Download 58 Limbic System Physiology

Behavioral and Motivational
Mechanisms of the Brain
Functional Brain Systems
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Networks of neurons working together
and spanning wide areas of the brain
The two systems are:
– Limbic system
– Reticular formation
Diencephalon
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Central core of the forebrain
Thalamus, hypothalamus and epithalamus
Encloses the third ventricle
Reticular Formation
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Composed of three broad columns along the length
of the brain stem
– Raphe nuclei
– Medial (large cell) group
– Lateral (small cell) group
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Has axonal connections with hypothalamus,
thalamus, cerebellum, and spinal cord
Reticular Formation
Functions of the Reticular Formation
1. Excitatory stimulus to the brain & Consciousness
2. Regulation of muscle relfexes
3. Co-ordination of the autonomic reflexes
(Respiratory and Cardiovascular reflexes)
4. Regulation of pain sensation (Reticulospinal
pathways modulate impuls transmission in the
dorsal horn of the spinal cord)
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Brain stem monoaminergic systems play important
roles in the control of these functions
Activating-Driving Systems of the Brain
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Continuous transmission of nerve signals from the
lower brain to the cerebrum
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Blockage by tumors (e.g. Pineal tumor)
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1) Direct stimulation of background level of neuronal
activity in wide areas of the brain
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2) Activation of neurohormonal systems that specific
facilitatory or inhibitory neurotransmitters to selected
areas of the brain
Continuous Excitatory Signals
from the Brain Stem
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Reticular excitatpry area of the brain
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Located in the reticular substance of the pons and
mesencephalon
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Also called “bulboreticular facilitatory area”
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This system also maintain tone in the antigravity
muscles and controls the levels of spinal reflexes
Continuous Excitatory Signals
from the Brain Stem
Continuous Excitatory Signals
from the Brain Stem
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Two types of excitatory signals passing through the
thalamus:
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Rapid stimulus (ACh) and Small neurons of the brain
stem (Monoamines)
Excitation of the excitatory area
by peripheral sensory signals
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Level of activity of the excitatory area in the brain
stem is determined by the peripheral sensory signals
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Stimulation by pain signals
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Entrance of 5th cranial nerve to the pons
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Transection of the brain stem below or above the
5th cranial nerve
Excitation by the feedback
signals from the cerebral cortex
A reticular inhibitory area
located in the lower brain stem
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This inhibitory area is located in the medulla
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This area can inhibit reticular facilitatory area
and thus decrease activity in the brain
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Inhibitory signals from serotonergic neurons
Neurohormonal Control of Brain Activity
Neurohormonal Control of Brain Activity
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Norepineprine system and locus coeruleus: located at the
juncture between the pons and mesencephalon
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Dopaminergic system and Substantia nigra: It lies anteriorly in
the superior mesencephalon
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Serotonergic system and the raphe nuclei: Located in the
midline of pons and medulla, several thin nuclei called raphe
nuclei
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ACh system: Gigantocellular neurons of the reticular formation
(pons and mesencephalon) : tracts go both to the brain and
spinal cord
Neurohormonal Control of Brain Activity
Central Noradrenergic System
Central Serotonergic System
Central Dopaminergic System
Acetylcholinergic System
LDT: Latero Dorsal Tegmental Nucleus
PPT: Pedunculopontine Tegmental Nucleus
Other Neurotransmitters and
Neurohormonal Substances
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Enkephalins
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Glutamate
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Vasopressin
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Epinephrine
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Histamine
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Endorphins
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In most places in the brain ACh functions as an
excitatory neurotransmitter
Limbic System
(The Emotional & Motivational Brain)
Emotions
If only it were as simple as the diagrams
below…
Limbic System
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Limbic system
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Rhinencephalon = smell brain
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Hypothalamus, hippocampus, anterior nucleus of thalamus,
septal nuclei, amygdala, paraolfactory area, portions of basal
ganglia
Limbic System
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Medial forebrain bundle connects the limbic system
to the brain stem
Hypothalamus
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Thalamus and the third ventricle
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Mammillary bodies
Relay station for olfactory pathways
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Infundibulum – the pituitary gland
Hypothalamus
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Output signals from the hypothalamus:
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1) Brain stem
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2) Diencephalon and Cerebrum
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3) Infundibulum – the pituitary gland
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Hypothalamus represents less than 1 % of the brain
mass
Papez Circuit (circa 1930)
Hypothalamic Function
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Regulates blood pressure, rate and force of
heartbeat, digestive tract motility, rate and depth of
breathing, and many other visceral activities
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Perception of pleasure, fear, and rage
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Regulation of body temperature
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Regulates feelings of hunger and satiety
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Regulates sleep and the sleep cycle
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Endocrine functions of the hypothalamus
Vegetative and Endocrine
Functions of the Hypothalamus
Vegetative and Endocrine
Functions of the Hypothalamus
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Cardiovascular regulation: Stimulation of posterior
and lateral hypothalamus increases arterial pressure
and HR; preoptic area produces opposite effects
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Regulation of body temperature (preoptic area)
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Regulation of body water: ADH (vasopressin)
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Uterine contractility and milk ejection: Oxytocin
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Control of anterior pituitary hormone secretion
Behavioral Functions of the Hypothalamus
and Associated Limbic Structures
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Stimulation of lateral hypothalamus
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Ventromedial nucleus and surrounding areas
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Periventricular nuclei – 3rd ventricle
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Sexual drive – anterior and posterior
hypothalamus
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Effects of hypothalamic lesions
Reward and Punishment Function of
the Limbic System
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Reward centers: Medial forebrain bundle, VMN, LHA
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Less potent reward centers reside in the septum and
some basal ganglial areas
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Punishment centers: Central gray surrounding the
aqueduct of Sylvius in the mesencephalon,
Periventricular area
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Less potent punishment areas are found in the
amygdala and hippocampus
Reward and Punishment Function of
the Limbic System
Reward and Punishment Function of
the Limbic System
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Rage and its association with the punishment
centers
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Effects of tranquilizers on the reward or punishment
centers
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Importance of reward or punishment in learning and
memory
Associative Learning (Fear Response)
Before Training – a
transient orienting
response is induced
to the sound
Training – sound is
paired with the shock
After Training –
placement in the box
induces freezing when
the sound is present.
Memory & Hippocampus
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Memory is the storage and retrieval of information
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The three principles of memory are:
– Storage – occurs in stages and is continually
changing
– Processing – accomplished by the hippocampus
and surrounding structures
– Memory traces – chemical or structural changes
that encode memory
Hippocampus
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Hippocampus and adjacent temporal and parietal
structures are called “hippocampal formation”
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This formation has connections with the cerebral
cortex, hypothalamus, septum, amygdala, limbic
cortex and mamillary bodies
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Hippocampus is hyperexcitable
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Epileptic sezures
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Less layers in the hippocampal cortex
Functions of Amygdala
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The amygdala is a complex multiple small
nuclei located immediately beneath the
cerebral cortex of medial anterior pole of
each temporal lobe
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It has abundant directional connections with
the hypothalamus and other parts of the
limbic system
Functions of Amygdala
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Effects initiated from the amygdala and sent through
the hypothalamus – mostly autonomic functions
Direct stimulation of amygdala results in several types
of involuntary movements
Bilateral ablation of amygdala (Klüwer-Bucy Syndrome)
– Not afraid of anything
– Extreme curiosity about everything
– Forgets rapidly
– Tendency to place everything in mouth & eating objects
– Strong sexual drive
Functions of Limbic Cortex
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Cerebral association areas for control of behavior