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Histology > Muscle Tissue > Flashcards

Muscle Tissue Flashcards

1
Q

what is muscle tissue in general responsible for?

A

movement of the body and for changes in size and shape of internal organs

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2
Q

what two types of filaments (myofilaments) can be found in muscle cell and what are they responsible for?

A

myofilaments are responsible for contraction of a muscle cell/fiber

there are two types of myofilaments:
1. thin filaments - 6-8nm diameter, 1um long
- composed of actin
- fibrous actin (F-actin) formed from globular actin
(G-actin) molecules

  1. thick filaments - 10-15nm diameter, 1.5um long
    - composed of myosin II
    - 200-300 mysin II mols compose each filament
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3
Q

what is another name for cytoplasm in a muscle cell?

A

sarcoplasm

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4
Q

what is another name for the plasma membrane (and basal lamina and reticular lamina) of a muscle cell?

A

sacrolemma

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5
Q

how is muscle classified?

what are the classifications of muscles and subclassifications?

A

muscle tissue is classified by the appearance of the contractile cells.

there are two principle types of muscle:

1. striated muscle
2. smooth muscle

striated muscle can be subclassified due to location into:
1. skeletal striated muscle - attached to bone, responsible for posture and body position

  1. visceral striated muscle - restricted to soft tissue but identical to skeletal muscle. tongue, larynx, oesophagus
  2. cardiac muscle - found in wall of the heart
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6
Q

what are the 3 stages of connective tissue investments of skeletal muscle?

A
  1. endomysium - surrounds individual muscle fibers, composed of reticular fibres and an external lamina
  2. perimysium - surrounds fasicles of muscle cells
  3. epimysium - surrounds the entire muscle (forming aponeuroses and tendons)
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7
Q

what are the functions of the connective tissue investments found in skeletal muscle?

A

connective tissue investments:
1. convey neural and vascular elements to muscle cells

  1. provide a vehicle that harness the forces of muscle contraction
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8
Q

what are the types of skeletal muscle cells?

A
  1. Red (slow contraction, do not tire easily)
  2. White (fast contraction, do tire easily)
  3. Intermediate

All can be found in the same muscle

A change of innervation can change a fibre type to another
Red cell can be changed to white cell by innervating the red cell by that of a white cell

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9
Q

what is the difference between the 3 types of skeletal muscle cells? (Red/White/Intermediate)

A
  1. the amount of myoglobin
  2. number of mitochondria
  3. concentrations of various enzymes
  4. the rate of contraction
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10
Q

what are T tubules?

A

T (transverse) tubules are invaginations of the sarcolemma which extend into the cell, that lie along the A-I band junction of each sarcomere.

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11
Q

what are myofibrils?

A

skeletal muscles contain cylindrical collections of myofibrils which extend the entire length of the muscle cell.

myofibrils are 1-2um in diameter

each myofibril is composed of thick and thin myofilaments

  • the precise arrangement of myofibrils result in a characteristic banding pattern of alternating dark and light bands
  • the dark band constitues the A band and the light band the I Band. the I band is dissected by the Z line (formed from Z disks tethers together by Desmin)
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12
Q

what is a sarcomere?

A

a sarcomere is a functional unit of contraction found within a myofibril.
a sarcomere is the regular repeating pattern between two successive Z disks

Z disk, 1/2 I band, A band(H band (M line)), 1/2 I band, Z disk

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13
Q

what is sarcoplasmic reticulum?

location and function?

A

SR is modified SER
SR surrounds myofilaments and forms a meshwork around each myofibril
- SR forms a pair of dilated terminal cisternea, which encircle the myofibrils ar the junction of each A and I band (part of the triad)
- SR regulates muscle contraction through sequestering and releasing Ca2+ ions

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14
Q

what are triads in skeletal muscle cells?

A

triads are specialised complexes consisting of a narrow central T tubule (formed from the sarcolemma) flanked by the terminal cisternea of SR.

triads are located at the A-I junction of skeletal muscle cells and jelp provide uniform contraction throughout the muscle cell.

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15
Q

where are satellite cells found within skeletal muscle tissue?
what are there functions?

A

satellite cells lie within the external lamina of skeletal muscle cells
satellite cells are regenerative, they can differentiate and fuse together to form skeletal muscle cells when needed.

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16
Q

skeletal muscle striations - what is the Z line?

A

Z disk - dense region disecting each I band

 - the Z disk consists of a-actinin and Cap-Z, two proteins that bind to thin filaments and anchor them with the assistance of nebulin
- the Z-disks are held together by desmin and plectin to form the Z line. 
- Z disks are anchored to the regions of the sarcolemma at the periphery through vinculin and dystophin (costameres)
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17
Q

skeletal muscle striations - what is the I band?

A

the I band is the lighter band of the myofibril banding pattern
the I band is disected by the Z line
the I band is isotropic
the I band is lighter compared to the adjacent A band as it contains only the thin filaments

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18
Q

skeletal muscle striations - what is the A band

A

the A band is found adjacent to the I band
the A band is Anisotrpic
the A band is darker compared to the I band as it contains both the thin and thick filaments - 6 thin filaments surround each thick filament

the A band is disected by the H band

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19
Q

skeletal muscle striations - what is the H band?

A

the H band disects the A band and is the lighter region within the A band.
the H band contains only the thick filaments and is therefore lighter than the A band
the H band is disected by the M line

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20
Q

skeletal muscle striations - what is the M line?

A

the M line disects the H band and is a dark line.

the M line is formed by several cross-connections at the centres of adjacent thick filaments

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21
Q

molecular organisation of myofilaments

what are the Thin filaments of skeletal muscle cells composed of?

A

thin filaments are composed of F-actin, tropomyosin and troponin and associated with nebulin

22
Q

molecular organisation of myofilaments

describe actin of thin filaments

A

actin: F-actin is a polamer of G-actin molecules arranged into a double helix
- each G-actin possessan active site that can interact with myosin
- F-actin is present as filaments that exhibit polarity. (+)-end tethered to Cap-Z of a Z-disk. (-)-end is the growing end and capped by tropomodulin located in the H band
- slow turnover rate at both ends

23
Q

molecular organisation of myofilaments

describe the role of tropomyosin in thin filaments

A

tropomyosin - 40nm in length - bind head to tail forming filaments located in the grooves of F-actin Helix

24
Q

molecular organisation of myofilaments

describe the role of troponin in thin filaments

A

troponin is associated with each tropomyosin molecule

  1. troponin T (TnT) - is the tail that binds troponin to tropomyosin
  2. troponin C (TnC) - forms the 4 binding sites for Ca2+
  3. troponin I (TnI) - binds to actin, inhibiting myosin and actin interaction
25
Q

molecular organisation of myofilaments

describe the role of Nebulin in thin filaments

A

Nebulin is a long inelastic protein. two nebulin molecules wrap around each thin filament and assists in anchoring it tot he Z disk

  1. each nebulin molecule anchors into the Z disk by its carboxy terminal but does not span the entire disk
  2. the amino terminal of each nebulin molecule ends in the A band
26
Q

molecular organisation of myofilaments

what does the thick filament consist of?

A

each thick filament contains around 250 myosin II molecules plus associated proteins - myomesin, titin and C protein

27
Q

molecular organisation of myofilaments

describe the role of Myosin II in thick filaments

A

Myosin II is composed of two identical heavy chains and two light chains.

  1. myosin heavy chains consist of a long rod-like tail and a globular head. the tails wind around each other in an a-helical fashion
  2. myosin light chains are of two types; one of each is associated to the heads of each heavy chain
28
Q

molecular organisation of myofilaments

describe the role of myomesin and C protien in thick filaments

A

myomesin is a protein at the M line that cross links adjacent thick filaments to one another to maintain their spatial relations

C protein binds to thick filaments near the M line

29
Q

molecular organisation of myofilaments

Describe the role of titin in thick filaments

A

titin is a large linear protein that displays axial periodicity. titin forms an elastic lattice that parallels the thick and thin filaments
two titin filaments anchors each thick filaments to the Z disk
1. amino terminal of titin anchors the the Z disk binding to a-actinin and Z proteins. spans the entire thickness of Z disk
2. carboxyl terminal spans the entire M line binding to myomesin

30
Q

the contraction of skeletal muscle is principally based on the involvment of…? (energy)

A

ATP (binding, hydrolysis and release of)

31
Q

what is the Huxely slding filament model?

A

Huxely’s sliding filament model describes the movement of the thin and thick filaments in a sacromere.

the two types of filaments slide over each other, increasing the overlapping region of the two; therefore the length if the filaments remain constant.

During contraction, the A band is constant as the I and H bands shorten bringing the Z disks closer together.

32
Q

describe the initiation and regulation of contraction of skeletal muscle ….

A
  1. depolarisation and release of Ca2+ triggers binding of actin and myosin leading to muscle contraction through the huxely sliding model
    - sacrolemma is depolarised at the neuromuscular junction)
    - T tubules convey the depolartion wave
    - Ca2+ is released into the cystol at A-I junctions
  2. Activation of actin by Ca2+
    - Ca2+ binding to TnC results in a conformation change breaking the TnI-actin bond, uncovering the Myosin active site (Active form)
33
Q

what is the structure of a neuromuscular junction? (myoneural junction)

A

three major structural sites:
1. axon terminal: lacks myelin but has swchann cell on its non-synaptic surface. axon terminal contains mitochondria, synaptic vesicles (containing neurotransmitters) and SER elements. presynaptic membrane.

  1. synaptic celft: narrow space between pre- and post- synaptic membranes. contains amorphous external lamina
  2. muscle cell: sarcolemma invaginations of postsyaptic membrane (junctional folds) extend inwards from the synaptic celft. neurotransmitter recptors found on the post synaptic membrane. sarcoplasm is rich in mitochondria, ribosomes and RER.
34
Q

what is a muscle spindle? structure and function…

A

a muscle spindle is an elongated, fusiform sensory organ within skeletal muscle. functions as a stretch receptor.

structure:
- bounded by connective tissue capsule enclosing a fluid-filled periaxial space and 8-10 modified skeletal muscle fibres.
- surtounded by normal skeletal muscle fibres
- anchored to the perimysium and endomysium via the capsule

function:

  • stretching of muscle
  • muscle overstimulation
35
Q

what is a golgi tendon organ? structure and function…

A

located in tendons they counteract the effects of muscle spindles.

structure: composed of encapsulated collagen fibres surrounded by terminal branches of type 1B sensory nerves
function: stimulated when the muscle contraction is too strenuous, increasinf tension on the tendon, preventing previous contraction.

36
Q

what are the general features of cardiac muscle cells? (7 points)

A
  1. contract spontaneously and display an rhythmic beat - modified by hormonal and neural stimuli
  2. may branch at their ends to form connections with adjacent cells
  3. contain one (maybe two) centrally located nucleus
  4. contain glycogen granules, at either pole of the nuclues. sarcoplasm is rich in myoglobin
  5. possess thick and thin filaments - poorly defined myofibrils
  6. exhibit identical cross-banding pattern as skeletal muscle
  7. do not regenerate, repaired by fibrous connective scar tissue by fibroblasts.
37
Q

what are the structural differences between cardiac and skeletal muscle cells? (9 differences)…

A
  1. T tubules: larger and lined with external lamina. invaginations by the sarcolemma at Z disks
  2. Dyadsformed from poorly defines SR and one T tubule. SR also in Z disk vicinity as small basketlike saccules known as corbular sarcoplasmic reticulum - rich in Ca2+-release channels.
  3. Intercalated disks - end-to-end attachments (complex steplike junctions) between adjacent cardiac muscle cells
    - transverse portion: runs across muscle fibres at right angles possess 3 specialisations: 1. desmosomes 2. fasciae adherentes 3. gap junctions
    - lateral portion: desmosomes and large gap junctions
  4. calcium
  5. connective tissue elements: support capillary bed to supple sufficient nutrients and oxygen to maintain high metabolic rate. 90% of energy is produced by aerobic respiration
  6. purkinje fibres: modified cardiac muscle cells located in bundle of HIS.
  7. thin filaments secured to Z disks by a-actinin as well as nebulettes
  8. abundant mitochindria parallel to I bands and adjacent to lipdis
  9. atrial granules present in atrial cardiac muscle cells. contains precursor of atrial natriuretic peptide, acts to decrease reabsorption of sodium and water in kidneys - reducing body fluid volume and blood pressure
38
Q

what is the general structure of smooth muscle cells?

A

smooth muscle cells are non-striated, fusiform cells that range in length from 20um to 500um.
they contain a single nuclues
they actively divide and regenerate
surrounded by external lamina and a reticular fibre network
may be arranged in layers, small bundles and helices

39
Q

smooth muscle contraction…?

A

occurs more slowly and lasts longer because rate of ATP hydrolysis is slower (compared to skeletal muscle cells)

40
Q

inhibition of smooth muscle contraction occurs through:

  • vascular
  • visceral
  • uterus
  • elsewhere
A

inhibition is trigger by:

  • nerve impulses with little spread in vascular SM
  • myogenically (stretching) in visceral SM
  • oxytocin in uterus SM
  • epinephrine in SM elsewhere
41
Q

does skeletal muscle cells contain triads or dyads?

A

skeletal muscle cells contain triads.
triads are found at the A-I band junction.
triads are formed of cental T tubule (invagination of sarcolemma) flanked by dilated terminal cisternae of SR.

42
Q

are T tubules present in cardiac muscle?

A

yes. T tubules form dyads, not triads as in skeletal muscle located along the Z disk in cardiac muscle.
the T tubule are wider than those in skeletal muscles.

43
Q

in smooth muscle are T tubules present?

A

no

44
Q

do smooth muscle contain caveolae?

what are caveolae?

A

yes, caveolae store and release calcium ions.
contraction may be initiated through several ways and not dependent on troponin.

calcium ions are stored and released by caveolae. calcium ions binds to calmodulin, which activates myosin light-chain kinase.

45
Q

what does tropoin do?

A

troponin binds and sequesters Ca2+ ions through one of its subunits - TnC leading to the uncovering of myosin-binding sites on actin (thin filaments)

46
Q

describe the nucleus of smooth muscle cells….

A

each smooth muscle cell contains one centrally located nuclues.

47
Q

how are thick filaments anchored to Z disks?

A

through titin

48
Q

what connective tissue investment surrounds individual musle fibers?

A

endomysium

49
Q

what connective tissue investment surrounds an entire muscle?

A

epimysium

50
Q

how are cardiac muscle cells joined together?

A

cardiac muscle cells are joined end-to-end through intercalculated disks (steplike junctions)

Histology (16 decks)

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