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(LUSUMA) Body Logistics > S13) Muscle > Flashcards

S13) Muscle Flashcards

1
Q

Define the following terms:

  • Myalgia
  • Myasthenia
A
  • Myalgia: muscle pain

- Myasthenia: muscle weakness

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2
Q

Define the following terms:

  • Myocardium
  • Myopathy
  • Myoclonus
A
  • Myocardium: muscular component of the heart

- Myopathy: disease of the muscles

- Myoclonus: sudden spasm of the muscles

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3
Q

Define the following terms:

  • Sarcolemma
  • Sarcoplasm
  • Sarcoplasmic reticulum
A
  • Sarcolemma: outer membrane of a muscle cell

- Sarcoplasm: cytoplasm of a muscle cell

- Sarcoplasmic reticulum: smooth endoplasmic reticulum of a muscle cell

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4
Q

What are the three histological forms of muscle?

A
  • Skeletal muscle (striated)
  • Cardiac muscle (striated)
  • Smooth muscle (non-striated)
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5
Q

Describe the morphology, connections, control and power of skeletal muscle

A
  • Morphology: long parallel cylinders, multiple nuclei, striations
  • Connections: fascicle bundles, tendons
  • Control: somatic, voluntary
  • Power: rapid, forceful
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6
Q

Describe the morphology, connections, control and power of cardiac muscle

A
  • Morphology: short branched cylinders, central nucleus, striations
  • Connections: junctions
  • Control: intrinsic rhythm, involuntary autonomic
  • Power: lifelong variable rhythm
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7
Q

Describe the morphology, connections, control and power of smooth muscle

A
  • Morphology: spindle-shaped, tapering ends, central nucelus
  • Connections: connective tissue, gap junctions
  • Control: involuntary, autonomic
  • Power: slow, sustained or rhythmic
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8
Q

What is myoglobin and what does it do?

A

Myoglobin is a red protein containing haem, which functions as an oxygen-storing molecule, providing oxygen to the working muscles

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9
Q

Which type of muscle contains myoglobin?

A

It is present in skeletal and cardiac muscle only

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10
Q

Explain the relationship between haemoglobin and myoglobin

A
  • 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
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11
Q

What is a muscle fibre?

A

A muscle fibre is a striated muscle cell

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12
Q

Describe skeletal muscle structure

A
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13
Q

What is muscle atrophy?

A

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

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14
Q

What is muscle hypertrophy?

A

Muscle hypertrophy involves an increase in size of skeletal muscle through a growth in size of its component cells

Replacement > destruction

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15
Q

What are the causes of atrophy?

A
  • Muscle inactivity
  • Malnutrition
  • Cancer
  • Neurogenic
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16
Q

What are the changes that accompany hypertrophy?

A
  • More contractile proteins (increase in fibre diameter)
  • Metabolic increases: enzyme activity for glycolysis, mitochondria, stored glycogen, blood flow
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17
Q

Outline the arrangement of skeletal muscle

A
  • 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)
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18
Q

Explain and describe the use of Troponin in enzyme assays

A
  • 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
19
Q

Describe the structure of a myosin molecule

A
  • 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
20
Q

Describe the structure of a thin actin filament

A
  • The actin filament forms a helix around which tropomyosin molecules coil, to reinforce it
  • A troponin complex is attached to each tropomyosin molecule
21
Q

What is creatine kinase and what is it used for?

A
  • 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)
22
Q

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?

A
  • Intramuscular injection
  • Vigorous physical exercise
  • A fall
  • Rhabdomyolysis (severe muscle breakdown)
23
Q

Identify the steps in the contraction mechanism

A
  • Stage 1: Attachment
  • Stage 2: Release
  • Stage 3: Bending
  • Stage 4: Force Generation
  • Stage 5: Reattachment
24
Q

Outline the 5 stages in the contraction mechanism

A

⇒ 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.

25
Q

What is the role of ionic calcium in the contraction mechanism?

A
  • 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
26
Q

What is a neuromuscular junction?

A

A neuromuscular junction is a chemical synapse formed by the contact between a motor neuron and a muscle fibre

27
Q

What happens at a neuromuscular junction?

A

A nerve impulse causes the release of ACh which binds to receptors on the sarcolemma to intiate an action potential propagated along the muscle

28
Q

Outline the 9 steps involved in the contraction of skeletal muscle

A

⇒ 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

29
Q

Differentiate between hyperplasia and hypertrophy

A
  • Hypertrophy: enlargement of their individual cells
  • Hyperplasia: multiplication of their cells
30
Q

Why is there is a close association of T tubules and diads the sarcoplasmic reticulum?

A

It permits the release of ionic calcium into the sarcoplasm and allows for subsequent muscle contraction

31
Q

What are natriuretic peptides?

A

Natriuretic peptides are peptide hormones that are synthesized by the heart, brain and other organs:

  • Atrial natriuretic peptide (ANP)
  • Brain-type natriuretic peptide (BNP)
32
Q

Why are natriuretic peptides released?

A

Release stimulated by atrial and ventricular distension (response to heart failure)

33
Q

What do natriuretic peptides do?

A

They reduce arterial pressure by decreasing blood volume and systemic vascular resistance (counter-regulatory system for RAAS)

34
Q

What is ANP?

A

ANP is a peptide that is synthesized, stored, and released by atrial myocytes in response to atrial distension

35
Q

What is BNP?

A

BNP is a peptide synthesised largely by the ventricles (and brain)

36
Q

What are Purkinje fibres?

A

Purkinje fibres are specialised myocardial cells which carry impulses to ventricular muscle from the AVN

37
Q

Identify 3 unique cellular features of purkinje fibres

A
  • Abundant glycogen
  • Sparse myofilaments
  • Extensive gap junction sites
38
Q

What do Purkinje fibres do?

A

Purkinje fibres conduct action potentials rapidly, enabling the ventricles to contract in a synchronous manner

39
Q

Where can smooth muscle be found?

A

Smooth muscle often forms the contractile walls of passageways or cavities e.g. of vascular structures, respiratory tract and genitourinary system

40
Q

What are indicators of muscle injury/necrosis?

A
  • Creatine kinase (all muscle)
  • Myoglobinuria (skeletal muscle)
  • Troponin I (cardiac)
41
Q

Identify some diseases caused by smooth muscle dysfunction

A
  • Asthma
  • Irritable Bowel Syndrome
  • Primary hypertension
  • Atherosclerosis
42
Q

Modified smooth muscle cells can occur as myoepithelial cells or myofibroblast cells.

What are myoepithelial cells?

A

Myoepithelial cells are stellate cells which form a basketwork around the secretory units of some exocrine glands e.g sweat, salivary and mammary glands

43
Q

Modified smooth muscle cells can occur as myoepithelial cells or myofibroblast cells.

What are myofibroblast cells and what do they do?

A

Myofibroblasts are modified fibroblasts which produce collagenous matrix and contract at sites of wound healing

44
Q

Compare and contrast the limited nature of repair possible in the different forms of mature muscle

A
  • 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

(LUSUMA) Body Logistics (19 decks)

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