Chapter 11 - Fundamentals of the nervous system and nervous tissue (part b). In this chapter, you will learn: Define resting membrane potential and describe its electrochemical basis, compare and contrast graded potentials and action potentials, explain how action potentials are generated and propagated along neurons,...
Trang 1PowerPoint ® Lecture Slides
prepared by Janice Meeking, Mount Royal College
Nervous Tissue: Part B
Trang 2Copyright © 2010 Pearson Education, Inc.
Neuron Function
an action potential (nerve impulse)
stimulus
Trang 3Copyright © 2010 Pearson Education, Inc.
Principles of Electricity
charges across a membrane
toward one another
has potential energy
Trang 4Copyright © 2010 Pearson Education, Inc.
Definitions
generated by separated charge
between two points
between two points
Trang 5Copyright © 2010 Pearson Education, Inc.
Definitions
(provided by the plasma membrane)
resistance
resistance
Trang 6Copyright © 2010 Pearson Education, Inc.
Role of Membrane Ion Channels
Trang 7Copyright © 2010 Pearson Education, Inc.
Role of Membrane Ion Channels
channels—open with binding of a specific neurotransmitter
close in response to changes in membrane potential
close in response to physical deformation of receptors
Trang 8Copyright © 2010 Pearson Education, Inc. Figure 11.6
(b) Voltage-gated ion channels open and close in response
to changes in membrane voltage.
Na+
Na+
Receptor
(a) Chemically (ligand) gated ion channels open when the
appropriate neurotransmitter binds to the receptor,
allowing (in this case) simultaneous movement of
Chemical binds
Membrane voltage changes
Trang 9Copyright © 2010 Pearson Education, Inc.
Gated Channels
along their electrochemical gradients
higher concentration to lower concentration
electrical charge
voltage changes across the membrane
Trang 10Copyright © 2010 Pearson Education, Inc.
Resting Membrane Potential (Vr)
resting cell
side of membrane is negatively charged relative to outside)
membrane
Trang 11Copyright © 2010 Pearson Education, Inc. Figure 11.7
Trang 12Copyright © 2010 Pearson Education, Inc.
Resting Membrane Potential
than ECF
Trang 13Copyright © 2010 Pearson Education, Inc.
Resting Membrane Potential
Trang 14Copyright © 2010 Pearson Education, Inc.
Resting Membrane Potential
diffusion into the cell
membrane potential by maintaining the
Trang 15Copyright © 2010 Pearson Education, Inc. Figure 11.8
Finally, let’s add a pump to compensate for leaking ions.
Na + -K + ATPases (pumps) maintain the concentration gradients, resulting in the resting membrane potential.
Suppose a cell has only K + channels
K + loss through abundant leakage channels establishes a negative membrane potential
Now, let’s add some Na + channels to our cell
Na + entry through leakage channels reduces the negative membrane potential slightly
The permeabilities of Na + and K + across the membrane are different.
The concentrations of Na + and K + on each side of the membrane are different.
Cell interior –70 mV
Cell interior –70 mV
maintain the concentration gradients of Na + and K +
across the membrane.
Trang 16Copyright © 2010 Pearson Education, Inc.
Membrane Potentials That Act as Signals
change
used to receive, integrate and send
information
Trang 17Copyright © 2010 Pearson Education, Inc.
Membrane Potentials That Act as Signals
Trang 18Copyright © 2010 Pearson Education, Inc.
Changes in Membrane Potential
zero)
negative than the resting potential
impulse
Trang 19Copyright © 2010 Pearson Education, Inc. Figure 11.9a
Depolarizing stimulus
Time (ms)
Inside positive
Inside negative
Resting potential
Depolarization
(a) Depolarization: The membrane potential
moves toward 0 mV, the inside becoming less negative (more positive).
Trang 20
Copyright © 2010 Pearson Education, Inc.
Changes in Membrane Potential
zero)
negative than the resting potential
impulse
Trang 21Copyright © 2010 Pearson Education, Inc. Figure 11.9b
Hyperpolarizing stimulus
Time (ms)
Resting potential
polarization
Hyper-(b) Hyperpolarization: The membrane
potential increases, the inside becoming more negative.
Trang 22Copyright © 2010 Pearson Education, Inc.
Graded Potentials
potential
change the membrane potential of adjacent regions
Trang 23Copyright © 2010 Pearson Education, Inc. Figure 11.10a
Depolarized region
Stimulus
Plasma membrane
(a) Depolarization: A small patch of the
membrane (red area) has become depolarized.
Trang 24Copyright © 2010 Pearson Education, Inc. Figure 11.10b
(b) Spread of depolarization: The local currents
(black arrows) that are created depolarize
adjacent membrane areas and allow the wave of depolarization to spread.
Trang 25Copyright © 2010 Pearson Education, Inc.
flow and diffuse through leakage channels
Trang 26Copyright © 2010 Pearson Education, Inc. Figure 11.10c
Distance (a few mm)
–70
Resting potential
Active area (site of initial depolarization)
(c) Decay of membrane potential with distance: Because current
is lost through the “leaky” plasma membrane, the voltage declines
Consequently, graded potentials are short-distance signals.
Trang 27Copyright © 2010 Pearson Education, Inc.
Action Potential (AP)
total amplitude of ~100 mV
distance
communication
Trang 28Copyright © 2010 Pearson Education, Inc.
Action potential
Trang 29Copyright © 2010 Pearson Education, Inc.
Generation of an Action Potential
Trang 30Copyright © 2010 Pearson Education, Inc.
Properties of Gated Channels
Trang 31Copyright © 2010 Pearson Education, Inc.
Properties of Gated Channels
gate
Trang 32Copyright © 2010 Pearson Education, Inc.
channels, and a reversal of membrane
polarity to +30mV (spike of action potential)
Trang 33Copyright © 2010 Pearson Education, Inc.
Repolarizing Phase
resting levels
restored
Trang 34Copyright © 2010 Pearson Education, Inc.
Trang 35Copyright © 2010 Pearson Education, Inc.
Action potential
Time (ms)
2 3
Trang 36Copyright © 2010 Pearson Education, Inc.
Role of the Sodium-Potassium Pump
neuron
is restored by the thousands of
sodium-potassium pumps
Trang 37Copyright © 2010 Pearson Education, Inc.
Propagation of an Action Potential
membrane to depolarize
inactivated and not affected by the local
currents
Trang 38Copyright © 2010 Pearson Education, Inc.
Propagation of an Action Potential
Trang 39Copyright © 2010 Pearson Education, Inc. Figure 11.12a
Voltage
at 0 ms
Recording electrode
(a) Time = 0 ms Action
potential has not yet reached the recording electrode.
Resting potential Peak of action potential Hyperpolarization
Trang 40Copyright © 2010 Pearson Education, Inc. Figure 11.12b
Trang 41Copyright © 2010 Pearson Education, Inc. Figure 11.12c
Trang 42Copyright © 2010 Pearson Education, Inc.
Threshold
Trang 43Copyright © 2010 Pearson Education, Inc.
Threshold
depolarization that does not reach threshold
the membrane potential toward and beyond threshold
potentials either happen completely, or not at all
Trang 44Copyright © 2010 Pearson Education, Inc.
Coding for Stimulus Intensity
independent of stimulus intensity
a weak stimulus and a strong one?
more often than weaker stimuli
frequency of impulses
Trang 45Copyright © 2010 Pearson Education, Inc. Figure 11.13
Threshold
Action potentials
Stimulus
Time (ms)
Trang 46Copyright © 2010 Pearson Education, Inc.
Absolute Refractory Period
until the resetting of the channels
impulses
Trang 47Copyright © 2010 Pearson Education, Inc. Figure 11.14
Stimulus
Absolute refractory period
Relative refractory period
Trang 48Copyright © 2010 Pearson Education, Inc.
Relative Refractory Period
resting state
an AP
Trang 49Copyright © 2010 Pearson Education, Inc.
Conduction Velocity
local current flow and have faster impulse conduction
is slower than saltatory conduction in myelinated axons
Trang 50Copyright © 2010 Pearson Education, Inc.
Conduction Velocity
charge
about 30 times faster
the nodes
node
Trang 51Copyright © 2010 Pearson Education, Inc. Figure 11.15
Size of voltage
Voltage-gated ion channel
Stimulus Myelin
sheath
Stimulus Stimulus
Node of Ranvier
Myelin sheath
(a) In a bare plasma membrane (without voltage-gated
channels), as on a dendrite, voltage decays because current leaks across the membrane.
(b) In an unmyelinated axon, voltage-gated Na + and K +
channels regenerate the action potential at each point along the axon, so voltage does not decay Conduction
is slow because movements of ions and of the gates
of channel proteins take time and must occur before voltage regeneration occurs.
(c) In a myelinated axon, myelin keeps current in axons
(voltage doesn’t decay much) APs are generated only
in the nodes of Ranvier and appear to jump rapidly
from node to node.
1 mm
Trang 52Copyright © 2010 Pearson Education, Inc.
Multiple Sclerosis (MS)
adults
muscular control, speech disturbances, and urinary incontinence
Trang 53Copyright © 2010 Pearson Education, Inc.
Multiple Sclerosis: Treatment
including interferons and Copazone:
Trang 54Copyright © 2010 Pearson Education, Inc.
Nerve Fiber Classification
Trang 55Copyright © 2010 Pearson Education, Inc.
Nerve Fiber Classification
and motor fibers