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

Sensory Nerves and Sensory Nerve Fibres  Sensory Nerve Fibre: 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  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

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

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

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

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

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

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

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

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

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

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

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

References  Web Sites: Archive ol=46&noissue=4&startpage=469Science Direct _ob=ArticleURL&_ud  Books: Medical Phyiology, Guytons 11th edition - Pg. 312, 313, , f