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The central nervous system

The Brain

The brain is the most important part of the system, as it is the main communication centre and contains 100 billion neurons.  The brain receives and stores messages as well as transmitting them to all parts of the body to stimulate organs to do their work.  As the brain is such a vital organ, it has various safety features designed to protect it.  It is protected firstly by the cranial bones of the skull then by the cranial meninges, then finally the subarachnoid space.

The brain is responsible for:

  • Storing messages that it receives from all different parts of the body via the sensory nerve endings
  • Transmitting messages via motor nerves to all different parts of the body to stimulate the required response
  • Co-ordinating the body’s movements
  • Controlling feeding
  • Controlling sleeping patterns
  • Controlling temperature regulation
  • Controlling salt/water balance in the body
  • Storing information in our memory
  • Emotional and intellectual processes

The brain is protected by the bones of the skull, whilst the spinal cord is protected by the vertebrae.

A connective tissue called the meninges surrounds the central nervous system, and is made up of three layers.

The dura mater layer is an outer sheath, whilst the pia mater layer is attached to the surface of the organs. This layer nourishes underlying tissue through its supply of blood vessels.

The arachnoid mater layer provides space for the blood vessels and the circulation of cerebrospinal fluid. Not only does the central nervous system contain neurones, it also has another type of nervous tissue known as neuroglia.

Neuroglia cells are a type of connective tissue that supports and nourishes the neurones. They are smaller cells than the neurones and are found in large numbers.

The cerebrum (forebrain) is the largest portion of the brain.  It is a dome shaped area of nervous tissue split into two halves:

  • The left hemisphere – which controls the right side of the body.  In most people the left hemisphere is more important for language, numerical and scientific skills
  • The right hemisphere – which controls the left side of the body.  The right side is the creative side and is important for musical and artistic ability.

The grey matter on the surface of the brain is made up of nerve cell bodies and is where the main functions of the cerebrum are carried out.  These include all conscious activities such as touch, taste, smell, hearing, vision and all voluntary muscular movement.  The cerebrum also controls the powers of reasoning, learning, emotion and memory.

The white matter of the brain and spinal cord consists of nerve fibres (axons) in white myelinated sheaths.

Cerebellum

The cerebellum deals with movement.  It helps to control our balance and posture.  It maintains muscle tone and co-ordinates muscles during activities such as walking and running.  It is also responsible for learning skills such as playing the piano or riding a bike.  It is found in the posterior aspect of the brain.

 

Medulla Oblongata

The medulla oblongata is a mass of grey matter that is the continuation of the spinal cord.  It controls what you have no conscious control over such as regulating the heart and breathing rates, constriction and dilation of the blood vessels, body temperature and the reflex actions of sneezing, coughing, vomiting and swallowing.

Pons 

The pons forms a bridge (pons is Latin for bridge) that transmits messages between the spinal cord, cerebellum and cerebrum.  It controls what you have no conscious control over such as blood pressure or body temperature.

Thalamus

The thalamus co-ordinates impulses from sense organs such as the skin, eyes, nose and taste buds before they reach the cerebrum.

Hypothalamus

The hypothalamus controls the activities of the autonomic nervous system and an endocrine gland called the pituitary gland.  The hypothalamus is one of the main regulators of homeostasis, helping to maintain a constant internal environment in the body.

 

The spinal cord

The spinal cord is a continuation of the medulla oblongata and extends downwards through the vertebral column, finishing on a level with the lumbar vertebrae.  It is protected by the vertebral column, 3 meninges and the cerebro-spinal fluid.

The functions of the spinal cord are:

  • It conveys sensory impulses from one area of the spine to another and from the skin and muscles of the trunk and limbs to the brain
  • It allows and co-ordinates spinal reflex actions, which are a rapid response to a stimulus without any conscious thought of the brain.  This action protects the body from danger before any harm is caused.