Histology Of Nerve Anf Muscle In Health And Disease Flashcards
What is the basic structure of skeletal muscle
Skeletal muscle has the individual muscle fibres arranged in myofibers and arranged in bundles called fascicles.
There is 3 types of connective tissue within skeletal muscle including epimysium, perimysium and endomysium.
The skeletal muscle does have a basement membrane which surrounds the individual myofibers with collagen, glycoproteins and proteoglycans.
They also have a vascular supply
What is the innervation of the skeletal muscle
Each muscle fibre is innervated by one nerve which has cell bodies in the anterior horn of the spinal cord/brainstem
One neurone is able to innervate multiple motor units of multiple muscle fibres
Nerve impulses pass over neuromuscular junctions
How does a nerve impulse travel across the synapse at the neuromuscular junction
The nerve impulse reaches the synapse of the pre-synaptic neurone and this stimulates the release of acetyl-choline into the synaptic cleft which binds to post-synaptic acetyl-choline receptors on the post-synaptic membrane to allow the nerve impulse to continue to travel
What does enzyme histochemistry
This revels different fibre types in a muscle biopsy
What are type 1 muscle fibres
Type 1 fibres are reliant on oxidative, fatigue resistant but have a slow twitch
What are type 2 muscle fibres
They are fatigued rapidly but are able to generate a large peak of muscle tension. Type 2 muscle fibres have a fast twitch
What are the sub types of type 2 muscle fibres
2a- intermediate- glycolytic and oxidative
2b- glycolytic
Why does the size of the motor unit vary between the muscles
Because of the need for fine motor skills
What can loss of innervation of the muscle fibre cause
Can cause fibre atrophy
What allows re innervation of muscle fibres which lose innervation
Collateral spouting of axons from adjacent motor units to re innervate that muscle fibre
What does re innervation of muscle fibres result in
Larger motor units within the body
Conversion of fibre types in the muscle in fibre type grouping
What is a sarcomere
Basic unit of contraction
What is a sarcomere made up of
Repeating arrangements of thick filaments which are myosin and thin filaments which are actin
What other proteins are present in a sarcomere
Alpha actinin
Titin
Nebulin
Desmin
What is desmin for in a sarcomere
This links the myofibrils to each other and the sarcolemma
What is linked to actin in skeletal muscle
Troponin C
Troponin I
Troponin T
Tropomyosin
What is the tropomyosin complex linked to in skeletal muscle
Calcium regulation for contraction
What is the theory of muscle contraction
The sliding filament theory
What happens during sliding filament theory which causes the muscle contraction
The heads of the myosin bind to actin due to the presence of calcium ions which bind to troponin C lifting the tropomyosin complex from the actin. The heads of the myosin then bend at the hinge region and in turn pull the actin which shortens it and in turn shortening the length of the sarcomere and so producing the muscle contraction
Where does the energy for immediate contraction come from
ATP
What is creating kinase
This is an enzyme which binds phosphate to something so in this example phosphate is blinded to creating to replenish the creative phosphate energy stores in muscle fibres
How can mitochondrial cytopathies be diagnosed
Through muscle biopsies
What is a dystrophy
A dystrophy is a genetically determined destructive and progressive disorders affecting muscles
What causes a muscle dystrophy
Defects of proteins that confer stability to the sarcolemma
What protein maintains muscle stability
Dystrophin
Where is dystrophin located
X-linked process, found on the short arm of chromosome 21
What are disorders that can affect neuromuscular transmission
The most common is myasthenia gravis which is an autoimmune disease where anti-acetyl-choline receptor antibodies which reduces the binding of acetyl-choline could show progressive weakness
How can neuromuscular transmission disorders be improved
Myasthenia gravis can be improved by acetyl cholinesterase
What cell is responsible for the myelin sheath in the PNS
The Schwann cells
What is a node of ranvier
This is a node on a axon where depolarisation of the axon occurs
What does myelination of an axon allow for
Myelination allows for saltatory conduction
What are pathologies of damage to motor/sensory neurons
Neuropathies
What are pathologies of the damage to axons known as
Axonopathies
What is it called when there is selective damage to the myelin sheath
Demyelination
How does demyelination occur
Injury to Schwann cells or myelin sheath
How does demyelination begin on an axon
With a thin myelin sheath
What does demyelination result in
Functional impairment with slow conduction of action potential
