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Chapter 4
Neural and Hormonal
Communication
Objectives
Neural Communication
• Neurons are excitable cells because they
produce electric signals when excited
• Terms to know
– Polarization
– Depolarization
– Repolarizatin
– Hyperpolarization
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Electrical Signals
• Produced by changes in ion movement across the
plasma membrane
– Leak or gated channels
• Voltage gated channels
– Membrane permeability changes due to triggering
events
• Two types of signals
– Graded potentials
– Action potentials
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Action Potentials
• Transient, large changes in membrane potential
– Potential will typically reverse within the cell
• Inside becomes positive
• Occur when a graded potential reaches a threshold
potential (-50mV in neuron)
• Caused by the opening of voltage-gated Na+ and K+
channels
–
–
–
–
Open only if threshold is reached
Ions move down their gradients
Depolarization caused by Na+ entering cell
Repolarization caused by K+ leaving cell
Action Potential
• Contiguous conduction
– Action potential spreads down
the membrane of the axon
• Refractory period
– Ensure the one way transmission
of the action potential
• Absolute
• Relative
• All-or-none law
– Responds to a triggering event
with maximal potential or not
• Frequency of action potential
determines strength
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Action Potential Velocity
• Myelination increases speed of conduction
– Voltage gated channels only found at nodes
– Saltatory conduction
– Schwann cells and oligodendrocytes
• Fiber diameter
– The larger the diameter the faster the actin
potential is propagated
Synapses and Neural Integration
• How do neurons communicate with other cells?
– Can terminate at a muscle, gland, or neuron
• Synapse
– Two types
• Electrical and chemical
– Pre-synaptic and post-synaptic
– Neurotransmitter
•
•
•
•
Release promoted by Ca2+
Can excite or inhibit
Quickly removed from synaptic cleft
See table 4-2 P. 107 for common neurotransmitters
Synapse
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Grand Postsynaptic Potential
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Endocrine System: Hormones
• Endocrine Glands: ductless organs
• Hormones:
– Chemical messengers
– Circulate in the bloodstream
– Stimulate physiological response
Characteristics
• Access to every cell
• Each hormone acts only on specific cells (target cells)
• Endocrine control slower than nervous system
• Endocrine and nervous systems interact
• Three chemical classes
– Steroids
– Peptides
– monoamines
Hormone Chemistry
• Steroids
• derived from cholesterol
• secreted by gonads and adrenal glands
• estrogens, progesterone, testosterone, cortisol,
corticosterone, aldosterone, DHEA, and calcitriol
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H
OH
CH3
CH2
I
O
Testosterone
I
O
OH
CH3
I
I
OH
Thyroxine
OH
HO
HO
Estradiol
(a) Steroids
CH
HO
Epinephrine
(b) Monoamines
• Monoamines
• derived from amino acids
• secreted by adrenal, pineal, and thyroid glands
• epinephrine, norepinephrine, melatonin, and
thyroid hormone
• all hormones made from either cholesterol or
amino acids with carbohydrate added to make
glycoproteins.
COOH
CH3
• Peptides and glycoproteins
• created from chains of amino acids
• secreted by pituitary and hypothalamus
• oxytocin, antidiuretic hormone, releasing and
inhibiting hormones, and anterior pituitary
hormones
C
H2N
Insulin
Angiotensin II
(c) Peptides
Figure 17.14 a-c
CH2
NH
CH2
Hormone Synthesis: Steroid Hormones
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
CH3
CH3
CH3
CH3
HO
Cholesterol
CH3
CH3
C
O
CH3
O
Progesterone
CH2OH
OH
C
CH3
HO
CH3
CH3
O
O
OH
HO
CH3
O
O
O
Testosterone
C
CH3
CH3
O
HC
CH2OH
Cortisol (hydrocortisone)
Aldosterone
OH
Figure 17.16
HO
Estradiol
Peptides and Monoamines
Peptides
• Synthesized like any protein
• At first, inactive
preprohormone
• Modified by RER and Golgi
to produce hormone
Monoamines
• Synthesized from AA
tryptophan and tyrosine
Hormone Classification: Steroid
• Steroid hormones:
– Chemically derived from cholesterol, lipid soluble
– Enter target cells
– Activate specific genes to produce specific proteins
– Slower acting than nonsteroid hormones, minutes to
hours
Steroid and Thyroid Hormone Action
scienceblogs.com
Hormone Classification: Peptides
• Nonsteroid hormones:
– Partly derived from amino acids, water soluble
– Bind to receptors on target cell membranes
– Work through intermediate mechanisms to activate
existing enzymes
• Cascade mechanism
– Faster action than steroid hormones, seconds to
minutes
Amino Acid Hormone Action
legacy.owensboro.kctcs.edu
Other Second Messengers
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Inositol triphosphate (IP3) pathway
Diacylglycerol (DAG) pathway
Ca2+-gated
Ca2+
ion channel
Hormone
Hormone
IP3-gated Ca2+ channeI
1
1
Receptor
Phospholipase
Phospholipase
3
2
DAG
IP3
G
G
4
Inactive
PK
Receptor
G
G
6
Activated
PK
2
8
5
IP3
Ca2+
Enzyme
Various
metabolic
effects
7
Calmodulin
Inactive
PK
Key
DAG
G
IP3
PK
IP3
10
Activated
PK
Hormones
ADH
TRH
OT
LHRH
Catecholamines
9
Smooth
ER
Diacylglycerol
G protein
Inositol triphosphate
Protein kinase
• diacylglycerol (diglyceride) second-messenger system
• Inositol triphosphate second-messenger system
Figure 17.23