BL Session 8 - Muscular System and Cardiovascular System Flashcards Preview

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Flashcards in BL Session 8 - Muscular System and Cardiovascular System Deck (65)
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Define the following terms:

- Myalgia

- Myasthenia

- Myocardium

- Myopathy

- Myoclonus

- Myalgia: Muscle pain.

- Myasthenia: Weakness of the muscles.

- Myocardium: Muscular component of the heart.

- Myopathy: Any disease of the muscles.

- Myoclonus: A sudden spasm of the muscles.


Define the following terms:

- Sarcolemma

- Sarcoplasm

- Sarcoplasmic reticulum

- Sarcolemma: The outer membrane of a muscle cell.

- Sarcoplasm: The cytoplasm of a muscle cell.

- Sarcoplasmic reticulum: The smooth endoplasmic reticulum of a muscle cell.


Identify the three histological forms of muscle.


Characterise the three major categories of muscle in terms of:

- Morphology

- Connections

- Control

- Power

- Morphology:

I. Skeletal - striations, long parallel bundles, multiple peripheral nuclei

II. Cardiac - striations, short and branched, small central nucleus

III. Smooth - no striations, spindle shaped, small central nucleus

- Connections:

I. Skeletal - fascicles, tendons

II. Cardiac - junctions 

III. Smooth - connective tissue 

- Control:

I. Skeletal - somatic voluntary 

II. Cardiac - autonomic involuntary

III. Smooth - autonomic involuntary

- Power:

I. Skeletal - rapid and forceful 

II. Cardiac - lifelong variable rhythm 

III. Smooth - slow and sustained


Outline the appearance of skeletal muscle.

Histologists have identified

- Narrower red skeletal muscle fibres.

- Wider white skeletal muscle fibres.

- Intermediate skeletal muscle fibres.


Red, white and intermediate skeletal muscle fibres are present in any given muscle, but their proportions depend on the functional role of the muscle. Compare and contrast the different forms on the basis of:

- Diameter

- Vascularisation

- Myoglobin

- Mitochondria

- Contraction

- Fatigue

- Enzymes

- Innervation

- Typical location


Describe the structure and function of myoglobin, as well as where it can be found.

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

- It is structurally similar to a subunit of haemoglobin.

- It is present in skeletal and cardiac muscle but is said not to be present in smooth muscle.


Outline the structure of skeletal muscle

A striated muscle cell is called a muscle fibre 


Describe the appearance of skeletal muscle in an H&E stained light micrograph.

- Peripheral nuclei can be observed (TS)

- Nuclei in rows can be observed (LS)

- Dashed line shows boundary of a fascicle

- Each fasicle is surrounded by perimysium


Outline the remodeling of muscles.

- Continual - Replacement of contractile proteins in 2 weeks

- Destruction > replacement = atrophy

- Replacement > destruction = hypertrophy


What are the types of muscle atrophy?

- Denervation atrophy

I. Signs of lower motor neurone lesions: weakness, flaccidity, muscle atrophy

II. Re-innervation within 3 months for recovery


- Disuse atrophy:

I. E.g. Bed rest, limb immobilisation, sedentary behaviour

II. Loss of protein - reduced fibre diameter - loss of power


Explain how muscle length may adjust.

- Increases by frequent stretching (addition of sarcomeres)

- Converse is true: consider limb in plaster


Describe the appearance of the skeletal muscle ultrastructure in transverse section in a TEM.


Describe the appearance of the skeletal muscle sarcomere bands in TEM.


Actin, troponin and tropomyosin molecules complex to form the thin filaments of skeletal and cardiac muscle. Outline the significance of Troponin.

- Troponin Assays are a useful diagnostic tool

- Troponin used as a marker for cardiac ischaemia

- Released from ischaemic cardiac muscle within an hour.

- Must measure within 20 hours.

- The smallest changes in troponin levels in the blood are indicative of cardiac muscle damage.

- However, the quantity of troponin is not necessarily proportional to the degree of damage.

- Used by emergency units as the assay of choice, superseding muscle enzyme assays.


Briefly outline the composition of skeletal muscles.

- Skeletal muscles are composed of fascicles

- Fascicles are composed of muscle fibres (cells)

- Muscle fibres are composed of myofibrils

- Myofibrils are composed of myofilaments (actin & myosin)


Describe the structure of an individual myosin molecule.

- An individual myosin molecule has a rod-like structure from which two 'heads' protrude.

- Each thick filament consists of many myosin molecules, whose heads protrude at opposite ends of the filament


Describe the structure of the actin filament and troponin complex.

- The actin filament forms a helix.

- Tropomyosin molecules coil around the actin helix, reinforcing it.

- A troponin complex is attached to each tropomyosin molecule

- In the centre of the sarcomere, the thick filaments are devoid of myosin heads.

- The myosin heads extend towards the actin filaments in regions of potential overlap.


Outline the role and significance of Creatine Kinase.

- CK is an important enzyme in metabolically active tissues like muscle.

- CK used to be measured to diagnose heart attacks (MIs), enzyme increase being largely proportional to infarct size, but has been largely 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:

I. Intramuscular injection

II. Vigorous physical exercise

III. A fall (especially in the elderly)

IV. Rhabdomyolysis (severe muscle breakdown)

V. muscular dystrophy

VI. Acute kidney injury


Outline the contraction mechanism in light of the following stages:

- Attachment

- Release

- Bending

- Force Generation

- Reattachment

- Stage 1: Attachment – Myosin head tightly binds to actin molecule in regions of overlap.

- Stage 2: Release – ATP binds the myosin head causing it to uncouple from the actin filament.

- Stage 3: Bending – Hydrolysis of the ATP causes the uncoupled myosin head to bend and advance a short distance 

- Stage 4: Force Generation – The myosin head binds weakly to the actin filament causing release of inorganic phosphate which strengthens binding, and causes the ‘power stroke’ in which the myosin head returns to its former position.

- Stage 5: Reattachment – ATP binds to the myosin head causing detachment from actin. The myosin head will bind tightly again and the cycle will repeat. 


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

- When increased amounts of ionic calcium bind to TnC of troponin, a conformational change moves tropomyosin away from actin's binding sites.

- This displacement allows myosin heads to bind actin, and contraction begins.


Describe the structure of a neuromuscular junction as well as its role.

- Small terminal swellings of the axon that contain vesicles of acetylcholine.

- A nerve impulse causes the release of acetylcholine which binds receptors on the sarcolemma to initiate an action potential propagated along the muscle


Outline the contraction of skeletal muscle.

- Initiation: nerve impulse along motor neuron axon arrives at neuromuscular junction.

- Impulse prompts release of acetylcholine (Ach) into synaptic cleft causing local depolarization of sarcolemma.

- Voltage-gated Na+ channels open; Na+ enters cell.

- General depolarization spreads over sarcolemma and into T tubules, causing them to change their conformation.

- Ca2+ is rapidly released from the terminal cisternae into the sarcoplasm.

- Ca2+ binds to the TnC subunit of troponin.

- The contraction cycle is initiated and Ca2+ is returned to the terminal cisternae of sarcoplasmic reticulum.


The cardiac muscle fibres in LS show:

- Striations

- Centrally positioned nuclei (1 or 2 per cell)

- Intercalated discs (for electrical & mechanical coupling with adjacent cells - see asterisks)

- Branching (arrows)


The cardiac muscle fibres in TS show:

- Central nuclei

- Endomysium bearing a rich supply of capillaries

- Some lobular profiles representing incipient branching of fibres


Describe the appearance of the ultrastructure of the cardiac muscle in TS in a TEM.

- In contrast to skeletal muscle, the distinct myofibrils are absent; instead myofilaments of actin and myosin form continuous masses in the cytoplasm.

- Mitochondria and sarcoplasmic reticulum penetrate through the cytoplasm between the myofilaments.


Outline the structure and location of T tubules and the sarcoplasmic reticulum of cardiac muscle.

- In contrast to skeletal muscle, the T tubules of cardiac muscle lie in register with the Z bands and not with the A-I band junction.

- The close association of the sarcoplasmic reticulum and the T tubules at the diads permits the release of ionic calcium into the sarcoplasm and subsequent muscle contraction.


What are natriuretic peptides?

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

- The release of these peptides by the heart is stimulated by atrial and ventricular distension, usually in response to heart failure.


What are the functions of natriuretic peptides?

Reduce arterial pressure by:

- Decreasing blood volume

- Decreasing systemic vascular resistance.



Outline ANP.

- Atrial natriuretic peptide (ANP) is a peptide that is synthesized, stored, and released by atrial myocytes in response to atrial distension (amongst other stimulations).

- Therefore, elevated levels of ANP are found during hypervolemic states (elevated blood volume), which occur in congestive heart failure (CHF).