Diencephalon Physiology
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Transcript of Diencephalon Physiology
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DIENCEPHALON PHYSIOLOGY
HYPOTHALAMUS, THALAMUS & EPITHALAMUS
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OUTLINE
• Introduction
• Hypothalamus
• Nuclei
• Endocrine & Vegetative functions
• Emotion and other behaviours
• Thalamus
• Nuclei
• Thalamus and Sensation
• Thalamus and Motor function
• Thalamic syndrome
• Epithalamus
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INTRODUCTION TO DIENCEPHALON
• Literally means “between-brain” (or b/n brain stem and cerebrum)
• The third ventricle is a narrow midline cavity within the diencephalon.
• The diencephalon, together with the telencephalon (cerebrum), constitutes the forebrain
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HYPOTHALAMUS
• Most inferior portion.
• Located below the thalamus.
• Less than 1% of total brain volume.
• Center for homeostasis.
• Centers for behavioral drives.
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HYPOTHALAMUS: NUCLEI
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HYPOTHALAMUS: ENDOCRINE AND VEGETATIVE FUNCTIONS
• Regulation of the Pituitary Gland
• Pituitary gland immediately inferior to the hypothalamus.
• Releasing and inhibiting hormones.
• Supraoptic: produce ADH.
• Paraventricular: Oxytocin.
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HYPOTHALAMUS: ENDOCRINE AND VEGETATIVE FUNCTIONS
• Regulation of Circadian Rhythms
• Suprachiasmatic nuclei (SCN) is the major region.
• Electrical activity that oscillates automatically.
• SCN influenced by way of tracts from the retina.
• Synchronized to the day/night cycles.
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HYPOTHALAMUS: ENDOCRINE AND VEGETATIVE FUNCTIONS
• Cardiovascular Regulation
• Different areas of the hypothalamus can cause many neurogenic effects.
• Posterior and lateral hypothalamus: inc AP and HR.
• Preoptic area: dec AP and HR.
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HYPOTHALAMUS: ENDOCRINE AND VEGETATIVE FUNCTIONS
• Body Temperature Regulation
• Body’s “thermostat” is located.
• Preoptic-anterior hypothalamus.
• Correct deviations in a negative feedback fashion.
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HYPOTHALAMUS: ENDOCRINE AND VEGETATIVE FUNCTIONS
• Body Water Regulation
• Creates sensation of thirst.
• Thirst center: lateral hypothalamus.
• Control excretion of water in the urine.
• Supraoptic nuclei: secretes ADH.
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HYPOTHALAMUS: ENDOCRINE AND VEGETATIVE FUNCTIONS
• Gastrointestinal and Feeding Regulation
• Lateral hypothalamic area: hunger.
• Damage causes the animal to lose desire for food.
• Ventromedial nuclei: satiety center.
• If damaged the animal can’t be satiated obesity.
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HYPOTHALAMUS: EMOTION AND OTHER BEHAVIORS
• Interacts with limbic system to influence behavior and emotions.
• Stimulation of visceral responses during emotional situations.
• A major part of the limbic system.
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HYPOTHALAMUS: EMOTION AND OTHER BEHAVIORS
• Sends signals in three directions:
• Backward and downward to the brain stem.
• Upward toward many higher areas of the diencephalon and cerebrum.
• Into the hypothalamic infundibulum.
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THALAMUS
• Bilateral ovoid mass of gray matter
• 80% of diencephalon.
• Intermediate mass or interthalamic adhesion.
• Hypothalamic sulcus
• Thalamus (except reticular nucleus) --------Cerebral cortex
• All part of Cerebral Cortex -------- Thalamus
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THALAMIC NUCLEI ANATOMIC CLASSIFICATION:
Lateral Group of nuclei Medial Group of Nuclei
Anterior Group of Nuclei
Other Nuclei
Ventral Group Dorsal Group
Centromedian N.
Reticular Nucleus
Ventral Anterior/Lateral N.
Pulvinar N Midline Nucleus
Intralaminar Nuclei
Ventral Posterior N(VPL, VPM)
Lateral Posterior N.
Dorsomedial N.
Medial Geniculate body
Lateral Dorsal N.
Lateral Geniculate Body
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THALAMIC NUCLEI ANATOMIC CLASSIFICATION:
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FUNCTIONAL DIVISION OF THALAMIC NUCLEI
• Specific Relay Nuclei: project to specific parts of Cerebral cortex
Specific relay nuclei Cortical Projection sites
LGB Visual Cortex
MGB Auditory Cortex
VPL Somatosensory Cortex (trunk & limbs)
VPM Somatosensory Cortex (head)
Ventral Lateral (afferent from basal ganglia & Cerebellum)
Motor cortex
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FUNCTIONAL DIVISION OF THALAMIC NUCLEI
• Association Nuclei: project to association cortices
• Afferent: from cerebral cortex
• Efferent: only to cortical association areas
Association Nuclei Cortical Projection sites
Lateral Dorsal Cingulate gyrus & Precuneus
Lateral Posterior Parietal Association cortex
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FUNCTIONAL DIVISION OF THALAMIC NUCLEI
• Non-specific Nuclei: project to wide areas of the cortex.
• Afferent from Ascending reticular activating system
• Efferent to: Hypothalamus, Limbic system & Cerebral Cortex
• Function:- They increase cortical excitability and responsiveness
• Subcortical Nuclei: these nuclei don’t project to the cortex. E.g. Reticular nucleus (projects to other thalamic nuclei)
Nonspecific Nuclei Projection sites
Intralaminar Diffuse cortical areas
Anterior Nuclei Limbic structures
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FUNCTIONS OF THALAMUS
• Sensory functions
• Center for sexual sensation (perception of sexual sensations)
• Role in arousal & alertness reactions (because of its connections with nuclei of reticular formation)
• Center for reflex activity
• Center for integration of motor activity
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THALAMUS AND SENSATIONS
• The nervous pathways of somatic sensations:
• Dorsal Column pathway
• Spinothalamic Pathway
• Trigeminal pathway
• Other pathways related to thalamus:
• Visual pathway through LGN of thalamus
• Auditory system through MGN of thalamus
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THALAMUS AND SENSATIONS
• Trigeminal pathway:
• Sensation of head’s pain, temperature, tactile & proprioception.
• 1st order neurons: primarily from trigeminal ganglion to trigeminal nuclei.
• 2nd order neurons: from the nuclei to both ipsilateral and contralateral VPM of thalamus (primarily contralateral)
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THALAMUS AND SENSATION: SENSORY FUNCTIONS
• Relay center for sensations:
• Almost all sensations reach thalamic nuclei (particularly VPM, VPL) to be processed before reaching cerebral cortex
• Center for processing of sensory information and functional gateway for cerebral cortex
• All the peripheral sensory impulses reaching thalamus are integrated and modified before being sent to specific areas of cerebral cortex
• Determining the Affective nature of sensations
• Affective nature is the capacity to determine whether a sensation is pleasant or unpleasant and agreeable or disagreeable
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THALAMUS AND MOTOR FUNCTION
• Through the connections with cerebellum and basal ganglia, thalamus serves as a center for integration of motor functions.
• Role in arousal/wakefulness & alertness reactions (because of its connections with nuclei of reticular formation)
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THALAMIC OR DEJERINE-ROUSSY SYNDROME
• Cause blockage (due to thrombosis) in thalamogeniculate branch of posterior cerebral artery leading to infarction of posteroventral part of thalamus.
• Medial and Intralaminar nuclei are not affected in this syndrome.
• Symptoms are:
• Loss of all sensations (anesthesia) initially but weeks later pain sensibility regained due to facilitation of medial and intralaminar nuclei
• Astereognosis
• Sensory Ataxia (loss of kinesthetic sensation)
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THALAMIC OR DEJERINE-ROUSSY SYNDROME
• Symptoms continued….
• Thalamic Phantom limb: the illusion of limb loss
• Anosognosia
• Lack of awareness or denial of existance of a neurological defect or general illness or any disability
• Involuntary Movements like intention tremor
• Thalamic/Athetoid Hand
• Abnormal attitude of hand w/c wrist moderately flexes and all fingers hyperextend
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EPITHALAMUS
• Dorsal segment of the diencephalon.
• Choroid plexus over the third ventricle.
• Contains the pineal gland
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EPITHALAMUS: PINEAL GLAND
• Secretes the hormone melatonin.
• Helps regulate circadian rhythms.
• Lacks direct nervous connections to the rest of the brain.
• Highly innervated by SNS.
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EPITHALAMUS: PINEAL GLAND
• SCN of the hypothalamus regulates pineal secretion.
• Through hypothalamic control of SNS.
• Activity of the SCN + secretion of melatonin:
• Increase with darkness.
• Decrease with light.
• Neural pathways from retina depress activity of SCN.
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EPITHALAMUS: PINEAL GLAND
• Different functions of Melatonin:
• Powerful free-radical scavenger and wide spectrum antioxidant.
• Have positive immunological effect.
• Involved in the initiation of puberty.
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REFERENCE:
• John Mendoza, Anne Foundas; Clinical Neuroanatomy: A Neurobehavioral Approach
• K Sembulingam, Prema Sembulingam; Essentials of Medical Physiology 6th edition, 2012
• Martini, Timmons, Tallitsch; Human Anatomy 7th edition, 2012
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