muscle Flashcards
Skeletal muscle
Skeletal muscles are for posture and locomotion and provide for most of body heat; these contain much of body protein.
Nerve / Muscle relationship
One lower motor neuron and the (several) muscle cells that it innervates make up a motor unit.
So muscle diseases may be primary (originating in the muscle) or a consequence of a neuronal disease (e.g. loss)
Units of muscle
not important
The muscles are composed of muscle fibres (myocytes) - up to 100 in thickness and as long as the muscle itself.
Muscle fibres are of two types:
Slow twitch (red fibres, dark meat, type I)
For posture and strength
Fast twitch (white fibres, white meat, type II)
For bursts of speed
Sprain vs Strain!!!!
Sprains are damaged ligaments!!
The pain is from small hemorhages and edema
Strains result from physical stretching of muscle in opposite directions
The pain is from tears the muscle-tendon junction.
Muscular Dystrophy
Group of hereditary myopathies considered together by custom
Common to these diseases is muscle atrophy and loss of muscle fibres in the absence of nerve disease.
31 types of muscular dystrophy.
Most are autosomal recessive.
Some are sex-linked or autosomal dominant.
They may be severe or mild and occur at different times during life, even into the 60s.
There is no treatment.
Duchenne Muscular Dystrophy!!
Sex-linked recessive disorder.
Only males are affected.
Common - 1 in 3500
Is caused by a deficiency of dystrophin!!!, causing muscle degeneration
Duchenne Muscular Dystrophy- what happens
Children appear normal at birth but the muscles are abnormal - symptoms begin at 3-5 years
There is symmetrical weakness
The child will never run.
Become wheelchair bound in their teens
Use arm support!!! to get up ( Gower’s sign!!!)
Progressive. Death in 20s.
why do they die
Duchenne Muscular Dystrophy
Diagnosis requires clinical assessment, pathologic examination and molecular tests.
At autopsy - pseudohypertrophy can be shown to be due to fatty infiltration of atrophic muscle
-microorganism grow in lungs because cant breath enough- pneumonia- macrophages come in -REPIRATORY FAILURE
thighs and calfs can get large by pseudohypertrophy - replaced by fat
BIG MUSCLES
Myasthenia gravis
Neuromuscular junction is the site of the pathology in MG.
An autoimmune disorder: antibodies attack the receptors for the neurotransmitter - acetylcholine (Ach) - in the post synaptic membrane.
Binding of Ach is blocked - no signal - muscle weakness.
MOST DELICATE MUSCLE IN THE BODY- EYELIDS
Muscle weakness and fatigability increases with time.
The disease usually begins in the eyes (drooping eyelids, double vision)
The patient will eventually develop a respiratory infection (weak and fatigued chest muscles and diaphragm) and die.
Incidence is 1:10,000
M:F::3:2
Affects women earlier (20-35) than men (50-60)
Associated with enlargement of thymus in 75% of pts.
Thymus cells have Ach receptor epitopes providing cross reactivity.
Treatment of Myasthenia gravis!!!
dushene and sprains and strains
Palliative; Ach not bound to the receptors is destroyed by the enzyme cholinesterase in MG
Rationale: So give anti-cholinesterase so that the amount of Ach is increased and some of it might be able to bind with the receptors that have not been destroyed.
