Nerve And Muscle Pathology Flashcards
What does the normal functioning of skeletal muscle require?
Metabolic demands of tissue are met
The muscle is used
There is innervation
What makes nerve fibres ‘myelinated’?
Nerve fibres surrounded by compacted multiple Schwann Cell membranes
Gaps between Schwann Cells = Node of Ranvier
What are the gaps between Schwann Cells called? What do they allow to occur?
Node of Ranvier
They allow for high speed conduction of impulses
What elements make up the motor unit? (4)
Lower motor neuron
Axon
Neuromuscular Junction
Muscle Fibres
What are the two types of nerve degeneration?
Axonal Degeneration
Segmental Demyelination
What two subtypes of Axonal Degeneration are there?
Wallerian Degeneration
Distal Axonal Degeneration
How does Wallerian degeneration occur?
Portions of axon distal to trauma degenerate
If myelinated- secondary myelin breakdown
In Wallerian degeneration, how does regeneration occur?
Regeneration starts at site of injury (after 3-4 days), progressing at 1-3mm per day
Requires intact Schwann Cells to guide direction of growth
In Wallerian Degeneration, if Schwann cells are not intact, what happens during regeneration?
Traumatic Neuroma develops
What happens in Distal Axonal Degeneration?
Neuron metabolism is disrupted
Degeneration occurs form distal end (‘dying back’)
Regeneration can occur
What can cause Distal Axonal Degeneration?
Vitamin E
B1 deficiencies
Drugs
What happens in Segmental Demyelination?
Axon remains intact, but myelin breaks down
Results in slower conduction
Demyelination can occur
What are the two main types of Segmental Demyelination?
Primary
Allergic
What are the causes of Primary Segmental Demyelination?
Damage to Schwann Cells -> Myelin gets phagocytosed
E.g. Ischaemia, diphtheria, inherited leucodystrophies
What are the causes of Allergic Segmental Demyelination?
Activated macrophages and T lymphocytes strip myelin sheath
E.g. Guillain Barré
