)
A. Types of electrical signals
B. Types of Connections
Nervous System II
I. Electrical signaling II. Resting Potential III. Nernst Equation IV. Action Potentials (AP) V. Action Potentials Features VI. Action Potentials Propagation
I. Electrical signaling
A. Types of Electrical Signals
- Action potentials
- Postsynaptic potentials
- Generator potentials (GPs)
Action Potentials (APs)
Conduct signals over long distances
e.g. always axon
Postsynaptic potentials (PsPs)
Localized signal at synapses
-in postsynaptic cell
Generator Potentials (GPs)
Localized signals in sensory neuron; transducer physical stimulus to electrical
I. Electrical signaling
B. Types of connections
- Cell type
- Purpose
- Signal _> 10^5 interneurons / motor neurons
(Flow Chart)
Sensory neurons
Purpose?
Detect sensation
Sensory neurons
Signal?
GP➡️AP
Generator potentials ➡️ action potentials
Inter neurons
Purpose?
Process information
Inter neurons
Signal?
PsPs ➡️ AP
Postsynaptic potentials ➡️ action potentials
Motor neurons
Purpose?
Issue commands
Motor neurons
Signal?
PSP ➡️ AP
Postsynaptic potentials? ➡️ action potentials
Effector cells (muscle, glands) Purpose?
Carry out commands
Effector cells (muscle, glands) Signal?
PsPs ➡️AP➡️Effect
Postsynaptic potentials ➡️ action potentials ➡️ effector cells?
Cell types order (flow chart top line)
[sensory neurons] ➡️ [interneurons] ➡️ [motor neurons] ➡️ [effector cells ]
II. Resting Potentials (RP) (parts)
A. Potentials
B. Magnitude of RP
C. Ionic bases of RP
D. Ionic Bases -schematic
II. Resting Potentials
A. Potentials
Arise from charge separation
(Note: potential = voltage)
e.g. Na+ + Cl- separated in solution
➡️high voltage: force of attraction
II. Resting Potentials
B. Magnitude of RP
About 60-70 mV
Drawing: gland, amplifier, oscilloscope
Figure 37.8 research method: intercellular recording
Drawing chart
II. Resting Potentials
C. Ionic Bases of Resting Potentials (RP)
- ion concentration GRADIENTS across membrane at rest
(produced by ion pumps driven by ATP) / due to pumps: Na+, K+, and
ATPase - SELECTIVE permeability of membrane to certain ions at rest
➡️ charge separation (permeable ions diffusing down their
concentration gradients) ➡️ Resting Potential (RP)
II. Resting Potentials
D. Ionic Bases - schematic
- 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
III. Nernst Equation - definition
How much K+ leaves cell?
How negative will RP be?
III. Nernst Equation - parts
A. At equilibrium
B. Nernst Equation
III. Nernst Equation
A. At Equilibrium
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
III. Nernst Equation
B. Nernst Equation
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”
Given the normal ion gradients at rest:
E(K) = about - 90mV
proof: 62mV log(5M/140mM) = -90mV
E(Na) = about + 62 mV
proof: 62mV log(150mM/15mM) = +62
at rest the cell is mostly permeable to
K+ ➡ ️E(K)
butsome permeability to Na+ ➡ small contribution E(Na)
RP is more
positive than E(K)
E(K) about = to -90mV
RP about= to -70
E(Na) about= to 62 mV
Note: very little K+
leaves cell to RP
➡-70 mV
what maintains the concentration gradient?
Na+, K+, ATPase
IV. Action Potentials (AP)
parts
A. Electrical events
B. Initiation of AP
C. Termination of AP
IV. Action Potentials
A. Electrical Event
drawing of Vm Vs. Time rising phase (depolarization) overshoot falling phase (repolarization) undershoot
IV. Action Potentials
B. Initiation of AP
- Input of neuron (PSP or electrical stimulus)
- small depolarization
- P Vm - The
IV. Action Potentials
C. Termination of AP
- Time- dependent inactivation of VGNaCs at high Vm.
2. Voltage gated K+ channels (VGNaCs)
Time- dependent inactivation of VGNaCs at high Vm
diagram
circle
open -> inactivated -> closed -> open
Voltage gated K+ channels (VGKCs)
- 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”
- NEED VGNCs to inactivate so they don’t work against VGKC
- 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
V. Action Potential Features
parts
A. Threshold for AP
B. All-or-none APs (non-additive)
C. Normal Activation
V. Action Potential Features
A. Threshold for AP
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]
V. Action Potential Features
B. All-or-none APs (non-additive)
(limited only by E(Na))
trigger an AP - get the full AP. limited only by E(Na)
e.g. can’t exceed E(Na)
V. Action Potential Features
C. Normal Activation
- APs triggered by electrical signals: PSPs & GPS
- Alternative: use electrode to drive current into the cell, producing a depolarization to reach threshold for eliciting an AP
VI. Action Potential Propagation
define
- active, regenerative, process
- serial induction of AP along axons
(no reduction in amplitude = active regeneration)
diagram
Figure 37.12: conduction of an action potential
