Nervous Tissue 1

• Nervous tissue


  Group of organs brought together for the purpose of making us react to the environment
• Nervous System


  • Formed by nerve cells (Neurons) and supporting cells (Glial cells)
  • Comprises of CNS and 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

  
• 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)
  • Includes Ganglia- small group of nerve cells outside CNS

  
• Two 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

  
• Cell body / Perikaryon / Soma


  Primarily a tropic center/ nutritive center and genetic center of a neuron
• Cell body / Perikaryon / Soma


  • Nucleolus - spherical or oval
  • Chromatin pattern - finely dispersed or uncoiled (euchromatic)
  • Cytoplasm - contains Nissl's granules/substance/bodies (basophilic granule)
• Dendrites


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


  • Specialized in generating and conducting nerve impulses to other cells (nerve, muscle or glands)
  • Starts as short pyramid-shaped initial segment called AXON HILLOCK
• Myelinated axons


  • Axons surrounded by myelin sheath
  • Presence of myelin speeds up the transmission of action potentials along the axon
  • Nodes of Ranvier- Unmyelinated gaps left when myelin laid down in segments (internodes) along the axon
• Axon Versus Dendrite


  • Axons conducts impulse away from soma
  • Dendrites conducts impulse towards soma
• Synaptic Terminal / Synapse


  • Unique sites in the neuron that send stimuli
  • Synapse -area where neuron communicates with another cell (muscle cell, another neuron attached or close to it)

  
• At the 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

  
• Neuron Classification: Structural


  • Anaxonic neurons
  • Bipolar neuron
  • Unipolar (pseudounipolar) neuron
  • Multipolar neuron

  
• Neuron Classification: Functional


  • Sensory (afferent) neurons
  • Motor (efferent) neurons
  • Association (interneurons)

  
• Anatomical Organization of Neurons

  • Axons of Neurons tend to group together into organized bundles
  • Most axons are surrounded by myelin sheath
  • Cell bodies of neurons are clustered together

  
• Glial Cells (Neuroglia)


  • Support neuronal survival and activities
  • More abundant in the mammalian brain than neurons
  • CNS, has very small amount of connective tissue and collagen; glial cells served as replacement for the cells of the connective tissues in some aspects
• Types of Glial Cells


  • CNS Neuroglia: Astrocytes, Oligodendrocytes, Microglia, Ependymal cells
  • PNS Neuroglia: Schwann cells (neurolemmocytes), Satellite cells

  
• Astrocytes


  • Star shaped with central nuclei
  • Most abundant glial cells in CNS
  • Form barrier between capillaries and neurons (Blood-Brain Barrier)
  • Controls chemical environment of CNS
  • Create supportive framework for neurons
• Oligodendrocytes


  • Create myelin sheath in the CNS
  • Most common glial cells in the white matter (color is due to the lipid concentrated in the membrane wrapped sheaths
  • Microscopically seen as small cells with rounded, condensed nuclei over unstained cytoplasm
• Microglia/Mesoglia


  • Small phagocytic type, mesodermal in origin
  • Small cells with short processes distributed evenly in the gray and white mater
  • "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
  • Embryo: ciliated
  • Adult: some are ciliated
  • Produce, monitor & help circulate CSF (cerebrospinal fluid)
  • Columnar to cuboidal in shape
• 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- one Schwann cell forms myelin sheath in one segment of an axon
• 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
• The central nervous system (CNS) consists of the brain and spinal cord.
• Neurons are specialized cells that communicate with one another through electrical impulses called action potentials.
• The peripheral nervous system (PNS) includes all other nerves outside of the CNS.
• Neurons have three main parts: dendrites, soma, and axon.
• Dendrites receive signals from other neurons and transmit them towards the cell body.
• Glial cells support and protect neurons by providing nutrients, removing waste products, and forming myelin sheaths around axons.
• The peripheral nervous system (PNS) is composed of nerves that extend from the CNS to other parts of the body, including sensory neurons that carry information into the CNS and motor neurons that transmit signals out of the CNS.
• Myelination is the process where glial cells wrap themselves around axons to increase conduction speed and efficiency of nerve signals.
• Dendrites receive signals from other neurons and transmit them to the cell body.
• Axons are long extensions from neurons that transmit information between different parts of the body.
• Axons carry nerve impulses away from the cell body to other neurons or effector organs such as muscles or glands.
• Axons carry information away from the cell body towards target tissues.
• Axons carry information away from the cell body to other neurons or effector organs such as muscles or glands.
• Glial cells support and protect neurons by providing nutrients, removing waste products, and forming barriers between different regions of the nervous system.
• Sensory receptors detect stimuli such as light, sound, touch, taste, smell, temperature, pain, pressure, vibration, and movement.