Nervous Tissues

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


  • Elongated processes extending from soma
  • Specialized in receiving stimuli from the environment, from the sensory epithelial or from other neurons at unique sites called synapses
• Neuron structure: 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
• Neuron structure: Axon

  • 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 vs Dendrite

  • Axons conducts impulse away from soma
  • Dendrites conducts impulse towards soma
• Neuron structure: 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 there are

  • 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 - 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), Found in cerebrospinal ganglia or sensory ganglia located at the dorsal root of the spinal cord
  • Multipolar neuron - multiple dendrites & single axon, most common type, Ex: motor nerve cells of CNS and PNS
• Neuron Classification: Functional

  • Sensory (afferent) neurons - transmit information from receptors of PNS to CNS, most sensory neurons are unipolar, few are bipolar
  • Motor (efferent) neurons - transmit motor information from CNS to effectors (muscles/glands/adipose tissue) in periphery of body, all are multipolar
  • Association (interneurons) - transmit information between neurons within CNS; analyze inputs, coordinate outputs, most common type of neuron (approx. 20 billion), are all multipolar
• Anatomical Organization of Neurons

  • Axons of Neurons tend to group together into organized bundles
  • Nerves in PNS
  • Tracts/pathways in the CNS
  • Most axons are surrounded by myelin sheath
  • White matter- myelinated
  • Gray matter- unmyelinated
  • Cell bodies of neurons are clustered together
  • Called "Ganglia" in the PNS
  • Called "Nuclei or Centers" in the CNS
• Neuroglia (glial cells)


  • 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
• Neuroglia vs Neuron

  • Neuroglia divide; neurons do not
  • Neurons are excitable; most neuroglia are not
  • Most brain tumors involve neuroglial cells and not neurons
• Types of Glial Cells: 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)
  • Controls chemical environment of CNS
  • Create supportive framework for neurons
• Oligodendrocytes


  • With less processes and Shorter than other neuroglia
  • 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)
  • Myelinated axons transmit impulses faster than unmyelinated axons
• 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
• Two Anatomical Divisions of the Nervous System

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

  • Neurons
  • Neuroglia / Glial Cells
• Types of Glial Cells in the CNS

  • Astrocytes
  • Oligodendrocytes
  • Microglia
  • Ependymal cells
• Types of Glial Cells in the PNS

  • Schwann cells (neurolemmocytes)
  • Satellite cells
• CNS


  The Brain and the Spinal Cord
• Functions of the 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 the CNS

  • Cerebrum
  • Cerebellum
  • Spinal cord
• Meninges


  Three layers of connective tissue covering the CNS
• Gray matter


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


  Made by regions of the nervous system containing groupings of myelinated axons, composed of capillaries, neuroglia, nerve fibers
• CNS COVERING

  • Dura mater (Pachymeninx)
  • Arachnoid mater
  • Pia mater
• Dura mater (Pachymeninx)


  • Dense connective tissue
  • Separated from the periosteum by epidural space, which is loose connective tissue with thin walled veins and fat cells
  • Separated from arachnoid by subdural space
  • The tough outer layer of tissue that covers and protects the brain and spinal cord and is closest to the skull. The dura mater is one of the three layers that form the meninges. Derived from the Latin for tough mother (or hard mother)
• Arachnoid mater


  • Delicate impermeable membrane made up of loose connective tissue
  • Membrane has cobweb-like appearance
  • Devoid of blood vessels
• Pia mater


  • A vascular membrane closely investing the brain and spinal cord
  • Composed of loose connective tissue with fine elastic fibers