Muscle Tissue - Function and Disease Flashcards
State 2 similarities between cardiac and smooth muscle
- Central nuclei
- One contractile cell type
- Act as a syncytium
- Cells communicate through gap junctions
State 2 differences between cardiac and smooth muscle
- Smooth muscle has no sarcomeres
- Cardiac muscle has specialised conduction
- Smooth muscle has no troponins
- Cardiac muscle has intercalated discs
What are the parasympathetic and sympathetic types of cardiac innervation
Parasympathetic - Cardiac plexus receives signals from the vagus nerve
Sympathetic - Composed or sympathetic trunk fibres
Name one effect of parasympathetic and sympathetic cardiac innervation
Parasympathetic - Reduces heart rate, vasoconstriction of coronary arteries
Sympathetic - Increases heart rate, fight or flight response
What elements are involved in cardiac contraction? Name 2
- T-tubules
- Calcium ions
- Troponin complex
- Actin
- Myosin
What happens between myosin and actin in cardiac contraction?
Myosin head binds to ATP and pulls actin filaments causing contraction
What type of nerve fibres supply smooth muscles and what specialised organelle do they contain?
- Autonomic nerve fibres
- Synaptic vesicles full of neurotransmitters
Which enzyme is involved in smooth muscle contraction and what is it activated by?
- Myosin chain kinase
- Activated by Calcium-Calmodulin complex
Name 2 characteristics of smooth muscle cell ultrastructure
- Dense body with bundles of thick and thin filaments
- Each contractile unit have 3 subunits
- Actin passes through gap junctions
- Fibres line up prior to contraction
What is contained in the axon vesicles of skeletal muscle fibres?
Acetylcholine
What does Acetylcholine bind to in skeletal muscle cells and what is its effect?
- Binds to sarcolemma receptors
- Initiates an action potential
How to nerve fibres correlate to fine motor control?
Small amount of fibres per motor unit allows fine motor control
Where does skeletal muscle contraction occur?
Neuromuscular junction
What 2 ions are involved in skeletal muscle contraction?
Na+ and Ca2+
Where does depolarisation spread to after the sarcolemma?
T-tubules
What does Ca2+ bind to in skeletal muscle to start the contraction cycle?
Troponin complex
What is the effect of antibodies in Myasthenia Gravis? What does this result in?
- They block Ach receptors
- Results in reduced synaptic transmission
- Sufferers have intermittent muscle weakness
Name 2 myofilament proteins in sliding filament theory
- Titin
- Tropomyosin
Describe the structure of myosin
- Rod-like structure with 2 heads
- Heads protrude at opposite ends of the filament
What are the 2 protein components of Actin?
- F-Actin fibres
- G-Actin globules
What complex sits on top of Actin binding sites?
Tropomyosin-Troponin complex
How many Troponin complexes are there in each Actin twist?
2
What joins together in the functional contraction unit to cause contraction?
Myosin heads and actin filaments
Where are myosin heads not present in the functional contraction unit?
M region (middle of the sarcomere)
In terms of contractile unit structure, what stays the same and what changes during contraction?
- Length of actin and myosin filaments remains the same
- Sarcomeres shorten and Z-lines move closer together
What molecule causes detachment of myosin and actin?
ATP
What are the 5 muscle roles in movement?
- Agonist
- Antagonist
- Synergist
- Neutraliser
- Fixator
What is the mechanism of first, second and third class levers?
First - “see-saw”
Second - “wheelbarrow”
Third - “fishing rod”
What is compartment syndrome? What are the symptoms and how is it treated?
- Trauma Results in high pressure in one of the fascia compartments
Symptoms - prolonged cap refill, shiny/swollen skin
Treatment - Fasciotomy and skin graft
Define muscle strength and muscle tone
Muscle Strength - Muscle’s ability to contract and create force in response to resistance
Muscle Tone - Tension in a muscle at rest
What is muscle atrophy and muscle hypertrophy?
Muscle Atrophy - Destruction > Replacement
Muscle Hypertrophy - Replacement > Destruction
Name 2 characteristics of muscle hypertrophy
- A and I bands are overstretched
- New muscle fibrils and sarcomeres produced
- Muscle fibres arise from mesenchymal cells
Name 3 causes of muscle atrophy
- Muscle disuse
- Surgery
- Disease
Describe the mechanism of Duchenne Muscular Dystrophy
- Dystrophin gene mutation affects membrane material movement
- Excess calcium and water enter muscle cells
- Muscle cells burst and are replaced by adipose tissue
What levels are high in the blood in Duchene Muscular Dystrophy?
- CK
- Myoglobin
What is Creatinine Kinase and when is it released into the blood?
- Enzyme found in metabolically active tissue
- Released into the blood when skeletal muscle is damaged
What is the mechanism and effect of Botox?
- Blocks neurotransmitter release at the motor end plate
- Causes non-contractile state of skeletal muscle
What does Organophosphate Poisoning inhibit and what is the effect of this?
- Inhibits the normal function of Ach esterase
- Active site is blocked and muscle is continuously stimulated
What are the muscarinic symptoms of Organophosphate Poisoning?
Salivation Lacrimation Urination Defecation GI cramping Emesis “SLUDGE”
What are the nicotinic symptoms of Organophosphate Poisoning?
Muscle cramps Tachycardia Weakness Twitching Fascicultations “Monday - Friday”
