THE CEREBRAL CORTEX

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THE CEREBRAL CORTEX

• Institute of Anatomy, 2nd Medical Faculty
• R. Druga

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NEOCORTEX

• Laminar pattern 6 layers
• 10 20 billion neurons
• 95 surface of the hemisphere

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NEOCORTEX, types of neurons

• Pyramidal neurons
• Apical and basal dendrites
• Dendritic spines
• Excitatory (glutamate)
• Homogenous group
• 60 70

• Non-pyramidal neurons
• Aspiny
• Heterogenous group
• Inhibitory (GABA)
• 30 40

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Pyramidal neurons Layer V. M I Golgi impregnation
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Projection neurons, excitatory, glutamate Long
axons
Local circuit neurons, inhibitory, GABA
Interneurons, short axons
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My investigations showed that the functional
superiority of the human brain is intimately
bound up with the prodigious abundance and
unusual wealth of forms of the so-called neurons
with the short axons. S. R. y Cajal Recuerdos
de mi vida. 1917. Interneurons are butterflies
of the soul. S.R. y Cajal 1923
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Characteristics of layers

• I.. Molecular layer local inhibitory
  interneurons
• II. External granular association neurons
• III. External pyramidal commissural neurons
• IV. Internal granular receives thalamocortical
  projections
• V. Internal pyramidal projecting neurons (basal
  ganglia, brain stem, spinal cord
• VI. Multiform layer corticothalamic neurons

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K.Brodmann, 1907, 1911
11 regions 52 areas
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Association areas
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Afferent neocortical connections

• Thalamic nuclei (thalamocortical fibers)
• Amygdala
• Claustrum
• Nc. basalis (Meynert)-cholinergic system
• Hypothalamus
• Raphe nuclei (serotonin)
• Locus coeruleus (noradrenalin)
• Subst. Nigra (VTA) - dopamin

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Excitatory connections in the neocortex

• Layer 4 termination of thalamocortical
  projections
• Layer 4 projects to layer 3
• Layer 3 projects to layer 5

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Efferent neocortical connections

• Thalamic nuclei
• Basal ganglia (striatum, amygdala, claustrum)
• Brain stem (pretectal area, tectum, nc. ruber,
  RF, nuclei of cranial nerves, pontine ncc., nc.
  gracilis, nc. cuneatus)
• Spinal cord ( corticospinal pathway,
  interneurons, motoneurons)

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Motor cortical area

• G. Fritsch and E. Hitzig (1870) demonstrated that
  electrical stimulation of the dogs frontal lobe
  results in contralateral muscular contractions
  (movements)

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Primary motor area M I

• Precentral gyrus, area 4
• Part of the cortex from which movements are
  easily produced by electrical stimulation
• Motor homunculus (overrepresentation muscles of
  the thumb, hand, face, tongue, somatotopic
  representation)
• Afferents S I, thalamic VL
• Efferents basal ganglia, thalamus, (VL) RF,
  superior colliculus, nc. ruber, RF, pontine
  ncc., spinal cort
• Control of distal muscles
• Damage produces paralysis of contralateral
  muscles (namely upper limb, tongue, facial
  muscles)

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Premotor area, PM

• Area 6
• Somatotopic representation of the body
  musculature, less precisely organized
• Efferents M I, basal ganglia, RF, Spinal cord
  (influences paravertebral and proximal limb
  musculature)
• Afferents thalamic VA (basal ganglia), S I,
• Preparation to move

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Supplementary motor area

• Area 6, medial surface of the hemisphere
• Somatotopic organization,less precisely organized
• Afferents thalamic VA (basal ganglia), parietal
  cortex
• Efferents MI, Basal ganglia, RF, Spinal cord
• Area is involved in organizing and planning the
  sequence of muscle activation

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Somatosensory area S I

• Postcentral gyrus
• Areas 3a, 3b, 1, 2
• Afferents VPL, VPM
• Efferents M I, thalamus (VPL, VPM), pontine
  ncc., nuclei of cranial nerves (V.), spinal cord
• 3a signals from muscle spindles
• 3b cutaneous receptors
• 2 joint receptors
• 1 all modalities

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Sensory homunculus
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LANGUAGE AREAS Broca patient losses the
ability to speak, produces single words, or
syllables. Understanding of language is
preserved. Often combined with agraphia.
Wernicke sensory or receptive aphasia,
spontaneous speech is fluent, but sounds are
often put together into meaningless words
word salad . Often combined with alexia the
inability to read.
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Auditory cortex

• Area 41
• Afferents auditory pathway (thalamic medial
  geniculate body)
• Efferents thalamus (medial geniculate body),
  inferior colliculus, associative cortical areas
  (what and where paths)

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Visual cortex

• Area 17, granular cortex
• Afferents visual pathway, thalamic lateral
  geniculate body
• Efferents thalamus (lateral geniculate body),
  area 18, 19, parietal cortex, temporal cortex.
• Dorsal stream parietal cortex (where rods,
  periphery of retina, area 7)
• Ventral stream temporal cortex (what- colors,
  form cones, central area of retina, area 37,
  inferior. temporal cortex

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Corpus callosum transekce
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Cerebral cortex

• All mammals depend on it
• A man without a cortex is almost vegetable,
  speechless, sightless, senseless (D. Hubel and T.
  Wiesel 1979).
• The cortex supports sensory perception,
  reasoning, planning and execution of behaviors

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