Case 9 Flashcards
What is a myofibril?
Basic rod-like unit of muscle composed of actin, myosin and titin and other proteins held together.
The proteins are organised in thin (actin) and thick (myosin) filaments in repeated sections called the sarcomere
What is the structure of the sarcomere?
L Band = light bands consisting of Z disc and thin filaments
A Band = dark bands containing thick and thin filaments, and H zone (section just containing thick filaments)
What is the sarcoplasm?
Cytoplasm of the muscle - space between myofibrils filled with intracellular fluid
Fluid has a lot of myoglobin (oxygen binding molecule); potassium, magnesium and phosphate ions; sarcoplasmic reticulum and protein enzymes; mitochondria
What is titin?
The titin is an elastic type of band attaching the myosin to the Z disc
It changes size as the muscle contracts or relaxes
What is Actin?
Actin filaments is formed of a double stranded F-actin protein molecule - each strand made up of G-actin molecule
Tropomyosin wraps around the strands to prevent active site exposure
Troponin binds to action, tropomyosin and calcium ions
What is myosin?
A molecule composed of a head, neck and tail
- head attaches to actin filament(functions as ATPase enzyme)
- tail connects myosin head to body
What happens at the neuromuscular junction?
AP travels through alpha motor neurone to synaptic terminal > open calcium-voltage gated channels > influx of calcium ions > release ACh > binds to ligand-gated ion channels (NI receptors) > sodium influx causes end plate potential > opens sodium voltage gated channels > influx of sodium > AP > dihydropyridine receptors in the t-tubule are stimulated > binds to ryanodine receptors bound to SR > ryanodine receptors are pulled out so calcium ions flow out > contraction
What does calcium ions interact with to cause contraction?
They interact with troponin C to initiate cross-bridge formation and contraction
This is the dependent of muscle contraction
What happens at the cross-bridge to cause contraction?
Calcium ion causes the myosin binding site to be exposed by pulling tropomyosin away
Myosin head hydrolyses ATP to ADP + P > the ADP + P bind to myosin head as it attaches to actin > ADP + P releases causing the head to change position and actin filament to move > ATP their binds to cause the myosin to detach > hydrolysis of ATP returns myosin to resting position
How does summation in muscular contraction occur?
- Increasing motor units contracting simultaneously
2. Increasing frequency of contraction (leads to tetanisation)
What are the types of muscle of contraction?
Isometric - contraction with unchanged muscle length
Isotonic - contraction with decreasing muscle length but constant tension
Concentric - contraction in direction of muscle
Eccentric - contraction away from muscle
What are the different muscle remodelling types?
Fibre Hypertrophy - increase in number of actin and myosin filaments in each muscle fibre
Fibre Aplasia - failure of fibre to function properly
Fibre atrophy - protein degradation in a muscle due to lack of use causing increase in rate of breakdown than build up
What is the gait cycle?
Stance + swing cycle
Stance (60%):
- heel strike: glut. maximum and tibialis ant.
- loading response: quadricep femoris
- midstance: soleus and gastrocnemius
- terminal stance: soleus and gastrocnemius
Swing (40%):
- preswing: recrus femoris
- initial midswing: iliopsoas and rectus femoris
- terminal swing: hamstrings, tibialis ant. and ankle dorsiflexers
What is the cause of abnormal gait?
Apraxia - frontal lobe damage = shuffling
Waddling - muscle/hip disease
Cross over - bilateral spasticity
Parkinsonian - basal ganglia dysfunction
Hemiplegic - unilateral UMN lesion
Cerebellar - cerebellar lesion = broad-based fait
Sensory - peripheral neuropathy(bilateral) and common perineal nerve lesion (unilateral)
What is a stress fracture?
Fracture occurring in normal bone that has been subject to excessive and repeated trauma causing cumulative microscopic fractures
Treatment:
protected weight bearing, rest, cross-training
