Chapter 4
Principles of Neural and
Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Outline
•
•
•
•
•
•
•
Graded Potentials
Action Potentials
Synapses and integration
Intracellular communication
Signal Transduction
Hormonal Communication
Nervous vs. Endocrine System
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Communication is critical for the survival of the
cells that compose the body.
Two major regulatory systems of the body –
nervous and endocrine - communicate with the
cells/tissues/organs/systems they control.
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Neural Communication
• Nerve and muscle are excitable tissues
• Can undergo rapid changes in their membrane
potentials
• Can change their resting potentials into electrical
signals
– Electrical signals are critical to the function of the
nervous system and all muscles
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Neural Communication
• Membrane electrical states
– Polarization
• Any state when the membrane potential is other than
0mV
– Depolarization
• Membrane becomes less polarized than at resting
potential
– Repolarization
• Membrane returns to resting potential after having been
depolarized
– Hyperpolarization
• Membrane becomes more polarized than at resting
potential
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Types of Changes in Membrane
Potential
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Neural Communication
• Two kinds of potential change
– Graded potentials
• Serve as short-distance signals
– Action potentials
• Serve as long-distance signals
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Graded Potential
• Occurs in small, specialized region of excitable
cell membranes
• Magnitude of graded potential varies directly
with the magnitude of the triggering event
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Portion of
excitable cell
Initial site of
potential change
Loss of charge
Direction of current
flow from initial site
Loss of charge
Direction of current
flow from initial site
Chapter 4 Principles of Neural and Hormonal Communication
* Numbers refer to the local
potential
in mV
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
at various points along the membrane.
Fig. 4-4, p. 89
Current Flow During a Graded Potential
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Graded Potentials
Examples of graded potentials:
•
•
•
•
•
Postsynaptic potentials
Receptor potentials
End-plate potentials
Pacemaker potentials
Slow-wave potentials
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Action Potentials
• Brief, rapid, large (100mV) changes in
membrane potential during which potential
actually reverses
• Involves only a small portion of the total
excitable cell membrane
• Do not decrease in strength as they travel from
their site of initiation throughout remainder of cell
membrane
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 4-7, p. 91
Action Potentials
• When membrane reaches threshold potential
– Voltage-gated channels in the membrane
undergo conformational changes
– Flow of sodium ions into the ICF reverses the
membrane potential from -70 mV to +30 mV
– Flow of potassium ions into the ECF restores the
membrane potential to the resting state
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Action Potentials
• Additional characteristics
– Sodium channels open during depolarization by
positive feedback.
– When the sodium channels become inactive, the
channels for potassium open. This repolarizes
the membrane.
– As the action potential develops at one point in
the plasma membrane, it regenerates an identical
action potential at the next point in the
membrane.
– Therefore, it travels along the plasma membrane
undiminished.
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Action Potentials
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Action Potentials
Permeability Changes and Ion Fluxes During an Action Potential
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Action Potentials
The Na+/K+ pump gradually restores the
concentration gradients disrupted by
action potentials.
• Sodium is pumped into the ECF
• Potassium is pumped into the ICF
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Neuron
• Once initiated, action potentials are conducted
throughout a nerve fiber
• Action potentials are propagated from the axon
hillock to the axon terminals
• Basic parts of neuron (nerve cell)
– Cell body
– Dendrites
– Axon
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Neuron
• Cell body
– Houses the nucleus and organelles
• Dendrites
– Project from cell body and increase surface area
available for receiving signals from other nerve
cells
– Signal toward the cell body
Dendrite and cell body serve as the neurons input
zone.
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Neuron
• Axon
– Nerve fiber
– Single, elongated tubular extension that conducts action
potentials away from the cell body
– Conducting zone of the neuron
– Collaterals
• Side branches of axon
– Axon hillock
• First portion of the axon plus the region of the cell body fro m
which the axon leaves
• Neuron’s trigger zone
– Axon terminals
• Release chemical messengers that simultaneously influence
other cells with which they come into close association
• Output zone of the neuron
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Neuron
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Action Potentials
• Two types of propagation
– Contiguous conduction
• Conduction in unmyelinated fibers
• Action potential spreads along every portion of
the membrane
– Saltatory conduction
• Rapid conduction in myelinated fibers
• Impulse jumps over sections of the fiber
covered with insulating myelin
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Contiguous Conduction
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Saltatory Conduction
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Saltatory Conduction
• Propagates action potential faster than
contiguous conduction because action potential
does not have to be regenerated at myelinated
section
• Myelinated fibers conduct impulses about 50
times faster than unmyelinated fibers of
comparable size
• Myelin
– Primarily composed of lipids
– Formed by oligodendrocytes in CNS
– Formed by Schwann cells in PNS
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Regeneration of Nerve Fibers
• Regeneration of nerve fibers depends on its
location
• Schwann cells in PNS guide the regeneration of
cut axons
• Fibers in CNS myelinated by oligodendrocytes
do not have regenerative ability
– Oligodendrocytes inhibit regeneration of cut
central axons
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Synapses
• Junction between two neurons
• Primary means by which one neuron directly interacts
with another neuron (muscle cells or glands as well)
• Anatomy of a synapse
– Presynaptic neuron – conducts action potential toward
synapse
– Synaptic knob – contains synaptic vesicles
– Synaptic vesicles – stores neurotransmitter (carries signal
across a synapse)
– Postsynaptic neuron – neuron whose action potentials are
propagated away from the synapse
– Synaptic cleft – space between the presynaptic and
postsynaptic neurons
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 4-16, p. 103
Synapses
Signal at synapse either excites or inhibits the
postsynaptic neuron
• Two types of synapses
– Excitatory synapses
– Inhibitory synapses
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Table 4-2, p. 105
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Table 4-3, p. 108
Neurotransmitters
• Vary from synapse to synapse
• Same neurotransmitter is always released at a particular
synapse
• Quickly removed from the synaptic cleft
• Some common neurotransmitters
–
–
–
–
–
–
–
–
–
–
Acetylcholine
Dopamine
Norepinephrine
Epinephrine
Serotonin
Histamine
Glycine
Glutamate
Aspartate
Gamma-aminobutyric acid (GABA)
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Synaptic inputs
(presynaptic axon terminals)
Dendrites
Cell body of
postsynaptic
neuron
Axon
hillock
Myelinated
axon
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 4-15, p. 102
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 4-16, p. 103
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 4-17, p. 104
Neuropeptides
• Large molecules consisting of from 2 to 40
amino acids
• Synthesized in neuronal cell body in the
endoplasmic reticulum and Golgi complex
• Packaged in large, dense-core vesicles present
in axon terminal
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Comparison of Classical Neurotransmitters and Neuropeptides
Characterist Classical
Neuropeptides
ic
Neurotransmitters
Size
Small, one amino acid or
similar chemical
Large, 2 to 40 amino acids in length
Site of
Synthesis
Cytosol of synaptic knob
Endoplasmic reticulum and Golgi complex in cell
body, travel to synaptic knob by axonal transport
Site of Storage
In small synaptic vesicles in
axon terminal
In large dense-core vesicles in axon terminal
Site of Release
Axon terminal
Axon terminal, may be cosecreted with
neurotransmitter
Speed and
Duration of
Action
Rapid, brief response
Slow, prolonged response
Site of Action
Subsynaptic membrane of
postsynaptic cell
Nonsynaptic sites on either presynaptic or
postsynaptic cell at much lower concentrations
than classical neurotransmitters
Effect
Usually alter potential of
postsynaptic cell by opening
specific ion channels
Usually enhance or suppress synaptic
effectiveness by long-term changes in
neurotransmitter synthesis or postsynaptic
receptor sits (act as neuromodulators)
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Neuronal Integration
• Multiple EPSP and IPSP’s from numerous
synapses converge on one neuron.
• These signals can cause different changes in
the postsynaptic neuron
– Cancellation
– Spatial summation
– Temporal summation
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Threshold = approx -55mv
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 4-18, p. 106
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 4-19, p. 109
Presynaptic
inputs
Convergence of input
(one cell is influenced
by many others)
Postsynaptic
neuron
Presynaptic
inputs
Divergence of output
(one cell influences
many others)
Postsynaptic
neurons
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Arrows indicate direction in which information is being conveyed.
Fig. 4-20, p. 111
The Retina
Example of convergence and divergence
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Synaptic Drug Interactions
• Possible drug actions
– Altering the synthesis, axonal transport, storage,
or release of a neurotransmitter
– Modifying neurotransmitter interaction with the
postsynaptic receptor
– Influencing neurotransmitter reuptake or
destruction
– Replacing a deficient neurotransmitter with a
substitute transmitter
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Examples of drugs that alter synaptic transmission
• Cocaine
– Blocks reuptake of neurotransmitter dopamine at
presynaptic terminals
• Strychnine
– Competes with inhibitory neurotransmitter glycine
at postsynaptic receptor site
• Tetanus toxin
– Prevents release of inhibitory neurotransmitter
GABA, affecting skeletal muscles
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chemical Messengers
• Four types of chemical messengers
– Paracrines
• Local chemical messengers
• Exert effect only on neighboring cells in immediate
environment of secretion site
– Neurotransmitters
• Short-range chemical messengers
• Diffuse across narrow space to act locally on adjoining
target cell (another neuron, a muscle, or a gland)
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chemical Messengers
– Hormones
• Long-range messengers
• Secreted into blood by endocrine glands in response to
appropriate signal
• Exert effect on target cells some distance away from
release site
– Neurohormones
• Hormones released into blood by neurosecretory
neurons
• Distributed through blood to distant target cells
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chemical Messengers
• Extracellular chemical messengers bring about
cell responses primarily by signal transduction
– Process by which incoming signals are conveyed
to target cell’s interior
• Binding of extracellular messenger (first
messenger) to matching receptor brings about
desired intracellular response by either
– Opening or closing channels
– Activating second-messenger systems
• Activated by first messenger
• Relays message to intracellular proteins that carry out
dictated response
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Hormones
• Endocrinology
– Study of homeostatic activities accomplished by
hormones
• Two distinct groups of hormones based on their
solubility properties
– Hydrophilic hormones (Proteins, peptides)
• Highly water soluble
• Low lipid solubility
– Lipophilic hormones (Steroids)
• High lipid solubility
• Poorly soluble in water
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Fig. 4-21, p. 112
Table 4-4, p. 114
Fig. 4-22, p. 115
Fig. 4-23, p. 116
Fig. 4-24, p. 118
Fig. 4-25, p. 119
Fig. 4-26, p. 122
Comparison of Nervous System and
Endocrine System
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Action Potential
Neuron
Voltage Gated