11) Muscle Tissue Flashcards
What is myoglobin?
A red protein, similar to one subunit of haemoglobin - provides O2 to working striated muscles
Has a higher affinity to O2 than Hb
Does myoglobin or haemoglobin bind more strongly to O2?
Myoglobin - so O2 is not taken away from respiring muscle cells during exercise
What is the outer membrane of a muscle cell called?
Sarcolemma
What is the cytoplasm of a muscle cell called?
Sarcoplasm
What is the mitochondrion called in a muscle cell?
Sarcosome
What is a sarcomere
The most basic contractile unit in striated muscle
What is the Sarcoplasmic reticulum?
The smooth endoplasmic reticulum of a muscle cell
What are the 3 types of muscle contraction speeds?
Slow, intermediate, fast
what colours are the 3 muscle fibre types?
Slow - red
Intermediate - red to pink
Fast - white
What 2 factors/molecules affect continued muscle contraction?
Ca2+ ions
Amount of ATP
How does nucleus placement differ between cardiac, smooth and skeletal muscle?
Nucleus positioned centrally in cardiac and smooth muscle cells.
Nucleus positioned on the edge of the cell in skeletal muscle
Name some unique structural features of cardiac muscle cells.
- Intercalated disks (for electrical and mechanical coupling with adjacent cells)
- branching
Where is ANP released?
Released by atria
Where is BNP released?
Released by ventricles
What do ANP and BNP do?
Act to decrease blood pressure during heart failure
What is hypertrophy?
Enlargement of individual cells
What is hyperplasia?
Multiplication of cells
What is atrophy?
Decrease in size of individual cells
Where are the pacemaker cells located?
Right atrium of heart
What are purkinje fibres?
Large cells found in the ventricle walls of the heart which propagate an electrical signal rapidly to allow the ventricles to contract synchronously.
They have abundant glycogen, sparse myofibrils and extensive gap junction sites
Where do purkinje fibres transmit action potentials from?
The atrioventricular node
Give some similarities between cardiac and skeletal muscle.
- striated
- similar contraction mechanisms
Give some ways in which cardiac muscle differs to skeletal muscle.
- nuclei in cardiac muscle are central (sometimes 2 per cell)
- sarcomere not so well developed
- reduced number of T-tubules associated with sarcoplasmic reticulum
- only one contractile cell type - cardiomyocyte
- cardiomyocytes communicate through gap junctions (intercalated disk)
Describe smooth muscle
Spindle shaped with single, central, large nucleus
Compare and contrast smooth muscle to other muscle types.
- Can stretch
- Not striated
- No sarcomeres
- No T-tubules
- Capable of being stretched substantially
- Contraction still relies on actin-myosin interactions
- Contraction is slower, more sustained and requires less ATP
- May remain contracted for hours or days
- Respond to numerous stimuli (nerve signals, hormones, drugs, blood gases)
- Form sheets, bundles or layers containing many cells
- Each cell has numerous pinocytic caveolae
Can skeletal muscle repair itself?
Skeletal muscle cells cannot divide, they generate by mitotic activity of satellite cells
Can cardiac muscle repair itself?
Generally considered incapable of regeneration. However new research suggests 1% division.
Fibroblasts invade after damage and lay down scar tissue
Can smooth muscle repair itself?
Can retain their mitotic activity and form new muscle cells
What effect does the sympathetic nervous system have on the heart?
Increases HR
What effect does the parasympathetic nervous system have on the heart?
Decreases HR
What are the differences between cardiac and smooth muscle?
- No sarcomeres in smooth muscle
- Specialised cells/routs for electrical conduction in cardiac muscle
- No troponins in smooth muscle
Describe events leading to contraction of skeletal muscle
Nerve impulse along motor neuron axon arrives at neuromuscular junction. Impulse prompts release of Ach into synaptic cleft causing local depolarisation of sarcolemma. Voltage-gated Na+ channels open and Na+ ions enter cell
What is the role of ionic calcium in contraction?
Ca2+ binds to TnC of troponin. Conformational change moves tropomyosin away from actin’s binding sites. This allows myosin heads to bind actin and contraction begins. Tropomyosin sits in cleft of G-actin ‘spheres’
What is Ptosis?
The drooping of upper eyelid which can occur in one or both eyes
What is atrophy and hypertrophy in terms of muscle remodelling
Destruction > replacement = atrophy
Replacement > destruction = hypertrophy
Describe duchene. Muscular dystrophy.
- Most common muscular dystrophy. Inherited through X-linked recessive pattern.
- Mutation in the dystrophin gene. Absence of dystrophin allows:
- excess calcium to enter muscle cell
- calcium taken up by mitochondria, along with water
- mitochondria burst. Muscle cells burst
- keratins kinase and myoglobin levels are extremely high in the blood.
- Multiple skeletal muscle related symptoms and signs
- Muscle cells replaced by adipose tissue
Describe the pathophysiology of myasthenia gravis
- autoimmune disease
- antibodies directed against Ach receptor
- 30% reduction in receptor number sufficient for symptoms
- endplate ‘invaginations’ in synaptic clefts reduced
- reduced synaptic transmission
- intermittent muscle weakness
What proteins are present in the blood in high quantities over a number of days after a heart attack?
Troponin I&T
If these are present in the blood, this is an indication of a heart attack having happened.
What is the effect of organophosphate (a type of pesticide) poisoning?
Inhibits the normal function of Ach esterase
Ach activity at the neuromuscular junction is potentiated
