Objectives o Define Sensory Nerve Fibre o Outline

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

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

The Course of Sensory Nerve Fibres

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

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

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

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

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

Type IV Sensory Nerve Fibres o Innervates mainly slow, burning pain and temperature receptors o Origin: Skin o Insertion: CNS o Diameter: 0. 5 -2 um o Unmyelinated o Conduction Velocity: 0. 7 -1. 4 m/s

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

Clinical: Deep Gash o Symptoms: n Sharp burst of pain n Throbbing sensation

Clinical: Deep Gash o Specific Sensory Nerve Fibres Involved: n Impulse from Sensory Nerve Fibre Type III n Impulse from Sensory Nerve Fibre Type IV

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

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

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

References o Web Sites: n n o http: //www. pubmedcentral. nih. gov/articlerender. fcgi? artid=1422013 Circulation http: //circ. ahajournals. org/cgi/content/full/circulationaha%3 B 101/14/1665 Journal Archive http: //www. journalarchive. jst. go. jp/english/jnlabstract_en. php? cdjournal =aohc 1982&cdv ol=46&noissue=4&startpage=469 Science Direct http: //www. sciencedirect. com/science _ob=Article. URL&_ud Books: n Medical Phyiology, Guytons 11 th edition - Pg. 312, 313, 585 -597, 664 -665 f