Histology of nerve and muscle in health and disease 07.02.23

Question 1

What are the three basic types of muscle?

Answer 1

• Skeletal (striated, voluntary)
• Smooth (Visceral, involuntary)
• Cardiac

Question 2

How are myofribres arranged in skeletal muscle?

Answer 2

In fascicles (big bundles of fibres)

Question 3

What three connective tissue is in skeletal muscle?

Answer 3

• Epimysium
• Perimysium
• Endomysium

Question 4

What is contained in the basement membrane of skeletal muscle?

Answer 4

• Collagen, glycoproteins, proteoglycans
• Surrounds individual myofibres

Question 5

How is skeletal muscle innervated?

Answer 5

• Each fibre is innervated by one nerve, with cell bodies in anterior horn of spinal cord or brainstem

Question 6

What can one neuron innervate?

Answer 6

It innervates multiple muscle fibres

Question 7

What is at a neuromuscular junction?

Answer 7

• The synapse (rapid transmission of depolarising impulse)
• Acetyl choline

Question 8

What is proprioception?

Answer 8

The sense that lets us perceive the location, movement, and action of parts of the body.

Question 9

How can skeletal muscle be studied histologically?

Answer 9

• By a muscle biopsy (needs to use frozen sections for this)
• Electron microscopy
• Molecular tests

Question 10

What are the two twitch muscle fibre types?

Answer 10

• 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)

Question 11

What fibres can a neuron innervate?

Answer 11

• Neuron and fibres it innervates are the same type
• Fibre type dependent on neuron
• Density of innervation to hand, tongue, mouth etc is bigger

Question 12

What is re-innervation?

Answer 12

• 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

Question 13

How are myofibrils organised?

Answer 13

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…

Question 14

What is the sliding filament theory?

Answer 14

• Myosin and actin filaments overlap using ATP energy so sarcomere shortens
• This is initiated by increased intracellular Ca2+

Question 15

What energy stores are used for the sarcomere shortening?

Answer 15

• ATP
• Creatine phosphate for short term (this is replenished by creatine kinase)

Question 16

When is CK released and how is this clinically helpful?

Answer 16

• CK is released on muscle fibre damage
• So the amount of CK in your body lets doctors know how much muscle damage there is

Question 17

What type of mutation particularly affects muscle fibres

Answer 17

Mitochondrial muation

Question 18

What proteins are part of the membrane for stability?

Answer 18

• Merosin (Extracellular) Which anchors muscle fibre for stability
• Dystrophin (Intracellular) Links membrane and actin for stability

Question 19

What are the steps of a neuromuscular transmission?

Answer 19

• 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

Question 20

What are the two layers of the peripheral nerve?

Answer 20

• perineurium
• epineurium

Question 21

What is the Schwann cell responsible for in the PNS?

Answer 21

• For the myelin sheath
• Each Schwann cell is responsible for one segment of myelin

Question 22

What is between myelin segments?

Answer 22

• Node of Ranvier (there is no myelinated sheath so this is where depolarisation takes place as no insulation)

Question 23

How does an axon regenerate if damaged?

Answer 23

• 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)

Question 24

How does demyelination occur?

Answer 24

• Injuries to Schwann cells or myelin sheath
• Remyelination begins with a thin myelin sheath
• Demyelination results in slowing of conduction velocity