THE LIMBIC SYTEM€¦ · 1. Downwards to the reticular system and then to peripheral nerves through...
Transcript of THE LIMBIC SYTEM€¦ · 1. Downwards to the reticular system and then to peripheral nerves through...
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
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
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