The Nervous System part 3

28/02/2014 11:26

Nerves

Nerves are packages of axons in the peripheral nervous system whose principal function is to carry signals between the brain and the spinal cord and the rest of the body. There are different types of nerves, such as: Afferent, Efferent and Mixed Nerves, Cranial Nerves and Spinal Nerves.

  • Afferent, Efferent, and Mixed Nerves:The nerves that carry information from the sensory receptors to the central nervous system is known as afferent nerves. Efferent nerves are the one that carry signals from the central nervous system to the effectors. The mixed nerves contain both afferent and efferent axons.
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  • Cranial Nerves: there are 12 pairs of cranial nerves. Each cranial nerve pair is identified by a Roman numeral 1 to 12 also each nerve has a descriptive name (olfactory, optic, others) that identifies its function or location. The cranial nerves provide a direct connection to the brain for the special sense organs.
     
  • Spinal Nerves: there are 31 pairs of spinal nerves located along the spinal cord. The spinal nerves are mixed nerves that carry both sensory and motor signals. The 31 spinal nerves are split into 5 groups named for the 5 regions of the vertebral column.

Meninges

The main purpose of the meninges is to protect the central nervous system. There are three important layers: The Dura Mater, Arachnoid Mater and Pia Mater.

  • Dura mater: this layer is the thickest one and the most superficial layer of the meninges. It protects the nervous system from external damage, it contains the cerebrospinal fluid and provides blood to the nervous tissues.
     
  • Arachnoid mater: this is a much thinier layer that is located beneath the dura mater. This layer contains many fibers that conects it with the pia mater, those fibers, cross a space called subarachnoid space.
     
  • Pia mater: This layer is the delicate one that is on the outside of the brain and the spinal cord.
  • Fig 1. The meninges with the subarachnoid space (retrieved from: google images)
  • Fig 2. The meninges (retrieved from: google image)
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