1. Objectives  Define Sensory Nerve Fibre  Outline the various types of sensory nerve fibres  Describe two clinical aspects in which damage to sensory nerve fibres is prevalent

2. Sensory Nerves and Sensory Nerve Fibres  Sensory Nerve Fibre: a threadlike process that conveys impulses from the sensory receptors to the Central Nervous System

3. The Course of Sensory Nerve Fibres

4. Types of Sensory Nerve Fibres  Different sensory nerve fibres innervate different sensory receptors  A numerical system is used by physiologists to classify sensory nerve fibres  There are five types of sensory nerve fibres: Ia, Ib, II, III and IV

5. Type Ia Sensory Nerve Fibre  Origin: muscle spindles  Insertion: CNS  Function: Proprioception  Largest and fastest sensory nerve fibre Diameter: 17 um Myelinated Conduction Velocity: 102m/s

6. Type Ib Sensory Fibre  Origin: Golgi tendon organ  Insertion: CNS  Function: Proprioception  Diameter: 16 um  Myelinated  Conduction Velocity: 96m/s

7. Type II Sensory Nerve Fibre  Innervates touch and pressure receptors  Origin: muscle spindle  Insertion: CNS  Diameter: 8 um  Myelinated  Conduction Velocity: 48 m/s

8. Type III Sensory Nerve Fibre  Innervates sharp pain and cold receptors as well as some touch receptors  Origin:Skin  Insertion: CNS  Diameter: 3 um  Myelinated  Conduction Velocity: 18m/s

9. Type IV Sensory Nerve Fibres  Innervates mainly slow, burning pain and temperature receptors  Origin: Skin  Insertion: CNS  Diameter: 0.5-2 um  Unmyelinated  Conduction Velocity: 0.7-1.4 m/s

10. Damage To Sensory Nerve Fibres  Causes hyperactivity in neighbouring sensory nerve fibres of the same type  Causes localized loss of sensation

11. Clinical: Deep Gash  Symptoms: Sharp burst of pain Throbbing sensation

12. Clinical: Deep Gash  Specific Sensory Nerve Fibres Involved: Impulse from Sensory Nerve Fibre Type III Impulse from Sensory Nerve Fibre Type IV

13. Clinical: Diabetic Neuropathy  Diabetes  Definition: Nerve damage caused by diabetes  Cause: High blood glucose levels combined with lack of insulin formation or the inability to use insulin  Symptoms: Numbness, tingling or pain in the feet, legs arms, hands, fingers Loss of sensation in one ore more of these areas so that a person will be unable to detect temperature or to notice pain

14. Clinical: Diabetic Neuropathy  Specific Sensory Nerve Fibres involved: Increasing damage to Type Ia, Type Ib, Type II, Type III and Type IV Sensory Nerve Fibres  Treatment: Lower blood glucose levels

15. Conclusion  Sensory Nerve Fibres transmit sensation in the form of impulses from receptors to the CNS  The Four types of Sensory Nerve Fibres are classified as Ia, Ib, II, III,IV  Initial damage to Sensory Nerve Fibres cause over activation in nearby Sensory Nerve Fibres which in the case of pain receptors cause enhanced pain  Extensive damage to Sensory Nerve Fibres results in a localized loss of sensation

16. References  Web Sites: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1422013Circulation http://circ.ahajournals.org/cgi/content/full/circulationaha%3B101/14/1665Journal Archive http://www.journalarchive.jst.go.jp/english/jnlabstract_en.php?cdjournal=aohc1982&cdv ol=46&noissue=4&startpage=469Science Direct http://www.sciencedirect.com/science _ob=ArticleURL&_ud  Books: Medical Phyiology, Guytons 11th edition - Pg. 312, 313, 585-597, 664-665f