1. Principles of Communication
Neural and Chemical
2 - 4. Cell-to-Cell Communication
Intercellular communication
How cells talk to each other
Mechanisms
Direct: gap junctions
Indirect: chemical messengers
Messenger produced by source cell
Messenger transported to target cell
Target cell has receptors for messenger
Messenger binds to receptor
Binding triggers response
5 - 10. Messenger Classification - Function
Paracrine
Signals a nearby cell
Example: Histamine
Autocrine
Signals “self”
Source and target are the same
Neurotransmitter
Chemical produced by neurons
Released into the ECF at synaptic cleft
Examples: Acetylcholine, glycine, serotonin
Hormone
Chemical produced by endocrine cells
Secreted into blood via interstitial fluid
Examples: Insulin, estrogen, thyroxin
Neurohormone
Chemical produced by neurons
Secreted into blood via interstitial fluid
Examples: Antidiuretic hormone (ADH),
oxytocin
11 - 12. Messenger Classification - Solubility
Lipophobic ligand
Water soluble
Does not easily cross cell membrane
Receptors on cell membrane
General response
Enzyme activation
Membrane permeability changes
Lipophilic ligand
Lipid soluble
Easily crosses cell membrane
Receptor location within cell (intracellular
location)
General response via gene activation
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13. Synthesis and Release
Lipophillic ligands
Synthesized on demand
Immediate release from source
Release rate depends on synthesis
Lipophobic ligands
Synthesis is independent of demand
Stored in vesicles of source until needed
Release by exocytosis
Release rate determined by exocytosis
14 - 16.Messenger Transport
Diffusion through interstitial fluid
Source and target are close
Ligand is quickly degraded
Examples
Paracrines, autocrines, neurotransmitters,
and most cytokines
Blood borne transport
Source and target are distant
Lipophobic ligands dissolve in plasma
Lipophilic ligands bind to carrier protein
Examples
Hormones, neurohormones, and some
cytokines
17. Signal Transduction Overview
Messenger binds to receptor
Binding results in cell response
Signal transduction
Process of producing response in target
18 –20.Receptor Binding
Specificity
Binding is brief and reversible
Affinity = strength of binding
Location of binding
Lipophobic ligands
cell membrane
Lipophilic ligands
within cell
21. Agonists and Antagonists
Agonist
Chemical which binds to receptor
Action mimics normal response
Antagonist
Chemical which binds to receptor
Binding does not result in response
Competes with normal ligand
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22 - 25. Membrane Bound Receptors
Response of the target
Movement of ions
Phosphorylation of enzymes
Mechanisms
Channel-linked receptors
Enzyme-linked receptors
G protein-linked receptors
26 – 28. Long Distance Communication
Nervous system
Nerve cells transmit signals
Within neuron via long axons
Between cells via the synapse
Signals of axon = action potentials
Axons via action potentials span distance to
target
Endocrine system
Endocrine target secretes hormone
Hormone enters blood
Blood spans distance to target
http://www.cartage.org.lb/en/themes/Sciences/LifeScience/Ge
neralBiology/Physiology/EndocrineSystem/NervousEndocrine/e
ndocrorgs.gif
Property
Nervous System
Anatomy
Structural
Glands and targets
continuity
widely dispersed
Neurotransmitters Hormones
Chemical
messenger
Method of travel
by chemical
messenger
Distance traveled
by chemical
messenger
Speed of Response
Endocrine System
Diffusion across
synapse
Distribution by
circulatory system
Short
Long
Rapid –
Slow – minutes to
milliseconds
hours
Duration of Action Brief - milliseconds Long – minutes to
months
Specificity
Close anatomical Cell binding
proximity
Function
Rapid, precise
Activities of long
responses
duration
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29 - 31. Neurons
Gather and transmit information by:
Responding to stimuli
Producing and sending electrochemical
impulses
Releasing chemical messages
http://www.enchantedlearning.com/subjects/anatomy/brain/gif
s/Neuron.GIF
Cell body
Nucleus
Synthesis of macromolecules
Dendrites
Receive & convey information to cell body
Axon
conduct impulses away from cell body
32. Functional Classification of Neurons
Sensory/Afferent
PNS CNS
Motor/Efferent
CNS
PNS
Association/ Interneurons
integrate
within CNS
33 - 34. Structural Classification of Neurons
Pseudounipolar:
single process
sensory neurons
Bipolar:
two major processes
retinal neurons
Multipolar:
many dendrites and a single axon
motor neurons
35. Terminology
Myelinated
Unmyelinated
36. Myelin Sheath Formation
37 - 38. Function of Nervous System
Input of sensory information
Integration
Motor output
39. Resting Potential
40. Electrical Potential
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http://regentsprep.org/Regents/physics/phys03/apotdif
/battery.gif
41 - 43. Leak Channels
Chemical Gradient
Concentration
High to low
Electrical Gradient
+ and - charges held apart by membrane
Potential difference
44 - 45. Definitions
Transmembrane potential
Potential difference
Measured across cell membrane
Expressed in millivolts (mV)
Results from uneven distribution of + and – ions
across membrane
Resting potential
Transmembrane potential under homeostatic
conditions
46. Graded Potential.
47 - 49. Change in Membrane Potential
Passive
Leak channels
Widespread
Always open
Active
Gated channels
Closed at rest
Types
Chemical - widespread
Voltage - axon
(Mechanical)
(Temperature)
States
Closed but able to open
Open (activated)
Closed and not able to open (inactivated)
50 - 52. Definitions
Depolarization
Transmembrane potential moves toward zero
or toward a more positive value
Hyperpolarization
Transmembrane potential moves away from
resting potential and toward a more negative
value
Repolarization
Transmembrane potential moves away from a
positive value and toward the resting potential
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Restoring resting transmembrane potential
53 - 59. Graded Potential
Open sodium channels
Influx of Na+
Depolarization
Open potassium channels
Efflux of K+
Hyperpolarization
Graded Potential
Local changes
Limited spread
Trigger cell functions
Trigger action potential
Types
Postsynaptic
Receptor
End-plate
Pacemaker
60 - 68. Action Potentials
Triggered by graded potentials
All-or-none phenomenon
Threshold
http://www.learner.org/channel/courses/biology/a
rchive/images/1968.html
Handout
69 - 71. Refractory Period
Absolute
Opening of sodium activation gates to closing of
inactivation gates
Relative
Requires greater than normal stimulus
Sodium gates closed but able to open
72. Comparison of Potentials
Graded Potentials
Depolarizing or hyperpolarizing
No threshold
Intensity of stimulus determines polarization
Effect on membrane potential decreases with
distance
No refractory period
Most cells
Action Potentials
Depolarizing
Requires depolarization to threshold
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All-or-none
Propagates along entire membrane without
change in strength
Refractory period
Excitable membranes of neurons, muscles
73. Rate of Impulse Conduction
Nerve diameter
Myelination
Saltatory conduction
Multiple sclerosis
Factors that influence excitability
pH
electrolytes
74 - 75. Conduction in an Unmyelinated Axon
Axon hillock reaches threshold
AP occurs
Na+ influx depolarizes adjacent regions to threshold
new AP
Slow
76 – 77. Conduction in Myelinated Axon
Ions can't cross myelin
APs occur only at nodes of Ranvier
Voltage-gated Na+ channels are present only at
nodes
Fast
Saltatory conduction
78. Propagation of Action Potentials
Action potential is generated at each new
membrane patch
Continuous - unmyelinated
Transmembrane potential becomes positive
Local currents established
Can only move in one direction, away from
stimulus
Saltatory- myelinated
Local current skips internodes, jumping
from node to node
79. Synapse
Specialized junction between a neuron and another
cell
Chemical
Synaptic transmission via neurotransmitters
(NT)
Electrical synapses
Rare in nervous system
http://www.mirrorservice.org/sites/home.ubalt.ed
u/ntsbarsh/Business-stat/opre/neurons.gif
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80. Electrical Synapse
Ions move through gap junctions
Found in smooth and cardiac muscles, brain,
and glial cells
81. Chemical Synapse
http://universe-review.ca/I10-40-synapse.jpg
82 - 83. Synaptic Terminology
Presynaptic
Postsynaptic
Synaptic knob
Synaptic vesicles
Synaptic cleft
Subsynaptic membrane
84 - 87. Sequence of Events
1. Action potential reaches synaptic knob
2. Local change in potential opens voltage gated
Ca2+ channels
3. Ca2+ enters synaptic knob
4. Release of neurotransmitter from synaptic
vesicles by exocytosis
5. Neurotransmitter diffuses across synaptic cleft
6. Neurotransmitter binds to receptors on
postsynaptic membrane
7. Binding to receptor triggers opening of
chemically-gated ion channels in subsynaptic
membrane
88 - 89. Excitatory Synapses
Neurotransmitter binding opens a chemically-gated
channel that permits passage of Na+ and K+
Net movement of cations (Na+) into the cell
Small depolarization
Excitatory postsynaptic potential - EPSP
90 - 91. Inhibitory Synapses
Neurotransmitter binding opens a chemically-gated
channel that permits passage of Cl- or K+
Net movement of anions (Cl-) into the cell or net
movement of cations (K+) out of the cell
Small hyperpolarization
Inhibitory postsynaptic potential - IPSP
92 - 93. Synapses
Always excitatory or always inhibitory
Same neurotransmitter is always released
Synaptic delay
Removal of neurotransmitters from cleft
Diffusion
Inactivated by enzymes
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Taken up into axon terminal
94. Grand Post Synaptic Potential
GPSP
Composite of all EPSPs and IPSPs occurring at
approximately the same time
95 - 101. How Is Threshold Reached?
Temporal Summation
Time
A presynaptic neuron firing repeatedly in a very
short period of time can bring the postsynaptic
membrane to threshold
Amount of neurotransmitter released is related
to frequency of Aps
More NT = more open channels = more ion
movement = greater depolarization
Spatial Summation
Different points in space
Multiple presynaptic neurons firing
simultaneously can bring the postsynaptic
membrane to threshold
Amount of neurotransmitter released is related
to number of presynaptic neurons
More NT = more open channels = more ion
movement = greater depolarization
102. Information Processing
103. Convergence/Divergence
104.
http://www.mfi.ku.dk/ppaulev/chapter1/images/n16ok.jpg
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