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No thalamus

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									                No. 25
   Telencephalon
        Ⅳ. The Telencephalon

   The telencephalon consists of right and
    left cerebral hemispheres, which together
    are referred to as the cerebrum.
   The cerebrum has an outer surface of gray
    matter and an inner white matter.
   The gray matter is composed primarily of
    nerve cell bodies and unmyelinated nerve
    fibers. This surface layer is called the
    cerebral cortex.
   The white matter is called medullary
    substance, which is composed of tracts
    of myelinated nerve fibers.
   Within the hemispheres, there are several
    masses of gray matter known as the
    basal nuclei.
   A fluid-filled cavity called a lateral
    ventricle is located within each cerebral
    hemisphere.
 Ⅰ) External Features and lobes of
  telencephalon
 Two hemispheres of cerebrum are almost
  completely separated by the cerebral
  longitudinal fissure.
 At the bottom of this fissure a large
  bundle of transverse fibers, the corpus
  callosum, crosses between the two
  hemispheres.
 The cerebral transverse fissure
  intervenes between the hemispheres and
  the cerebellum.
     1. The sulci, fissures, gyri and the lobes of the
    cerebrum
     1) The sulci, fissures, gyri
   The surface of the cerebrum has many rounded
    ridges called gyri (singular: gyrus). Separating
    the gyri are furrows. The deeper furrows are
    called fissures; the shallower ones are sulci
    (singular: sulcus). The folding of the cortex that
    produces the gyri and sulci makes the surface
    area of the cerebral cortex much greater than it
    would be if the brain’s surface were smooth. As it
    is, a significant percentage of the cerebral cortex
    is located in the fissures and sulci and is not
    visible from the surface.
   There are three constant sulci (or fissures) for
    demarcation on the surface of the hemispheres.
    ① The lateral sulcus begins as a deep furrow on
    the inferior surface of the hemisphere and runs
    posteriorly and upward onto the dorsolateral
    surface.
    ② The central sulcus runs from the lateral
    sulcus to the longitudinal fissure at right angle.
    Each hemisphere is further divided into a frontal
    lobe and a parietal lobe by the central sulcus.
    ③ The parietooccipital sulcus lies on the
    medial surface and separates the parietal and
    occipital lobes as its name indicates.
    2) The lobes of the cerebrum
   There are five lobes of each hemisphere.
   The hemisphere can be divided by these
    three sulci and an imaginary line into five
    lobes.
   The imaginary line is drawn from the
    upper end of the parietooccipital sulcus to
    the preoccipital notch which lies about 4
    cm anterior to the occipital pole on the
    inferolateral border. They are frontal,
    parietal, occipital, temporal lobes and
    insula.
    ① The frontal lobe
   The frontal lobe is the area in front of the
    central sulcus and above the lateral sulcus.
    ② The parietal lobe
   The parietal lobe is the area bounded by
    central sulcus, the imaginary line and the
    lateral sulcus.
    ③ The occipital lobe
   The occipital lobe is the area posterior to
    the imaginary line and the parietooccipital
    sulcus.
  ④ The temporal lobe
 The temporal lobe occupies the area
  inferior to the lateral sulcus and in front of
  the imaginary line.
 ⑤ The insula
 The insula lies deeply in the floor of the
  lateral sulcus, and is overlapped by
  portions of the frontal, parietal and
  temporal lobes.
    2. The gyri and sulci on the dorsolateral
    surface of the hemisphere
    1) In the frontal lobe
   Precentral sulcus and precentral gyrus
   Superior, middle, and inferior frontal
    gyri
   Superior, middle and inferior frontal
    sulci
    2) In the parietal lobe
   Postcentral sulcus and postcentral gyrus
   Intraparietal (or interparietal) sulcus
   Superior and inferior parietal lobules
   Supramarginal gyrus and angular gyrus
    3) In the temporal lobe
   Superior and inferior temporal sulci
   Superior, middle and inferior temporal gyri
   Transverse temporal gyri
    4) In the occipital lobe
   Not constant.
    3. The gyri and sulci on the medial and inferior
    surfaces of the hemisphere
    1) The gyri and sulci on the medial surface
   Paracentral lobule,
   Corpus callosum,
   Callosal sulcus,
   Cingulate gyrus and cingulate sulcus,
   Paracentral sulcus and Marginal ramus,
   Calcarine sulcus,
   Cuneus and Lingual gyrus,
    2) The gyri and sulci on the inferior surface
    ① The inferior surface of frontal lobe
   Olfactory bulb, olfactory tract and olfactory
    trigone,
   Anterior perforated substance.
    ② The inferior surface of temporal lobe
   Lateral and medial occipitotemporal gyri,
   Occipitotemporal sulcus,
   Collateral sulcus,
   Parahippocampal gyrus and uncus,
   Hippocampal sulcus,
   Dentate gyrus,
   Hippocampus,
   Hippocampal formation: It includes
    hippocampus and dentate gyrus.
   Limbic lobe: On the medial surface of the
    cerebral hemisphere, a large arcuate convolution
    formed primarily by the cingulate,
    parahippocampus gyri and the hippocampus and
    dentate gyrus surrounding the upper brain stem,
    constitute the limbic lobe.
 Ⅱ) Functional Localization of the Cerebral
  Cortex
 On the basis of the effects of electrical
  stimulation of specific areas of the
  cerebral cortex in humans, from observing
  the clinical manifestations of brain disease
  or damage in humans, and from the
  results obtained from detailed
  experiments on other mammals, it has
  been determined that certain areas of the
  cortex are related to specific functions.
   Some of these areas have been precisely
    mapped and numbered in a system called
    the Brodmann classification, but for our
    purposes it is sufficient to consider only
    the general locations of the major
    functional areas.
    1. First (Primary) somatic motor area, or
    motor center
    (1) Location
   It is located in the precentral gyrus and the
    anterior part of the paracentral lobule.
   It is equivalent to the 4 and 6 areas of the
    Brodmann classification.
    (2) Function
   The neurons of this area control the conscious
    and precise voluntary contractions of skeletal
    muscles.
   The axons of the neurons of this area form the
    pyramidal tract.
    (3) Characteristics
     ① Inverted image
    The projection of all parts of body in this area is
     inverted image, but the projection of head and
     face is the right image. The cortex of the upper
     1/3 part of precentral gyrus and the anterior part
     of paracentral lobule control the muscles of
     inferior limb. The middle 1/3 part of precentral
     gyrus manipulates the muscles of upper limb.
     The inferior 1/3 part of precentral gyrus
     manipulates the muscles of head and face.
    ② Crossed controlling
   The first somatic motor area controls the
    movement of contralateral limb.
    ③ Projection area in the motor center
   The projection areas of all parts of the
    body are related to the functions and
    meticulous level of the corresponding
    controlled region.
    2. First (Primary) somatic sensory area
    (general sensory area)
    (1) Location
   It occupies the postcentral gyrus and the
    posterior part of the paracentral lobule.
   It consists of areas 3, 1 and 2 of Brodmann’ map.
    (2) Function
   Within this area are the terminations of the
    sensory pathways that carry general sensory
    information concerning temperature, touch,
    pressure, pain, and proprioception from the body
    to the cortex of the brain.
 (3) Characteristics
 The projecting images in the primary
  sensory area of all the parts of body are
  similar to that in the primary somatic
  motor area.
  ① Inverted image
 The projection of all parts of body in this
  area is inverted image, but the projection
  of head and face is the right image. The
  inverted image of human body. The right
  image of head and face.
    ② Crossed controlling.
   The contralateral half of the body is
    represented as inverted.
    ③ Projection area
   The size of the cortical area for a
    particular part of the body is determined
    by the functional importance of the part
    and its need for sensitivity.
   Thus the area for the face, especially the
    lips, is disproportionately large, and a
    large area is signed to the hand,
    particularly the thumb and index fingers.
 3. The visual area
 It surrounds the calcarine sulcus on the
  medial surface of the occipital lobe,
  corresponding to area 17 of Brodmann’s
  map.
 This area contributes to the interpretation
  of visual experience.
 The chief source of afferent fibers to area
  17 area is the lateral geniculate nucleus of
  thalamus by way of the geniculocalcarine
  tract.
    4. The auditory area (acoustic area)
   It is located in the transverse temporal
    gyri corresponding to areas 41 and 42 of
    Brodmann’s map.
   This area contributes to the interpretation
    of acoustic experience.
   The medial geniculate nucleus of the
    posterior thalamus is the principal source
    of fibers ending in the acoustic cortex;
    these fibers constitute the acoustic
    radiation in the medullary center.
    5. Vestibular area
   It is located in front of superior temporal
    gyrus.
    6. Olfactory area
   In the medial part of uncus of
    parahippocampal gyrus.
    7. Gustatory area
    8. Visceral activation area
   In the limbic lobe.
     9. The language areas
   Four language cortical areas of special
    importance in language have been
    demonstrated. They are situated in the
    left hemisphere, with few exceptions, and
    this hemisphere is therefore the dominant
    hemisphere as a rule with respect to
    language.
    1) The motor speech area (Broca’s area)
   It occupies the posterior 1/3 portion of the
    inferior frontal gyrus (to Brodmann’s map 44 and
    45 ).
   Motor aphasia, caused by a lesion in Broca’s area.
    2) The writing area
   The posterior portion of the middle frontal gyrus
    (Brodmann’s map 8) is the written word area.
   Written aphasia is caused by a lesion in the
    written word area.
    3) The auditory speech area (sensory
    language area)
   This area occupies the posterior part of the
    superior temporal gyrus (Brodmann’ map 22).
   Sensory aphasia, in which comprehension of
    language, naming of objects, and repetition of a
    sentence spoken by the examiner are all
    defective, is caused by a lesion in the sensory
    language area, more specifically in sensory
    language area.
     4) The visual speech area (reading area)
   It locates in the angular gyrus (39 area if
    Brodmann).
   Visual aphasia is caused by a lesion in the visual
    speech area.
    Ⅲ) Internal Structures
   Each cerebral hemisphere includes a large
    volume of white matter constituting the
    medullary center, the basal ganglia and
    lateral ventricle.
    1. The basal nuclei
   Located deep within each cerebral
    hemisphere are several masses of gray
    matter known collectively as the basal
    nuclei.
    ① Caudate nucleus
   It is a long, arching nucleus, remaining in
    the wall of the lateral ventricle and grows
    around with it in C-shaped course. It
    consists of an anterior portion or head,
    which tapers into a slender tail extending
    backward and then forward into the
    temporal lobe and terminates at the
    amygdaloid nucleus.
    ② Lentiform nucleus
   It is subdivided into the putamen and the
    globus pallidus;
   The caudate nucleus and the lentiform
    nucleus are sometimes referred to as the
    corpus striatum.
   The caudate nucleus and putamen are
    new structures phylogenetically, which
    have the similar connections, so both
    together are called the neostriatum,
    while the globus pallidus is referred to as
    the paleostriatum.
    ③ Claustrum
   It is a thin layer of gray matter just deep to the
    cortex of the insula; between the insula cortex
    and the putamen of the lentiform nucleus, from
    which it is separated by the fibers of the external
    capsule.
    ④ Amygdaloid nucleus
   It is located at the tip of the tail of the caudate
    nucleus.
   The band of white matter located between the
    basal nuclei and the thalamus is called the
    internal capsule.
    2. The medullary center
   It composed of three kinds of fibers depending on
    the nature of their connections.
    1) The association fibers
   They are confined to a hemisphere connecting
    one cortical area with another.
   Superior longitudinal fasciculus,
   Inferior longitudinal fasciculus,
   Cingulum.
   Uncinate fasciculus.
   Arcuate fibers.
    2) The commissural fibers
   They connect the gyri in one hemisphere to the
    gyri in the other hemisphere.
   Corpus callosum:
   From forward back, it can be divided into 4 parts:
    the
   rostrum,
   genu,
   body,
   splenium.
   Anterior and posterior commissures.
    3) The projection fibers
   They are connections between the cortex and the
    subcortical structures. The fibers fan out as the
    corona radiata in the medullary center. The
    projection fibers are concentrated in the internal
    capsule.
   The internal capsule
   It is between the thalamus, caudate nucleus and
    lentiform nucleus.
   Constitution:
   It consists of an anterior limb, a genu and a
    posterior limb, which have topographic
    relationships with adjacent gray messes.
    ① Anterior limb
   The anterior limb is bounded by the lenticular
    nucleus and the head of the caudate nucleus.
   Projection fibers:
   Anterior thalamic radiation.
   Frontopontine tract.
    ② Genu
   The genu is medial to the apex of the lentiform
    nucleus.
   Projection fibers:
   Corticonuclear tract.
    ③ Posterior limb
   The posterior limb is bounded by the lenticular
    nucleus and the dorsal thalamus.
   Projection fibers:
   Central thalamic radiation (Thalamocortical
    tract).
   Corticospinal tract.
   Corticorubral tract.
   Parieto-occiptto-temporo-pontine tract
    (corticopontine tract).
   Optic radiation.
   Acoustic radiation.
   A lesion on one side of the posterior limb
    of the internal capsule may results in:
   “three hemiplegia syndorm”.
    a. the abnormalities of voluntary motion
    of the contralateral trunk and limbs
    b. the abnormalities of sensation of the
    contralateral half body.
    c. the blindness in contralateral halves of
    both visual fields.
 3. The lateral ventricles
 They are roughly C-shaped cavities lined
  by ependymal epithelium one in each
  cerebral hemisphere, and filled with
  cerebrospinal fluid.
 Each lateral ventricle consists of a body in
  the region of the parietal lobe from which
  anterior, posterior and inferior horns
  extend into the frontal, occipital and
  temporal lobes, respectively.
   The lateral ventricles communicate with
    the third ventricle through the
    interventricular foramen.
   Portions of lateral ventricle contain choroid
    plexus, formed by an invagination of pia
    matter covering layer of ependyma on the
    medial surface of the cerebral hemisphere.
    This plexus presents in the body and the
    inferior horn of the lateral ventricle and is
    the main structure for production of
    cerebral spinal fluid (CSF).
    Ⅳ) The Limbic System
   The limbic system is used to include the limbic
    lobe as well as associated subcortical structures,
    such as the amygdaloid complex,
    hypothalamus, epithalamus, anterior thalamic
    nuclei.
   Functions:
   The limbic system is concerned with:
    ① emotional and genesis, together with visceral
    response to the emotions
    ② survival of individual and species
    ③ processes involved in memory
   The limbic system is also known as the visceral
    brain because of its substantial influence on
    visceral functions through the autonomic nervous
    system.

								
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