Comparison between tract and nerve

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  Comparison between tract and nerve Nerve Nerve contain bundle of axons (nerve fibers) in the peripheral nervous system (PNS) that transmits signals between the central nervous system (CNS) and other parts of the body. It is the most important part of peripheral nervous system Location: Peripheral nervous system. Structure: Made of axons, connective tissue layers (endoneurium: axon is surrounded by it , perineurium: bundle of axons are surrounded by it, epineurium: whole nerve trunk is surrounded by it), and blood vessels. It gets myelination by Schwann cell   Function: Carries sensory signals to the CNS (afferent) from peripheral part of body or motor signals carry from from the CNS (efferent) to target organs like skeletal muscle, cardiac muscle, smooth muscle or glands Example: Sciatic nerve, median nerve, except optic nerve (though optic nerve is technically part of CNS in develop...
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Difference between granular, agranular, homotypical and heterotypical cortex

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Difference between granular, agranular, homotypical and heterotypical cortex or different cytoarchitectural composition of cerebrum

Classification Based on Cytoarchitecture (Cellular Composition)

  1. Granular Cortex (Koniocortex)
    • Description: it is well-developed layer IV (internal granular layer), rich in neuron , known as small granular (stellate) cells.
    • Function: it is done sensory processing (receives input from the thalamus).
    • Example:
      • Primary somatosensory cortex (Brodmann areas 3, 1, 2).
      • Primary visual cortex (Brodmann area 17).
      • Primary auditory cortex (Brodmann areas 41, 42).
  2. Agranular Cortex
    • Description: it is poorly developed or absent layer IV, contain neuron with large size known as  large pyramidal cells in layer V.
    • Function: it controls motor function  (sends output to spinal cord and brainstem).
    • Example:
      • Primary motor cortex (Brodmann area 4).
      • Premotor cortex (Brodmann area 6).
  3. Homotypical Cortex
    • Description: All six layers of cerebrum are well-developed and balanced in cell types.
    • Function: it is found in association areas, involved in higher cognitive functions (thinking, learning, planning).
    • Example: Prefrontal cortex, parietal association cortex.
  4. Heterotypical Cortex
    • Description: in this type of cerebrum or cortex one or more layers are disproportionately developed.
    • Type:
      • Granular heterotypical cortex (Sensory areas – thick layer IV, thin layer V).
      • Agranular heterotypical cortex (Motor areas – thin or absent layer IV, thick layer V).

Summary Table

Type of Cortex

Features

Function

Examples

Archicortex

3 layers

Memory & emotions

Hippocampus

Paleocortex

3-5 layers

Smell & emotions

Olfactory bulb

Neocortex

6 layer

Higher cognitive functions

Most of the cerebral cortex

Granular Cortex

prominent layer IV, small granular cells

Sensory processing

primary sensory, visual, auditory cortex

Agranular Cortex

thin/absent layer IV, large pyramidal cells in layer V

Motor control

Primary motor & premotor cortex

Homotypical Cortex

All 6 layers well-balanced

Higher cognition

Prefrontal, parietal association cortex

Heterotypical Cortex

Disproportionate layer development

Specialized processing

Sensory (granular), Motor (agranular)

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