Telencephalon

• Cerebral cortex is a dense layer of neuronal cells bodies that lines the outer surface of cerebral hemispheres just bellow the pia matter of meninges.

  
• Cerebral cortex has a convoluted apperception due to presence of many elevated rigdes of tissue - gyri alternating with grooves - sulci. Due to this architecture only about 1/3 of total area of cerebral cortex is seen
• Cerebral cortex has. 6 types of cells

  • Pyramidal
  • fusiform
  • stellate
  • horizontal cells of cajal-retzus
  • cells of martinotti
• Histologically the cerebral cortex is organized into 6 layers based on the types of cells and shape of the neuronal cell bodies

  1. Molecular layer
  2. External granular layer
  3. External pyramidal layers
  4. Internal granular layer
  5. internal pyramidal
  6. Multiform layer
• The molecular layer of cerebral cortex is the outermost layer.

  • predominantly axons and dendrites of pyramidal cells, glias cells, and horizontal cells of cajal-retzus.
  • Plays role in synaptic integration and communication
  • Contributes to cortical development thro acivity of cajal retzius cells and reelin secretion
• EXTERNAL granular layer is located just bellow molecular layer.

  • contains small pyramidal cells and granule cells.
  • receives input from other cortical areas
• External pyramidal layer: bellow external granular layer.

  • contains medium sized pyramidal cells that sends axons across other cortical areas and subcortical structures.
• Internal granular layer ( layer 5)

  • contains different types of granule cells and small pyramidal neurons and high concentration of horizontally arranged fibers
  • receives input from thalamus
• Internal pyramidal layer. (Layer 6)

  • medium sized to large pyramidal cells that send axons to subcortical structures (thalamus and brainstem)
  • in primary motor area it contains large pyramidal cells of betz
• Multimorphic layer (layer 6)

  • Contains diff kinds of neurons but mostly fusiform cells and small pyramidal cells.
  • send afferent fibers to thalamus connecting thalamus and cortex
• • Granular cells are afferent in connection
  • Pyramidal cells are efferent in nature
  • pyramidal cells are more pronounced in motor areas
  • granular cells are more conspicious in sensory areas
  • Neuroglias element: astrocytes, oligodendrocytes and microglias.
• Phylogenetically cortex can be classified into two different types:

  • neocortex: represents 90% of cortex. part of cortex that is evolutionary newer. characteristic 6-layered organisation with layers containing pyramidal cells and interneurons.
  • Allocortex: have different structur from cortex and fewer layers. Include regions such as olfactory cortex, hippocampus and parts of paracentral gyrus.
• Pyramidal cells


  Represent about 2/3 of all cortical neurons
• Pyramidal cells


  • Cell bodies are triangular in shape
  • Have an apical dendrite that extends towards brain surface
  • Have basal dendrite that spreads horizontally
• Pyramidal cells


  • Most abundant neurons in neocortex
  • Variants in density and morphology across different cortical layers
• Neurotransmitters of pyramidal cells

  Aspartate, glutamate
• Types of pyramidal cells

  • Small
  • Medium
  • Large
  • Giant cells of bets
• Function of pyramidal cells


  • Primary excitatory neurons of cerebral cortex
  • Transmit excitatory signal to other cortical areas
• Pyramidal cell function


  1. Receive input from other cortical neurons

  2. Receive input from thalamic nuclei and sensory receptor

  3. Integrate these inputs

  4. Generate action potentials along axons to other neurons within cortex and subcortical structures
• Stellate cells


  Start-shape interneurons
• Stellate cells


  • Small, oval shaped cell bodies
  • Multipolar dendrites radiating outwards in all directions
• Primary location of stellate cells

  Middle layers, particularly in sensory cortices: visual and auditory
• Function of stellate cells

  Inhibitory interneurons playing role in internal circuit
• Input to stellate cells

  From nearby pyramidal cells + interneurons
• Role of stellate cells

  Provide local inhibition of neighbouring neurons helping regulate activity of pyramidal cells
• Contribution of stellate cells

  Contributes to balance between excitation/inhibition within cortical circuit
• Types of stellate cells

  • Spiny stellate (use glutamate)
  • Non-spiny stellate (gabanergic)
• Cerebral cortex diagram

  
• telencephalon

  • aka cerebrum
  • largest part of the brain
  • responsible for many higher brain functions, including sensory perception, cognition, generation of motor commands, spatial reasoning, and language.

  
• Telencephalon consists of two cerebral hemispheres, which are further divided into lobes.

  • The surface of the telencephalon is marked by grooves called sulci and raised areas called gyri.
  • These structures increase the surface area of the cerebral cortex, allowing for a greater number of neurons and more complex brain functions

  
• • Cerebrum is made of 2 cerebral hemisphere which are completely separated from each orher by the medial longitudinal fissure
  • Each hemisphere is connected to each other by corpus callosum
  • Each hemisphere contain a cavity called lateral ventricle

  
• External features of cerebral hemisphere

  Each hemisphere has: 3 surfaces, 3 poles and 4 borders

  • 3 surfaces: Superiolateral: convex, related to cranial vault
  • Medial surface: flat and vertical: separated from opposite hemisphere by falx cerebri and longitudinal fissure
  • Inferior surface: irregular. Divided into orbital surface and tentorial surface separated from each other by stem of lateral sulcus.

  
• Borders of cerebral hemisphere

  1. Superiomedial border: separates superiolateral suf from medial
  2. Inferior boder: separates superiolateral from inferior surface
  3. Medial orbital border: separates medial suf from orbital suf
  4. Medial occipital border: separates medial suf from tentorial suf

  
• Lobes of cerebral hemisphere

  • Each hemisphere is divided into 4 lobes: Frontal, parietal, occipital, temporal And insular lobes

  The sulci separating the lobes are:

  1. Central sulci: Separates frontal lobe from parietal lobe.
  2. Lateral sulci: Separates frontal and parietal lobes from the temporal lobe.
  3. Parieto-occipital sulcus: Separates the parietal lobe from the occipital lobe.
  4. Calcarian sulcus: Located in the occipital lobe and involved in visual processing
• Brain sulci

  
• Sulci and gyrus on superiolateral surface

  1. Central sulci
  2. Lateral sulci

  On frontal lobe:

  • Precentral sulcus: in front of central sulcus
  • Precentral gyrus: in btw central and precentral sulci
  • Superior and inferior frontal sulci: divide area in front of precentral sulcus into: superior, middle and inferior frontal gyrus.
  • Ascending horizontal and anterior rami of lateral sulcus: subdivided inferior frontal gyrus into pars orbitalis, pars triangularis and pars opercularis.

  
• Sulci and gyrus on parietal lobe

  • Poscentral sulci: behind central sulcus and between them is postcentral gyrus
  • Intraprietal sulcus: behing postcentral gyrus. Divided into superior and inferior parietal lobules by intraparietal sulci
  • Ends of posterior ramus of lateral sulci and superior and inferior temporal sulcu invaded inferior parietal lobule dividing it into anterior part (supramarginal gyrus), middle (angular gyrus) and posterior parts.

  
• Sulci and gyri on temporal lobe

  1. Superior snd inferior temporal sulci: divided temporal lobe into superior, middle and inferior temporal gyri.

  
• Sulci and gyri on occipital lobe on superiolateral surface

  • Lateral occipital sulci: divided it into superior and inferior occipital gyri
  • Lunate sulcu separates these gyru from occipital pole
  • Area around parieto-occipital sulcus is the arcus parieto-occipitalis. It is separated from superior occipital gyrus by transverse gyri

  
• Sulci and gyri on medial surface

  • Central part of medial aspect of the hemisphere is occupied by corpus callosum (genu, body, splenium)
  • Bellow corpus callosum: septum pellucidum, formix and thalamus

  Gyri on medial surface:

  1. Cingulate gyri: btw corpus callosum and cingulate sulci
  2. Paracentral lobule: V-shaped gyrud around end of central sulci
  3. Medial frontal gyru: area btw cingulate gyri and superiomedial border
  4. Precuneus
  5. Cuneus
  6. Isthmus: btw splenium and calcarine sulcus
  7. Paraterminal gyri: in front of lamina terminalis
  8. Paraolfactory gyru: btw ant and posy paraolfactory sulci