Download Maintaining the Inner Environment

Chemical Control of
Behavior
Homeostasis
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Keeping the internal environment of the body
the same (constant) regardless of changes
externally.
Communication is accomplished by three
systems:
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Central nervous system (hypothalamus)
Brain stem (diffuse modulatory systems)
Autonomic and diffuse enteric (visceral) systems
of the peripheral nervous system.
Purpose of Homeostasis
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Maintains internal temperature.
Maintains blood sugar level.
Maintains balance of essential salts and
minerals.
Maintains fluids (level of hydration) in cells
and intracellular.
Central Regulation (CNS)
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Hypothalamus – integrates visceral
functioning:
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Activates the autonomic nervous system
Regulates hormones secreted from the pituitary
gland and thereby controls the endocrine system.
Three Parts of Hypothalamus
Periventricular Zone – regulates temperature,
salt concentration, levels of hormones.
 Medial Zone – produces vasopressin and
oxytocin in posterior pituitary.
 Lateral Zone – permits cortex and limbic
system to over-ride hypothalamic activity,
manages long-term regulation.
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Medulla Oblongata
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Responsible for monitoring:
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Spontaneous respiratory movement (breathing)
Blood pressure
Cardiac rhythm
“Brain death” occurs with loss of
hypothalamic and medullary control over
respiration, lack of EEG waves.
Endocrine System

Endocrine organs include:
Pituitary gland
 Adrenal Cortex
 Gonads (ovaries and testes)
 Thyroid and parathyroid
 Adrenal cortex
 Islet cells of pancreas
 Secretary cells that line intestinal tract
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Autonomic Nervous System
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Two parts:
Sympathetic
 Parasympathetic
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Includes sensor and effector components.
Sensors monitor internal functioning.
 Effectors activate or inhibit target structures such
as blood vessels or glands.
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What Do Sensors Monitor?
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Chemical variations in blood composition.
Tension changes in the vascular system (blood
vessels).
Distension of the intestines, bladder and gall
bladder.
Where Sensor Neurons Go
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Sensor neurons from the viscera (visceral
afferent nerves) go:
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To the spinal cord
From spinal cord to ganglia in the sympathetic
and parasympathetic systems.
Postganglionic fibers go to the targets.
ACh is the neurotransmitter for neurons from
spinal cord to ganglia.
Parts of the Autonomic System
Different in function.
 Preganglionic fibers emerge from different
spots in the spinal cord.
 Ganglia are in different places:

Close to organs for parasympathetic
 Close to spinal cord for sympathetic
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Postganglionic effectors use different
neurotransmitters (NE vs ACh)
Sympathetic
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Mobilizes body for “fight or flight” response.
In addition to direct NE to targets, adrenal
medulla secretes NE in bloodstream to
sympathetic targets.
Nicotine in cigarettes activates sympathetic
nervous system.
Parasympathetic
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Initiates rest and recuperation.
Activation comes from the brainstem.
Vagus nerve carries sensor and effector information
from heart, lungs and intestines.
Preganglionic axons are very long.
Postganglionic fibers use ACh not NE – receptors are
muscarinic (blocked by atropine) not nicotinic.
Coordination of the Systems
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Systems are complementary.
Both are active to some extent at the same time – not
alternating.
What happens during anger?
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Sympathetic arousal increases blood pressure.
Medulla detects that arousal and activates the
parasympathetic to keep blood pressure within normal
limits.
Hypertension occurs with deficient feedback.
Diffuse Enteric System
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A third major division of the autonomic
nervous system.
Neural control unit between the autonomic
postganglionic nerves and the gastrointestinal
system.
Contractions of muscles propels food through
digestive system (peristalsis).
Diffuse Modulatory Systems
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A small set of diffuse modulatory neurons
arise from the brain stem.
Each neuron has an axon that can influence
more than 100,000 postsynaptic neurons
spread widely across the brain.
Their synapses release neurotransmitter into
the extracellular fluid, not into a confined
synaptic cleft.
Origins of Diffuse Neurons
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Origins vary depending on the
neurotransmitter involved:
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NE system – locus coeruleus (waking, arousal,
attention, memory, anxiety, pain, mood).
5-HT serotonin system – raphe nuclei
(wakefulness, mood, emotional behavior).
DA system – substantia nigra & ventral
tegmentum (reward).
ACh system – basal forebrain (unknown)
Effects of Drugs
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Many abused drugs act directly on the
modulatory systems.
Hallucinogens such as LSD – agonist for
serotonin, decreasing activity of raphe nuclei.
Stimulants (cocaine, amphetamine) – affect
DA and NE systems, causing increased
alertness, self-confidence, euphoria.
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Mimic effects of sympathetic ANS activation.
Drug Effects (Cont.)
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Stimulants block catecholamine reuptake and
stimulate release of DA (dopamine),
intensifying effects of DA and NE.
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This causes the stimulant effect.
Because cocaine and amphetamine affect the
reward systems, drug-seeking behaviors are
reinforced leading to addiction or
psychological dependence.