Histology of nerve and muscle Flashcards
What are the three types of muscle
- ) Skeletal
- ) Smooth
- ) Cardiac
Skeletal muscle
- Myofibres are arranged in fascicles
- Connective tissue made up of:
1. ) Epimysium
2. ) Perimysium
3. ) Endomysium - Rich vascular supply
- Innervation: efferents and afferents
Skeletal muscle: innervation
- Wach fibre is innervated by one nerve with cell bodies in the anterior horn of spinal cord/brainstem
- One neuron innverates multiple muscle fibres: motor unit
- Neuromuscular junction: synapse and acetyl choline
- Proprioception: length/tension/rates of contraction fo muscle
Muscle fibre types
- ) Slow twitch (red fibres)
2. ) Fast twitch
Details of slow twitch fibres
- Type 1
- Oxidative
- Fatigue resistant
Details of fast twitch fibres
- Fatigue rapidly
- Generate a large peak of muscle tension
- 2A: glycolytic + oxidative
- 2B: glycolytic (white)
Skeletal muscle histology
- Can be studied by muscle biopsy
- Requires use of frozen sections and good orientation
- EM
- Molecular tests
Enzyme histochemistry
- method to look at activity of an enzyme in a tissue
- Will develop a colour substrate from the reaction that takes place
Motor units
- lower motor neurons and the fibres it innervates
- neurone + its fibres of same type
- fibre type dependent on neuron
- size varies: smaller muscles for hands need finer coordination so needs a smaller motor unit
How are motor units altered in denervating diseases
- ) Loss of innervation causes fibre atrophy
- ) Collateral sprouting from adjacent motor units allows reinnervation
- ) Larger motor units result: can be detected electro physiologically
- ) Conversion of fibres in fibre type grouping
Organisation of myofibrils
There are repeating assemblies of thick and thin filaments
What are the types of thick and thin filaments?
Thin filaments
- ) Actin
- ) Troponin
- ) Tropomyosin
Thick filaments:
1.) Myosin
What are the requirements for energy?
- High energy requirement from ATP
- Creatine phosphate: a short term energy store
- CP replenished by creatine kinase
- CK is released on muscle fibre damage
- Measurement of serum CK: clinically useful
What are mitochondrial cytopathies
- Disorders due to mutations of mitochondrial genes
- Mitochondrial mutations: maternal inheritance
- Brain is often affected
- E.g. MERRF/MELAS/CPE
- Heteroplasmy
How can mitochondrial diseases be diagnosed?
By muscle biopsy
How can mitochondrial diseases be diagnosed?
- By muscle biopsy
- Ragged red fibres
- Electron transport chain defects: cytochrome oxidase negative fibres
- Abnormal mitochondrial morphology
Membrane structure
- Has dystroglycans in the extracellular space
- In the intracellular space: sarcoglycans/dystrophin/actin
Dystrophies + defects of sarcolemmal related proteins
- They are genetically determines
- Destructive + progressive disorders
- Affect muscle
- Defects of proteins that confer stability to the sarcolemma are one group of causes
Dystrophin
- A large protein encoded by a 2.4 million bp on Xp21
- Confers stability to the muscle cell membrane
- Deletion resulting in disruption of the reading frame
Neuromuscular transmission features
- Nerve impulse results in the release of ACh from synaptic vesicles
- ACh binds to receptor
- Cation entry results in depolarisation (end-plate potential)
- An action potential travels across the muscle cell membrane + into the T-tubule system
- Calcium is released from the sarcoplasmic reticulum (leading to contravtion)
- Dissociated ACh is hydrolysed by acetyl cholinesterase in the NMJ
What are disorders of neuromuscular transmission
- ) Myasthenia gravis
- ) Autoimmune disease
- ) Anti-AChR antibodies (reduction in ACh receptors)
- ) Acetyl cholinesterase inhibitors can improve muscle function
Basic histology of peripheral nerves
- Have perineurium
- Have epineurium
Myelinated fibres
- PNS: schwann cell is responsible for the myelin sheath
- They are neural crest derived cells
- Schwann cell: one is responsible for one segment of myelin
- Nodes of Ranvier: where depolarisation of the membrane occurs. The nodes lie between adjacent myelin segments
- ## Myelination allows saltatory conduction
What are peripheral neuropathies?
- Damage to motor/sensory neurons (neuronopathies)
- Damage to axons (axonopathies)
- Selective damage to myelin sheaths (demyelination)
Axonial degeneration
- Injury to axon: distal fragmentation
- Globules of myelin + axon are taken up by the schwann cells
Reinnervation is attempted: axonal sprouts form from proximal part of damaged axon - Regenerated axons can remyelinate
What is demyelination
- Injuries primarily to schwann cell
