nervous tissue

• Nervous tissuecells

  Neurons, Glial Cells, Nerves

  
• Nervous system

  • Integration and control system involved in transmission of nerve impulses
  • Information (stimuli) is processed resulting in coordinated response of the body

  
• Response to stimuli

  Stimuli or information - nerve impulses - sensory neuron - CNS (spinal cord, brain) - motor neuron - target organ

  
• Neurotransmitters


  Rapid, Precise, Brief
• Anatomical division of nervous system

  • Central nervous system
  • Peripheral nervous system
• Functional division of nervous system

  • Sensory division
  • Motor division
• Central nervous system


  • Brain & Spinal Cord
  • Encased in skull & vertebral column

  
• Peripheral nervous system


  • Cranial Nerves, Spinal Nerves, Peripheral Nerves, Ganglia

  
• Sensory division


  Transmit impulses from periphery CNS (input)

  
• Types of sensory division

  • Somatic - perceived consciously
  • Visceral - not perceived consciously
• Motor division


  Transmit impulses from CNS periphery (output)
• Types of motor division

  • Somatic - voluntary
  • Autonomic - involuntary
• Sympathetic division


  • Increased heartbeat, blood pressure; sense of excitement
  • 'Fight or Flight or Freeze'
  • Thoracic & Lumbar Spinal Nerves
• Parasympathetic division


  • Slowing of heartrate, dilation of blood vessels, constriction of pupil
  • 'Rest and Relax'
  • Cranial & Sacral Spinal Nerves
• Enteric division


  • Forms plexuses: walls of Gastrointestinal tract, pancreas, gall bladder
• Nervous tissue

  • Embryonic origin: ECTODERM
  • Develop during the 3rd week of life
• Neural crest cells


  Cells of PNS
• Types of cells in nervous tissue

  • Neurons
  • Glial cells

  
• Neurons


  • Functional unit of the nervous system
  • Exhibits: excitability

  
• Glial cells


  • Supporting cells
• Excitability


  Ability to respond to environmental changes or stimuli
• Conductivity


  Respond to stimuli by initiating electrical signals that travel quickly to other cells at distant locations
• Secretion


  Upon arrival of the impulse at a distant location the neuron usually secretes a chemical neurotransmitter at a synapse that crosses the synaptic gap and stimulates the next cell
• Cell body (Perikaryon; Soma)

  • Nucleus – aggregates of cell bodies in the CNS
  • Ganglion/ganglia – cell bodies in the PNS
  • Gray matter
• Dendrites

  • Short, small processes emerging and branching off the soma; become thinner as they branch
  • Function: principal signal reception and processing site on neurons
  • Dendritic spines protrusions along the small dendritic branches
  • Initial processing site for synaptic signals
  • Morphology depends on actin filaments
  • Important in neural plasticity role in development of brain (embryo); learning, adaptation, & memory (adult)
• Axon

  • Function: conduct impulses away from the soma and sends it to effector/target organs or adjacent nervous tissue
  • Abundant mitochondria
  • Axon hillock –pyramidal shaped portion of soma where axons originate
  • Axoplasm (axonal cytoplasm) – contains sER, rER and long mitochondria
  • Axolemma – plasma membrane of axon
  • Axon terminals – ends of axon; axonal bulbs
• Myelin sheath


  • Insulating layer around a nerve fiber
  • Formed by oligodendrocytes in CNS and Schwann cells in PNS
  • Consists of the plasma membrane of glial cells
  • 20% protein and 80 % lipid
  • Function: Protection of the axon, Electrically insulating fibers from one another, Increasing the speed of nerve impulse transmission
  • Saltatory conduction – faster impulse conduction in myelinated

  
• Types of neurons by number of processes

  • Unipolar
  • Bipolar
  • Multipolar
  • Anaxonic

  
• Types of neurons by function

  • Sensory neuron (afferent)
  • Motor neuron (efferent)
  • Interneuron (association neuron)

  
• Synapse


  • Point of contact and site of transmission of a nerve impulse between a neuron and another cell (another type of cell, or another neuron)
  • Allow neurons to communicate with each other or with effector cells (target)
  • The nerve impulse can be excitatory or inhibitory

  
• Oligodendrocytes

  • Branched cells that wrap CNS nerve fibers
  • Fewer branches than astrocytes
  • Forms myelin sheath in CNS

  
• Astrocytes


  • Largest, most numerous, versatile, and highly branched glial cells
  • They cling to neurons and cover capillaries
  • GFAP – glial fibrillary acid protein
  • Intermediate filaments in the proximal regions of the processes; distal portion lack this
  • Marker used to detect Astrocytoma (a type of tumor in the brain)
  • Support and brace neurons
  • Anchor neurons to their nutrient supplies
  • Guide migration of young neurons
  • Control the chemical environment
  • Form scar tissues in damaged areas

  
• Ependymal cells


  • Simple Cuboidal Ciliated Epithelium
  • Epithelial cells that line ventricles and central cavities of brain and spinal cord – secrete cerebrospinal fluid (CSF)
  • Ciliated to help circulate CSF
• Microglia


  • Features: small cell bodies from which radiate many long, branched processes
  • Motile cells used in immune surveillance in the CNS
  • Phagocytic function in CNS
  • Originated from monocytes
• Schwann cells


  • Form myelin sheath around peripheral axons
  • Aka Neurolemmocytes
  • Node of Ranvier separates each Schwann cell
• Satellite cells


  • Surround neuron cell bodies within ganglia
  • Provide nutrients, remove metabolites etc
• Dura mater


  • Connected to the endosteum of the skull; dense irregular CT
  • Thickest, toughest
  • In the brain – areas called dural venous sinuses
  • In the spinal cord – forms epidural space

  
• Arachnoid mater


  • 2 layers: Sheet of CT in contact with dura mater, Trabeculae composed of collagen fibers and fibroblasts continuous with pia mater
  • Contains network (cobweb) of blood vessels
• Pia mater


  • Covers the brain parenchyma

  
• Blood-brain barrier (BBB)


  • Functional barrier between the brain and blood
  • Made up of: Capillary endothelium, Basement membrane, Foot processes of astrocytes (glia limitans)