Muscle Flashcards
What are the three types of muscle?
Non striated - smooth muscle
Striated - skeletal muscle
- cardiac muscle
What type(s) of muscle is myoglobin present in?
Skeletal and cardiac muscle
More muscle destruction than muscle replacement = ____________
Atrophy
More muscle replacement than muscle destruction = _____________
Hypertrophy
What are the two types of atrophy in skeletal muscle?
Disuse atrophy - weakness due to not using muscle e.g. In elderly, loss of protein, reduced muscle diameter, loss of power and loss of temperature regulation
Denervation atrophy - lower motor neurone lesions - weakness, flaccidity. Re-nervation within 3 months for recovery
What is skeletal muscle hypertrophy?
More contractile proteins, increased fibre diameter. Increased enzyme activity for glycolysis, increased mitochondria, stored glycogen and blood flow (gym gains)
What is the power stroke?
Activated myosin heads bind to actin filaments, myosin pull actin towards M line (sarcomere gets shorter)
What proteins regulate actin in skeletal muscle?
Troponin - globular
Tropomyosin - fibrous
How does calcium control muscle contraction?
When Ca ions released from sarcoplasmic reticulum in response to depolarisation travelling down T tubules, binds to TnC of troponin which displaces tropomyosin - exposing binding sites
What happens in irreversible overstretching?
A and I lines no longer overlap (thought to feature in some cardiac pathologies such as enlarged ventricles)
How is skeletal muscle contraction initiated?
Nerve impulse along motor neurone arrives at NMJ, causes realease on acetyl Choline. Binds sarcolemma and causes local depolarisation, voltage gated sodium channels open, sodium floods in - depolarisation spreads over sarcolemma into T tubules. Voltage sensor proteins change conformation, activating voltage gated calcium channels on adjacent cisternae - calcium released into sarcoplasmic
What is cell hyperplasia?
Increase in cell number
What are natriuretic peptides? And when are they released?
Peptide hormones synthesised in the heart and brain. Release by the heart is stimulated by atrial and ventricular distension (stretching) usually in response to heart failure
What is the function of natriuretic peptides?
To lower arterial pressure by decreasing blood volume and systemic vascular resistance (promote Na release in kidneys)
How is smooth muscle contraction different from skeletal muscle?
Still relies on actin-myosin interactions (no sarcomeres) - sower, more sustained and requires less ATP
How much circulating blood volume is there in the average 70kg person?
5L circulating blood - 2L red cells and 3L plasma
What major arteries arise from the aorta?
Carotid arteries - to brain
Subclavian arteries - down arms
Descending aorta down abdomen splits into two iliac arteries
What is systole?
Contraction of the heart- left ventricle contraction causes increases in blood pressure in the aorta - walls of aorta stretch
What is diastole?
Aortic valve closes (and pulmonary). Aorta walls recoils - maintains pressure on blood - move if towards heart and smaller vessels. Aortic pressure drops
What shape are skeletal muscle cells?
Long parallel cylinders
Multiple peripheral nuclei
What shape are cardiac muscle cells?
Short branched cylinders
Single central nucleus
What shape are smooth muscle cells?
Spindle shaped
Single central nucleus
Creatine kinase in the blood may be high due to…
Intramuscular injection Vigorous exercise A fall Severe muscle breakdown Acute kidney injury
How are actin and myosin arranged in cardiac muscle cells?
Distinct myofibrils are absent, actin and myosin firm continuous masses in the cytoplasm
Intercalated discs in a step-type arrangement substitute for the Z band (where cells meet end to end) and allow electrical and mechanical coupling to adjacent cells
Natriuretic peptides serve as a counter regulatory system for what?
The renin- angiotensin- aldosterone system
What are purkinje fibres?
Specialised myocardial cells that carry electrical impulses from the AV node to the ventricles rapidly - enables the ventricle to contact in synchronicity
What are the structural features of purkinje fibres?
Large Demi’s with abundant glycogen, sparse myofilaments and extensive gap junctions
What stimuli does smooth muscle respond to?
Nerve signals
Hormones
Drugs
Local blood gas concentrations