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Brain physiology-1-

Brain physiology-1-

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Cns 12 Cns 12 Presentation Transcript

    • Dr. Mohanad R. Alwan
  • The Diencephalon
    • Forms the central core of the forebrain and is surrounded by the cerebral hemispheres
  • The Diencephalon
    • The diencephalon consists of three structures
      • Thalamus
      • Hypothalamus
      • Epithalamu s
    • These structures effectively enclose the third ventricle
    Hypothalamus Thalamus Epithalamus View slide
  • Thalamus
    • The egg shaped thalamus makes up 80% of the diencephalon and forms the superolateral walls of the third ventricle
    View slide
  • Thalamus
    • The thalamus is composed of bilateral masses of gray matter held together by a mid- line commissure called the intermediate mass
    Thalamus Third Ventricle Intermediate mass
  • Thalamus
    • The thalamus has many different nuclei, most named for their location
    • Each of these nuclei has a functional specialization
    • Each projects fibers receives fibers from a specific region of the cerebral cortex
  • The Thalamus
    • Sensory inputs are not the only type of information relayed( communicate) 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
  • Thalamus
    • Afferent impulses from all senses and all parts of the body converge( meet) on the thalamus and synapse with at least one of its nuclei
    • Within the thalamus, a sorting-out and information “editing ” process occurs
  • Thalamus
    • Impulses having to do with similar functions are grouped together and then
    • relayed via the internal capsule to the appropriate area of the sensory cortex as well as specific cortical association areas
  • Thalamus
    • In addition to sensory inputs, virtually all inputs ascending to the cerebral cortex funnel through thalamic nuclei
  • = ANT-MED (limbic) = ANT-LAT (EPS) = POST (sensory) = NON-SPECIFIC (relay)
  • 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
  • Thalamus
    • Pulvinar, medial dorsal and lateral nuclei are involved in the integration of sensory information and projection to specific association cortices
  • = ANT-MED (limbic ) = ANT-LAT (EPS) = POST (sensory) = 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- to thal)
  • Mamillary bodies Cingulate gyrus Prefrontal ctx
  • Area 6 Area 4 GP, SN (EPS) Area 4 + EPS GP, SN, cerebellum (EPS + dentatothalamic tract)
  • Areas 3,1,2 Sensory--body Sensory--face Vision Hearing Area 17 Areas 41,42 Integration of somesthetic, visual, & auditory Areas 18,19
  •  
  • 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 sensations
    • 3. It is an integrating centre for sleep
    • 4 . 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 EEG
    • 7 .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
  • 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 limb
    • 4. Overreaction to pain
    • 5. visual field defect
    • 6. motor disturbances : abnormal movements, tremor, hemiparesis etc
  • The Hypothalamus
    • The hypothalamus is located below the thalamus, capping the brain stem
    Hypothalamus
  • Hypothalamus
    • Merging into the midbrain inferiorly, it extends from the optic chiasma to the posterior margin of the mammillary bodies
    Mammillary bodies Optic chiasma
  • Mammillary Bodies
    • The mammillary bodies are paired nuclei that bulge anteriorly from the hypothalamus which receive and relay olfactory impulses
  • Hypothalamus
    • Between the optic chiasma and the mammillary bodies is the infundibulum as a stalk of the hypothalamic tissue connects the pituitary gland to the base of hypothalamus
  • Hypothalamus
    • The hypothalamus contains about a dozen functionally important nuclei
    • Despite its small size, the hypothalamus is the main vital and visceral control center of the body and is vitally important to overall body homeostasis
  • Connections- Afferent
    • I. Limbic system - Medial forebrain bundle
    • - Stria terminalis
    • - Fornix - pre and post commissural fibers
    • - Medial corticohypothalmic tract
    • II Midbrain tegmentum ( It forms the floor of the midbrain which surrounds the cerebral aqueduct)
    • - adrenergic fibers
    • - serotonergic fibers
    • - nor adrenergic fibers
    • III Retina, thalamus , basal ganglia
    • - Retinohypothalamic tract
    • - Thalamohypothalamic tract
    • - Pallidohypothalamic tract
  • Connections- Efferent
    • Ventral pathways
    • Stria terminals amygdalae (are considered part of the limbic system)
    • Medial forebrain bundle
    • Mammillo-thalamic tract
    • Mammillotegmental tract
    • Hypothalamo-hypophyseal tract ( pertaining to the hypothalamus and pituitary complex).
    • Neurons having hypophysiotropic hormones
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  • Suprachiasmatic nuc (direct retinal input, circadian rhythms ) Preoptic area (Medial Preoptic Nuc) (sexually dimorphic, regulates Gonadotropic hormones) Ant Hypothal Nuc (dissipates heat, parasympathetic) Lat Nuc (appetite center, stim. induces eating, destruction causes starvation) Ventromedial Nuc (satiety center, stops eating) Dorsomedial Nuc (stim causes obesity & savage behavior) PVN & SON (produce oxytocin & ADH/vasopression H,) contain SUPRAOPTICO-HYPOPHYSIAL TRACT –and- Magno cellular Neuron Post Hypothal Nuc (conserves heat, sympathetic) P arvocellular PVN supraoptic nucleus SON
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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
  • 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( angry) , as well as those involved in the biological rhythms and drives of sex are found in the hypothalamus
  • 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
  • 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)
  • Body Temperature Regulation
    • Hypothalamic receptors in the preoptic region monitor the temperature of the blood flowing through the hypothalamus
  • 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
      • Hypothalamic centers also induce fever
  • 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)
  • HUNGER LACK OF FOOD REDUCED AVAILABILITY OF GLUCOSE CONTRACTIONS OF EMPTY STOMACH LOW TRIGLYCERIDE LEVELS IN FAT CELLS GLUCOSE RECEPTORS IN HYPOTHALAMUS (Satiety center) MECHANO- RECEPTORS IN STOMACH PANCREAS HUNGER LONG TERM SHORT TERM
  • 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
  • THIRST WATER DEFICIENCY OSMORECEPTORS IN SUPRAOPTIC AND SUPRA- VENTRICULAR NUCLEI OF HYPOTHALAMUS THIRST ADH SERETION BY PITUITARY WATER RETENTION BY KIDNEY
  • 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
  • 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
  • Control of Endocrine Functioning
    • The Hypothalamus acts as the helmsman (coordinator) 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 or hormone of love)
  • 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
  • Control of Circadian Rhythm
    • Circadian Rhythm: is a roughly 24-hour cycle in the biochemical, physiological, or behavioural processes of living entities, including plants, animals, fungi and bacteria
    • Adrenocorticotropic ( ACTH), GH, Melotonin, sleep waking cycle, body temperature rhythm, gonadotropin secretion and menstrual cycle
    • Diurnal variation: fluctuations that occur during each day
    • 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
  • Epithalamus
    • The epithalamus is the posterior portion of the diencephalon
    • It forms the roof of the third ventricle
    Epithalamus
  • 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
  • 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
    Pinal Body
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