Changes

*Myofibrils removed by disintegration -> sacrolemma too large -> forms folds

*Myofibrils removed by disintegration -> sacrolemma too large -> forms folds

*Caused by:

*Caused by:

**<u>'''Disuse'''</u> (e.g. fracture, failure to use limb, recumbency)

**<u>'''Disuse atrophy'''</u> (e.g. fracture, failure to use limb, recumbency)

***Slower than denervation atrophy

***Slower than denervation atrophy

***Reversible unless too prolonger or severe to cause loss of myofibres

***Reversible unless too prolonger or severe to cause loss of myofibres

**<u>'''Denervation'''</u>

**<u>'''Denervation atrophy'''</u>

***Any interference or damage to its nerve supply results in muscle atrophy

***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]]

****Can be rapid - over 50% of muscle mass may be lost in a few weeks e.g. roarer horses with [[Laryngeal Hemiplegia|laryngeal hemiplegia]]

****End result in muscle consisting of almost only fibrous tissue  

****End result in muscle consisting of almost only fibrous tissue  

***Sometimes replaced by fat tissue -> increased size of muscle = ''pseudohypertrophy''

***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

***Muscle may have a mixture of atrophied and [[Muscle Hypertrophy|hypertrophied]] (due to increased work load) fibres if some motor units are not damaged

**<u>'''Metabolisation of muscle protein'''</u> for nutrients during:

**<u>'''Nutritional atrophy'''</u> for nutrients during:

***Malnutrition, cachexia, senility

***Malnutrition, cachexia, senility

***Gradual onset except for some febrile diseases causing cachexia

***Gradual onset except for some febrile diseases causing cachexia

***Postural muscles are not affected, sometimes even [[Muscles Hyperplastic and Neoplastic - Pathology#Hypertrophy|hypertrophy]]

***Postural muscles are not affected, sometimes even [[Muscle Hypertrophy|hypertrophy]]

***Histologically:

***Histologically:

****Some nuclei disappear as myofibre volume is decreased

****Some nuclei disappear as myofibre volume is decreased

***Grossly:

***Grossly:

****Smaller, darker, thinner muscles

****Smaller, darker, thinner muscles

[[Category:Muscles - Degenerative Pathology]]

[[Category:Muscles - Degenerative Pathology]]