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: 0.5-2 um Unmyelinated Conduction Velocity: 0.7-1.4 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:

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&cdvol=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