Nervous tissue

• Nervous System

  • CNS
  • PNS
• Nervous System


  • Three major functions: Sensory - monitors internal & external environment through presence of receptors
  • Integration - interpretation of sensory information
  • Motor - response to information processed through stimulation of effectors
• Anatomical Divisions of Nervous System


  • Central nervous system (CNS)
  • Peripheral nervous system (PNS)
• Central nervous system (CNS)


  Consists of Brain and Spinal cord
• Peripheral nervous system (PNS)


  Consists all the neural tissue outside CNS (cranial, spinal and peripheral nerves)
• Ganglia


  Small group of nerve cells outside CNS
• Types of nerve cells in nervous system

  • Neurons or Nerve cell - processing, transfer, and storage of information
  • Neuroglia or Glial cell - support, regulation & protection of neurons
• Neurons


  • Primarily a tropic center/ nutritive center and genetic center
  • Nucleolus - spherical or oval
  • Chromatin pattern - finely dispersed or uncoiled (euchromatic)
  • Cytoplasm - contains Nissl's granules/substance/bodies (basophilic granule)
• Cell body / Perikaryon / Soma


  Neuron structure
• Dendrites


  Elongated processes extending from soma, specialized in receiving stimuli
• Axon


  Specialized in generating and conducting nerve impulses to other cells
• Myelinated axons


  Axons surrounded by myelin sheath, presence of myelin speeds up the transmission of action potentials
• Nodes of Ranvier


  Unmyelinated gaps left when myelin laid down in segments (internodes) along the axon
• Axons


  Conducts impulse away from soma
• Dendrites


  Conducts impulse towards soma
• Synapse


  Area where neuron communicates with another cell (muscle cell, another neuron attached or close to it)
• Components of a synapse

  • Pre-synaptic cell - Neuron that sends message
  • Postsynaptic cell - Neuron that receives message
  • Synaptic cleft - small gap that separates pre-synaptic membrane and post-synaptic membrane
  • Synaptic Knob (aka Synaptic Terminals / Terminal Buttons) - expanded portion of axon of presynaptic neuron; contain vesicles of neurotransmitters
• Structural classification of neurons

  • Anaxonic neurons - no anatomical clues to determine axons from dendrites, functions unknown
  • Bipolar neuron - two processes coming off cell body – one dendrite & one axon, only found in eye, ear & nose
  • Unipolar (pseudounipolar) neuron - single process coming off cell body, giving rise to dendrites (at one end) & axon (making up rest of process)
  • Multipolar neuron - multiple dendrites & single axon, most common type
• Functional classification of neurons


  • Sensory (afferent) neurons - transmit information from receptors of PNS to CNS
  • Motor (efferent) neurons - transmit motor information from CNS to effectors (muscles/glands/adipose tissue) in periphery of body
  • Association (interneurons) - transmit information between neurons within CNS; analyze inputs, coordinate outputs
• Nerves


  Axons of Neurons grouped together into organized bundles in the PNS
• Tracts/pathways


  Axons of Neurons grouped together into organized bundles in the CNS
• Anatomical organization of neurons


  • White matter - myelinated
  • Gray matter - unmyelinated
  • Ganglia - cell bodies of neurons clustered together in the PNS
  • Nuclei or Centers - cell bodies of neurons clustered together in the CNS
• Neuroglia (glial cells)


  Support neuronal survival and activities, more abundant in the mammalian brain than neurons
• Types of CNS Neuroglia

  • Astrocytes
  • Oligodendrocytes
  • Microglia
  • Ependymal cells
• Astrocytes


  Star shaped with central nuclei, most abundant glial cells in CNS, form barrier between capillaries and neurons (Blood-Brain Barrier), control chemical environment of CNS, create supportive framework for neurons
• Oligodendrocytes


  Create myelin sheath in the CNS, most common glial cells in the white matter, microscopically seen as small cells with rounded, condensed nuclei over unstained cytoplasm
• Microglia/Mesoglia


  Small phagocytic type, mesodermal in origin, "brain macrophages", phagocytize cellular wastes & pathogens together with neutrophils, increased in injury and infection
• Ependymal cells


  Cuboidal or columnar cells lining the cavities of CNS, line ventricles of brain & central canal of spinal cord, produce, monitor & help circulate CSF (cerebrospinal fluid)
• Types of PNS Neuroglia


  • Schwann cells or Neurolemmocytes
  • Satellite cells
• Schwann cells or Neurolemmocytes


  Produce myelin in jelly-roll like fashion, allows for potential regeneration of damaged axons, creates myelin sheath around most axons of PNS
• Satellite cells


  Serve as covering for the large neuronal cell bodies in the ganglia of PNS, support groups of cell bodies of neurons w/in ganglia of PNS with insulation, nutrition and regulation of their environment
• Two Anatomical Divisions


  • Central nervous system (CNS)
  • Peripheral nervous system (PNS)
• Two types of cells in nervous system


  • Neurons
  • Neuroglia / Glial Cells
• Types of GLIAL Cells

  • CNS neuroglia: astrocytes
  • oligodendrocytes
  • microglia
  • ependymal cells
  • PNS neuroglia: Schwann cells (neurolemmocytes)
  • satellite cells
• CNS


  The Brain and the Spinal Cord
• Brain and Spinal Cord

  • Nerve tissue, Connective tissues and Blood vessels
• Functions of CNS

  • To process and coordinate sensory data from inside and outside of body
  • Motor commands: control activities of peripheral organs (e.g. skeletal muscles, glands, etc.)
  • Higher functions of brain: intelligence, memory, learning, emotion
• Major Regions of CNS


  • Cerebrum
  • Cerebellum
  • Spinal cord
• Meninges


  3 layers of connective tissue covering the CNS
• Gray matter


  Mainly comprised of groups of neuron cell bodies, dendrites & synapses (connections between neurons)