8.1 Muscle Flashcards
Describe the structure of skeletal muscle, how its cells are joined, somatic/autonomic and power.
- Long parallel cylinders, multiple peripheral nuclei, striations
- Cells joined by fascicles
- Somatic
- Rapid, forceful
Describe the structure of smooth muscle, how its cells are joined, somatic/autonomic and power.
- Spindle shaped, single central nucleus no striations
- Joined by connective tissue, gap and desmosome junctions
- Autonomic
- Slow, sustained
Describe the structure of cardiac muscle, how its cells are joined, somatic/autonomic and power.
- Short branched cylinders, single central nucleus, striations
- Joined by gap junctions cell to cell
- Autonomic
- Variable but lifetime rhythm!
What is myalgia?
Muscle pain
What is myasthenia?
Weakness of the muscles
What is myopathy?
Any disease of the muscles
What is a myoclonus?
A sudden spasm of the muscles
What is the sarcolemma?
The outer membrane of the muscle cell
What is the sarcoplasmic reticulum?
The smooth endoplasmic reticulum of a muscle cell
What is a myocardium?
Muscular component of the heart and contains cardiomyocytes
What is atrophy? Name the 3 types.
Destruction of muscle > replacement of muscle
- Disuse atrophy - muscle fibres do not fire so loss of protein
- Age
- Denervation - nerve cut and muscle receives no firing so loss of protein
What is hypertrophy?
Replacement > destruction
Increase in fibre diameter
E.g. Due to exercise
What is myoglobin and which type of muscle is it present in?
Oxygen storing molecule in blood to give to muscles
Similar to 1 sub unit of Hb
Contained in skeletal and cardiac but not present in smooth
What is fibrillation?
Contraction of individual muscle cells
What is fasciculation?
Contraction of whole groups of muscle cells
Describe the structure of skeletal muscle.
Myofibrils formed by actin, myosin, troponin and tropomyosin
Myofibrils come together and form muscle fibre (cell)
Muscle fibres held together by endomysium forming fascicles
Fascicles held together by perimysium forming muscle
Muscle wrapped in epimysium
Goes onto form tendon, which attaches to bone
Ultra structure of actin myosin filaments
A band darker (actin + myosin)
I band lighter (just actin)
Z band (just actin zig zag) in I band M band (half way) in A band
Name the two types of muscle fibre
Red and white
Where do T tubules lie in skeletal and cardiac muscle respectively?
Skeletal - A-I band
Cardiac - Z band
What is cell hypertrophy
Cells become enlarged (abundance does not change)
What is cell hyperplasia
Cells multiply and become more abundant (size does not change)
What are satellite cells?
Precursor of skeletal muscle
Plays a part in repair
Talk briefly about the ability to repair skeletal, cardiac and smooth muscle
Skeletal - cells cannot divide but mitotic activity of satellite cells repairs. Satellite cells then fuse with existing muscle cells (hypertrophy).
Cardiac - incapable of regeneration, fibroblasts just repair damage by laying down scar tissue
Smooth - cells retain mitotic acitivity e.g. Woman’s uterus (hyperplasia)
What is a sarcomere?
Z-Z containing actin and myosin
What are the markers for muscle damage?
- Creatine Kinase - present in all muscle
- Myoglobinuria - skeletal muscle and passed into urine
- Troponin I - cardiac
- ANP/BNP - atrial and ventricular stretching. Levels correlate with symptom severity.
Outline the muscle contraction process.
- A nerve impulse arrives via motor neurone axon and reaches the neuromuscular junction
- ACh released into the synaptic cleft, binds and depolarise the sarcolemma
- Voltage gated Na+ channels open causing Na+ to enter
- Depolarisation travels down T tubules
- Gated Ca2+ released from SR to sarcoplasm
- Increased amount of calcium, Ca2+ binds to TnC of troponin and causes a conformational change, causing tropomyosin to move away from actins binding sites
- Myosin head tightly binds to actin molecule (Cross bridge)
- ATP hydrolysis uncoupled myosin and causes the head to bend and advance a short distance
- Myosin binds weakly this time causing release of Pi which causes power stroke - the myosin returns to its former position
- ATP binds causing detachment from actin
- Cycle repeats
What are the two types of modified smooth muscle cells that occur in smooth muscle?
- Myoepithelial cell - basketwork around secretory units of exocrine glands - contraction of glands!
- Myofibroblasts - produce collageneous matrix, for wound healing, they have actin and myosin so contract too!
Why is muscle striated?
Longitudinal nature of actin and myosin
What are the two types of muscle fibres?
Red
- more vascularised, mitochondria, myoglobin
- slow repetitive contractions so not easily fatigued
- lots of oxidative enzymes, not much ATPase
- limb muscle e.g.
White
- less vascularised, mitochondria, myoglobin
- faster, stronger contractions but easily fatigued
- not much oxidative enzyme, but rich in ATPase
- muscles controlling fingers e.g.
What is the H zone?
Section of myosin where there is no overlap with actin
Contains the M line
What are the Purkinje fibres? (4)
- Modified muscle cell
- Sparse myofilaments and extensive gap junction sites
- Carry action potentials from AV node to ventricle muscle
- Allow rapid and synchronous contraction
Where are T tubules found in smooth muscle?
They are not present.
How are thick and thin filaments arranged in smooth muscle cells and how do they contract?
Arranged diagonally spiralling down long axis
Muscle contracts in a twisting way
Less ATP needed than cardiac/skeletal muscle but still relies on actin and myosin
What do smooth muscle contractions rely on?
They are innervated by the ANS that release NT from varicosities to wide synaptic cleft.
They respond to stimuli from nerve signals, hormones, drugs and local conc of blood gases
Why do muscles stiffen after death and what is it called?
Rigor mortis - no ATP
What can happen from the dysfunction of smooth muscle?
Asthma
IBS
Hypertension
Detrusor muscle instability (found in wall of bladder)
