The Muscular System Flashcards
What is atrophy?
destruction – loss of protein, reduced fibre diameter, loss of power, 50% loss by 80yrs
What is Hypertrophy?
getting bigger, replacement – increase in fibre diameter
What is Hyperplasia?
proliferation of more cells, number increases (not size)
What is Myalgia?
muscle pain
What is Myasthenia?
weakness of muscles
What is Myoclonus?
sudden spasm of muscle
What is Sarcolemma?
outer membrane of muscle cell
What is Sarcoplasm?
cytoplasm of muscle cell
What is Sarcoplasmic reticulum?
smooth ER of muscle cell
In skeletal muscle what organelles are abundant?
mitochondria
Where are the nuclei placed in skeletal muscle?
peripheral, multinucleated
How does skeletal muscle regenerate?
via satellite cells
What is the structure of skeletal muscle?
epimysium wraps multiple fasicles –> perimysium wraps single fasicle –> endomysium on top of sarcolemma wraps a muscle fibre –> muscle fibre = myofibrils (actin/myosin) + sarcoplasm
Outline the muscle contraction process
Nerve impulse travels nerve to neuromuscular junction between axon terminal and muscle fibre, ACh released, 2 bind, nAChRs, depolarises sarcolemma, Na+ channels open, Depolarisation travels down T tubules. Ca2+ released from sarcoplasmic reticulum, Ca2+ binds TnC of troponin on actin moving tropomyosin revealing myosin binding site, ATP –> ADP + P = myosin head extends, Myosin binds forming cross-bridges, Power stroke triggered = myosin pulls actin towards M line (shortening sarcomere) = sliding filament mechanism, ADP + P released during power stroke, ATP binds bringing myosin back to relaxed position
In skeletal muscle where do T tubules lie?
A-I band junction
Where are the nuclei in cardiac muscle?
Central
In cardiac muscle where do T tubules lie?
Z band
What are the functions of purkinje fibres?
Modified muscle cell = Carry action potentials from the AV node to the ventricle muscle, Allow rapid conduction = synchronous contraction
How does cardiac muscle regenerate?
Incapable of regeneration – damage = fibroblasts invade = lay down scar tissue
Which muscle type has no myoglobin?
Smooth
In smooth muscle where are the T tubules found?
Nowhere, they are not present
Where are the nuclei placed in cardiac muscle?
Central
What is the difference between a smooth muscle contraction and a cardiac/skeletal?
Smooth = Slower contraction, more sustained, requires less ATP for actin-myosin
List muscle injury markers
CK: all. Myoglobinuria: myoglobin from muscle secreted in urine, skeletal. Troponin: cardiac ischemia, measure in 20hrs, not proportional to amount of damage. Natriuretic peptide: secreted by atria/ventricles in response to excessive stretching of cardiomyocytes – levels correlate with symptom severity, aim = reduce arterial pressure by decreasing blood volume - ANP: released by atrial myocytes, found during hypovolemic states = congestive heart failure, BNP: released by ventricles
Why is muscle striated?
Longitudinal nature of actin and myosin
What is the H Zone?
Section of myosin where there is no overlap of actin
Describe a smooth muscle cell
Spindle shape, central nucleus
What are the 2 cell types present in smooth muscle?
Myoepithelial = contraction of glands. Myofibroblasts = wound healing
What is the structure of cardiac muscle cell?
Striated, central nuclei
What is a sarcomere?
Contractile unit, from one Z band to another
What is the M line?
Line that holds myosin fibres together
What can happen from the dysfunction of smooth muscle?
Asthma, irritable bowel, hypertension
What happens when ANP/BNP is released?
Na excretion by the kidneys = water travels with = lowers water volume = lowers BP = allows heart to rest when over-stretched
What are the 2 different types of muscle fibre?
Red = high mitochondria, sustained contraction. White = powerful but easily fatigued
What are the markers of muscle damage?
CK = all muscle. Myoglobinuria = skeletal muscle. Troponin I = cardiac. ANP/BNP = ventricular stretching
What are the different types of atrophy?
Disuse - muscle not used = wasting. Denervation = motor neurone lesion - 3 month recovery. Age = 50% loss by 80yrs
Outline the banding structure in a sarcomere
A - myosin I - actin with no myosin overlap H - myosin with no actin overlap M - holds myosin together Z-Z - sarcomere
A-I - skeletal T tubules
Z - cardiac T tubules
