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Created page with "right|thumb|100px|<small><center>Atrophic muscle fibres (Image sourced from Bristol Biomed Image Archive with permission)</center></small> *..."
[[Image:Atrophic muscle fibres.jpg|right|thumb|100px|<small><center>Atrophic muscle fibres (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
*Decreased myofibre or whole muscle diameter
*Myofibrils removed by disintegration -> sacrolemma too large -> forms folds
*Caused by:
**<u>'''Disuse'''</u> (e.g. fracture, failure to use limb, recumbency)
***Slower than denervation atrophy
***Reversible unless too prolonger or severe to cause loss of myofibres
**<u>'''Denervation'''</u>
***Any interference or damage to its nerve supply results in muscle atrophy
****Can be rapid - over 50% of muscle mass may be lost in a few weeks e.g. roarer horses with [[Laryngeal Hemiplegia|laryngeal hemiplegia]]
***May be reversible if innervation re-established
***Histologically:
****Fibres become rounded in cross section unless compressed by normal fibres
****Increased concentration of nuclei as they take much longer to disintegrate
****Fibrous stroma of epimysium and endomysium condenses -> more prominent
****End result in muscle consisting of almost only fibrous tissue
***Sometimes replaced by fat tissue -> increased size of muscle = ''pseudohypertrophy''
***Muscle may have a mixture of atrophied and [[Muscles Hyperplastic and Neoplastic - Pathology#Hypertrophy|hypertrophied]] (due to increased work load) fibres if some motor units are not damaged
**<u>'''Metabolisation of muscle protein'''</u> for nutrients during:
***Malnutrition, cachexia, senility
***Gradual onset except for some febrile diseases causing cachexia
***Postural muscles are not affected, sometimes even [[Muscles Hyperplastic and Neoplastic - Pathology#Hypertrophy|hypertrophy]]
***Histologically:
****Some nuclei disappear as myofibre volume is decreased
***Grossly:
****Smaller, darker, thinner muscles
[[Category:Muscles - Degenerative Pathology]]
*Decreased myofibre or whole muscle diameter
*Myofibrils removed by disintegration -> sacrolemma too large -> forms folds
*Caused by:
**<u>'''Disuse'''</u> (e.g. fracture, failure to use limb, recumbency)
***Slower than denervation atrophy
***Reversible unless too prolonger or severe to cause loss of myofibres
**<u>'''Denervation'''</u>
***Any interference or damage to its nerve supply results in muscle atrophy
****Can be rapid - over 50% of muscle mass may be lost in a few weeks e.g. roarer horses with [[Laryngeal Hemiplegia|laryngeal hemiplegia]]
***May be reversible if innervation re-established
***Histologically:
****Fibres become rounded in cross section unless compressed by normal fibres
****Increased concentration of nuclei as they take much longer to disintegrate
****Fibrous stroma of epimysium and endomysium condenses -> more prominent
****End result in muscle consisting of almost only fibrous tissue
***Sometimes replaced by fat tissue -> increased size of muscle = ''pseudohypertrophy''
***Muscle may have a mixture of atrophied and [[Muscles Hyperplastic and Neoplastic - Pathology#Hypertrophy|hypertrophied]] (due to increased work load) fibres if some motor units are not damaged
**<u>'''Metabolisation of muscle protein'''</u> for nutrients during:
***Malnutrition, cachexia, senility
***Gradual onset except for some febrile diseases causing cachexia
***Postural muscles are not affected, sometimes even [[Muscles Hyperplastic and Neoplastic - Pathology#Hypertrophy|hypertrophy]]
***Histologically:
****Some nuclei disappear as myofibre volume is decreased
***Grossly:
****Smaller, darker, thinner muscles
[[Category:Muscles - Degenerative Pathology]]