Download LIMBIC SYSTEM

LIMBIC SYSTEM
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OBJECTIVES
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What is limbic system
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Structures included in limbic system
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Functions of limbic system
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Connections of limbic system
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The Brain and Memory
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LIMBIC SYSTEM
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The term limbic system is applied to the part of the brain that consists of a rim of
cortical tissue around the hilum of cerebral hemisphere and a group of associated
deep structures (amygdala, hippocampus and septal nuclei).
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The hypothalamus & limbic system are intimately concerned with emotional
expression and with genesis of emotion.
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Emotions have both mental and physical components.
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THEY INVOLVE :
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Cognition, an awareness of the sensation and usually its cause.
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Affect, the feeling of itself
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Conation, the urge to take action
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Physical changes, such as sweating, tachycardia and hypertension.
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The limbic system is a group of forebrain structures that form a border
around the upper part of brainstem and corpus callosum on the inner border
of cerebrum and the floor of diencephalon,
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Involved in emotion, motivation, learning and memory.
THE LIMBIC SYSTEM
The limbic (limbus –border) system named for the medial border of the
temporal lobe, is a loop of cortical structures surrounding corpus callosum
and thalamus.
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But still some neuroanatomists have argued that the components of this
system have so little in common that there is no point to calling it the limbic
system.
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Includes nuclei and tracts along the border between the cerebrum and the
diencephalon.
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Functional grouping rather than anatomical
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THE STRUCTURES INCLUDED IN THE LIMBIC SYSTEM
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The limbic system consists of a number of structures:
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The limbic lobe of cerebrum (consist of 3 gyri that curve along the corpus
callosum and medial surface of temporal lobe) is a rim of cerebral cortex on
the medial surface of each hemisphere and includes:
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Cingulate gyrus (cingul – belt) lies above the corpus callosum,
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Parahippocampal gyrus in the temporal lobe below.
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Hippocampus is a portion of the Para hippocampus gyrus that extends into
the floor of lateral ventricle.
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Dentate gyrus lies b/w hippocampus and parahippocampal gyrus.
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Amygdala (almond shaped) composed of several groups of neurons located
close to the tail of caudate nucleus
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Thalamic nuclei (anterior and medial) participate in limbic circuits.
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Mammillary bodies of hypothalamus close to the midline near cerebral
peduncles.
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Septal nuclei within the septal area formed by the regions under corpus
callosum and the paraterminal gyrus.
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The olfactory bulbs.
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The fornix and other tracts are linked by bundles of interconnecting axon.
Hypothalamus, frontal lobe…
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Information flows through the system in what is called the Papez Circuit and
loops around and around.
THE LIMBIC SYSTEM
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Refers to several forebrain structures that function together
o Cingulate gyrus
o Hippocampus
o Amygdala
o Septal nuclei
o Closed circuit of information flow between the limbic system and the
thalamus and hypothalamus
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Information flows through the system in what is called the Papez Circuit and
loops around and around.
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Limbic system and hypothalamus - cooperate in the neural basis of
emotional states.
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Limbic system  the center of emotion – anger, fear, sexual arousal,
pleasure, and sadness.
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It appears to be primarily responsible for our emotional life, and has a lot to do
with the FORMATION OF MEMORIES
COMPONENTS OF LIMBIC SYSTEM
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It includes :
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Nuclei called the amygdala and hippocampus on the medial side of temporal
lobe.
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A tract called the fornix leading to the mammillary bodies of the hypothalamus,
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A fold of cortex called cingulate gyrus that arches over the corpus callosum.
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THE LIMBIC SYSTEM
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The hippocampus is known as the "emotional brain" because it controls most of
the involuntary aspects of emotional behavior related to survival: feelings of
pleasure and pain such as anger, fear, and affection.
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THE BRAIN AND MEMORY
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The amygdala is an almond-shaped forebrain structure that is part of the
limbic system and is involved in emotion and memory.
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It encodes the emotional qualities associated with particular memories such
as fear or anger.
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THE AMYGDALA
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It is also involved in encoding memories of sensory stimuli that are
associated with rewards and punishment.
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If damaged or destroyed, the fear response may be impaired or destroyed
(ablation).
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A large projection from the hippocampus goes to the amygdala.
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Plays a major role in the emotional aspects of memory and learning.
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Stimulation of this area will cause “furious defensive reaction with aggressive
noises and gestures.
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Damage to this area removes fear.
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THE LIMBIC SYSTEM
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The prefrontal cortex plays an important role in memory, especially in the ability
to remember the order of information
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The cerebellum is involved in learning motor skills, classical conditioning of
simple reflexes, and other procedural memories (movement).
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FUNCTIONS OF LIMBIC SYSTEM
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The limbic lobe was formerly called rhinencephalon b/c of its relation to olfaction
but only a small part of it is actually concerned with smell.
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In addition to its role in olfaction, the limbic system is concerned with autonomic
responses (changes in BP & respiration)
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Along with hypothalamus it is also concerned with sexual behavior, the
emotions of rage and fear and motivation.
FUNCTIONS OF LIMBIC SYSTEM
Include:
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Establishing emotional states.
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Linking conscious cerebral cortical functions with unconscious functions of
the brainstem.
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Facilitating memory storage and retrieval.
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Plays a key role in emotions and works with the higher cerebral cortex to
control behavioral patterns.
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Aggression --> lesions of amygdala produce docility, while stimulation
results in rage and aggression
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Fear --> stimulation of amygdala and hypothalamus can produce fear, while
ablation (destruction) results in an absence of fear
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Goal-directed behavior - reward and punishment system- stimulation of
certain areas functions as a reward, while stimulation of other areas results
in a punishment shock.
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AFFERENTS & EFFERENTS CONNECTIONS
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The major connections of limbic system :
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The fornix connects the hippocampus to the mammillary bodies, which are in turn
connected to the anterior nuclei of the thalamus by the mammillothalamic tract.
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The anterior nuclei of the thalamus project to the cingulate cortex and from
there, connections to the hippocampus complete a complex closed circuit.
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This circuit was originally described by Papez and has been called Papez circuit
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CONNECTIONS
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Afferents:
o Much of cortex is reciprocally connected to entorhinal cortex
o Cholinergic and GABA input via septal nuclei
o Amygdala
o VTA, LC, Raphe
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Efferent
o Via the fornix
o Precommissural: septal nuclei
o Post- commissural: mammillary bodies (to anterior thalamic nucleus via
mammillothalamic tract)