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Foundations To Medicine 2 > Muscles > Flashcards

Muscles Flashcards

1
Q

What are myocytes and sarcoplasms?

A

Myo—> myocyte—> muscle cell

Sarco—> sarcoplasm(cytoplasm), sacrolemma (plasma membrane

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2
Q

What are myofilaments?

A

Muscle tissue contains filamentous cytoplasmic organelles —> myofilaments which gives the tissue its contractile property

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3
Q

What’s the function of muscle?

A

Contraction of muscle tissue produce movement of body parts and changes in volume and shape of internal organs and vessels

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4
Q

What does the arrangement of myofilaments?

A

The arrangement of myofilaments allows for morphological classification based on the appearance under light microscope

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5
Q

What are striated muscle?

A

These tissue subtypes have visible cross striations due to regular arrangement of contractile organelles within their cells

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6
Q

Describe smooth muscle

A

No cross striations

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7
Q

What are the types of striated muscle?

A

Skeletal- voluntary

Cardiac- involuntary

Visceral- voluntary

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8
Q

Where is skeletal muscle found?

A

Somatic/body wall

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9
Q

Where is visceral muscle found?

A

Soft tissue origin. Tongue,pharynx, larynx, diaphragm and upper esophagus

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10
Q

What are the locations for cardiac muscle?

A

Heart and roots of great veins that empty into heart

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11
Q

Where are smooth Muscle located?

A

Walls of visceral organs, stomach, gut tube

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12
Q

Compare smooth, cardiac and skeletal muscle

A

Skeletal muscle- multiple nuclei peripherally nucleated, long cylindricAl cells, striations

Cardiac muscle-intercalated cells, centrally located nucleus, branched cells striations

Smooth- spindle-shaped cells, centrally located nucleus

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13
Q

What is dystrophin?

A

A rod-shaped cytoskeletal protein which links to ECM proteins laminin & argin found in the external lamina of the myocyte —> Clinical route: Duchenne & Becker’s muscular dystrophy

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14
Q

What does dystrophin do?

A

Forms a complex with two groups of transmembrane proteins:

  • Dystroglycans —> links dystrophin and laminin of the ECM
  • Sarcoglycans—> associated with membrane dystroglycans—> clinical correlate: limb girdle associated dystrophy

Congenital muscular dystrophy: is another group of muscular dystrophy associated with ECM components

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15
Q

What causes duchenne muscular dystrophy ?

A

Results from a defect in the gene coding for dystrophin associated proteins on X chromosome —> muscular fiber fragility

  • Most common inherited myopathy
  • more prevelant in males
  • X-linked recessive
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16
Q

What are the symptoms of Duchenne Muscular Dustrophy?

A

Patients are unable to stand unaided in early childhood and develop progressive muscle weakness, becoming wheelchair-bound by their mid-teens and typically dying in early adult life

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17
Q

What are the other muscular dystrophy?

A
  • Becker muscular dystrophy
  • limb bridle dystrophy
  • congenital muscular dystrophy
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18
Q

What is the triad?

A

1 T tubule + 2 terminal cisternae at the A-I junction

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19
Q

What are sarcoplasmic reticulum?

A

Forms a network arounf the myofibrils (calcium reservoir)

-Extends-from one A-I junction to the next A-I

Forms the terminal cisterna at the end of each network

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20
Q

What is a transverse tubule?

A

Invagination of the sarcolemma at the A-I junction.

Have voltage sensor protein/ channels activated by membrane depolarization

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21
Q

Where. Is a myofibrils arranged?

A

Arranged in the center 9f the cell, surrounded by mitochondria

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22
Q

How does the transverse tubule work?

A

Depolarization of t tubule membrane triggers release of Ca2+ from terminal cisterna & initiates muscle contraction cycle

23
Q

Describe the neuromuscular Junction

A

Neuromuscular junction or motor end plate

-Contact between the terminal branches of an axon and muscle fiber

  • Axons branch as they near the muscle and give rise to twigs that end on individual muscle fibers= motor unit
    - All muscles within a motor unit are of the same type (I,IIa, or IIb etc.)

Covered by thin portion of external Lamina

24
Q

What is involved in a muscle contraction physiologically?

A

1 neuromuscular junction per muscle fiber

Enters close to the origin of the muscle fiber

Depolarization is propagated along the entire length in a sequential manner

-Each sarcomere contracts independently allowing for smooth singular action in a particular direction

25
Q

Explain the struct7ure of the neuromuscular junction

A

Presynaptic membrane : synapt8c vesicles contain ACh can be observed

Synaptic cleft(SnC) where acetylcholine is released

Post synaptic membrane (of the muscle): junctional folds with acetylcholine receptors

NMJ is covered by Schwann cell external lamina

26
Q

What is a muscle spindle?

A
  • encapsulated sensory receptors
  • specialized stretch receptor located in the muscle belly
  • Senses changes in muscle length or stretch
  • Contains modified muscle fibers or spindle cells
27
Q

What is the Golgi tendon organ?

A
  • encapsulated prioceptor located in the myotendinous junction
  • senses tension in the muscle
  • Sensiry component of the Golgi tendon reflex
28
Q

What 8s myasthenia grav8s?

A
  • myasthenia Gravis is an autoimmune disease which affects neuromuscular junction
  • common cause: ACh receptor antibodies, which block and attack ACh receptors in the postsynaptic membrane.

Fewer ACh receptors results in:
-Fluctuating weakness and fatigue of skeletal muscles

-OCCULAR, bulbar, limb and respiratory muscles are affected

29
Q

What are the requirements for skeletal muscle?

A

Myofibril

Sarcoplasmic reticulum

Transverse tubules

Mitichondria

30
Q

What are the structural requirements f9r contraction in cardiac muscle?

A

Sarcoplasmic reticulum

Transverse tubule

Diad

31
Q

What is the function of the sarcoplasmic reticulum in cardiac muscle?

A
  • single network along the sarcomere
  • extends fromZ line to Z line
  • Less developed than in skeletal muscle
  • Terminal cisterna
    • Contain Ca2+ release channels
      • Release Ca2+ into sarcoplasm
32
Q

Describe the transverse tubular system in cardiac muscle

A

Located at Z line (compare to skeletal muscle)

-T tubules contain voltage-sensor proteins

33
Q

What is the Diad in cardiac muscle?

A

Complex of o;e t tubule and one aadjacent terminal cisternae at the Z line

34
Q

Describe intercalated discs in cardiac muscles

A

Intercalated discs are attachment sites between adjacent cardiac myocytes

The transversely oriented parts of the intercalated disk (T) which is at right angle to the myofibril like the risers of a stairway

The longitudinal or lateral parts (L) are parallel to myofibrils like the steps of a stairway

Mitochondria(m) are abundant in card8ac muscle due to high metabolic demands of these cells

35
Q

Describe the “arterial component of the intercalated d7sc

A

Gap junctions (communicating junctions)

Macula adherens(desmosomes)

36
Q

Describe the transverse component in intercalated disks

A 
Fascia adherents (adhering junctions)
-Major structural element
  • Binds cardiac muscle cells at their ends
  • Serves as attachment site for thin filaments in terminal sarcomere

(MA) Macula adherens (desmosomes)
-Bind individual muscle cells to each other

  • Reinforce fascia adherens
  • Found in both transverse & lateral components
37
Q

What are Purkinje fibers?

A

Large, modified muscle cells located just deep to the endocardium in the subendicardial connective tissue

Specialized to conduct impulses of the A-V valve bundle and allow synchronization of ventricle contraction

Abundant in mitichondria

38
Q

Why are Purkinje fibers pale staining ?

A
  • few myofibrils (these are located peripherally)

- Large amount of glycogen

39
Q

How are smooth muscles connected?

A

Interconnected by gap junctions or nexus

  • Communicating junctions
  • Small molecules & ions pass from cell to cell
  • Provode communication links to regulate contraction of entire bundle or sheet

Sarcoplasmic reticulum

Pinocytic vesicles

Dense bodies

40
Q

Explain smooth muscles secreting connective tissue matrix

A
  • Well developed rER & Golgi
  • Synthesize both type IV collagen and type III collagen
  • Elastin, proteoglycans, and multi-adhesive glycoproteins
  • Vascular and uterine SM also secrete large amounts of type 1 collagen and elastin
41
Q

What do the thick filaments of smooth muscle contain?

A
  • Myosin II scattered throughout the sarcoplasm

- Side polar vs striated muscle where it is oriented towards the center of the sarcomere

42
Q

What do thin filaments contain in smooth muscle?

A
  • Actin
  • Tropomyosin (no associated protein)
  • Smooth muscle specific proteins Caldsmon and Calponin which bind to Actin proteins blocking the myosin binding site
43
Q

What are the accessory proteins of smooth muscle?

A
  • Myosin light chain kinase(MLCK): initiates contraction
  • a-actinin (see dense bodies)
  • Calmodulin- Ca2+ binding protein
  • Ca2+ calmodulin complex binds & activates MLCK
44
Q

Describe dense bodies of smooth muscles

A

Cytoplasmic densities) which attach thin and intermediate filaments
-Contain a-actinin

-analogs of Z lines in striated muscle

  • Distributed throughout the sarcoplasm in a network of intermediate filaments
    • Desmin
    • Vascular smooth muscles contains vimentin in addition to desmin
45
Q

Describe smooth muscles having no T tubules systems

A

-Analogous system of:
Caveolae—> invaginations of cell membrane

Sarcoplasmic reticulum

Cytoplasmic vesicles

46
Q

Summarize smooth muscle contraction

A
  • Contractile myofilaments are oriented obliquely to the long axis of the myocyte
  • These are anchored to cytoplasmic and cell membrane densities
  • Therefore during concentration there is a net shortening of the cell
  • The cell adopts a globular shape and the nucleus adopts a “cork screw” shape
47
Q

What are the steps in smooth muscle contraction

A

Contraction regulated by the Ca2+-calmodulin-MLCK system

  1. Increase in Ca2+ concentration
  2. Ca2+ binds to calmodulin forming the Ca2+ -calmodulin complex
  3. Ca2+ xcalmodulin complex binds MLCK

4 . MLCK-phosphorylates regulatory light chain of myosin

  1. Actin-binding site kf myosin head is activated & attaches to actin
48
Q

How is smooth muscle contraction regulated?

A

Mechanical: passive stretching of vascular smooth muscle activates myogenic reflex

Electrical: neural stimulation leading to release of ACh and NE

Chemical: Angiotensin II, vasopressin, thromboxane A2- uses second m3ssanger pathways such as IP3, and NO-cGMP pathways

49
Q

Why can the force of smooth muscles be sustained for such long periods of time ?

A

Latch state when the myosin head is unable to detach from actin filament

50
Q

Which muscles undergo hypertrophy?

A

All muscle types - cardiac in hypertensive cardiomyopathy

51
Q

Which muscle types with injury repair?

A

Cardiac and skeletal don’t undergo hyperplasia

Smooth muscle undergoes hyperplasia, the uterine proliferates during the normal menstrual cycle and pregnancy

SM of blood vessels increase in size as well as number due to hypertensive conditions etc.

52
Q

How does skeletal muscle respond to atrophy?

A

Skeletal- limited capacity

Satellites cells are myogenic precursor cells located between the sarcolemma of a muscle fiber and its external lamina

Satellite cells are responsible for skeletal muscle regeneration

Regenerative capacity is limited

53
Q

How does cardiac muscle respond to injury?

A

No regenerative capacity

After the death of cardiac muscle cells, the tissue is replaced with fibrous connective tissue. Cardiac function is lost at site of injury

54
Q

How does smooth muscle respond to injury?

A

Smooth muscle of blood vessels divide regularly differentiating from Mesenchymal stem cells in the adventitia or from division and differentiation of endothelial cells and pericytes in capillaries and post-capillary venues during the repair process following a vascular injury

Foundations To Medicine 2 (37 decks)

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