Nervous Tissue

• Nervous tissue


  The main tissue component of the nervous system
• Nervous system


  The master controlling system of the body. It includes the brain, cranial nerves, spinal cord, and associated peripheral nerves

  
• Functions of the nervous system

  • Maintaining homeostasis
  • Receiving sensory input
  • Integrating information
  • Controlling muscles and glands
  • Establishing and maintaining mental activity
• Central Nervous System (CNS)

  Consists of the brain and the spinal cord. The major site for processing information, initiating responses, and integrating mental processes

  
• Peripheral Nervous System (PNS)

  Composed of cranial nerves, spinal nerves and their branches, ganglia and sensory receptors

  
• Divisions of the PNS

  • Sensory division
  • Motor division
• Sensory division


  Transmits action potentials to the CNS and usually consists of single neurons that have their cell bodies in ganglia

  
• Sensory division subdivisions


  • Somatic sensory
  • Autonomic sensory
• Somatic sensory


  Senses touch, pressure, pain, temperature, vibration and proprioception in skin, body wall and limbs
• Autonomic sensory


  Senses stretch, pain, temperature, chemical changes and irritation in viscera
• Motor division


  Transmits action potentials from the CNS to effector organs, such as muscles and glands
• Motor division subdivisions


  • Somatic motor
  • Autonomic motor
• Somatic motor


  Innervates skeletal muscle and is mostly under voluntary control. It consists of single neurons that have their cell bodies located within the CNS

  
• Autonomic motor


  Controls our unconscious activities, such as contractions of smooth muscle, cardiac muscle, and secretion by certain glands
• Nervous tissue


  Composed of neurons and neuroglial (supporting) cells

  
• Neuroglial cells


  • Astrocytes
  • Oligodendrocytes
  • Microglia
  • Ependymal cells
  • Schwann cells
  • Satellite cells

  
• Neurons


  Also called nerve cells, are the structural units of the nervous system. They receive stimuli and transmit action potentials to other neurons or to effector organs
• Components of neurons


  • Cell body
  • Nerve cell processes (dendrites, axon)

  
• Cell body


  Contains a single, relatively large, and centrally located nucleus with a prominent nucleolus. The cell body's nucleus is the source of information for protein synthesis
• Nuclei


  Clusters of neuron cell bodies in the CNS

  
• Ganglia


  A collection of neuron cell bodies located outside the CNS. Ganglia play an essential role in connecting the parts of the peripheral and central nervous systems

  
• Types of ganglia


  • Sensory ganglia
  • Motor ganglia
• Nerve cell processes


  Elongated cytoplasmic processes that take origin from the cell body and may travel long distances from neurons

  
• Types of nerve cell processes

  • Dendrites
  • Axons
• Dendrites


  Much shorter than axons and have multiple branches at their ends. Usually receive action potentials
• Axons


  Long, single fiber that usually conducts action potentials away from the cell body
• Myelinated axons


  Wrapped by several layers of plasma membrane from Schwann cells (PNS) or oligodendrocytes (CNS). Conduct action potentials rapidly

  
• Unmyelinated axons


  Conduct action potentials slowly

  
• Classification of neurons


  • Unipolar
  • Pseudo-unipolar
  • Bipolar
  • Multipolar

  
• Unipolar neurons


  Only one process present
• Pseudo-unipolar neurons

  One process that extends from the cell body and divides into two branches, one to the CNS and one to the periphery

  
• Bipolar neurons


  Have two processes: one dendrite and one axon
• Multipolar neurons


  Have many dendrites and a single axon. Most of the neurons within the CNS and motor neurons are multipolar

  
• Neuroglia


  Also known as glia or glial cells, are diverse cells that support, insulate, and protect neurons

  
• Neuroglial cells of the CNS

  • Ependymal cells
  • Astrocytes
  • Oligodendrocytes
  • Microglia

  
• Ependymal cells


  Arranged in a single layer, line the ventricles (cavities) of the brain and central canal of spinal cord. Responsible for the formation of Cerebrospinal fluid

  
• Astrocytes


  Star-shaped cells that help in providing nutrients to neurons, formation of blood-brain barrier, maintaining chemical environment, metabolism of neurotransmitter, and migration of neurons
• Oligodendrocytes


  Small round or oval cells that form myelin sheath around axons in CNS and form a supportive network around CNS neurons

  
• Microglia


  Thorny bushes appearance, become mobile and phagocytic in response to inflammation. The smallest glia, rarely found
• Neuroglial cells of the PNS

  • Schwann cells
  • Satellite cells