S13) Muscle Flashcards
Define the following terms:
- Myalgia
- Myasthenia
- Myalgia: muscle pain
- Myasthenia: muscle weakness
Define the following terms:
- Myocardium
- Myopathy
- Myoclonus
- Myocardium: muscular component of the heart
- Myopathy: disease of the muscles
- Myoclonus: sudden spasm of the muscles
Define the following terms:
- Sarcolemma
- Sarcoplasm
- Sarcoplasmic reticulum
- Sarcolemma: outer membrane of a muscle cell
- Sarcoplasm: cytoplasm of a muscle cell
- Sarcoplasmic reticulum: smooth endoplasmic reticulum of a muscle cell
What are the three histological forms of muscle?
- Skeletal muscle (striated)
- Cardiac muscle (striated)
- Smooth muscle (non-striated)
Describe the morphology, connections, control and power of skeletal muscle
- Morphology: long parallel cylinders, multiple nuclei, striations
- Connections: fascicle bundles, tendons
- Control: somatic, voluntary
- Power: rapid, forceful
Describe the morphology, connections, control and power of cardiac muscle
- Morphology: short branched cylinders, central nucleus, striations
- Connections: junctions
- Control: intrinsic rhythm, involuntary autonomic
- Power: lifelong variable rhythm
Describe the morphology, connections, control and power of smooth muscle
- Morphology: spindle-shaped, tapering ends, central nucelus
- Connections: connective tissue, gap junctions
- Control: involuntary, autonomic
- Power: slow, sustained or rhythmic
What is myoglobin and what does it do?
Myoglobin is a red protein containing haem, which functions as an oxygen-storing molecule, providing oxygen to the working muscles
Which type of muscle contains myoglobin?
It is present in skeletal and cardiac muscle only
Explain the relationship between haemoglobin and myoglobin
- Haemoglobin gives up oxygen to myoglobin, especially when pH is lowered
- Active muscles produce CO2 (or lactic acid - anaerobic respiration) both of which result in the more acidic conditions that promote this transfer
What is a muscle fibre?
A muscle fibre is a striated muscle cell
Describe skeletal muscle structure
What is muscle atrophy?
Muscle atrophy is a decrease in the mass of the muscle due to a reduction in the number of cells and/or size of cells
Destruction > replacement
What is muscle hypertrophy?
Muscle hypertrophy involves an increase in size of skeletal muscle through a growth in size of its component cells
Replacement > destruction
What are the causes of atrophy?
- Muscle inactivity
- Malnutrition
- Cancer
- Neurogenic
What are the changes that accompany hypertrophy?
- More contractile proteins (increase in fibre diameter)
- Metabolic increases: enzyme activity for glycolysis, mitochondria, stored glycogen, blood flow
Outline the arrangement of skeletal muscle
- Skeletal muscle is composed of fascicles
- Fasciscles are composed of muscle fibres (cells)
- Muscle fibres are composed of myofibrils
- Myofibrils are composed of myofilaments (actin& myosin)
Explain and describe the use of Troponin in enzyme assays
- Troponin is used as a marker for cardiac ischaemia as it is released from ischaemic cardiac muscle within an hour
- The smallest changes in troponin levels in the blood are indicative of cardiac muscle damage
Describe the structure of a myosin molecule
- A myosin molecule has a rod-like structure with two protruding ‘heads’
- Each thick filament contains many myosin molecules, whose heads protrude at opposite ends
Describe the structure of a thin actin filament
- The actin filament forms a helix around which tropomyosin molecules coil, to reinforce it
- A troponin complex is attached to each tropomyosin molecule
What is creatine kinase and what is it used for?
- CK is an important enzyme in metabolically active tissues like muscle
- Used to measure and diagnose heart attacks as the enzyme increase is proportional to infarct size (superseded by troponin assay)
CK is an enzyme that is also released into the blood by damaged skeletal muscle and brain.
A rise in plasma CK can result from which events/conditions?
- Intramuscular injection
- Vigorous physical exercise
- A fall
- Rhabdomyolysis (severe muscle breakdown)
Identify the steps in the contraction mechanism
- Stage 1: Attachment
- Stage 2: Release
- Stage 3: Bending
- Stage 4: Force Generation
- Stage 5: Reattachment
Outline the 5 stages in the contraction mechanism
⇒ Attachment – myosin head tightly binds to actin molecule
⇒ Release – ATP binds to myosin head causing it to uncouple from the actin filament
⇒ Bending – ATP hydrolysis causes uncoupled myosin head to bend and advance a short distance
⇒ Force Generation – myosin head binds weakly to actin filament, releasing Pi which strengthens binding, (power stroke → myosin head returns to former position)
⇒ Reattachment – ATP binds to the myosin head causing detachment from actin.
What is the role of ionic calcium in the contraction mechanism?
- Ionic calcium bind to TnC of troponin which moves tropomyosin away from actin’s binding sites
- This displacement allows myosin heads to bind actin and contraction begins
What is a neuromuscular junction?
A neuromuscular junction is a chemical synapse formed by the contact between a motor neuron and a muscle fibre
What happens at a neuromuscular junction?
A nerve impulse causes the release of ACh which binds to receptors on the sarcolemma to intiate an action potential propagated along the muscle
Outline the 9 steps involved in the contraction of skeletal muscle
⇒ Nerve impulse arrives at neuromuscular junction
⇒ Ach released into synaptic cleft
⇒ Local depolarization of sarcolemma
⇒ Voltage-gated Na+ channels open (Na+ enters cell)
⇒ General depolarization spreads over sarcolemma (& into T tubules)
⇒ Activation of voltage gated Ca2+ channels
⇒ Ca2+ rapidly released into sarcoplasm
⇒ Ca2+ binds to troponin
⇒ Initation of contraction cycle
Differentiate between hyperplasia and hypertrophy
- Hypertrophy: enlargement of their individual cells
- Hyperplasia: multiplication of their cells
Why is there is a close association of T tubules and diads the sarcoplasmic reticulum?
It permits the release of ionic calcium into the sarcoplasm and allows for subsequent muscle contraction
What are natriuretic peptides?
Natriuretic peptides are peptide hormones that are synthesized by the heart, brain and other organs:
- Atrial natriuretic peptide (ANP)
- Brain-type natriuretic peptide (BNP)
Why are natriuretic peptides released?
Release stimulated by atrial and ventricular distension (response to heart failure)
What do natriuretic peptides do?
They reduce arterial pressure by decreasing blood volume and systemic vascular resistance (counter-regulatory system for RAAS)
What is ANP?
ANP is a peptide that is synthesized, stored, and released by atrial myocytes in response to atrial distension
What is BNP?
BNP is a peptide synthesised largely by the ventricles (and brain)
What are Purkinje fibres?
Purkinje fibres are specialised myocardial cells which carry impulses to ventricular muscle from the AVN
Identify 3 unique cellular features of purkinje fibres
- Abundant glycogen
- Sparse myofilaments
- Extensive gap junction sites
What do Purkinje fibres do?
Purkinje fibres conduct action potentials rapidly, enabling the ventricles to contract in a synchronous manner
Where can smooth muscle be found?
Smooth muscle often forms the contractile walls of passageways or cavities e.g. of vascular structures, respiratory tract and genitourinary system
What are indicators of muscle injury/necrosis?
- Creatine kinase (all muscle)
- Myoglobinuria (skeletal muscle)
- Troponin I (cardiac)
Identify some diseases caused by smooth muscle dysfunction
- Asthma
- Irritable Bowel Syndrome
- Primary hypertension
- Atherosclerosis
Modified smooth muscle cells can occur as myoepithelial cells or myofibroblast cells.
What are myoepithelial cells?
Myoepithelial cells are stellate cells which form a basketwork around the secretory units of some exocrine glands e.g sweat, salivary and mammary glands
Modified smooth muscle cells can occur as myoepithelial cells or myofibroblast cells.
What are myofibroblast cells and what do they do?
Myofibroblasts are modified fibroblasts which produce collagenous matrix and contract at sites of wound healing
Compare and contrast the limited nature of repair possible in the different forms of mature muscle
- Skeletal muscle cells cannot divide but regenerate through satellite cells, (hyperplasia follows muscle injury)
- Cardiac muscle cells are incapable of regeneration (scar tissue forms after damage)
- Smooth muscle cells retain their mitotic activity and can form new smooth muscle cells
