The Nervous system

A description of the CNS, PNS, ANS, nerve structure and conduction aswell as general and special senses.

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The Nervous System

  • The nervous system is a control and communication system of the body.
  • It detects and responds rapidly to changes in the internal and external environments of the body.

The nervous system can be divided into three main sections:

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


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The nervous system is made up of neurones:

  • Cell body
  • Axon
  • Dentrites 
  • Myelin sheath
  • Nodes of ranvier


  • Sensory (afferent)
  • Motor (efferent)
  • Mixed

Nerve conduction is:

  • very rapid ( 0.5m/s)
  • Polarisation, depolarisation, Propagation, repolarisation.
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  • Cereberum
  • Midbrain
  • Pons varolli
  • Medulla oblongata
  • Cerebellum

Spinal cord: Situated in the vertebral canal, and extends from the atlas to the first lumbar vertebrate.

Both the spinal cord and brain are covered in three continuous sheets of connective tissue, the meninges. From outside in, these are the

  • dura mater — pressed against the bony surface of the interior of the vertebrae and the cranium
  • the arachnoid
  • the pia mater
  • The region between the arachnoid and pia mater is filled with cerebrospinal fluid (CSF).
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There are 31 pairs of Spinal nerves:- (nerves that emerge from the segments of spine)

  • 8 Cervical
  • 12 Thoraic
  • 5 Lumbar
  • 5 Sacreal
  • 1 Coccygeal

Ramus Communicans -( a branch connecting two nerves or arteries)

  • Posterior supplies skin and muscle of head, neck and trunks.
  • Anterior supplies neck, trunk and upper and lower limbs.


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PNS cont.

Plexuses - ( a network of intersecting nerves)

  • Cervical
  • Brachial
  • Lumbar
  • Sacreal
  • Cooccygeal




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The Cranial Nerves (PNS)

Cranial Nerves - (nerves that directly emmerge from the brain)

  • I - Olfactory, sensory, sense of smell.
  • II - Optic, sensory, sense of sight.
  • III - Oculomotor,motor, movement of the eye.
  • IV - Trochlear, motor, movement of the eye.
  • V - Trigeminal, mixed, S- sense of pain, temp and touch. M- muscles of mastication.
  • VI - Abducens, motor, movement of the eye.
  • VII - Facial, misxed, S- sense of taste, M- Muscles of Mastc.
  • VIII - Auditory, sensory, sense of hearing and balance
  • IX - Glossopharyngeal, mixed, S - sense of tatse, M - muscles of tongue and pharynx.
  • X - Vagus, mixed, S - lining membranes of major organs, M, smooth muscle and scretory glands of same organs.
  • XI - Accessory, motor, movement of head.
  • XII - Hypoglossal, motor, movement of tongue.
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Sympathetic -

  • Prepares for the fight or flight (deals with exciting and stressful situations)

Parasympathetic -

  • Prepares the body for rest, and for the restoration of its organs processes.

The special sense of the body are :

  • Hearing
  • Sight
  • Smell
  • Touch
  • Taste


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