Cns 12
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Transcript of Cns 12
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The Diencephanlon
• Forms the central core of the forebrain and is surrounded by the cerebral hemispheres
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The Diencephalon• The diencephalon
consists of three structures– Thalamus– Hypothalamus– Epithalamus
• These structures effectively enclose the third ventricle
Hypothalamus
Thalamus
Epithalamus
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Thalamus
• The egg shaped thalamus makes up 80% of the diencephalon and forms the superolateral walls of the third ventricle
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Thalamus• The thalamus is
composed of bilateral masses of gray matter held together by a mid- line commissure called the intermediate mass
Thalamus
ThirdVentricle
Intermediatemass
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Thalamus• The thalamus has
many different nuclei, most named for their location
• Each of these nuclei has a functional specialization
• Each projects fibers to and receives fibers from a specific region of the cerebral cortex
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The Thalamus• Sensory inputs are not the only type of
information relayed through the thalamus
• Every part of the brain that communicates with the cerebral cortex must relay signals through the nucleus of the thalamus
• The thalamus can therefore be thought of as the gateway to the cerebral cortex
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Thalamus• Afferent impulses
from all senses and all parts of the body converge on the thalamus and synapse with at least one of its nuclei
• Within the thalamus, a sorting-out and information “editing” process occurs
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Thalamus• Impulses having to
do with similar functions are grouped together and relayed via the internal capsule to the appropriate area of the sensory cortex as well as specific cortical association areas
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Thalamus• In addition to
sensory inputs, virtually all inputs ascending to the cerebral cortex funnel through thalamic nuclei
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VA
VPL VPM
LGNMGN
Pulvinar
Ant
VL
MD
Int medullary laminaInt medullary lamina
Ext medullary laminaExt medullary lamina
THALAMIC NUCLEITHALAMIC NUCLEI
= ANT-MED (limbic)= ANT-MED (limbic)
= ANT-LAT (EPS)= ANT-LAT (EPS)
= POST (sensory)= POST (sensory)
= NON-SPECIFIC (relay)= NON-SPECIFIC (relay)
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= ANT-MED (limbic)= ANT-MED (limbic)
= ANT-LAT (EPS)= ANT-LAT (EPS)
= POST (sensory)= POST (sensory)
= NON-SPECIFIC (relay)= NON-SPECIFIC (relay)
VA/VL (GP+SN)
Ant+MD (Papez)
VPL (sensory--body)
VPM (sensory--head)
LGN (vision)
MGN (hearing)
Pulvinar (visual sensory association)
Intralaminar
CM (very diffuse to cerebral ctx, ends in layer I for cortical
excitability)
Reticular (GABA-ergic to thal)
VA/VL (GP+SN)
Ant+MD (Papez)
VPL (sensory--body)
VPM (sensory--head)
LGN (vision)
MGN (hearing)
Pulvinar (visual sensory association)
Intralaminar
CM (very diffuse to cerebral ctx, ends in layer I for cortical
excitability)
Reticular (GABA-ergic to thal)
VA
VPL VPM
LGNMGN
Pulvinar
Ret
icul
ar
Ret
icul
arAnt
VL
MDIntralaminar
Intralaminar
CMCM
THALAMIC NUCLEITHALAMIC NUCLEI
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VA
VPL VPM
LGNMGN
Pulvinar
Ret
icul
ar
Ret
icul
ar
Ant
VL
MDIntralaminar
IntralaminarCMCM
Mamillary bodies
Cingulate gyrus
Prefrontal ctx
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VA
VPL VPM
LGNMGN
Pulvinar
Ret
icul
ar
Ret
icul
ar
Ant
VL
MDIntralaminar
IntralaminarCMCM
Area 6
Area 4
GP, SN (EPS)
Area 4 + EPSGP, SN,
cerebellum (EPS +
dentatothalamic tract)
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VA
VPL VPM
LGNMGN
Pulvinar
Ret
icul
ar
Ret
icul
ar
Ant
VL
MDIntralaminar
IntralaminarCMCM
Areas 3,1,2
Sensory--body
Sensory--face
Vision
Hearing
Area 17
Areas 41,42
Integration of somesthetic, visual, & auditory
Areas 18,19
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Thalamus• Ventral posterior lateral nucleus
– General somatic sensory receptors (touch, pain pressure)
• Lateral geniculate body– Visual relay from retina
• Medial geniculate body– Auditory inputs
• Anterior nuclear group– Regulation of emotion and
visceral function• Ventral lateral nuclei
– Direct motor activity of cerebellum
• Ventral anterior nuclei– Direct motor activity of basal
nuclei
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Thalamus• Pulvinar, medial
dorsal and lateral nuclei are involved in the integration of sensory information and projection to specific association cortices
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Functions 1. It is a great sensory relay station and integrating centre
for most inputs before relaying to the cerebral cortex 2. It is the subcortical perception for some sensations3. It is an integrating centre for sleep4. It is concerned with recent memory and emotion 5. It is concerned with language function 6. It plays an imp role in genesis of synchronization of EEG7.Being incorporated in the motor loops it serves very imp
role in motor activity 8. It plays important roles by acting as a link between basal
ganglia and cerebellum with the cortex
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Thalamic syndrome
• Typically results due to damage of the posterior thalamic nuclei due to blockage of thalamogeniculate artery
1. Sensations from the opp. side of the body are diminished
2. Sensory ataxia 3. Thalamic phantom limb4. Overreaction to pain 5. visual field defect 6. motor disturbances : abnormal movements,
tremor, hemiparesis etc
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The Hypothalamus
• The hypothalamus is located below the thalamus, capping the brain stem
Hypothalamus
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Hypothalamus
• Merging into the midbrain inferiorly, it extends from the optic chiasma to the posterior margin of the mammillary bodies
Mammillarybodies
Opticchiasma
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Mammillary Bodies• The mammillary
bodies are paired nuclei that bulge anteriorly from the hypothalamus that serve as relay stations in the olfactory pathways
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Hypothalamus• Between the
optic chiasma and the mammillary bodies is the infundibulum
• A stalk of the hypothalamic tissue connects the pituitary gland to the base of hypothalamus
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Hypothalamus
• The hypothalamus contains about a dozen functionally important nuclei
• Despite its small size, the hypothalamus is the main visceral control center of the body and is vitally important to overall body homeostasis
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Connections- Afferent I. Limbic system - Medial forebrain bundle - Stria terminalis - Fornix - pre and post commissural fibers - Medial corticohypothalmic tract II Midbrain tegmentum - adrenergic fibers - serotonergic fibers - nor adrenergic fibers III Retina, thalamus , basal ganglia - Retinohypothalamic tract - Thalamohypothalamic tract - Pallidohypothalamic tract
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Connections- Efferent
• Ventral pathways • Stria terminals • Medial forebrain bundle • Mammillo-thalamic tract • Mammillotegmental tract • Hypothalamo-hypophyseal tract • Neurons having hypophysiotropic
hormones
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Suprachiasmatic nuc (direct retinal input, circadian rhythms)
Suprachiasmatic nuc (direct retinal input, circadian rhythms)
Preoptic area (Medial Preoptic Nuc) (sexually dimorphic, regulates gonadotropic
hormones)
Preoptic area (Medial Preoptic Nuc) (sexually dimorphic, regulates gonadotropic
hormones)
Ant Hypothal Nuc (dissipates heat,
parasympathetic)
Ant Hypothal Nuc (dissipates heat,
parasympathetic)
Lat Nuc (appetite center,
stim induces eating, destruction causes
starvation)
Lat Nuc (appetite center,
stim induces eating, destruction causes
starvation)
Ventromedial Nuc (satiety
center, stim stops eating, destruction causes obesity & savage behavior)
Ventromedial Nuc (satiety
center, stim stops eating, destruction causes obesity & savage behavior)
Dorsomedial Nuc (stim causes
obesity & savage behavior)
Dorsomedial Nuc (stim causes
obesity & savage behavior)
Arcuate Nuc (DOPA-ergic neurons
inhib prolactin release) TUBERO- INFUNDIBULAR
TRACT
Arcuate Nuc (DOPA-ergic neurons
inhib prolactin release) TUBERO- INFUNDIBULAR
TRACT
PVN & SON (produce oxytocin &
ADH/vasopression, destruction causes DI)
SUPRAOPTICO-HYPOPHYSIAL
TRACTMagnocellular
PVN
Post Hypothal Nuc (conserves heat,
sympathetic)
Post Hypothal Nuc (conserves heat,
sympathetic)
Parvocellular PVN
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Autonomic Control Center• The hypothalamus regulates involuntary
nervous activity by controlling the activity of autonomic centers in the brain stem and spinal cord
• In this role the hypothalamus influences– Blood pressure– Rate and force of heart contraction– Motility of the digestive system– Respiratory rate and depth– Secretion of sweat and salivary glands
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Center for Emotional Response
• The hypothalamus has numerous connections with cortical association areas, lower brain stem centers, and it lies at the center of the limbic system which is the emotional part of the brain
• Nuclei involved in the perception of fear, pleasure, and rage, as well as those involved in the biological rhythms and drives of sex are found in the hypothalamus
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Center for Emotional Response
• The hypothalamus acts through the autonomic nervous system to initiate most physical expressions of emotion– Physical manifestations of fear
• Pounding heart• Elevated blood pressure• Pallor• Sweating• Dry mouth
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Body Temperature Regulation• The body’s thermostat is in the
hypothalamus
• The hypothalamus receives input from the thermoreceptors located in other parts of the brain as well as in the body periphery
• Homeostatic adjustments are then made to either cool or heat the body (sweating or shivering)
• Hypothalamic centers also induce fever
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Body Temperature Regulation• Hypothalamic
receptors in the preoptic region monitor the temperature of the blood flowing through the hypothalamus
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Body Temperature Regulation
• According to signals received by the preoptic nuclei the hypothalamus initiates mechanisms to maintain relatively constant body temperature – Cooling / sweating– Heat generation / shivering
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Regulation of Hunger & Thirst• In response to
changing levels of glucose, amino acids, hormones, and salts in the blood, the hypothalamus regulates feelings of hunger and satiety (ventro- medial nuclei)
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HUNGER
LACK OF
FOOD
REDUCEDAVAILABILITYOF GLUCOSE
CONTRACTIONS OF EMPTYSTOMACH
LOWTRIGLYCERIDELEVELSIN FAT CELLS
GLUCOSE RECEPTORSIN HYPOTHALAMUS(Satiety center)
MECHANO-RECEPTORSIN STOMACH
PANCREAS
HUNGER
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Regulation of Water Balance• When body fluids become too
concentrated, hypothalamic neurons called osmoreceptors are activated
• These receptors excite hypothalamic nuclei that trigger the release of antidiuretic hormone (ADH) from the posterior pituitary
• ADH causes the kidneys to retain water
• The same conditions also stimulate hypothalamic neurons in the thirst center, causing to drink fluids
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THIRST
WATERDEFICIENCY
OSMORECEPTORSIN SUPRAOPTICAND SUPRA-VENTRICULARNUCLEI OFHYPOTHALAMUS
THIRST
ADHSERETIONBY PITUITARY
WATERRETENTION BY KIDNEY
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Regulation of Sleep-Wake Cycles
• Acting with other brain regions, the hypothalamus helps regulate the complex phenomenon of sleep
• It is responsible for the timing of the sleep wake cycle
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Regulation of Sleep-Wake Cycles• Hypothalamus
through the operation of its suprachiasmatic nucleus (our biological clock) sets the timing of the sleep-wake cycle in response to day-light darkness cues from visual pathways
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Control of Endocrine Functioning • The hypothalamus acts as
the helmsman of the endocrine system– By producing releasing
hormones, it controls the secretion of hormones by the anterior pituitary gland
– The supraoptic and paraventricular nuclei produce hormones (ADH and oxytocin)
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Formation of Memory
• The nucleus of the mammillary body receives many inputs from the major memory-processing structures of the cerebrum, the hippocampal formation and therefore may relate to memory formation
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Control of circadian rhythm
• ACTH, GH, Melotonin, sleep waking cycle, body temperature rhythm, gonadotropin secretion and menstrual cycle
• -Diurnal variation
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Endogenous circadian rhythms
• rhythms that last about a day• humans’ last around 24.2 h
Examples:-activity-temperature-waking and sleeping-secretion of hormones-eating and drinking
Circadian Rhythms
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Epithalamus
• The epithalamus is the posterior portion of the diencephalon
• It forms the roof of the third ventricle
Epithalamus
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The Epithalamus
• The epithalmus consists of one tiny group of nuclei and a small, unpaired knob called the pineal body
• This gland, which derives from ependymal glial cells, is a hormone secreting organ
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Epithalamus• The pineal gland
extends from the posterior border of the epithalamus
• The pineal gland secretes the hormone melatonin which signals the sleep- wake cycle
PinalBody
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The Epithalamus
• A cerebrospinal fluid-forming structure called a choroid plexus is also part of the epithalamus
ChoroidPlexus