action potential 3
TRANSCRIPT
-
7/29/2019 Action Potential 3
1/38
Ginus Partadiredja
Department of Physiology
Faculty of Medicine GMU
THE GRADED POTENTIAL &THE ACTION POTENTIAL
http://thecomplementarynature.com/wordpress/all-posts/tcn-book
-
7/29/2019 Action Potential 3
2/38
Learning Objectives
1. To understand basic concepts related to graded potentials
2. To understand basic concepts related to action potentials
3. To understand the differences between graded potentials
and action potentials
-
7/29/2019 Action Potential 3
3/38
Neuron: Functional unit of nervous system, with
excitability and conductivity characteristics
The number of neurons in the CNS = 1011 = 10 billion
Glial cells (neuroglia): Non conductive cells which protect,
maintain, and support the nervous system
The number of glial cells = 10 50 x of neurons
-
7/29/2019 Action Potential 3
4/38
THE HISTOLOGY OF NEURON
Dendrite Cell body/ soma
Axon hillock
Axon Myelin sheath
Synaptic knobs/
terminal buttons/axon telodendria
-
7/29/2019 Action Potential 3
5/38
(pseudounipolar)
Pyramidal
-
7/29/2019 Action Potential 3
6/38
Dendrites & somareceptive segment
Axon closest to axon hillock initial
segment
Axonconductive segment
Axon terminaltransmissive segment
-
7/29/2019 Action Potential 3
7/38
Stimulus: Any change in the environment that is strong
enough to initiate an action potential
Action potential: An electrical signal that propagates alongthe surface of the membrane of a neuron
Graded potential: A small deviation from the resting
membrane potential that occurs because ligand-gated or
mechanically gated channels open or close
hyperpolarizing ordepolarizing graded potential
Receptor potential (sensory receptors)
Post-synaptic potential (mainly in dendrites & soma):
Excitatory post-synaptic potential (EPSP)
Inhibitory post-synaptic potential (IPSP)
-
7/29/2019 Action Potential 3
8/38
Action potential generator potential/ receptor potential
Receptor - sensory receptor
- proteins bind to hormones/ neurotransmitters
Sensory receptors: Transducers which alter various energy
in the environment into action potentials in neurons
Sensory organs = receptor + non neural cells
-
7/29/2019 Action Potential 3
9/38
Mechanism:
Stimulus receptor/ generator potential (EPSP like;
does not spread, graded, local) reach firing level/
neuronal threshold action potential
-
7/29/2019 Action Potential 3
10/38
-
7/29/2019 Action Potential 3
11/38
THE PHYSIOLOGY OF NEURON
Recording with an electrode inside an axon resting
membrane potential/ polarization typically -70 mV
(the potential difference between the inside and outside of the
axon, the inside being more negative than the extra-cellular
fluid)
-
7/29/2019 Action Potential 3
12/38
Resting membrane potential small build-up of negative
ions along the inside of membrane, and positive ions along
the outside
Neurons range: -40 to -90 mV (ranges of membrane
potential of cells: +5mV to -100 mV)
Resting
membrane
potential
-
7/29/2019 Action Potential 3
13/38
ECF Na+ and Cl-
ICF
K+
and phosphates (attached to ATP and aminoacids)
Factors causing the negativity inside neurons:
1. Leakage of K+
to ECF (K+
channels > Na+
channels)2. Negative ions inside neurons cannot leave cells
(attached to ATP, proteins, or larger molecules)
3. Na+/K+ ATPase pumps (3 Na+ out for 2 K+ in)
contributes only -3 mV
-
7/29/2019 Action Potential 3
14/38
Threshold stimulus: a stimulus which is strong enough to
depolarize the membrane to threshold
Subthreshold stimulus; suprathreshold stimulus
Firing level/ threshold: The point where depolarization
accelerates (following the increase by 15 mV)
-
7/29/2019 Action Potential 3
15/38
Na+ channels open Na+ enters the cell
-
7/29/2019 Action Potential 3
16/38
Depolarization: The reversal of potential membrane +
inside and outside
-
7/29/2019 Action Potential 3
17/38
Overshoots exceeds the isopotential + 35 mV
Spike potential: The sharp upward and downward curve of
action potential
-
7/29/2019 Action Potential 3
18/38
Repolarization: The potential returns K+ channels open
(slower than Na+ channels) K+ exits
K+
-
7/29/2019 Action Potential 3
19/38
After-hyperpolarization: Under the level of polarization
-
7/29/2019 Action Potential 3
20/38
Refractory periods: Unresponsive period to adequate
stimulus
Absolute: firing level 1/3 repolarization
Relative: 1/3 repolarization the beginning of after-
depolarization (neurons can be stimulated by a larger-
than-normal stimulus)
-
7/29/2019 Action Potential 3
21/38
All or none law
Saltatory conduction: The
jump of depolarization from one
Ranvier node to the next Ranvier
node
many voltage-gatedchannels present in Ranvier
nodes ionic currents flow
through cytosol & ECF
energy-efficient mode of
conduction (less ATP for Na+/K+
pumps)
-
7/29/2019 Action Potential 3
22/38
Factors affecting the speed of conduction:
1. The amount of myelination
2. The diameter of axon (the larger the diameter of an axon,
the faster the propagation of impulses larger surface
areas)
3. Temperature (slower conduction at lower temperature)
Encoding stimulus intensity
Frequency of impulses
Number of sensory neurons activated
-
7/29/2019 Action Potential 3
23/38
The Types of Nerve Fibers in Mammalian Nerves
Type Function Diameter(m)
Conduction(m/sec)
Duration(msec)
Absoluterefractory
period
A Proprioceptive,
somatic motor
12 -20 70 - 120
A Touch,
pressure
5 - 12 30 - 70 0,4 0,5 0,4 - 1
A Motor in
muscle spindle
3 - 6 15 - 30
A Pain, cold,touch
2 - 5 12 - 30
-
7/29/2019 Action Potential 3
24/38
Type Function Diameter
(m)
Conduction
(m/sec)
Duration
(msec)
Absolut
refractory
periodB Autonomic pre-
ganglion
-
7/29/2019 Action Potential 3
25/38
Synapses
Axodendritic
Axosomatic
Axoaxonic
Synapses
Electrical synapses gap junctions connexons
Chemical synapses neurotransmitters
-
7/29/2019 Action Potential 3
26/38
Once the action potential reaches the axon terminal:
Voltage-gated Ca+2 channels open Ca+2 enters the cells
exocytosis of synaptic vesicles neurotransmitters
released
-
7/29/2019 Action Potential 3
27/38
-
7/29/2019 Action Potential 3
28/38
Synaptic delay: The interval for the transmitters to traverse
the synaptic cleft neurotransmitters receptors in ligand-
gated channels
One-way conduction: transmitters are only in pre-synaptic
cells
Orthodromic conduction
Antidromic conduction
Post-synaptic potentials graded local potentials
spread around local cells membrane
-
7/29/2019 Action Potential 3
29/38
Excitatory Post-Synaptic Potentials (EPSP)
Partial depolarization which decreases membrane potential/
increases neuronal excitability
Cation channels open (Na+, K+, Ca+2)
Na+ enters cells > Ca+2 inflow or K+ outflow
Local depolarization action potential, but facilitating action
potential
-
7/29/2019 Action Potential 3
30/38
I hibit P t S ti P t ti l (IPSP)
-
7/29/2019 Action Potential 3
31/38
Inhibitory Post-Synaptic Potentials (IPSP)
The increase of negative potential inside cells -90 mV
(hyperpolarizing post-synaptic potential)
Opening of Cl- or K+ channels (Cl- enter to the cells and K+
exit from the cells), or
Na+ and Ca+2 channels are closed
Cells body/ soma integrates EPSP and IPSP
An example of excitatory and inhibitory system skeletal
muscles motor neuron Examples of inhibitory system organization:
Negative feedback (Renshaw cell), spinal motor neuron
Cerebral cortex, limbic system, cerebellum
-
7/29/2019 Action Potential 3
32/38
-
7/29/2019 Action Potential 3
33/38
Spatial summation Temporal summation
Repeated stimulation of one
pre-synaptic neuron on a
post-synaptic neuronSimultaneous stimulation
of many pre-synaptic
neurons on one post-
synaptic neurons
-
7/29/2019 Action Potential 3
34/38
-
7/29/2019 Action Potential 3
35/38
C G
-
7/29/2019 Action Potential 3
36/38
Characteristics Graded Potential Action Potential
Origin Dendrites/ Soma Trigger zone of an
axonChannels Ligand-gated/
mechanically gated
Voltage-gated (Na+
and K+)
Conduction Local, not
propagated
Propagated
Amplitude Stimulus intensity(1 mV 50 mV)
All-or-none (100
mV)
Duration Longer (msec
min)
Shorter (0.5 2
msec)
Polarity Hyperpolarizing/Depolarizing
Depolarizing
Polarizing
Refractory period Not present Present
-
7/29/2019 Action Potential 3
37/38
Ion Channels
1. Leakage channels K+ leakage channels > Na+ leakage
channels2. Voltage-gated channels open/ close in response to a
change in membrane potential Na+, K+, Ca+
3. Ligand-gated channels open/ close in response to a
specific chemical stimulus (neurotransmitter, hormones,
ions) directly or indirectly (second messenger system)
Na+, Ca+ inward, K+ outward
4. Mechanically gated channel
open/ close in response tomechanical stimulation (vibration, pressure, stretching)
auditory receptors, stretch receptors of internal organs,
touch receptors of skin
-
7/29/2019 Action Potential 3
38/38
References
1. Barrett KE, Barman SM, Boitano S, Brooks HL (2010).
Ganongs Review of Medical Physiology. 23rd ed.
Chapter 4, Pages: 79-89; Chapter 6, Pages: 115-123.
2. Carola R, Harley JP, Noback CR (1990). Human
Anatomy & Physiology. Chapter 11, Pages: 309-327
3. Guyton AC, Hall JE (2006). Textbook of Medical
Physiology, 11th ed. Chapter 5, Pages: 57-71; Chapter
45, Pages: 555-571
4. Tortora GJ, Derrickson BD (2009). Principles of
Anatomy and Physiology. 12th ed. Chapter 12, Pages:
417-447