Histology of nerve and muscle in health and disease 07.02.23 Flashcards
What are the three basic types of muscle?
- Skeletal (striated, voluntary)
- Smooth (Visceral, involuntary)
- Cardiac
How are myofribres arranged in skeletal muscle?
In fascicles (big bundles of fibres)
What three connective tissue is in skeletal muscle?
- Epimysium
- Perimysium
- Endomysium
What is contained in the basement membrane of skeletal muscle?
- Collagen, glycoproteins, proteoglycans
- Surrounds individual myofibres
How is skeletal muscle innervated?
- Each fibre is innervated by one nerve, with cell bodies in anterior horn of spinal cord or brainstem
What can one neuron innervate?
It innervates multiple muscle fibres
What is at a neuromuscular junction?
- The synapse (rapid transmission of depolarising impulse)
- Acetyl choline
What is proprioception?
The sense that lets us perceive the location, movement, and action of parts of the body.
How can skeletal muscle be studied histologically?
- By a muscle biopsy (needs to use frozen sections for this)
- Electron microscopy
- Molecular tests
What are the two twitch muscle fibre types?
- Slow twitch *red fibres (type 1- oxidative, fatigue resistant)
- Fast twitch * glycolytic so white fibres (Type 2A and 2B - Fatigue rapidly but generate a large peak of muscle tension)
What fibres can a neuron innervate?
- Neuron and fibres it innervates are the same type
- Fibre type dependent on neuron
- Density of innervation to hand, tongue, mouth etc is bigger
What is re-innervation?
- Occurs after denervation
- Means that if a fibre is re-innervated by a different type of neuron then it will take on that new function
How are myofibrils organised?
Into sarcomeres
- Repeating arrangement of thick (myosin = dark) and thin (actin = light) filaments
At the Z line with other proteins e.g. Titin, Nebulin, Troponin etc…
What is the sliding filament theory?
- Myosin and actin filaments overlap using ATP energy so sarcomere shortens
- This is initiated by increased intracellular Ca2+
What energy stores are used for the sarcomere shortening?
- ATP
- Creatine phosphate for short term (this is replenished by creatine kinase)
When is CK released and how is this clinically helpful?
- CK is released on muscle fibre damage
- So the amount of CK in your body lets doctors know how much muscle damage there is
What type of mutation particularly affects muscle fibres
Mitochondrial muation
What proteins are part of the membrane for stability?
- Merosin (Extracellular) Which anchors muscle fibre for stability
- Dystrophin (Intracellular) Links membrane and actin for stability
What are the steps of a neuromuscular transmission?
- Nerve impulse releases acetyl choline from synaptic vesicles
- ACh binds to its receptor
- Resulting in depolarisation
- Action potential travels across muscle cell membrane and into T-tubule system
- Calcium released from sarcoplasmic reticulum leading to contraction
What are the two layers of the peripheral nerve?
- perineurium
- epineurium
What is the Schwann cell responsible for in the PNS?
- For the myelin sheath
- Each Schwann cell is responsible for one segment of myelin
What is between myelin segments?
- Node of Ranvier (there is no myelinated sheath so this is where depolarisation takes place as no insulation)
How does an axon regenerate if damaged?
- globules of myelin and axon debris form, with Schwann Cell
- Axonal sprouts form and grow along columns
- Regenerated axons can re-myelinate (but they are thinner and have a slower action potential)
How does demyelination occur?
- Injuries to Schwann cells or myelin sheath
- Remyelination begins with a thin myelin sheath
- Demyelination results in slowing of conduction velocity
