THE LIMBIC SYTEM

By

Dr. Sumaira Iqbal

LEARNING OBJECTIVES

By the end of the session, students should be able to

• Understand the activation of brain

• Explain the physiological anatomy of limbic system

• Explain the functional roles of limbic system

– Hypothalamus

– Hippocampus

– Amygdala

• State the lesions of various parts of limbic system

Activation of cerebral cortex

• Cerebral cortex is activated in two ways

– By direct stimulation of neuronal activity in wide areas of brain

– Neurohormonal system

Direct stimulation

• Bulboreticular facilitatory (excitatory) area

• Located in reticular substance of pons and mesencephalon

• Send excitatory signals to cerebral cortex in upward direction

• Excite thalamus followed by signals to cerebral cortex

• Excitation depends the signals from periphery and feedback signals back to cortex

Neurohormonal control

• Norepinephrine system

• Dopamine system

• Serotonin system

• Acetylcholine system

• Others include GABA, Glutamate, ACTH, enkephalins, vasopressin

Neurohormonal control

1. Norepinephrine system

• Excitatory hormone----increase activity

• Located in locus ceruleus---bilaterally and posteriorly at junction of pons and mesencephalon

• Role in dreaming and REM sleep

Neurohormonal control

2. Dopaminergic system

• Excitatory as well as inhibitory hormone

• Located in substantia nigra in the superior part of mesencephalon

• Send nerve endings to caudate and putamen

• Inhibitory to basal ganglia and excitatory to some areas of brain

Neurohormonal control

3. Serotonin system

• Several thin nuclei in midline of midbrain and pons----raphe nuclei

• Inhibitory hormone

• Fibers both upward and downward

• Suppress pain

• Role in normal sleep

Neurohormonal control

4. Acetylcholine system

• Acetylcholine excitatory hormone

• Gigantocellular neurons of reticular area of pons and mesencephalon

• Send signals both upward and downward----reticulospinal tract

THE LIMBIC SYTEM

• Named by Paul Broca

• Limbic means border

• Comprised of structures forming a border between hypothalamus and cerebral cortex

• Plays a role in emotions, learning and autonomic regulation

THE LIMBIC SYTEM

• Function as interconnection of cortical and subcortical structures

• Major centre for processing of information between the hypothalamus and cortical areas

THE LIMBIC SYTEM

• Parts of cerebral cortex

• Allocortex

• Also named as limbic cortex

• 3 layers

– Cingulate gyrus

– Parahippocampal gyrus

– Dentate gyrus

THE LIMBIC SYTEM

• Parts of diencephalon

– Hypothalamus

– Thalamus

– Subthalamus

– Mamillary body

– Hippocampus

– Amygdala

THE LIMBIC SYSTEM• Structures forming limbic system are

– Olfactory pathways

– Anterior perforated substance

– Pyriform lobe

– Septal area

– Amygdaloid body

– Limbic cortex

– Hippocampal formation

– Elements of diencephalon

– Bundles of axons connecting the above region

HYPOTHALAMUS

• Diencephalic structure, below the thalamus

• Less than 1% of brain mass(4g )

• A group of nuclei

– Anterior group – preoptic, supraoptic, paraventricular

– Middle group – dorsomedial, ventromedial, lateral, tuberal

– Posterior group – posterior, mamillary body

HYPOTHALAMUS

• Send signals in three directions

1. Downwards to the reticular system and then to peripheral nerves through autonomic nervous system

2. Upwards towards higher centers of diencephalon and cerebral cortex especially to the limbic cortex and thalamus

3. To the pituitary gland

The hypothalamus also divide anteroposteriorly into four regions

PreopticAdjoins lamina terminalis

Supraoptic (chiasmatic)Lie above optic chiasma

Tuberal(infundibulotuberal)includes infundibulumtubercinereum

Mamillary(posterior)consists ofmamillary

body andarea above it)

Medial Zone(Periventricular and

intermediate)Lateral Zone

Preoptic region Preoptic nucleus

Supraoptic region Paraventricular nucleusSuprachiasmatic

nucleus

Suprachiasmaticnucleus

Tuberal region Dorsomedial nucleusVentromedial nucleusArcuate/infundibular

nucleusPremamillary nucleus

Lateral tuberalnucleus

Mamillary or posterior region

Posterior nucleus Tuberomamillarynucleus

Mamillary body Mamillary nuclei

FUNCTIONS OF HYPOTHALAMUS

• ENDOCRINE FUNCTIONS

• NON-ENDOCRINE FUNCTIONS

– Vegetative functions

– Sexual functions

– Behavioral functions

– Body rhythm control

ENDOCRINE FUNCTIONS

• Regulation of uterine contraction and milk ejection

– Release of oxytocin--- paraventricular nuclei

• Regulation of osmolality

– Supraoptic & Para ventricular nuclei

– Osmoreceptors – AV3V Region

• Release of inhibitory and releasing hormones

ENDOCRINE FUNCTIONS

• Regulation of water balance

–Regulation of thirst

• Lateral hypothalamus

–Regulation of osmolality

• Supraoptic & Para ventricular nuclei

• Osmoreceptors – AV3V Region

ENDOCRINE FUNCTIONS

• Regulation of uterine contractility and milk ejection

– Release of oxytocin by paraventricular nuclei

• Contraction of myoepithelial cells in breast

• Contraction of uterus towards end of pregnancy

NON-ENDOCRINE FUNCTIONS1. VEGETATIVE FUNCTIONS:

• Regulation of autonomic nervous system

– Hypothalamus – head ganglion of ANS

– Parasympathetic – anterior & medial parts

– Sympathetic – posterior nuclei

• Regulation of CVS

– Vasomotor center

• Regulation of arterial pressure

– Increase HR and BP – lateral and posterior

– Decrease HR and BP – preoptic area

1. VEGETATIVE FUNCTIONS:

• Temperature regulation

– Posterior nuclei – anti fall

– Anterior nuclei– anti rise

• Regulation of food intake

– Hunger, eating – lateral nuclei

– Satiety – ventromedial nuclei

– Partially contributes in food intake, control of feeding reflexes like licking the lips and swallowing---- mamillary body

2. Sexual Functions

– Amygdala

– Stria terminalis

– Piriform cortex

– Few anterior and posterior portions of hypothalamus

3. Behavioral functions

i. Appetitive functions

ii. Defense

iii. Motivation

Appetitive Function

• Thirst

– Lateral hypothalamus

• Hunger

– Lateral hypothalamus (opp to ventromedial nucleus)

– Perifornical area

– Arcuate nuclei

– Paraventricular nuclei

• Satiety

– Ventromedial nuclei

Defense

• RAGE

– Lateral hypothalamus

– Perifornical area

• FEAR

– Thin zone of Periventricular nuclei

– Amygdala

Motivation

• REWARD– lateral hypothalamus

– ventromedial nuclei

– Amygdala

• PUNISHMENT– Periventricular nuclei

– Central grey area of aqueduct of sylvius

– Amygdala

– Hippocampus less potent

4. Body Rhythm Control

– Sleep-wakefulness cycle

– Diurnal rhythm- SCN

5. Memory and learning

• Reward and punishment centers

• Hippocampus (consolidation)

Clinical Physiology

• Bilateral lesion to lateral hypothalamic nuclei

• Decrease drinking and eating

• Decrease activity

• Passivity

Clinical Physiology

• Bilateral lesion to ventromedial hypothalamic nuclei

• Increase drinking and eating

• Increase activity/overactivity

• Tremendous obesity

Clinical Physiology

• Tranquilizers-----inhibits the reward and punishment center

• FOCAL EPILEPSY

– Overexcitation of hippocampus

– Bilateral removal for treatment of epilepsy

Clinical Physiology

KLUVER BUCY SYNDROME

Due to ablation of anterior temporal cortex

• Not afraid of anything

• Extreme curiosity

• Forgetfulness

• Extreme sexual drive

CLINICAL PHYSIOLOGY

Ablation of posterior orbital frontal cortex

• Insomnia

• Restlessness

Ablation of anterior cingulate and subcallosalgyri

• Rage center is over activated

THANK YOU