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ESA1 - Tissues Of The Body > Muscle > Flashcards

Muscle Flashcards

1
Q

What is a SARCOLEMMA?

A

Outer membrane that surrounds the muscle cell (also includes the basal lamina and reticular fibres)

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2
Q

What are the 3 types of muscle?

A
  • Voluntary SKELETAL
  • Involuntary CARDIAC
  • Involuntary SMOOTH
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3
Q

Describe how skeletal muscles are stimulated to contract

A
  • Stimulus from somatic motor neurones to motor end plate
  • Action potential triggers release of ACh which diffuses across synapse and binds to sarcolemma causing DEPOLARISATION, which spreads down T tubules and triggers the release of Ca2+ from SR, which leads to contraction
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4
Q

Describe the formation of skeletal muscle fibres from myogenic stem cells

A
  • Mesenchymal multipotent cells give rise to MYOBLASTS
  • Myoblasts fuse synchronously forming a primary MYOTUBE with a chain of central nuclei
  • Nuclei displaced to periphery following formation of myofilaments
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5
Q

How does the formation of muscle fibres from myoblasts in cardiac muscle differ from that of skeletal muscle?

A
  • NO FUSION OF MYOBLASTS

- Gap junctions formed at early stage

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6
Q

Describe the characteristics of skeletal muscle

A
  • Cell length ranges from 1mm-20cm (width 10-100μm)
  • STRIATED (darker A band, lighter I band)
  • Long parallel cylinders with multiple peripheral nuclei
  • Muscle fibres bundle into fascicles surrounded by perimysium (bundle to form muscle tissue surrounded by epimysium)
  • T tubules in line with A-I band overlap junction
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7
Q

Describe the action of skeletal muscle

A
  • Rapid forceful contractions for movement of skeleton (joined at tendons)
  • Controlled by somatic motor neurones (VOLUNTARY)
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8
Q

How are muscle cells arranged and joined in cardiac muscle?

A
  • Muscle fibres are BRANCHED

- Joined end to end by INTERCALATED DISCS (composed of gap junctions and adherent-like structures called desmosomes)

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9
Q

What is the purpose of INTERCALATED DISCS in cardiac muscle?

A
  • GAP JUNCTIONS allow coupling of electrical impulses between cells
  • ADHERENT-LIKE structures (desmosomes) anchor cells and actin filaments
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10
Q

What is the purpose of the ENDOMYSIUM?

A
  • Runs between muscle fibres

- Contains blood vessels and nerves

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11
Q

Describe the ultrastructural arrangement of cell components in cardiac muscle fibres

A
  • IRREGULAR arrangement of myofilaments mitochondria and SR
  • Mitochondria and SR penetrate through myofibrils
  • Actin and myosin form CONTINUOUS MASSES in sarcoplasm
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12
Q

Explain how the arrangement of muscle fibres and connective tissue assist in the mobility of the tongue

A
  • Connective tissue (TENDONS) terminate to muscle via interdigitation in multiple directions
  • Multidirectional orientation of muscle fibres and plasticity/strength of tendons allows for mobility
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13
Q

Describe the regions of the contractile unit of the muscle fibre

A
  • A band (region of myosin with some overlapping actin)
  • I band (region of only actin)
  • H zone (region of only myosin)
  • Z disc (runs down centre if I band)
  • M line (runs down centre of H zone)
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14
Q

What is a SARCOMERE?

A
  • Contractile unit of muscle fibre
  • Distance between two Z discs
  • Shortens during contraction
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15
Q

Explain how the SARCOMERE changes during contraction

A
  • Z discs move closer together - SHORTENS
  • H zone and I band also shorten
  • A band remains unchanged
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16
Q

Describe the ultrastructure of skeletal muscle

A
  • Myofilaments bundled together into myofibrils, each surrounded by sarcoplasmic reticulum
  • Abundant mitochondria arranged in rows between myofibrils
  • Nucleus displaced to periphery
17
Q

Explain how TROPONIN can be used as a marker for cardiac iscaemia

A
  • Released from iscaemic cardiac muscle within 1 hour
  • Detection can indicate damage to heart muscle (possibly MI)
  • Must measure within 20 hrs
  • More useful that using enzyme assays
  • QUANTITY OF TROPONIN IS NOT NECESSARILY LINKED TO DEGREE OF DAMAGE
18
Q

Describe the structure of an actin filament

A
  • Actin helix
  • TROPOMYOSIN wrapped around each helix, reinforcing them (blocks myosin binding sites)
  • TROPONIN complexes attachted to tropomyosin
19
Q

Explain the arrangement of myosin in the contractile unit

A
  • Centre of contractile unit is devoid of myosin heads (M line)
  • Myosin heads protrude at opposite ends of the filament
  • Myosin heads extend towards actin filaments in regions of potential overlap
20
Q

Explain the role of Ca2+ ions in the contraction of muscle

A
  • Bind to TnC of troponin causing a conformational change of the protein
  • Conformational change DISPLACES tropomyosin, exposing the myosin binding site on actin
  • Myosin heads can bind and initiate the power stroke
21
Q

Explain the sequence of events involved in the SLIDING FILAMENT MODEL during contraction of muscle

A
  • Ca2+ binds to TnC of troponin, which changes shape and moves tropomyosin, exposing the myosin binding site on actin
  • Myosin head binds to actin and bends, pulling the actin filament towards the M line - this is know as the POWER STROKE (ADP and Pi are released)
  • ATP binds to myosin head, breaking cross bridge
  • ATP –> ADP and Pi and myosin head cocks back (resets)
22
Q

Explain the sequence of events that occur at the NEUROMUSCULAR JUNCTION which lead to contraction of muscle

A
  • Action potential arrive at presynaptic knob and stimulates vesicles containing ACh to fuse with the presynaptic membrane
  • ACh released into neuromuscular cleft and diffuse across to bind with receptors on Na+ channels on motor end plate
  • Na+ channels open causing DEPOLARISATION, which passes down T tubules
  • Stimulates release of Ca2+ from SR which leads to contraction
23
Q

Explain how RIGOR MORTIS occurs shortly after death

A
  • Lack of ATP so myosin heads remain attached to actin (cross bridges cannot be broken)
  • Muscle remains in contracted state
24
Q

Describe the arrangement of T tubules and sarcoplasmic reticulum within striated muscle fibres

A
  • SR wraps around myofibrils with T tubules running in line with A-I band junction (skeletal) or in line with Z discs (cardiac)
  • T tubules in contact with terminal cisternae of SR
  • T tubules and SR arranged in TRIAD arrangement in skeletal muscle and DIAD arrangement in cardiac muscle
25
Q

State the main features of cardiac muscle that distinguish it from other muscle types

A
  • STRIATED like skeletal muscle
  • BRANCHING of muscle fibres
  • INTERCALATED DISCS
  • Centrally positioned nuclei (1 or 2 per cell)
26
Q

What is the role of the sarcoplasmic reticulum (SR)?

A
  • Specialised smooth endoplasmic reticulum of muscle cells
  • Regulates Ca2+ ion concentrations in sarcoplasm of striated muscle
  • Stimulated to release Ca2+ by T tubules receiving wave of depolarisation from motor end plate
27
Q

Explain the contraction exhibited by cardiac muscle and how this is controlled

A
  • Spontaneous, RHYTHMIC
  • Action potentials generated by SAN (sinoatrial node) spread to AVN, which sends a wave of excitation down Purkinje fibres, stimulating ventricular contraction
  • FREQUENCY of action potentials controlled by MEDULLA OBLONGATA in brain (control of heart rate)
28
Q

Describe the structure of the Purkinje fibres of the heart muscle

A

Large (light staining) cells with:

  • Abundant glycogen
  • Few myofilaments
  • Extensive gap junction sites
29
Q

Explain the role of the Purkinje fibres in the contraction of the heart muscle

A
  • Carries impulses from atrioventricular node (AVN) down to apex of heart and up the walls of the ventricles
  • Depolarisation of cardiac muscle fibres stimulates contraction of ventricles in a synchronous manner
  • Speed of conduction is very quick (3-4m/s)
30
Q

Describe the main features of smooth muscle cells

A
  • NON STRIATED
  • Spindle shaped with centrally positioned nuclei
  • Thousands of cells clump together forming bundles or layers
  • NO sarcomeres and NO T tubules
31
Q

How does the contraction of smooth muscle differ from that of skeletal or cardiac?

A
  • SLOWER, requires less ATP
  • Still relies on actin and myosin interactions but NO SARCOMERES
  • Can be stimulated by hormones, drugs and local blood gas concentrations AS WELL AS NERVE SIGNALS
32
Q

Explain the roles of the different smooth muscle cells

A
  • Form contractile walls of passageways or cavities
  • MYOFIBROBLASTS - Important in wound healing (contract to close wound and produce extracellular matrix containing collagen fibres)
  • MYOEPITHELIAL - Form basketwork around secretory units of some exocrine glands and ocular iris
33
Q

List 5 places in the body where you would find smooth muscle

A
  • Walls of blood vessels (tunica media)
  • Muscularis externa of gut wall (2 layers)
  • Ocular iris of eye
  • Genitourinary tract
  • Respiratory tract (bronchioles, trachea)
34
Q

Describe the arrangement of myofilaments in smooth muscle and how this affects contraction

A
  • Arranged DIAGONALLY and spiral down cell
  • Contracts in a TWISTED action, compressing cell
  • Intermediate filaments attached by DENSE BODIES to sarcolemma
35
Q

Explain how skeletal muscle can repair itself following injury

A

_ Muscle cells CANNOT DIVIDE

  • HYPERPLASIA due to increased mitotic activity of SATELLITE cells can increase number of muscle fibres
  • HYPERTROPHY where satellite cells fuse with existing muscle leading to increase in muscle mass
36
Q

Briefly explain the healing of the heart muscle following iscaemic MI

A
  • Death of muscle tissue due to lack of oxygen
  • Cardiac muscle CANNOT REGENERATE
  • Fibroblasts invade following damage and lay down SCAR TISSUE which reduces the force of contraction (less muscle present)
37
Q

Explain why smooth muscle cells are able to regenerate

A
  • Retain their mitotic ability so can form new cells

- Can repair smooth muscle by hyperplasia and hypertrophy of new cells

38
Q

Explain the functions of skeletal muscle

A
  • Movement
  • Posture
  • Heat generation
  • Stability of joints

ESA1 - Tissues Of The Body (19 decks)

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