09 Control and Coordination - part 06 - Human Nervous System

 

09 Control and Coordination - part 06 - Human Nervous System

Human Nervous System :

  • Nervous system in humans is well developed and complex. 
  • Broadly classified into three parts. viz, 
  1. CNS
  2. PNS and 
  3. ANS.
1. Central nervous system (CNS) : 
  • The brain and spinal cord are the parts of CNS which lie along the mid dorsal axis. 
  • Brain is enclosed within the brain box/cranium of the skull, whereas the spinal cord occupies the vertebral canal of the vertebral column. 
  • Inner to these bony coverings, are three protective membranes called meninges that protect the brain and spinal cord.
a. Dura mater : 
  • Outermost tough, non vascular, thick and fibrous meninx.
  • Attached to the inner side of the cranium. 
  • Separated from the underlying arachnoid mater by the subdural space, filled with a serous fluid.
b. Arachnoid mater : 
  • Middle, thin and non vascular layer of connective tissue.
  • Having web like appearance. 
  • Separated from the mater below by a narrow subarachnoid help in this process along with the astrocytes. 
  • space filled with cerebro spinal fluid - CSF.
c. Pia mater : 
  • Innermost delicate, highly vascular membrane
  • Lies in close contact with the CNS.
CSF (cerebrospinal fluid) : 
  • Lymph like extra cellular fluid secreted by choroid plexuses of pia mater.
  • Present inner to subarachnoid space in the ventricles of the brain within the central canal of spinal cord. 
  • Secreted by the pia mater, the choroid plexuses and the ependymal cells lining the ventricles of the brain and central canal of spinal cord. 
  • The three openings in the roof of medulla oblogata help in draining out the CSF from brain to the outside. 
  • The meninges and CSF act as a shock absorber.
  • Protect the brain and spinal cord from mechanical injuries. 
  • Maintains constant pressure inside cranium. 
  • Helps in exchange of nutrients and wastes between blood and brain tissue. 
  • Helps in the supply of oxygen to the brain.
  • Protects the brain from desiccation.
  • Slightly alkaline fluid with a specific gravity of 1.005. 
  • A total of 100 -120 cc of CSF is present in and around the CNS.
Curiosity Box:
  • CSF is released by the pia mater. 
  • Inside the ventricles/cavities of the brain, there is release of CSF by the choroid plexuses and the ependymal cells.
Do you know ?
Blood brain barrier (BBB) -
  • Keeps a check on passage of ions and large molecules from the blood to the brain tissue.
  • Endothelial cells lining the blood capillaries help in this process along with the astrocytes.

Always Remember :
  • CSF is continuously generated by the ependymal cells lining the ventricles and central canal and simultaneoulsy drained out of the brain into the blood stream.
  • CSF maintains a constant pressure inside the cranium. 
  • The nervous tissue is without lympatic vessels.

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