Histology Flashcards
Skeletal muscle structure
Myofibres arranged in fascicles
Connective tissue in skeletal muscle
Epimysium
Perimysium
Endomysium
Basement membrane in skeletal muscle
Surrounds individual myofibres
Collage, glycoproteins and proteoglycans
Role of basement membrane in skeletal muscle
Tensile strength, regeneration and development
Myotendinous junction
Transmits force of muscle contraction the the tendon
Skeletal muscle innervation
Each fibre innervated by one nerve, with cell bodies in anterior horn of spinal cord or brainstem
Motor unit
One neuron innervated multiple muscle fibres
Neuromuscular junction
Synapse- rapid transmission of depolarising impulse
ACh binds post-synaptic AChR
Role of proprioception
Length and tensiom
Muscle spindles
Encapsulated intrafusal fibres
Mediate stretch reflexes and proprioception
Golgi tendon organs
Tension
Control of skeletal muscle
Primary motor cortex
Basal ganglia/ cerebellar systems
Dessucation of Corticospinal tract in medulla
Anterior horn cell
LMN
Neuromuscular junction
Muscle control is
Somatotopic
Contalateral
Studying skeletal muscle
Muscle biopsy
Requires the use of frozen sections and good orientation
Electron microscopy
Molecular tests
Muscle fibre types
Slow twitch
Fast twitch
Slow twitch muscle fibres
Type 1
Oxidative
Fatigue resistant
Slow twitch muscle fibres stain ….
Red
Fast twitch muscle fibres
Fatigue rapidly but generate a large peak of muscle tension
2A- glycolytic and oxidative
2B- glycolytic
Colour of 2A fast twitch muscle fibres
Intermediate - pink
Colour of 2B fast twitch muscle fibres
White
Motor unit
Lower motor neurone and the fibres it innervates
Neurone and its fibres the same type
Fibre type dependent on neuron
Size of motor unit varies between muscles
What causes fibre atrophy (shrinks)
Loss of innervation of motor units
What allows reinnervation of a motor unit
Collateral sprouting from adjacent motor units- larger motor units form (can be detected electrophysiologically)
Conversion of fibres results in fibre type grouping
Fibre type grouping
Conversion of fibres resulting in larger motor units with same fibre type following reinnervation
Sarcomere
Basic unit of contraction
Repeating arrangement of think (myosin) and thin (actin) filaments
Other proteins at the Z-line of a sarcomere
Alpha-actinin
Titin
Nebulin
Desmin
Role of desmin
Links myofibrils to each other and the sarcolemma
What is linked to actin
Troponin and tropomyosin complex- calcium regulation
A band
Both actin and myosin
I band
Only actin
H band
Only myosin
Z disc
Attachment of actin
M line
Attachment for myosin
Sliding filament theory
Myosin heads bind to actin
Binding of ATP allows release and hydrolysis to ADO allows movement of myosin head
ADP released during power trike
Initiated by increased cytosolic Ca2+
Creatine phosphate
Short term energy storage
CP replenished by creatine kinase
What cause creatine kinase to be released
Muscle fibre damage
What is used to measure damage of muscle tissue
Serum CK (creatine kinase)
Mitochondrial cytopathies
Ragged red fibres
Electron transport chain deficits- cytochrome oxidase negative fibres
Abnormal mitochondrial morphology
Gene defects
Dystrophin
A large protein encoded by a 2.4million base pair gene on Xp21
Confers stability to the muscle cell membrane
Cause of duchenne dystrophy
Deletion of dystrophin gene resulting in disruption of the reading frame
No production of dystrophin
Dystrophies
Genetically determined, destructive and mainly progressive disorders of muscle
Neuromuscular transmission
Nerve impulse results in the release of ACh from synaptic vesicles
ACh binds to its receptor
Cation entry results in depolarisation - end-plate potential
Action potential travels across the cell membrane and into the T-tubule system
Calcium is released from the sarcoplasmic reticulum leading to activation of contraction
Dissociated ACh is hydrolysed by acetyl cholinesterase in the NMJ
Transmembrane proteins important in stability of sarcolemma
5 sarcoglycans
Dystroglycan
Role of transmembrane proteins in sarcolemma
Links merosin through sarcolemma to dystrophin and then to actin
Causes of Becker’s dystrophy
In-frame deletion results in a truncated product
Milder phenotype than duchenne dystrophy
Still produce some normal structure and some dystrophin
Which neurotransmitter involved in NMJ
Acetyl choline
Myasthenia gravis
Variable weakness
Progressive with sustained effort
Eye signs- ptosis
Autoimmune disease
Anti-AChR antibodies resulting in a reduction in ACh receptors
Acetyl cholinesterase inhibitors can improve muscle function
What is responsible for myelination of PNS nerves
Schwann cells
Nodes of ranvier
Lie between adjacent myelin segments
Where depolarisation of membrane occurs
Neuronopathies
Damage to motor or sensory neurons
Axonopathies
Damage to acins
Demyelination
Selective damage to myelin sheaths
Axonal degeneration / regeneration – Wallerian degeneration
Injury to axon – distal fragmentation
Globules of myelin and axon debris form, initially within Schwann cell
Axonal sprouts form from proximal part of damaged axon and grow along columns of proliferating Schwann cells
Regenerated axons can remyelinate
Demyelination results from
Injuries primarily to Schwann cell or myelin sheath
Demyelination segmental
Demyelination results in functional impairment with slowing of conduction velocity
Remyelination
Begins with a thin myelin sheath
Shorter than original
Slower conduction
