C6

• Nervous system


  Provides an animal with sensitivity to environmental energy and thereby awareness of self and surroundings. It initiates and controls movement of most secretions, thus, responsible for the all inborn and learned behavior. The perception of internal and external stimuli is the primary function of the cells in the nervous tissue and the nervous system.
• Nervous system


  • Receives millions of bits of information from different sensory organs and integrates them to determine the response to be made by the body. Responsible for sending, receiving, and processing nerve impulses. All of the body's muscles and organs rely upon these nerve impulses to function.
• Anatomical divisions of the nervous system

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


  Consists of the brain and the spinal cord, is the integrating and communicating center of the body. Enclosed in a protective membrane called the meninges.
• Peripheral nervous system (PNS)


  Consists of the spinal and cranial nerves, including associated nerve roots and ganglia. Nerves and ganglia innervating viscera are designated as the autonomic nervous system (ANS), which is composed of the sympathetic and parasympathetic nervous systems.
• Geographic groupings of nerve cell and/or processes

  • Nerve
  • Tracts or fasciculi
  • Ganglia
  • Nuclei
• Principal cell types of the nervous tissue

  • Nerve cells or neurons
  • Supporting cells or neuroglia ("nerve glue") or glial cells
• Neuron


  The basic structural and functional unit of the nervous tissue. Primary function is to receive stimuli from the internal and external environment and transmit information to the effector organs of the body.
• Neurons


  • Highly specialized for irritability, conductivity, and the synthesis of neuroactive substances like neurotransmitters and neurohormones.
• Distinct regions of a single neuron

  • Dendritic zone
  • Telodendritic zone
  • Axons
  • Cell body (cyton, soma or perikaryon)
• Myelin sheath


  A coat of white, fatty tissue that covers nerves of the peripheral nervous system. Acts like insulation on a wire and greatly promotes speed and reliability of nerve impulse conduction.
• Nodes of Ranvier


  Small-constricted portions of the neuron's myelin sheath that separate the axon along the cells length. More permeable to potassium and sodium ions than the rest of the axon body, allowing nerve implies to be transmitted from the axon.
• Schwann's cell (neurolemma, neurolemmocytes)


  Layers of cells which cover the myelin sheath segments of some nerve cells, and constrict at the nodes of Ranvier. Provide a protected immediate environment for PNS neurons and can become phagocytic in case of nerve damage.
• Functional classification of neurons

  • Sensory (afferent) neurons
  • Motor (efferent) neurons
  • Interneurons (mixed)
• Types of neurons according to number of processes

  • Multipolar neurons
  • Bipolar neurons
  • Unipolar neurons (Pseudo-unipolar)
• Classification of synapses


  • Axodendritic synapse
  • Axosomatic synapse
  • Axoaxonic synapse
  • Dendrodenritic synapse
• Structural components of a synapse

  • Presynaptic membrane
  • Synaptic cleft (Synaptic Gap)
  • Postsynaptic membrane
• Types of neuroglial cells in the CNS

  • Ependymal cells
  • Astrocytes
• Astrocytes


  The largest neuroglial cells, consisting of fibrous astrocytes and protoplasmic astrocytes. Support neurons, repair CNS tissue after injury or disease, and form scar tissue after neuronal damage. May be involved in energy metabolism and supporting metabolic exchanges between neurons and capillaries.
• Neuroglial cells comprise well over 90% of the cells that make up the nervous system
• Neuroglial cells do not conduct impulses and are morphologically and functionally different from the neurons
• Types of neuroglial cells in the CNS

  • Ependymal cells
  • Astrocytes
  • Oligodendrocytes
  • Microglial cells
• Ependymal cells


  • Line the ventricular cavities of the brain and the central canal of the spinal cord
• Astrocytes


  • The largest neuroglial cells
  • Consist of two types: fibrous astrocytes and protoplasmic astrocytes
  • Attached to the walls of the capillaries
  • Support the neurons, repair the CNS tissue after injury or disease, and form scar tissue after neuronal damage
  • May be involved in the energy metabolism and supporting metabolic exchanges between neurons and the capillaries of the CNS
  • White matter contains fibrous astrocytes, gray matter contains protoplasmic astrocytes
  • Astrocyte processes terminate in expansions called the end feet
  • Collections of end feet form the glial limiting membrane at the CNS boundary
• Oligodendrocytes


  • Function by forming myelin sheaths around the axon in the CNS
  • A single oligodendrocyte can surround and myelinate numerous axons
• Microglial cells


  • Considered the macrophages of the CNS
  • Found throughout the CNS
  • Proliferate, become phagocytic, and remove dead tissue from the CNS when nervous tissue is injured or damaged
• Neuroglial cells in the PNS

  • Neurolemmocytes (Schwann's cells)
  • Satellite cells
• Neurolemmocytes (Schwann's cells)


  • Gliocytes in PNS that ensheath the axons or encapsulate nerve cell bodies as ganglionic gliocytes
  • Provide a protected immediate environment for PNS neurons
  • Can become phagocytic in case of nerve damage
• Satellite cells


  • Specialized Schwann's cells in craniospinal and autonomic ganglia
  • Form a one-cell-thick covering over the cell bodies of the neurons (ganglion cells)
  • Have spheric nuclei with mottled chromatin
  • Appear as a 'string of pearls' surrounding the much larger ganglion cell bodies
• Nerves contain axons of various size and their surrounding sheaths
• In the PNS, Schwann's cells surround all axons and extend along the length of peripheral axon, from its origin or its termination in the muscle or gland
• In the CNS, the cells that surround the axons of different size are the oligodendrocytes
• Unmyelinated axons


  Smaller axons, such as those of the autonomic nervous system, surrounded only by the cytoplasm of the Schwann's cell
• Myelinated axons


  Larger axons surrounded by an increased number of successive layers of plasma membrane of the Schwann's cell, forming the myelin sheath
• Nodes of Ranvier


  • Small gaps in the myelin sheath between individual Schwann's cells
  • Represent the discontinuity between the Schwann's cells along the axon
  • In these nodal regions, the axon is exposed to the extracellular environment
• Saltatory conduction


  The nerve impulse jumps from node to node in myelinated axons, resulting in a much more efficient and faster conduction of the impulse
• Larger, heavy-myelinated axons have the highest velocity of impulse conduction
• Classification of Neuron Types

  • Multipolar
  • Bipolar
  • Pseudounipolar
  • Unipolar
• Neuron Types by Function

  • Motor neurons
  • Sensory neurons
  • Interneurons
• Neuron Types by Neurotransmitter Released

  • Cholinergic neurons
  • Adrenergic and noradrenergic neurons
  • GABAergic neurons
  • Dopaminergic neurons
  • Seratonergic neurons
  • Glycinergic neurons