Diencephalon and telencephalon

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Diencephalon and telencephalon
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Surface structure

• medial surface of the diencephalon
• interthalamic adhesion or massa intermedia
  connects two thalami
• bundle of nerve fibers called stria medullaris
  thalami
• dorsal surface
• concealed by fornix, curves over the thalamus

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Components

• Diencephalon
• Thalamus, the largest component. Receives sensory
  information and involves emotion, memory, sleep
• Subthalamus, ventral to thalamus. reticular
  formation, red nucleus, and substantia nigra
  project fibers into subthalamus
• Epithalamus, dorsalmedial to thalamus. Includes
  pineal body
• Hypothalamus, outgrow into posterior pituitary,
  controls endocrine system

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Thalamus

• Almost all the nuclei send fibers to the cortex.
  However, there is no interconnection fibers among
  different nuclei groups within the thalamus.

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Thalamus

• Reticular nucleus
• not connected with the brain stem, unknown
  function
• Intralaminar nuclei
• Receive afferent fibers from reticular formation
  of the brain stem.
• Also receive collateral fibers from spinothalamic
  and trigeminothalamic fibers (main destination is
  the ventral posterior nuclei of thalamus), also
  receives fibers from cerebellum, and the globus
  pallidus. There is extensive connection between
  intralaminar nuclei and frontal, parietal lobes.
  Connection between reticular formation to cortex
  through this area involves alertness and
  consciousness. 

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Ventral group of Nuclei

• Medial geniculate body
• Afferent fibers
• inferior brachium fibers from inferior
  colliculus, which receive lateral lemniscus.
  Medial geniculate body receives fibers from both
  sides but predominately from contralateral side.
  The bilateral distribution is caused by crossed
  fiber from ventral cochlear nucleus and by the
  commissural fibers between the inferior
  colliculi.
• Efferent
• ipsilateral side of the temporal cortex,
  conscious awareness of sound, and the adjacent
  association area is responsible for hearing
  recognition with previous experience.

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Ventral group of Nuclei

• Lateral geniculate body
• has six layer of neurons (crossed fibers to 1, 4,
  6 and uncrossed fibers to 2, 3, 5)
• Afferent fibers
• fibers from optic nerve. Point to point project
  from retina to lateral geniculate body.
• Efferent fibers
• geniculocalcarine tract ipsilateral side of the
  occipital cortex

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Ventral posterior nucleus

• pathway for conscious awareness of somatic
  sensation, like pain, temperature info, touch,
  proprioception
• Afferent fibers
• all fibers of medial lemniscus, and most of the
  spinothalamic and trigeminothalamic tracts
• also fibers from vestibular nuclear complex and
  fibers from gustatory nucleus concerning with
  sensation about position, and taste,
  respectively.
• There is a detailed projection of the opposite
  body on the ventral posterior nucleus. The lower
  limb is represented in its dorsolateral part with
  upper limb in an intermediate position and the
  head the most medial. The importance (not area)
  of certain body part determines the area in the
  ventral posterior nucleus. Same as the cerebral
  cortex.
• Ventral posterior nucleus also receives afferent
  fibers involving taste, and vestibular
  information
• The medial region of the nucleus that receives
  info from head is also referred as ventral
  posteromedial division (VPm), the lateral portion
  for the rest of the body called ventral
  posterolateral division (VPl).
• Efferent fibers
• project to the somesthetic cortex of parietal
  lobe.

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Ventral lateral nucleus

• Includes posterior and anterior divisions. 
• Afferent fibers
• From cerebellum
• Efferent fibers
• Enter internal capsule and proceed to frontal lobe

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Other nuclei

• Posterior group of nucleus
• Associated with pain reception
• Lateral group of nuclei
• lateral dorsal nucleus part of the limbic system
• lateral posterior nucleus connected with the
  somatosensory associate ion area of the parietal
  lobe
• Medial group of nuclei
• mediodorsal nucleus may be related with memory,
  seen with Korsakoff's syndrome, and perception of
  pain
• Afferent fibers are from entorhinal cortex,
  amygdaloid body and corpus striatum
• medioventral nucleus little is known
• Anterior group of nuclei
• part of the limbic system

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Thalamic syndrome

• most often caused by vascular lesion, usually in
  ventral posterior region
• Opposite side of the body
• proprioception and the sensations of touch, pain,
  and temperature are affected contralaterally
• could also involve emotional disturbance

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Subthalamus

• sensory fasciculi
• includes medial lemniscus, spinothalamic tract,
  and trigeminothalamic tract
• substantia nigra and red nucleus extend from
  midbrain into subthalamus
• Efferent fiber from pallidus pallidus (part of
  the basal ganglia, more later) contained in two
  bundles, lenticular fasciculus and ansa
  lenticularis. Both terminate in the subthalamus.

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Fig 11-7
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Fig 11-8
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Epithalamus

• The epithalamus consists of the hebenular nuclei
  and the pineal gland.
• Habenular neuclei
• Afferent fibers are received through the stria
  medularis thalami
• Efferent fibers known as habenulointerpeduncular
  fasciculus terminate in the interpeduncular
  nuclei in the roof of the interpeduncular fossa.
  The interpeduncular nuclei influence neurons in
  the hypothalamus and preganglionic autonomic
  neurons via relays in reticular formation.

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Fig 11-9
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Fig 11-7
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Pineal gland

• influenced by light, regulate time and day night
  changes and onset of puberty in human

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Hypothalamus

• The hypothalamus can be divided into medial and
  lateral zones

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Medial Zone

• contains suprachiasmatic, tuberal, and mamillary
  regions.
• Within suprachiasmatic region, it contains
  supraoptic, paraventricular, suprachiasmatic and
  anterior nuclei
• Supraoptic large cells, above the optic chiasm
• Paraventricular nucleus large cells
• Both supraoptic and paraventricular nuclei
  secrete hormones (ADH and Oxytoxin), form the
  hypothalamo-hypophysial tract
• Suprachiasmatic neurons are releasing action
  potential spontaneously at rugular rhythm and
  pattern. Axons from retina leave the optic chisma
  and termiate into this area and regulate the
  light-dark cycle.
• Anterior nucleus some neurons in this area are
  twice as many in males as in females (one
  possible reason is females experience neuronal
  death after 4 yr. old)
• Tuberal region contains ventromedial,
  dorsomedial, and infundibular nuclei
• Mamillary region contains mamillary body and the
  posterior nucleus.

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Lateral Zone

• large nerve cells sparsely located and
  collectively constitute the lateral nucleus of
  the hypothalamus.
• Lateral zone includes the lateral tuberal nucleus
• Fibers of hypothalamus
• hypothalamus served as the main integrator of the
  autonomic and endocrine systems

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Afferent fibers

• Ascending afferents convey information of
  visceral origin
• Most of the ascending fibers originate from
  nuclei of reticular formation
• Medial forebrain bundle originates from septal
  area, with fibers originate from intermediate and
  lateral olfactory areas, conducts information
  related to basic emotional drives and the sense
  of smell, smaller in humans
• Fibers from amygdaloid body also involve smell
  and emotional drives by stria terminalis (arise
  from amygdaloid body and ends in the preoptic
  area, anterior nucleus, and the septal area).
• Fornix
• originates from hippocampal formation
  (hippocampus) and parahippocampal gyrusends in
  the hypothalamus

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Efferent fibers

• Originate from hypothalamus (paraventricular
  nucleus), starts as periventricular fibers
  underneath the third ventricle and continue into
  the dorsal longitudinal fasciculus in the
  periaqueductal gray matter of the midbrain. Some
  terminate into dorsal nucleus of vagus nerve and
  other may end in the intermediolateral cell
  column and sacral autonomic nucleus (via spinal
  cord). Thus the influence from hypothalamus to
  the preganglionic fibers of sympathetic and
  parasympathetic nervous system.
• Hypothalamus also influence cells in motor nuclei
  of trigeminal, facial nerves, nucleus of ambiguus
  and the hypoglossal nucleus to regulate muscles
  used in feeding and drinking. Motor neurons in
  spinal cord is also affected by hypothalamus thus
  in shivering response.
• Fibers originate from mamillary body
• mamillothalamic fasciculus project to anterior
  nuclei of the thalamus
• collateral branches of the fibers of the
  mamillothalamic fasciculus are also called
  mamillotegmental fasciculus, end in nuclei of the
  reticular formation of the midbrain and pons.

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Functional aspect of hypothalamus

• Stimulation of anterior hypothalamus( preoptic
  area and anterior nucleus)
• slowing heart rate, vasodilation, lowering blood
  pressure, salivation, increased peristalsis in
  the gastrointestinal gract, contraction of
  urinary bladder, sweating. Action of
  parasypathtic system.
• Stimulation of posterior and lateral nuclei
• sympathetic activation cardia accelaeration,
  elevation of blood pressure, cessation of
  peristalsis, dalation off pupil, hyperglycemia.
• Hypothalamus is also responsible for regulating
  temperature control, Neurons in anterior
  hypothalamus are sensitive to temperature
  changes. If temperature is high, heat loss
  mechanism will be activated including cutaneous
  vasodilation, sweating. Lesion of anterior
  hypothalamus gt hyperthemia.

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Functional aspect of hypothalamus

• Cells in posterior hypothalamus are responsible
  for lowering blood temperature, triggering heat
  conservation response, including coetaneous
  vasoconstriction, and shivering. Lesion in
  posterior hypothalamus impairs temperature
  regulation, causes hypothemia.
• Hypothalamus is also responsible for regulation
  food intake and water intake. Hunger or feeding
  center is located in the lateral zone and satiety
  center in the region of ventromedial nucleus.
  Lesion of ventromedial nucleus results excessive
  food intake and obesity.
• Hypothalamus and pituitary
• Hypothalamus constitute the posterior part of
  pituitary. Secrete ADH and Oxytoxin.