NERVOUS TISSUE PART 1

• Nervous System


  Group of organs brought together to make us react to the environment
• Nervous System


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

  
• 3 Major Functions of Nervous System

  • Sensory (Input) - monitors external and internal environment through presence of receptors
  • Integration - interpretation of sensory information
  • Motor (Output) - response to information through effectors

  
• Central Nervous System (CNS)

  • Consists of brain and spinal cord
  • Sensory activities, memories and emotions

  
• Peripheral Nervous System (PNS)

  • Cranial, spinal and peripheral nerves (all neural tissue outside CNS)
  • Includes Ganglia - small group of nerve cells outside CNS
  • Motor activities

  
• Sensory Division


  • Afferent - from latin "ADHERENS" or "to bring to"
  • Towards the brain

  
• Motor Division


  • Efferent - "to carry out" or "away" or "bring forth"
  • Away from the brain
• Somatic Nervous System


  • Voluntary
  • Skeletal muscle contractions
• Autonomic Nervous System (ANS)


  • Involuntary
  • Autonomic regulation of smooth and cardiac muscle, glands and fat tissues (adipose)
• Division of ANS


  • Sympathetic - fight and flight
  • Parasympathetic- rest or relax
• Neurons or Nerve Cells


  • Process
  • Transfer
  • Storage
• Cell Body


  • Also known as perikaryon or soma
  • Nutritive and genetic center of a neuron

  
• Parts of Cell Body

  • Nucleolus - spherical or oval
  • Chromatin Pattern - finely dispersed or uncoiled (euchromatic)
  • Cytoplasm - contains Nissl's Granules/bodies (basophilic granules)
  • Nissl's granules - large masses of polysomes and RER - Indication of high rate of protein synthesis
• Dendrites


  • Elongated processes extending from soma
  • Receives stimuli from the environment or other neurons at synapses

  
• Axon


  Generates and conducts nerve impulses to other cells
• Parts of Axon


  • Axon Hillock - initial segment that connects CB and Axon
  • Myelinated Axons - axons surrounded by myelin sheath (Schwann Cells) - speeds up the transmission of action potential along the axon
  • Nodes of Ranvier (internodes) - Unmyelinated gaps when myelin is laid in segments
• Synaptic Terminal (Synapse)


  Sites that sends stimuli
• Types of Synapse


  • Pre-synaptic cell - neuron that sends message
  • Postsynaptic cell - receives message
  • Synaptic Cleft - gaps that separates presynaptic and postsynaptic membrane
  • Synaptic Knob (Synaptic Terminal) - Expanded portion of axon of presynaptic neuron - neurotransmitters

  
• Structural Classification of Neurons

  • Anaxonic Neuron - Cannot differentiate axons from dendrites
  • Bipolar Neuron - One dendrite and one axon
  • Pseudounipolar or Unipolar Neuron - Dendrites at one end and axon at the rest of processes
  • Multipolar - Multiple dendrites and one axon

  
• 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

  
• Anatomical Organization of Neurons

  • Axons tends to group together in organized bundles - Nerves in PNS, Tracts/pathways in CNS
  • Most are surrounded by myelin sheath - White Matter = Myelinated, Gray Matter = Unmyelinated
  • Cell bodies, clustered together - Ganglia in PNS, Nuclei or Centers in CNS

  
• Glial Cells or Neuroglia


  • Support neuronal and survival activities
  • Support cells of CNS
  • Replacement of cells in connective tissue
• Characteristics of Glial Cells


  • More abundant in mammalian brain
  • Does not synapse with other cells
  • Has small amount of connective tissue and collagen
  • Only nuclei are seen
• Differences between Neuroglia and Neurons

  • Neuroglia - Divides, Involves Brain Tumors, Not Excitable
  • Neurons - Does not divide, Does not involve Brain Tumors, Excitable

  
• Types of Glial Cells in CNS


  • Astrocytes - star-shaped w/ central nuclei, Most abundant in CNS. Blood-Brain Barrier
  • Oligodendrocytes - Lesser processes and shorter than others, Small rounded, condensed nuclei over unstained cytoplasm. Creates Myelin Sheath in CNS.
  • Microglia - Also known as "mesoglia", Phagocytic, Small and short processes. Brain Macrophages.
  • Ependymal Cells - Cuboidal or columnar cells that lines the cavities of CNS. Produce, monitor and circulate CSF
• Types of Glial Cells in PNS

  • Schwann Cells - Creates myelin sheath in most axons of PNS (jelly-roll like fashion)
  • Satellite Cells - Serves as covering for large neuronal cell bodies