HISTO LEC

• Nervous system


  Stimulus-response mechanism made up of well-coordinated interconnecting/intercommunicating network of cells and fibers linking all and every part of the body to coordinate all body activities in response to external and internal stimuli
• Integrating coordinating systems of the body

  • Nervous system
  • Endocrine system
• Neuroendocrine system


  Combined nervous and endocrine systems that coordinate metabolic activities
• Divisions of the nervous system

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
  • Autonomic Nervous System (ANS)
• Central Nervous System (CNS)

  • Consists of organs and structures located within the cranial cavity and vertebral canal
  • Includes brain and spinal cord
  • Brain consists of: Cerebrum, Cerebellum, Brainstem (Diencephalon, Midbrain, Pons, Medulla oblongata)
• Peripheral Nervous System (PNS)

  • Includes organs and structures located outside the cranial cavity and vertebral canal
  • Includes: 12 pairs of Cranial nerves, 31 pairs of Spinal nerves, Sympathetic, Peripheral and Spinal ganglia, Sensory receptors
• Autonomic Nervous System (ANS)


  • Also called "Vegetative/Involuntary/Visceral Nervous System"
  • Functional division of the Nervous System
  • Innervates viscera, smooth and cardiac muscles and glands which are all involuntary
  • Divided into Sympathetic & Parasympathetic
• Nervous tissue


  • Tissue that makes up the nervous system
  • Basic property: Conductivity (Conduction of nerve impulses)
  • Made up of cells and fibers
• Components of nervous tissue

  • Cellular component: Neurons/Nerve cells, Supporting Cells (Neuroglia/Glial Cells)
  • Nerve fibers
  • Blood-brain barrier

  
• Neurons


  • Structural and functional units of the NS
  • Number of neurons in the body: 1010 - 1011

  
• Parts of a neuron

  • Cell body or soma
  • Perikaryon
  • Nissl bodies
  • Neuronal protoplasmic processes: Axons, Dendrites
  • Axon collaterals
  • Synapses
  • Axon terminal
  • Axolemma
  • Axoplasm

  
• Classification of neurons based on function

  • Afferent/Sensory neurons
  • Efferent/Motor neurons
  • Internuncial/Interneurons/Central/Intercalated neurons

  
• Classification of neurons based on action

  • Inhibitory neurons
  • Excitatory neurons
  • Both Excitatory and Inhibitory

  
• Classification of neurons based on shape

  • Round/spherical/oval
  • Polyhedral/stellate/flask-shaped
  • Pyramidal
  • Polygonal

  
• Classification of neurons based on size

  • Dwarf neurons
  • Giant neurons
• Classification of neurons based on number of neuronal processes

  • Unipolar/ Pseudounipolar
  • Bipolar
  • Multipolar

  
• Classification of neurons based on axon length

  • Golgi Type I (long axons)
  • Golgi Type II (short axons)

  
• Classification of neurons based on location

  • Nuclei
  • Ganglia

  
• Neurons can be myelinated or unmyelinated
• Ganglia


  Only one process; usually the axon; no dendrites
• Amacrine cells of retina

  • No axons; have one dendrite
• Ganglion cells
• Bipolar neurons


  • 1 axon, 1 dendrite
  • Neurons of the special senses
  • In retinal, gustatory, vestibulocochlear, olfactory epithelium
• Multipolar neurons


  • Numerous dendrites; one axon
  • Motor neurons of the spinal cord
  • Internuncial neurons
  • Most of the cells in NS are multipolar

  
• Based on Axon Length


  • Golgi Type I (Long axons, originate in the CNS and terminates distant from its origin to the periphery, e.g. Cranial nerves)
  • Golgi Type II (Short axons, Terminates within the same vicinity, e.g. Purkinje cells of cerebellum)
• Based on location


  • Nuclei (clusters of neurons in the CNS, islands of gray matter/ clusters of nerve cell bodies in the CNS sharing a common function, e.g. Edinger-Westphal nucleus, red nucleus)
  • Ganglia (clusters of neurons in the PNS, e.g. Auerbach's plexus, Meissner plexus, Dorsal root ganglia)

  
• Neurons


  • Myelinated
  • Unmyelinated
• Schwann cells


  • Slender cells that synthesize myelin in the PNS
  • Form a sheathe called the Sheath of Schwann/ Neurilemmal sheath
  • Myelin in the PNS is rich in phospholipids
  • Schmidt-Lanterman clefts are oblique discontinuities in the Schwann sheath

  
• Ependymal cells


  • Cuboidal/columnar cells lining the ventricles of the brain and central spina canal that synthesize CSF
  • Beneath ependymal cell layer are numerous BV that form the choroid plexus
  • Choroid plexus is made up of ependymal cells + BV that synthesize CSF
  • Cells in the 3rd ventricle that interdigitate with the ependymal cells are called TANYCYTES

  
• Neuroglial/Neuroglial cells


  • Astrocytes
  • Oligodendrocytes
• Astrocytes


  • Largest neuroglial cell
  • Take part in the formation of tight junctions that make up the BBB (fluid and electrolyte balance)
  • Have "End-feet" that impinge on BV and neuron to form the BBB
  • Protoplasmic astrocytes form BBB in the gray matter
  • Fibrous astrocytes form BBB in the white matter
  • Specialized astrocytes include Bergman Glial cells in the cerebellum, Muller cells, and Pituicytes in neurohypophysis
• Oligodendrocytes


  • Synthesize myelin in the CNS
  • Myelin in CNS is rich in glycolipids
  • Interfascicular oligodendrocytes are located in between the fascicles and along and in between axons which they myelinate
  • Satellite oligodendrocytes are found in the cerebrum and cerebellum and myelinate several axons (unlike Schwann cells which myelinate one nerve fiber)

  
• Pontine nuclei


  • Motor
• Pontine nuclei, Transverse pontine fibers, Descending Longitudinal fibers (Pyramid) and facial nuclei

  3P's
• Pontine tegmentum is the upwards continuation of medulla posteriorly of pons
• Along the mid line lies the Raphae nuclei
• Medulla Oblangata


  • Lower most part of brainstem
  • Between pons and spinal cord at foramen magnum
  • Connected to cerebellum by inferior cerebellar peduncle
• Structures in Medulla Oblangata


  • Inferior olive
  • Hypoglossal nuclei
  • Pyramids
• The brain stem has no cortex but with grey matter

  
• Grey matter


  Makes up the nuclei, mostly nuclei of origin and nuclei of termination of the cranial nerves